Resonant cell of metasurface, and metasurface

Abstract

A metasurface (10) comprises a substrate (20), a plurality of first conductive films (30) formed on the substrate (20), a dielectric layer (40) formed on the substrate (20) and covering the plurality of first conductive films (30), and a plurality of second conductive films (50) formed on the dielectric layer (40). A set of a first conductive film (30) and a second conductive film (50) facing each other on a one-to-one basis along the Z direction constitutes a resonant cell (10A) that changes the phase of electromagnetic waves incident on the metasurface (10). The first conductive film (30) is provided with a rectangular annular portion, the middle of which is broken by a gap. The second conductive film (50) is provided with a rectangular annular portion, the middle of which is broken by a gap. Through this configuration, the resonance frequency can be adjusted without changing the footprint of the resonance cell.

Description

Metasurface resonant cells and metasurfaces

[0001] The present invention relates to a metasurface resonant cell and a metasurface.

[0002] A metasurface with periodically arranged resonant cells (also called unit cells) is known. Non-Patent Document 1 discloses a resonant cell of such a metasurface that includes two I-shaped conductive films facing each other in the thickness direction.

[0003] Q. Lou, et al., "High-Efficiency Metalens Antenna Using Huygens' Metasurface With Glide Symmetric I-Shape Metal Strips," IEEE Trans. Antennas Propag. 69(11), 7394-7403(2021).

[0004] In Non-Patent Document 1, the resonant frequency of the resonant cell is adjusted by the amount of misalignment between the two conductive films, which results in a large footprint (area of ​​the resonant cell when viewed from the thickness direction) of each resonant cell depending on the value of the resonant frequency.

[0005] An object of the present invention is to make it possible to adjust the resonant frequency of a resonant cell without changing the footprint of the resonant cell.

[0006] The resonant cell of the metasurface of the present invention comprises a first conductive film having a first annular portion interrupted in the middle by a first void, and a second conductive film having a second annular portion interrupted in the middle by a second void and facing the first conductive film along the thickness direction of the first conductive film.

[0007] The metasurface of the present invention comprises a plurality of periodically arranged resonant cells, each of which comprises a first conductive film having a first annular portion interrupted in the middle by a first void, and a second conductive film having a second annular portion interrupted in the middle by a second void, and facing the first conductive film along the thickness direction of the first conductive film.

[0008] According to the above configuration, the resonant frequency of the resonant cell can be adjusted without changing the footprint of the resonant cell.

[0009] FIG. 1 is a plan view of a metasurface according to an embodiment of the present invention. FIG. 2 is a perspective view of a resonant cell. FIG. 3 is a plan view of a first conductive film. FIG. 4 is a plan view of a second conductive film. FIG. 5 is a graph of the frequency characteristics of the change in transmittance and phase angle. FIG. 6 is a graph of the Y ｅｓ and Z ｍｓ 7 is a graph of frequency characteristics of the resonant cell. FIG. 7 is a diagram showing the simulation results of the electric field generated during electrical resonance. FIG. 8 is a diagram showing the state of the resonant cell during electrical resonance. FIG. 9 is a diagram showing the simulation results of the magnetic field generated during magnetic resonance. FIG. 10 is a diagram showing the state of the resonant cell during magnetic resonance. FIG. 11 is a diagram showing how the positions of the gaps in the first and second conductive films are changed. FIG. 12 is a diagram showing the change in Y depending on the position of the gap. ｅｓ 13 is a graph showing the frequency characteristics of Z ｍｓ 14 is a graph showing frequency characteristics of the change in transmittance and phase angle depending on the position of the gap. FIG. 15 is a graph showing frequency characteristics of the change in transmittance and phase angle depending on the position of the gap. FIG. 16 is a graph showing the relationship between the transmittance and the distance between two conductive films for the resonant cell according to the embodiment and the resonant cell according to the comparative example. FIG. 17 is a perspective view of a resonant cell according to a modified example. FIG. 18 is a graph showing the relationship between the transmittance and the distance between two conductive films for the resonant cell according to the embodiment and the resonant cell according to the comparative example. ｅｓ 19 is a graph showing the frequency characteristics of Z as a function of the position of the air gap of the resonant cell of FIG. ｍｓ Fig. 20 is a graph showing frequency characteristics of the transmittance and phase angle of the resonant cell of Fig. 17. Fig. 21 is a plan view of a first conductive film according to a modified example.

[0010] Hereinafter, metasurfaces according to embodiments of the present invention will be described with reference to the drawings. In each drawing, only some of the elements may be labeled with a symbol. In addition, multiple elements that correspond to each other and have the same or similar functions may be labeled with the same symbol.

[0011] As shown in Figure 1, the metasurface 10 according to this embodiment includes a substrate 20, a plurality of first conductive films 30 formed on the substrate 20, a dielectric layer 40 formed on the substrate 20 and covering the plurality of first conductive films 30, and a plurality of second conductive films 50 formed on the dielectric layer 40. The elements 20 to 50 form a layered structure. In the following description, the thickness direction of the metasurface 10 (elements 20 to 50) is referred to as the Z direction. Two directions that are perpendicular to the Z direction and perpendicular to each other are referred to as the X direction and the Y direction, respectively. Viewing from the Z direction is also referred to as a planar view.

[0012] The substrate 20 is made of, for example, a dielectric substrate. The first conductive films 30 and the second conductive films 50 are each made of, for example, a low-resistance metal film such as copper. The dielectric layer 40 is made of any dielectric material.

[0013] The plurality of first conductive films 30 face the plurality of second conductive films 50 in a one-to-one relationship along the Z direction, with the dielectric layer 40 interposed therebetween. The plurality of conductive films 30 and 50 are arranged in a matrix in the X and Y directions. The plurality of first conductive films 30 are formed to have the same shape as one another. The plurality of second conductive films 50 are also formed to have the same shape as one another.

[0014] FIG. 2 shows a pair of first conductive films 30 and second conductive films 50 facing each other along the Z direction. Each pair of facing conductive films 30 and 50 constitutes a resonant cell 10A that changes the phase of an electromagnetic wave incident on the metasurface 10. As shown in FIG. 1, the multiple conductive films 30 and 50 are arranged in a matrix in the XY direction, and therefore the multiple resonant cells 10A are arranged in a matrix in the XY direction. The multiple resonant cells 10A may be arranged, for example, periodically, and do not have to be arranged in a matrix. Each of the multiple resonant cells 10A is formed with dimensions smaller than the wavelength of an electromagnetic wave of a specific frequency (e.g., an electromagnetic wave used to transmit information, such as a millimeter wave) whose phase is to be changed, e.g., beamformed.

[0015] 3, the first conductive film 30 includes a rectangular annular portion 30B having a portion 30A (enclosed by a dashed line) interrupted by a void 30G, and a rectangular annular portion 30C sharing the portion 30A with the annular portion 30B. The portion 30A is linear and extends along the Y direction.

[0016] The first conductive film 30 can also be said to have a rectangular ring-shaped outer wall 31 and linear portions 32 (portions surrounded by dotted lines) interrupted midway by gaps 30G. The linear portions 32 are disposed inside the outer wall 31 and extend linearly in the Y direction. Both ends of the linear portions 32 are connected to the outer wall 31.

[0017] The outer shell 31 includes the annular portions 30B and 30C in the regions other than the portion 30A, and both end portions of the portion 30A. The linear portion 32 includes the regions other than the both end portions of the portion 30A.

[0018] 4, the second conductive film 50 includes a rectangular annular portion 50B having a portion 50A (enclosed by a dashed line) interrupted by a void 50G, and a rectangular annular portion 50C sharing the portion 50A with the annular portion 50B. The portion 50A is linear and extends along the Y direction.

[0019] The second conductive film 50 can also be said to have a rectangular ring-shaped outer wall 51 and linear portions 52 (portions surrounded by dotted lines) interrupted midway by gaps 50G. The linear portions 52 are disposed inside the outer wall 51 and extend linearly in the Y direction. Both ends of the linear portions 52 are connected to the outer wall 51.

[0020] The outer shell 51 includes the annular portions 50B and 50C in the regions other than the portion 50A, and both end portions of the portion 50A. The linear portion 52 includes the regions other than the both end portions of the portion 50A.

[0021] The outer walls 31 and 51 are formed in the same shape. The center C3 of the outer wall 31 and the center C5 of the outer wall 51 coincide in a planar view. The centers C3 and C5 are also the centers of the conductive films 30 and 50, respectively. The void 30G and the void 50G are rectangular in shape and are formed at positions offset in the Y direction. In a planar view, the linear portion 32 (or portion 30A) and the linear portion 52 (or portion 50A) are arranged in an overlapping position. The linear portions 32 and 52 are formed in the same shape except that the positions of the void 30G and the void 50G are offset.

[0022] The amount of deviation D3 of the center C31 of the gap 30G from the center C3 of the first conductive film 30 and the amount of deviation D5 of the center C51 of the gap 50G from the center C5 of the second conductive film 50 are the same but in opposite directions. In a plan view, the shape of the second conductive film 50 matches the shape of the first conductive film 30 rotated around an axis AX that passes through the center C3 and extends in the X direction. The rotation angle here is 180 degrees.

[0023] Here, we will explain the resonance phenomenon that occurs in each resonant cell 10A of the metasurface 10 shown in FIG. 1. Here, the widths W31 to W35 (FIG. 2) of the annular portions 30B and 30C (outer frame 31 and linear portion 32) of the first conductive film 30 are 40 μm. Furthermore, the gap G3 (FIG. 2), which is the length of the void 30G in the Y direction, is 40 μm. The length Y3 (FIG. 2) of the first conductive film 30 in the Y direction is 300 μm, and the length X3 (FIG. 2) in the X direction is 260 μm. The deviation D3 (FIG. 2) of the center C31 of the void 30G from the center C3 of the first conductive film 30 is 20 μm. The distance between the centers C31 of the first conductive films 30 adjacent in the X direction and the distance between the centers C31 of the first conductive films 30 adjacent in the X direction are 400 μm. Similarly, the widths W51 to W55 (FIG. 3) of the annular portion 50B and the annular portion 50C (outer frame 51 and linear portion 52) of each second conductive film 50 were set to 40 μm. Furthermore, the gap G5 (FIG. 3), which is the length of the void 50G in the Y direction, was set to 40 μm. The length Y5 (FIG. 3) of the second conductive film 50 in the Y direction was set to 300 μm, and the length X5 (FIG. 3) in the X direction was set to 260 μm. The deviation D5 (FIG. 3) of the center C51 of the void 50G from the center C5 of the second conductive film 50 was set to 20 μm. The distance between the centers C51 of the second conductive films 50 adjacent in the X direction and the distance between the centers C51 of the second conductive films 50 adjacent in the Y direction were set to 400 μm.

[0024] Figure 5 shows the results of a simulation of the transmission characteristics when an electromagnetic wave with a fixed polarization and an electric field in the Y direction is incident on a metasurface 10 with the above dimensions. In the simulation, an infinite number of resonant cells 10A with the same structure are arranged. The simulation results are for each resonant cell 10A. This is also true for the other simulations described below. In Figure 5, S21 is the S (Scattering) parameter S21 and indicates the transmittance of the electromagnetic wave. Phase indicates the phase change of the electromagnetic wave after transmission through the metasurface 10 relative to the electromagnetic wave before transmission. From the above transmission characteristics and separately simulated reflection characteristics, the magnetic response and electrical response can be obtained from the following equations (1) and (2).

[0025]

[0026]

[0027] FIG. 7 shows the electric field distribution in the resonant cell 10A during electrical resonance. As shown in FIG. 7, a large set of electric field vectors, Ev, is generated in the central portion where the gaps 30G and 50G (FIGS. 3 and 4) are provided. This is because, as shown in FIG. 8, currents I1 and I2 flow in the same direction in the conductive films 30 and 50, respectively, causing the gaps 30G and 50G to function as capacitors. This generates electric fields E1 and E2 in the same direction in the gaps 30G and 50G, respectively, and a strong electric field E3 is generated by the superposition of these electric fields. Furthermore, by including two annular portions 30B and 30C in the conductive film 30, more current flows through the conductive film 30 than when the conductive film is formed with only one annular portion, thereby making the electric field E3 stronger. The same holds true for the conductive film 50.

[0028] FIG. 9 shows the magnetic field distribution in the resonant cell 10A when magnetic resonance occurs. As shown in FIG. 9, a set of many magnetic field vectors, Mv, is generated at both ends of the resonant cell 10A in the X direction. This is because, as shown in FIG. 10, at frequencies where magnetic resonance occurs, surface currents I3 and I4 flow in opposite directions in the conductive films 30 and 50, respectively, causing the conductive films 30 and 50 to function like coils. Note that FIG. 10 does not illustrate the surface currents on the opposite side of the X direction. Because the conductive films 30 and 50 function like coils, an induced magnetic field is generated at both ends of the resonant cell 10A in the X direction, thereby generating a strong magnetic field M1. By forming the outer peripheries 31 and 51 of the conductive films 30 and 50 into rectangular shapes, the coils can be flattened, aligning the magnetic field vectors.

[0029] The resonance of the resonant cell 10A in which the electrical resonant frequency (hereinafter also referred to as the ED frequency) and the magnetic resonant frequency (hereinafter also referred to as the MD frequency) match (including almost match) each other is called a Huygens dipole.

[0030] To match the ED frequency and the MD frequency, the positions of the gaps 30G and 50G of the resonant cell 10A are moved along the Y direction (see dashed lines) as shown in FIG. 11 . The movement directions of the gaps 30G and 50G are opposite to each other, and the movement amounts (shift amounts) D3 and D5 of the gaps 30G and 50G are the same (D3 = D5). The movement amounts D3 and D5 are based on, for example, when the gaps 30G and 50G are both located at the center of the resonant cell 10A (when C31 and C3 in FIG. 3 coincide, and when C51 and C5 in FIG. 4 coincide). This allows similar currents to flow through both conductive films 30 and 50, reducing bias in the electric and magnetic fields generated in the resonant cell 10A. To achieve this reduction effect, as in this embodiment, the shape of the second conductive film 50 may be made to coincide with the shape of the first conductive film 30 when rotated around the axis AX that passes through the center C3 and extends in the X direction in a plan view. Furthermore, changes in the ED frequency and the MD frequency in response to changes in the positions of the gaps 30G and 50G are simplified, which simplifies the design of, for example, the resonant cell 10A.

[0031] 12 and 13 show the simulation results of the frequency characteristics of the electric response and the magnetic response when the above dimensions are adopted for the resonant cell 10A and an electromagnetic wave with fixed polarization is incident on the metasurface 10 with the Y direction as the electric field when the positions of the gaps 30G and 50G are changed. Here, the movement amounts D3 and D5 (referred to as movement amount D in FIGS. 12 and 13, and the same applies to other figures) when the positions of the gaps 30G and 50G are changed are changed to 0 μm, 70 μm, and 105 μm.

[0032] As can be seen from FIGS. 12 and 13 , the ED frequency and MD frequency shift by changing the displacements D3 and D5 of the gaps 30G and 50G. Even with the same displacement, the ED frequency shifts more than the MD frequency, so there are values ​​of displacements D3 and D5 at which the ED and MD frequencies match. In this example, when the displacements D3 and D5 of the gaps 30G and 50G are 105 μm, the ED and MD frequencies match, i.e., a Huygens dipole is generated. Thus, in this embodiment, a Huygens dipole is obtained with a small resonant cell 10A, using the resonant cell 10A composed of two conductive films 30 and 50. During the Huygens dipole, for example, the states shown in FIGS. 8 and 10 appear at different times within one cycle of the electromagnetic wave.

[0033] 14 and 15 show simulation results of the frequency dependence of the transmittance (S21) and phase change (Phase), which are transmission characteristics, when the gaps 30G and 50G are moved. Here, the movement amounts D3 and D5 were changed to 0 μm, 35 μm, 70 μm, and 105 μm. When the movement amounts D3 and D5 = 0 μm, the transmittance is poor. As the gaps 30G and 50G are moved, the two frequencies at which the transmittance drops significantly become closer to each other. When the movement amounts D3 and D5 = 105 μm, that is, when a Huygens dipole is generated, it can be confirmed that the transmittance improves and a phase change of 360 degrees (2π) is obtained in the frequency range of 280 to 330 GHz (a range near the frequency of the Huygens dipole). Therefore, it can be said that the resonant cell 10A according to this embodiment can generate a phase change over a wide range from 0 to 2π with good transmittance. The frequency range with good transmittance and a wide range of phase shift (the frequency range of the Huygens dipole) can be adjusted by adjusting the various dimensional parameters (e.g., W31 to W35, X3, Y3, G3, etc. in FIG. 3 ) of the conductive films 30 and 50. After determining the various dimensional parameters of the resonant cell 10A, the resonant frequency may be adjusted by adjusting the displacements D3 and D5, i.e., the positions of the gaps 30G and 50G.

[0034] Next, Figure 16 shows the relationship between the inter-film distance h, which is the distance between the first conductive film 30 and the second conductive film 50 (the thickness of the dielectric layer 40 in Figure 1), and the transmittance of the metasurface 10 for electromagnetic waves having a specific wavelength λ0. The horizontal axis of Figure 16 represents the distance h as a ratio to the specific wavelength λ0. The vertical axis represents the transmittance S21 for electromagnetic waves having a specific wavelength λ0. Figure 16 also shows the relationship between the inter-film distance h and the transmittance of a metasurface according to a comparative example. The metasurface according to the comparative example has multiple resonant cells formed by two I-shaped conductive films, as described in the above-mentioned non-patent document 1 (Q. Lou, et al., "High-Efficiency Metalens Antenna Using Huygens' Metasurface With Glide Symmetric I-Shape Metal Strips," IEEE Trans. Antennas Propag. 69(11), 7394-7403(2021).).

[0035] The inter-membrane distance h with the highest transmittance in the comparative example is 0.21 (P21: -0.34 dB), which is twice the inter-membrane distance h = 0.105 (P11: -0.95 dB) with the highest transmittance in this embodiment. Furthermore, the inter-membrane distance h at which a loss of 3 dB occurs in the comparative example is 0.11 (point P22: -3.03 dB), which is more than twice the inter-membrane distance h = 0.04 (point P12: -3.07 dB) with which a loss of 3 dB occurs in this embodiment. Therefore, it can be seen that this embodiment achieves equivalent transmittance with a thinner structure than the comparative example. Reducing the thickness of the resonant cell 10A also leads to a thinner and lighter metasurface 10. Furthermore, the distance between adjacent resonant cells is 0.4 * λ0 in this embodiment, whereas it is 0.7 * λ0 in the comparative example. Therefore, the area of ​​each resonant cell as viewed from the Z direction can be reduced. This allows the resonant cells to be smaller.

[0036] As described above, in the resonant cell 10A according to this embodiment, the distance of the concentrated portion of the electric field lines during resonance can be adjusted by changing the positions of the gaps 30G and 50G, thereby adjusting the resonant frequency (ED frequency and / or MD frequency). Changing the positions of the gaps 30G and 50G does not affect the area of ​​the resonant cell 10A in a plan view, i.e., the footprint of the resonant cell 10A (see, for example, FIG. 11 ). Therefore, the resonant cell 10A according to this embodiment is a resonant cell whose resonant frequency can be adjusted without changing the footprint of the resonant cell 10A, for example, during design. This effect can be achieved by including in the resonant cell 10A a first conductive film 30 having an annular portion 30B interrupted by the gap 30G, and a second conductive film 50 having an annular portion 50B interrupted by the gap 50G and facing the first conductive film 30 along the Z direction. In addition, the volume (footprint and inter-membrane distance) of the resonant cell 10A can be made smaller than that of a resonant cell using a conventional I-type conductive membrane. Furthermore, by adjusting the positions of the gaps 30G and 50G, a Huygens dipole whose ED frequency and MD frequency match can be generated in the resonant cell 10A.

[0037] The first conductive film 30 and the second conductive film 50 each have an annular portion, which shortens the path length required to cause resonance, similar to a split-ring resonator. Such a resonant cell 10A is suitable for miniaturization.

[0038] By miniaturizing the resonant cell 10A, for example, one side of the resonant cell 10A can be made 1 / 2.5 or less of the wavelength of the electromagnetic wave, and the thickness can be made 1 / 10 or less of the wavelength.

[0039] The shapes of the first conductive film and the second conductive film can be changed as appropriate. Fig. 17 shows a resonant cell 110A according to a modified example. A metasurface (not shown) according to the modified example has multiple resonant cells 110A. The resonant cell 110A includes a first conductive film 130 and a second conductive film 150. The conductive films 130 and 150 have outer edges 131 and 151 each having an annular shape. Accordingly, the annular portions 130B, 130C, 150B, and 150C are formed in a D-shape or an inverted D-shape.

[0040] 18 and 19 show the simulation results of the frequency characteristics of the electric and magnetic responses when an electromagnetic wave with fixed polarization and an electric field in the Y direction is incident on a metasurface incorporating the resonant cell 110A. Here, the displacements D3 and D5 when the positions of the gaps 30G and 50G are changed are varied to 0 μm, 45 μm, and 90 μm. FIG. 20 shows the simulation results of the frequency dependence of the transmittance (S21) and phase change (Phase) of the resonant cell 110A when the displacements D3 and D5 are set to 90 μm.

[0041] As can be seen from Figures 18 and 19, when the displacements D3 and D5 of the air gaps 30G and 50G are 90 μm, the ED frequency and the MD frequency coincide, resulting in a Huygens dipole. At this time, as shown in Figure 20, the phase changes by 360 degrees, and the transmission loss is low at 0.5 dB or less.

[0042] As another example, the portion 30A of the first conductive film 30 of the resonant cell 10A may be modified to a portion 230A that is linear but has a wider shape than the other portions where the void 30G is formed, as shown in Figure 21. In this case, the first conductive film 230 has annular portions 230B and 230C that share the portion 230A. Such a modification can also be made to the second conductive film.

[0043] The first and second conductive films of the resonant cell may each have only one annular portion, for example, the first and second conductive films may each be formed of only the annular portions 30B and 50B shown in FIGS.

[0044] When using a metasurface as a beamformer, the shape of each resonant cell is determined during metasurface design so as to obtain a phase change distribution that forms a desired beam shape for electromagnetic waves at a specific frequency, for example, any frequency band within the range of 3 GHz to 3 THz. The metasurface is then fabricated based on this determination. During this determination, the resonant frequency can be adjusted by adjusting the position of the void that interrupts the annular portion of the first conductive film and the position of the void that interrupts the annular portion of the second conductive film. Furthermore, the shape of the resonant cell, including the position of each void, is adjusted so that the resonant cell generates a Huygens dipole at the specific frequency. This increases the transmittance of each resonant cell and allows the phase shift of each resonant cell to be set over a wide range (e.g., 0 to 2π). Therefore, a high-performance Huygens metasurface can be obtained as a beamformer, with high transmittance, good directivity, and so on. In addition to the position of the void, the resonant frequency can also be adjusted by adjusting the inter-film distance between two conductive films. Resonant cells with fixed sizes and varying resonant frequencies can also be arranged.

[0045] The maximum angle at which beamforming is possible is determined by the length of the outer periphery of one resonant cell. In this embodiment, the resonant cell can be made smaller, allowing the outer periphery to be made longer accordingly. This increases the maximum angle at which beamforming is possible. Furthermore, by making the resonant cells smaller, the number of resonant cells per unit area of ​​the metasurface can be increased. For example, the number of resonant cells that can be arranged in the X direction per unit area can be increased from two to four. This allows four types of resonant cells that change the phase of the electromagnetic wave to 0 degrees, 90 degrees, 180 degrees, and 270 degrees, respectively, to be arranged, whereas previously only two types of resonant cells that change the phase of the electromagnetic wave to 0 degrees and 180 degrees could be arranged. In other words, the amount of phase change can be finely set for each resonant cell, resulting in improved beam quality during beamforming.

[0046] The first conductive film and the second conductive film that constitute the resonant cell, in particular, the outer edges and / or the linear portions thereof may not necessarily coincide in a planar view; the two may be formed in different shapes, or their positions may be misaligned in a planar view.

[0047] The dielectric layer 40 in FIG. 1 may be used as the substrate, and the substrate 20 may be omitted. An air layer or a liquid layer may be placed between the conductive films 30 and 50. For example, the conductive films 30 and 50 may be formed on two substrates with an air layer or a liquid layer sandwiched between them via a spacer or the like. A dielectric layer may be formed on the outside of the conductive films 30 and 50. The metasurface may be formed using a flexible substrate. A protective layer may be provided to cover and protect the second conductive film 50.

[0048] The present invention is not limited to the above-described embodiments and modifications. For example, the present invention includes various modifications to the above-described embodiments and modifications that can be understood by a person skilled in the art within the scope of the technical concept of the present invention. The configurations listed in the above-described embodiments and modifications can be combined as appropriate within a range that does not cause contradictions. In addition, any of the above-described configurations can be deleted.

[0049] (Notes) The following are examples of the above-described embodiments and modifications. Only a partial configuration of the above-described embodiments and modifications may be applied to each note. Furthermore, parts of each note may be combined.

[0050] (Supplementary Note 1) A metasurface resonant cell comprising: a first conductive film having a first annular portion interrupted midway by a first void; and a second conductive film having a second annular portion interrupted midway by a second void, the second conductive film facing the first conductive film along a thickness direction of the first conductive film. (Supplementary Note 2) The resonant cell of Supplementary Note 1, wherein the first annular portion has a first portion interrupted midway by the first void, the first conductive film further comprises a third annular portion sharing the first portion with the first annular portion, the second annular portion has a second portion interrupted midway by the second void, and the second conductive film further comprises a fourth annular portion sharing the second portion with the second annular portion. (Supplementary Note 3) The resonant cell according to Supplementary Note 1 or 2, wherein the first annular portion has a first portion, the first void being located midway along the first annular portion, and the second annular portion has a second portion, the first portion and the second portion extending along a direction perpendicular to the thickness direction and arranged at positions overlapping when viewed from the thickness direction, and the first void and the second void being located at positions offset along the orthogonal direction. (Supplementary Note 4) The resonant cell according to Supplementary Note 3, wherein the second conductive film extends along a direction perpendicular to the thickness direction and the orthogonal direction and coincides with the first conductive film rotated 180 degrees around a rotation axis passing through a center of the first conductive film when viewed from the thickness direction. (Supplementary Note 5) The resonant cell according to any of Supplements 1 to 4, wherein the first conductive film and the second conductive film are formed into shapes such that an electrical resonant frequency and a magnetic resonant frequency of electromagnetic waves of the resonant cell change depending on the positions of the first void and the second void. (Supplementary Note 6) The resonant cell according to any one of Supplementary Notes 1 to 5, wherein the first air gap and the second air gap are arranged at positions that match an electrical resonant frequency and a magnetic resonant frequency of an electromagnetic wave of the resonant cell to generate a Huygens dipole.(Supplementary Note 7) The resonant cell described in Supplementary Note 2, wherein the first conductive film includes a first annular outer wall and a first linear portion that is arranged inside the first outer wall, includes both ends connected to the first outer wall, and extends along an orthogonal direction that is perpendicular to the thickness direction; the first outer wall includes a region other than the first portion of the first annular portion, a region other than the first portion of the third annular portion, and both ends of the first portion; the first linear portion includes a region other than the both ends of the first portion; the second conductive film includes a second annular outer wall and a second linear portion that is arranged inside the second outer wall, includes both ends connected to the second outer wall, and extends along the orthogonal direction; the second outer wall includes a region other than the second portion of the second annular portion, a region other than the second portion of the fourth annular portion, and both ends of the second portion; and the second linear portion includes a region other than the both ends of the second portion. (Supplementary Note 8) The resonant cell according to Supplementary Note 7, wherein the first outer contour and the second outer contour have a rectangular annular shape. (Supplementary Note 9) The resonant cell according to any of Supplements 1 to 8, wherein the first annular portion has a first portion, the first void being located midway, the second annular portion has a second portion, the first void being located midway, the first void being located at a position shifted from a center of the first portion along the orthogonal direction, the second void being located at a position shifted from a center of the second portion along the orthogonal direction, a direction in which the first void is shifted from the center of the first portion is opposite to a direction in which the second void is shifted from the center of the second portion, and an amount of shift of the first void from the center of the first portion is the same as an amount of shift of the second void from the center of the second portion. (Supplementary Note 10) A metasurface comprising a plurality of periodically arranged resonant cells, each of the plurality of resonant cells comprising: a first conductive film having a first annular portion interrupted by a first void in the middle, and a second conductive film having a second annular portion interrupted by a second void in the middle, the second conductive film facing the first conductive film in a thickness direction of the first conductive film. (Supplementary Note 11) The plurality of resonant cells include a first resonant cell and a second resonant cell, and the shape of the first conductive film and the shape of the second conductive film differ between the first resonant cell and the second resonant cell. The metasurface according to Supplementary Note 10.(Supplementary Note 12) A method for designing a metasurface, comprising: a first step of determining a frequency and a beam shape of an electromagnetic wave to be beamformed by a metasurface; and a second step of setting, for one or more resonant cells according to the determined frequency and the beam shape, the shapes of a first conductive film having a first annular portion interrupted by a first void in the middle and a second conductive film having a second annular portion interrupted by a second void in the middle and facing the first conductive film along a thickness direction of the first conductive film, the second step including a step of determining a position of the first void in the first conductive film and a position of a second void in the second conductive film. (Supplementary Note 13) A method for fabricating a metasurface, comprising: the design method according to Supplementary Note 12; and a third step of fabricating a plurality of resonant cells with the shapes determined in the second step.

[0051] 10...Metasurface, 10A...Resonant cell, 20...Substrate, 30...First conductive film, 30A...Part, 30B to 30C...Annular portion, 30G...Gap, 31...Outer shell, 32...Linear portion, 40...Dielectric layer, 50...Second conductive film, 50A...Part, 50B to 50C...Annular portion, 50G...Gap, 51...Outer shell, 52...Linear portion, 110A...Resonant cell, 130...First conductive film, 130B to 130C...Annular portion, 131...Outer shell, 150...Second conductive film, 150B to 150C...Annular portion minute, 151...outer shell, 230...first conductive film, 230A...part, 230B to 230C...annular portion, AX...axis, C3...center, C5...center, C31...center, C51...center, D3...movement amount (shift amount), D5...movement amount (shift amount), E1...electric field, E2...electric field, E3...electric field, Ev...electric field vector set, G3...gap, G5...gap, h...intermembrane distance, I1...current, I2...current, I3...surface current, I4...surface current, M1...magnetic field, Mv...magnetic field vector set.

Claims

1. A metasurface resonant cell comprising: a first conductive film having a first annular portion interrupted by a first void; and a second conductive film having a second annular portion interrupted by a second void, the second conductive film facing the first conductive film along the thickness direction of the first conductive film.

2. The resonant cell described in claim 1, wherein the first annular portion has a first portion interrupted by the first void, the first conductive film further comprises a third annular portion sharing the first portion with the first annular portion, the second annular portion has a second portion interrupted by the second void, and the second conductive film further comprises a fourth annular portion sharing the second portion with the second annular portion.

3. The resonant cell described in claim 1, wherein the first annular portion has a first portion in the middle of which the first void is formed, the second annular portion has a second portion in the middle of which the second void is formed, the first portion and the second portion extend along an orthogonal direction perpendicular to the thickness direction and are arranged in positions where they overlap when viewed from the thickness direction, and the first void and the second void are arranged in positions that are offset along the orthogonal direction.

4. A resonant cell as described in claim 3, wherein the second conductive film extends in a direction perpendicular to the thickness direction and the perpendicular direction and coincides with the first conductive film rotated 180 degrees around a rotation axis passing through the center of the first conductive film when viewed from the thickness direction.

5. The resonant cell according to claim 1, wherein the first conductive film and the second conductive film are formed in shapes that change the electrical resonant frequency and magnetic resonant frequency of the electromagnetic waves of the resonant cell depending on the positions of the first gap and the second gap.

6. A resonant cell as described in claim 1, wherein the first air gap and the second air gap are positioned so as to match the electrical resonant frequency and magnetic resonant frequency of the electromagnetic waves of the resonant cell to generate a Huygens dipole.

7. The resonant cell described in claim 2, wherein the first conductive film includes a first annular outer wall and a first linear portion that is arranged inside the first outer wall, includes both ends connected to the first outer wall, and extends along an orthogonal direction perpendicular to the thickness direction; the first outer wall includes a region other than the first portion of the first annular portion, a region other than the first portion of the third annular portion, and both ends of the first portion; the first linear portion includes a region other than the both ends of the first portion; the second conductive film includes a second annular outer wall and a second linear portion that is arranged inside the second outer wall, includes both ends connected to the second outer wall, and extends along the orthogonal direction; the second outer wall includes a region other than the second portion of the second annular portion, a region other than the second portion of the fourth annular portion, and both ends of the second portion; and the second linear portion includes a region other than the both ends of the second portion.

8. A metasurface comprising a plurality of periodically arranged resonant cells, each of the plurality of resonant cells comprising: a first conductive film having a first annular portion interrupted in the middle by a first void; and a second conductive film having a second annular portion interrupted in the middle by a second void, the second conductive film facing the first conductive film along the thickness direction of the first conductive film.

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