Electromagnetic wave reflector

Abstract

To provide an electromagnetic wave reflector that can handle both vertical and horizontal polarization, and that can obtain desired reflection phase characteristics for a desired frequency band even with a thin liquid crystal layer. [Solution] The electromagnetic wave reflector has a reflective surface comprising: a first electrode arranged on a first substrate, to which electrodes of a second pattern that are 90 degrees rotationally symmetric with respect to the first pattern are connected along a first direction; a second electrode arranged on a second substrate, to which electrodes of a third pattern that are 90 degrees rotationally symmetric with respect to the first pattern electrode and electrodes of a fourth pattern that are 90 degrees rotationally symmetric with respect to the second pattern electrode are connected along a second direction; and a liquid crystal layer arranged between the first and second substrates. The electrodes of the first and third patterns and the electrodes of the second and fourth patterns form non-overlapping and overlapping portions when viewed projected from the reflective surface. The non-overlapping portions, the overlapping portions, and the liquid crystal layer arranged in the overlapping portions form a split-ring resonator structure.

Description

Technical Field

[0001] The present disclosure relates to an electromagnetic wave reflector.

Background Art

[0002] An electromagnetic wave reflector is known that can reflect incident electromagnetic waves in a specific direction that cannot occur by reflection with ordinary natural substances by using metamaterial elements as reflection elements. In recent years, an electromagnetic wave reflector with a variable reflection direction of electromagnetic waves has also been known by dynamically controlling the reflection of each reflection element. In this type of electromagnetic wave reflector, the reflection direction of the reflected wave as their combined wave changes by changing the reflection phase of the reflected wave for each reflection element. The reflection surface of this type of electromagnetic wave reflector has a resonator structure formed by a repeating pattern of electrodes. By causing resonance to occur in the resonator structure with respect to the incident electromagnetic wave, control of the reflection phase around the resonance frequency can be performed. In recent years, a device using a liquid crystal element as a phase modulation element for dynamically changing the reflection phase has been known. In the phase modulation element using a liquid crystal element, control of the reflection phase can be performed by controlling the dielectric constant of the liquid crystal by applying a voltage.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Liquid crystal, which is the dielectric layer, often has a certain thickness. Electromagnetic wave reflectors using thick liquid crystal as a phase modulation element are unsuitable for applications requiring high response speeds because the response of the liquid crystal characteristics to changes in bias voltage is slow. On the other hand, a certain thickness of liquid crystal is necessary to obtain the desired reflection phase characteristics for a desired frequency band. Recently, there has been a demand for electromagnetic wave reflectors that can achieve the desired reflection phase characteristics for a desired frequency band while keeping the liquid crystal thickness thin. Furthermore, electromagnetic waves have both horizontal and vertical polarization. Therefore, it is desirable for electromagnetic wave reflectors to be able to handle both horizontally and vertically polarized electromagnetic waves.

[0005] The present disclosure aims to provide an electromagnetic wave reflector that can handle both vertical and horizontal polarization and can obtain desired reflection phase characteristics for a desired frequency band even with a thin liquid crystal layer. [Means for solving the problem]

[0006] An electromagnetic wave reflector in one embodiment has a reflective surface comprising a first substrate, a second substrate, a first electrode, a second electrode, and a liquid crystal layer. The second substrate is positioned opposite the first substrate. The first electrode is positioned on the first substrate, and an electrode row is formed by connecting a first pattern electrode and a second pattern electrode that is 90 degrees rotationally symmetric with respect to the first pattern electrode along a first direction. The second electrode is positioned on the second substrate, and an electrode row is formed by connecting a third pattern electrode that is 90 degrees rotationally symmetric with respect to the first pattern electrode and a fourth pattern electrode that is 90 degrees rotationally symmetric with respect to the second pattern electrode along a second direction. The liquid crystal layer is positioned between the first substrate and the second substrate. The first pattern electrode and the third pattern electrode, and the second pattern electrode and the fourth pattern electrode, each form a non-overlapping portion and an overlapping portion when viewed projected from the reflective surface. The closed circuit formed by the non-overlapping portion, the overlapping portion, and the liquid crystal layer positioned in the overlapping portion forms a split-ring resonator structure aligned in the direction of the polarization magnetic field amplitude. [Effects of the Invention]

[0007] According to this disclosure, an electromagnetic wave reflector is provided that can handle both vertical and horizontal polarization, and can obtain desired reflection phase characteristics for a desired frequency band even with a thin liquid crystal layer. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a front view showing the configuration of the reflective surface of an electromagnetic wave reflector according to an embodiment. [Figure 2] Figure 2 is a magnified view of one unit. [Figure 3A] Figure 3A shows the structure of the first electrode. [Figure 3B] Figure 3B shows the structure of the second electrode. [Figure 4] Figure 4 is a cross-sectional view of the SRR1 portion in Figure 2. [Figure 5] Figure 5 shows the operating mechanism of the electromagnetic wave reflector. [Figure 6] Figure 6 shows the various parameters defined in an electromagnetic wave reflector. [Figure 7A] Figure 7A shows the simulation results of the reflection amplitude characteristics of vertically polarized waves due to changes in dielectric constant. [Figure 7B] Figure 7B shows the simulation results of the reflection amplitude characteristics of horizontal polarization due to changes in dielectric constant. [Figure 8A] Figure 8A shows the simulation results of the reflection phase characteristics of vertical polarization due to changes in dielectric constant. [Figure 8B] Figure 8B shows the simulation results of the reflection phase characteristics of horizontal polarization due to changes in dielectric constant. [Figure 9A] Figure 9A shows the simulation results of the electric field distribution in each unit cell when a vertically polarized electromagnetic wave is incident on each unit cell that makes up the unit. [Figure 9B] Figure 9B shows the simulation results of the electric field distribution in each unit cell when horizontally polarized electromagnetic waves are incident on each unit cell that makes up the unit. [Figure 10A] FIG. 10A is a diagram showing the simulation result of the magnetic field distribution in each unit cell when an electromagnetic wave with a vertical polarization is incident on each unit cell constituting the unit. [Figure 10B] FIG. 10B is a diagram showing the simulation result of the magnetic field distribution in each unit cell when an electromagnetic wave with a horizontal polarization is incident on each unit cell constituting the unit. [Figure 11A] FIG. 11A is a diagram showing the dependence of the maximum phase difference frequency on the liquid crystal layer thickness in the electromagnetic wave reflector in the embodiment. [Figure 11B] FIG. 11B is a diagram showing the dependence of the maximum phase difference on the liquid crystal layer thickness in the electromagnetic wave reflector in the embodiment. [Figure 12A] FIG. 12A is a diagram showing the dependence of the maximum phase difference frequency on W1 in the electromagnetic wave reflector in the embodiment. [Figure 12B] FIG. 12B is a diagram showing the dependence of the maximum phase difference on W1 in the electromagnetic wave reflector in the embodiment. [Figure 13A] FIG. 13A is a diagram showing the dependence of the maximum phase difference frequency on W2 in the electromagnetic wave reflector in the embodiment. [Figure 13B] FIG. 13B is a diagram showing the dependence of the maximum phase difference on W2 in the electromagnetic wave reflector in the embodiment. MODE FOR CARRYING OUT THE INVENTION

[0009] Hereinafter, embodiments will be described with reference to the drawings. FIG. 1 is a front view showing the configuration of the reflecting surface of the electromagnetic wave reflector according to the embodiment. Here, in FIG. 1, the X-axis is set in the vertical direction of the reflecting surface of the electromagnetic wave reflector 1, the Y-axis is set in the horizontal direction, and the Z-axis is set in the normal direction.

[0010] The electromagnetic wave reflector 1 has a reflecting surface 11. A plurality of unit cells C as phase modulation elements are arranged on the reflecting surface 11. And four unit cells C in two in the X-axis direction × two in the Y-axis direction form one unit U. This unit U is repeatedly arranged in the X-axis direction and the Y-axis direction. In FIG. 1, the number of unit cells C arranged along the X-axis direction and the number of unit cells C arranged along the Y-axis direction are both N (N is an even number). On the other hand, as long as a unit U can be formed, the number of unit cells C arranged along the X-axis direction and the number of unit cells C arranged along the Y-axis direction do not necessarily have to be the same. For example, an arrangement where the number of unit cells C arranged along the X-axis direction is 4 and the number of unit cells C arranged along the Y-axis direction is 2 may be possible.

[0011] FIG. 2 is an enlarged view of one unit U. FIG. 3A is a diagram showing the structure of the first electrode. FIG. 3B is a diagram showing the structure of the second electrode. FIG. 4 is a cross-sectional view of the SRR1 portion in FIG. 2. Here, in FIGS. 2, 3A, and 3B, the illustrations of the X-axis, Y-axis, and Z-axis are omitted, but the X-axis, Y-axis, and Z-axis in FIGS. 2, 3A, and 3B are the same as those in FIG. 1. On the other hand, FIG. 4 is a cross-sectional view of the SRR1 portion in FIG. 2 as viewed from the X-axis direction.

[0012] As shown in FIG. 2, one unit U is composed of two unit cells C of the A / Bi pattern and two unit cells C of the Ai / B pattern. The unit cells C of the A / Bi pattern and the unit cells C of the Ai / B pattern are arranged along the diagonal direction, respectively. Here, "A" indicates that the first electrode is of the A pattern, and "Ai" indicates that the first electrode is of the Ai pattern which is a 90-degree rotational symmetry of the A pattern. On the other hand, "B" indicates that the second electrode is of the B pattern that completely overlaps with the A pattern, and "Bi" indicates that the second electrode is of the Bi pattern that completely overlaps with the Ai pattern.

[0013] Each unit cell C is composed of a first electrode 102, a second electrode 103, and a liquid crystal layer 104, which are formed between a first substrate 101 and a second substrate 105. The first substrate 101 and the second substrate 105 are, but are not limited to, glass substrates. In addition, a third electrode 106 is provided on the back surface of the second substrate 105 as a ground electrode. The third electrode 106 is, but is not limited to, a copper electrode, for example.

[0014] The first electrode 102 is formed on the first substrate 101. The first electrode 102 is not limited to this, but for example, a copper electrode may be used. The first electrode 102 is constructed by arranging A-pattern and Ai-pattern electrodes alternately in the X direction and also by arranging A-pattern and Ai-pattern electrodes alternately in the Y direction. In the X direction, which is the first direction, adjacent A-pattern electrodes and Ai-pattern electrodes are electrically connected via wiring electrodes that are integrally formed with the electrodes of each pattern, thereby forming an electrode row. On the other hand, adjacent A-pattern electrodes and Ai-pattern electrodes in the Y direction are not electrically connected.

[0015] Although not shown in Figure 3A, the first electrode 102 constituting the unit cell C at one end of the reflective surface 11 in the X direction, the lower end in Figure 1, is drawn out to the outside of the reflective surface 11 to form a wiring electrode. A voltage signal Van (where n is 1, 2, ..., N) is applied to this wiring electrode drawn out from the lower end unit cell C from an external driver (not shown). On the other hand, the first electrode 102 constituting the unit cell C at the other end of the reflective surface 11 in the X direction, the upper end in Figure 1, is also drawn out to the outside of the reflective surface 11 to form a wiring electrode. This wiring electrode drawn out from the upper end unit cell C is connected to the third electrode 106.

[0016] The electrodes of pattern A and pattern Ai each have a substantially square-shaped frame-shaped electrode portion 102a. From the frame-shaped electrode portion 102a of pattern A and pattern Ai, an SRR electrode portion 102b and a reflection phase adjustment electrode portion 102c are formed.

[0017] The SRR electrode portion 102b is an electrode portion formed from, for example, the central part of each side that forms the frame-shaped electrode portion 102a of the electrode for each pattern, and when viewed from the projection direction shown in Figure 4, it partially overlaps with the SRR electrode portion 103b of the second electrode 103 to form a split-ring resonator (SRR) structure. The SRR electrode portion 102b corresponds to the SRR1, SRR2, SRR3, and SRR4 portions in Figure 2.

[0018] The SRR electrode portion 102b has an extended portion and a bent portion. The extended portion is a part formed to extend toward the opening center of the electrode of each pattern. The extended portion is a part that does not overlap with the extended portion of the SRR electrode portion 103b when viewed from the projection direction shown in Figure 4. The bent portion is a part formed to bend from the tip of the extended portion. The bent portion is a part that overlaps with the bent portion of the SRR electrode portion 103b when viewed from the projection direction shown in Figure 4. In this embodiment, the four SRR electrode portions 102b in the A pattern electrode are formed to be rotationally symmetric by 90 degrees each. On the other hand, the four SRR electrode portions 102b in the Ai pattern electrode are formed to be rotationally symmetric by 90 degrees each with respect to each of the SRR electrode portions 102b in the A pattern.

[0019] The reflection phase adjustment electrode portion 102c is a square-shaped portion formed from diagonal positions of the frame-shaped electrode portion 102a. In the A-pattern electrode, the two reflection phase adjustment electrode portions 102c are formed from the upper left corner and lower right corner of the frame-shaped electrode portion 102a, respectively. On the other hand, in the Ai-pattern electrode, the two reflection phase adjustment electrode portions 102c are formed from the upper right corner and lower left corner of the frame-shaped electrode portion 102a, respectively, so as to be rotationally symmetrical by 90 degrees with respect to each of the reflection phase adjustment electrode portions 102c in the A-pattern.

[0020] The second electrode 103 is formed on the second substrate 105. The second electrode 103 is not limited to this, but for example, a copper electrode may be used. The second electrode 103 is constructed by arranging Bi pattern electrodes and B pattern electrodes alternately in the X direction, and B pattern electrodes and Bi pattern electrodes alternately in the Y direction. Unlike the first electrode 102, in the second electrode 103, adjacent Bi pattern electrodes and B pattern electrodes in the Y direction (the second direction) are electrically connected via wiring electrodes integrally formed with the electrodes of each pattern, thereby forming an electrode row. On the other hand, adjacent B pattern electrodes and Bi pattern electrodes in the X direction are not electrically connected.

[0021] Furthermore, although not shown in Figure 3B, the second electrode 103 constituting the unit cell C at one end of the reflective surface 11 in the Y direction, the left end in Figure 1, is drawn out to the outside of the reflective surface 11 to form a wiring electrode. A voltage signal Vbn is applied to this wiring electrode drawn out from the unit cell C at the left end from an external driver (not shown). On the other hand, the second electrode 103 constituting the unit cell C at the other end of the reflective surface 11 in the Y direction, the right end in Figure 1, is also drawn out to the outside of the reflective surface 11 to form a wiring electrode. This wiring electrode drawn out from the unit cell C at the right end is connected to the third electrode 106.

[0022] The electrodes for the B pattern and the Bi pattern each have a substantially square-shaped frame-shaped electrode portion 103a. From the respective frame-shaped electrode portions 103a of the B pattern and the Bi pattern, an SRR electrode portion 103b and a reflection phase adjustment electrode portion 103c are formed. The electrodes for the B pattern have the same shape as the electrodes for the A pattern. On the other hand, the electrodes for the Bi pattern have the same shape as the electrodes for the Bi pattern.

[0023] As shown in Figure 2, when the A-pattern electrode and the Bi-pattern electrode face each other, and the Ai-pattern electrode and the B-pattern electrode face each other, a non-overlapping portion 12, a non-overlapping portion 13, and an overlapping portion 14 are formed in each unit cell C. The non-overlapping portion 12 is the portion of the first electrode 102 that does not overlap with the second electrode 103. The non-overlapping portion 13 is the portion of the second electrode 103 that does not overlap with the first electrode 102. The overlapping portion 14 is the overlapping portion of the first electrode 102 and the second electrode 103. In Figure 2, the non-overlapping portion 12, the non-overlapping portion 13, and the overlapping portion 14 are shown with different hatching. On the other hand, the portion not shown with hatching is the portion where neither the first electrode 102 nor the second electrode 103 is formed.

[0024] Now, let's focus on the SRR1 portion in Figure 2. As mentioned earlier, the four SRR electrode portions 102b in the A-pattern electrode are formed to be rotationally symmetrical by 90 degrees each. Furthermore, the four SRR electrode portions 102b in the Bi-pattern electrode are formed to be rotationally symmetrical by 90 degrees each with respect to each of the SRR electrode portions 102b in the A-pattern. In this case, when the non-overlapping portion 12, non-overlapping portion 13, and overlapping portion 14 in the SRR1 portion are orthographically projected from the projection direction of Figure 4, i.e., the direction of incidence of the electromagnetic wave, the shape is such that the non-overlapping portion 12, non-overlapping portion 13, and overlapping portion 14 are arranged in a loop shape, as shown in the left diagram of Figure 5. The arrangement of the non-overlapping portion 12, non-overlapping portion 13, and overlapping portion 14 in a loop shape forms a slot S with respect to the direction of incidence of the electromagnetic wave. The non-overlapping portion 12 is formed by the extended portion of the SRR electrode portion 102b. Furthermore, the non-overlapping portion 13 is formed by the extended portion of the SRR electrode portion 103b. The overlapping portion 14 is formed by the bent portion of the SRR electrode portion 102b, the bent portion of the SRR electrode portion 103b, and the liquid crystal layer 104 sandwiched between these electrode portions, as well as by the frame-shaped electrode portion 102a, the frame-shaped electrode portion 103a, and the liquid crystal layer 104 sandwiched between these electrode portions.

[0025] When electromagnetic waves are incident on slot S, induced currents I1 and I2 are generated in the non-overlapping portions 12 and 13 at the boundary of slot S, in accordance with the magnetic field M passing through slot S. Due to the induced currents I1 and I2, charges move to each of the two overlapping portions 14, and an electric field is generated between the electrodes forming the overlapping portion 14. This electric field causes current to flow in the non-overlapping portions 12 and 13. As a result, the closed circuit formed by the non-overlapping portions 12, 13, and 14 resonates. Due to the resonance, a magnetic field larger than the magnetic field M passing through slot S is generated in a direction that cancels out the magnetic field M passing through slot S. This is emitted from the electromagnetic wave reflector 1 as reflected electromagnetic waves. A resonator with such a mechanism is modeled by the equivalent circuit shown in the right diagram of Figure 5. Here, C_Line in the right-hand diagram of Figure 5 is the capacitance of the equivalent capacitor formed by the bent portion of the SRR electrode portion 102b, the bent portion of the SRR electrode portion 103b, and the liquid crystal layer 104 sandwiched between these electrode portions. Also, C_Ws is the capacitance of the equivalent capacitor formed by the frame-shaped electrode portion 102a, the frame-shaped electrode portion 103a, and the liquid crystal layer 104 sandwiched between these electrode portions. In this embodiment, the dielectric constant of the liquid crystal layer 104 is changed by changing the voltage applied to the liquid crystal layer 104, and the resonant frequency and the reflection phase of electromagnetic waves are changed by the change in dielectric constant.

[0026] In this embodiment, four SRR structures, namely SRR1, SRR2, SRR3, and SRR4, are formed in each unit cell C. SRR1 and SRR2 are resonator structures for vertical polarization, with the longer side of the slot S parallel to the Y-axis and arranged to align in the amplitude direction of the vertically polarized magnetic field. In SRR1 and SRR2, the arrangement of the non-overlapping portion 12, non-overlapping portion 13, and overlapping portion 14 is symmetrical with respect to the Y-axis. On the other hand, SRR3 and SRR4 are resonator structures for horizontal polarization, with the longer side of the slot S parallel to the X-axis and arranged to align in the amplitude direction of the horizontally polarized magnetic field. In SRR3 and SRR4, the arrangement of the non-overlapping portion 12, non-overlapping portion 13, and overlapping portion 14 is symmetrical with respect to the X-axis. Here, vertical polarization in this embodiment is an electromagnetic wave whose polarization direction is parallel to the X-axis. On the other hand, horizontal polarization in this embodiment is an electromagnetic wave whose polarization direction is parallel to the Y-axis.

[0027] In this embodiment, a voltage signal Van is applied to SRR3 and SRR4. On the other hand, a voltage signal Vbn is applied to SRR1 and SRR2. In other words, in this embodiment, the dielectric constant can be changed independently for SRR1 and SRR2 and SRR3 and SRR4.

[0028] Furthermore, in this embodiment, the design of the reflection phase adjustment electrode section 102c and the reflection phase adjustment electrode section 103c makes it possible to change the range of change in the reflection phase, i.e., the range of change in the reflection direction, without changing the frequency.

[0029] The effects of the electromagnetic wave reflector in the embodiment will be explained below with specific examples. Hereinafter, for the purpose of explaining the specific examples, the various design parameters of the electromagnetic wave reflector 1 will be defined as shown in Figure 6.

[0030] Lx and Ly, shown in Figure 6, are the cell sizes of a single unit cell C. Lx is the size in the X-axis direction, and Ly is the size in the Y-axis direction. Px and Py are the outer dimensions of the frame-shaped electrode section that forms a single unit cell C. Px is the size in the X-axis direction, and Py is the size in the Y-axis direction. Lw is the width of the wiring electrode. W1 is the length of each side of the reflection phase control electrode section. W2 is the electrode width of the frame-shaped electrode section. Wsx and Wsy are the slot widths of slot S, i.e., the lengths of the shorter sides. Wsx is the slot width of slot S in the vertical polarization resonator structure, i.e., SRR1 and SRR2. On the other hand, Wsy is the width of slot S in the horizontal polarization resonator structure, i.e., SRR3 and SRR4. Lsx and Lsy are the slot lengths of slot S, i.e., the lengths of the longer sides. Lsx is the slot length of slot S in the horizontal polarization resonator structure, i.e., SRR3 and SRR4. On the other hand, Lsy is the slot length of slot S in the vertical polarization resonator structure, i.e., SRR1 and SRR2.

[0031] In this embodiment, the lengths of the non-overlapping sections 12 and 13 in the vertical polarization resonator structure are designed as 3Wsy, and the width is designed as Wsx. Similarly, the lengths of the non-overlapping sections 12 and 13 in the horizontal polarization resonator structure are designed as 3Wsx, and the width is designed as Wsy.

[0032] Furthermore, the parameters for the thickness of the electromagnetic wave reflector 1 are as follows: tt is the thickness of the first substrate in the Z-axis direction, bt is the thickness of the second substrate in the Z-axis direction, tt is the thickness of the first electrode in the Z-axis direction (= the thickness of the second electrode in the Z-axis direction), Lct is the thickness of the liquid crystal layer interposed between the first and second electrodes, and gnd_t is the thickness of the third electrode in the Z-axis direction.

[0033] The simulation was performed by setting each parameter defined above as shown in the table below. In this simulation, the relative permittivity εr of the liquid crystal layer 104 was changed from ε(vertical) = 2.5 to ε(horizontal) = ε(vertical) + 1.0 = 3.5. The dielectric loss tangents tanδ(vertical, horizontal) at this time are 0.0082 and 0.0053, respectively. In the simulation, the first substrate 101 and the second substrate 105 were assumed to be glass substrates. The relative permittivity εr of each substrate input into the simulation was 5.63, and the dielectric loss tangent tanδ was 0.009. In addition, the first electrode 102, the second electrode 103, and the third electrode 106 were assumed to be copper electrodes. The conductivity σ of each electrode substrate input into the simulation was 5.8 × 10⁻⁶. 7 It is [S / m]. [Table 1]

[0034] Figure 7A shows the simulation results of the reflection amplitude characteristics of vertical polarization due to a change in dielectric constant. Figure 7B shows the simulation results of the reflection amplitude characteristics of horizontal polarization due to a change in dielectric constant. The horizontal axis in Figures 7A and 7B represents the resonant frequency of the corresponding resonator structure. On the other hand, the vertical axis in Figures 7A and 7B represents the input reflection coefficient S11, which is one of the parameters of the scattering matrix. Furthermore, the solid lines in Figures 7A and 7B show the reflection amplitude characteristics before the change in dielectric constant (ε (vertical)), and the dashed lines in Figures 7A and 7B show the reflection amplitude characteristics after the change in dielectric constant (ε (horizontal)).

[0035] As shown in Figures 7A and 7B, the reflection amplitude characteristics of the vertically polarized resonator structure and the horizontally polarized resonator structure are identical before and after the change in dielectric constant. This indicates that the resonant frequencies of the vertically polarized resonator structure and the horizontally polarized resonator structure can be changed independently and by controlling the same dielectric constant.

[0036] Figure 8A shows the simulation results of the reflection phase characteristics of vertical polarization due to a change in dielectric constant. Figure 8B shows the simulation results of the reflection phase characteristics of horizontal polarization due to a change in dielectric constant. The horizontal axis in Figures 8A and 8B represents the resonant frequency of the corresponding resonator structure. On the other hand, the vertical axis in Figures 8A and 8B represents the phase. The solid lines in Figures 8A and 8B show the reflection phase characteristics before the change in dielectric constant (ε (vertical)), and the dashed lines in Figures 8A and 8B show the reflection phase characteristics after the change in dielectric constant (ε (horizontal)).

[0037] As shown in Figures 8A and 8B, the reflection phase characteristics of the vertically polarized resonator structure and the horizontally polarized resonator structure are identical before and after the change in dielectric constant. This indicates that the reflection phases of the vertically polarized resonator structure and the horizontally polarized resonator structure can be changed independently and by the same control of dielectric constant. Furthermore, in this embodiment, a large phase difference occurs at the same frequency before and after the change in dielectric constant between the vertically polarized resonator structure and the horizontally polarized resonator structure.

[0038] A table summarizing the results from Figures 7A, 7B, 8A, and 8B is shown below. As shown in the table below, for example, at the maximum phase difference frequency of 27.7 GHz, a phase difference of 250° or more is achieved in both the vertically polarized resonator structure and the horizontally polarized resonator structure. The fact that the maximum phase difference is obtained at 27.7 GHz indicates that the reflection phase of millimeter-wave electromagnetic waves can be significantly altered. [Table 2] Furthermore, a large difference in reflection phase with respect to changes in dielectric constant means that the reflection phase can be significantly changed by changing the dielectric constant without significantly altering the resonant frequency. Since the reflection phase corresponds to the reflection direction of the composite wave, being able to change the reflection phase without changing the resonant frequency makes it possible to increase the range of change in the reflection direction for incident radio waves of specific frequencies.

[0039] Figure 9A shows the simulation results of the electric field distribution in each unit cell C constituting unit U when a vertically polarized electromagnetic wave is incident on each unit cell C constituting unit U. Figure 9B shows the simulation results of the electric field distribution in each unit cell C constituting unit U when a horizontally polarized electromagnetic wave is incident on each unit cell C constituting unit U. Figure 10A shows the simulation results of the magnetic field distribution in each unit cell C constituting unit U when a vertically polarized electromagnetic wave is incident on each unit cell C constituting unit U. Figure 10B shows the simulation results of the magnetic field distribution in each unit cell C constituting unit U when a horizontally polarized electromagnetic wave is incident on each unit cell C constituting unit U.

[0040] When vertically polarized electromagnetic waves are incident, as shown in Figure 9A, an electric field distribution is generated in SRR1 and SRR2, which are resonator structures for vertical polarization, while no electric field distribution is generated in SRR3 and SRR4. Similarly, when vertically polarized electromagnetic waves are incident, as shown in Figure 10A, a magnetic field distribution is generated in SRR1 and SRR2, which are resonator structures for vertical polarization, while no magnetic field distribution is generated in SRR3 and SRR4. Conversely, when horizontally polarized electromagnetic waves are incident, as shown in Figure 9B, an electric field distribution is generated in SRR3 and SRR4, which are resonator structures for horizontal polarization, while no electric field distribution is generated in SRR1 and SRR2. Similarly, when horizontally polarized electromagnetic waves are incident, as shown in Figure 10B, a magnetic field distribution is generated in SRR3 and SRR4, which are resonator structures for horizontal polarization, while no magnetic field distribution is generated in SRR1 and SRR2. Figures 9A, 9B, 10A, and 10B show that in the electromagnetic wave reflector 1 of the embodiment, the resonator structure that functions is different for each polarization direction, so that the characteristics can be controlled independently for each polarization direction.

[0041] Figure 11A shows the dependence of the maximum phase difference frequency on the liquid crystal layer thickness in an electromagnetic wave reflector according to the embodiment. Here, the horizontal axis of Figure 11A shows the change in the liquid crystal layer thickness Lct (μm). The vertical axis of Figure 11A shows the change in the maximum phase difference frequency. The maximum phase difference frequency is the frequency at which the phase difference between ε (vertical) and ε (horizontal) is maximum. As shown in Figure 11A, the increase in the maximum phase difference frequency fc with respect to the increase in the liquid crystal layer thickness Lct is approximately the same for cases where vertically polarized electromagnetic waves are incident and cases where horizontally polarized electromagnetic waves are incident.

[0042] Figure 11B shows the dependence of the maximum phase difference on the liquid crystal layer thickness in the electromagnetic wave reflector according to the embodiment. Here, the horizontal axis of Figure 11B shows the change in the liquid crystal layer thickness Lct (μm). The vertical axis of Figure 11B shows the change in the maximum phase difference. The maximum phase difference is the maximum phase difference between ε (vertical) and ε (horizontal). As shown in Figure 11B, the maximum phase difference does not change when the liquid crystal layer thickness Lct is between 5 μm and 8 μm, regardless of whether the electromagnetic wave is incident with vertically polarized or horizontally polarized electromagnetic waves. Specifically, a maximum phase difference of 250° or more is maintained when the liquid crystal layer thickness Lct is between 5 μm and 8 μm. In other words, the electromagnetic wave reflector according to the embodiment can be controlled to obtain a large maximum phase difference even with a thin liquid crystal layer thickness of 10 μm or less.

[0043] The above describes the control of the resonant frequency and maximum phase difference by controlling the dielectric constant. In this embodiment, the range of change in the reflection phase difference can also be changed without changing the frequency by adjusting W1 and W2. The following describes how to adjust the range of change in the reflection phase difference.

[0044] Figure 12A shows the W1 dependence of the maximum phase difference frequency in an electromagnetic wave reflector according to the embodiment. Here, the horizontal axis of Figure 12A shows the change in W1 (mm). The vertical axis of Figure 12A shows the change in the maximum phase difference frequency. As shown in Figure 12A, in both vertical and horizontal polarization, the maximum phase difference frequency fc hardly changes even when W1 changes. On the other hand, Figure 12B shows the W1 dependence of the maximum phase difference in an electromagnetic wave reflector according to the embodiment. Here, the horizontal axis of Figure 12B shows the change in W1 (mm). The vertical axis of Figure 12B shows the change in the maximum phase difference. As shown in Figure 12B, in both vertical and horizontal polarization, the maximum phase difference Δφ changes significantly with a change in W1.

[0045] Figure 13A shows the W2 dependence of the maximum phase difference frequency in the electromagnetic wave reflector in the embodiment. Here, the horizontal axis of Figure 13A shows the change in W2 (mm). The vertical axis of Figure 13A shows the change in maximum phase. As shown in Figure 13A, in both vertical and horizontal polarization, the maximum phase difference frequency fc hardly changes even when W2 changes. On the other hand, Figure 13B shows the W2 dependence of the maximum phase difference in the electromagnetic wave reflector in the embodiment. Here, the horizontal axis of Figure 13B shows the change in W2 (mm). The vertical axis of Figure 13B shows the change in maximum phase difference. As shown in Figure 13B, in both vertical and horizontal polarization, the maximum phase difference Δφ changes significantly with a change in W2.

[0046] Thus, in the electromagnetic wave reflector 1 of this embodiment, by adjusting W1 and / or W2, the magnitude of the maximum phase difference can be changed without changing the frequency at which the maximum phase difference is obtained. Here, as is clear from the comparison of Figure 12B and Figure 13B, the change in the maximum phase difference due to the change in W1 is more abrupt than the change in the maximum phase difference due to the change in W2. For this reason, adjusting W1 is suitable for coarse adjustment of the maximum phase difference, and adjusting W2 is suitable for fine adjustment of the maximum phase difference. It should be noted that although the embodiment illustrates the adjustment of the maximum phase difference, it goes without saying that other phase differences can also be adjusted by adjusting W1 and W2.

[0047] As described above, according to the embodiment, the electromagnetic wave reflector has a first electrode and a second electrode that partially overlap with the liquid crystal layer in between to form a split-ring resonator structure. With this configuration, the electromagnetic wave reflector is capable of reflecting incident electromagnetic waves. In addition, in the embodiment, four SRR electrode sections with a 90-degree rotationally symmetric shape are formed in each unit cell of the first electrode and the second electrode, and electrodes with a pattern that is 90 degrees rotationally symmetric to each other are arranged to face each other. Therefore, in the embodiment, in each unit cell, two resonator structures for vertical polarization are formed, which are aligned in the amplitude direction of the vertically polarized magnetic field, and two resonator structures for horizontal polarization are formed, which are aligned in the amplitude direction of the horizontally polarized magnetic field. Since the vertically polarized resonator structure and the horizontally polarized resonator structure can be controlled independently of each other, the electromagnetic wave reflector of the embodiment can reflect both horizontally polarized and vertically polarized electromagnetic waves in the appropriate direction, regardless of whether they are incident.

[0048] Furthermore, in the electromagnetic wave reflector according to this embodiment, a large reflection phase difference can be obtained, for example, in the millimeter wave band, even if the liquid crystal layer thickness is thin. Thus, the electromagnetic wave reflector according to this embodiment makes it possible to obtain desired reflection phase characteristics for a desired frequency band. Moreover, in the electromagnetic wave reflector according to this embodiment, the range of change in the reflection phase can be changed without changing the frequency by designing the reflection phase adjustment electrode section.

[0049] The present invention is not limited to the embodiments described above, and can be modified in various ways during implementation without departing from its essence. Furthermore, each embodiment may be combined as appropriate, and in that case, the combined effects can be obtained. Moreover, the above embodiments include various inventions, and various inventions can be extracted by selecting combinations from the multiple constituent elements disclosed. For example, if the problem can be solved and effects obtained even if some constituent elements are deleted from all the constituent elements shown in the embodiment, then the configuration with these deleted constituent elements can be extracted as an invention. [Explanation of Symbols]

[0050] 1 Electromagnetic reflector, 11 Reflective surface, 12 Non-overlapping portion, 13 Non-overlapping portion, 14 Overlapping portion, 101 First substrate, 102 First electrode, 102a Frame-shaped electrode portion, 102b SRR electrode portion, 102c Reflection phase adjustment electrode portion, 103 Second electrode, 103a Frame-shaped electrode portion, 103b SRR electrode portion, 103c Reflection phase adjustment electrode portion, 104 Liquid crystal layer, 105 Second substrate, 106 Third electrode.

Claims

1. First substrate and A second substrate is positioned opposite the first substrate, A first electrode is arranged on the first substrate, and a first pattern of electrodes and a second pattern of electrodes that are rotationally symmetrical to the first pattern of electrodes by 90 degrees are connected along a first direction to form an electrode array, A second electrode is arranged on the second substrate, and a third pattern of electrodes that is 90 degrees rotationally symmetric with respect to the first pattern of electrodes and a fourth pattern of electrodes that is 90 degrees rotationally symmetric with respect to the second pattern of electrodes are connected along the second direction to form an electrode array. A liquid crystal layer disposed between the first substrate and the second substrate, It has a reflective surface that includes, The electrodes of the first pattern and the third pattern, and the electrodes of the second pattern and the fourth pattern, each form a non-overlapping portion and an overlapping portion when viewed projected from the reflective surface. The closed circuit formed by the non-overlapping portion, the overlapping portion, and the liquid crystal layer disposed in the overlapping portion forms a split-ring resonator structure aligned in the direction of the polarization magnetic field amplitude. Electromagnetic wave reflector.

2. The non-overlapping portion includes a square-shaped reflection phase adjustment electrode portion. The reflection phase adjustment electrode portions of the first pattern electrode and the third pattern electrode are located diagonally opposite to each other. The reflection phase adjustment electrode portions of the second pattern electrode and the fourth pattern electrode are located diagonally opposite to each other. The electromagnetic wave reflector according to claim 1.

3. The thickness of the liquid crystal layer is 10 μm or less. The electromagnetic wave reflector according to claim 1.

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