METHOD FOR INCREASING THE TRANSMISSION OF ELECTROMAGNETIC HIGH-FREQUENCY WAVES THROUGH THERMALLY INSULATING GLASS PANES

Description

[0001] This patent application claims priority from French patent application FR15 / 55638. Domain

[0002] The present application relates to the transmission of radiofrequency electromagnetic waves through glazing, one face of which is coated with a conductive layer, and more particularly thermally insulating glazing, one face of which is coated with a metal oxide. Statement of Prior Art

[0003] Filters have been developed to shield a room or building from certain electromagnetic waves. Such filters can be made of films that shield the carrier frequencies of wireless telecommunications systems.

[0004] This type of film with a periodic pattern of conductive elements is called a frequency selective surface, and is generally referred to in the art by the acronym FSS, from the English "Frequency Selective Surface", cf. US 2003 / 080909, WO 2014 / 060203 or US 5,364,685.

[0005] There Figure 1A discloses an embodiment of an FSS film 10 comprising a pattern of conductive elements 11 periodically repeated in the vertical and horizontal directions, and arranged on a dielectric support 12. Each element 11 of the pattern has the shape of a square with an empty center. Each side of the square has a length d and a width s. The squares are repeated at a pitch p.

[0006] The motive of the Figure 1A is for example described in the article by RJ Langley, EA Parker, "Equivalent circuit model for arrays of square loops" - ELECTRONIC LETTERS 01.04.1982, Vol. 18, No. 7.

[0007] There Figure 1Bis a curve illustrating the transmission T (in decibels), as a function of the frequency f (in GHz), of an FSS film of the type of that of the Figure 1A when this film is placed on a partition or a window. This transmission curve shows a maximum attenuation peak at the transmission zero frequency, the decibel gain being substantially zero elsewhere. The aforementioned article indicates that the wavelength corresponding to the transmission zero frequency is substantially equal to the perimeter of a square 11.

[0008] Conversely, filters have been developed to compensate for the involuntary shielding of a room or building against certain electromagnetic waves. Indeed, glazing coated with a layer of metal oxide proves to be particularly effective for thermal insulation but significantly attenuates radiofrequency electromagnetic waves.

[0009] The article by GI Kiani, LG Olsson, A. Karlsson, KP Esselle, M Nilsson, "Cross-Dipole Bandpass Frequency Selective Surface for Energy Saving Glass Used in Buildings" - IEEE TRANSACTION ON ANTENNAS AND PROPAGATION, Feb. 2011, Vol. 59, No. 2, describes a periodic pattern of etched apertures in the metal oxide layer of such glazing that limits attenuation for certain RF frequencies. The article nevertheless mentions that this etching results in a significant degradation of the thermal insulation of the glazing. Summary

[0010] Thus, there is a need to compensate, for certain RF frequencies, the attenuation of electromagnetic waves due to glazing coated with a layer of metal oxide without modifying the thermal insulation performance of this glazing.

[0011] One embodiment provides glazing comprising a pane of which one face is coated with a conductive layer, comprising at a non-zero distance from the conductive layer a periodic pattern of conductive elements adapted to increase, for a determined frequency, the transmission of radiofrequency electromagnetic waves, said periodic pattern being chosen to present a transmission zero at a frequency between half and substantially double the frequency to be amplified.

[0012] Furthermore, the periodic pattern of conductive elements is formed on a flexible and transparent dielectric support.

[0013] According to one embodiment, the dielectric support is adherent to the glass.

[0014] According to one embodiment, each conductive element has the shape of a square with an empty center.

[0015] According to one embodiment, each conductive element has a circular shape.

[0016] According to one embodiment, the glazing comprises two or three panes, and the conductive layer is formed on an internal face of a pane.

[0017] According to one embodiment, the conductive layer has a resistance of 1 to 1000 Ω / □.

[0018] According to one embodiment, the conductive layer is a layer of a metal oxide or a polymer.

[0019] One embodiment provides a method for amplifying the transmission at a determined frequency of a glazing unit comprising a pane of which one face is coated with a conductive layer, consisting of coating a wall of the glazing unit with a periodic pattern of conductive elements, adapted to increase, for a determined frequency, the transmission of radiofrequency electromagnetic waves, said periodic pattern being chosen to have a transmission zero at a frequency between half and substantially double the frequency to be amplified.

[0020] According to one embodiment, said determined frequency is a frequency used by telecommunications systems. Brief description of the drawings

[0021] These and other features and advantages will be set forth in detail in the following description of particular embodiments given without limitation in relation to the attached figures, among which: there Figure 1A represents an FSS film comprising a periodic pattern of conductive elements on a dielectric support; the Figure 1B is a curve illustrating the transmission as a function of the frequency of an FSS film of the type of the Figure 1A ; there figure 2 is a sectional view of an embodiment of a thermally insulating double-glazed unit equipped with an FSS film; and the figure 3 illustrates the evolution of transmission T as a function of frequency, under various conditions, of a glazing with one face coated with a layer of metal oxide.

[0022] The same elements have been designated by the same references in the different figures and, moreover, the various figures are not drawn to scale. Detailed description

[0023] In the following description, the expressions "substantially" and "approximately" mean within 10%, preferably within 5%.

[0024] There figure 2 is a sectional view of a thermally insulating double-glazing unit 20. The double-glazing unit 20 comprises a first pane 21 and a second pane 22 that are parallel. The pane 21 has a thickness h 1 , an external face 23 and an internal face 24. The pane 22 has a thickness h 2 , an external face 25 and an internal face 26. The facing internal faces 24 and 26 are separated by a thickness h 3 of gas 28 that may be under vacuum. The internal face 26 of the pane 22 is coated with a layer of metal oxide 29.

[0025] In practice, the above-mentioned elements of a double-glazed unit are connected by a frame, the whole forming a window, a door or other partition. It is not possible to modify the assembly without destroying the product. The values of the parameters h 1 , h 2 and h 3 are therefore imposed by the manufacturer.

[0026] In figure 2 an FSS film 10 comprising a pattern of conductive elements 11 and a dielectric support 12, is placed against the external face 23 of the window 21. The pattern 11 corresponds for example to that of the Figure 1A .

[0027] There figure 3 illustrates the evolution, as a function of the frequency f (in GHz), of the transmission T (in decibels) of a double-glazing unit 20, one face of which is coated with a layer of metal oxide 29, under various conditions. The transmission values correspond to a double-glazing unit 20 as represented in figure 2 , whose parameters are: h 1 = 4 mm, h 2 = 6 mm, and h 3 = 16 mm.

[0028] Curve 40 corresponds to a double glazing 20 of which one face is coated with a layer of metal oxide 29, in the absence of an FSS film. Curve 40 shows that there is then a substantially constant attenuation of the transmission, of approximately 35 dB.

[0029] Curve 50 illustrates the transmission of a double-glazed unit 20, one face of which is coated with a layer of metal oxide 29, equipped with an FSS film 10 on the external face 23 of the window 21, as represented by the figure 2 . We then observe on the transmission attenuated by the double glazing 20 an attenuation peak 51 similar to that of the Figure 1B. We also observe an amplification peak 52 as well as two low amplification lobes 53 and 54. The attenuation peak 51 is located at the attenuation frequency of the FSS film 10. The amplification peak 52 is located at a higher frequency but close to the attenuation frequency and has an amplitude of approximately 10 dB greater than the average attenuation corresponding to the curve 40. The amplification lobes 53 and 54 are located on either side and at frequencies far from the attenuation frequency, their amplitudes are approximately 3 dB compared to the average attenuation corresponding to the curve 40.

[0030] Curve 60 illustrates the transmission of a double-glazing unit 20, one face of which is coated with a layer of metal oxide, equipped with an FSS film 10 on the external face 25 of the window 22. We then observe on the transmission attenuated by the double-glazing unit 20, an attenuation peak 61 similar to that of the Figure 1Bas well as an amplification peak 62. The attenuation peak 61 is located at the attenuation frequency of the FSS film 10. The amplification peak 62 is located at a frequency lower than but close to the attenuation frequency and has an amplitude approximately 10 dB greater than the average attenuation corresponding to curve 40.

[0031] It therefore appears that an FSS film placed against double glazing, one face of which is coated with a conductive layer of metal oxide, introduces not only a transmission zero, but also an amplification peak close to the transmission zero.

[0032] Tests and simulations carried out by the inventors show that, for a given double glazing (whose parameters h 1 , h 2 and h 3 are fixed), there is always an amplification peak close to the transmission zero. The frequency distance between the transmission zero and the amplification peak depends on the glazing parameters and can be determined by calculations involving simulation steps. In the case of loop FSS patterns of the type shown in Figure 1A , if we call f 0 the frequency of the amplification peak, the frequency of the transmission zero is between approximately f 0 / 2 and 2f 0 .

[0033] More specifically, the calculation of the position of the amplification peak (resonance) is done using commercial electromagnetic simulation calculation software (such as HFSS or CST). The first step of the method consists of making a 3-dimensional physical model of the FSS structure (for example using the principle of Floquet's theorem) superimposed on the glass and located at a non-zero distance from the weakly conductive metal oxide layer. To position the amplification peak, the second step consists of optimizing the dimensions of the FSS structure in an iterative manner by varying the dimensions of the FSS structure.

[0034] It is recalled that many studies indicate how to determine the elements of an FSS pattern to obtain an attenuation peak at a desired frequency. As indicated previously, in the case of a pattern corresponding to that of the Figure 1A, the wavelength corresponding to the attenuation frequency is substantially equal to the perimeter of a conductive element of this pattern.

[0035] The presence of these amplification peaks is attributed to the adaptation of the impedance of the reinforced insulation window to that of air (377 Ohm) thanks to the FSS structures deposited at a non-zero distance from the conductive layer.

[0036] Particular embodiments have been described. Various variations and modifications will occur to those skilled in the art.

[0037] The FSS patterns described above are formed on a flexible and transparent dielectric support or film which can be adhered to the glass in order to be applied to permanently assembled glazing, possibly already mounted. These FSS patterns can also be formed directly on a window.

[0038] The frequency of the amplification peak will correspond, for example, to a frequency used by telecommunications systems.

[0039] The conductive elements distributed according to the pattern represented by the Figure 1A may have a shape other than square, for example a circular or even rectilinear shape.

[0040] Furthermore, an embodiment has been described in which the invention is applied to double glazing. The invention also applies to the case of thermally insulating triple glazing or even a single pane of glass, one face of which is coated with a conductive layer having, for example, an anti-reflective function. This conductive layer will, for example, have a resistance of 1 to 1000 Ω / □. This layer will not necessarily be a metal oxide. It will, for example, be a polymer or a multilayer in the case of an anti-reflective coating.

Claims

1. A glazing comprising a glazing sheet one face of which is coated with a conductive layer (29), characterised in that it includes, at a non-zero distance from the conductive layer, a periodic pattern of conductive elements (11) adapted to increase, for a determined frequency, transmission of radiofrequency electromagnetic waves, said periodic pattern being chosen to have a transmission zero at a frequency between half and twice the frequency to be amplified, the periodic pattern of conductive elements being formed on a flexible and transparent dielectric support (12).

2. The glazing according to claim 1, wherein the dielectric support is adhering to the glass.

3. The glazing according to any of claims 1 to 2, wherein each conductive element has the shape of a square with an empty centre.

4. The glazing according to any of claims 1 to 2, wherein each conductive element has a circular shape.

5. The glazing according to any of claims 1 to 4, comprising two or three glazing sheets, wherein the conductive layer is formed on an inner face of a glazing sheet.

6. The glazing according to any of claims 1 to 5, wherein the conductive layer has a resistance of 1 to 1000 Ω / □.

7. The glazing according to claim 6, wherein the conductive layer is a layer of a metal oxide or a polymer.

8. Method for amplifying transmission at a determined frequency of a glazing comprising a glazing sheet one face of which is coated with a conductive layer (29), consisting in coating a wall of the glazing with a periodic pattern of conductive elements (11), adapted to increase, for a determined frequency, transmission of radiofrequency electromagnetic waves, said periodic pattern being chosen to have a transmission zero at a frequency between half and twice the frequency to be amplified, the periodic pattern of conductive elements being formed on a flexible and transparent dielectric support (12).

9. The method according to claim 8, wherein said determined frequency is a frequency used by telecommunication systems.