Radio wave absorption device and radio wave absorption system provided with radio wave absorption device

Abstract

This radio wave absorption device includes: a patch electrode; a counter electrode that faces the patch electrode and that is formed from a different material than the patch electrode; and a liquid crystal layer between the patch electrode and the counter electrode. Another radio wave absorption device includes a first patch electrode, a second patch electrode that can be controlled separately from the first patch electrode, a counter electrode that faces the first patch electrode and the second patch electrode, and a liquid crystal layer between the first patch electrode and the counter electrode and between the second patch electrode and the counter electrode, with a first relative permittivity of the liquid crystal layer interposed between the first patch electrode and the counter electrode differing from a second relative permittivity of the liquid crystal layer interposed between the second patch electrode and the counter electrode.

Description

Radio wave absorber and radio wave absorption system equipped with the radio wave absorber

[0001] An embodiment of the present invention relates to a radio wave absorbing device capable of absorbing incident radio waves and a radio wave absorbing system including the radio wave absorbing device.

[0002] In recent years, devices using high frequencies of 10 GHz to 100 GHz have become increasingly common. As a result, problems such as radio wave interference or congestion have arisen between multiple high-frequency devices. To solve these problems, there is a growing demand for radio wave absorption devices that reduce radio wave interference or congestion.

[0003] Japanese Patent Application Laid-Open No. 2022-047398

[0004] Conventional radio wave absorbing devices are designed to absorb radio waves having a specific frequency. Therefore, after the radio wave absorbing device is installed, it is not possible to change the frequency of the radio waves that the radio wave absorbing device absorbs. Furthermore, conventional radio wave absorbing devices cannot be switched between a radio wave absorbing state and a radio wave reflecting state.

[0005] An object of one embodiment of the present invention is to provide a radio wave absorbing device capable of adjusting the performance of absorbing radio waves.

[0006] A radio wave absorption device according to one embodiment of the present invention includes a patch electrode, a counter electrode facing the patch electrode and made of a material different from that of the patch electrode, and a liquid crystal layer between the patch electrode and the counter electrode.

[0007] A radio wave absorption device according to one embodiment of the present invention includes a first patch electrode, a second patch electrode that is controllable independently of the first patch electrode, a counter electrode that faces the first patch electrode and the second patch electrode, and a liquid crystal layer between the first patch electrode and the counter electrode and between the second patch electrode and the counter electrode, wherein a first relative dielectric constant of the liquid crystal layer sandwiched between the first patch electrode and the counter electrode is different from a second relative dielectric constant of the liquid crystal layer sandwiched between the second patch electrode and the counter electrode.

[0008] A radio wave absorption system according to one embodiment of the present invention comprises the radio wave absorption device described above and a control device that controls voltages supplied to the patch electrode and the counter electrode, and the control device controls the voltages supplied to the patch electrode and the counter electrode to change the absorption amount of the radio wave absorption device for radio waves having any frequency.

[0009] A radio wave absorption system according to one embodiment of the present invention comprises the radio wave absorption device described above, and a control device that controls voltages supplied to the first patch electrode, the second patch electrode, and the counter electrode, and the control device controls the voltages supplied to the first patch electrode, the second patch electrode, and the counter electrode, thereby changing the absorption amount of the radio wave absorption device for radio waves having any frequency.

[0010] 1 is a cross-sectional view and a functional block diagram showing an overview of a radio wave absorbing system according to an embodiment of the present invention; FIG. 2 is a cross-sectional view showing an overview of a radio wave absorbing device according to an embodiment of the present invention; FIG. 3 is a plan view of an absorption plate unit cell used in a radio wave absorbing device according to an embodiment of the present invention; FIG. 4 is a cross-sectional structure of an absorption plate unit cell used in a radio wave absorbing device according to an embodiment of the present invention; FIG. 5 is a diagram showing a state in which a control voltage is not applied between a patch electrode and a counter electrode in an absorption plate unit cell used in a radio wave absorbing device according to an embodiment of the present invention; FIG. 6 is a diagram showing a state in which a control voltage is applied between a patch electrode and a ground electrode in an absorption plate unit cell used in a radio wave absorbing device according to an embodiment of the present invention; FIG. 7 is a simulation result showing the relationship between the voltage supplied to the patch electrode and the ground electrode and the frequency band in which radio waves are absorbed in a radio wave absorbing device according to an embodiment of the present invention; FIG. 8 is a simulation result showing the frequency band in which radio waves are absorbed in a radio wave absorbing device according to an embodiment of the present invention; FIG. 9 is a diagram showing the configuration of a radio wave absorbing device of a collective control type according to an embodiment of the present invention; FIG. 10 is a diagram showing the configuration of a radio wave absorbing device of an individual control type according to an embodiment of the present invention; FIG. 11 is a cross-sectional structure of an absorption plate unit cell in a radio wave absorbing device according to an embodiment of the present invention; and FIG. 12 is a diagram explaining a method of driving a radio wave absorbing device according to an embodiment of the present invention. FIG. 1 is a simulation result showing the relationship between a method for driving a radio wave absorbing device and radio wave absorption in a radio wave absorbing device according to one embodiment of the present invention. FIG. 2 is a diagram explaining a method for driving a radio wave absorbing device according to one embodiment of the present invention. FIG. 3 is a diagram explaining a method for driving a radio wave absorbing device according to one embodiment of the present invention. FIG. 4 is a simulation result showing the relationship between a method for driving a radio wave absorbing device and radio wave absorption in a radio wave absorbing device according to one embodiment of the present invention. FIG. 5 is a simulation result showing the relationship between a thickness of a substrate and radio wave absorption in a radio wave absorbing device according to one embodiment of the present invention. FIG. 6 is a cross-sectional view showing an overview of a radio wave absorbing device according to one embodiment of the present invention.1 is a plan view showing an outline of a patch electrode of a radio wave absorbing device according to an embodiment of the present invention.

[0011] Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention can be implemented in many different forms, and should not be construed as being limited to the description of the following exemplary embodiments. For clarity of explanation, the drawings may show schematic representations of the width, thickness, shape, etc. of each part compared to the actual form, but these are merely examples and do not limit the interpretation of the present invention. In this specification and each drawing, components similar to those described above with respect to the previous drawings are designated by the same reference numerals (or reference numerals with a, b, etc. suffixed thereto), and detailed descriptions may be omitted as appropriate. Furthermore, the letters "first" and "second" attached to each element are convenient labels used to distinguish each element and have no further meaning unless otherwise specified.

[0012] In this specification, unless otherwise specified, the expression that a certain member or region is "on (or under)" another member or region includes not only the case where the member or region is directly above (or directly under) the other member or region, but also the case where the member or region is above (or under) the other member or region. The above expression also includes the case where another component is included between a certain member or region and the other member or region.

[0013] In this specification, unless otherwise specified, expressions such as "α includes A, B, or C," "α includes any of A, B, and C," and "α includes one selected from the group consisting of A, B, and C" do not exclude cases where α includes multiple combinations of A to C. Furthermore, these expressions do not exclude cases where α includes other elements.

[0014] The following embodiments can be combined with each other as long as no technical contradiction occurs.

[0015] 1. First Embodiment A radio wave absorption system 10 according to one embodiment of the present invention will be described with reference to FIGS.

[0016] 1 is a cross-sectional view and a functional block diagram showing an outline of a radio wave absorbing system according to one embodiment of the present invention. As shown in FIG. 1, the radio wave absorbing system 10 includes a radio wave absorbing device 100, a control circuit 500, and a drive circuit 600.

[0017] The radio wave absorbing device 100 absorbs radio waves in a predetermined frequency band. The detailed configuration of the radio wave absorbing device 100 will be described later, but the radio wave absorbing device 100 includes a patch electrode, a counter electrode, and a liquid crystal layer. In the radio wave absorbing device 100, the orientation of liquid crystal molecules contained in the liquid crystal layer is controlled in accordance with voltages (control voltages) supplied to the patch electrode and the counter electrode. The frequency band of radio waves absorbed by the radio wave absorbing device 100 is controlled by controlling this orientation.

[0018] The control circuit 500 outputs a control signal corresponding to an input setting value (e.g., a frequency value) based on the input setting value. For example, when a user inputs a predetermined frequency value via a user interface provided by the radio wave absorbing system 10, the control circuit 500 outputs a control signal for controlling the radio wave absorbing device 100 to absorb radio waves of that frequency based on the input frequency value. For example, the control circuit 500 may generate the control signal by performing an arithmetic process using the input setting value as a parameter. Alternatively, the control circuit 500 may include a look-up table (LUT) in which setting values ​​and control signals are associated with each other, and may read out the generated signal by referring to the LUT using the input setting value.

[0019] The drive circuit 600 is connected to the control circuit 500 and the radio wave absorbing device 100. The drive circuit 600 drives the radio wave absorbing device 100 (supplies a drive voltage to the radio wave absorbing device 100) based on a control signal output by the control circuit 500. In other words, the drive circuit 600 supplies a control voltage to the patch electrode and the counter electrode of the radio wave absorbing device 100 so as to absorb radio waves in a frequency band corresponding to a setting value input by a user. When the radio wave absorbing device 100 is provided with a plurality of patch electrodes and counter electrodes, the drive circuit 600 may control the plurality of patch electrodes and counter electrodes collectively, may control the plurality of patch electrodes in groups, or may control each of the plurality of patch electrodes individually.

[0020] The control circuit 500 and the drive circuit 600 may be collectively referred to as a "control device." In this case, it can be said that the control device controls the voltages supplied to the patch electrode and the counter electrode. In other words, the control device controls the voltages supplied to the patch electrode and the counter electrode, thereby changing the absorption amount of radio waves having a given frequency by the radio wave absorbing device 100. In yet other words, the control device receives, via the interface, a setting value related to the frequency of the radio waves to be absorbed by the radio wave absorbing device 100, and controls the voltages supplied to the patch electrode and the counter electrode based on the setting value.

[0021] [1-2. Radio Wave Absorber 100] FIG. 2 is a cross-sectional view showing an outline of a radio wave absorber according to one embodiment of the present invention. As shown in FIG. 2, the radio wave absorber 100 includes a plurality of absorbing elements (absorber plate unit cells 102). The plurality of absorber plate unit cells 102 are arranged in at least one direction. In FIG. 2, the plurality of absorber plate unit cells 102 are arranged in the Y-axis direction. The radio wave absorber 100 includes a dielectric substrate 104, a counter substrate 106, a patch electrode 108, a ground electrode 110, a liquid crystal layer 114, a sealant 128, a switching element 134, a terminal portion 126, and a printed circuit board (FPC) 160. The liquid crystal layer 114 contains liquid crystal molecules 116. A passivation layer 158 is provided between the patch electrode 108 and the dielectric substrate 104.

[0022] In the radio wave absorbing device 100, of the opposing electrodes (patch electrode 108 and ground electrode 110), the electrode provided on the radio wave incident surface side is called the "patch electrode," and the electrode opposing the patch electrode is called the "counter electrode." In this embodiment, the ground electrode 110 corresponds to the counter electrode. As will be described in detail later, when radio waves are incident from the counter substrate 106 side, the electrode corresponding to the ground electrode 110 is called the patch electrode.

[0023] Although details will be described later, when the radio wave absorbing device 100 controls a plurality of absorber plate unit cells 102 individually or in groups, each of the absorber plate unit cells 102 includes a switching element 134. On the other hand, when the radio wave absorbing device 100 controls a plurality of absorber plate unit cells 102 collectively, each of the absorber plate unit cells 102 does not necessarily need to include a switching element 134.

[0024] The absorber plate unit cell 102 includes at least a patch electrode 108, a ground electrode 110 (counter electrode), a liquid crystal layer 114, and a switching element 134. The patch electrode 108 is provided individually for each absorber plate unit cell 102. The patch electrode 108 is provided on the dielectric substrate 104 side. The ground electrode 110 faces the patch electrode 108 and is provided in common to the plurality of absorber plate unit cells 102. The ground electrode 110 is provided on the counter substrate 106 side. The detailed structure of the absorber plate unit cell 102 will be described later.

[0025] The liquid crystal layer 114 is provided between the patch electrode 108 and the ground electrode 110. The orientation of the liquid crystal molecules 116 contained in the liquid crystal layer 114 is controlled by a control voltage supplied to the patch electrode 108 and the ground electrode 110. A sealant 128 is provided to surround the periphery of the counter substrate 106. In other words, the liquid crystal layer 114 is sealed by the sealant 128. The patch electrode 108 and the ground electrode 110 are provided in an area surrounded by the sealant 128.

[0026] The material of the patch electrode 108 is different from the material of the ground electrode 110. The electrical conductivity (or electric conductance) of the material constituting the patch electrode 108 is different from the electrical conductivity of the material constituting the ground electrode 110. For example, the ratio of the electrical conductivity of the material constituting the patch electrode 108 to the electrical conductivity of the material constituting the ground electrode 110 is 10 times or more. As will be described in detail later, the amount of radio waves absorbed by the radio wave absorbing device 100 is affected by the balance between the electrical conductances of the patch electrode 108 and the ground electrode 110. When the electrical conductances of the patch electrode 108 and the ground electrode 110 have the above characteristics, the amount of radio waves absorbed by the radio wave absorbing device 100 can be increased.

[0027] The radio wave absorbing device 100 is divided into a radio wave absorbing region 162 and a peripheral region 164 surrounding the region. The radio wave absorbing region 162 is an area in which the patch electrode 108 and the ground electrode 110 are disposed. Radio waves incident on the radio wave absorbing device 100 from the dielectric substrate 104 side are absorbed in the radio wave absorbing region 162. By supplying a control voltage between the patch electrode 108 and the ground electrode 110 and controlling the orientation of the liquid crystal molecules 116, the radio waves incident on the radio wave absorbing device 100 are absorbed by the patch electrode 108. In other words, the patch electrode 108 functions as a receiving antenna for the incident radio waves. The reflection characteristics of the receiving antenna can be controlled by the control voltage supplied between the patch electrode 108 and the ground electrode 110, so that the frequency band of the radio waves absorbed by the patch electrode 108 can be controlled by controlling the control voltage. Although not shown, a part of the driving circuit 600 is disposed in the peripheral region 164.

[0028] The switching element 134 is connected to the patch electrode 108. The switching element 134 is provided at a position close to the incident surface of the radio wave with respect to the patch electrode 108. The switching element 134 is driven by a drive circuit 600 (see FIG. 1 ). The orientation of the liquid crystal molecules 116 is controlled in accordance with the driving state of the switching element 134. As will be described in detail later, by controlling the orientation of the liquid crystal molecules 116, the frequency band of the radio wave absorbed by the radio wave absorbing device 100 is controlled.

[0029] The terminal portion 126 is provided at an end of the dielectric substrate 104. The terminal portion 126 may be configured in the same layer as the patch electrode 108. The terminal portion 126 may be configured in the same layer as part or all of the conductive layer that configures the switching element 134. The terminal portion 126 is connected to the switching element 134 via wiring. An FPC 160 is connected to the terminal portion 126. A drive circuit 600 drives the switching element 134 in response to a control signal input from the outside via the FPC 160.

[0030] 3A and 3B are plan views of an absorber plate unit cell used in a radio wave absorber according to one embodiment of the present invention. Fig. 3A is a plan view of the absorber plate unit cell 102 as seen from above (the side onto which radio waves are incident). Fig. 3B is a cross-sectional view taken along the line A1-A2 shown in the plan view.

[0031] As shown in Figures 3A and 3B, the absorber plate unit cell 102 includes a dielectric substrate 104, a counter substrate 106, a patch electrode 108, a ground electrode 110, a liquid crystal layer 114, a first alignment film 112a, and a second alignment film 112b. Within the absorber plate unit cell 102, the dielectric substrate 104 may be considered as a single layer (dielectric layer). The patch electrode 108 is disposed on the dielectric substrate 104, and the ground electrode 110 is disposed on the counter substrate 106. A first alignment film 112a is disposed on the dielectric substrate 104 to cover the patch electrode 108. A second alignment film 112b is disposed on the counter substrate 106 to cover the ground electrode 110. The patch electrode 108 and the ground electrode 110 are disposed opposite each other, with a liquid crystal layer 114 disposed between them. The first alignment film 112a is interposed between the patch electrode 108 and the liquid crystal layer 114. A second alignment film 112 b is interposed between the ground electrode 110 and the liquid crystal layer 114 .

[0032] The patch electrode 108 preferably has a shape that is symmetrical with respect to the vertically and horizontally polarized waves of the incident radio wave. For example, the patch electrode 108 has a square or circular shape in a plan view. FIG. 3A shows a case where the patch electrode 108 is square in a plan view. The shape of the ground electrode 110 is not particularly limited, and it has a shape that extends over substantially the entire surface of the opposing substrate 106 so as to have a larger area than the patch electrode 108. The patch electrode 108 and the ground electrode 110 may be made of any material other than the material of the patch electrode 108, and the patch electrode 108 and the ground electrode 110 may be made of any material other than a conductive metal or metal oxide. The dielectric substrate 104 is provided with a first wiring 118. The first wiring 118 is connected to the patch electrode 108. The first wiring 118 is used when a control voltage is supplied to the patch electrode 108. When a plurality of absorber plate unit cells 102 are arranged in the radio wave absorber 100, the first wiring 118 is used to connect a certain patch electrode 108 to an adjacent patch electrode 108.

[0033] 3A and 3B, the dielectric substrate 104 and the counter substrate 106 are bonded together with a sealant 128. The dielectric substrate 104 and the counter substrate 106 are disposed opposite each other with a gap therebetween. The liquid crystal layer 114 is provided within a region surrounded by the sealant 128. The liquid crystal layer 114 is provided so as to fill the gap between the dielectric substrate 104 and the counter substrate 106.

[0034] For example, if the patch electrode 108 is a square with a side length of approximately 2 mm, the gap between the dielectric substrate 104 and the counter substrate 106 is 5 μm to 100 μm, 10 μm to 40 μm, or 15 μm to 25 μm. In other words, the ratio of the gap between the dielectric substrate 104 and the counter substrate 106 to the side length of the patch electrode 108 (approximately 2 mm) is 0.25% to 5%, 0.5% to 2%, or 0.75% to 1.25%.

[0035] A patch electrode 108, a ground electrode 110, a first alignment film 112a, and a second alignment film 112b are provided between the dielectric substrate 104 and the counter substrate 106. Therefore, to be precise, the distance between the first alignment film 112a and the second alignment film 112b provided on the dielectric substrate 104 and the counter substrate 106, respectively, is the thickness of the liquid crystal layer 114. Although not shown in Fig. 3B, a spacer may be provided between the dielectric substrate 104 and the counter substrate 106 to keep the distance constant.

[0036] A control voltage is applied to the patch electrode 108 to control the orientation of the liquid crystal molecules 116 in the liquid crystal layer 114. For example, the control voltage may be a DC voltage signal or a polarity reversal voltage signal in which positive and negative DC voltages alternate. In the latter case, a ground level or an intermediate voltage between the polarity reversal voltages is applied to the ground electrode 110. Application of the control voltage to the patch electrode 108 changes the orientation state of the liquid crystal molecules in the liquid crystal layer 114. A liquid crystal material having dielectric anisotropy is used for the liquid crystal layer 114. For example, nematic liquid crystal, smectic liquid crystal, cholesteric liquid crystal, or discotic liquid crystal may be used for the liquid crystal layer 114. The dielectric constant of the liquid crystal layer 114 changes depending on the orientation state of the liquid crystal molecules. The absorber unit cell 102 can change the dielectric constant of the liquid crystal layer 114 by applying a control voltage to the patch electrode 108, thereby adjusting the frequency band of radio waves absorbed by the absorber unit cell 102.

[0037] FIG. 4A shows a state where no voltage is applied between the patch electrode 108 and the ground electrode 110 or where the potential difference between the two electrodes is zero (referred to as the "first state"). FIG. 4A also shows a case where the first alignment film 112a and the second alignment film 112b are horizontal alignment films. In the first state, the long axes of the liquid crystal molecules 116 are aligned horizontally relative to the surfaces of the patch electrode 108 and the ground electrode 110 by the first alignment film 112a and the second alignment film 112b. FIG. 4B shows a state where a control voltage is applied to the patch electrode 108 (referred to as the "second state"). In the second state, the liquid crystal molecules 116 are subjected to the action of an electric field, and their long axes are aligned perpendicular to the surfaces of the patch electrode 108 and the ground electrode 110. Depending on the magnitude of the control voltage applied to the patch electrode 108 (the magnitude of the voltage between the counter electrode and the patch electrode), the angle at which the long axes of the liquid crystal molecules 116 are aligned can also be controlled to a direction intermediate between the horizontal and vertical directions.

[0038] When the liquid crystal molecules 116 have positive dielectric anisotropy, the dielectric constant is larger in the second state than in the first state. On the other hand, when the liquid crystal molecules 116 have negative dielectric anisotropy, the dielectric constant is smaller in the second state than in the first state. The liquid crystal layer 114 having dielectric anisotropy can also be considered as a variable dielectric layer. The absorber plate unit cell 102 can adjust the frequency band of the radio waves to be absorbed by utilizing the dielectric anisotropy of the liquid crystal layer 114.

[0039] The absorber plate unit cell 102 is used as an absorber plate for absorbing radio waves. It is preferable that the absorber plate unit cell 102 reflect as little radio waves as possible when they are incident on the absorber plate unit cell 102. As is clear from the structure shown in FIG. 3B , when radio waves propagating through the air are incident on the absorber plate unit cell 102, the radio waves pass through the dielectric substrate 104 twice. The dielectric substrate 104 is formed of a dielectric material such as glass or resin. When radio waves pass through a dielectric, the phase velocity of the radio waves changes. Therefore, in order to prevent the amplitude of the reflected wave from increasing, it is preferable to set the thickness of the dielectric substrate 104 to a thickness that is different from ¼ wavelength of the incident radio wave (for example, ⅛ wavelength).

[0040] [1-4. Simulation Results of Radio Wave Absorber 100] Fig. 5 shows simulation results showing the relationship between the voltages supplied to the patch electrode and the ground electrode and the frequency band in which radio waves are absorbed in a radio wave absorber according to one embodiment of the present invention. The simulation results shown in Fig. 5 are the result of simulating the reflection characteristics of one absorber plate unit cell 102. In this simulation, calculations were performed based on a model in which the periodic structure of the absorber plate unit cells 102 is assumed to extend infinitely. This simulation was performed using CST Studio Suite (manufactured by Dassault Systèmes). The parameters of the radio wave absorber 100 used in the simulation are as follows: Arrangement pitch of patch electrodes 108: 3 mm Size of patch electrode 108: 2 mm x 2 mm Thickness of liquid crystal layer 114: 30 µm Relative dielectric constant ε of liquid crystal layer 114: 2.5, 3.5 Thickness of substrate 101: 1.0 mm

[0041] In the graph shown in Fig. 5, the vertical axis represents reflection amplitude, and the horizontal axis represents frequency. In the graph of Fig. 5, a large reflection amplitude (closer to zero) means that the radio wave absorbing device 100 reflects more of the incident radio wave. In other words, in the graph of Fig. 5, a small reflection amplitude (farther from zero) means that a larger amount of the incident radio wave is absorbed by the radio wave absorbing device 100.

[0042] FIG. 5 shows two simulation results. These simulation results are for cases where the liquid crystal layer 114 has different dielectric constants (dielectric constants ε = 2.5 and 3.5). In FIG. 5, the simulation results for a dielectric constant ε of 2.5 are shown by a dotted line, and the simulation results for a dielectric constant ε of 3.5 are shown by a solid line. In the radio wave absorbing device 100, the simulation results for a dielectric constant ε of 2.5 correspond to the simulation results for a state where no control voltage is supplied to the patch electrode 108 and the ground electrode 110 (a state where the potential difference between the two electrodes is zero). On the other hand, the simulation results for a dielectric constant ε of 3.5 correspond to the simulation results for a state where a control voltage is supplied to the patch electrode 108 and the ground electrode 110. The dielectric constant ε can be adjusted within a range of 2.5 to 3.5 by controlling the control voltage supplied to the patch electrode 108 and the ground electrode 110.

[0043] 5, when the relative dielectric constant ε is 2.5, the frequency at which the reflection amplitude has a minimum value is 42.9 GHz. That is, in this case, the radio wave absorbing device 100 most effectively absorbs radio waves with a frequency of 42.9 GHz. On the other hand, when the relative dielectric constant ε is 3.5, the frequency at which the reflection amplitude has a minimum value is 37.4 GHz. That is, in this case, the radio wave absorbing device 100 most effectively absorbs radio waves with a frequency of 37.4 GHz.

[0044] To put the above results in other words, for radio waves with a frequency of 42.9 GHz, if the relative dielectric constant ε is 2.5, the radio wave absorbing device 100 absorbs the incident radio waves (42.9 GHz), but if the relative dielectric constant ε is 3.5, the radio wave absorbing device 100 reflects the incident radio waves (42.9 GHz). Similarly, for radio waves with a frequency of 37.4 GHz, if the relative dielectric constant ε is 2.5, the radio wave absorbing device 100 reflects the incident radio waves (37.4 GHz), and if the relative dielectric constant ε is 3.5, the radio wave absorbing device 100 absorbs the incident radio waves (37.4 GHz). In other words, the radio wave absorbing device 100 can switch between an absorbing state and a reflecting state for radio waves of a certain frequency.

[0045] [1-5. Influence of Materials of Patch Electrode 108 and Ground Electrode 110] Fig. 6 shows simulation results showing the frequency band in which radio waves are absorbed in a radio wave absorption device according to one embodiment of the present invention. Fig. 6 shows four simulation results 1000 ([A] to [D]) with different combinations of patch electrode 108 and ground electrode 110, as follows: The electrical conductivity of Al used in the simulation shown in Fig. 6 is 3.5 × 10 ７ [S / m], and the electrical conductivity of ITO is 6.7 × 10 ５ [S / m]. [A] Patch electrode 108 / ground electrode 110 = Al / ITO [B] Patch electrode 108 / ground electrode 110 = ITO / Al [C] Patch electrode 108 / ground electrode 110 = ITO / ITO [D] Patch electrode 108 / ground electrode 110 = Al / Al

[0046] 6A, when the patch electrode 108 / ground electrode 110 is made of Al / ITO and the relative dielectric constant ε of the liquid crystal layer 114 is 2.5, the minimum value of the reflection amplitude is approximately -50 dB. When the patch electrode 108 / ground electrode 110 is made of Al / ITO and the relative dielectric constant ε of the liquid crystal layer 114 is 3.5, the minimum value of the reflection amplitude is approximately -21 dB.

[0047] 6B, when the patch electrode 108 / ground electrode 110 is ITO / Al and the relative dielectric constant ε of the liquid crystal layer 114 is 2.5, the minimum value of the reflection amplitude is approximately -34 dB. When the patch electrode 108 / ground electrode 110 is ITO / Al and the relative dielectric constant ε of the liquid crystal layer 114 is 3.5, the minimum value of the reflection amplitude is approximately -20 dB.

[0048] 6[C], when the patch electrode 108 / ground electrode 110 is ITO / ITO and the relative dielectric constant ε of the liquid crystal layer 114 is 2.5, the minimum value of the reflection amplitude is approximately -14 dB. When the patch electrode 108 / ground electrode 110 is ITO / ITO and the relative dielectric constant ε of the liquid crystal layer 114 is 3.5, the minimum value of the reflection amplitude is approximately -10 dB.

[0049] As shown in FIG. 6D, when the patch electrode 108 / ground electrode 110 is Al / Al, the minimum value of the reflection amplitude is approximately −8 dB whether the relative dielectric constant ε of the liquid crystal layer 114 is 2.5 or 3.5.

[0050] As described above, the minimum value of the reflection amplitude when the patch electrode 108 and the ground electrode 110 are made of different materials ([A] and [B]) is smaller than the minimum value of the reflection amplitude when the patch electrode 108 and the ground electrode 110 are made of the same material ([C] and [D]). That is, a radio wave absorbing device 100 having a patch electrode 108 and a ground electrode 110 made of different materials absorbs a greater amount of radio waves than a radio wave absorbing device 100 having a patch electrode 108 and a ground electrode 110 made of the same material. The radio wave absorption amount of the radio wave absorbing device 100 can be increased by setting the ratio of the electrical conductivity of the material constituting the patch electrode 108 to the electrical conductivity of the material constituting the ground electrode 110 to be 10 times or more. This ratio may be 20 times or more, 30 times or more, or 50 times or more. Similarly, the above result can be restated as follows: the material of the patch electrode 108 is one of a metallic material and a transparent conductive material, and the material of the ground electrode 110 is the other of a metallic material and a transparent conductive material. That is, when the material of the patch electrode is a metal material, the material of the counter electrode is a transparent conductive material, and when the material of the patch electrode is a transparent conductive material, the material of the counter electrode is a metal material.

[0051] Fig. 7 shows simulation results showing the relationship between the electrical conductivity of the patch electrode and the ground electrode and radio wave absorption in a radio wave absorbing device according to one embodiment of the present invention. In Fig. 7, the horizontal axis represents the common logarithm (Log(Conduct_G)) of the electrical conductivity of the ground electrode 110, and the vertical axis represents the common logarithm (Log(Conduct_P)) of the electrical conductivity of the patch electrode 108. The two-dimensional map in Fig. 7 plots the average values ​​of the minimum values ​​of the reflection amplitude when the relative dielectric constant ε of the liquid crystal layer 114 is 2.5 and the minimum values ​​of the reflection amplitude when the relative dielectric constant ε of the liquid crystal layer 114 is 3.5, for the simulation results for each electrical conductivity.

[0052] 7, the region where the minimum value of the reflection amplitude is relatively small (the region below -20 dB) is distributed in a quadratic curve (curving from the upper left to the lower right of the graph). The region where the minimum value of the reflection amplitude is below -20 dB is affected by the balance of the electrical conductivities of the patch electrode 108 and the ground electrode 110. This is because the smaller the difference between the characteristic impedance of air and the impedance of the metasurface, the greater the amount of radio wave absorption in the radio wave absorber 100.

[0053] As described above, according to the radio wave absorbing device 100 of this embodiment, the frequency band of radio waves absorbed by the radio wave absorbing device 100 can be adjusted by controlling the control voltages supplied to the patch electrode 108 and the ground electrode 110 .

[0054] 8 to 10, a control method for the radio wave absorber 100 in which the absorption plate unit cells 102 are integrated will be described. There are two control methods for the radio wave absorber 100: a collective control method and an individual control method. Each control method will be described below.

[0055] [1-6-1. Collective Control Method] FIG. 8 is a diagram showing the configuration of a radio wave absorber of the collective control method according to one embodiment of the present invention. The radio wave absorber 100a has an absorbing plate 120. The absorbing plate 120 is composed of a plurality of absorbing plate unit cells 102. The plurality of absorbing plate unit cells 102 are arranged, for example, in a first direction (the X-axis direction shown in FIG. 8 ) and a second direction (the Y-axis direction shown in FIG. 8 ) intersecting the first direction. The absorbing plate unit cells 102 are arranged so that the patch electrode 108 faces the radio wave incident surface. The absorbing plate 120 is flat, and a plurality of patch electrodes 108 are arranged in a matrix within the flat surface. The radio wave absorber 100a shown in FIG. 8 does not necessarily include a switching element 134.

[0056] The radio wave absorbing device 100a has a structure in which a plurality of absorbing plate unit cells 102 are integrated on a single dielectric substrate 104. As shown in Fig. 8, the radio wave absorbing device 100a has a structure in which a dielectric substrate 104 on which a plurality of patch electrodes 108 are arranged and a counter substrate 106 on which a ground electrode 110 is provided are overlapped, and a liquid crystal layer 114 is provided between the two substrates. The absorbing plate 120 is formed in a region where the plurality of patch electrodes 108 and the ground electrode 110 overlap. For each patch electrode 108, the cross-sectional structure of the absorbing plate 120 is the same as the structure of the absorbing plate unit cell 102 shown in Fig. 3B. The dielectric substrate 104 and the counter substrate 106 are bonded together with a sealant 128, and the liquid crystal layer 114 is provided in a region inside the sealant 128.

[0057] The dielectric substrate 104 has a thickness that is different from 1 / 4 of the wavelength of the radio waves to be absorbed (for example, a thickness of 1 / 8 of the wavelength). In addition to the region facing the opposing substrate 106, the dielectric substrate 104 has a peripheral region 122 that extends outward from the opposing substrate 106. A first drive circuit 124 and a terminal section 126 are provided in the peripheral region 122. The first drive circuit 124 supplies a control voltage to the patch electrode 108. In this configuration, the first drive circuit 124 corresponds to the drive circuit 600. The terminal section 126 is a section that connects to an external circuit, and is a section to which the FPC 160 is connected. A signal that controls the first drive circuit 124 is input to the terminal section 126.

[0058] As described above, the dielectric substrate 104 has a plurality of patch electrodes 108 arranged in a first direction (X-axis direction) and a second direction (Y-axis direction). The dielectric substrate 104 also has a plurality of first wirings 118 extending in the second direction (Y-axis direction) and a plurality of second wirings 119 extending in the first direction (X-axis direction). Each of the plurality of first wirings 118 electrically connects the plurality of patch electrodes 108 arranged in the second direction (Y-axis direction). In other words, the plurality of patch electrodes 108 arranged in the second direction (Y-axis direction) are connected by the first wirings 118. Similarly, each of the plurality of second wirings 119 electrically connects the plurality of patch electrodes 108 arranged in the first direction (X-axis direction). In other words, the plurality of patch electrodes 108 arranged in the first direction (X-axis direction) are connected by the second wirings 119. The absorbing plate 120 has a configuration in which a matrix-like patch electrode array connected by a first wiring 118 and a second wiring 119 is arranged to extend across the XY plane.

[0059] The plurality of first wirings 118 arranged on the absorbing plate 120 extend into the peripheral region 122 and are connected to a first driving circuit 124. The first driving circuit 124 supplies a control voltage to the patch electrodes 108. The first driving circuit 124 supplies a control voltage of the same voltage level to each of the plurality of first wirings 118. As a result, on the absorbing plate 120, the control voltage is supplied collectively to the plurality of patch electrodes 108 arranged in the first direction (X-axis direction) and the second direction (Y-axis direction).

[0060] [1-6-2. Individual Control Method] The following radio wave absorber 100b can individually control the absorption plate unit cells 102. In the following explanation, differences from the above radio wave absorber 100a will be mainly described.

[0061] 9 shows the configuration of a radio wave absorber 100b according to this embodiment. In the following explanation, the differences from the radio wave absorber 100a shown in FIG.

[0062] The radio wave absorbing device 100b has, on the absorbing plate 120, a plurality of first wirings 118 extending in the second direction (Y-axis direction) and a plurality of second wirings 132 extending in the first direction (X-axis direction). The plurality of first wirings 118 and the plurality of second wirings 132 are arranged to intersect with an insulating layer (not shown) sandwiched therebetween. In other words, the first wirings 118 and the second wirings 132 are insulated from each other. The plurality of first wirings 118 are connected to a first drive circuit 124, and the plurality of second wirings 132 are connected to a second drive circuit 130. The first drive circuit 124 supplies a control voltage, and the second drive circuit 130 outputs a scanning signal. In this configuration, the first drive circuit 124 and the second drive circuit 130 correspond to the drive circuit 600. In FIG. 9 , the first drive circuit 124 is shown as an IC chip or the like mounted on the dielectric substrate 104. The second drive circuit 130 is shown as a drive circuit using thin film transistors formed on the conductive substrate 104 in the same manner as the inductive switching elements 134. However, this embodiment is not limited to this configuration.

[0063] The lower part of Figure 9 shows an inset diagram enlarging the arrangement of the four patch electrodes 108, two first wirings 118, and two second wirings 132. Each of the four patch electrodes 108 is provided with a switching element 134. The switching (on and off) of the switching element 134 is controlled by a scanning signal supplied to the second wiring 132. When the switching element 134 is turned on, the patch electrode 108 is electrically connected to the first wiring 118. A control voltage is supplied to the patch electrode 108 via the switching element 134. The switching element 134 is formed of, for example, a thin film transistor. With this configuration, it is possible to select a plurality of patch electrodes 108 arranged in the first direction (X-axis direction) for each row and supply control signals of different voltage levels to each row.

[0064] 9 can individually control the absorber plate unit cells 102. Therefore, as in the first embodiment described above, it is possible to control all of the absorber plate unit cells 102 collectively, and as in the second embodiment described below, it is also possible to control each absorber plate unit cell 102 differently.

[0065] 10 shows an example of the cross-sectional structure of an absorber plate unit cell 102 in which a switching element 134 is connected to a patch electrode 108. The switching element 134 is provided on a dielectric substrate 104. The switching element 134 is a transistor, and has a stacked structure of a first gate electrode 138, a first gate insulating layer 140, a semiconductor layer 142, a second gate insulating layer 146, and a second gate electrode 148. An undercoat layer 136 may be provided between the first gate electrode 138 and the dielectric substrate 104. A first wiring 118 is provided between the first gate insulating layer 140 and the second gate insulating layer 146. The first wiring 118 is provided so as to be in contact with the semiconductor layer 142. A first connecting wiring 144 is provided in the same layer as the conductive layer that forms the first wiring 118. The first connecting wiring 144 is provided so as to be in contact with the semiconductor layer 142. The connection structure of the first wiring 118 and the first connection wiring 144 to the semiconductor layer 142 shows a structure in which one wiring is connected to the source of the transistor and the other wiring is connected to the drain.

[0066] A first interlayer insulating layer 150 is provided to cover the switching element 134. A second wiring 132 is provided below the first interlayer insulating layer 150. The second wiring 132 is connected to the second gate electrode 148 through a contact hole formed in the first interlayer insulating layer 150. Although not shown, the first gate electrode 138 and the second gate electrode 148 are electrically connected to each other in a region that does not overlap with the semiconductor layer 142. A second connection wiring 152 is provided below the first interlayer insulating layer 150 and is made of the same conductive layer as the second wiring 132. The second connection wiring 152 is connected to the first connection wiring 144 through a contact hole formed in the first interlayer insulating layer 150.

[0067] A second interlayer insulating layer 154 is provided to cover the second wiring 132 and the second connection wiring 152. Furthermore, a planarizing layer 156 is provided to fill in the step of the switching element 134. By providing the planarizing layer 156, the patch electrode 108 can be formed without being affected by the placement of the switching element 134. A passivation layer 158 is provided below the flat surface of the planarizing layer 156. The patch electrode 108 is provided below the passivation layer 158. The patch electrode 108 is connected to the second connection wiring 152 via a contact hole that penetrates the passivation layer 158, the planarizing layer 156, and the second interlayer insulating layer 154. A first alignment film 112a is provided below the patch electrode 108.

[0068] 3B , the counter substrate 106 includes a ground electrode 110 and a second alignment film 112b. The surface of the dielectric substrate 104 on which the switching elements 134 and the patch electrode 108 are provided is disposed opposite the surface of the counter substrate on which the ground electrode 110 is provided, and a liquid crystal layer 114 is provided therebetween. The thickness t of the liquid crystal layer 114 corresponds to the length from the surface of the patch electrode 108 on the liquid crystal layer 114 side to the surface of the ground electrode 110 on the liquid crystal layer 114 side.

[0069] Each layer formed on the dielectric substrate 104 is formed using the following materials. For example, the undercoat layer 136 is formed of a silicon oxide film. For example, the first gate insulating layer 140 and the second gate insulating layer 146 are formed of a silicon oxide film or a stacked structure of a silicon oxide film and a silicon nitride film. The semiconductor layer is formed of a silicon semiconductor such as amorphous silicon or polycrystalline silicon, or an oxide semiconductor including a metal oxide such as indium oxide, zinc oxide, or gallium oxide. For example, the first gate electrode 138 and the second gate electrode 148 may be composed of molybdenum (Mo), tungsten (W), or an alloy thereof. The first wiring 118, the second wiring 132, the first connection wiring 144, and the second connection wiring 152 are formed of a metal material such as titanium (Ti), aluminum (Al), or molybdenum (Mo). For example, the gate electrode and wiring may be formed of a titanium (Ti) / aluminum (Al) / titanium (Ti) stacked structure or a molybdenum (Mo) / aluminum (Al) / molybdenum (Mo) stacked structure. The planarization layer 156 is formed of a resin material such as acrylic or polyimide. For example, the passivation layer 158 is formed of a silicon nitride film or the like. The patch electrode 108 and the ground electrode 110 are formed of a metal film such as aluminum (Al) or copper (Cu), or a transparent conductive film such as indium tin oxide (ITO).

[0070] 10 , the second wiring 132 is connected to the gate of a transistor used as a switching element 134, the first wiring 118 is connected to one of the source and drain of the transistor, and the patch electrode 108 is connected to the other of the source and drain, thereby enabling a predetermined patch electrode to be selected from the plurality of patch electrodes 108 arranged in a matrix and supplied with a control voltage. Then, by providing the switching element 134 to each patch electrode 108 in the absorbing plate 120, a control voltage can be supplied to each of the patch electrodes 108 arranged in a horizontal row along the first direction (X-axis direction) or each of the patch electrodes 108 arranged in a vertical row along the second direction (Y-axis direction).

[0071] 11 and 12, a radio wave absorbing system 10C according to one embodiment of the present invention will be described. The configuration of the radio wave absorbing system 10C according to the second embodiment is similar to that of the radio wave absorbing system 10 according to the first embodiment. In the following explanation, a description of the configuration similar to that of the radio wave absorbing system 10 will be omitted, and only the configuration different from that of the radio wave absorbing system 10 will be described. When describing the configuration similar to that of the first embodiment, the alphabet "C" will be added after the reference numerals shown in these drawings with reference to FIGS. 1 to 10.

[0072] [2-1. Radio Wave Absorbing Device 100C] The radio wave absorbing device 100C in the radio wave absorbing system 10C according to this embodiment is controlled by the individual control method shown in Fig. 9. In the radio wave absorbing device 100 according to the first embodiment, a control voltage is supplied collectively to all of the patch electrodes 108 provided on the absorbing plate 120. On the other hand, in the radio wave absorbing device 100C according to this embodiment, the patch electrodes 108C provided on the absorbing plate 120C are divided into a plurality of groups, and a control voltage is supplied to the patch electrodes 108C on a group-by-group basis. Specifically, the patch electrodes 108C are divided into a group formed by first patch electrodes 108C-1 and a group formed by second patch electrodes 108C-2.

[0073] The radio wave absorbing device 100C is controlled by an individual control system, so that the first patch electrode 108C-1 and the second patch electrode 108C-2 can be controlled individually. Similar to the radio wave absorbing device 100 according to the first embodiment, the radio wave absorbing device 100C includes a ground electrode 110C (counter electrode) and a liquid crystal layer 114C. The ground electrode 110C (counter electrode) faces each of the first patch electrode 108C-1 and the second patch electrode 108C-2. The liquid crystal layer 114C is provided between the first patch electrode 108C-1 and the ground electrode 110 (counter electrode) and between the second patch electrode 108C-2 and the ground electrode 110 (counter electrode).

[0074] 11, the first patch electrode 108C-1 and the second patch electrode 108C-2 are arranged in a checkerboard pattern or a staggered pattern. That is, the first patch electrode 108C-1 is adjacent to the second patch electrode 108C-2 in each of the up, down, left, and right directions. Similarly, the second patch electrode 108C-2 is adjacent to the first patch electrode 108C-1 in each of the up, down, left, and right directions. The arrangement in FIG. 11 is an example of this embodiment, and this embodiment is not limited to this arrangement.

[0075] Different control voltages are supplied to the first patch electrode 108C-1 and the second patch electrode 108C-2. That is, the relative dielectric constant ε (first relative dielectric constant) of the liquid crystal layer 114C sandwiched between the first patch electrode 108C-1 and the ground electrode 110C is different from the relative dielectric constant ε (second relative dielectric constant) of the liquid crystal layer 114C sandwiched between the second patch electrode 108C-2 and the ground electrode 110C. For example, a control voltage is supplied to the first patch electrode 108C-1, and the same voltage as that of the ground electrode 110C is supplied to the second patch electrode 108C-2. That is, a potential difference based on the control voltage is generated between the first patch electrode 108C-1 and the ground electrode 110C. Meanwhile, the potential difference between the second patch electrode 108C-2 and the ground electrode 110C is zero. As a result, the relative dielectric constant ε of the liquid crystal layer 114C belonging to the first patch electrode 108C-1 is 3.5. On the other hand, the liquid crystal layer 114C belonging to the second patch electrode 108C-2 has a relative dielectric constant ε of 2.5.

[0076] In this embodiment, a control voltage is supplied to the first patch electrode 108C-1 so that the relative dielectric constant ε of the liquid crystal layer 114C is 3.5, and a control voltage is supplied to the second patch electrode 108C-2 so that the relative dielectric constant ε of the liquid crystal layer 114C is 2.5. However, control voltages other than those described above may be supplied to the first patch electrode 108C-1 and the second patch electrode 108C-2. For example, the relative dielectric constant ε of the liquid crystal layer 114C belonging to the first patch electrode 108C-1 may be fixed to 3.5, and the relative dielectric constant ε of the liquid crystal layer 114C belonging to the second patch electrode 108C-2 may be adjusted within a range from 2.5 to 3.5.

[0077] 12 shows simulation results showing the relationship between the driving method of the radio wave absorber and radio wave absorption in a radio wave absorber according to one embodiment of the present invention. A simulation result 1100 shown in FIG. 12 is the result of simulating the reflection characteristics of the absorption plate unit cells 102C arranged in a 2×2 matrix. This simulation was performed using CST Studio Suite (manufactured by Dassault Systèmes). The parameters of the radio wave absorber 100C used in the simulation are as follows: Arrangement pitch of patch electrodes 108C: 3 mm Size of patch electrode 108C: 2 mm×2 mm Thickness of liquid crystal layer 114C: 30 μm Relative permittivity ε of liquid crystal layer 114C belonging to first patch electrode 108C-1: 3.5 Relative permittivity ε of liquid crystal layer 114C belonging to second patch electrode 108C-2: 2.5 to 3.4 Thickness of substrate 101C: 1.0 mm

[0078] Four simulation results are shown in Fig. 12. The simulation results marked [X1] to [X3] are simulation results calculated using the above parameters.

[0079] The simulation results marked [X1] are simulation results when the relative dielectric constant ε of the liquid crystal layer 114C belonging to the second patch electrode 108C-2 is 2.5 to 2.8. The simulation results marked [X2] are simulation results when the relative dielectric constant ε of the liquid crystal layer 114C belonging to the second patch electrode 108C-2 is 2.9 to 3.1. The simulation results marked [X3] are simulation results when the relative dielectric constant ε of the liquid crystal layer 114C belonging to the second patch electrode 108C-2 is 3.2 to 3.4.

[0080] The simulation results marked with [Y] are simulation results for the radio wave absorbing device 100 according to the first embodiment, not for the radio wave absorbing device 100C according to this embodiment. In other words, the simulation results marked with [Y] are simulation results when the relative dielectric constants ε of the liquid crystal layers 114 belonging to all patch electrodes 108 are the same.

[0081] 12, when the dielectric constant ε of the liquid crystal layer 114C belonging to the first patch electrode 108C-1 is 3.5 and the dielectric constant ε of the liquid crystal layer 114C belonging to the second patch electrode 108C-2 is 3.0, the frequency at which the reflection amplitude has a minimum value is 39.3 GHz, which is approximately −48 dB.

[0082] On the other hand, in the collective control method shown in the first embodiment, when the frequency at which the reflection amplitude has a minimum value is adjusted to approximately 39.3 GHz, it is necessary to control the relative dielectric constant ε of the liquid crystal layer 114 to 3.2. However, as shown in the graph [Y] in Figure 12, when the collective control method is used and the relative dielectric constant ε of the liquid crystal layer 114 is 3.2, the minimum value of the reflection amplitude is approximately -13 dB. In other words, the minimum value of the reflection amplitude can be made smaller by using the individual control method to control the minimum value of the reflection amplitude to a desired frequency rather than using the collective control method to control the minimum value of the reflection amplitude to a desired frequency.

[0083] As in the first embodiment, when the first patch electrode 108C-1 and the ground electrode 110C are made of different materials, the minimum value of the reflection amplitude is smaller than the minimum value of the reflection amplitude when they are made of the same material. Similarly, when the second patch electrode 108C-2 and the ground electrode 110C are made of different materials, the minimum value of the reflection amplitude is smaller than the minimum value of the reflection amplitude when they are made of the same material. In other words, by using different materials for the opposing electrodes, it is possible to increase the amount of radio waves absorbed by the radio wave absorber 100C.

[0084] In the present embodiment, the first patch electrode 108C-1 and the second patch electrode 108C-2 are arranged in a checkerboard pattern or a staggered pattern, but the present invention is not limited to this configuration. For example, the first patch electrode 108C-1 and the second patch electrode 108C-2 may be arranged as shown in FIG. 13. In other words, the first patch electrodes 108C-1 may be adjacent to each other, and the second patch electrodes 108C-2 may be adjacent to each other.

[0085] 14 and 15, a radio wave absorbing system 10D according to one embodiment of the present invention will be described. The configuration of the radio wave absorbing system 10D according to the third embodiment is similar to that of the radio wave absorbing system 10 according to the first embodiment. In the following explanation, a description of the configuration similar to that of the radio wave absorbing system 10 will be omitted, and only the configuration different from that of the radio wave absorbing system 10 will be described. When describing the configuration similar to that of the first embodiment, the alphabet "D" will be added after the reference numerals shown in these drawings with reference to FIGS. 1 to 10.

[0086] [3-1. Radio Wave Absorbing Device 100D] In the radio wave absorbing device 100D in the radio wave absorbing system 10D according to this embodiment, either the collective control method shown in Fig. 8 or the individual control method shown in Fig. 9 may be used. In the radio wave absorbing device 100 according to the first embodiment, all of the patch electrodes 108 provided on the absorbing plate 120 have the same size (for example, the length of one side). On the other hand, in the radio wave absorbing device 100D according to this embodiment, the patch electrodes 108D provided on the absorbing plate 120D are divided into a plurality of groups, and the sizes of the patch electrodes 108D differ for each group.

[0087] Specifically, as shown in Fig. 14, the patch electrodes 108D are divided into a group consisting of the first patch electrode 108D-3 and a group consisting of the second patch electrode 108D-4. The size of the first patch electrode 108D-3 is different from the size of the second patch electrode 108D-4. In the example of Fig. 14, the size of the first patch electrode 108D-3 is smaller than the size of the second patch electrode 108D-4. The size of the second patch electrode 108D-4 may be within ±10% of the size of the first patch electrode 108D-3.

[0088] The same control voltage is supplied to the first patch electrode 108D-3 and the second patch electrode 108D-4. That is, the relative dielectric constant ε (first relative dielectric constant) of the liquid crystal layer 114D sandwiched between the first patch electrode 108D-3 and the ground electrode 110D is the same as the relative dielectric constant ε (second relative dielectric constant) of the liquid crystal layer 114D sandwiched between the second patch electrode 108D-2 and the ground electrode 110D.

[0089] As shown in Fig. 14, the first patch electrode 108D-3 and the second patch electrode 108D-4 are arranged in a checkerboard pattern or a staggered pattern. That is, the first patch electrode 108D-3 is adjacent to the second patch electrode 108D-4 in each of the up, down, left, and right directions. Similarly, the second patch electrode 108D-4 is adjacent to the first patch electrode 108D-3 in each of the up, down, left, and right directions. The arrangement in Fig. 14 is an example of this embodiment, and this embodiment is not limited to this arrangement.

[0090] 15 shows simulation results showing the relationship between the driving method of the radio wave absorber and radio wave absorption in a radio wave absorber according to one embodiment of the present invention. The simulation results shown in FIG. 15 are the results of simulating the reflection characteristics of the absorption plate unit cells 102D arranged in a 2×2 matrix. This simulation was performed using CST Studio Suite (manufactured by Dassault Systèmes). The parameters of the radio wave absorber 100D used in the simulation are as follows: Arrangement pitch of patch electrodes 108D: 3 mm Size of first patch electrode 108D-3: 2 mm×2 mm Size of second patch electrode 108D-4: 2.1 mm×2.1 mm Thickness of liquid crystal layer 114D: 30 μm Relative permittivity ε of liquid crystal layer 114D: 2.5, 3.5 Thickness of substrate 101D: 0.8 mm

[0091] FIG. 15 shows two simulation results. These simulation results are for cases where the liquid crystal layer 114D has different dielectric constants (dielectric constants ε = 2.5 and 3.5). In FIG. 15, the simulation results for a dielectric constant ε of 2.5 are shown by a dotted line, and the simulation results for a dielectric constant ε of 3.5 are shown by a solid line. In the radio wave absorption device 100D, the simulation results for a dielectric constant ε of 2.5 correspond to the simulation results for a state where no control voltage is supplied to the patch electrode 108D and the ground electrode 110D (a state where the potential difference between the two electrodes is zero). On the other hand, the simulation results for a dielectric constant ε of 3.5 correspond to the simulation results for a state where control voltages are supplied to the patch electrode 108D and the ground electrode 110D. The dielectric constant ε can be adjusted within a range of 2.5 to 3.5 by the control voltages supplied to the patch electrode 108D and the ground electrode 110D.

[0092] As shown in Fig. 15, the spectrum indicating the reflection amplitude has two minimum values ​​regardless of the value of the relative dielectric constant ε. As a result, compared to the simulation result shown in Fig. 5, the simulation result shown in Fig. 15 shows that the frequency band of radio waves that the radio wave absorber 100D can absorb is wider. In other words, by varying the size of the patch electrode 108D as described above, the frequency band of radio waves that the radio wave absorber 100D can absorb can be widened. The arrangement of the first patch electrode 108D-3 and the second patch electrode 108D-4 may be such that the first patch electrodes 108D-3 are adjacent to each other, as shown in Fig. 13, or such that the second patch electrodes 108D-4 are adjacent to each other.

[0093] [4. Fourth Embodiment] With reference to Fig. 16, a radio wave absorbing system 10E according to one embodiment of the present invention will be described. The configuration of the radio wave absorbing system 10E according to the fourth embodiment is similar to that of the radio wave absorbing system 10 according to the first embodiment. In the following explanation, a description of the configuration similar to that of the radio wave absorbing system 10 will be omitted, and only the configuration different from that of the radio wave absorbing system 10 will be described. When describing the configuration similar to that of the first embodiment, reference will be made to Figs. 1 to 10, and the alphabet "E" will be added after the reference numerals shown in these drawings.

[0094] [4-1. Simulation Results of the Radio Wave Absorbing Device 100E] In the radio wave absorbing device 100E in the radio wave absorbing system 10E according to this embodiment, either the collective control method shown in Fig. 8 or the individual control method shown in Fig. 9 may be used. In the radio wave absorbing device 100E according to this embodiment, a substrate 101E having a thickness suitable for absorbing radio waves is provided.

[0095] Fig. 16 shows the results of a simulation showing the relationship between the thickness of the substrate and radio wave absorption in a radio wave absorber according to one embodiment of the present invention. The simulation results shown in Fig. 16 are the results of a simulation of the reflection characteristics of one absorption plate unit cell 102E. This simulation was performed using CST Studio Suite (manufactured by Dassault Systèmes). The parameters of the radio wave absorber 100E used in the simulation are as follows: Arrangement pitch of patch electrodes 108E: 3 mm Size of patch electrodes 108E: 2 mm x 2 mm Thickness of liquid crystal layer 114E: 30 µm Relative dielectric constant ε of liquid crystal layer 114E: 2.5, 3.5 Thickness of substrate 101E: 0.2 mm to 2.0 mm

[0096] Fig. 16 is a graph plotting the minimum values ​​of reflection amplitude under each condition in the simulation results shown in Fig. 5. In the graph shown in Fig. 16, the vertical axis represents reflection amplitude, and the horizontal axis represents the thickness (T) of the substrate 101E relative to the wavelength of the radio wave used as a parameter in the simulation, and the wavelength (λ) of the radio wave propagating through the substrate 101E. ｇ ) divided by (T / λｇ ) is shown. The value of the reflection amplitude in FIG. 16 is the average value of the minimum value of the reflection amplitude when the relative dielectric constant ε of the liquid crystal layer 114E is 2.5 and the minimum value of the reflection amplitude when the relative dielectric constant ε is 3.5. As shown in FIG. 16, the minimum value of the reflection amplitude exhibits periodic behavior with respect to the thickness of the substrate 101E. This behavior is considered to be caused by the interference effect of the radio waves reflected by the radio wave absorbing device 100E. Specifically, the reflection amplitude tends to become smaller under the condition that the thickness T of the substrate 101E is different from ¼ of the wavelength of the radio waves incident on the radio wave absorbing device 100E. More specifically, when the thickness T of the substrate 101E is λ ｇ / 8+(n-1)λ ｇ Therefore, for example, by setting the thickness of the substrate 101E to λ / 8, the apparent amount of radio wave absorption of the radio wave absorber 100E can be increased due to the interference effect of the reflected waves.

[0097] [5. Fifth Embodiment] With reference to Fig. 17, a radio wave absorbing system 10F according to one embodiment of the present invention will be described. The configuration of the radio wave absorbing system 10F according to the fifth embodiment is similar to that of the radio wave absorbing system 10 according to the first embodiment. In the following explanation, a description of the configuration similar to that of the radio wave absorbing system 10 will be omitted, and only the configuration different from that of the radio wave absorbing system 10 will be described. When describing the configuration similar to that of the first embodiment, reference will be made to Figs. 1 to 10, and the alphabet "F" will be added after the reference numerals shown in these drawings.

[0098] [5-1. Simulation Results of the Radio Wave Absorbing Device 100F] In the radio wave absorbing device 100F in the radio wave absorbing system 10F according to this embodiment, either the collective control method shown in Fig. 8 or the individual control method shown in Fig. 9 may be used. In the radio wave absorbing device 100F according to this embodiment, the liquid crystal layer 114F is provided with a thickness suitable for absorbing radio waves.

[0099] Fig. 17 shows the results of a simulation showing the relationship between the thickness of the substrate and radio wave absorption in a radio wave absorber according to one embodiment of the present invention. The simulation results shown in Fig. 17 are the results of a simulation of the reflection characteristics of one absorption plate unit cell 102F. This simulation was performed using CST Studio Suite (manufactured by Dassault Systèmes). The parameters of the radio wave absorber 100F used in the simulation are as follows: Arrangement pitch of patch electrodes 108F: 3 mm Size of patch electrodes 108F: 2 mm x 2 mm Thickness of liquid crystal layer 114F: 5 μm to 70 μm Relative permittivity ε of liquid crystal layer 114F: 2.5, 3.5 Thickness of substrate 101F: 0.8 mm

[0100] Fig. 17 is a graph plotting the minimum values ​​of reflection amplitude under each condition, similar to Fig. 16 . In the graph shown in Fig. 17 , the horizontal axis represents the thickness of the liquid crystal layer 114F. The value of the reflection amplitude in Fig. 17 is the average value of the minimum value of reflection amplitude when the relative dielectric constant ε of the liquid crystal layer 114F is 2.5 and the minimum value of reflection amplitude when the relative dielectric constant ε is 3.5. As shown in Fig. 17 , by adjusting the thickness of the liquid crystal layer 114F to be in the range of 10 μm or more and 40 μm or less, the amount of radio wave absorption of the radio wave absorber 100F can be increased.

[0101] 18 and 19, a radio wave absorbing device 100G according to one embodiment of the present invention will be described. The configuration of the radio wave absorbing device 100G according to the sixth embodiment is similar to that of the radio wave absorbing device 100 according to the first embodiment. In the following description, a description of the configuration that is the same as that of the radio wave absorbing device 100 will be omitted, and only the configuration that differs from that of the radio wave absorbing device 100 will be described. In the following description, when a configuration that is the same as that of the first embodiment is described, reference will be made to FIGS. 1 to 10, and the alphabet "G" will be added after the reference numerals shown in FIGS. 1 to 10.

[0102] [6-1. Radio Wave Absorbing Device 100G] FIG. 18 is a cross-sectional view showing an outline of a radio wave absorbing device according to one embodiment of the present invention. As shown in FIG. 18, the radio wave absorbing device 100G includes a plurality of absorbing elements (absorber plate unit cells) 102G. The plurality of absorbing plate unit cells 102G are arranged in at least one direction. In FIG. 18, the plurality of absorbing plate unit cells 102G are arranged in the Y-axis direction. The radio wave absorbing device 100G includes a dielectric substrate 104G, a counter substrate 106G, a drive electrode 109G (counter electrode), a patch electrode 111G, a liquid crystal layer 114G, a sealing material 128G, a switching element 134G, a terminal portion 126G, and an FPG 160G. The liquid crystal layer 114G contains liquid crystal molecules 116G. In this configuration, an electrode 111G provided on the counter substrate 106G side functions as a patch electrode that absorbs radio waves. The dielectric constant changes as the liquid crystal is oriented in accordance with the potential difference between the potential applied to the drive electrode 109G and the potential applied to the patch electrode 111G. A passivation layer 158G is provided between the drive electrode 109G and the dielectric substrate 104G.

[0103] Each absorber plate unit cell 102G includes at least a drive electrode 109G, a patch electrode 111G, a liquid crystal layer 114G, and a switching element 134G. While the patch electrode 111G appears to be provided individually for each absorber plate unit cell 102G in FIG. 18 , in reality, it is provided commonly to multiple absorber plate unit cells 102G, as shown in FIG. 19 . The drive electrode 109G is provided on the dielectric substrate 104G side. The drive electrode 109G faces the patch electrode 111G and is provided individually for each absorber plate unit cell 102G. The patch electrode 111G is provided on the counter substrate 106G side.

[0104] The switching element 134G is connected to the drive electrode 109G. In FIG. 18 , the drive electrode 109G is arranged on the switching element 134G so as to overlap with the switching element 134G. This makes it possible to make the switching element 134G less susceptible to the effects of radio waves. The switching element 134G is driven by a drive circuit 600G (see FIG. 1 ). The orientation of the liquid crystal molecules 116G is controlled according to the driving state of the switching element 134G. As described above, by controlling the orientation of the liquid crystal molecules 116G, it is possible to adjust the frequency band of radio waves absorbed by the radio wave absorbing device 100G.

[0105] As described above, in the case of the radio wave absorption device 100G of this embodiment, the radio waves incident on the radio wave absorption device 100G are blocked or absorbed by the patch electrode 111G, and therefore, adverse effects such as heat generation in the switching element 134G caused by irradiation of the radio waves can be suppressed.

[0106] 19 is a plan view showing an outline of a patch electrode of a radio wave absorption device according to one embodiment of the present invention. As shown in Fig. 19, the patch electrode 111G includes a resonating portion 1111G and a connecting portion 1112G.

[0107] The resonating portions 1111G are portions that resonate with the wavelength of the radio wave incident on the radio wave absorption device 100G, and are arranged in a matrix in the X-axis direction and the Y-axis direction. The sizes of the resonating portions 1111G in the X-axis direction and the Y-axis direction are calculated using the wavelength of the radio wave as well as the dielectric constant of the liquid crystal layer 114G, etc.

[0108] The connection portions 1112G connect the resonator units 1111G adjacent in the X-axis direction or the Y-axis direction. The resonator units 1111G arranged in a matrix are electrically connected by the connection portions 1112G. Therefore, the resonator units 1111G arranged in a matrix are at the same potential. The connection portions 1112G have their elongated direction in the X-axis direction or the Y-axis direction. The connection portions 1112G connecting the resonator units 1111G adjacent in the X-axis direction have their elongated direction in the X-axis direction. The connection portions 1112G connecting the resonator units 1111G adjacent in the Y-axis direction have their elongated direction in the Y-axis direction.

[0109] The width (width in the Y-axis direction) of the connecting portion 1112G, which has its elongated side in the X-axis direction, is 1 / 100 or less of the size of the resonating portion 1111G in the Y-axis direction. The width (width in the X-axis direction) of the connecting portion 1112G, which has its elongated side in the Y-axis direction, is 1 / 100 or less of the size of the resonating portion 1111G in the X-axis direction. With this configuration, it is possible to reduce the effect of the connecting portion 1112G on the resonance of the resonating portion 1111G.

[0110] The various configurations of the radio wave absorber and absorption plate unit exemplified as one embodiment of the present invention can be combined as appropriate as long as they are not mutually contradictory. Furthermore, those in which a person skilled in the art appropriately adds or deletes components or modifies the design, or adds or omits processes or modifies conditions, based on the radio wave absorber and absorption plate unit disclosed in this specification and drawings, are also included in the scope of the present invention as long as they comply with the gist of the present invention.

[0111] Even if there are other effects and advantages different from those brought about by the aspects of the embodiments disclosed in this specification, those that are clear from the description in this specification or that can be easily predicted by a person skilled in the art are naturally understood to be brought about by the present invention.

[0112] 10: radio wave absorption system, 100: radio wave absorption device, 101: substrate, 102: absorption plate unit cell, 104: dielectric substrate, 106: opposing substrate, 108: patch electrode, 108C-1: first patch electrode, 108C-2: second patch electrode, 108D-3: first patch electrode, 108D-4: second patch electrode, 109G: driving electrode, 110: ground electrode, 111G: patch electrode, 112a: first alignment film, 112b: second alignment film, 114: liquid crystal layer, 116: liquid crystal molecules, 118: first wiring, 119: second wiring, 120: absorption plate, 122: peripheral region, 124: first driving circuit, 126: terminal portion, 128: sealing material, 130: second driving circuit, 132: Second wiring, 134: Switching element, 136: Undercoat layer, 138: First gate electrode, 140: First gate insulating layer, 142: Semiconductor layer, 144: First connection wiring, 146: Second gate insulating layer, 148: Second gate electrode, 150: First interlayer insulating layer, 152: Second connection wiring, 154: Second interlayer insulating layer, 156: Planarization layer, 158: Passivation layer, 162: Radio wave absorption region, 164: Peripheral region, 500: Control circuit, 600: Drive circuit, 1000, 1100: Simulation results, 1111G: Resonator, 1112G: Connection section

Claims

1. A radio wave absorbing device comprising: a patch electrode; a counter electrode facing the patch electrode and made of a material different from that of the patch electrode; and a liquid crystal layer between the patch electrode and the counter electrode.

2. The radio wave absorbing device according to claim 1, wherein the electrical conductivity of the material constituting said patch electrode is different from the electrical conductivity of the material constituting said counter electrode.

3. The radio wave absorbing device according to claim 1, wherein the ratio of the electrical conductivity of the material constituting said patch electrode to the electrical conductivity of the material constituting said counter electrode is 10 times or more.

4. The radio wave absorbing device according to claim 1, wherein when the material of the patch electrode is a metallic material, the material of the counter electrode is a transparent conductive material, and when the material of the patch electrode is a transparent conductive material, the material of the counter electrode is a metallic material.

5. A radio wave absorption device comprising: a first patch electrode; a second patch electrode that is controllable separately from the first patch electrode; a counter electrode that faces the first patch electrode and the second patch electrode; and a liquid crystal layer between the first patch electrode and the counter electrode and between the second patch electrode and the counter electrode, wherein a first relative dielectric constant of the liquid crystal layer sandwiched between the first patch electrode and the counter electrode is different from a second relative dielectric constant of the liquid crystal layer sandwiched between the second patch electrode and the counter electrode.

6. The radio wave absorbing device according to claim 5, wherein the material constituting said first patch electrode is different from the material constituting said counter electrode, and the material constituting said second patch electrode is different from the material constituting said counter electrode.

7. The radio wave absorbing device according to claim 5, wherein the ratio of the electrical conductivity of the material constituting said patch electrode to the electrical conductivity of the material constituting said counter electrode is 10 times or more.

8. The radio wave absorbing device according to claim 5, wherein when the material of said patch electrode is a metallic material, the material of said counter electrode is a transparent conductive material, and when the material of said patch electrode is a transparent conductive material, the material of said counter electrode is a metallic material.

9. A radio wave absorbing device as claimed in any one of claims 1 to 8, further comprising a substrate provided on the side of said radio wave absorbing device on which radio waves are incident with respect to said liquid crystal layer, and the thickness of said substrate is different from λ / 4 where λ is the wavelength of the radio wave incident on said radio wave absorbing device.

10. The radio wave absorbing device according to any one of claims 1 to 8, wherein the thickness of said liquid crystal layer is not less than 10 µm and not more than 40 µm.

11. The radio wave absorbing device according to any one of claims 1 to 4, wherein the patch electrodes include a first patch electrode and a second patch electrode, and a size of the first patch electrode is different from a size of the second patch electrode.

12. The radio wave absorbing device according to any one of claims 5 to 8, wherein the size of said first patch electrode is different from the size of said second patch electrode.

13. A radio wave absorbing system comprising: a radio wave absorbing device according to any one of claims 1 to 4; and a control device that controls the voltage supplied to the patch electrode and the counter electrode, wherein the control device controls the voltage supplied to the patch electrode and the counter electrode, thereby varying the absorption amount of the radio wave absorbing device for radio waves having an arbitrary frequency.

14. The radio wave absorbing system according to claim 13, wherein the control device receives a set value relating to the frequency of the radio waves to be absorbed by the radio wave absorbing device, and controls the voltages supplied to the patch electrode and the counter electrode based on the set value.

15. A radio wave absorbing system comprising: a radio wave absorbing device according to any one of claims 5 to 8; and a control device which controls the voltages supplied to the first patch electrode, the second patch electrode, and the counter electrode, wherein the control device controls the voltages supplied to the first patch electrode, the second patch electrode, and the counter electrode, thereby varying the absorption amount of the radio wave absorbing device for radio waves having an arbitrary frequency.

16. The radio wave absorbing system according to claim 15, wherein the control device receives a set value relating to the frequency of the radio waves to be absorbed by the radio wave absorbing device, and controls the voltages supplied to the patch electrode and the counter electrode based on the set value.