Radio wave control plate

Abstract

This radio wave control plate is capable of emitting incident radio waves in a prescribed direction, and includes a plurality of unit structures arranged on a first surface. The unit structure includes: a substrate; an electrode provided on the substrate and formed in a mesh shape in plan view to have a gap; an alignment film for controlling the alignment of liquid crystal molecules; and a liquid crystal layer containing liquid crystal molecules and provided on the alignment film.

Description

Radio Control Board

[0001] The present disclosure relates to a radio wave control board.

[0002] There are known techniques for controlling radio waves without using a dielectric lens. For example, Patent Document 1 describes a technique for refracting radio waves by changing the parameters of each element in a structure in which resonator elements are arranged. Furthermore, techniques for controlling radio waves have been studied from various perspectives (for example, Non-Patent Document 1).

[0003] JP 2015-231182 A

[0004] Hong, I.-P. Reviews Based on the Reconfigurable Intelligent Surface Technical Issues. Electronics 2023, 12, 4489. https: / / doi.org / 10.3390 / electronics12214489

[0005] The radio wave control plate of the present disclosure is a radio wave control plate capable of emitting incident radio waves in a predetermined direction, and includes a plurality of unit structures arranged on a first surface, the unit structures including a substrate, an electrode formed in a mesh shape in a planar view and having gaps therein, an alignment film that controls the alignment of liquid crystal molecules, and a liquid crystal layer that includes the liquid crystal molecules and is arranged on the alignment film.

[0006] FIG. 1 is a diagram for explaining an overview of a radio wave control plate. FIG. 2 is a top view showing a configuration example of a unit structure according to a first embodiment. FIG. 3 is a diagram showing a configuration example of an electrode according to the first embodiment. FIG. 4 is a diagram showing a configuration example of a unit structure according to a first example of a second embodiment. FIG. 5 is a diagram showing a configuration example of a unit structure according to a second example of the second embodiment. FIG. 6 is a diagram showing a configuration example of a unit structure according to a third embodiment.

[0007] Hereinafter, an embodiment of the present invention will be described in detail with reference to the accompanying drawings. Note that the present invention is not limited to this embodiment, and in the following embodiments, the same components are designated by the same reference numerals, and redundant explanations will be omitted.

[0008] [Outline] (Radio wave control board) An outline of the radio wave control board will be described with reference to Fig. 1. Fig. 1 is a diagram for explaining the outline of the radio wave control board.

[0009] The radio wave control plate 1 is configured to be able to control the direction of travel of incident radio waves. For example, when receiving radio waves transmitted from a base station, the radio wave control plate 1 is configured to reflect or refract the radio waves at a predetermined angle. The radio wave control plate 1 may be made of, for example, a metamaterial that changes the phase of the incident wave. The radio wave control plate 1 may be capable of controlling not only the reflection direction of the radio waves or the transmission (refraction) direction, but also both. In the present disclosure, reflection and refraction are sometimes collectively referred to as emission.

[0010] 1, the radio wave control plate 1 may include, for example, a substrate 2 and unit structures 10a, 10b, 10c, and 10d. When there is no need to distinguish between the unit structures 10a to 10d, they will be collectively referred to as unit structures 10. The unit structures 10 are also called metasurface elements.

[0011] The unit structures 10a, 10b, 10c, and 10d may be formed on a substrate 2. The substrate 2 may be, for example, a dielectric substrate made of a dielectric material. The substrate 2 may have, for example, but is not limited to, a rectangular shape. The unit structures 10a, 10b, 10c, and 10d may be arranged two-dimensionally.

[0012] In the radio wave control board 1, a plurality of unit structures 10a are arranged along the X-axis direction on one tier. A plurality of unit structures 10b are arranged along the X-axis direction on the tier above the tier on which unit structures 10a are arranged. A plurality of unit structures 10c are arranged along the X-axis direction on the tier above the tier on which unit structures 10b are arranged. A plurality of unit structures 10d are arranged along the X-axis direction on the tier above the tier on which unit structures 10c are installed. In the example shown in FIG. 1 , unit structures 10a, 10b, 10c, and 10d are periodically arranged along the Y-axis direction. Note that the unit structures do not need to be arranged parallel to the X-axis and Y-axis directions. For example, the arrangement direction of the plurality of unit structures 10a does not need to intersect perpendicularly with the arrangement direction of unit structures 10a, 10b, 10c, and 10d.

[0013] By varying the properties of each of unit structures 10a to 10d (for example, the relative dielectric constant of the liquid crystal layer, described later), it is possible to vary the phase change amount (the difference between the phase of the incident radio wave and the phase of the outgoing radio wave) of each of unit structures 10a to 10d. By varying the properties of each of unit structures 10a to 10d so that the phase change amount increases (or decreases) sequentially, radio wave control board 1 has a gradient of phase change amount. Due to the gradient of phase change amount, radio wave control board 1 can reflect and / or refract incident radio waves in a predetermined direction. Note that, although unit structures 10a to 10d are rectangular in shape in FIG. 1, the shape of the unit structures is not limited to rectangular.

[0014] [First embodiment] (Unit structure) A configuration example of a unit structure according to the first embodiment will be described with reference to Fig. 2 and Fig. 3. Fig. 2 is a top view showing a configuration example of a unit structure according to the first embodiment. Fig. 3 is a diagram showing a configuration example of an electrode according to the first embodiment.

[0015] As shown in FIGS. 2 and 3, the unit structure 10 includes a first substrate 2-1, a second substrate 2-2, a first electrode 12-1, a second electrode 12-2, a first alignment film 14-1, a second alignment film 14-2, and a liquid crystal layer 16.

[0016] When there is no need to distinguish between the first substrate 2-1 and the second substrate 2-2, they are collectively referred to as the substrate 2. When there is no need to distinguish between the first electrode 12-1 and the second electrode 12-2, they are collectively referred to as the electrode 12. When there is no need to distinguish between the first alignment film 14-1 and the second alignment film 14-2, they are collectively referred to as the alignment film 14.

[0017] The substrate 2 is preferably formed of a dielectric material. In particular, it is preferably formed of a dielectric material that is substantially transparent to visible light, such as glass or a PET film, because this makes the appearance of the substrate 2 less conspicuous. The substrate 2 formed of a dielectric material that is substantially transparent to visible light is also called a dielectric layer.

[0018] FIG. 2 is a diagram showing an example of the configuration of an electrode according to the first embodiment. The electrode 12 functions as a resonator. When viewed from the XY plane, the electrode 12 is formed into a mesh (network) shape using multiple metal wires. The metal wires may contain elements other than metal elements. While the shape of the mesh (the gaps between the electrodes) is shown as a rectangle in FIG. 2 , it may be another polygonal shape or may be formed from curves. That is, there are no particular limitations on the shape of the mesh. Furthermore, the size of the mesh may be the same for all of the meshes, as shown in FIG. 2 , or may vary in part. The metal wires are formed from a material with a higher effective conductivity than the transparent conductive film (e.g., ITO (Indium Tin Oxide)). Examples of materials with a higher effective conductivity than the transparent conductive film include, but are not limited to, silver, copper, and aluminum. From the viewpoint of conductivity, the metal wires are preferably silver or copper.

[0019] The first electrode 12-1 is provided on the first substrate 2-1. The first electrode 12-1 extends in the XY plane. Because the first electrode 12-1 is formed in a mesh shape, gaps are formed between the multiple metal wires that make up the first electrode 12-1 (between two adjacent metal wires) so that the top surface of the first substrate 2-1 is exposed. The first alignment film 14-1 is formed on the top surfaces of the first electrode 12-1 and the first substrate 2-1. The first alignment film 14-1 is formed of, for example, polyimide.

[0020] The second substrate 2-2 is provided at a position spaced apart from the first substrate 2-1 in the -Z direction. The second electrode 12-2 is provided on the second substrate 2-2. Because the second electrode 12-2 is formed in a mesh shape, gaps are formed between the multiple metal wires that make up the second electrode 12-2 (between two adjacent metal wires) through which the top surface of the second substrate 2-2 is exposed. The second alignment film 14-2 is formed on the top surfaces of the second electrode 12-2 and the second substrate 2-2. The second alignment film 14-2 is formed of, for example, polyimide.

[0021] The first substrate 2-1, the first electrode 12-1 and the first alignment film 14-1, and the second substrate 2-2, the second electrode 12-2 and the second alignment film 14-2 are opposed to each other.

[0022] The liquid crystal layer 16 is provided between a first alignment film 14-1 and a second alignment film 14-2. The first alignment film 14-1 and the second alignment film 14-2 control the alignment of the liquid crystal molecules contained in the liquid crystal layer 16.

[0023] 3, the unit structure 10 includes two resonators, a first electrode 12-1 and a second electrode 12-2, but the present disclosure is not limited to this. The unit structure 10 may have a multi-stage structure in which multiple electrodes 12 are arranged in multiple stages. In the present disclosure, the multiple electrodes 12 can function as resonators or grounds.

[0024] In the first embodiment, the use of a mesh-shaped electrode makes it difficult to recognize the electrode from the outside. Furthermore, the first embodiment can increase the effective conductivity of the electrode compared to when a transparent conductive film is used as the electrode.

[0025] Furthermore, in the first embodiment, the unit features 10 have a liquid crystal layer 16. By applying a voltage to the liquid crystal layer 16, the orientation of the liquid crystal molecules contained in the liquid crystal layer 16 can be dynamically changed. This makes it possible to dynamically change the relative dielectric constant of the liquid crystal layer 16 of each unit feature 10. Therefore, it is possible to dynamically change the gradient of the amount of phase change of the radio wave control plate 1. This makes it possible to dynamically change the direction of reflection and / or transmission of radio waves by the radio wave control plate 1.

[0026] Second Embodiment A second embodiment will be described. In the first embodiment, the electrode 12 is formed in a mesh shape, and therefore the surface of the alignment film 14 has irregularities due to the shape of the electrode 12. This may cause a disturbance in the alignment of the liquid crystal molecules contained in the liquid crystal layer 16. As a result, it may not be possible to appropriately control the refraction direction and / or reflection direction of radio waves. In the second embodiment, a layer is provided on the substrate 2 to suppress the disturbance in the alignment of the liquid crystal molecules contained in the liquid crystal layer 16.

[0027] (First Example) A configuration example of a unit structure according to a first example of the second embodiment will be described with reference to Fig. 4. Fig. 4 is a diagram showing a configuration example of a unit structure according to the first example of the second embodiment.

[0028] As shown in Fig. 4, the unit structure 10A includes a first substrate 2-1, a second substrate 2-2, a first electrode 12-1, a second electrode 12-2, a first alignment film 14-1, a second alignment film 14-2, a liquid crystal layer 16, a first layer 18-1, and a second layer 18-2. The unit structure 10A differs from the unit structure 10 shown in Fig. 3 in that it includes a first layer 18-1 and a second layer 18-2. When it is not necessary to distinguish between the first layer 18-1 and the second layer 18-2, they will be collectively referred to as layer 18.

[0029] The material of the layer 18 is not particularly limited, but it is preferable that the layer 18 is formed from a substance that is substantially transparent to visible light, because this makes the appearance of the layer 18 less conspicuous. Examples of substances that are substantially transparent to visible light include SiO ２ , ITO, or a resin-based material.

[0030] The first layer 18-1 is provided on the first substrate 2-1. The first layer 18-1 is provided so as to fill the gap (electrode gap) between the metal wire constituting the first electrode 12-1 and the adjacent metal wire (so as to reduce the depth of the gap). In FIG. 4, the first layer 18-1 is provided so that the thickness of the first layer 18-1 and the thickness of the first electrode 12-1 are the same or approximately the same (so that the depth of the gap is approximately zero), but this is not limited to this. For example, the first layer 18-1 may be thinner than the first electrode 12-1. The first alignment film 14-1 is provided on the first electrode 12-1 and the first layer 18-1. Therefore, the surface irregularities of the first alignment film 14-1 in the first example of the second embodiment are smaller than those in the first embodiment in which the first layer 18-1 is not present. As a result, the alignment disorder of the liquid crystal molecules contained in the liquid crystal layer 16 can be reduced.

[0031] The second layer 18-2 is provided on the second substrate 2-2. The second layer 18-2 is provided so as to fill the gap between the metal wires constituting the second electrode 12-2 and the adjacent metal wires. For example, the second layer 18-2 is provided so that the thickness of the second layer 18-2 and the thickness of the second electrode 12-2 are the same or approximately the same, but this is not limited to this. For example, the second layer 18-2 may be thinner than the second electrode 12-2. The second alignment film 14-2 is provided on the second electrode 12-2 and the second layer 18-2. Therefore, the surface irregularities of the second alignment film 14-2 in the first example of the second embodiment are smaller than those in the first embodiment in which the second layer 18-2 is not present. As a result, the alignment disorder of the liquid crystal molecules contained in the liquid crystal layer 16 can be reduced.

[0032] (Second Example) A configuration example of a unit structure according to a second example of the second embodiment will be described with reference to Fig. 5. Fig. 5 is a diagram showing a configuration example of a unit structure according to the second example of the second embodiment.

[0033] 5, the unit structure 10B includes a first substrate 2-1, a second substrate 2-2, a first electrode 12-1, a second electrode 12-2, a first alignment film 14-1, a second alignment film 14-2, a liquid crystal layer 16, a first layer 18B-1, and a second layer 18B-2. When it is not necessary to distinguish between the first layer 18B-1 and the second layer 18B-2, they will be collectively referred to as layer 18B.

[0034] The material of the layer 18B is not particularly limited, but it is preferable that the layer 18B be made of a substance that is substantially transparent to visible light, because this makes the appearance of the layer 18 less conspicuous. Examples of substances that are substantially transparent to visible light include SiO ２ , ITO, or a resin-based material.

[0035] The first layer 18B-1 is provided so as to cover the entire first electrode 12-1. The thickness of the first layer 18B-1 is greater than the thickness of the first electrode 12-1. The surface of the first layer 18B-1 is formed substantially parallel to the XY plane. The first alignment film 14-1 is provided on the first layer 18B-1. Therefore, the surface of the first alignment film 14-1 is substantially parallel to the XY plane and is substantially free of irregularities due to the shape of the first electrode 12-1.

[0036] The second layer 18B-2 is provided so as to cover the entire second electrode 12-2. The surface of the second layer 18B-2 is formed substantially parallel to the XY plane. The second alignment film 14-2 is provided on the second layer 18B-2. Therefore, the surface of the second alignment film 14-2 is substantially parallel to the XY plane and is substantially free of irregularities due to the shape of the second electrode 12-2.

[0037] In the second embodiment, in both the first and second examples, the unevenness of the surfaces of the first alignment film 14-1 and the second alignment film 14-2 is smaller than in the first embodiment. Therefore, the second embodiment can suppress the disturbance of the alignment of the liquid crystal molecules contained in the liquid crystal layer 16. Note that even when only one of the first layer 18-1 and the second layer 18-2, or only one of the first layer 18B-1 and the second layer 18B-2, is provided, the unevenness of the surface of the alignment film 14 is smaller than in the first embodiment, and therefore the disturbance of the alignment of the liquid crystal molecules contained in the liquid crystal layer 16 can be suppressed more than in the first embodiment.

[0038] [Third Embodiment] A third embodiment will be described. As described above, in the first embodiment, the electrode 12 is formed in a mesh shape, and therefore the surface of the alignment film 14 has irregularities due to the shape of the electrode 12. This may cause the alignment of the liquid crystal molecules contained in the liquid crystal layer 16 to be disturbed. As a result, it may not be possible to appropriately control the refraction direction and / or reflection direction of radio waves. In the third embodiment, the thickness of the electrode 12 is adjusted to suppress the alignment of the liquid crystal molecules contained in the liquid crystal layer 16.

[0039] A configuration example of a unit structure according to the third embodiment will be described with reference to Fig. 6. Fig. 6 is a diagram showing a configuration example of a unit structure according to the third embodiment.

[0040] 6, the unit structure 10C includes a first substrate 2-1, a second substrate 2-2, a first electrode 12C-1, a second electrode 12C-2, a first alignment film 14-1, a second alignment film 14-2, and a liquid crystal layer 16. In the unit structure 10C, the thicknesses of the first electrode 12C-1 and the second electrode 12C-2 are different from the thicknesses of the first electrode 12-1 and the second electrode 12-2 of the unit structure 10 shown in FIG.

[0041] The thicknesses of the first electrode 12C-1 and the second electrode 12C-2 are formed thinner than a predetermined reference value. The thicknesses of the first electrode 12C-1 and the second electrode 12C-2 are formed as thin as possible within a range in which the unit structure 10C satisfies desired characteristic values. For example, the thicknesses of the first electrode 12C-1 and the second electrode 12C-2 are formed so as to be approximately the same as the skin depth at the frequency of the radio waves to be controlled (radio waves reflected and / or refracted in a predetermined direction by the radio wave control plate). By reducing the thicknesses of the first electrode 12C-1 and the second electrode 12C-2, unevenness on the surface of the alignment film 14 caused by the shape of the electrodes 12 is reduced.

[0042] The first alignment film 14-1 is formed on the upper surface of the first electrode 12C-1 and the upper surface of the first substrate 2-1. The second alignment film 14-2 is formed on the upper surface of the second electrode 12C-2 and the upper surface of the second substrate 2-2. Therefore, the unevenness of the surfaces of the first alignment film 14-1 and the second alignment film 14-2 according to the third embodiment is smaller than the unevenness of the surfaces of the first alignment film 14-1 and the second alignment film 14-2 according to the first embodiment.

[0043] In the third embodiment, the unevenness of the surfaces of the first alignment film 14-1 and the second alignment film 14-2 can be reduced, and therefore, the third embodiment can suppress disturbance of the alignment of the liquid crystal molecules contained in the liquid crystal layer 16.

[0044] The second embodiment may be combined with the third embodiment. For example, the layer 18 may be provided, and the thickness of the electrode 12 may be set to be substantially the same as the skin depth at the frequency of the radio wave to be controlled.

[0045] The present disclosure may also have the following configurations. (1) A radio wave control board capable of emitting incident radio waves in a predetermined direction, the radio wave control board including a plurality of unit structures arranged on a first surface, the unit structures including: a substrate; an electrode formed in a mesh shape in a plan view and having gaps, the electrode being provided on the substrate; an alignment film for controlling the alignment of liquid crystal molecules; and a liquid crystal layer including the liquid crystal molecules and provided on the alignment film. (2) The radio wave control board according to (1), further including a layer provided so as to fill at least a portion of the gaps between the electrodes, at least a portion of the alignment film being provided on the layer. (3) The radio wave control board according to (1), the layer being provided so as to cover the entire electrode. (4) The radio wave control board according to (2) or (3), the layer being formed of a material that is substantially transparent to visible light. (5) The layer is made of a material such as SiO ２ (6) The radio wave control board according to any one of (1) to (5), wherein the electrode has a thickness substantially equal to a skin depth at a frequency of the radio wave emitted in the predetermined direction.

[0046] 1 Radio wave control board 2 Substrate 2-1 First substrate 2-2 Second substrate 10, 10A, 10B, 10C Unit structure 12 Electrode 12-1 First electrode 12-2 Second electrode 14 Alignment film 14-1 First alignment film 14-2 Second alignment film 16 Liquid crystal layer 18 Layer 18-1, 18B-1 First layer 18-2, 18B-2 Second layer

Claims

1. A radio wave control board capable of emitting incident radio waves in a predetermined direction, comprising a plurality of unit structures arranged on a first surface, the unit structures comprising: a substrate; an electrode provided on the substrate, the electrode having a mesh shape in a planar view and gaps therebetween; an alignment film that controls the alignment of liquid crystal molecules; and a liquid crystal layer including the liquid crystal molecules and provided on the alignment film.

2. The radio wave control board according to claim 1, further comprising a layer provided so as to fill at least a part of the gaps between the electrodes, and at least a part of the alignment film is provided on the layer.

3. The radio wave control board according to claim 2, wherein the layer is provided so as to cover the entire electrode.

4. The radio wave control board according to claim 2 or 3, wherein the layer is formed of a material that is substantially transparent to visible light.

5. The layer is made of SiO ２ The radio wave control board according to claim 2 or 3, which is made of ITO or a resin-based material.

6. A radio wave control board according to any one of claims 1 to 5, wherein the thickness of the electrode is approximately the same as the skin depth at the frequency of the radio wave emitted in the specified direction.

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