Antenna for wireless charging systems

<u>TECHNICAL FIELD</u>

This application generally relates to wireless charging systems, and in particular, to metamaterial unit cells configured to radiate wireless power signals to power electronic devices.

<u>BACKGROUND</u>

Wireless charging systems have been made to wirelessly transmit energy to electronic devices, where a receiver device can consume the transmission and convert it to electrical energy. Wireless charging systems are further capable of transmitting the energy at a meaningful distance. The wireless charging systems make use of an array of antennas to provide spatial diversity, focus the wireless transmission waves at a target location, direction-finding, and increased capacity.

Numerous attempts have been made in new generation wireless charging systems to incorporate techniques to achieve high performance goals. The performance achievable by the new generation wireless charging systems is still limited due to a number of practical design factors including the design of the antenna array. The accommodation of the multiple antennas with large spacing in modern wireless charging systems has become difficult due to stringent space constraints in the new generation wireless charging systems. Typically, the dimensions of an antenna are determined by the frequency at which the antenna is designed to function. The ideal antenna is some multiple of the electromagnetic wavelength such that the antenna can support a standing wave. The antennas usually do not satisfy this constraint because antenna designers either require the antenna to be smaller than a particular wavelength, or the antenna is simply not allotted the required volume in a particular design in the new generation wireless charging systems. When the antenna is not at its ideal dimensions, the antenna loses efficiency. The antenna is also often used to capture information encoded on an electromagnetic wave. However, if the antenna is smaller than an incoming electromagnetic wavelength, the information is captured inefficiently and considerable power is lost. In order to meet such demanding design criteria, antenna designers have been constantly driven to seek better materials on which to build antenna systems for the new generation wireless charging systems.

In recent times, antenna designers have used metamaterials. Metamaterials are a broad class of synthetic materials that have been engineered to yield permittivity and permeability values or other physical characteristics, not found in natural materials, aligned with the antenna system requirements. It has been theorized that by embedding specific structures in some host media usually a dielectric substrate, the resulting material can be tailored to exhibit desirable characteristics. These promise to miniaturize antennas by a significant factor while operating at acceptable efficiencies.

In the context of antenna systems for the new generation wireless charging systems, metamaterials have been used as substrates or superstrates on existing antennas to enhance their properties. In current art, the metamaterial is usually integrated behind the antenna, either monolithically on the same PCB as the printed antenna, or as a separate structure in close proximity to the antenna. Alternatively, the metamaterial can be integrated on an already directive antenna to further enhance its directivity and gain. The benefit of integrating the metamaterial to the antenna enhances various properties of the antennas such as it creates one or more directive beams. It has been noted that certain metamaterials can transform an omnidirectional antenna into a very directive one while maintaining very thin profiles. However, due to the presence of a layer of antennas along with metamaterials layer, an optimal size and performance is not achieved by the metamaterial antenna systems for the new generation wireless charging systems. Accordingly, there is a need in the art for metamaterial antenna systems that provide an optimal size and performance for modern wireless charging systems having stringent space constraints.

<u>SUMMARY</u>

There is provided a wireless power transmission apparatus in line with claim 1. Metamaterials are artificial composites that achieve material performance beyond the limitation of uniform materials and exhibit properties not found in naturally-formed substances. Such artificially structured materials are typically constructed by patterning or arranging a material or materials to expand the range of electromagnetic properties of the material. When an electromagnetic wave enters a material, the electric and magnetic fields of the wave interact with electrons and other charges of the atoms and molecules of the material. These interactions alter the motion of the wave changing the electromagnetic wave propagation properties in the material, e.g., velocity, wavelength, direction, impedance, index of refraction, and the like. Similarly, in a metamaterial, the electromagnetic wave interacts with appropriately designed artificial unit cells that macroscopically affect these characteristics. In an embodiment, the metamaterial may comprise an array of unit cells formed on or in a dielectric substrate and are configured to radiate wireless power signals to power electronic devices.

In one example, a wireless transmission apparatus comprises a metamaterial unit cell. The metamaterial unit cell may include a surface having a metal patch with an aperture. The aperture is defined such that a periphery of the aperture is within a periphery of the surface by a spacing distance. An antenna element is disposed within the aperture.

In another example, a method of forming a unit cell is provided. The method comprises forming a metamaterial layer using metamaterial substrate. A surface on the metamaterial layer may be created, and a metal patch with an aperture in the surface of the metamaterial layer may be created. An antenna element may be disposed in the aperture to form the unit cell.

In another example, a metamaterial system (or a metamaterial board) of a wireless transmission apparatus comprises a metamaterial layer. The metamaterial layer may include an array of metamaterial unit cells, where each of the metamaterial unit cells may include a surface having an aperture. The aperture is defined such that a periphery of the aperture is within a periphery of the surface by a spacing distance. An antenna element is disposed within the aperture. The metamaterial system may further include at least one input RF port disposed on a backing layer that is positioned below the metamaterial layer such that there is no short-circuit between the conductive backing layer and the metamaterial layer. At least one set of vias may connect the array of metamaterial unit cells with the input RF port(s).

In another example, a method of forming a metamaterial system is provided. The method comprises forming a backing layer. A metamaterial layer may be formed from a metamaterial substrate. The metamaterial layer may be formed above the backing layer. Multiple partitions may be created in the metamaterial layer, where each of the partitions define a portion of a unit cell of a plurality of unit cells. The method further includes creating an aperture in each of the partitions, where the aperture is defined such that a periphery of the aperture is within a periphery of a partition in which the aperture is created by a spacing distance. An element may be disposed in the aperture in each of the plurality of partitions. At least one input RF port may be formed on the backing layer such that there is no short-circuit between the backing layer and the metamaterial layer. The unit cells may be connected with the input RF port(s) by at least one set of vias.

<u>BRIEF DESCRIPTION OF THE DRAWINGS</u>

The accompanying drawings constitute a part of this specification and illustrate an embodiment of the invention and together with the specification, explain the invention. <ul id="ul0001" list-style="none"><li><figref idref="f0001"><b>FIG. 1A</b></figref> illustrates an isometric view of a structure of a metamaterial board having a contactless capacitive coupling mechanism, according to an exemplary embodiment.</li><li><figref idref="f0002"><b>FIG. 1B</b></figref> illustrates a graph depicting a return loss of a metamaterial board having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0003"><b>FIG. 1C</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0004"><b>FIG. 1D</b></figref> illustrates a profile view of a radiation gain pattern in linear scale of a metamaterial board having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0005"><b>FIG. 1E</b></figref> illustrates a polar plot of a radiation gain pattern on a principal Y-Z plane of a metamaterial board having a contactless capacitive coupling mechanism of <figref idref="f0003"><b>FIG. 1C</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0006"><b>FIG. 1F</b></figref> illustrates a magnitude of electric current surface density distribution on metamaterial cells layer of a metamaterial board having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref> at operational frequencies, according to an exemplary embodiment.</li><li><figref idref="f0007"><b>FIG. 1G</b></figref> illustrates a magnitude of electric current surface density distribution on backing conductor layer of a metamaterial board having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref> at operational frequencies, according to an exemplary embodiment.</li><li><figref idref="f0008"><b>FIG. 2</b></figref> illustrates an isometric view of a structure of a metamaterial board having a co-planar coupling mechanism, according to an exemplary embodiment.</li><li><figref idref="f0009"><b>FIG. 3A</b></figref> illustrates an isometric view of a structure of a metamaterial board having a direct feeding excitation mechanism, according to an exemplary embodiment.</li><li><figref idref="f0010"><b>FIG. 3B</b></figref> illustrates a graph depicting a return loss of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0009"><b>FIG. 3A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0011"><b>FIG. 3C</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0009"><b>FIG. 3A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0012"><b>FIG. 3D</b></figref> illustrates a magnitude of electric current surface density distribution on metamaterial cells layer of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0009"><b>FIG. 3A</b></figref> at operational frequencies, according to an exemplary embodiment.</li><li><figref idref="f0013"><b>FIG. 3E</b></figref> illustrates an isometric view of a structure of a metamaterial board having a direct feeding excitation mechanism, according to an exemplary embodiment.</li><li><figref idref="f0014"><b>FIG. 3F</b></figref> illustrates a graph depicting a return loss of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0013"><b>FIG. 3E</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0015"><b>FIG. 4</b></figref> illustrates an enlarged sectional view of a structure of a metamaterial board having a contactless capacitive coupling mechanism, a co-planar coupling mechanism, and a direct feeding excitation mechanism, according to an exemplary embodiment.</li><li><figref idref="f0016"><b>FIG. 5A</b></figref> illustrates an isometric view of a structure of a metamaterial board having a direct feeding excitation mechanism, according to an exemplary embodiment.</li><li><figref idref="f0017"><b>FIG. 5B</b></figref> illustrates a graph depicting a return loss of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0016"><b>FIG. 5A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0018"><b>FIG. 5C</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0016"><b>FIG. 5A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0019"><b>FIG. 5D</b></figref> illustrates an isometric view of a structure of a metamaterial board having a direct feeding excitation mechanism, according to an exemplary embodiment.</li><li><figref idref="f0020"><b>FIG. 5E</b></figref> illustrates a graph depicting a return loss of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0019"><b>FIG. 5D</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0021"><b>FIG. 5F</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board having a direct feeding excitation mechanism of <figref idref="f0019"><b>FIG. 5D</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0022"><b>FIG. 6A</b></figref> illustrates a configuration of metamaterial unit cells for use as wearable antennas, according to an exemplary embodiment.</li><li><figref idref="f0023"><b>FIG. 6B</b></figref> illustrates an enlarged sectional view of a metamaterial unit cells as wearable antennas, according to an exemplary embodiment.</li><li><figref idref="f0024"><b>FIG. 6C</b></figref> illustrates a graph depicting a return loss metamaterial unit cells as wearable antennas of <figref idref="f0022"><b>FIG. 6A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0025"><b>FIG. 6D</b></figref> illustrates an isometric view of a radiation gain pattern of metamaterial unit cells as wearable antennas of <figref idref="f0022"><b>FIG. 6A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0026"><b>FIG. 7A</b></figref> illustrates a structure of metamaterial unit cells configured as wearable antennas, according to an exemplary embodiment.</li><li><figref idref="f0027"><b>FIG. 7B</b></figref> illustrates an enlarged sectional view of a structure of metamaterial unit cells configured as wearable antennas, according to an exemplary embodiment.</li><li><figref idref="f0028"><b>FIG. 8A</b></figref> illustrates an isometric view of a structure of a metamaterial board configured as an antenna array, according to an exemplary embodiment.</li><li><figref idref="f0029"><b>FIG. 8B</b></figref> illustrates a graph depicting a return loss of a metamaterial board configured as an antenna array of <figref idref="f0028"><b>FIG. 8A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0030"><b>FIG. 8C</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board configured as an antenna array of <figref idref="f0028"><b>FIG. 8A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0031"><b>FIG. 9A</b></figref> illustrates an isometric view of a metamaterial board including two orthogonal sub-arrays, according to an exemplary embodiment.</li><li><figref idref="f0032"><b>FIG. 9B</b></figref> illustrates a planar view of a radiation gain pattern of a metamaterial board including two orthogonal sub-arrays of <figref idref="f0031"><b>FIG. 9A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0033"><b>FIG. 9C</b></figref> illustrates a planar view of a radiation gain pattern of a metamaterial board including two orthogonal sub-arrays of <figref idref="f0031"><b>FIG. 9A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0034"><b>FIG. 9D</b></figref> illustrates a planar view of a radiation gain pattern of a metamaterial board including two orthogonal sub-arrays of <figref idref="f0031"><b>FIG. 9A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0035"><b>FIG. 9E</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board including two orthogonal sub-arrays of <figref idref="f0031"><b>FIG. 9A</b></figref>, according to an exemplary embodiment.</li><li><figref idref="f0036"><b>FIG. 10</b></figref> illustrates a method of forming a metamaterial board, according to an exemplary embodiment.</li></ul>

<u>DETAILED DESCRIPTION</u>

The present disclosure is herein described in detail with reference to embodiments illustrated in the drawings, which form a part here. Other embodiments may be used and/or other changes may be made without departing from the scope of the present disclosure. The illustrative embodiments described in the detailed description are not meant to be limiting of the subject matter presented here.

In an embodiment, a response of a structure in any material to electromagnetic waves may be described by overall parameters, such as permittivity and permeability of the material, where the dimensions of the structure are far smaller than the wavelength of the electromagnetic wave. The permittivity and the permeability at each point of the material may be the same or different, so that the overall permittivity and the overall permeability of the material are distributed regularly to some extent. The regularly distributed permeability and permittivity can cause the material to exhibit a macroscopic response to the electromagnetic wave, for example, converging the electromagnetic wave, diverging the electromagnetic wave, and the like. Such a material with regularly distributed permeability and permittivity is called metamaterial. In other words, metamaterials are a broad class of synthetic materials that are engineered to yield permittivity and permeability characteristics compliant with the system requirements. By embedding specific structures, usually periodic structures, in some host media, usually a dielectric substrate, the resulting material is tailored to exhibit desirable characteristics. These metamaterials enable miniaturizing antennas by a significant factor while operating at acceptable efficiencies. The metamaterials may also convert omnidirectionally radiating antennas into directively radiating antennas.

In an embodiment, metamaterials of the present disclosure do not need an additional layer of antennas for the metamaterials to radiate. The metamaterials radiate on their own, and at the same time, the metamaterials maintain the properties of a traditional antenna-type metamaterials. In other words, the metamaterials act as very thin reflectors, and at the same time, the metamaterials do not need antennas for radiating as the metamaterials radiate themselves.

In an embodiment, the metamaterials of the present disclosure work like artificial magnetic conductors. The metamaterials are configured as very thin reflectors, and therefore the metamaterials are easy to integrate in very thin profiles of products, such as wearable bracelets.

In an embodiment, there is provided a metamaterial system (also referred as metamaterial board) that comprises at least two metal layers and a thin substrate. The structure of the metamaterial system of the present disclosure provides for no antenna placement layers in relation to prior art implementations that require at least three metallization layers because of the additional antenna layer for the placement of antennas. Further, the metamaterial system of the present disclosure is much thinner in size than the prior art implementations as absence of additional antenna layers, often at prescribed non-negligible distances from the ordinary metamaterials, reduce significantly the overall system thickness that incorporates the metamaterial system. Therefore, the metamaterial system of the present disclosure due to absence of any layer of antennas results in very thin profiles, and is appropriate for dense integration at reduced cost.

In an embodiment, there is provided a metamaterial system composed of several sub-wavelength-sized "artificial atoms" or radiative metamaterial unit cells. The metamaterial system operates by electromagnetically exciting all of the radiative metamaterial unit cells simultaneously. The metamaterial system also have many degrees of freedom that may translate into beam-forming possibilities that are unavailable with a conventional single antenna. In one example, some regions of the metamaterial system contain the radiative metamaterial unit cells that have different design and radiative properties than other regions of the same metamaterial system. The radiative metamaterial unit cells facilitate creation of beam-forming and/or beam steering without introduction of any phase-shifting networks.

In an embodiment, there is provided a metamaterial system composed of several radiative metamaterial unit cells. The metamaterial system may obtain linear, circular or elliptical polarization by appropriately designing the radiative metamaterial unit cells. The linear, circular or elliptical polarization properties may be obtained by the metamaterial system that is composed of regions of the radiative metamaterial unit cells, where each of the radiative metamaterial unit cell has a different design with respect to other metamaterial unit cells. In other words, since the radiative metamaterial unit cells radiate on their own, designing the radiative metamaterial unit cells appropriately may obtain various different functionalities, such as linear, circular, circular, or elliptical polarization.

In an embodiment, there is provided a metamaterial system composed of radiative metamaterial unit cells. The radiative metamaterial unit cells may be electrically interconnected by switches realized by integrated diodes, RF microelectromechanical (MEM) devices, or other means, to form larger radiative domains or different metamaterial "super-cells" that scan selected frequencies of operation over which the electromagnetic radiation is desired.

In an embodiment, there is provided a metamaterial system composed of an array of unit cells. The array of unit cells radiate on their own and have engineered metamaterials. In one implementation, an array of switches may be constructed by connecting adjacent unit cells of the array of unit cells. In other words, the metamaterial system is composed of a lattice of unit cells, and a lattice of switches can be manufactured by connecting adjacent unit cells through diodes. The lattice of switches may be superimposed on the lattice of the unit cells, and because the switches connect adjacent unit cells electronically, there may be a configuration where the metamaterial has two types of unit cells, one type of unit cells that are not connected, and the other type of unit cells where a pair of unit cells are connected. In the latter case, the electrical size may be variable according to whether the switches are open or closed. In this configuration, the frequency may be varied according to whether or not the switches to connect adjacent unit cells. This is also called smart radiative metamaterials, where the frequency tuning is arranged through the connectivity of the switches.

In an embodiment, there is provided a metamaterial system composed of radiative metamaterial unit cells. The metamaterial unit cells are extremely small in size due to which resulting metamaterial antennas occupy small form factors and are ideally suited to follow the curved shapes of wearable and other conformal applications. In other words, the form factors are proportional to the size of the metamaterial unit cells. Due to smaller size, the metamaterial unit cells may be placed on flexible/wearable substrates to realize wearable antennas or antennas in curved geometries.

In an embodiment, there is provided a metamaterial system that is composed of several radiative metamaterial unit cells. The metamaterial unit cells are extremely small in size due to which there are smaller form factors, and because of the small form factors, the radiative metamaterial unit cells may be placed in closely spaced orthogonal orientations, and thus forming dual linearly-polarized antenna systems that are able to transmit or receive electromagnetic waves simultaneously in orthogonal linear polarizations. The simultaneous transmission and receiving of the electromagnetic waves in orthogonal linear polarizations can be realized within very small areas, such as curved wearable platforms (e.g., wearable bracelets).

In an embodiment, there is provided a metamaterial system that is composed of radiative metamaterial unit cells. The radiative metamaterial unit cells in a receiving mode operate as uniform materials that absorb electromagnetic radiation with high absorption efficiency. The radiative metamaterial unit cells may further operate over a wide range of frequencies, including a microwave spectrum. The radiative metamaterial unit cells have a very high absorption efficiency (90% or higher). In another embodiment, the radiative metamaterial unit cells may be tapped by inserting localized radio frequency (RF) ports to arbitrary metamaterial unit cells. This power is then directed specifically to these RF ports. Thus, the radiative metamaterial unit cells work as a dense antenna array with many RF ports that receive the absorbed energy. Such metamaterial system is ideal for very small receivers, where the received power may be distributed to multiple channels simultaneously. A high density of the RF ports may be achieved, with each such RF port tapping adjacent radiative metamaterial unit cells. An even higher density of the RF ports may be achieved, with some RF ports tapping the same radiative metamaterial unit cell, provided additional decoupling techniques are employed. In addition, these multiple densely placed RF ports can accept phase control, resulting in electronically modulated RF patterns.

Reference will now be made to the illustrative embodiments illustrated in the drawings, and specific language will be used here to describe the same. It will nevertheless be understood that no limitation of the scope of the invention is thereby intended. Alterations and further modifications of the inventive features illustrated herein, and additional applications of the principles of the inventions as illustrated herein, which would occur to one skilled in the relevant art and having possession of this disclosure, are to be considered within the scope of the invention.

<figref idref="f0001"><b>FIG. 1A</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>100</b> having a contactless capacitive coupling mechanism, according to an exemplary embodiment. The metamaterial board <b>100</b> illustrated here is realized in standard Printed Circuit Board (PCB) technology utilizing three metal layers. Three metal layers may include a conductive backing layer <b>102</b>, a metamaterial layer <b>104</b>, and a coupling layer <b>106</b>. Also, a dielectric layer <b>108</b> is disposed between the conductive backing layer <b>102</b> and the metamaterial layer <b>104</b>.

In the metamaterial board <b>100</b> fabrication, the conductive backing layer <b>102</b> is placed at the bottom of the structure of the metamaterial board <b>100</b>. The metamaterial layer <b>104</b> may be deposited above the conductive backing layer <b>102</b>, and then may be etched to create an array of metamaterial unit cells <b>104a</b>. Hereinafter, the term "unit cell" and "metamaterial unit cell" may be interchangeably used. In an embodiment, a distance between the conductive backing layer <b>102</b>, and the metamaterial layer <b>104</b> is such that there is no short-circuit between the conductive backing layer <b>102</b>, and the metamaterial layer <b>104</b> in order to make the metamaterial unit cells <b>104a</b> radiate. Below the metamaterial layer <b>104</b> and above the conductive backing layer <b>102</b> may be deposited a layer of dielectric <b>108</b> or insulating material, often a silicon dioxide.

The metamaterial layer <b>104</b> comprises the array of unit cells <b>104a</b>. In the illustrative figure, the metamaterial layer <b>104</b> of the metamaterial board <b>100</b> comprises sixteen radiative metamaterial unit cells <b>104a</b> in a four-by-four (4x4) arrangement. Each of the metamaterial unit cell <b>104a</b> may include a surface. In one embodiment, the surface may be a substantially flat surface. In another embodiment, the surface may not be a flat surface or a substantially flat surface. The substantially flat surface of each of the array of metamaterial unit cells <b>104a</b> may be a square surface containing a square metal patch <b>104b</b> with an aperture <b>104c</b> inscribed within it. The square metal patch <b>104b</b> does not completely fill the metamaterial unit cell surface, but is slightly smaller than the metamaterial unit cell. The aperture <b>104c</b> is defined such that a periphery of the aperture <b>104c</b> is within a periphery of the square metal patch <b>104b</b> by a spacing distance. In one example, the aperture <b>104c</b> may be a circular aperture. An element <b>104d</b> may be disposed within the aperture <b>104c</b> to form a circular slot. In another example, the aperture may be a narrow shaped circular slot formed by the circular shape aperture <b>104c</b> and the element <b>104d</b> disposed within it. In the illustrated embodiment, since the aperture <b>104c</b> is circular in shape, the element <b>104d</b> is a circular metal disk that is disposed within aperture <b>104c</b> to form the circular slot. It will be appreciated by a person having ordinary skill in the art that the shape of the aperture <b>104c</b> is not limited to circular shape, and the aperture <b>104c</b> may be of any other suitable shape without moving out from the scope of the disclosed embodiments. Also, the array composed of metamaterial unit cells <b>104a</b> contains square metal patches that do not touch each other, but are separated by narrow straight slots, since the metamaterial unit cell surface is slightly larger than that of the square metal patch <b>104b</b> inscribed therein.. Further, there is a thin slot separating the circular element <b>104d</b> from the periphery of the square metal patch <b>104b</b>. In an embodiment, one subset of the array of the metamaterial unit cells <b>104a</b> may be of one shape and size, and another subset of the array of the metamaterial unit cells <b>104a</b> may be of another shape and size.

In one embodiment, one metamaterial unit cell <b>104a</b> on its own does not radiate efficiently and also does not match the required impedance value. In other words, one metamaterial unit cell <b>104a</b> does not have properties for a standard antenna. The array or the collection of the metamaterial unit cells <b>104a</b> work together as an antenna. Therefore, the metamaterial board <b>100</b> may include 16 unit cells <b>104a</b>. However, it is to be noted that the metamaterial board <b>100</b> may comprise any number of unit cells <b>104a</b> in other embodiments without moving out from the scope of the disclosed embodiments.

In another embodiment, the metamaterial layer <b>104</b> may comprise the array of unit cells <b>104a</b> formed on or in a dielectric substrate. In some embodiments, the metamaterial layer <b>104</b> may comprise a stack of 2D arrays of unit cells <b>104a</b>, where each 2D array of unit cells <b>104a</b> is formed on or in a respective dielectric substrate. In this implementation, magnetic permeability enhanced metamaterials are constructed by stacking up the unit cells <b>104a</b> that can store magnetic energy by virtue of their structure. The unit cell <b>104a</b> in embodiments of the present disclosure is composed of the circular element <b>104d</b> and the square metal patch <b>104b</b>, where the circular element <b>104d</b> may be embedded in a dielectric material. The magnetic energy storage is created in the unit cell <b>104a</b> when a magnetic field passes normally to the plane of the circular element <b>104d</b> and inducing a current in the loop.

The dielectric layer <b>108</b> may be masked and etched to open narrow profile openings known as vias <b>110</b>. Each of the vias <b>110</b> respectively extend as an opening through the dielectric layer <b>108</b> to a portion of the uppermost coupling layer <b>106</b>. In one embodiment, the vias <b>110</b> may be present to provide electrical paths between different metal layers of the metamaterial board <b>100</b>. The vias <b>110</b> may run from a surface of the metamaterial board <b>100</b> through each of the layers of the metamaterial board <b>100</b>. In another embodiment, the vias <b>110</b> may run from one layer of the metamaterial board <b>100</b> or a surface of the metamaterial board <b>100</b> and through other layers of the metamaterial board <b>100</b> but stop short of running through one of the layers. At a first surface of the metamaterial board <b>100</b>, the vias <b>110</b> may terminate on bond pads that couple to the integrated circuit. An opposite surface of the metamaterial board <b>100</b> is to be coupled to a PCB. As discussed above, certain vias <b>110</b> may go entirely through entire core of the metamaterial board <b>100</b>. Other vias <b>110</b> may be isolated vias <b>110</b>, which are present through only a portion of the metamaterial board <b>100</b>. The particular layering and the vias <b>110</b> pattern configuration utilized is a matter of design choice involving several factors related to the purposes to be served by the particular metamaterial board <b>100</b>. In order to form the metamaterial board <b>100</b> with the vias <b>110</b> as described above, once a pattern of the vias <b>110</b> to traverse the layers is determined, these particular vias <b>110</b> may be machine drilled, punched, or etched through the layers. Alternative techniques for providing electrical paths between the layers may be utilized.

In the illustrated figure, the vias <b>110</b> extend from the uppermost coupling layer <b>106</b> to input RF ports <b>112</b>. The input RF ports <b>112</b> may be located on or behind the conductive backing layer <b>102</b>. The input RF ports <b>112</b> may include a housing having any arbitrary shape, and manufactured from plastic, metal, or any other convenient material. The input RF ports <b>112</b> may be configured such that two or more submodules may be removably located within or attached to housing. That is, the submodules are removably coupled electrically, and may be removably inserted within housing. In an alternate embodiment, the submodules are removably attached to the exterior of housing. The input RF ports <b>112</b> are not limited to two submodules, and may be configured to accommodate 3, 4, or even more such submodules. The submodules may include a variety of electrical components that communicate via RF energy. In general, the submodules are capable of fulfilling many of the functions of the components.

In another embodiment, another layer of metal may be deposited over the dielectric layer <b>108</b>. The deposited metal fills the vias <b>110</b>, forming metallic contact structures engaging the exposed underlying metal at the bottom of the vias and making points of contact through layer between the conductive backing layer <b>102</b> and the uppermost coupling layer <b>106</b>. The geometries of the vias <b>110</b> and the contact structures that now fill the vias <b>110</b> are usually circular, although the vias <b>110</b> may also form other shapes such as a trench shape. The vias <b>110</b> have been positioned so that the metallic structures which fill the vias <b>110</b> provide contacts between two separated metal layers of the metamaterial board <b>100</b>.

In an embodiment, the contactless capacitive coupling excitation mechanism is used to excite the structure of the metamaterial board <b>100</b>. Some of the components utilized for the contactless capacitive coupling excitation mechanism are provided above the metamaterial layer <b>104</b> at the center of the metamaterial board <b>100</b> to excite the structure of the metamaterial board <b>100</b>. The components at least include a plurality of pads <b>114</b> on the coupling layer <b>106</b>. The plurality of pads <b>114</b> are used to excite the metamaterial unit cells of the metamaterial board <b>100</b>. The plurality of pads <b>114</b> are connected through the vias <b>110</b> that traverse though the metamaterial layer <b>104</b> of the metamaterial board <b>100</b> up to the conductive backing layer <b>106</b> of the metamaterial board <b>100</b>. In the present embodiment, the excitation of the metamaterial unit cells of the metamaterial layer <b>104</b> is achieved without direct contact by a capacitive structure (of small size) that couples RF power from the input RF port <b>112</b> to the metamaterial layer <b>104</b>. Also, the plurality of pads <b>114</b> (of square shape) placed above the metamaterial layer <b>104</b>, and going through the vias <b>110</b> behind the structure of the metamaterial board <b>100</b> excite the metamaterial unit cells as a capacitor, and therefore such a coupling is called the capacitive coupling. The contactless capacitive coupling excitation mechanism enables three metal layers of the metamaterial board <b>100</b>. In alternate embodiments described further herein, the excitation of the metamaterial board <b>100</b> may utilize fewer than or more than three metal layers.

In an embodiment, the two vias <b>110</b> connect to the RF port <b>112</b>, and therefore have a positive polarity and a negative polarity. One of the vias <b>110</b> at a negative potential is configured to excite half of the metamaterial unit cells <b>104a</b>, and the other of two vias <b>110</b> at a positive potential is configured to excite remaining half of the metamaterial unit cells <b>104a</b>. In the contactless capacitive coupling mechanism, a single via <b>110</b> with the corresponding pad <b>114</b> excites the adjacent metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> simultaneously because of a finite size of the corresponding pad <b>114</b> and since the corresponding pad <b>114</b> couples to both of the adjacent metamaterial unit cells <b>104a</b> equally.

In illustrative embodiment, the metamaterial unit cell <b>104a</b> is a square surface surrounding the square metal <b>104b</b> comprising the aperture, and the metallic element <b>104d</b> disposed within the aperture <b>104c</b>. The metallic element <b>104d</b> is a circular metal disk that has a smaller diameter than the aperture <b>104c</b>. The size of the aperture <b>104c</b> is inversely proportional to a frequency of operation. If the size of the aperture <b>104c</b> is reduced, the size of the metallic element <b>104d</b> disposed within the aperture <b>104c</b> is also reduced, and then the frequency of the operation moves up. If the size of the aperture <b>104c</b> is increased, the size of the metallic element <b>104d</b> disposed within the aperture <b>104c</b> also becomes larger, and then the frequency at which the metamaterial unit cell <b>104a</b> operates goes down. The aperture <b>104c</b> may be of circular shape. In an alternate embodiment, the aperture <b>104c</b> may be of an elliptical shape. Alternate shapes may be utilized.

In illustrative embodiment, the radiating structure of the metamaterial board <b>100</b> is linearly polarized, and has a transmit mode and a receive mode. In the transmit mode/configuration, the radiating structure of the metamaterial board <b>100</b> emits radiation where the electric field has a specific direction along a single line. In the receive mode/configuration, the radiating structure of the metamaterial board <b>100</b> receives the radiation.

<figref idref="f0002"><b>FIG. 1B</b></figref> illustrates a graph depicting the return loss of a metamaterial board <b>100</b> having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial board <b>100</b> having the contactless capacitive coupling is measured in dB. The metamaterial board <b>100</b> having the contactless capacitive coupling mechanism resonates at a center frequency of 6 GHz. The impedance matching here to a 50 Ohm RF port is at below -25 dB. The impedance matching represents matching of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism to a standard RF port, which is typically 50 ohm. The impedance matching bandwidth at the -10 dB level is 350 MHz, or 6% with respect to a center frequency of the metamaterial board <b>100.</b> The impedance matching defines the operation frequency band of the structure of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism. In one embodiment, the dimensions of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism may be chosen so that the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism tune to a standard operation frequency around 500 GHz. In another embodiment, impedance matching to other RF port values is possible with modifications of the presented shapes without moving out from the scope the disclosed embodiments.

<figref idref="f0003"><b>FIG. 1C</b></figref> illustrates an isometric view of a radiation gain pattern, in dB, of a metamaterial board <b>100</b> having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref>, according to an exemplary embodiment. As shown, the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism has a single directive electromagnetic beam of energy that is radiating upward/forward along the z-axis. The single directive electromagnetic beam is generated by excitation of entire sixteen metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b>.

<figref idref="f0004"><b>FIG. 1D</b></figref> illustrates a polar plot of a radiation gain pattern in linear scale of a metamaterial board <b>100</b> having a contactless capacitive coupling of <figref idref="f0001"><b>FIG. 1A</b></figref>, according to an exemplary embodiment. As shown, the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism has a single directive electromagnetic beam of energy that is directed broadside, with negligible radiation behind the metamaterial board <b>100.</b> The single directive electromagnetic beam is generated by excitation of entire sixteen metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b>.

<figref idref="f0005"><b>FIG. 1E</b></figref> illustrates a polar plot of a radiation gain pattern, in dB, on a principal Y-Z plane of a metamaterial board <b>100</b> having a contactless capacitive coupling of <figref idref="f0003"><b>FIG. 1C</b></figref>, according to an exemplary embodiment. The electromagnetic radiation emitted from the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism is linearly polarized, with a cross-polarization level at about 40 dB below a co-polarized radiation. In an embodiment, the metamaterial board <b>100</b> back-side radiation is suppressed and a front-to-back gain ratio is about 17 dB.

<figref idref="f0006"><b>FIG. 1F</b></figref> illustrates a magnitude of electric current surface density distribution on metamaterial unit cells layer <b>104</b> of a metamaterial board <b>100</b> having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref> at operational frequencies, according to an exemplary embodiment. The magnitude of the electric current surface density distributed on the radiative metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, at the operating frequency band, where the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> radiates is shown. In one embodiment, a plurality of metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> are excited from the contactless capacitive coupling mechanism and subsequently strong electric currents develop both on square patch edges and on circular slot edges of each of the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100.</b> This results in the plurality of metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> contributing to the electromagnetic radiation simultaneously, thereby leading to a high radiative gain of the metamaterial board <b>100.</b> In another embodiment, all the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> are excited from the contactless capacitive coupling mechanism due to strong electric currents that develop both on the square patch edges and on the circular slot edges of each of the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100.</b> In this embodiment, all the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> contributing to the electromagnetic radiation simultaneously, thereby leading to a high radiative gain of the metamaterial board <b>100.</b> It is contemplated that an alternate embodiment may actively or passively engage a plurality, but not all, metamaterial unit cells <b>104a</b> to contribute to the electromagnetic radiation. In an embodiment, although the excitation of the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> is localized at the center of the metamaterial board <b>100</b> using the contactless capacitive coupling mechanism, however as shown in the figure, the electric current spreads on all of the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> in order for radiation to occur. In an alternate embodiment, the excitation of the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> may be localized at any location of the metamaterial board <b>100</b> using the contactless capacitive coupling mechanism such that the electric current spreads on the plurality of the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> in order for radiation to occur.

In an embodiment, in order for radiation to occur, the metamaterial board <b>100</b> using the contactless capacitive coupling mechanism results in more than one metamaterial unit cell <b>104a</b> being excited for radiation to happen. In such a case, the multiple metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> has properties to work as a standard antenna. In an alternate embodiment, in order for radiation to occur, the metamaterial board <b>100</b> using the contactless capacitive coupling mechanism may have only a single metamaterial unit cell <b>104a</b> that may be excited for radiation to happen. In such a case, the single metamaterial unit cell <b>104a</b> has properties to work as a standard antenna.

<figref idref="f0007"><b>FIG. 1G</b></figref> illustrates a magnitude of electric current surface density distribution on a backing conductor layer <b>102</b> of a metamaterial board <b>100</b> having a contactless capacitive coupling mechanism of <figref idref="f0001"><b>FIG. 1A</b></figref> at operation frequencies, according to an exemplary embodiment. As shown, the electric current concentrates at the center of the conductive backing layer <b>102</b> of the metamaterial board <b>100</b>, and thereby creating a focusing effect that directs the electromagnetic power radiated by the metamaterial unit cells <b>104a</b> of the metamaterial board <b>100</b> in an upward direction, that is, along the z-axis.

<figref idref="f0008"><b>FIG. 2</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>200</b> having a co-planar coupling mechanism, according to an exemplary embodiment. In this embodiment, the co-planar coupling mechanism is used to excite an array of metamaterial unit cells of the metamaterial board <b>200.</b> The co-planar coupling mechanism is a contactless coupling mechanism, where a fewer number of metal layers may be utilized, and thereby resulting in reduction of manufacturing cost.

The metamaterial board <b>200</b> illustrated may be realized in standard Printed Circuit Board (PCB) technology utilizing two metal layers. The two metal layers comprise a conductive backing layer <b>202</b> and a metamaterial layer <b>204</b>. Also, a dielectric layer <b>206</b> is disposed between the conductive backing layer <b>202</b>, and the metamaterial layer <b>204</b>. In the metamaterial board <b>200</b> fabrication, the conductive backing layer <b>202</b> is placed at the bottom of the structure of the metamaterial board <b>200</b>. The metamaterial layer <b>204</b> may be deposited above the conductive backing layer <b>202</b>, and then may be etched to create an array of unit cells <b>204a</b>. In an embodiment, a distance between the conductive backing layer <b>202</b> and the metamaterial layer <b>204</b> is such that there is no short-circuit between the conductive backing layer <b>202</b> and the metamaterial layer <b>204</b> in order to make the metamaterial unit cells <b>204a</b> radiate. Below the metamaterial layer <b>204</b> and above the conductive backing layer <b>202</b> may be deposited a layer of dielectric <b>206</b> or insulating material, often a silicon dioxide.

The metamaterial layer <b>204</b> comprises the array of unit cells <b>204a</b>. In the illustrative figure, the metamaterial layer <b>204</b> of the metamaterial board <b>100</b> comprises sixteen radiative metamaterial unit cells <b>204a</b> in a four-by-four (4x4) arrangement. Each of the metamaterial unit cell <b>204a</b> may include a surface. In one embodiment, the surface may be a substantially flat surface. In another embodiment, the surface may not be a flat surface or a substantially flat surface. The substantially flat surface of each of the array of unit cells <b>204a</b> may be a square surface containing a square metal patch <b>204b</b> with an aperture <b>204c</b> inscribed within it. The square metal patch <b>204b</b> does not completely fill the unit cell surface, but is slightly smaller than the unit cell. The substantially flat surface of each of the array of unit cells <b>204a</b> may be a square metal patch <b>204b</b> with an aperture <b>204c</b> inscribed therein. The aperture <b>204c</b> is defined such that a periphery of the aperture <b>204c</b> is within a periphery of the square metal patch <b>204b</b> by a spacing distance. In one example, the aperture <b>204c</b> may be a circular aperture. An element <b>204d</b> may be disposed within the aperture <b>204c</b> to form a circular slot. In the illustrated embodiment, since the aperture <b>204c</b> is circular in shape, the element <b>204d</b> is a circular metal disk that is disposed within aperture <b>204c</b> to form the circular slot. It will be appreciated by a person having ordinary skill in the art that the shape of the aperture <b>204c</b> is not limited to circular shape, and the aperture <b>204c</b> may be of any other suitable shape without moving out from the scope of the disclosed embodiments. Also, the array composed of metamaterial unit cells <b>204a</b> contains square metal patches <b>204b</b> that do not touch each other, but are separated by narrow straight slots, since the unit cell surface is slightly larger than that of the square metal patches <b>204b</b> inscribed therein. In the illustrative figure, each of the unit cells <b>204a</b> is attached to the neighboring unit cell <b>204a</b>, but the inscribed square metal patches <b>204b</b> corresponding to these unit cells are separated by small-sized slots. Further, there is a thin slot separating the circular element <b>204d</b> from the periphery of the square metal patch <b>204b</b>. In an embodiment, one subset of the array of the metamaterial unit cells <b>204a</b> may be of one shape and size, and another subset of the array of the metamaterial unit cells <b>204a</b> may be of another shape and size.

The dielectric layer <b>206</b> is masked and etched to open narrow profile openings known as vias <b>208</b>. Each of the vias <b>208</b> respectively extends as an opening through the dielectric layer <b>206</b> to a portion of the uppermost layer. The vias <b>208</b> may be present to provide electrical paths between different metal layers of the metamaterial board <b>200</b>. In the illustrated figure, the vias <b>208</b> extend from the metamaterial layer <b>204</b> to input RF ports <b>210</b>. The input RF ports <b>210</b> may be located on or behind the conductive backing layer <b>202</b>. The geometries of the vias <b>208</b> and the contact structures that now fill the vias <b>208</b> are usually circular although the vias <b>208</b> may also form other shapes such as a trench shape. The vias <b>208</b> have been positioned so that the metallic structures that fill the vias <b>208</b> provide contacts between two separated metal layers of the metamaterial board <b>200</b>. In order to form the metamaterial board <b>200</b> with the vias <b>208</b> as described above, once a pattern of the vias <b>208</b> to traverse the layers is determined, these particular vias <b>208</b> may be machine drilled, punched, or etched through the layers. Alternative techniques for providing electrical paths between the layers may be utilized.

In an embodiment, excitation components of the co-planar coupling mechanism may be placed on the plane of the metamaterial unit cells <b>204a</b> of the metamaterial board <b>200</b> to excite the structure of the metamaterial board <b>200</b>. In the present embodiment, the excitation of the metamaterial unit cells <b>204a</b> of the metamaterial layer <b>204</b> is achieved without direct contact by a capacitive structure which couples RF power from the input RF port <b>210</b> to the metamaterial layer <b>204</b>. The RF port <b>210</b> is placed on the conductive backing layer <b>202</b>, where the RF port <b>210</b> feeding pads are placed within a small aperture in the conductive backing layer <b>202</b>. The co-planar coupling excitation mechanism utilize two metal layers of the metamaterial board <b>200</b>.

In an embodiment, the two vias <b>208</b> connect to the RF port <b>210</b>, and therefore have a positive polarity and a negative polarity. One of the vias <b>208</b> at a negative potential is configured to excite half of the metamaterial unit cells <b>204a</b> and the other via of two vias <b>208</b> at a positive potential is configured to excite the remaining half of the metamaterial unit cells <b>204a</b>.

In illustrative embodiment, the metamaterial unit cell <b>204a</b> is a square surface surrounding the square metal <b>204b</b> comprising the aperture <b>204c</b>, and the metallic element <b>204d</b> disposed within the aperture <b>204c</b>. The size of the aperture <b>204c</b> is inversely proportional to a frequency of operation. If the size of the aperture <b>204c</b> is reduced, the size of the metallic element <b>204d</b> disposed within the aperture <b>204c</b> is also reduced, and then the frequency of the operation moves up. If the size of the aperture <b>204c</b> is increased, the size of the metallic element <b>204d</b> disposed within the aperture <b>204c</b> also becomes larger, and the frequency at which the metamaterial unit cell <b>204a</b> operates goes down. The aperture <b>204c</b> may be of circular shape. In an alternate embodiment, the aperture <b>204c</b> may be an elliptical shape. Alternate shapes may be utilized as well.

The radiating structure of the metamaterial board <b>200</b> is linearly polarized, and has a transmit mode and a receive mode. In the transmit mode/configuration, the radiating structure of the metamaterial board <b>200</b> emits radiation, where the electric field has a specific direction along a single line. In the receive mode/configuration, the radiating structure of the metamaterial board <b>200</b> receives the radiation. In an embodiment, the radiation and impedance matching properties of the metamaterial board <b>200</b> having the co-planar coupling mechanism is identical to the structure of the metamaterial board <b>100</b> of <figref idref="f0001"><b>FIG. 1A</b></figref><b>.</b>

<figref idref="f0009"><b>FIG. 3A</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>300</b> having a direct feeding excitation mechanism, according to an exemplary embodiment. In this embodiment, the excitation mechanism used is the direct feeding mechanism through conductive vias. The direct feeding excitation mechanism may utilize two metal layers, thereby resulting in reduction of manufacturing cost. In the direct feeding excitation mechanism, the excitation of the metamaterial unit cells of the metamaterial board <b>300</b> does not happen with coupling either capacitively or coplanar, but happens when the vias directly connect to metamaterial unit cells.

The metamaterial board <b>300</b> illustrated here may be realized in standard Printed Circuit Board (PCB) technology utilizing two metal layers. The two metal layers may include a conductive backing layer <b>302</b>, and a metamaterial layer <b>304</b>. Also, a dielectric layer <b>306</b> may be disposed between the conductive backing layer <b>302</b>, and the metamaterial layer <b>304</b>. In the metamaterial board <b>300</b> fabrication, the conductive backing layer <b>302</b> is placed at the bottom of the structure of the metamaterial board <b>300</b>. The metamaterial layer <b>304</b> is deposited above the conductive backing layer <b>302</b>, and then may be etched to create an array of unit cells <b>304a</b>. In an embodiment, a distance between the conductive backing layer <b>302</b> and the metamaterial layer <b>304</b> is such that there is no short-circuit between the conductive backing layer <b>202</b> and the metamaterial layer <b>204</b> in order to make the metamaterial unit cells <b>304a</b> radiate. Below the metamaterial layer <b>304</b> and above the conductive backing layer <b>302</b> may be deposited a layer of dielectric <b>306</b> or insulating material, often a silicon dioxide.

The metamaterial layer <b>304</b> comprises the array of unit cells <b>304a</b>. In the illustrative figure, the metamaterial layer <b>304</b> of the metamaterial board <b>300</b> comprises sixteen radiative metamaterial unit cells <b>304a</b> in a four-by-four (4x4) arrangement. In the illustrative figure, each of the unit cells <b>304a</b> not attached to the other, and there is a small sized slot separating these unit cells <b>304a</b> from each other. Each of the metamaterial unit cell <b>304a</b> may include a surface. In one embodiment, the surface may be a substantially flat surface. In another embodiment, the surface may not be a flat surface or a substantially flat surface. The substantially flat surface of each of the array of unit cells <b>304a</b> may be a square surface containing a square metal patch <b>304b</b> with an aperture <b>304c</b> inscribed within it. The square metal patch <b>304b</b> does not completely fill the unit cell surface, but is slightly smaller than the unit cell. The substantially flat surface of each of the array of unit cells <b>304a</b> may be a square metal patch <b>304b</b> with an aperture <b>304c</b> inscribed within it. The aperture <b>304c</b> is defined such that a periphery of the aperture <b>304c</b> is within a periphery of the square metal patch <b>304b</b> by a spacing distance. In one example, the aperture <b>304c</b> may be a circular aperture. An element <b>304d</b> may be disposed within the aperture <b>304c</b> to form a circular slot. In the illustrated embodiment, since the aperture <b>304c</b> is circular in shape, the element <b>304d</b> is a circular metal disk that is disposed within aperture <b>304c</b> to form the circular slot. It will be appreciated by a person having ordinary skill in the art that the shape of the aperture <b>304c</b> is not limited to circular shape, and the aperture <b>304c</b> may be of any other suitable shape without moving out from the scope of the disclosed embodiments. Also, the array composed of metamaterial unit cells <b>304a</b> contains square metal patches <b>304b</b> that do not touch each other, but are separated by narrow straight slots, since the unit cell surface is slightly larger than that of the metal patch inscribed in it. In the illustrative figure, each of the unit cells <b>304a</b> is attached to the neighboring unit cell <b>304a</b>, but the inscribed square metal patches <b>304b</b> corresponding to these unit cells <b>304a</b> are separated by small-sized slots. Further, there is a thin slot separating the circular element <b>304d</b> from the periphery of the square metal patch <b>304b</b>. In an embodiment, one subset of the array of the metamaterial unit cells <b>304a</b> may be of one shape and size, and another subset of the array of the metamaterial unit cells <b>304a</b> may be of another shape and size.

The dielectric layer <b>306</b> may be masked and etched to open narrow profile openings known as vias <b>308</b>. Each of the vias <b>208</b> respectively extend as an opening through the dielectric layer <b>306</b> to a portion of the uppermost layer. The vias <b>308</b> may be present to provide electrical paths between different metal layers of the metamaterial board <b>300</b>. In the illustrated figure, the vias <b>308</b> extend from the metamaterial layer <b>304</b> to input RF ports <b>310</b>. The input RF ports <b>310</b> may be located on or behind the conductive backing layer <b>302</b>. The geometries of the vias <b>308</b> and the contact structures which now fill the vias <b>308</b> are usually circular although the vias <b>308</b> may also form other shapes such as a trench shape. The vias <b>308</b> have been positioned so that the metallic structures which fill the vias <b>308</b> provide contacts between two separated metal layers of the metamaterial board <b>300</b>.

In an embodiment, excitation components of the direct feeding mechanism may be placed on the plane of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> to excite the metamaterial board <b>300</b>. In the present embodiment, the excitation of the metamaterial unit cells <b>304a</b> of the metamaterial layer <b>304</b> is achieved by the vias <b>308</b>. In an embodiment, the vias <b>308</b> may connect to the RF port <b>310</b> and therefore have a positive polarity and a negative polarity. One of the vias <b>308a</b> at a negative potential is configured to excite half of the metamaterial unit cells <b>304a</b> and the other via of two vias <b>308b</b> at a positive potential is configured to excite remaining half of the metamaterial unit cells <b>304a</b>.

In illustrative embodiment, the metamaterial unit cell <b>304a</b> may be a square surface surrounding the square metal <b>304b</b> comprising the aperture <b>304c</b>, and the metallic element <b>304d</b> may be disposed within the aperture <b>304c.</b> The size of the aperture <b>304c</b> is inversely proportional to a frequency of operation. If the size of the aperture <b>304c</b> is reduced, the size of the metallic element <b>304c</b> disposed within the aperture <b>304c</b> is also reduced, and then the frequency of the operation moves up. If the size of the aperture <b>304c</b> is increased, the size of the metallic element <b>304c</b> disposed within the aperture <b>304c</b> is also becomes larger, and then the frequency at which the metamaterial unit cell <b>304a</b> operates goes down. The aperture <b>304c</b> may be of circular shape. In an alternate embodiment, the aperture <b>304c</b> may be an eclipse shape. Alternate shapes may be utilized.

The radiating structure of the metamaterial board <b>300</b> is linearly polarized, and has a transmit mode and a receive mode. In the transmit mode/configuration, the radiating structure of the metamaterial board <b>300</b> emit radiation, where the electric field has a specific direction along a single line. In the receive mode/configuration, the radiating structure of the metamaterial board <b>200</b> receives the radiations.

<figref idref="f0010"><b>FIG. 3B</b></figref> illustrates a graph depicting a return loss of a metamaterial board <b>300</b> having a direct feeding excitation mechanism of <figref idref="f0009"><b>FIG. 3A</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial board <b>300</b> having the direct feeding excitation mechanism is measured in dB. The metamaterial board <b>300</b> having the direct feeding excitation mechanism resonates at a center frequency of 5.9 GHz. The impedance matching here to a 50 Ohm RF port <b>310</b> is at -25 dB. The impedance matching represents matching of the metamaterial board <b>300</b> having the direct feeding excitation mechanism to a standard RF port <b>310</b> which is typically 50 ohm. The impedance matching bandwidth at the -10 dB level is 350 MHz, or 6% with respect to a center frequency of the metamaterial board <b>300</b>. The impedance matching defines the operation frequency band of the metamaterial board <b>300</b> having the direct feeding excitation mechanism.

<figref idref="f0011"><b>FIG. 3C</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board <b>300</b> having a direct feeding excitation mechanism of <figref idref="f0009"><b>FIG. 3A</b></figref>, according to an exemplary embodiment. As shown, the metamaterial board <b>300</b> having the direct feeding excitation mechanism has a single directive electromagnetic beam of energy that is radiating upward/forward, that is, along the z-axis. The single directive electromagnetic beam is generated by excitation of entire sixteen metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b>.

<figref idref="f0012"><b>FIG. 3D</b></figref> illustrates a magnitude of electric current surface density distribution on metamaterial cells layer <b>302</b> of a metamaterial board <b>300</b> having a direct feeding excitation mechanism of <figref idref="f0009"><b>FIG. 3A</b></figref> at operation frequencies, according to an exemplary embodiment. The magnitude of the electric current surface density distributed on the radiative metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> having the direct feeding excitation mechanism, at the operating frequency band, where the metamaterial board radiates is shown. In one embodiment, a plurality of metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> are excited from the direct feeding excitation mechanism and subsequently strong electric currents develop both on square patch edges and on circular slot edges of each of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b>. This results in the plurality of metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> contributing to the electromagnetic radiation simultaneously, thereby leading to a high radiative gain of the metamaterial board <b>300</b>. In another embodiment, all the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> are excited from the direct feeding excitation mechanism due to strong electric currents that develop both on the square patch edges and on the circular slot edges of each of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b>. In this embodiment, all the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> contributing to the electromagnetic radiation simultaneously, thereby leading to a high radiative gain of the metamaterial board <b>300</b>.

In an embodiment, although the excitation of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> is localized at the center of the metamaterial board <b>300</b> using the direct feed coupling mechanism, however as shown in the figure, the electric current spreads on all of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> in order for radiation to occur. In an alternate embodiment, the excitation of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> may be localized at any location of the metamaterial board <b>300</b> such that the electric current spreads on the plurality of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> in order for radiation to occur.

In an embodiment, in order for radiation to occur, the metamaterial board <b>300</b> using the direct feed coupling mechanism may utilize more than one metamaterial unit cell <b>304a</b> that causes excitation for radiation to happen. In such a case, the multiple metamaterial unit cells <b>304a</b> of the metamaterial board <b>300</b> has properties to work as a standard antenna. In an alternate embodiment, in order for radiation to occur, the metamaterial board <b>300</b> using the direct feed coupling mechanism may have a single metamaterial unit cell <b>304a</b> that may be excited for radiation to happen. In such a case, the single metamaterial unit cell <b>304a</b> has properties to work as a standard antenna.

<figref idref="f0013"><b>FIG. 3E</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>300a</b> having a direct feeding excitation mechanism, according to an exemplary embodiment. The structure of the metamaterial board <b>300a</b> of <figref idref="f0013"><b>FIG. 3E</b></figref> is similar to the structure of the metamaterial board <b>300</b> of <figref idref="f0009"><b>FIG. 3A</b></figref> other than the dimensions and sizes of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300a</b>. The difference in the dimensions and sizes of the components such as metamaterial unit cells <b>304a</b> of the metamaterial board <b>300a</b> in comparison to the dimensions and sizes of the components such as metamaterial unit cells of the metamaterial board <b>300</b> aids to achieve the scaling of the operation frequency. In this embodiment, circular slots on each of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300a</b> are narrower than the circular slots on each of the metamaterial unit cells of the metamaterial board <b>300</b> of <figref idref="f0009"><b>FIG. 3A</b></figref>. Also, spacing distance between the square patches of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300a</b> is narrower than the spacing distance between the square patches of metamaterial unit cells of the metamaterial board <b>300</b> of <figref idref="f0009"><b>FIG. 3A</b></figref>. In the illustrated example, the circular slots on each of the metamaterial unit cells <b>304a</b> of the metamaterial board <b>300a</b> are 0.1mm wide in comparison to the circular slots on each of the metamaterial unit cells of the metamaterial board <b>300</b> of <figref idref="f0009"><b>FIG. 3A</b></figref> which were 0.15mm wide. In the illustrated example, the total size of the metamaterial board in the embodiments described in <figref idref="f0009"><b>FIG. 3A</b></figref> and <figref idref="f0013"><b>FIG. 3E</b></figref> is 20mm × 20mm, however it is to be appreciated by a person having ordinary skill in the art that in other embodiments the size may vary without moving out from the scope of the disclosed embodiments.

<figref idref="f0014"><b>FIG. 3F</b></figref> illustrates a graph depicting a return loss of a metamaterial board <b>300a</b> having a direct feeding excitation mechanism of <figref idref="f0013"><b>FIG. 3E</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial board <b>300a</b> having the direct feeding excitation mechanism is measured in dB. The metamaterial board <b>300a</b> having the direct feeding excitation mechanism resonates at a center frequency of 5.8 GHz. The center frequency is reduced by 150-100 MHz relative to the embodiments discussed in <figref idref="f0009"><b>FIG. 3A</b></figref> without increase in the size of the overall structure of the metamaterial board <b>300a</b>. The impedance matching to a 50-Ohm RF port is at -28 dB. The impedance matching represents matching of the metamaterial board <b>300a</b> having the direct feeding excitation mechanism to a standard RF port which is typically 50 ohm. The impedance matching bandwidth at the -10 dB level is 350 MHz, or 6% with respect to a center frequency of the metamaterial board <b>300a</b>.

<figref idref="f0015"><b>FIG. 4</b></figref> illustrates an enlarged sectional view of a structure of a metamaterial board having a contactless capacitive coupling, a co-planar coupling mechanism, and a direct feeding excitation mechanism, according to an exemplary embodiment. The metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism have the same or substantially the same physical characteristics, operation bandwidth and performance. In another embodiment, other excitation mechanisms to excite the metamaterial board for radiation to happen may be used. In yet another embodiment, hybrid combinations of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism may be employed.

In an embodiment, the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism uses three metal layers. The metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism uses two metal layers. The metamaterial board <b>100</b> having the contactless capacitive coupling mechanism uses an extra metallic layer in comparison to the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism. Each layer of metal increases the cost of manufacturing and therefore the manufacturing cost of the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism is less than the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism. As the metamaterial board <b>300</b> having the direct feeding excitation mechanism uses two metal layers, the control of manufacturing process is more robust in the metamaterial board <b>300</b> having the direct feeding excitation mechanism by directly having the vias positioned on the actual metamaterial unit cells without having any circular patches with a specific slot exciting the central metamaterial unit cells of the metamaterial board <b>300</b>.

In an embodiment, the size of the metamaterial unit cell in the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism is selected based on a desired operating frequency. The size of the metamaterial unit cell along with its adjacent metamaterial unit cells determines the frequency of operation of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism. The frequency of the unit cell is configured to operate in a frequency band ranging from 900 MHz to 100 GHz. In an embodiment, the shape of the metamaterial unit cell in the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism such as thin slots are important for frequency tuning. In an embodiment, the diameter of each of the metamaterial unit cell of the metamaterial board <b>100</b> having the contactless capacitive coupling mechanism, the metamaterial board <b>200</b> having the co-planar coupling mechanism, and the metamaterial board <b>300</b> having the direct feeding excitation mechanism is about one-tenth of the wavelength of the frequency of operation.

<figref idref="f0016"><b>FIG. 5A</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>500</b> having a direct feeding excitation mechanism, according to an exemplary embodiment. As previously described, number of metamaterial unit cells affects the performance of metamaterial board. In the illustrative embodiment, the size of the metamaterial board <b>500</b> is identical or substantially identical to the size of the metamaterial board <b>300</b> illustrated in <figref idref="f0009"><b>FIG. 3A</b></figref>, but the metamaterial board <b>500</b> of the illustrative embodiment comprises four metamaterial unit cells <b>502</b> in comparison to the sixteen unit cells <b>304a</b> of the metamaterial board <b>300</b> illustrated in <figref idref="f0009"><b>FIG. 3A</b></figref>. In this embodiment, the excitation mechanism used is direct feeding excitation mechanism through conductive vias. The direct feeding excitation mechanism utilizes two metal layers, and thereby resulting in reduction of manufacturing cost. In the direct feeding excitation mechanism, the excitation of the metamaterial unit cells <b>502</b> of the metamaterial board <b>500</b> does not happen with coupling either capacitively or coplanar, but happens when vias <b>504</b> directly connect to metamaterial unit cells <b>502</b>. The direct feeding excitation mechanism is explained in detail in <figref idref="f0009"><b>FIG. 3A</b></figref>.

<figref idref="f0017"><b>FIG. 5B</b></figref> illustrates a graph depicting a return loss of a metamaterial board <b>500</b> having a direct feeding excitation mechanism <figref idref="f0016"><b>FIG. 5A</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial board <b>500</b> having the direct feeding excitation mechanism is measured in dB. The metamaterial board <b>500</b> having the direct feeding excitation mechanism resonates at a center frequency of 5.8 GHz. This illustrates that the resonant frequency of operation is determined by design of the metamaterial unit cells <b>502</b> and is not dependent on the number of the metamaterial unit cells <b>502</b>. The impedance matching to a 50-Ohm RF port is at or below -30 dB, which is smaller than the embodiments discussed earlier having sixteen metamaterial unit cells. The impedance matching represents matching of the metamaterial board <b>500</b> to a standard RF port, which is typically 50 ohm. The impedance matching bandwidth at the -10 dB level is 240 MHz, or 4% with respect to a center frequency of the metamaterial board <b>500</b>. The impedance matching defines the operation frequency band of the structure of the metamaterial board <b>500</b>.

<figref idref="f0018"><b>FIG. 5C</b></figref> illustrates a 3-dimensional isometric view of a radiation gain pattern of a metamaterial board <b>500</b> having a direct feeding excitation mechanism of <figref idref="f0016"><b>FIG. 5A</b></figref>, according to an exemplary embodiment. As shown, the metamaterial board <b>500</b> having the direct feeding excitation mechanism has a single directive electromagnetic beam of energy that is radiating upward/forward. The single directive electromagnetic beam is generated by excitation of entire four metamaterial unit cells <b>502</b> of the metamaterial board <b>500</b>. In the illustrative embodiment, the maximum gain is 5 dBi, which is 1 dB lower than the earlier embodiments discussed comprising sixteen metamaterial unit cells. Since the size of the conductive backing layer is same in earlier and the present embodiment, the directive radiation is caused by the collective excitation of a plurality of metamaterial unit cells <b>502</b> in the present embodiment as well as earlier embodiments.

<figref idref="f0019"><b>FIG. 5D</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>500a</b> having a direct feeding excitation mechanism, according to an exemplary embodiment. The illustrative embodiment has the metamaterial board <b>500a</b> that may be identically configured to the metamaterial board <b>500</b> described in <figref idref="f0016"><b>FIG. 5A</b></figref>, but not identical in all facets and thus this results in a compact form factor in this structure.

<figref idref="f0020"><b>FIG. 5E</b></figref> illustrates a graph depicting a return loss of a metamaterial board <b>500a</b> having a direct feeding excitation mechanism <figref idref="f0019"><b>FIG. 5D</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial board <b>500a</b> having the direct feeding excitation mechanism is measured in dB. The metamaterial board <b>500a</b> resonates at a center frequency of 5.75 GHz. The impedance matching to a 50 Ohm RF port is at or below -25 dB. The impedance matching represents matching of the metamaterial board <b>500a</b> to a standard RF port, which is typically 50 ohm. The impedance matching bandwidth at the -10 dB level is 160 MHz, or 3% with respect to a center frequency of the metamaterial board <b>500a</b>. The impedance matching defines the operation frequency band of the structure of the metamaterial board <b>500a</b>.

<figref idref="f0021"><b>FIG. 5F</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board <b>500a</b> having a direct feeding excitation mechanism of <figref idref="f0019"><b>FIG. 5D</b></figref>, according to an exemplary embodiment. As shown, the metamaterial board <b>500a</b> has a single directive electromagnetic beam of energy that is radiating upward/forward. The single directive electromagnetic beam is generated by excitation of entire four metamaterial unit cells <b>502</b>. In the illustrative embodiment, the maximum gain is 4.4 dBi, which 0.6 dB lower relative to earlier embodiment described with respect to <figref idref="f0016"><b>FIG. 5A</b></figref> and 1.6 dB lower than the earlier embodiments comprising sixteen metamaterial unit cells. Since the size of a conductive backing layer is same in earlier and the present embodiments, the directive radiation is caused by the collective excitation of all metamaterial unit cells <b>502</b> in the present embodiment as well as earlier embodiments.

<figref idref="f0022"><b>FIG. 6A</b></figref> illustrates a configuration of metamaterial unit cells for use as wearable antennas, according to an exemplary embodiment, and <figref idref="f0023"><b>FIG. 6B</b></figref> illustrates an enlarged sectional view of the structure depicted in <figref idref="f0022"><b>FIG. 6A</b></figref>. The metamaterial unit cells <b>602</b> are of small size and the size of the metamaterial unit cells <b>602</b> is smaller than a radius of curvature of a curved surface of any wrist wearable bracelet. This flexibility in size allows the metamaterial unit cells <b>602</b> to be etched on the curved surface of the bracelet. In the illustrated example, there is a wearable bracelet <b>604</b>. The wearable bracelet <b>604</b> is made of a flexible plastic and is a flexible isolator. In one example, the thickness of the plastic is about 1.5 millimeters, and the inner diameter is about 60 millimeters. The number of the metamaterial unit cells <b>602</b> is four, and the metamaterial unit cells <b>602</b> are arranged in a linear array configuration. In the illustrated example, the size of each of the four metamaterial unit cells <b>602</b> is about six millimeters, however, it is to be noted that in other embodiments the metamaterial unit cells <b>602</b> can be of different size without moving out from the scope of the disclosed embodiments.

In the illustrated embodiment, the excitation mechanism employed for exciting the metamaterial unit cells <b>602</b> is a direct feeding exciting mechanism. It is to be noted that in other embodiments of the present disclosure, any other exciting mechanism may be employed for exciting the metamaterial unit cells <b>602</b> without moving out from the scope of the disclosed embodiments. In the direct feed exciting mechanism, a set of vias may directly excite the metamaterial unit cells <b>602</b>. In the illustrative embodiment, there is only a single row of the metamaterial unit cells <b>602</b>, and therefore a double set of vias may not be utilized, and a single set of vias may be utilized to excite the single row of the metamaterial unit cells <b>602</b>. In the single set of vias, one via <b>606a</b> is configured to have a positive polarity contact and another via <b>606b</b> is configured to have a negative polarity contact. The positive polarity via <b>606a</b> feeds and/or excite half proportion of the row of the metamaterial unit cells <b>602</b>, and the negative polarity via <b>606b</b> feeds and/or excite the other half proportion of the row of the metamaterial unit cells <b>602</b>. The direct feed exciting mechanism is explained in detail in <figref idref="f0009"><b>FIG. 3A</b></figref>.

In the illustrated example, the size of the each of the metamaterial unit cells <b>602</b> is 6mm × 6mm × 1.5mm (bracelet thickness) or 0.11 × 0.11 × 0.03 λ³, where λ is the wavelength at a frequency of operation. An inner diameter of the bracelet <b>604</b> is 60 mm which is similar to that of a standard-size wrist-worn bracelet. Alternate dimensions of the bracelet <b>604</b> may be utilized for different purpose.

<figref idref="f0024"><b>FIG. 6C</b></figref> illustrates a graph depicting a return loss of metamaterial unit cells as wearable antennas of <figref idref="f0022"><b>FIG. 6A</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial unit cells <b>602</b> as wearable antennas is measured in dB. The metamaterial unit cells <b>602</b> as wearable antennas resonates at a center frequency of 5.75 GHz where the reflection is at the minimum. The resonant frequency of operation is determined by design of the metamaterial unit cells <b>602</b> and is not dependent on the number of the metamaterial unit cells <b>602</b>. The impedance matching is to a 50-Ohm RF port and is at or below -10 dB. The impedance matching represents matching of the structure to a standard RF port, which is typically 50 ohms. The impedance matching bandwidth at the -10 dB level is 500 MHz, which is quite large, and defines the operation frequency band of the structure of the metamaterial unit cells <b>602</b> configured as wearable antennas. In addition to the other advantages described above, the present embodiment is ideal for wearable antennas due to this large natural bandwidth because it is desirable to have spare bandwidth to accommodate impedance because the impedance provides a tuning effect from adjacent structures, such as from objects behind the bracelet <b>604</b> (e.g., human hand).

<figref idref="f0025"><b>FIG. 6D</b></figref> illustrates a 3-dimensional isometric view of a radiation gain pattern of metamaterial unit cells as wearable antennas of <figref idref="f0022"><b>FIG. 6A</b></figref>, according to an exemplary embodiment. As shown, the metamaterial unit cells <b>602</b> as wearable antennas has a single directive electromagnetic beam of energy that is radiating upward/forward, that is, along the z-axis. The single directive electromagnetic beam is generated by excitation of a plurality of the metamaterial unit cells <b>602</b> and there is minimum radiation towards the inside of the bracelet <b>604</b> and into a human wrist. In the illustrative embodiment, a maximum gain is 3.7 dBi, and an antenna radiation efficiency is 91%.

<figref idref="f0026"><b>FIG. 7A</b></figref> illustrates a structure of metamaterial unit cells configured as wearable antennas, according to an exemplary embodiment, and <figref idref="f0027"><b>FIG. 7B</b></figref> illustrates an enlarged sectional view of the structure depicted in <figref idref="f0026"><b>FIG. 7A</b>. <b>FIG. 7A</b></figref> shows another embodiment of radiative metamaterials unit cells <b>702</b> as wearable/flexible/conformal antennas. In this embodiment, a bracelet <b>704</b> may have the same dimensions as of the bracelet <b>604</b> depicted in the embodiment of the <figref idref="f0022"><b>FIG. 6A</b></figref>, however, there are three metamaterials unit cells <b>702</b> of smaller size attached on a curved surface of the bracelet <b>704</b>.

In the illustrative embodiment, the three metamaterials unit cells <b>702</b> are probed with four RF ports <b>706</b>, making the structure equivalent to an extremely dense 4-antenna array. In a receiving mode configuration, the three metamaterials unit cells <b>702</b> absorbs RF energy which is directed to distinct prescribed locations. In other words, the three metamaterials unit cells <b>702</b> operate as uniform materials that absorb electromagnetic radiation with high absorption efficiency.

The three metamaterials unit cells <b>702</b> can be tapped by inserting four localized RF ports <b>706</b> to the three metamaterials unit cells <b>702</b>. This power is then directed specifically to the localized RF ports <b>706</b>. In view of that, this structure with the metamaterials unit cells <b>702</b> works as a dense antenna array with many RF ports <b>706</b> that receive the absorbed energy. Such structure is ideal for very physically small receivers where there is a need to distribute the received power to multiple channels simultaneously. In addition, these multiple densely placed RF ports <b>706</b> can accept phase control, resulting in electronically modulated RF patterns.

In an embodiment, this structure with the metamaterials unit cells <b>702</b> has a very small form factor that matches a receiver ASIC (not shown). The ASIC is positioned in middle behind a conductive backing layer positioned at the bottom of the structure, and would be configured to connect its inputs to the four RF ports <b>706</b>. Since the tapping can be performed at different places, the ASIC may require less power per RF port. In order to obtain bandwidth in the structure, both the space as well as thickness of a substrate is required. In the illustrative embodiment, a 2 GHz bandwidth may be obtained using a structure including three metamaterial unit cells <b>702</b> and four RF ports <b>706</b>.

<figref idref="f0028"><b>FIG. 8A</b></figref> illustrates an isometric view of a structure of a metamaterial board <b>800</b> configured as a flat antenna array that can be fabricated on standard PCB boards, according to an exemplary embodiment. In an embodiment, radiative metamaterials unit cells <b>802</b> are configured as the antenna arrays to receive and/or transmit RF signals. The metamaterials unit cells <b>802</b> are connected to 4 RF ports, making this structure equivalent of four antennas that are extremely closely spaced. The present embodiment is the equivalent of the wearable configuration of <figref idref="f0026"><b>FIG. 7A</b></figref>, but on a flat platform appropriate for systems realized on standard flat boards. In a receive mode of operation, the absorbed power is then directed specifically to localized RF ports <b>804</b> and <b>806</b>. The structure is ideal for physically small receivers where there is a need to distribute the received power to multiple channels simultaneously. In addition, the multiple densely placed RF ports <b>804</b> and <b>806</b> can accept phase control, resulting in electronically modulated RF patterns.

In the illustrated example, the metamaterial unit cell <b>802</b> size is 6mm × 6mm × 1.5mm (bracelet thickness) or 0.11 × 0.11 × 0.03 λ³, where λ is the wavelength at the frequency of operation. The overall metamaterial structure dimension is 6mm × 18mm × 1.5mm or 0.11 × 0.33 × 0.03 λ³. Alternate dimensions of the metamaterial unit cell 802 and bracelet thickness may be utilized.

<figref idref="f0029"><b>FIG. 8B</b></figref> illustrates a graph depicting a return loss of a metamaterial board <b>800</b> configured as an antenna array of <figref idref="f0028"><b>FIG. 8A</b></figref>, according to an exemplary embodiment. The return loss (reflected power) of the metamaterial board <b>800</b> as the antenna array is measured in dB. The impedance matching is at -10 dB. The impedance matching represents matching of the metamaterial board <b>800</b> as antenna array to a standard RF port, which is typically 50 ohm. The impedance matching bandwidth at the -10 dB level is 2 GHz, or 35% with respect to a center frequency of the metamaterial board <b>800</b>. This defines the operation frequency band of the metamaterial board <b>800</b> as flat antenna array.

<figref idref="f0030"><b>FIG. 8C</b></figref> illustrates an isometric view of a radiation gain pattern of a metamaterial board configured as an antenna array of <figref idref="f0028"><b>FIG. 8A</b></figref>, according to an exemplary embodiment. As shown, the metamaterial board <b>800</b> as the antenna array has a single directive electromagnetic beam of energy that is radiating upward/forward, that is, along the z-axis. The single directive electromagnetic beam is generated by excitation of all of the metamaterials unit cells <b>802</b>. In the illustrative embodiment, the maximum gain is 3.6-3.8 dBi. Since the size of a conductive backing layer (positioned at the bottom of the metamaterial board <b>800</b>) is same as defined in earlier embodiments, a directive radiation is caused by the collective excitation of a plurality of metamaterials unit cells <b>802</b> in the present embodiment as well as earlier embodiments. Also, there is minimal radiation on the backside of the metamaterial board <b>800</b>, and an antenna radiation efficiency is about 90%.

<figref idref="f0031"><b>FIG. 9A</b></figref> illustrates an isometric view of a structure of a metamaterial board including two orthogonal sub-arrays, according to an exemplary embodiment. In the illustrated embodiment, there are two sub-arrays <b>902a</b> and <b>902b</b> that are laid out on a common dielectric substrate. Each of the two sub-arrays <b>902a</b> and <b>902b</b> has three metamaterials unit cells that are connected to 4 RF ports, thereby making the structure of each of the two sub-arrays <b>902a</b> and <b>902b</b> equivalent of four antennas that are extremely closely spaced. The impedance matching of the two sub-arrays <b>902a</b> and <b>902b</b>, for all 8 RF ports, may be identical to each metamaterial board <b>800</b>, shown in <figref idref="f0029"><b>FIG. 8B</b></figref>.

In an embodiment, if only the metamaterials unit cells of the sub-array <b>902a</b> of <figref idref="f0031"><b>FIG. 9A</b></figref> are active, the 3D radiation gain as seen from the top is shown in <figref idref="f0032"><b>FIG. 9B</b></figref>. The polarization, which is the electric field direction, of the structure, at a far-field point on the z-axis, is also shown in <figref idref="f0032"><b>FIG. 9B</b></figref>. In an embodiment, if the metamaterials unit cells of the sub-array <b>902b</b> of <figref idref="f0031"><b>FIG. 9A</b></figref> are active, the 3D radiation gain as seen from the top is shown in <figref idref="f0033"><b>FIG. 9C</b></figref>. The polarization of the structure, at a far-field point on the z-axis, is also shown in <figref idref="f0033"><b>FIG. 9C</b></figref> and the polarization along the z-axis is orthogonal to the polarization of <figref idref="f0033"><b>FIG. 9C</b></figref>.

In the illustrative embodiment, when all eight RF ports of the structure are active, i.e., when both two sub-arrays <b>902a</b> and <b>902b</b> have active RF ports, the radiation gain is shown in <figref idref="f0034"><b>FIGS. 9D</b></figref> and <figref idref="f0035"><b>9E</b></figref>. The radiation gain has a rhombic, or rotated square shape. When the structure is implemented as a receiver, per the radiation gain pattern shown, it is clear that the structure receives electromagnetic power polarized either in the x-axis or the y-axis direction, equally. Thus, this metamaterial board structure with the two sub-arrays <b>902a</b> and <b>902b</b> is a very compact and extremely efficient dual linear polarization receiver array. The structure may be able to receive both polarizations, and therefore a signal may always be present to charge a battery or other chargeable device from received RF signals.

<figref idref="f0036"><b>FIG. 10</b></figref> illustrates a method of forming a metamaterial board, according to an exemplary embodiment.

At step <b>1002</b>, a backing layer is formed. In the metamaterial board fabrication, the conductive backing layer is placed at the bottom of the structure of the metamaterial board. At step <b>1004</b>, a metamaterial layer is formed. The metamaterial layer may be formed by a metamaterial substrate. In one embodiment, the metamaterial layer may be deposited above the conductive backing layer, and then may be etched to create an array of metamaterial unit cells at step <b>1006</b>. Hereinafter, the term "unit cell" and "metamaterial unit cell" may be interchangeably used. In an embodiment, a distance between the conductive backing layer, and the metamaterial layer is such that there is no short-circuit between the conductive backing layer and the metamaterial layer in order to make the metamaterial unit cells radiate. Below the metamaterial layer and above the conductive backing layer <b>102</b> may be deposited a layer of dielectric or insulating material, often a silicon dioxide.

At step <b>1006</b>, a plurality of partitions may be created. A surface is created in the metamaterial layer. In one embodiment, the surface created is a substantially flat surface. In another embodiment, the surface created is not a substantially flat surface or a flat surface. The surface of the metamaterial layer may be composed of a plurality of partitions The plurality of partitions are created on the surface of the metamaterial layer. Each of the plurality of partition includes identical unit cells. In an alternative embodiment, two different partitions may contain different unit cells.

At step <b>1008</b>, a unit cell is created in each partition. The unit cell is defined as a surface, which by periodic repetition fills the surface of each partition. Within the surface of the unit cell, a metal patch of a square or other arbitrary shape may be inscribed. Within the metal patch an aperture exists. The aperture is defined such that a periphery of the aperture is within a periphery of the metal patch by a spacing distance. At step <b>1010</b>, a metallic element is disposed in each aperture to form unit cells. In one embodiment, the element is a circular element (or disk) that may be disposed within each aperture to form unit cells. The unit cell is therefore defined as the composite shape composed of the unit cell surface, the inscribed metal patch, the aperture within the metal patch and the metallic element within that aperture. Each different partition in the plurality of partitions that collectively forms the metamaterial layer, may be composed of different types of unit cells.

At step <b>1012</b>, RF port is formed on backing layer. The RF ports may be located on or behind the conductive backing layer. The RF ports may include a housing having any arbitrary shape, and manufactured from plastic, metal, or any other convenient material. At step <b>1014</b>, unit cells are connected to RF port. The dielectric layer may be masked and etched to open narrow profile openings known as vias. The vias respectively extend as an opening through the dielectric layer to a portion of the metamaterial layer. In one embodiment, the vias may be present to provide electrical paths between different metal layers of the metamaterial board by connecting the unit cells with the RF port.

The foregoing method descriptions and the process flow diagrams are provided merely as illustrative examples and are not intended to require or imply that the steps of the various embodiments must be performed in the order presented. As will be appreciated by one of skill in the art the steps in the foregoing embodiments may be performed in any order. Words such as "then," "next," etc. are not intended to limit the order of the steps; these words are simply used to guide the reader through the description of the methods. Although process flow diagrams may describe the operations as a sequential process, many of the operations can be performed in parallel or concurrently. In addition, the order of the operations may be rearranged. A process may correspond to a method, a function, a procedure, a subroutine, a subprogram, etc. When a process corresponds to a function, its termination may correspond to a return of the function to the calling function or the main function.

The various illustrative logical blocks, modules, circuits, and algorithm steps described in connection with the embodiments disclosed herein may be implemented as electronic hardware, computer software, or combinations of both. To clearly illustrate this interchangeability of hardware and software, various illustrative components, blocks, modules, circuits, and steps have been described above generally in terms of their functionality. Whether such functionality is implemented as hardware or software depends upon the particular application and design constraints imposed on the overall system. Skilled artisans may implement the described functionality in varying ways for each particular application, but such implementation decisions should not be interpreted as causing a departure from the scope of the present invention.

Embodiments implemented in computer software may be implemented in software, firmware, middleware, microcode, hardware description languages, or any combination thereof. A code segment or machine-executable instructions may represent a procedure, a function, a subprogram, a program, a routine, a subroutine, a module, a software package, a class, or any combination of instructions, data structures, or program statements. A code segment may be coupled to another code segment or a hardware circuit by passing and/or receiving information, data, arguments, parameters, or memory contents. Information, arguments, parameters, data, etc. may be passed, forwarded, or transmitted via any suitable means including memory sharing, message passing, token passing, network transmission, etc.

The actual software code or specialized control hardware used to implement these systems and methods is not limiting of the invention. Thus, the operation and behavior of the systems and methods were described without reference to the specific software code being understood that software and control hardware can be designed to implement the systems and methods based on the description herein.

When implemented in software, the functions may be stored as one or more instructions or code on a non-transitory computer-readable or processor-readable storage medium. The steps of a method or algorithm disclosed herein may be embodied in a processor-executable software module which may reside on a computer-readable or processor-readable storage medium. A non-transitory computer-readable or processor-readable media includes both computer storage media and tangible storage media that facilitate transfer of a computer program from one place to another. A non-transitory processor-readable storage media may be any available media that may be accessed by a computer. By way of example, and not limitation, such non-transitory processor-readable media may comprise RAM, ROM, EEPROM, CD-ROM or other optical disk storage, magnetic disk storage or other magnetic storage devices, or any other tangible storage medium that may be used to store desired program code in the form of instructions or data structures and that may be accessed by a computer or processor. Disk and disc, as used herein, include compact disc (CD), laser disc, optical disc, digital versatile disc (DVD), floppy disk, and Blu-ray disc where disks usually reproduce data magnetically, while discs reproduce data optically with lasers. Combinations of the above should also be included within the scope of computer-readable media. Additionally, the operations of a method or algorithm may reside as one or any combination or set of codes and/or instructions on a non-transitory processor-readable medium and/or computer-readable medium, which may be incorporated into a computer program product.