Vehicle glazing with an electroconductive layer

p0001The invention relates to a glazing comprising a transparent electroconductive layer; it constitutes at least a part of the enclosure forming a space within which is located a receiving or transmitting antenna microwave radiation, and can be in particular an automobile pane coated with an infrared-reflecting layer.

p0002Glazing, fitted with an electrically conductive low-impedance wire, are used as insulating glass and / or as electrically heated glass, both in the building and in the industr ie automobile. Regarding automobiles, such glazings, combined with a metal body, forms a Faraday cage that isolates the interior of the vehicle electromagnetic fields; in the field of construction, the use of glazing, covered with an electrically conductive layer, also helps to electrically insulate fitted in parts other adequately walls. This type of insulation can also ensure the protection of sensitive facilities as guides consoles against disturbances exerted by powerful radio transmitters or radar equipment.

p0003Such electrical insulation, which may extend to the glazing, prevents transmission of electromagnetic radiation in the microwave. It follows that we can not use cell phone in a vehicle that is equipped with this type of glazing. This poses considerable problems if we consider the implementation of search positioning systems of the vehicle, remote control, identification, electronic toll collection, or if the transmitter or receiver is with the antenna inside of the vehicle.

p0004The purpose of this invention is to provide a window of an electro-conductive layer, while maintaining the insulation effect against the electromagnetic radiation of wavelengths and infrared reflection effect, allow microwave to pass.

p0005The method, described herein, solves the problem as follows: the electroconductive layer contains at least one slot whose length is a function of microwave radiation; this slot allows an electromagnetic wave passing through the field of microwave and absorbed by the conductive layer, to be reissued.

p0006Automotive glazing described in EP 0,332,898 B1 is an electric heating glazing covered with a metal layer of low impedance, in which a slot is acting as an antenna for receiving FM radio. In this well-known slot antenna system, the electrically conductive layer is however connected directly to the middle of the slot, on the one hand to the inner conductor, on the other hand to the outer conductor of a coaxial cable which is connected receptor.

p0007Contrary to this slot antenna, already used for automotive glazing, the method described by this invention does not provide for direct contact between the electrically conductive layer of the glazing and the transmitter and / or receiver inside the vehicle. In this case, the retransmission of the energy of microwave is a simple effect of radiation, which in turn is received by the antenna of the receiving device. The antenna of the glazing naturally produces this effect in both directions, that is to say irrespective of the side of the electrically insulated area where the receiver and transmitter are located.

p0008Microwave means of electromagnetic waves with a length less than 20 cm. Therefore, the length of the slot in the layer is between 0.2 and 10 cm; we shorten this length depending on the dielectric constant of the glass.

p0009We naturally obtain the best results when the length of the wave, by which information is transmitted, is fixed, and which is the door of the slot at a resonant length of lambda / 2, depending on the constant dielectric glass. Using a transmission frequency of 5.8 GHz for example, which represents a wavelength of lambda = 52 mm, a measurement of 18 mm as the ideal length of the slot is obtained.

p0010To assemble the invention, will be chosen for the slot of the electrically conductive layer, a width of 0.01 to 1 mm, preferably between 0.1 and 0.5 mm.

p0011The slot may be produced by mechanical means, for example mechanically using a pointed tool, by microetching in sand blasting, or by thermal means, in particular by using a laser beam. With a very narrow laser beam, can be obtained slots of a very small width, of less than 0.1 mm for example, which are so thin you can not distinguish with the naked eye. The effect produced by the slot is not dependent on the width thereof.

p0012If microwaves are used linearly polarized, one or more rectilinear slits in the layer sufficient to render the layer transparent enough to the field of microwaves. For this purpose, the interruption must be directed straight in a direction should be perpendicular to the polarization direction of the microwave.

p0013If, however, the microwaves were to use circularly polarized for transmission, a single straight slot in the layer is not sufficient. In this case, in order to be fully effective in the invention, it will take practice interruptions in the layer, which will consist of two intersecting slots preferably at an angle of 90 degrees.

p0014In principle, only one slot of this type can be enough to make sufficiently transparent glazing microwave. In this case, the extent of the permeability, or, in other words, the level of damping caused by the glazing coated, depends on the place where is placed the transmitting or receiving antenna to that of the slot interrupting layer. One can combat this dependence and increase the permeability of the glazing coated by providing numerous slots, which may be, for example, distributed over the entire surface of the glazing. this permeability if each slit is remote from the other by an interval of lambda / 2 of the wavelength used, taking into account the dielectric constant of the glass can be further improved.

p0015The following drawings provide a better understanding of the invention.

p0016These sketches show:<ul><li><b>Figure 1 :</b> a car windshield presented in a semi-open angle and constructed according to the method in question,</li><li><b>Figure 2:</b> an enlargement of the portion II of FIG 1, and </li><li><b>Figure 3</b> : A slot in the layer in the case of circularly polarized microwaves.</li></ul>

p0017The windshield is a laminated glazing consists of an outer glass sheet (1) with a thickness of 3 mm for example, a thermoplastic adhesive layer (3) of the type polyvinyl butyral with a thickness of 0.76 mm and a glass sheet (4) which looks inside the vehicle 2 mm thick for example. The outer glass sheet (1) is connected to the inner sheet (3) facing it by a thin transparent electroconductive layer (2), which plays the role of a layer thermoprotectrice through its infrared reflecting properties . The outer surface of the glass sheet (4), which faces the vehicle interior, is surrounded by a frame (5) covered with an opaque enamel paint; the latter in particular provides protection to the adhesive layer fixing the windshield body frame against ultraviolet rays, and prevents one sees the adhesive layer from the outside.

p0018Several layers have proved indispensable to form the thin electrically conductive layer (2); are applied on the glass sheet, for example by a sputtering process assisted by magnetic fields; the functional layer is actually made money. the assembly method is known of these layers. Such thin layers have a proportionately low electrical resistance in the range of 3 to 100 ohms per unit area.

p0019The thin film (2) is provided with multiple vertical slots (8) distributed at regular intervals over a part or over the entire surface of the layer (2). The slots (8) are made in the layer (2) by linearly recessing the layer by thermal or mechanical means. The use of the laser beam is particularly useful for making these slots because it can produce extraordinarily thin slits.

p0020If the working frequency for the transmission of information is 5.8 Ghz, for example, as provided for accounting for tolls on motorways, and the slots (8) are intended primarily for the transmission of micro -ondes this frequency, the slots (8) will be brought in an appropriate manner to a resonant length of lambda / 2, taking account of the dielectric constant of the glass. To a frequency corresponding to a wavelength lambda = 52 mm, the length L of the slots (8) will be L = 18 mm.

p0021Comparing the damping action of a microwave emission to the frequency of 5.8 GHz on an uncoated laminated glazing, laminated glazing coated and laminated glazing with a slot of the type of Figure 2, the following applies for depreciation:<ul><li>laminated glazing not covered: 2-7 dB</li><li>Laminated glazing coated: 20 to 40 dB</li><li>laminated glazing slit: 6 to 10 dB</li></ul>

p0022Compared to the depreciation of an uncoated laminated glass, that of a split laminated glazing is increased only slightly.

p0023If the information transmission is done by circularly polarized microwaves, slots in the form of crosses will be provided accordingly, as seen in Figure 2 which shows a detail of a cross-shaped slot (10) in a thin layer (12). The cross slot (10) is formed by two straight slots (13) and (14), which intersect at their center at right angles. The length L of the two slots (13, 14) is again a function of the wavelength of the microwave used and is, taking into account the dielectric constant of the glass, the value Lambda / 2 of the microwave used .