Electromagnetic heating

ES 2 425 395 T3

DESCRIPTION

Electromagnetic heating

Field of the invention

The present invention is generally related to the heating of materials with electromagnetic energy.

Background of the invention

The microwave oven is a ubiquitous item in modern society. However, its limitations are well known. This includes, for example, uneven heating and slow absorption of heat. In fact, normal microwave ovens, when used for heating (eg defrosting), cause temperature differences of up to 100 ° C between different locations on the heated object, resulting in the creation of hot spots, leak regions thermal. For example, frozen foods that are thawed in a microwave oven may have one or more parts (for example the outside) that is hot or even partially cooked before other parts or other parts are even thawed (for example the inside) . Also known are hot spots that occur within a heated rate of liquid that can result in personal injury to a user. A common method that attempts to reduce hot spots is to rotate the heated item. This method does not provide the uniform heating as would be desired.

One method of providing uniform heating is to allow the heat deposited in a hot spot to diffuse to the surrounding regions and heat them through conduction. Such methods may include an intermittent heating procedure in which heating is periodically stopped to allow diffusion of heat. Although this method can be used in conjunction with the methods of the present invention, the heating stop-start method by itself is either extremely slow (due to the low heat conductivity of most foods, which require long periods of time). to make the method effective) or are relatively inefficient. Another method is to heat at a very low power. This can be used, for example, with large frozen bodies. If the heating is slow enough, then the excess heat in the hot spots diffuses before the rise in temperature in the hot spot becomes unpleasant. However, this method requires up to 10 to 20 times longer for heating to be fully effective. Due to the convection of the object, it is not a serious option for cooking or heating well above room temperature.

A number of papers have been published in which a theoretical analysis of the problem of microwave heating of a cryogenic sample has been carried out. Due to the difficulties of such an analysis, such an analysis has only been carried out on regular shapes, such as spherical and ellipsoidal shapes. Experimental attempts have apparently been made on kidney-sized samples, but the results of these experiments do not indicate that a viable solution for thawing kidneys is available.

On the other hand, it does not appear to be a solution for defrosting other organs, or for defrosting cooked or hot food, in more arbitrary ways.

Prior art publications include:

S. Evans, Electromagnetic Rewarming: The effect of CPA concentration and radio source frequency on uniformity and efficiency of heating, Cryobiology 40 (2000) 126-138

S. Evans, et al., Design of a UHF applicator for rewarming of cryopreserved biomaterials, IEEE Trans. Biomed. Eng. 39 (1992) 217-225

MP Robinson, et al., Rapid electromagnetic warming of cells and tissues, IEEE Trans. Biomed. Eng. 46 (1999) 1413-1425

MP Robinson, et al., Electromagnetic re-warming of cryopreserved tissues: effect of choice of cryoprotectant and sample shape on uniformity of heating, Phys. Med. Biol. 47 (2002) 2311-2325.

MC Wusteman, Martin et al., Vitrification of large tissues with dielectric warming: biological problems and some approaches to their solution, Cryobiology 48 (2004) 179-189.

An article entitled Control of Thermal Runaway and Uniformity of Heating in the Electromagnetic Warming of a Cryopreserved Kidney Phantom by JDJ Penfold, et al., In Cryobiology 30, 493-508 (1993) describes a theoretical analysis and experimental results. Although some experiments were apparently done with a spectrum the size of a kidney, the main reported results are with a uniform spherical object.

As reported a cavity was fed with electromagnetic energy at 434 MHz in three orthogonal directions (x, y, z). The fed x and y were provided from the same generator and a phase shift was introduced so that the field was circularly polarized. The frequency was varied in 32 kHz steps (apparently up to

ES 2 425 395 T3 about 350 kHz maximum) to adjust the input impedance as it changed with increasing temperature.

US-A-5961871 describes a method of and apparatus for electromagnetic heating as set forth in the preambles of independent claims 1 and 9.

Summary of the invention

A method and apparatus for electromagnetic heating is characterized by the characteristics set forth in the portions characterizing claims 1 and 9.

The present inventors have realized that the measurements taken by the prior art researchers to provide uniform heating were insufficient and cannot, by themselves, lead to a viable methodology for uniform heating (or thawing) of shaped objects. irregular such as organs, foods or the like. In particular it was discovered that the prior art suffered from many problems. As used herein, the term "irregular" means objects that protrude in a spherical or ellipsoidal shape by more than 5% RMS volume.

Conventional microwave ovens are configured to be powered by microwave energy from the oven chamber which is basically single frequency. Due to the limitations of the device the power is supplied at different frequencies in a small range, usually between 2.4 and 2.5 MHz. The inventors realized that the limitations of using a substantially constant frequency, or constantly tracking a single dissipation peak over a small frequency range, significantly limits the ability to achieve uniform heating. In fact, heating at a single frequency is found to be one of the main reasons for hot spots. However, using different frequencies (using one or more feeds) can improve the uniformity of heating.

Although some proposed prior art heaters used more than one microwave input, the frequency differences between the two inputs are small, less than 6 MHz.

The inventors also found that the cavity structure of a conventional microwave oven, and especially the cavity mode structure, did not inherently allow the success of uniform heating. Generally, the fields for a given mode in a cavity vary with position and heating varies with the resistance of the fields.

In the art, attempts were made to set microwave oven parameters to adjust the characteristics of a heated object before heating begins. However, during heating the characteristics of a heated object change (for example the tendency to absorb energy of a given frequency). Therefore the inventors realized that even if a heater was tuned to a heated object before operation, even before a short period of operation the characteristics of the object would change and the tuning would not be significant.

Another problem is that sometimes, the absorption in a given location of an object is greater when the temperature increases. This can lead to a thermal runaway problem (even in the conventional microwave oven), where a relatively hot place absorbs more than a colder one thus continuously increasing the temperature difference. When an effort is made to tune the power input of the device to the impedance of the object, the performance of the power supply to the object can be maximized, but hot spots are generally also increased.

The inventors have also noted that the known publications deal with the dissipation of energy according to the absorption of the energy by the resonator (eg surface currents) and not necessarily the object. Furthermore, no attention was paid to the distribution of energy dissipation in the object (with the exception of some description of the depth of penetration).

Also, when feeding from multiple directions in a cavity, the coupling between the feeds can be a serious problem. Although for spherical samples these effects are minimal, for even moderate variations of this shape, the coupling between the inputs can be quite large. Such coupling caused a number of problems including uneven heating and poor power output.

Some exemplary embodiments of the invention address one or more of these problems.

As used herein the term heating means supplying electromagnetic (EM) energy to an object. Sometimes an object can be heated in accordance with the present invention without increasing the temperature (for example when it is concomitantly cooled at a rate that is at least equal to the heating rate or a phase change where the transmitted energy is collected for phase change). Heating includes defrosting, thawing, heating, cooking, drying etc., using electromagnetic energy.

ES 2 425 395 T3

As used herein the term "object" means any object, including a composition of one or more objects. In one embodiment of the invention, the hottest part of a thawed organ is 6 ° C or less, when the coldest part reaches 0 ° C. This has been confirmed with a cow liver. In experiments with a cow liver, after thawing from -50 ° C, the range of temperatures in the thawed liver varied from 8 ° C to 10 ° C. Generally, it is desirable to thaw the object so that all parts are above the freezing point, to avoid recrystallization. In another embodiment the objects are heated to other temperatures (for example holding or firing temperatures, or a temperature below zero that is above the object temperature before heating), while preserving a terminal heating uniformity of the temperature within 50 ° C. Sometimes the temperature uniformity on a heated (or thawed) object is maintained during heating so that at all times the temperature uniformity is within 50 ° C or even within 10 ° C or 5 ° C.

Some embodiments of the invention sweep the feed frequency (or feeds) over a finite set of frequency sub-bands (ie feed energy at the heater over many frequencies belonging to each sub-band). For example, energy dissipation is measured for a band of RF frequencies (eg, the entire operating range of the heater), and based on the measured results, a finite set of frequency sub-bands is selected. The width of the band over which energy efficiency is measured can be for example up to 2 GHz. Sometimes the band can have a width between 0.5% (5/1000 [MHz]) and 25% (100/400 [ Mhz]) of the center frequency.

The measurement can be carried out before heating an object, one or more times during heating of the object, or in advance (with a sample object to define the sub-bands for additional identical objects basically).

In the invention, the power coupled to other supplies at each frequency in a certain band (Sij) and the return loss at each frequency (Si,) are taken into account to determine the heating performance and to adjust certain characteristics of the apparatus, for example, a decision of what power on which frequencies to transmit and when to transmit the frequencies at the matching powers. Optionally, the absorbed power (input power minus coupled power) introduced into the system from one supply is set to be the same as the absorbed power introduced into each of the other supplies.

Applicants have found that changing the transmitted frequency in some selected sub-bands and the input power at each frequency, within one of the selected sub-bands, optionally above the absorption peaks, results in a change in the pattern. heating inside the heated object. Therefore, by optionally sweeping the frequency in the selected subbands, while the powers are adjusted appropriately, various portions of the object are heated. Keeping the total energy absorbed at the different locations of a uniform object results in more uniform heating of the object.

Brief description of the drawings

Exemplary non-limiting embodiments of the invention are described below with reference to the accompanying figures. Drawings are illustrative and are generally not to an exact scale. The same or similar elements are referred to in the different figures using the same reference numerals.

Figs. 1A, 1B, and 1C are respective schematic side and top sectional views of a cavity 10, in accordance with an exemplary embodiment of the invention;

Figs. 2A and 2B show two exemplary mating elements, in accordance with one embodiment of the invention;

Fig. 3 is a schematic isometric drawing of the interior of the cavity of Fig. 1;

Fig. 4A is a schematic drawing of an antenna useful for coupling energy in the cavity, in accordance with one embodiment of the invention;

Fig. 4B is a schematic drawing of a helical antenna useful for coupling energy into the cavity, in accordance with one embodiment of the invention;

Fig. 4C shows a correlation graph of the adjusted free space frequencies and the adjusted cavity frequencies of a helical antenna feed;

Figs. 4D-4H are schematic drawings of various fractal antennas useful for coupling energy in the cavity, in accordance with one embodiment of the invention;

Figs. 5A-5C are schematic block diagrams of electromagnetic heating systems, according to one embodiment of the invention;

Fig. 6 is a simplified flow diagram of the operation of the system, in accordance with one embodiment of the invention;

Fig. 7 is a flow chart of a process for adjusting elements and frequency in the heating system illustrated in Fig. 5, in accordance with one embodiment of the invention;

Fig. 8 illustrates alternative RF circuitry, in accordance with one embodiment of the invention;

FIG. 9 is a graph of frequency versus time for a typical defrost process, illustrating an automatic shutdown capability in accordance with one embodiment of the invention;

ES 2 425 395 T3

Fig. 10 shows the distribution of a low frequency pressure structure, according to an embodiment of the invention;

Fig. 11A is a simplified flow diagram of a method for determining electrical scanning characteristics, in accordance with one embodiment of the invention;

Figs. 11B and 11C illustrate how a swept power spectrum is determined, in accordance with one embodiment of the invention;

Fig. 11D shows a pulse shape, for a pulse operative to provide the spectrum shown in Fig. 11B, in accordance with one embodiment of the invention;

Fig. 12A shows an RF heater with an auxiliary heating coil, in accordance with one embodiment of the invention;

Figs. 12B and 12C schematically illustrate a scheme for transferring waste heat from an amplifier to the heater of Fig. 12A; Y

FIG. 12D shows an external view of a high performance, low weight RF heater according to one embodiment of the invention.

Detailed description of the exemplary modalities

The present application describes a number of advancements in the field of RF heating (eg microwave or UHF). Although, for convenience, these advancements are described together in the context of various apparatus and methods, each advancement is generally independent and can be practiced with prior art methods or apparatus (as applicable) or with a non-existent version. optimal of the other advancements of the present invention. Therefore, for example, parts of the method for adjusting the input power can be used with the prior art apparatus of Penfold, et al. Referenced above. In contrast, the inventive apparatus of the present invention (or parts thereof) can be used with the method of Penfold et al. These combinations are not expected to be ideal, but they are expected to give improved results in prior art methods and apparatus.

Furthermore, advancements described in the context of one embodiment of the invention may be used in other embodiments and should be considered when incorporated as optional features in descriptions of other embodiments, to the extent possible. The modalities are presented in somewhat simplified form to emphasize certain inventive elements.

The invention provides control of the amount of power absorbed in the heated object, based on the measurement of energy absorption performance (eg by transmitting power to compensate for variations in energy absorption). This can be done by adjusting the input power at each transmitted frequency, and optionally selecting the frequencies to be transmitted, moving the field adjusting elements, moving the heated object, and / or changing the characteristics of the antennas. This can be done before operation, and also preferably one or more times during operation (eg several times per second), based on measurements of energy absorption during heating or during a short pause in heating.

Figs. 1A, 1B and 1C show respective top and side sectional views of a cavity 10, in accordance with an exemplary embodiment of the invention.

Cavity 10, as shown is a cylindrical cavity made of a conductor, for example a metal such as aluminum, and is resonant in the microwave or UHF frequency range, optionally between 300 MHz and 3 GHz, most preferably between 400 MHz and 1 GHZ. In some embodiments of the invention, the cavity is a spherical, rectangular, or elliptical cavity. However, it should be understood that the general methodology of the invention is not limited to any particular resonator cavity shape.

At one end 12 of the cylinder and on the two sides of the cylindrical portion 14 the feed antennas 16, 18 and 20 are positioned to supply the power at a frequency that is optionally selected using the methods described below. Various exemplary types but not limiting the utility of antennas for carrying out the invention are shown in Figs. 4A-4C.

In an exemplary embodiment of the invention, one or more mating elements 22, 24 are positioned within the cavity, optionally close to the feed antennas. Two types of field setting items are shown, however other materials and shapes can be used. The first field adjusting element 22, which is shown more clearly in Fig. 2A, is located at the end 12 of the cavity 10. In this embodiment the element is rotatable about an end-coupled shaft 28 in a direction 30. Optionally, it is isolated from the end by an insulating sheet 32 ​​that couples element 22 capacitively to end 12. Alternatively, it is conductively coupled .

Element 22 (as well as the other field adjusting element) is believed to have a dual effect, when properly adjusted. On the one hand, it changes the cavity modes in such a way that it selectively directs the energy of the

ES 2 425 395 T3 feeds into the object to be heated. A second related effect is to simultaneously adjust at least one of the feeds and reduce coupling on the other feeds.

Field adjusting element 24, shown more clearly in FIG. 2B, is positioned between feed 18 and end 12. One end of the element is optionally electrically coupled to cylindrical portion 14 of the cavity. The other end of element 24 is separated and isolated from end 12 by insulation material 36. It is free to slide along end 12 and the cylindrical portion as shown by arrows 33 and 34. This slip changes the spectral variation of the energy absorption performance.

Fig. 3 is a perspective drawing of the interior of the cavity to more clearly show the position and orientation of the feed and the elements.

Figs. 4A-4H show three different types of antennas that are useful in carrying out the invention. These antennas are either novel per se, or if they are known they have never been used for feeds in a microwave oven or heater, especially in a cavity type heater. Generally, in most microwave cavity type heaters, the feeds used are largely non-directional and not broadband, as defined outdoors. The purpose of the feedings is to stimulate the cavity modes. Since prior art cavities are stimulated at a single frequency or a narrow band of frequencies, the antennas were specifically designed to stimulate these modes. Additionally, prior art microwave cavities use waveguides or loop antennas that are not designed to decrease the coupling of energy from one feed to another (they are generally single feed). The present inventors have discovered that the use of directional antennas and / or broadband antennas allow better coupling to the heated object and less coupling to other feeds.

In some modalities the antennas are supplied as arrangements. There are some advantages to using an antenna array. The band can be larger and there is less dependence on the location of the heated object in the results. The directivity can be controlled, it can even be adjusted during warm-up. It is possible to control the phase of each single antenna in the array, which controls the RF mode. It is possible to alter the antenna structure, for example by using the helix antenna, the radius and height of the antenna can be changed in order to tune the impedance and change the RF mode.

Fig. 4A shows an antenna useful for coupling power from feeds 16, 18, and 20 into cavity 10, in accordance with one embodiment of the invention. As shown the feed 16 includes a coaxial feed 37 with its center conductor 36 curved and extending into the cavity. The center conductor is curved but does not touch the walls of the cavity. Optionally, the end of the wire is formed from a conductive element 40 to increase the bandwidth of the antenna. The present inventors have found that antennas of the type shown are capable of better coupling energy to an irregular object in the cavity. Such antennas are believed to transmit directionally and if the curve is directed toward the object being heated, then the coupling to the object (rather than the cavity) will be improved.

Fig. 4B shows a helix antenna useful for coupling power from feeds 16, 18, and 29 into cavity 10, in accordance with one embodiment of the invention. As shown the feed 16 includes a coaxial feed 37 with its center conductor 36 'having an extension that is formed into a helix. This antenna can be designed to coincide in free space over a relatively wide band of frequencies (such as that which is useful for the present invention) and can be made more or less directional by changing the number of turns. The clearance design is then adjusted for the presence of the cavity as described below with respect to Fig. 4C. The graph in Fig. 4C shows the experimental results for a 7-turn helix, with a diameter equal to the wavelength of free space and a turning tilt of less than 0.2 wavelengths. However, the present inventors have found that curves of the type shown in Fig. 4C can be found, through experimentation, for other turning characteristics as well.

Fractal antennas are known in the field. Reference is made to Xu Liang and Michael Yan Wan Chia, Multiband Characteristics of Two Fractal Antennas, John Wiley, MW and Optical Tech. Letters, Vol. 23, No. 4, pp. 242-245, November 20, 1999. Reference is also made to GJ Walker and JR James, Fractal Volume Antennas Electronics Letters, Vol. 34, No. 16, pp. 1536-1537, August 6, 1998.

Fig. 4D shows a simple loop antenna 50 as is known in the art, for radiation in free space. The loop bandwidth (in free space) is: 604 MHz @ 740 MHz the center frequency (-3 dB points) and 1917 MHz @ 2.84 GHz the center frequency. This antenna has a monopole directivity pattern but a broad band of one (which is an advantage over the narrow BW of the dipole antenna). However, the monopole directivity does not radiate in a direction parallel to the feed.

The bandwidth (BW) of this antenna varies between 10MHz and maximum of 70MHz depends on the position of load (object) within the cavity.

This and the following fractal antennas may be useful in the present invention to feed energy into a cavity.

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Fig. 4E shows a simple sierpinski antenna 52 useful in the practice of the present invention. Generally, the cross hatch areas 54 are metallic plates and the central white area 56 is a non-conductive region. The metal plates are mounted on a preferably low dielectric dielectric and are connected at the corners and on the center conductor 37 of the coaxial feed 36, as shown. It is characteristic that in the cavity they are similar to those of the loop antenna.

FIG. 4F shows a modified sierpinski antenna 58 useful in the practice of the present invention. Generally, the cross hatch areas 60 are metallic plates and the white areas 62 are non-conductive regions. The metal plates are mounted on a preferably low dielectric dielectric and are connected at the corners and on the center conductor 37 of the coaxial feed 36 as shown.

For a total extension of 103.8 mm using equilateral triangles of equal size, the center frequency of this antenna is approximately 600 MHz within the cavity.

Fig. 4G shows yet another modified sierpinski antenna 64 useful in the practice of the present invention. Generally, the cross hatch areas 66 are metal plates and the white areas 68 are non-conductive regions. The metal plates are mounted on a preferably low dielectric dielectric and are connected at the corners and on the center conductor 37 of the coaxial feed 36.

The dimensions are shown in Fig. 4G for an antenna having a center frequency of 900 MHz in the cavity.

Fig. 4H shows a multilayer fractal antenna 70 made of three fractal antennas separated by a small distance (eg 2mm) from each other.

The size of each of these antennas is staggered in order to expand the bandwidth of the antenna. In the example shown a first antenna 72 is scaled to 0.8 of the dimensions given in Fig. 4G. A second antenna 744 has the same dimensions as the antenna in Fig. 4G and a third antenna 76 is enlarged above antenna 74 by a factor of 1.2. The fractal volume of the antenna (Fig. 4G) has a total bandwidth of 100MHz - this is an improvement over the maximum of 70 MHz of BW achieved in a previous simple fractal antenna (Figs. 4D-4H).

Fractal antennas also show a center frequency shift when placed in a cavity. This difference is used (as with the helix antenna) to design the antennas for use in cavities by scaling the frequencies.

Generally, it is desired to use directional antennas, broadband antennas to power the power to the object being heated such antennas include patch antennas, fractal antennas, helix antennas, log antennas, and spiral antennas.

Figs. 5A to 5D are schematic block diagrams of an electromagnetic heating system, in accordance with one embodiment of the invention.

FIG. 5A shows a general block diagram of each of the power supplies 90 of the system, in an exemplary embodiment of the invention. The system is controlled by a computer 92 that controls through a control interface (controller) 130 an RF system 96 that provides power to the heated object 98.

FIG. 5B is a block diagram of the electronics of one of the RF power systems 96, in accordance with an exemplary embodiment of the invention. A VCO 102 receives a signal from a control circuit 130 (FIG. 5C) that sets the frequency of the power at the port. This energy is passed through an RF switch 104 and a voltage controlled dimmer (VAC) 106, both of which are controlled by control circuit 130. After passing through the VCA, the signal strength and frequency have been set. A load 108 is provided to discharge the signal generated by the VCO 102 when the signal from the VCO 102 is not interrupted at the VCA.

The signal is then sent through the main line of an optional first two-way coupler 110.

The VCA output is then amplified by a power amplifier 112 and then passed through an isolator 114. A signal proportional to the reflected power from the amplifier 112 is also fed into the control circuit.

Coupler 110 feeds back a portion of the signal entering it (after power sensing or measurement) to control circuit 130. A signal proportional to the power reflected by amplifier 112 is also sent to controller 130. These signals allow monitoring of the VCO / VCA and the amplifier. In a production system, the directional coupler may not be necessary.

An RF switch 116 interrupts power either to a load 118 or to the power to resonator 98, through

ES 2 425 395 T3 of a second two-way coupler 120. The two-way coupler 120 displays the power both inside and outside the resonator and sends the power measurement signals to the controller 130.

In one embodiment of the invention, RF amplifier 112 is a solid state amplifier based on LDMOS technology. Psat = 300W, performance = about 22%, the effective band - 800-1000 MHz such amplifiers either have a relatively narrow bandwidth or a low performance (<25%) or both. This limits the optimal utility of the advancements of the present invention. Recently, amplifiers have become available based on SiC (silicon carbide) or GaN (gallium nitride) semiconductor technology. Transistors using such technologies are commercially available from companies, such as Eudyna, Nitronex, and others. Amplifiers that have a maximum power output of 300-600 W (can be built from low-power modules (50-100 Watt)) and a 600 MHz bandwidth (at a 700 MHz center frequency) or a wide 400 MHz band (they are available on a 2.5 GHz core frequency), for example. Such amplifiers have much higher efficiency than prior art amplifiers (60% efficiency is available) and much higher tolerance for reflecting signals, so isolator 114 can often be omitted for these amplifiers. A particular configuration using this type of amplifier is described below in conjunction with Figs. 12A-D.

Turning now to Fig. 5C the controller 130 comprises the computer 92 which performs the calculations and provides a system registry function as well as acting as a user interface. It also controls the rest of the elements in which the calibration is carried out and the control method of the flow diagrams in Fig. 7.

Computer 132 is coupled to the rest of the system through an interface 134 that is designed to provide communication to, for example, an ALTERA FPGA 140, which interfaces with and provides the control signals for the various elements of the RF system. The Altera receives the inputs (as described above with respect to Figs. 5A-5C), through one or more multiplexers 136 and an A / D converter 138. Additionally, the frequency and power of each of the supplies (also described with respect to Figs. 5A and 5B) are established through the D / A converters 140 and the positions of the field adjustment element that optionally uses the method described with the help of the following flow charts. In a production system, the computer may not be necessary and the Altera or a similar controller can control and process all the necessary data. In some embodiments of the invention, the frequency is swept as described below.

FIG. 6 is a simplified flow diagram 150 of the operation of a heating system having the structure described above. FIG. 7 is a simplified flow chart of system calibration 160. As will be apparent, the calibration and operation of the system method can also be used with minor changes only for operating systems with lesser or greater numbers of power supplies and / or a greater or lesser number of matching elements.

In an object 152, for example a frozen organ or a frozen or unfrozen food object, is placed in cavity 10. A calibration or adjustment routine is then optionally carried out to establish the variable elements in the system. This may include the power output of the amplifiers 112 in each of the power supplies to the cavity at each frequency, selecting for transmission, the finite set of frequency subbands of each VCO 102, the method of providing power to the various frequencies (e.g. sweep or other frequency variation, or provision of a pulsed signal incorporating the desired frequency and power characteristics), the positioning of the matching elements (for example, 22, 24), the position of the heated object and any of the other variables that affect the various characteristics of the heating process, for example - the uniformity and / or performance of the power transfer to the object. A memory contains the criteria 156 for calibrating the system. Exemplary criteria are described below. Calibration 160 is performed to determine the new heating variables. An exemplary calibration routine is summarized in the flow chart of Fig. 7, described below.

After the new variables are determined, the new variables 158 are set and the warm-up 170 begins.

Periodically (for example a few times per second), the heating is interrupted for a short time (perhaps only a few milliseconds or tens of milliseconds) and 154 is determined, optionally based on a method described below, if the heating is due. end up. If it must, then warm-up ends 153. If the criterion or criteria for ending warm-up are not met, then the calibration (or readjustment) routine 160 is entered. If not, heating 170 resumes. It should be noted that during the measurement phase, the sweep is generally much wider than during the warm-up phase.

The calibration routine 160 for each individual channel will be described with reference to the flow chart of Fig. 7.

In order to carry out the calibration, the power is optionally set low enough 162 so that substantial heating does not take place, but high enough so that the generated signals can be reliably detected. Alternatively, calibration can take place at full or half power. Calibration at near operational power levels can reduce the dynamic range of some components, such as the VCA, and reduce their cost.

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Each of the inputs is then swept 164 between a minimum and a maximum frequency for the channel. Optionally, the upper and lower frequencies are 430 and 450 MHz. Other ranges can be used, such as 860-900 MHz and 420-440. It must be believed that substantially any range between 300-1000 MHz or even up to 3 GHz is useful depending on the heating task being carried out. When using broadband, the high-performance amplifiers described above, much greater bandwidth of several hundred MHz or more can be swept within the range of the amplifiers. The sweep can be above several non-contiguous bands, if more than one contiguous band meets the criteria for use in heating.

The input reflection coefficients Sn, S22, and S33 and the transfer coefficients S12 = S21, 813 = 831, S23 = S32 are measured during the sweep and a net power performance is determined as (for port I for example) , What:

η1 = 1- (reflected power from port 1 + power coupled to ports 2 and 3) / input power

The present inventor has found that under many operating regimes it is desirable to maximize certain criteria.

In a first embodiment of the invention, the maximum net power performance for each port is maximized, in the sense that the net power performance at a maximum performance point within the sweep range is made as high as possible. The performance and the frequency at which the performance is at a maximum is highlighted. Optionally, the width of the performance peak and a Q factor are also highlighted.

A second embodiment of the invention is based on a similar criterion. For this mode, the area under each resonance peak of the net transfer efficiency is determined. This area should be a maximum. The performance, the center frequency of the resonance having the maximum area and its width are highlighted.

In one embodiment of the invention, the criteria for determining whether the variables are properly set is when the net yield of the peak (first mode) or area or width (second mode) is above a certain predetermined level or a Q factor is below a certain predetermined level. For example, there may be a restriction that the net return area is maximized above 60% for each of the feeds.

It should be noted that energy is absorbed which is neither reflected nor transmitted to the other ports either on the walls of the cavity or on the object being heated. Since the absorption in the conductive walls is much lower than in the object by an important factor, the net efficiency is approximated by the proportion of the input power that is absorbed in the object. It should also be noted that the frequency of the maximum net return is not necessarily the same as the frequency at which the fit is best.

In one embodiment of the invention, the frequency is swept while the power is adjusted. The term "sweep" is to be understood to include the serial transmission of individual non-contiguous frequencies, and the transmission of synthesized pulses having the desired frequency / power spectral content.

The present inventors have found that each frequency has the maximum absorption at a specific location within an object within a cavity, that the locations can vary between the different frequencies. Therefore sweeping a range of frequencies can cause movement of the region of the heating peak within the object, computer simulations have shown that, at least when the Q factor of a peak is low (that is, a large amount of energy is dissipated in the object being heated) the movement of the region of the heating peak can be quite substantial. Furthermore, the inventors have found that each mode (represented by a different performance peak) acts differently when sweeping.

FIG. 11A is a simplified flow chart 200 of a method for determining sweep power characteristics, in accordance with one embodiment of the invention. This method corresponds to events 160 and 158 of the flow chart of Fig. 6.

After placing the object in the cavity (152) the cavity is scanned to determine the input efficiency as a function of the frequency (202) (eg, obtain a spectral image). The determination of the input performance was described in detail above. Alternatively, a pulse of energy, having a broad spectrum in the range of interest, is supplied to the input. The reflected energy and the transmitted energy at other inputs are determined and their spectra are analyzed, for example using Fourier analysis. Using either method, the net power output can be determined as a function of frequency.

Under some conditions, where similar objects have been previously heated, a set of tables for different types and sizes of objects can be developed and used as a shortcut instead of the closely spaced measurements.

FIG. 11B shows a simplified net power performance curve 250 at an input. It should be noted that

ES 2 425 395 T3 There are regions where performance is high and others where performance is low. Also, some of the performance peaks are wider and some are narrower.

Next, the total scan bandwidth (BW) (204) is determined. This can include sweeping through a single peak or across multiple peaks.

In one embodiment of the invention, during the warm-up phase, the frequency is swept through a portion of each of the peaks, high throughput. For example, to provide uniform heating of objects it is believed that the power introduced into the cavity at each frequency must be the same. Therefore, in one embodiment of the invention, the power at each frequency is adjusted so that P * j is a constant for all frequencies in the sweep. Since the available power is always limited to some value, it can set a limit on the bandwidth available for the sweep. An example of a lower limit of performance is shown as dotted line 252 in FIG. 11B. Sweep can be limited to frequencies that have performance above this value.

Next, the positions of the field setting items are set. This setting is optional and in some situations, even where such items are present, they do not need to be adjusted. Generally, the criteria for such a fit is that the peaks are as high throughput as possible with a peak as wide as possible specific applications can introduce additional objectives, such as moving the peak to a certain band.

An iterative process (206, 208) is used to determine a desired position and / or orientation of the field adjusting elements. When the search process is completed, which can be any iteration process as it is known in the art, the elements are established in the best position found. (210).

In one embodiment of the invention, the sweep is adjusted (212) to avoid feeding excess power to certain parts of the object - for example, if the object contains a metal bar or metal fastener, a high peak may be generated. in performance 254. A metal bar can cause a concentration of energy near the ends of the bar. Avoiding irradiation at this peak can sometimes reduce the effects of such objects on uniform heating.

Next, the scan parameters are determined (214).

FIG. 11C shows the power spectrum 256 of the input energy, in accordance with one embodiment of the invention. It should be noted that no energy is transmitted to the frequency characteristic of the bus and that for other frequencies for which the performance is above the minimum is shown at 252 in Fig. 11B. The power has a form that is such that the product of efficiency η and the power supplied is substantially constant.

In an alternative embodiment of the invention, energy is supplied to the port as a pulse rather than as sweep energy. A first pulse, such as that shown in Fig. 11C, is generated by a pulse synthesizer. This pulse is amplified and fed into the input. The pulse synthesizer would then replace the VCO 102 (Fig. 5B). It is understood that the pulse synthesizer can be further programmed to produce a sweep for use in determining the frequency dependence of η (event 164 of FIG. 7).

A search is carried out for a position of the matching elements where the net power performance on all supplies meets the criteria. This is indicated in boxes 214 and 216, which represent a search carried out by changing the positions and / or orientations of the matching elements. Standard search techniques (iteration) or a neural network can be used or another learning system can be used, especially if the same type of object is heated repeatedly, as is common for industrial uses.

When the criteria are met, then the power is raised to a suitable level for optional heating and sweeping. The power is optionally normalized in the respective amplifiers to provide the same net power in the cavity (and therefore in the object) for each port. Optionally, the least efficient port determines the power to the object. Although in prior art ovens the user decides the heating time, in some embodiments of the present invention the desired heating time can generally be predicted.

Returning back to Fig. 6, there are a number of methodologies for conducting heating 170.

In one embodiment of the invention, power is input to all feeds at the same time. This has the advantage that heating is faster. It has the disadvantage that all three separate sets of circuitry are required.

In a second embodiment of the invention, power is introduced to the serial feeds, for short periods. Potentially only a single set of most circuits is needed, with a switch being used to transfer power from feed to feed. However, for calibration, a method must be provided to measure port-to-port transmitted power. This circuitry could also be used to adjust the feeds when power is not supplied to them. A different type of circuitry to provide

Both the heating and the calibration functionality, according to one embodiment of the invention, are shown in Fig. 8, corresponding to the circuitry of Fig. 5B.

The same reference numerals are used in Fig. 8 as in Fig. 5B, except where indicated below. Such a system has the advantage of being much less expensive. It is, of course, slower. However, it does allow for an additional method of equalization, in which the length of time (either alone or in conjunction with the change in input power) during which each feed is supplied is adjusted so that the energy at each feed it is the same (or different if desired).

Fig. 8 is similar to Fig. 5B up to the output of the RF switch 116. The next RF switch 116 a second RF switch 192 transfers the power delivered by the amplifier to one of the feeds. Only circuitry 200 related to power 2 is shown.

Circuitry 200 operates in one of two modes. In a power transfer mode, a control signal 130 interrupts power from RF switch 192 to two-way coupler 120, via RF switch 194. The remainder of the port operation is as described above. . In a passive mode, the input to RF switch 194 does not receive power from amplifier 112. The switch 194 connects a load 190 to the input of the two-way coupler 120. In the passive mode, the load 190 absorbs the power that is supplied from the cavity in the feed. For further simplification of the production systems of the directional coupler 120 it may be possible to reposition the two-way coupler with a one-way coupler.

It should be noted that switches 116 and 192 and optionally local switches can be combined into a more complex switch network. Alternatively or additionally, the RF switch 194 can be replaced by the circulator so that the power returned from the supply is always discharged at the load 190.

Either in the mode of Fig. 5B or in the mode of Fig. 8, the frequency of the power supplied to a port can be supplied at the center frequency of the resonance mode that couples the highest net power, i.e. , the point of maximum efficiency of the transfer of energy to the object being heated. Alternatively, the frequency can be swept across the width of the resonance or, more preferably along a portion of the width, for example between the -3 dB points on the power performance curve, or as described above. with respect to Figs. 11A-11C. As noted above, optionally, the power is adjusted during this sweep so that the net input power remains constant or nearly constant during the sweep. This can be achieved by changing the power amplification of the power amplifier inversely to the power output of the instantaneous frequency being supplied.

Returning again to Fig. 6, reference is further made to Fig. 9, which shows a graph of the frequency of a particular peak over time for a typical thawing process. This graphic illustrates a method of using object property changes during a defrost process to determine when the process is complete.

The ordinate of Fig. 9 is the frequency selected as an input for one of the feeds. The abscissa is time. During the thawing of an object, the ice on the object turns into water. Ice and water have different UHF or microwave energy absorption, resulting in different return loss and coupling as a function of frequency. The adjustment not only makes this change, but at least after readjusting by adjusting the matching elements, it changes the frequency of the absorption performance peak. At point A, some of the ice has started to change into water and the set frequency changes. At point B, all the ice has turned into water and the setting frequency stops the change. By monitoring the frequency described above and especially its rate of change, you can determine the point at which all the ice turns to water and the heating is over, if you just want to defrost. It should be noted that the frequency change during defrosting is large, as described herein, compared to the frequency changes allowed in the prior art.

One of the problems with thawing a solid mass of irregular shape and irregular internal structure is that it is generally impossible to determine when all the ice has been converted to water. Therefore, generally, in the prior art, reheating is allowed to ensure that there is no ice, which, taking into account the uneven heating of the prior art, would improve recrystallization, if any ice remained.

The heating methods and apparatus of the present invention, which allow for both uniform heating and provide knowledge of thawing progress, can result in much less or even non-existent recrystallization.

The apparatus and method according to the present invention have been used to thaw a pork liver, sushi or maki and to cook an egg in the shell.

The following table shows a comparison of defrosting a cow liver by the system of the present invention and using a conventional microwave oven.

ES 2 425 395 T3

Table 1: Comparison of the inventive method and conventional microwave - cow liver

<td>Measurement</td><td>Inventive method</td><td>Conventional microwave</td>

<td>Initial temperature</td><td>-50 ° C</td><td>-50 ° C</td>

<td>Final temperature after defrosting</td><td>8 ° C to 10 ° C</td><td>-2 ° C to 80 ° C</td>

<td>Power</td><td>400 Watt</td><td>800 Watt</td>

<td>Defrost time</td><td>2 minutes</td><td>4 minutes</td>

<td>Visible damage</td><td>Neither</td><td>The texture of the thawed sample was destroyed. There are frozen regions along the burned side. There is no possibility of survival of living cells.</td>

The following table shows a comparison between thawing of maki containing raw fish covered by rice and wrapped in seaweed, by the system of the present invention and using a conventional microwave oven. Table 2: Comparison of the inventive method and conventional microwave-maki

<td>Measurement</td><td>Inventive method</td><td>Conventional microwave</td>

<td>Initial temperature</td><td>-80 ° C</td><td>-80 ° C</td>

<td>Final temperature after defrosting</td><td>2 ° C to 6 ° C</td><td>-5 ° C to 60 ° C</td>

<td>Power</td><td>400 Watt</td><td>800 Watt</td>

<td>Defrost time</td><td>40 seconds</td><td>1 minute</td>

<td>Visible damage</td><td>Neither</td><td>The defrosting process cooked part of the salmon, therefore it was no longer maki.</td>

An egg was cooked using the present method. Eggs will generally pop if an attempt is made to cook them in a microwave oven. However, using the system described above, an egg was cooked in the shell. The white part and the yellow part both cooked well, and the white part was no harder than the yellow part. No part was dry or rubbery and the taste was very good, little to no difference from a conventional hard-boiled egg. Additionally, the deep-frozen fish has been thawed without leaving any of the portions frozen and without any of the portions being heated above cooking temperatures.

In each of the above experiments, the frequency and power were adjusted automatically and the matching elements were adjusted manually, according to the method given above for automatic adjustment.

The inventors believe that the methodology of the present invention is capable of defrosting objects that are deep frozen to almost above zero with a temperature variation of less than 40 ° C, optionally less than 10 ° C, 5 ° C and even as low as a difference of 2 ° C. Such results have been achieved in experiments carried out by the inventors, for a cow liver, for example.

Thawing objects such as meat and fish with such low differences and at high speeds has the potential for preventing the development of salmonella, botulism, and other food toxins. Uniform, controlled thawing has important implications in thawing organs for transplantation, without destruction of tissues.

Fig. 10 shows apparatus for applying a DC or a relatively low frequency (up to 100 kHz or 100 MHz) to an object in the cavity, according to one embodiment of the invention. This figure is similar to Fig. 1, except that the cavity includes the two plates 250 and 252. A power supply (not shown) electrifies the plates with a high differential voltage at a DC or relatively low frequency. The goal of this low-frequency field is to reduce the rotation of the water molecules. Ice is water in a solid state, therefore its modes of rotation are restricted. One goal is to restrict the modes of rotation of liquid water in order to determine the rate of heating by that of ice. The present inventors also believe that low frequency fields can change the dielectric constant of materials which causes the object to heat up, allowing a better fit of the input to the object.

In an alternative embodiment of the invention a DC or low frequency magnetic field is applied by placing one or more coils inside or preferably outside the cavity to cause alignment of the molecules in the

ES 2 425 395 T3 object. It is possible to combine the low frequency or DC electric power and the low frequency or DC magnetic fields with possible different phases of different directions.

FIG. 12A shows a cavity 98 with an internal heater coil 600 positioned within the cavity. An inlet 602 and an outlet 604 are provided to feed a hot fluid through the coil to heat the air within the cavity.

Figs. 12B and 12C show two schematic illustrations of a system for transferring heat from a high power amplifier 606 to the winding. Even at 60% performance, the amplifier can generate several hundred watts. This energy (or at least part of it) can be transferred to heat the air and produce infrared radiation (as a resistance coil does) in the cavity to increase heating performance.

Fig. 12B shows a highly schematic diagram to illustrate how waste heat is captured from an amplifier 606. Fig. 12C shows a block diagram of the same system. Element 608 represents a cooling system for the return fluid and a pumping system for the fluid. Return fluid is received from outlet 604, liquid is cooled (if necessary), and liquid is pumped into a gap 610 between amplifier 606 and an optional heat sink 612. The temperature at the inlet of the separation and at its outlet are preferably measured by sensors 614 and 616 and input to a control system 618, which controls one and optionally more than one cooling and pumping rate to provide heat transfer. desired to the cavity. A 620 fan can be provided to cool the heatsink when required. The fluid that passes between the amplifier and the heatsink also works to transfer heat from the amplifier and the heatsink. Optionally the heat conducting equipment can transfer heat between the amplifier and the heat sink with the fluid that passes between the nerves to collect the heat.

Alternatively, heat pipes or other means can be used to collect and transfer energy to the cavity. Alternatively, hot air could be blown over the amplifier and / or heat sink and into the cavity.

The use of high performance amplifiers with or without heat transfer to the cavity can result in highly efficient systems, with a total efficiency of 40-50% or more. Since amplifiers with relatively high voltages (40V-75V) are used, the need for large transformers is obvious and the heat sinks can be small and even non-existent, with the amplifier transferring heat to the heater housing.

Optimizing the system, a heater like the one shown in Fig. 12D, which includes a housing 650, the amplifiers and the controller, as well as a user interface 652 and a door 654, like the one normally found in an oven microwave oven can weigh as little as 10-15 kg or less.

Although applicants have used the UHF frequencies for heating in the examples described above, rather than the much higher frequency of 2.45 GHz used in the prior art, for heating applications in addition to defrosting, a different frequency may be desirable. UHF frequencies are preferentially absorbed by ice and have a longer wavelength than higher frequencies, so the fields within the object are more uniform and ice is preferentially heated when compared to water. This provides for preferential heating of the ice and even uniform thawing.

Additional measurements that can be taken to improve uniformity are:

1) Various types and sizes of conductive materials such as small grains of powdered conductive material (gold) can be inserted into the sample prior to the freezing process (for example through blood circulation or cooling fluid) and serve as reflective sources. The insertion can be done using some non-conductive material template (absorbing or not) that supports the conductive objects. These passive energy sources can improve the uniformity of EM radiation absorption.

2) The penetration of materials that change their dielectric characteristics depends on the temperature in a way that is different from that of the sample. Injecting these materials will allow changes in the dielectric characteristics of the sample in the desired direction to achieve rapid and uniform heating.

3) The use of probes for the measurement of various parameters of the heating process such as temperature, pressure, and so on: These probes can be inserted into the sample prior to the freezing process or attached adjacent to the sample at any stage of process. Measurement of these parameters provides a means for monitoring (controlling) the heating process so that if the heating is not optimal it will be possible to make changes to various process parameters. Probes are available that are suitable for measurement during heating in a microwave device. These probes can also serve as an indication of when to stop a defrost or cook process.

Such probes can be included in a bag in which the object to be heated is placed and can include an element

ES 2 425 395 T3 resonant whose resonant frequency is made to vary with temperature by including an element dependent temperature such as a resistor or capacitor dependent temperature.

The probes can be provided with resonant circuits whose frequency is temperature dependent. Such probes can be scanned during the scan used to set the scanning parameters for determining the temperature. During power transfer, these frequencies should generally be avoided. In one embodiment of the invention, a temperature-sensitive label is paired with a temperature-insensitive label and changes in the frequency of the temperature-sensitive label are determined by a difference in frequency between the two. This allows for a more accurate measurement of temperature using an absolute measurement of the frequency of the temperature sensitive label.

4) Packing the sample in material that does not absorb EM radiation at specific frequencies: This type of packing can serve as a packing for the sample during transportation and as a part or probe system by which it is possible to measure the temperature and additional parameters at the edges of the sample. This packaging can serve as local cooling for the external surfaces of the sample (which usually have a tendency to heat up faster than the rest of the sample) in order to achieve uniform heating of the sample.

In addition, the packaging may include identification of the object to aid in tracking the object and further provide an indication to the system of a preferred protocol for heating the object. For example the packaging can be provided with a number of resonant elements that can be detected when the cavity is swept during calibration. The frequencies of the elements can be used to provide an indication of the identification of the object. This allows automatic or semi-automatic setting of start parameters for calibration and / or for a particular heating protocol, optimized for the particular object and conditions.

Alternatively or additionally, for resonant circuits, a recording / storage element of a different type is provided, for example in the form of an RFID element or a barcode, which includes therein an indication of the contents of a package or envelope that includes the object, the suggested treatment of the object and / or the heating instructions. In an exemplary embodiment of the invention, the instructions are provided exactly at a remote site, indexed to a key stored by the register element. Such instructions can be, for example, stored in a table or generated according to a request, based on the information related to the identification.

A reader is optionally provided in the heater, for example an RFID reader or a barcode reader to read the information on a package or a wrapper thereof.

In an exemplary embodiment of the invention, after the object is prepared, various types of information are optionally stored in (or in association with) the record item, for example, size, weight, type of packaging, and / or packing instructions. cooked / thawed / warming.

The register item has stored the specific cooking instructions with it. Alternatively or additionally, the recording element has stored in it information regarding the shape of the plate and / or the dielectric properties of its contents. It should be noted that for industrial-shaped portions, if the shape of the food is relatively regular between plates, movement of the food and / or changes in size and / or small changes in shape will generally not affect the uniformity too much, for example, the displacement of a heating region / boundary by 1-2 cm. Optionally, the plate includes a depression and / or other geometric structures that push the food product to maintain a desired position relative to the edges of the plate.

During the heating of food, for example, the heating parameters vary. The effect of variation can cause non-uniformity in space and / or time. In an exemplary embodiment of the invention, a sequence is provided defining how and what to vary. Optionally, the sequence includes decisions made according to time (eg estimation of an effect) and / or the state of the food (eg measurement). Various measurement methods were described above. The estimate is optionally based on a simulation or empirical results from previous heating cycles. Optionally, the sequence is conditional (e.g. modified, generated and / or selected), e.g. based on the position of a dish in the oven and / or personal preferences (which can be stored in the oven) .

In an exemplary embodiment of the invention, a sequence is provided at the record item or at a remote location. Optionally, a sequence is selected by a user who selects a desired heating effect.

In one example, a single food product can experience different potency levels for different times, in order to achieve a desired texture / flavor.

In an exemplary embodiment of the invention, a sequence is used to establish different energy levels and / or different times to apply such energies.

ES 2 425 395 T3

In one example, a sequence is as follows:

(a) Heat the entire plate so that the food reaches a relatively uniform temperature of 5 degrees Celsius.

(b) Heat the entire dish evenly at 80% for 5 minutes and then on maximum power for 10 minutes.

(c) Heat to 40 degrees centigrade.

(d) Keep warm for 10 minutes. It should be noted that a desired heat can be optionally maintained by estimating energy absorption while applying a known amount of cooling. Alternatively, the actual heat absorption can be estimated based on a known amount of energy absorption and a measurement of the temperature of the air leaving the cavity. Optionally, the oven includes a cooling air source and / or has coolable walls and / or tray.

(e) Reduce the heat to 30 degrees centigrade.

(f) Wait 10 minutes.

(g) Report done but leave at 30 degrees centigrade until removed.

In an exemplary embodiment of the invention, the sequence includes other conditions, eg, detecting changes in color (eg, tan), vapor (eg, by the phase change of water), volume (eg, increased of the dough will change the behavior of the cavity in a way that can be anticipated).

Optionally, the sequence includes a request to the user to add ingredients (eg, spices), or to mix or reposition the object.

In an exemplary embodiment of the invention, the sequence takes into account the quality of uniformity control achievable in the oven. For example, if a higher level of uniformity is desired than is primarily provided by the oven, the heating may include pauses where the power is reduced, to allow the heat to even out on the object. The length of the lags is optionally pre-calculated for food substances and a calibrated lack of oven uniformity. Alternatively or additionally to reduce power, the heating and / or food areas can be moved relative to each other so that the heating is better distributed.

In an exemplary embodiment of the invention, the sequence is not provided. Instead, the heating times and / or parameters are directly based on the desired results, measured food properties, and / or measured heating properties. Such desired results can be provided to the user or indicated by the record item.

5) Liquid injection: (similar to cooling liquid) which is suitable for a biological sample, the purpose of which is to cause uniform heating: This liquid is used in the field of hyperthermia. In this field the heating of a biological area is done in order to eliminate a cancerous tumor. From the knowledge derived from this field it is possible to understand that a liquid such as this can cause a drastic change in the uniformity of heating and can allow the use of a heating device that is more simplified than would be needed without its use.

6) The penetration of active radiation sources into the sample during the freezing process: These sources are active, which means that they are connected to an external supply line that will be used as a source of EM radiation that will emanate from within of the sample.

The present invention has been described in part in the context of thawing. The inventors believe that based on the results shown above, it can be expected that the methods of the present invention can be used for baking and cooking, areas where conventional microwave ovens are notoriously weak or for other heating operations, especially those for which a high level of uniformity or control is needed and / or in which a phase change takes place.

Using various embodiments of the invention, UHF or microwave energy can be uniformly deposited on an object just less than ± 10%, ± 20% or ± 30% more than 80% or 90% or more of the object.

The present invention has been described using detailed descriptions of embodiments thereof which are provided by way of example and are not intended to limit the scope of the invention. The modalities described

ES 2 425 395 T3 comprise different characteristics, not all of which are necessary in all embodiments of the invention. Some embodiments of the present invention use only some of the features or possible combinations of features. The variations of the embodiments of the present invention that are described and the embodiments of the present invention that comprise different combinations of the features outlined in the embodiments described will occur to those of the art.