Metasurface structure

Abstract

The present invention addresses the problem of providing a metasurface structure which is thin, has a large phase difference between transmitted electromagnetic waves, and also has a high transmittance of electromagnetic waves. The metal laminate is obtained by laminating a first structure layer in which a first metal microstructure is arranged, a second structure layer in which a second metal microstructure is arranged, a third structure layer in which a third metal microstructure is arranged, and a fourth structure layer in which a fourth metal microstructure is arranged at intervals. The problem is solved by a metasurface structure that acts on electromagnetic waves having a frequency of 10 THz or less.

Description

Technical Field

[0001] The invention relates to a super surface structure for refracting electromagnetic waves. Background Art

[0002] High-frequency electromagnetic waves (millimeter waves, terahertz waves, etc.) used in large-capacity wireless communications have high straightness, so it is necessary to control the directivity with respect to communication equipment.

[0003] In order to more effectively control directivity, it is necessary to give a phase difference to the electromagnetic waves emitted from the wave source by using an element having a convex lens effect to refract them and thus collimate them (convert them into plane waves).

[0004] In order to provide a phase difference to an electromagnetic wave using a common optical convex lens or a diffraction element, a size of about the wavelength of the target electromagnetic wave is required, which leads to an increase in the size of the element.

[0005] On the other hand, a metasurface structure is known as an element that functions as a convex lens despite being in a flat plate shape.

[0006] The metasurface structure can bend the electromagnetic wave in a desired direction by giving a phase difference to the transmitted electromagnetic wave through the microstructure arranged on the substrate. Therefore, the metasurface structure is expected to be applied to various elements such as convex lenses (condenser lenses) and deflection elements.

[0007] Here, as described above, the metasurface structure imparts a phase difference to the electromagnetic wave through the arranged microstructures, thereby refracting the electromagnetic wave, for example.

[0008] This metasurface structure is in the form of a flat plate and does not require the thickness of a normal optical refractive lens, nor does it require the formation of projections and recesses having a steep groove structure like a diffraction lens (Fresnel lens).

[0009] That is, by using a metasurface structure, it is possible to realize elements such as a very thin flat convex lens and a transmission-type refraction plate that can change the propagation direction of radio waves to a desired direction.

[0010] Here, in the conventional metasurface structure, a sufficient phase difference cannot be given to electromagnetic waves in a high frequency band, particularly called terahertz waves (THz waves), and a sufficient refractive index may not be obtained.

[0011] On the other hand, Non-Patent Document 1 discloses a super surface structure in which microstructures are arranged on both surfaces of a substrate.

[0012] Previous technical literature

[0013] Non-patent literature

[0014] Non-patent literature 1: Ruiqiang Zhao et al., High-efficiency Huygens' metasurface for terahertz wave manipulation, Optics Letters Vol.44, Issue 14, pp.3482-3485 (2019) Summary of the invention

[0015] Technical issues to be solved by the invention

[0016] According to the structure in which the super-surface structure in which the micro-structures are arranged on both surfaces of the substrate described in Non-Patent Document 1, a larger phase difference can be given even to the terahertz wave compared to a super-surface structure in which the micro-structures are arranged on only one surface of the substrate. However, even with this structure, there are many cases where the phase difference given to the terahertz wave is insufficient.

[0017] In addition, in a transmissive element such as a convex lens, not only a sufficient phase difference, that is, a refractive index, but also a high transmittance is required. However, in the conventional metasurface structure, the transmittance cannot be said to be sufficient.

[0018] The purpose of the present invention is to solve the problems of the prior art and to provide a metasurface structure which is thinner than a conventional optical convex lens and can obtain a transmitted wave with a large phase difference with the incident wave, and also has a high transmittance of electromagnetic waves.

[0019] Means for solving technical problems

[0020] In order to solve the problem, the present invention has the following structure.

[0021] [1] A metasurface structure, wherein the following structural layers are stacked at intervals from each other and act on electromagnetic waves with a frequency of 10 THz or less:

[0022] a first structural body layer, wherein a plurality of first metal microstructures are arranged in an in-plane direction;

[0023] a second structure layer, wherein a plurality of second metal microstructures are arranged in an in-plane direction;

[0024] a third structure layer, wherein a plurality of third metal microstructures are arranged in an in-plane direction; and

[0025] The fourth structure layer is formed by arranging a plurality of fourth metal microstructures in the in-plane direction.

[0026] [2] The metasurface structure according to [1], wherein:

[0027] In at least one of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, at least one metal microstructure is arranged to be offset in the in-plane direction with respect to the metal microstructures of the other structure layers.

[0028] [3] The metasurface structure according to [1] or [2], wherein:

[0029] In all of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, at least one metal microstructure is arranged to be offset in the in-plane direction with respect to the metal microstructures of the other structure layers.

[0030] [4] The supersurface structure according to any one of [1] to [3], wherein

[0031] A dielectric layer is provided at least between the first structural body layer and the second structural body layer, between the second structural body layer and the third structural body layer, and between the third structural body layer and the fourth structural body layer.

[0032] [5] The supersurface structure according to any one of [1] to [4], wherein

[0033] A spacer is provided between at least one of the first structural body layer and the second structural body layer, between the second structural body layer and the third structural body layer, and between the third structural body layer and the fourth structural body layer.

[0034] [6] The supersurface structure according to any one of [1] to [5], wherein

[0035] In at least one of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, at least one metal microstructure is a metal cutting wire.

[0036] [7] The supersurface structure according to any one of [1] to [6], wherein

[0037] In all the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, all the metal microstructures are metal cutting wires.

[0038] [8] The metasurface structure according to [6] or [7], wherein:

[0039] The length of the metal cutting line is 0.1 to 1.0 times the wavelength of the electromagnetic wave of the frequency with the highest transmittance.

[0040] [9] The supersurface structure according to any one of [1] to [8], wherein

[0041] The thickness between the first structural body layer and the second structural body layer, between the second structural body layer and the third structural body layer, and between the third structural body layer and the fourth structural body layer is 30 nm to 30 mm.

[0042]

[10] The metasurface structure according to any one of [1] to [9], which is a sheet lens.

[0043]

[11] The metasurface structure according to any one of [1] to [9], which is a transmission-type refraction plate.

[0044] Effects of the Invention

[0045] According to the present invention, there is provided a metasurface structure which is thinner than a conventional optical convex lens and the like and which can obtain a transmitted wave having a large phase difference with an incident wave and which also has a high transmittance of electromagnetic waves. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a diagram conceptually showing an example of the supersurface structure of the present invention.

[0047] Figure 2 This is a diagram conceptually showing another example of the supersurface structure of the present invention.

[0048] Figure 3 This is a diagram conceptually showing another example of the supersurface structure of the present invention.

[0049] Figure 4 This is a diagram conceptually showing another example of the supersurface structure of the present invention.

[0050] Figure 5 This is a diagram conceptually showing another example of the supersurface structure of the present invention.

[0051] Figure 6 This is a diagram conceptually showing an example of a supersurface structure for explaining the present invention.

[0052] Figure 7 This is a diagram conceptually showing an example of a sheet lens based on the metasurface structure of the present invention.

[0053] Figure 8 This is a diagram conceptually showing an example of a sheet lens of a metasurface structure according to the present invention.

[0054] Fig. 9 It is a conceptual diagram for explaining an embodiment of the present invention.

[0055] Fig.10 It is a conceptual diagram of an embodiment of the present invention.

[0056] Fig.11It is a conceptual diagram of an embodiment of the present invention.

[0057] Fig.12 It is a conceptual diagram of an embodiment of the present invention.

[0058] Fig.13 This is a conceptual diagram of a comparative example of the present invention.

[0059] Fig.14 This is a conceptual diagram of a comparative example of the present invention.

[0060] Fig.15 1 is a conceptual diagram for explaining units constituting a transmission-type refraction plate according to an embodiment of the present invention.

[0061] Fig.16 1 is a conceptual diagram for explaining a sheet lens according to an embodiment of the present invention.

[0062] Fig.17 1 is a conceptual diagram for explaining a sheet lens according to an embodiment of the present invention.

[0063] Fig.18 is a schematic top view of a sheet lens according to an embodiment of the present invention.

[0064] Fig.19 1 is a conceptual diagram for explaining a method for measuring the electromagnetic wave focusing capability of a sheet lens according to an embodiment of the present invention.

[0065] Fig. 20 1 is a diagram showing the measurement results of the electromagnetic wave focusing capability of the sheet lens according to the example of the present invention.

[0066] Fig.21 1 is a diagram showing the measurement results of the electromagnetic wave focusing capability of the sheet lens according to the example of the present invention.

[0067] Fig. 22 This is a conceptual diagram for explaining a method for measuring the directivity improvement effect of a sheet lens according to an embodiment of the present invention.

[0068] Fig.23 The graphs show the measurement results of the directivity improvement effect of the sheet lens according to the example of the present invention. DETAILED DESCRIPTION

[0069] Hereinafter, the super-surface structure of the present invention will be described in detail based on the preferred embodiments shown in the accompanying drawings.

[0070] In the present specification, a numerical range expressed using "to" means a range including the numerical values ​​described before and after "to" as the lower limit and the upper limit.

[0071] In this specification, “same” includes an error range generally allowed in the technical field.

[0072] The figures shown below are all conceptual figures for explaining the super surface structure of the present invention. Therefore, the positional relationship of the shape, size, thickness, and spacing of each component and the position in the in-plane direction in each layer may not be consistent with the actual.

[0073] Figure 1 An example of the supersurface structure of the present invention is conceptually shown in FIG.

[0074] Figure 1 The metasurface structure 10 shown in FIG. 1 includes a first substrate 12 , a second substrate 14 , a first structure layer 16 , a second structure layer 18 , a third structure layer 20 , a fourth structure layer 24 , and a dielectric layer 26 disposed between the first substrate 12 and the second substrate 14 .

[0075] in addition, Figure 1 This is a conceptual diagram showing a cross section obtained by cutting the super surface structure of the present invention orthogonally to the thickness direction, i.e., the stacking direction of the first structure layer 16 to the fourth structure layer 24, and cutting along the length direction of the first metal microstructure 16a to the fourth metal microstructure 24a described later. Figure 1 In order to clearly illustrate the structure of the super surface structure of the present invention, the hatching is omitted. Figure 2 to Figure 6 and Figure 10 to Figure 13 Same.

[0076] The first structural body layer 16 is a structural body layer formed using one surface (the upper surface in the figure) of the first substrate 12 , and is a structural body layer in which a plurality of first metal microstructures 16 a are arranged (arranged) on the surface of the first substrate 12 .

[0077] The second structural layer 18 is formed using the other surface (the lower surface in the figure) of the first substrate 12 , and is a structural layer in which a plurality of second metal microstructures 18 a are arranged (disposed) on the surface of the first substrate 12 .

[0078] The third structural body layer 20 is a structural body layer formed using one surface (the upper surface in the figure) of the second substrate 14 , and is a structural body layer in which a plurality of third metal microstructures 20 a are arranged (disposed) on the surface of the second substrate 14 .

[0079] The fourth structural layer 24 is a structural layer formed using the other surface (the lower surface in the figure) of the second substrate 14 , and is a structural layer in which a plurality of fourth metal microstructures 24 a are arranged (configured) on the surface of the second substrate 14 .

[0080] The first substrate 12 and the second substrate 14 are stacked and fixed with the dielectric layer 26 interposed therebetween so that the second structure layer 18 and the third structure layer 20 face each other.

[0081] Thus, in the supersurface structure 10 shown in the figure, the first structure layer 16 , the second structure layer 18 , the third structure layer 20 , and the fourth structure layer 24 are stacked at intervals.

[0082] In addition, as long as the supersurface structure of the present invention has the first to fourth structural body layers, it may have five or more structural body layers as shown in Example 7 described later.

[0083] The following description also applies to the supersurface structure of the present invention having five or more structural body layers.

[0084] The metasurface structure 10 of the present invention is a metasurface structure that acts on electromagnetic waves with a frequency of 10 THz or less, that is, acts on electromagnetic waves with a wavelength of 30 μm or more.

[0085] Specifically, a metasurface structure that acts on electromagnetic waves with a frequency below 10 THz means that when an electromagnetic wave with a certain frequency below 10 THz is incident, it functions as a high refractive index body for the electromagnetic wave. In other words, it means that it functions as a structure that can obtain a high diffraction angle.

[0086] In addition, the frequency of the electromagnetic wave on which the metasurface structure 10 of the present invention plays a role has no lower limit, but it is preferred that the metasurface structure 10 of the present invention is a metasurface structure that acts on a frequency of more than 10 GHz, that is, acts on an electromagnetic wave with a wavelength of less than 30 mm. More preferably, the metasurface structure 10 of the present invention is a metasurface structure that acts on a frequency of more than 100 GHz, that is, acts on an electromagnetic wave with a wavelength of less than 3 mm.

[0087] That is, the metasurface structure 10 of the present invention is preferably a metasurface structure that acts on electromagnetic waves with a frequency of 10 GHz to 10 THz, so-called terahertz waves (THz waves).

[0088] The metasurface structure of the present invention can be an electromagnetic wave with a gathering frequency below 10 THz, an electromagnetic wave with a diffusion frequency below 10 THz, or an electromagnetic wave with a refraction frequency below 10 THz in one direction.

[0089] As described above, the metasurface structure 10 is a structure formed by stacking a first substrate 12 having a first structure layer 16 on one surface and a second structure layer 18 on the other surface and a second substrate 14 having a third structure layer 20 on one surface and a fourth structure layer 24 on the other surface, with a dielectric layer 26 interposed therebetween.

[0090] In the metasurface structure 10 , both the first substrate 12 and the second substrate 14 are substrates formed of dielectrics.

[0091] That is, in the illustrated metasurface structure 10 , the first substrate 12 functions as a dielectric layer disposed between the first structure layer 16 and the second structure layer 18 , and the second substrate 14 functions as a dielectric layer disposed between the third structure layer 20 and the fourth structure layer 24 .

[0092] Furthermore, the dielectric layer 26 is a dielectric layer provided between the second structural body layer 18 and the third structural body layer 20 .

[0093] In addition, the supersurface structure 10 shown in the figure is not limited to a structure formed by providing metal microstructures on both surfaces of a substrate and stacking two substrates at intervals, thereby stacking the first to fourth structure layers at intervals.

[0094] For example, the supersurface structure of the present invention can be a structure formed as follows: by using four substrates including a substrate having a first structure layer provided on one surface, a substrate having a second structure layer provided on one surface, a substrate having a third structure layer provided on one surface, and a substrate having a fourth structure layer provided on one surface, and stacking the four substrates so that the structure layers are opposite to the substrates, and stacking the first structure layer to the fourth structure layer with intervals between them.

[0095] Alternatively, the supersurface structure of the present invention can be a structure formed as follows: by using three substrates, namely, a substrate having a first structure layer on one surface and a second structure layer on another surface, a substrate having a third structure layer on one surface, and a substrate having a fourth structure layer on one surface, and stacking the three substrates so that the structure layers are opposite to the substrates, and stacking the first to fourth structure layers with intervals between each other.

[0096] Alternatively, the metasurface structure of the present invention may be a structure formed as follows: a substrate is formed by coating a coating liquid containing a composition of a dielectric forming a substrate or a precursor thereof on a surface of a substrate having a first structural layer provided on one surface thereof, a second structural layer is provided on the formed substrate, and this operation is repeated, thereby stacking the first to fourth structural layers at intervals from each other.

[0097] The first substrate 12, the second substrate 14, and the dielectric layer 26 are not limited, and any sheet-like material (film, plate, layer) made of a dielectric material can be used as long as the dielectric material can transmit the target electromagnetic wave.

[0098] As an example, as the first substrate 12 and the second substrate 14 and the dielectric layer 26, as an example, there can be exemplified metal substrates having an oxide insulating layer such as a silicon substrate having silicon oxide, substrates formed of oxides such as silicon oxide, polyacrylic resin films such as polymethyl methacrylate, cellulose resin films such as cellulose triacetate, cycloolefin polymer films (for example, trade name "ARTON", manufactured by JSR Corporation, trade name "ZEONOR", manufactured by Zeon Corporation), resin films such as polyethylene terephthalate (PET) films, polycarbonate films, polyvinyl chloride films, polyimide (PI) films and polytetrafluoroethylene (PTFE) films, and glass plates, etc.

[0099] Among them, preferably, a cycloolefin polymer (COP) film, a cycloolefin copolymer (COC) film, a PTFE film, and the like can be exemplified.

[0100] Furthermore, the first substrate 12 and the second substrate 14 are generally formed of the same material, but may be formed of different materials.

[0101] Furthermore, the material forming the first substrate 12 and / or the second substrate 14 and the material forming the dielectric layer 26 may be the same as or different from each other.

[0102] There is no limitation on the thickness of the first substrate 12 and the second substrate 14. The thickness can be appropriately set according to the forming material, etc., so that the thickness can fully function as a dielectric and can support the first metal microstructure 16a and the second metal microstructure 18a, as well as the third metal microstructure 20a and the fourth metal microstructure 24a described later.

[0103] The thickness of the first substrate 12 and the second substrate 14 is preferably 0.001 to 1 times, more preferably 0.01 to 0.1 times, of the wavelength of the electromagnetic wave of the frequency with the highest transmittance of the metasurface structure 10. That is, the thickness of the first substrate 12 and the second substrate 14 is preferably 30 nm to 30 mm, more preferably 0.3 μm to 3 mm, further preferably 1 to 400 μm, and particularly preferably 10 to 100 μm.

[0104] By setting the thickness of the first substrate 12 and the second substrate 14 to 0.001 to 1 times the wavelength of the electromagnetic wave of the frequency with the highest transmittance of the metasurface structure 10, that is, to 30nm to 30mm, the electric resonance and magnetic resonance described later can be appropriately generated, and the phase difference of the transmitted wave with respect to the incident wave can be further increased, that is, the phase is greatly delayed to obtain a high refractive index, and it is preferred in terms of improving the transmittance of the electromagnetic wave, etc.

[0105] Furthermore, the first substrate 12 and the second substrate 14 generally have the same thickness, but may have different thicknesses.

[0106] Furthermore, the thickness of the dielectric layer 26 is not limited either, and may be appropriately set to a thickness that allows the dielectric layer 26 to function sufficiently according to the material used to form the dielectric layer 26 and the like.

[0107] The thickness of the dielectric layer 26 is preferably 0.001 to 1 times, more preferably 0.01 to 0.1 times, the wavelength of the electromagnetic wave of the frequency with the highest transmittance of the metasurface structure 10. That is, the thickness of the dielectric layer 26 is preferably 30 nm to 30 mm, more preferably 0.3 μm to 3 mm, further preferably 1 to 1000 μm, and particularly preferably 20 to 500 μm.

[0108] By setting the thickness of the dielectric layer 26 to 0.001 to 1 times the wavelength of the electromagnetic wave of the frequency with the highest transmittance of the metasurface structure 10, that is, to 30nm to 30mm, the electric resonance and magnetic resonance described later can be appropriately generated, the phase difference of the transmitted wave with respect to the incident wave can be further increased, and the transmittance of the electromagnetic wave can be improved, which is preferred.

[0109] The thickness is the same even when an air layer described later is provided instead of the dielectric layer 26 .

[0110] in addition, Figure 1 In the metasurface structure 10 shown in FIG. 1 , the second structure layer 18 and the third structure layer 20 are spaced apart by providing a dielectric layer 26 between the first substrate 12 and the second substrate 14 . However, the present invention is not limited thereto, and various structures can be used.

[0111] As an example, Figure 2As conceptually shown in FIG. 2 , a dielectric layer 26a can be partially provided between the first substrate 12 and the second substrate 14, and the dielectric layer 26a can be used as a spacer to separate the second structural body layer 18 from the third structural body layer 20. That is, in this example, an air layer is provided between the second structural body layer 18 and the third structural body layer 20 instead of the dielectric layer 26a.

[0112] And, if Figure 3 As conceptually shown in the figure, a column 30 formed of a dielectric such as a resin film can be erected between the first substrate 12 and the second substrate 14 in a manner avoiding the third metal microstructure 20a and the fourth metal microstructure 24a, and the column 30 can be used as a spacer to separate the second structure layer 18 from the third structure layer 20.

[0113] Although described later, in the example shown in the figure, the first to fourth metal microstructures 16a to 24a are all metal cutting lines, and Figure 1 ( Figure 2 ) in the lateral direction, and arranged so that the longitudinal direction is consistent. That is, Figure 3 This is a conceptual illustration of the super surface structure of the present invention from Figure 1 The orthogonal direction is Figure 1 A cross-sectional view obtained by cutting horizontally.

[0114] In addition, if Figure 4 As conceptually shown in FIG. 1 , the second structural body layer 18 and the third structural body layer 20 can be spaced apart by appropriately providing a spacer 32 .

[0115] Furthermore, as the spacer, for example, a rectangular frame can also be used. In this case, a beam or the like can be provided inside the frame in a cross shape, for example.

[0116] These spacers may be formed of a dielectric such as an ultraviolet curable resin.

[0117] The above-described method of separating the second structural body layer 18 and the third structural body layer 20 can also be used to separate the first structural body layer 16 and the second structural body layer 18 and to separate the third structural body layer 20 and the fourth structural body layer 24 .

[0118] As described above, in the metasurface structure 10, the first structural body layer 16 is a structural body layer formed by arranging a plurality of first metal microstructures 16a at intervals on one surface (upper surface in the figure) of the first substrate 12. The first structural body layer 16 is basically composed of an arrangement of unit cells formed by one first metal microstructure 16a and the space around the first metal microstructure 16a.

[0119] The second structural body layer 18 is a structural body layer formed by arranging a plurality of second metal microstructures 18a at intervals on the other surface (the lower surface in the figure) of the first substrate 12. The second structural body layer 18 is basically composed of an arrangement of unit cells formed by one second metal microstructure 18a and the space around the second metal microstructure 18a.

[0120] The third structural body layer 20 is a structural body layer formed by arranging a plurality of third metal microstructures 20a at intervals on one surface (the upper surface in the figure) of the second substrate 14. The third structural body layer 20 is basically composed of an arrangement of unit cells formed by one third metal microstructure 20a and the space around the third metal microstructure 20a.

[0121] The fourth structural body layer 24 is a structural body layer formed by arranging a plurality of fourth metal microstructures 24a at intervals on the other surface (the lower surface in the figure) of the second substrate 14. The fourth structural body layer 24 is basically composed of an arrangement of unit cells formed by one fourth metal microstructure 24a and the space around the fourth metal microstructure 24a.

[0122] As described above, in the supersurface structure 10 of the present invention, the first structure layer 16 to the fourth structure layer 24 all use the surface of the corresponding substrate, and the basic structure of the first metal microstructure 16a to the fourth metal microstructure 24a arranged on the surface is the same.

[0123] Therefore, in the following description, when there is no need to distinguish the first to fourth structural body layers 16 to 24, they are collectively referred to as structural body layers. Similarly, when there is no need to distinguish the first to fourth metal microstructures 16a to 24a, they are collectively referred to as metal microstructures.

[0124] In the metasurface structure 10 of the present invention, the structure of the structure layer has the same structure as a general metasurface structure (metamaterial) in which microstructures (unit cells) are arranged on one surface of a substrate.

[0125] Therefore, there are no restrictions on the shape of the metal microstructures, the arrangement of the metal microstructures, the intervals (pitch) of the metal microstructures, and the like.

[0126] In the supersurface structure 10 of the present invention, the metal microstructure is made of metal.

[0127] As described above, the metasurface structure of the present invention acts on electromagnetic waves with a frequency of 10 THz or less. Metals have high conductivity and transmittance for electromagnetic waves with a frequency of 10 THz or less.

[0128] Therefore, the metasurface structure 10 of the present invention can effectively refract electromagnetic waves having a frequency of 10 THz or less by using a metal microstructure.

[0129] The material for forming the metal microstructure is not limited as long as it is a metal, and various metals can be used.

[0130] As an example, copper, gold, silver, aluminum, platinum, palladium, etc. can be illustrated.

[0131] Among them, copper, gold, silver, and the like having high electrical conductivity are preferably used.

[0132] Likewise, the shape of the metal microstructure constituting the structure layer is not limited, and various shapes used as microstructures (resonators) in known metasurface structures can be used.

[0133] As an example, there can be illustrated metal cutting wires, cross-shaped and hook-cross-shaped metal cutting wires, rectangular, cylindrical and square plates, a solid with a V-shaped bottom surface such as a rectangular solid connected at the end as shown in Japanese Patent Gazette No. 2018-46395, a solid with a roughly H-shaped bottom surface such as H-steel, and a solid with a roughly C-shaped bottom surface such as a C channel, etc.

[0134] Furthermore, as shown in Japanese Patent Application Laid-Open No. 2018-46395, a solid having a V-shaped bottom surface and a solid having a cross-shaped bottom surface can utilize various shapes obtained by adjusting the angle formed by two rectangular parallelepipeds.

[0135] In addition, a solid having a bottom surface shape such as shown in Figure 5 of "Appl. Sci. 2018, 8(9), 1689; https: / / doi.org / 10.3390 / app8091689" can also be used.

[0136] Among them, it is preferable to use a metal cutting wire (rod-shaped metal wire).

[0137] There is no limitation on the shape of the metal cutting wire, and various columnar shapes such as quadrangular prism, triangular prism and cylindrical can be used. In a quadrangular prism, the cross section in the direction perpendicular to the length direction can be various shapes such as square, rectangle, parallelogram and trapezoid. Similarly, in a triangular prism, various shapes such as equilateral triangle and isosceles triangle can be used, and in a cylindrical shape, not only a circle but also an ellipse can be used.

[0138] In one structural body layer, only one type of metal microstructure may be used, or multiple types may be used simultaneously. Furthermore, in one structural body layer, metal microstructures of the same type but different sizes may be used simultaneously. As an example, when the metal microstructure is a metal cutting wire, multiple types of metal cutting wires having different lengths, widths, and thicknesses may be used simultaneously in one structural body layer.

[0139] Furthermore, the metal microstructures included in each structural body layer may be the same as or different from each other.

[0140] Here, it is preferred that at least one of the first structural body layer 16 , the second structural body layer 18 , the third structural body layer 20 , and the fourth structural body layer 24 has at least one metal cutting line as a metal microstructure.

[0141] Furthermore, it is more preferable that all the structural layers have at least one metal cutting line as the metal microstructure.

[0142] By using a metal cutting wire as a metal microstructure, it is more preferable to simultaneously produce an increase in the effective dielectric constant caused by the electric resonance described later and an increase in the effective magnetic permeability caused by the magnetic resonance. As a result, for electromagnetic waves with a frequency of 10 THz or less, the phase difference of the transmitted wave relative to the incident wave is increased by increasing the effective refractive index represented by the square root of the product of the effective dielectric constant and the effective magnetic permeability. In addition, by matching the effective impedance represented by the square root of the ratio of the effective dielectric constant to the effective magnetic permeability with the surrounding medium, the reflection of the electromagnetic wave is suppressed, and the transmittance of the electromagnetic wave can be improved.

[0143] At least one of the structural body layers having metal cutting lines as the metal microstructures, preferably all of the metal microstructures, are metal cutting lines.

[0144] Furthermore, in the structural body layer having metal cutting lines as the metal microstructures, it is more preferable that all the metal microstructures are metal cutting lines.

[0145] In addition, in the ultra-surface structure of the present invention, it is further preferred that all metal microstructures are metal cutting wires.

[0146] It is preferable that at least one of the structural body layers having metal cutting lines as the metal microstructures has the same longitudinal direction of all the metal cutting lines in the in-plane direction.

[0147] Furthermore, in the structural body layer having metal cutting lines as the metal microstructures, it is more preferable that the longitudinal directions of all the metal cutting lines are in the same direction in the in-plane direction.

[0148] Furthermore, it is further preferred that the length directions of all metal cutting lines are in the same in-plane direction, and it is particularly preferred that all metal microstructures are metal cutting lines and the length directions of all metal cutting lines are in the same in-plane direction.

[0149] When metal wires are used as the metal microstructures, all metal wires may have the same length, or metal wires having different lengths may be mixed.

[0150] Furthermore, when metal wires are used as the metal microstructures, all the metal wires may have the same thickness, or metal wires having different thicknesses may be mixed.

[0151] In addition, regarding the metal cutting lines, all the metal cutting lines may have the same shape of upper and lower surfaces, or metal cutting lines having different shapes of upper and lower surfaces may exist in a mixed state.

[0152] In the metasurface structure 10 of the present invention, there is no restriction on the size of the metal microstructure, but like the usual metasurface structure (metamaterial), it is smaller than the wavelength of the target electromagnetic wave, preferably smaller than 1.0 times the wavelength, and more preferably smaller than 0.5 times the wavelength.

[0153] For example, when the metal microstructure is a metal cutting line, the length of the metal cutting line (length L described below) is preferably 0.1 to 1.0 times the wavelength of the electromagnetic wave of the frequency with the highest transmittance of the metasurface structure 10, and more preferably 0.25 to 0.5 times.

[0154] By having such a structure, it is possible to efficiently perform phase modulation of the transmitted wave utilizing the resonance caused by the metal microstructure, and it is more preferable to simultaneously generate the electric resonance and magnetic resonance described later to increase the phase difference of the transmitted wave relative to the incident wave, and it is also possible to improve the transmittance of the electromagnetic wave, etc.

[0155] The length of the metal cutting line is the same for other metal microstructures. In these metal microstructures, the length along the polarization direction of the incident wave (incident electromagnetic wave) can be replaced by the length of the metal cutting line.

[0156] Furthermore, there is no limitation on the thickness of the metal cutting wire, as long as the thickness that functions as a metasurface structure is appropriately set according to the forming material, etc. The thickness of the metal cutting wire is preferably thicker than 1 / 4 of the epidermis thickness determined by the wavelength, magnetic permeability and electrical conductivity of the electromagnetic wave. That is, for a typical metal, the thickness of the metal cutting wire (unit [m]) is preferably greater than 1 / 20 million of the square root of the wavelength when the wavelength of the lowest frequency electromagnetic wave is expressed in mm, more preferably greater than 1 / 5 million, and further preferably greater than 1 / 2.5 million. Furthermore, the thickness of the metal cutting wire is preferably less than 1 / 4 of the wavelength of the highest frequency electromagnetic wave, more preferably less than 1 / 20, and further preferably less than 1 / 100.

[0157] In addition, the skin thickness δ can be represented by the following formula, where σ is the electrical conductivity, μ is the magnetic permeability, and ω is the angular frequency (ω=2πc / λ, where c is the speed of light and λ is the wavelength).

[0158] [Formula 1]

[0159]

[0160] As described above, the thickness refers to the dimension of the first structural body layer 16 to the fourth structural body layer 24 in the stacking direction.

[0161] The width of the metal cutting line (width W described later) is also not particularly limited, but is preferably about 0.01 to 1 times, more preferably about 0.05 to 0.2 times, the length of the metal cutting line.

[0162] In addition, in the above description, the electromagnetic wave of the lowest frequency (highest frequency) refers to the electromagnetic wave of the lowest frequency (highest frequency) that can obtain the target refractive property in the metasurface structure. For example, when the lower limit of the frequency of the electromagnetic wave on which the metasurface structure works is 10 GHz, the electromagnetic wave of the lowest frequency refers to an electromagnetic wave with a frequency of 10 GHz, i.e., a wavelength of 30 mm.

[0163] The actual metasurface structure is difficult to work well only within a limited frequency range (for example, the range of ±20% of the center frequency). If this is taken into account, the lowest frequency can also be said to be "the lower limit of the design frequency when designing a specific metasurface structure". For example, when the designed metasurface structure is a "terahertz lens" and a "millimeter wave lens", the lower limit frequency shown as the specification in which the lens can work becomes the "lowest frequency" electromagnetic wave.

[0164] exist Figure 1In the supersurface structure 10 shown in FIG, the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a and the fourth metal microstructure 24a are arranged to be offset from each other in the in-plane direction of the first substrate 12 and the second substrate 14.

[0165] In other words, when the metasurface structure 10 is observed from the normal direction of the substrate, the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a and the fourth metal microstructure 24a do not completely overlap.

[0166] In addition, the normal direction refers to the direction perpendicular to the main surface of the sheet-like object, which is the thickness direction in the supersurface structure 10, that is, the stacking direction of the structure layer, that is, the stacking direction of the first substrate 12, the dielectric layer 26 and the second substrate 14.

[0167] Furthermore, the main surface is the largest surface of the sheet-like object, usually two surfaces in the thickness direction.

[0168] The present invention is not limited to this. Figure 5 As conceptually shown in FIG. 1 , the first metal microstructure 16 a , the second metal microstructure 18 a , the third metal microstructure 20 a , and the fourth metal microstructure 24 a can be arranged to coincide with each other in the in-plane direction of the first substrate 12 and the second substrate 14 .

[0169] That is, when the super-surface structure of the present invention is observed from the normal direction of the substrate, the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a and the fourth metal microstructure 24a can be completely overlapped.

[0170] In the following description, the in-plane direction of the first substrate 12 and the second substrate 14 is also simply referred to as “in-plane direction”.

[0171] However, in the present invention, in at least one of the first metal microstructure 16a, the second metal microstructure 18a, the third metal microstructure 20a, and the fourth metal microstructure 24a, it is preferred that at least one metal microstructure is arranged offset in the in-plane direction relative to the metal microstructures of the other structural layers. In other words, in the present invention, it is preferred that in at least one of the first structural layer 16, the second structural layer 18, the third structural layer 20, and the fourth structural layer, the position of at least one metal microstructure in the in-plane direction is offset relative to the metal microstructures of the other structural layers.

[0172] That is, in the present invention, in at least one of the first structural layer 16, the second structural layer 18, the third structural layer 20 and the fourth structural layer, metal microstructures whose positions in the in-plane direction are offset from those of at least one other layer and metal microstructures whose positions in the in-plane direction are consistent with those of at least one other layer may be mixed.

[0173] In addition, in the present invention, the position of the metal microstructure in a structural body layer and the other structural body layer is offset in the in-plane direction, which means that a part of the metal microstructure exists in the same position in the in-plane direction, and the other part exists in a different position in the in-plane direction. In other words, in the present invention, the position of the metal microstructure in a structural body layer and the other structural body layer is offset in the in-plane direction, which means that when observed from the normal direction of the substrate, a part of the metal microstructure overlaps, but not all of it overlaps, and a part does not overlap.

[0174] Furthermore, in the present invention, the positions of the metal microstructures in one structural body layer and the other structural body layer are staggered in the in-plane direction, and also include the following case: although the positions of the ends in the in-plane direction are consistent, they do not completely overlap due to different sizes. For example, in the case where the metal microstructures are metal cutting lines, it also includes the following case: in one structural body layer and the other structural body layer, one end of the metal cutting line is consistent in the in-plane direction, but the other end is different depending on the length of the metal cutting line.

[0175] Furthermore, in the present invention, there is no limitation on the direction in which the metal microstructures in one structural layer and other structural layers are offset in the in-plane direction among the four structural layers, namely, the first structural layer 16, the second structural layer 18, the third structural layer 20 and the fourth structural layer.

[0176] For example, when one of the directions of arrangement of the two-dimensional metal microstructures is set to the x direction and the other direction is set to the y direction, the direction in which the metal microstructures in one structure layer are offset from those in other structure layers may be only in the x direction, only in the y direction, or in both the x direction and the y direction. In addition, in the arrangement of the two-dimensional metal microstructures, the x direction and the y direction may be orthogonal or non-orthogonal.

[0177] Furthermore, when the metal microstructure is a metal cutting line, the direction in which the position of the metal cutting line in a certain structure layer is offset from that in other structure layers may be only in the length direction, only in the width direction, or in both the length direction and the width direction.

[0178] The above points are also the same when the supersurface structure of the present invention has four or more structural layers.

[0179] The metasurface structure of the present invention can more preferably simultaneously produce an increase in the effective dielectric constant caused by the electric resonance described later and an increase in the effective magnetic permeability caused by the magnetic resonance. As a result, for electromagnetic waves with a frequency below 10 THz, the phase difference of the transmitted wave relative to the incident wave is increased by increasing the effective refractive index represented by the square root of the product of the effective dielectric constant and the effective magnetic permeability. In addition, the reflection of the electromagnetic wave is suppressed by matching the effective impedance represented by the square root of the ratio of the effective dielectric constant to the effective magnetic permeability with the surrounding medium, and the transmittance of the electromagnetic wave can also be improved.

[0180] In the super surface structure of the present invention, preferably, at least one of the first to fourth metal microstructures 16a to 24a is arranged offset in the in-plane direction relative to metal microstructures of other structure layers.

[0181] In particular, it is preferred that at least one of the second metal microstructure 18a and the third metal microstructure 20a is arranged to be offset in the in-plane direction. That is, it is preferred that at least one of the second structure layer 18 and the third structure layer 20 is arranged to be offset in the in-plane direction.

[0182] Furthermore, in the super surface structure of the present invention, it is preferred that more metal microstructures are arranged in a staggered manner in the in-plane direction relative to the metal microstructures of other structural layers among the first metal microstructure 16a to the fourth metal microstructure 24a. That is, it is more preferred that three or more of the first metal microstructure 16a to the fourth metal microstructure 24a are arranged in a staggered manner in the in-plane direction relative to the metal microstructures of other structural layers. In particular, Figure 1 As in the supersurface structure 10 shown in FIG. 1 , it is further preferred that all the metal microstructures are arranged so as to be offset in the in-plane direction relative to the metal microstructures of other structure layers.

[0183] In other words, in the present invention, it is more preferred that among three or more structural body layers, at least one metal microstructure of a certain structural body layer is arranged in an offset manner in the in-plane direction relative to the metal microstructures of other structural body layers. In particular, in the present invention, it is further preferred that among all four structural body layers, at least one metal microstructure is arranged in an offset manner in the in-plane direction relative to the metal microstructures of other structural body layers.

[0184] In one structural body layer, all of the metal microstructures arranged to be shifted in the in-plane direction with respect to the metal microstructures of the other structural body layers may be metal microstructures, or only one may be a metal microstructure.

[0185] For example, in the case where the metasurface structure is a focusing lens, in a certain structural layer, in the central area (near the optical axis) where the phase difference of the transmitted wave with respect to the incident wave needs to be increased, the metal microstructure can be staggered in the in-plane direction relative to the metal microstructures of other structural layers, and in the peripheral part, the metal microstructure can be arranged in the same in-plane direction as the metal microstructures of other structural layers.

[0186] The misalignment amount between the metal microstructure and the metal microstructure of another structure layer in the in-plane direction may be uniform, or may have regions with different misalignment amounts.

[0187] For example, when the metasurface structure is a focusing lens, it can have the following area: in the central area (near the optical axis) where the phase difference of the electromagnetic wave relative to the incident wave needs to be increased, the offset between the metal microstructure and the metal microstructure of other structural layers in the in-plane direction is increased, and the offset decreases continuously or in stages toward the periphery.

[0188] The amount of misalignment of the metal microstructures in the in-plane direction may be the same or different in the combination of two structure layers.

[0189] As an example, the misalignment amount of the metal microstructures in the first structure layer 16 and the second structure layer 18 and the misalignment amount of the metal microstructures in the second structure layer 18 and the third structure layer 20 may be the same or different.

[0190] The amount of misalignment of the metal microstructure in the in-plane direction is not limited and may be appropriately set according to the application and required performance of the metasurface structure.

[0191] As an example, the case where the metal microstructures are metal cutting lines and the length directions of all the metal microstructures are consistent in the in-plane direction is described. In addition, the following dimensions, except for the thickness of the dielectric layer 26, are the dimensions in the length direction of the metal cutting lines.

[0192] like Figure 6 As conceptually shown in FIG. 1 , the length of the metal microstructure is represented by L, the interval between the metal microstructures is represented by g, and the total of the length L and the interval g, which is the arrangement period of the metal microstructures, is represented by c.

[0193] In this example, the length L of the metal microstructure, the spacing g of the metal microstructure and the arrangement period c of the metal microstructure are made uniform in all structure layers, and the offset amount between the first metal microstructure 16a and the second metal microstructure 18a and the offset amount between the third metal microstructure 20a and the fourth metal microstructure 24a are set to a.

[0194] The amount of misalignment between the second metal microstructure 18a and the third metal microstructure 20a is represented by b.

[0195] In addition, the thickness of the dielectric layer 26 (the distance between the first substrate 12 and the second substrate 14 ) is denoted by d.

[0196] At this time, the metasurface structure of the present invention preferably has a staggered amount b and an arrangement period c that satisfy the following:

[0197] |b / c|<0.25.

[0198] Therefore, the metasurface structure of the present invention is preferred in that, for electromagnetic waves with a frequency of 10 THz or less, the phase difference of the transmitted wave with respect to the incident wave is increased, and further, the transmittance of the electromagnetic wave can be improved.

[0199] In addition, the metasurface structure of the present invention preferably has a staggered amount a, a staggered amount b, an arrangement period c and a thickness d that satisfy the following:

[0200] ([a / c]-0.5) 2 / (f(d) / c) 2 +(b / c) 2 / (0.25) 2 <1

[0201] Where, f(d) = 1.167 × 10 -4 d 2 +5.500×10 -3 d+0.093.

[0202] Therefore, the metasurface structure of the present invention is preferred in that, for electromagnetic waves with a frequency of 10 THz or less, the phase difference of the transmitted wave with respect to the incident wave is increased, and further, the transmittance of the electromagnetic wave can be improved.

[0203] As described above, the metasurface structure of the present invention is a metasurface structure which is formed by stacking a first structure layer comprising a first metal microstructure arranged in an in-plane direction, a second structure layer comprising a second metal microstructure arranged in an in-plane direction, a third structure layer comprising a third metal microstructure arranged in an in-plane direction, and a fourth structure layer comprising a fourth metal microstructure arranged in an in-plane direction at intervals from each other, and acts on electromagnetic waves with a frequency below 10 THz.

[0204] Figure 1 and Figure 5The super surface structure of the present invention shown in the above is composed of a first metal microstructure 16a having a plurality of first structural layers 16 arranged on one surface of a first substrate 12, a second metal microstructure 18a having a plurality of second structural layers 18 arranged on another surface of the first substrate 12, a third metal microstructure 20a having a plurality of third structural layers 20 arranged on one surface of a second substrate 14, and a fourth metal microstructure 24a having a plurality of fourth structural layers 24 arranged on another surface of the second substrate, and a dielectric layer 26 is sandwiched between the first substrate 12 and the second substrate 14 for stacking, thereby the four structural layers are stacked at intervals.

[0205] The metasurface structure of the present invention has 4 (or more) structural layers of metal microstructures, which can give a large phase difference to the incident electromagnetic waves with a frequency below 10 THz to achieve a high refractive index and a high electromagnetic wave transmittance.

[0206] As is known to all, a conventional metasurface structure is obtained by arranging microstructures smaller than the wavelength of the target electromagnetic wave on the surface of a substrate, arranging unit cells formed by a microstructure and the space around the microstructure, and imparting a phase difference to the transmitted electromagnetic wave through resonance caused by the microstructure, thereby refracting the electromagnetic wave according to the Huygens principle based on phase modulation.

[0207] Conventional metasurface structures cannot obtain a sufficient refractive index for terahertz waves. In contrast, as shown in Non-Patent Document 1, a metasurface structure in which microstructures are arranged on both surfaces of a substrate can obtain a large phase difference even in terahertz waves.

[0208] However, according to the research conducted by the present inventors, even the supersurface structure described in Non-Patent Document 1, in which microstructures are arranged on both surfaces of a substrate, can only obtain a phase difference of about 160° with respect to a terahertz wave, and a sufficient phase difference cannot necessarily be obtained.

[0209] In contrast, the metasurface structure of the present invention has four structural layers formed by arranging metal microstructures, and can provide a large phase difference to the transmitted terahertz wave, for example, a phase difference of 360° or more.

[0210] Below, reference Figure 5 Provide explanation.

[0211] If an electromagnetic wave with a frequency below 10 THz is incident on the metasurface structure of the present invention, electric resonance (electric resonance) caused by the metal microstructure is generated in the structural layer through the arrangement of unit cells in the same manner as a conventional metasurface structure, and a phase difference is given to the transmitted electromagnetic wave.

[0212] Here, if we focus on the first metal microstructure 16a on the far left in the figure, when an electromagnetic wave is incident, a portion with a high voltage is generated at both ends of the first metal microstructure 16a. Similarly, a portion with a high voltage is generated at both ends of the second metal microstructure 18a on the far left in the figure. This voltage will reverse positive / negative due to a change in phase, etc. when the electromagnetic wave passes through. For example, in the first metal microstructure 16a, the right side in the figure becomes positive, and the left side in the figure becomes negative, and in the second metal microstructure 18a, on the contrary, the right side in the figure becomes negative, and the left side in the figure becomes positive.

[0213] As a result, a clockwise loop current is generated between the first metal microstructure 16a and the second metal microstructure 18a. When the loop current flows, a magnetic field is generated according to the right-hand screw rule and the direction of the loop current. As a result, a state is achieved that is the same as a state in which a magnet exists, and magnetic resonance is generated in which the magnetic field in the direction orthogonal to the electric field becomes stronger.

[0214] Such electric resonance and magnetic resonance also occur in the third metal microstructure 20 a and the fourth metal microstructure 24 a on the second substrate 14 side.

[0215] In addition, in the super surface structure of the present invention formed by stacking 4 layers of structural body layers, the second metal microstructure 18a on the first substrate 12 side and the third metal microstructure 20a on the second substrate 14 side exist adjacent to each other. Therefore, such electric resonance and magnetic resonance are also generated in the second metal microstructure 18a on the first substrate 12 side and the third metal microstructure 20a on the second substrate 14 side. As a result, compared with the case where the first substrate and the second substrate exist independently, a larger electric resonance and magnetic resonance can be obtained. This effect can be more preferably obtained in the following case: the second metal microstructure 18a on the first substrate 12 side and the third metal microstructure 20a on the second substrate 14 side are preferably close to a distance of less than 1 times the wavelength of the electromagnetic wave, and more preferably close to a distance of less than 0.1 times the wavelength of the electromagnetic wave.

[0216] In order to increase the transmittance of electromagnetic waves such as terahertz waves, it is necessary to match the effective impedance of the metasurface structure with the surrounding medium, and therefore it is necessary to generate electric resonance and magnetic resonance at the same time.

[0217] In the super surface structure of the present invention formed by stacking 4 layers of structural body layers, as described above, electric resonance and magnetic resonance occur between each structural body layer, so electric resonance and magnetic resonance occur very evenly. As a result, according to the super surface structure of the present invention, a transmission wave with a large phase difference can be obtained for an electromagnetic wave (incident wave) with a frequency of less than 10THz, for example, a transmission wave with a phase difference of more than 360°, and in addition, a high transmittance of electromagnetic waves can be obtained.

[0218] Furthermore, since a metal microstructure having high electrical conductivity to electromagnetic waves having a frequency of 10 THz or less is used as the microstructure, such electric resonance and magnetic resonance occur with high efficiency.

[0219] In addition, it is preferred that at least one of the first to fourth metal microstructures 16a to 24a is arranged in a staggered manner in the plane relative to the metal microstructures of the other structure layers, thereby more preferably achieving the above-mentioned effects. In particular, Figure 1 As shown in the figure, among all the first to fourth metal microstructures 16a to 24a, at least one metal microstructure is arranged to be offset in the plane relative to the metal microstructures of other structure layers, thereby more preferably obtaining the above-mentioned effects.

[0220] Furthermore, the super surface structure of the present invention is a structure formed by stacking a structure layer of a metal microstructure on a substrate, so the thickness is much thinner than a common optical lens, etc. That is, the super surface structure of the present invention formed by stacking 4 layers of structure layers can all become a sheet-like element.

[0221] Therefore, the metasurface structure of the present invention can be used in various known elements such as convex lenses, concave lenses, transmission-type refraction plates that can change the propagation direction of electromagnetic waves to a desired direction, and deflection elements that bend electromagnetic waves.

[0222] How the metasurface structure of the present invention functions in electromagnetic waves with a frequency of 100 THz or less can be set by appropriately selecting the shape and forming material of the metal microstructures in each structural layer, the arrangement of the metal microstructures, and the spacing between the metal microstructures, and combining them. In other words, what kind of element the metasurface structure of the present invention functions as in electromagnetic waves with a frequency of 100 THz or less can be set by appropriately selecting the shape and forming material of the metal microstructures in each structural layer, the arrangement of the metal microstructures, and the spacing between the metal microstructures, and combining them.

[0223] That is, in the supersurface structure of the present invention, the metal microstructures used and the arrangement of the metal microstructures in each structure layer may be set by a known method so as to obtain the characteristics of the target supersurface structure.

[0224] For example, in the metasurface structure of the present invention, the metasurface structure can be used as a phase difference plate by regularly arranging the same unit cells in each structure layer.

[0225] Alternatively, in the metasurface structure of the present invention, the phase difference imparted to the electromagnetic wave transmitted in the plane of the structural layer can be adjusted by arranging unit cells with different characteristics in at least one structural layer, for example, a metasurface structure (element) having target characteristics such as a lens and a transmission-type refraction plate can be set. In other words, in the metasurface structure of the present invention, the distribution of the phase difference imparted to the electromagnetic wave transmitted in the plane of the structural layer can be set by arranging unit cells with different characteristics in at least one structural layer, and a metasurface structure with target characteristics can be set.

[0226] In an embodiment using unit cells having different characteristics, the same unit cells may be included in one structural layer.

[0227] In the super surface structure of the present invention using unit cells with different characteristics, the unit cells can be arranged in a manner that the characteristics are regularly changed, or in a manner that the characteristics are irregularly changed, or in a manner that the regions where the characteristics are regularly changed and the regions where the characteristics are irregularly changed are mixed. The change in the characteristics of the regular unit cells can be continuous or staged. The arrangement of the unit cells is also the same in the following units.

[0228] Furthermore, in the method of using unit cells with different characteristics, a plurality of unit cells with different characteristics can be used as one unit and the unit can be repeatedly arranged two-dimensionally to form a structural layer. In addition, in one unit, all unit cells can be different, or the same unit cells can be included in the unit.

[0229] In this way, in a structure in which a unit having a plurality of unit cells is repeatedly arranged, the unit constituting the structural body layer may be of one type.

[0230] Alternatively, in a structure in which a unit having a plurality of unit cells is repeatedly configured, a plurality of units including unit cells having different characteristics may also be used. In this case, the plurality of units may be regularly arranged to form a structural layer, the plurality of units may be irregularly arranged to form a structural layer, or the regular arrangement of units and the irregular arrangement of units may be used simultaneously to form a structural layer.

[0231] Furthermore, in a structure where the units are arranged to form a structural body layer, all structural body layers may be composed of the same units, or in one or more structural body layers, units different from those in other structural body layers may be used. In addition, even when all structural body layers are composed of the same units, the units (metal microstructures) constituting each structural body layer may be staggered in the in-plane direction from the units in other structural body layers.

[0232] Here, when different units are used in each structural layer, as described later, Fig.16 As conceptually shown in FIG. 1 , it is also possible to use a structure in which, in a plurality of structure layers, repeated units are aligned with the ends (one end or both ends) of the metal microstructure in the in-plane direction, and the metal microstructure is staggered in the in-plane direction inside the unit. This structure can be implemented by adjusting the length (size) of the metal structure and the amount of staggering in the in-plane direction.

[0233] By utilizing this structure, for example, it is possible to preferably cope with situations where it is desired to change the phase difference imparted to the transmitted electromagnetic wave from the center portion toward the peripheral portion. That is, in this structure, the ends of adjacent units in the structural layer in the in-plane direction are consistent with each other in each structural layer. In other words, in this structure, in the in-plane direction, each structural layer has a spacing of units that is consistent with other structural layers. Therefore, in this structure, regardless of the position (misalignment) of the metal microstructures in adjacent units in each structural layer, metal microstructures (unit cells) with different misalignments can be easily and independently configured in each unit. As a result, by utilizing this structure, it is possible to preferably cope with structures where it is desired to gradually change the characteristics imparted to the transmitted electromagnetic wave in one direction.

[0234] Furthermore, the characteristic of a unit cell refers to, specifically, the magnitude of a phase difference that the unit cell imparts to a transmitted electromagnetic wave.

[0235] The characteristics of the unit cell, that is, the magnitude of the phase difference that the unit cell imparts to the transmitted electromagnetic wave can be adjusted by selecting the dimensions of the metal microstructure such as the length, width and thickness of the metal cutting line, selecting the type of metal microstructure to be used, selecting the spacing between metal microstructures in adjacent unit cells, selecting the direction of the metal microstructure within the unit cell, and the material of the object between the metal microstructures and the presence or absence of gaps.

[0236] In addition, according to the metasurface structure of the present invention, as described above, it is possible to provide a larger phase difference than before to the transmitted electromagnetic waves, and the transmittance of the electromagnetic waves is also high.

[0237] As an example, if the metasurface structure is a sheet lens (convex lens), the arrangement density of the metal microstructure is reduced from the center to the periphery so that the phase difference given to the transmitted electromagnetic wave becomes smaller from the center to the periphery.

[0238] Alternatively, in the case where the metasurface structure is a transmission-type refraction plate, for example, the size of the metal microstructure is increased so that the phase difference imparted to the transmitted electromagnetic wave increases from one end toward the other end. Here, in the case where the transmission-type refraction plate is composed of the repetition of the above-mentioned units, for example, the size of the metal microstructure constituting the unit cell can be increased so that the phase difference imparted to the electromagnetic wave transmitted in the unit along the arrangement direction of the unit cell becomes larger. In the transmission-type refraction plate, the direction in which the phase difference imparted to the electromagnetic wave increases becomes the direction in which the electromagnetic wave is refracted.

[0239] In addition, in the above-mentioned sheet lens and transmission type refraction plate, the change of phase difference is not limited to linear, but can also be nonlinear. That is, in the sheet lens, as long as the phase difference given to the electromagnetic wave as a whole decreases from the center to the peripheral part, the reduction of the phase difference can be linear or nonlinear. And, in the transmission type polarizing plate, as long as the phase difference given to the electromagnetic wave as a whole increases toward the refraction direction of the electromagnetic wave, the increase of the phase difference can be linear or nonlinear. This is also the same in the above-mentioned unit.

[0240] As an example of these designs, commercially available simulation software is used to calculate the amplitude and phase of the electromagnetic wave that passes through the metal microstructure used, and the arrangement of the metal microstructure is set in a manner that achieves a distribution of the target phase difference (phase modulation amount (refractive index)).

[0241] exist Figure 7 and Figure 8 An example in which the metasurface structure of the present invention is used as a sheet-shaped condenser lens is conceptually shown.

[0242] In this example, Figure 7 The upper section is the first structural body layer 16, and the lower section is the second structural body layer 18. And, Figure 8 The upper stage is the third structural body layer 20 , and the lower stage is the fourth structural body layer 24 .

[0243] As described above, the metasurface structure is a sheet-shaped condenser lens, and therefore the arrangement of the metal microstructures is set so that the phase difference, that is, the phase modulation amount of the transmitted electromagnetic wave gradually decreases from the center toward the periphery.

[0244] And, to achieve this, Figure 7 and Figure 8In the focusing lens shown in FIG, at and near the center, the first to fourth metal microstructures 16a to 24a are shifted in the in-plane direction relative to the metal microstructures of other structural layers to obtain a larger phase difference in the transmitted electromagnetic wave.

[0245] Furthermore, in the central portion and the peripheral portion near the central portion, the amount of deviation of the metal microstructure is reduced so that the phase difference of the transmitted electromagnetic wave becomes smaller than the phase difference in the central portion.

[0246] Furthermore, by not providing a metal microstructure on the third structure layer 20 and the fourth structure layer 24, the phase difference of the electromagnetic wave passing through the peripheral portion of the metasurface structure, ie, the sheet lens, is further reduced.

[0247] The metasurface structure of the present invention has been described in detail above, but the present invention is not limited to the above examples, and various improvements or changes can be made without departing from the spirit of the present invention.

[0248] Example

[0249] Hereinafter, the features of the present invention will be described in more detail with reference to examples.

[0250] In addition, the embodiment shown below is an example showing an example of the present invention. Therefore, the present invention should not be interpreted as being limited to the specific examples shown below.

[0251] In the following examples and comparative examples, all the metal microstructures (metal cutting wires) were arranged so that their length directions were aligned.

[0252] And, if Fig. 9 As conceptually shown in FIG. 1 , in each structure layer, the metal microstructures are regularly arranged in a grid shape along two orthogonal directions in the in-plane direction. The length of the metal microstructure is set to L, the width of the metal microstructure is set to W, the interval between the metal microstructures in the length direction is set to g, and the interval between the metal microstructures in the width direction is set to y.

[0253] In addition, in Examples 1 to 8 and Comparative Example 1, when the supersurface structure has a plurality of structural body layers, the length L, width W, interval g, and interval y of the metal microstructure are set to be the same in all structural body layers. That is, in Examples 1 to 8 and Comparative Example 1, when the supersurface structure has a plurality of structural body layers, the same metal microstructures are arranged in the same manner in the in-plane direction in all structural body layers.

[0254] Furthermore, the offset amount between the first metal microstructure and the second metal microstructure and the offset amount between the third metal microstructure and the fourth metal microstructure are represented by a, and the offset amount between the second metal microstructure 18a and the third metal microstructure 20a is represented by b.

[0255] In addition, the distance between the first substrate 12 and the second substrate 14 is set to d (see above). Figure 6 ).

[0256] [Example 1]

[0257] Cycloolefin polymer films (thickness: 40 μm) were prepared as the first substrate and the second substrate.

[0258] The first substrate was cut into a size of 10×10 cm, and the surface was ultrasonically cleaned (45 kHz). Then, the cut first substrate was placed inside the sputtering device. After the inside of the device was depressurized, argon gas (0.27 Pa) was introduced, and sputtering was performed using copper as a target. The sputtering was performed on each surface of the first substrate in turn, and a copper layer with a thickness of 100 nm was formed on both surfaces of the first substrate.

[0259] The photosensitive transfer member (negative transfer material 1) described in Japanese Patent Gazette No. 2020-204757 was cut into a size of 9×9 cm, and the covering film was peeled off from the photosensitive transfer material. The first substrate and the photosensitive transfer material were laminated so that the surface of the photosensitive resin layer exposed by peeling off the covering film was in contact with the copper layer. The photosensitive transfer material was laminated on both surfaces of the first substrate one by one, and a laminate was obtained. The lamination was performed under the conditions of a roller temperature of 100°C, a linear pressure of 1.0 MPa, and a linear speed of 4.0 m / min.

[0260] Next, a photomask having a pattern complementary to the metal microstructure (metal cut line) was stacked on the pseudo support side of the photosensitive transfer material on both sides of the obtained laminate. Then, 100 mJ / cm 2 The photosensitive resin layer of the photosensitive transfer material was exposed using an ultra-high pressure mercury lamp (manufactured by Japan Science Engineering Co., Ltd., MAP-1200L, exposure main wavelength: 365 nm).

[0261] The patterns of the photomask are different on both surfaces of the first substrate, with one surface being designed to correspond to the arrangement of the metal microstructures in the first structural layer described later, and the other surface being designed to correspond to the pattern of the second structural layer described later.

[0262] The dummy supports of the photosensitive transfer material on both sides were peeled off from the exposed laminated body. Then, the laminated body was shower developed for 30 seconds using a 1.0% sodium carbonate aqueous solution at a liquid temperature of 25° C., thereby forming a resist pattern on the copper layers on both sides.

[0263] Next, the copper layer of the obtained laminate was etched for 30 seconds using a copper etching solution (Cu-02 manufactured by KANTO CHEMICAL CO., INC.) at 23° C. Furthermore, the resist pattern was peeled off using propylene glycol monomethyl ether acetate.

[0264] As described above, on one surface of the first substrate, the first metal microstructure (metal cutting line) having a length L of 0.36 mm and a width W of 0.05 mm is formed, and arranged in a grid shape with a spacing g of 0.03 mm in the length direction and a spacing y of 0.09 mm in the width direction (reference Fig. 9 ) is a first structural body layer. In addition, as described above, the thickness of the copper layer is 100 nm, so the thickness of the first metal microstructure is 100 nm.

[0265] Furthermore, a second structure layer in which second metal microstructures were arranged in the same manner was formed on the other surface of the first substrate. The second structure layer was formed so that the offset amount a between the first metal microstructures and the second metal microstructures was 0.11 mm.

[0266] Furthermore, the third structural body layer and the fourth structural body layer were formed on the second substrate in exactly the same manner as the first structural body layer and the second structural body layer.

[0267] A cycloolefin polymer film with a thickness of 40 μm (d=0.04 mm) is bonded to the second structural layer formed on the first substrate as a dielectric layer. In addition, the third structural layer formed on the second substrate is bonded in such a way that the offset b between the second metal microstructure 18a and the third metal microstructure 20a becomes 0.07 mm, and the end portions are fixed.

[0268] Thus, the Figure 1 The supersurface structure having four structural body layers, namely, the first structural body layer to the fourth structural body layer, is shown in FIG.

[0269] [Example 2]

[0270] A first substrate and a second substrate formed of the same cycloolefin polymer film as in Example 1 were prepared.

[0271] In the same manner as in Example 1, a copper layer with a thickness of 100 nm was formed on both surfaces of the first substrate.

[0272] Then, the sample was immersed in an acid degreasing agent (ATS PURE CLEAN N3 manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD.) at a liquid temperature of 45° C. for 5 minutes to perform an acid degreasing treatment. Furthermore, the sample was immersed in 10% sulfuric acid at room temperature for 3 minutes to perform an acid activation treatment.

[0273] Next, the photosensitive transfer member (negative transfer material 1) described in Japanese Patent Publication No. 2020-204757 was cut into a size of 10×10 cm, and the cover film was peeled off from the photosensitive transfer material. The first substrate and the photosensitive transfer member were bonded so that the surface of the photosensitive resin layer exposed by peeling off the cover film was in contact with the copper layer. In addition, bonding was performed only on one side of the copper layer.

[0274] Next, the obtained laminate was immersed in a copper sulfate plating solution (manufactured by OKUNO CHEMICAL INDUSTRIES CO., LTD., TOPRUCINA SF) and the plating temperature was set at 1 A / dm 2 The copper plating treatment was performed under the condition of . The copper-plated laminate was washed with water and dried, and then immersed in a 1 mass % potassium hydroxide aqueous solution (pH=13.5) at 50°C.

[0275] Next, after the dummy support of the photosensitive transfer member was peeled off, the photosensitive resin layer was peeled off using propylene glycol monomethyl ether acetate to obtain a first substrate having a copper layer thickened to 500 nm on one side (non-attached side of the photosensitive transfer member).

[0276] The other surface of the first substrate was also subjected to the same copper plating treatment, thereby obtaining a first substrate having a copper layer with a thickness of 500 nm on both surfaces.

[0277] In the same manner as in Example 1, a first structural body layer was formed on one surface of the first substrate having a copper layer with a thickness of 500 nm on both surfaces, and a second structural body layer was formed on the other surface.

[0278] Furthermore, the third structural body layer and the fourth structural body layer were formed on the second substrate in exactly the same manner as the first structural body layer and the second structural body layer.

[0279] That is, in this example, the arrangement pattern of the metal microstructures in each structure layer is the same as that in Example 1, but the thickness of the metal microstructures (metal cutting lines) is 100 nm in Example 1 and 500 nm in this example (Example 2).

[0280] [Example 3]

[0281] A supersurface structure was produced in the same manner as in Example 2 except that the thickness of the cycloolefin polymer film serving as the dielectric layer was changed to 460 μm (d=0.46 mm).

[0282] [Example 4]

[0283] The length L of the metal microstructure is changed to 0.41 mm, the interval g is changed to 0.06 mm, and the offset a between the first metal microstructure and the second metal microstructure and between the third metal microstructure and the fourth metal microstructure is changed to 0.22 mm. Except for this, the first structure layer to the fourth structure layer are formed in the same manner as in Example 2.

[0284] Then, a through hole having a size of 20×20 mm was cut out at the center of the cycloolefin polymer film (thickness 20 μm (d=0.02 mm)) to form a through hole.

[0285] The first substrate and the second substrate were laminated so that the second metal microstructure and the third metal microstructure were opposite to each other with the cycloolefin polymer film sandwiched therebetween. Therefore, in this example, an air layer was formed between the second structure layer and the third structure layer. In addition, the lamination was performed so that the offset amount b between the second metal microstructure and the third metal microstructure was 0.23 mm.

[0286] Thus, the Figure 2 The supersurface structure having four structural body layers, namely, the first structural body layer to the fourth structural body layer, is shown in FIG.

[0287] [Example 5]

[0288] The length L of the metal microstructure is changed to 0.4 mm, the interval g is changed to 0.02 mm, and the offset a between the first metal microstructure and the second metal microstructure and between the third metal microstructure and the fourth metal microstructure is changed to 0.28 mm. Except for this, the first structure layer to the fourth structure layer are formed in the same manner as in Example 2.

[0289] Then, a through hole was formed by cutting out a hole having a size of 20×20 mm at the center of the cycloolefin polymer film. In this example, the thickness of the cycloolefin polymer film was set to 100 μm (d=0.1 mm).

[0290] The first substrate and the second substrate were stacked so that the second metal microstructure and the third metal microstructure were opposite to each other with the cycloolefin polymer film sandwiched therebetween. Therefore, in this example, an air layer was formed between the second structure layer and the third structure layer. In addition, the stacking was performed so that the offset amount b between the second metal microstructure and the third metal microstructure was 0 mm.

[0291] Thus, the Fig.10 A supersurface structure having four structural body layers, namely, a first structural body layer to a fourth structural body layer, is conceptually shown.

[0292] [Example 6]

[0293] A supersurface structure was produced in the same manner as in Example 5, except that the thickness of the cycloolefin polymer film provided between the first substrate and the second substrate was changed to 600 μm (d=0.6 mm).

[0294] [Example 7]

[0295] The first structure layer and the second structure layer were formed in the same manner as in Example 2, except that the length L of the metal microstructure was changed to 0.28 mm, the interval g was changed to 0.01 mm, and the offset a between the first metal microstructure and the second metal microstructure was changed to 0 mm.

[0296] Furthermore, on the second substrate, a third structural body layer and a fourth structural body layer were formed in the same manner as the first structural body layer and the second structural body layer.

[0297] Furthermore, the same third substrate was prepared, and the fifth and sixth structural body layers were formed on the third substrate in the same manner as the first and second structural body layers.

[0298] A cycloolefin polymer film with a thickness of 40 μm (d=0.04 mm) is bonded to the second structural layer formed on the first substrate as a dielectric layer. In addition, the third structural layer formed on the second substrate is bonded in such a way that the offset b between the second metal microstructure 18a and the third metal microstructure 20a becomes 0 mm, and the end portions are fixed.

[0299] In addition, a cycloolefin polymer film with a thickness of 40 μm (d=0.04 mm) is bonded to the fourth structural layer formed on the second substrate as a dielectric layer, and the fifth structural layer formed on the third substrate is bonded in such a way that the offset b between the third metal microstructure and the metal microstructure of the third substrate becomes 0 mm, and the end portions are fixed.

[0300] Thus, the Fig.11 A supersurface structure having six structural body layers, namely, a first structural body layer to a sixth structural body layer, is conceptually shown.

[0301] [Example 8]

[0302] On one surface of the first substrate, in the same manner as in the second embodiment, a first structural body layer was formed.

[0303] Furthermore, on one surface of the second substrate, a fourth structural body layer was formed in the same manner as in the second embodiment.

[0304] In addition, a 40 μm thick cycloolefin polymer film was prepared as the third substrate, and a second structural body layer was formed on one surface in the same manner as in Example 2, and a third structural body layer was formed on the other surface in the same manner as in Example 2. The second structural body layer and the third structural body layer were formed so that the offset amount b between the second metal microstructure and the third metal microstructure was 0.07 mm.

[0305] The first substrate was laminated so that the surface on the side opposite to the first structural body layer was opposite to the second structural body layer of the third substrate, and the second substrate was laminated so that the surface on the side opposite to the fourth structural body layer was opposite to the third structural body layer of the third substrate to fix the end portion. However, the lamination was performed in such a manner that the offset amount a between the first metal microstructure and the second metal microstructure and the offset amount a between the third metal microstructure and the fourth metal microstructure was 0.11 mm.

[0306] Thus, the Fig.12 The supersurface structure having four structural body layers, namely, the first structural body layer to the fourth structural body layer, is conceptually shown in FIG.

[0307] [Comparative Example 1]

[0308] As a substrate, a cycloolefin polymer film having a thickness of 44 μm was prepared.

[0309] On one surface of the cycloolefin polymer film, a first metal microstructure (metal cutting line) having a length L of 0.1275 mm and a width W of 0.024 mm was formed in the same manner as in Example 2, and the first metal microstructure (metal cutting line) was arranged in a grid shape with a spacing g of 0.024 mm in the length direction and a spacing y of 0.22 mm in the width direction (reference Fig. 9 )'s first structural layer.

[0310] Furthermore, a second structure layer in which second metal microstructures identical to the first metal microstructures were arranged was formed on the other surface of the cycloolefin polymer film, wherein the offset amount a between the first metal microstructure and the second metal microstructure was set to 0 mm.

[0311] Thus, the Fig.13 A supersurface structure having two structural body layers, namely a first structural body layer and a second structural body layer, is conceptually shown.

[0312] [Comparative Example 2]

[0313] Used as Fig.14 An optical lens made of polytetrafluoroethylene is conceptually shown.

[0314] [evaluate]

[0315] The transmittance and transmission phase difference of electromagnetic waves with a frequency of 300 GHz (wavelength of 999 μm) were evaluated by numerical simulation of terahertz time-domain spectroscopy (THz-TDS).

[0316] In addition, regarding the phase difference, as an example, 360° is used as an evaluation standard, and the phase difference of the transmitted electromagnetic wave exceeding 360° is evaluated as A, and the phase difference of 360° or less is evaluated as B.

[0317] The transmittance was evaluated based on the transmittance when a phase delay of 370° was obtained compared to a vacuum. In the evaluation of the transmittance, as an example, the transmittance of 70% and 50% were used as the evaluation criteria, and the transmittance of 70% or more was evaluated as A, the transmittance of 50% or more and less than 70% was evaluated as B, and the transmittance of less than 50% was evaluated as C.

[0318] The results are shown in the following table. In addition, the thickness of the metasurface structure (optical lens) is also shown in the table.

[0319] [Table 1]

[0320]

[0321] The thickness of the metal microstructure (metal cutting line) was 100 nm in Example 1 and 500 nm in the other examples.

[0322] In Comparative Example 1, the phase difference was evaluated as B, and the phase difference (phase delay) was 360° or less, so the transmittance in this example could not be evaluated.

[0323] As shown in the above table, according to the metasurface structure of the present invention, a phase difference of more than 360° as a benchmark in this example can be given to the transmitted electromagnetic wave, and the transmittance of the electromagnetic wave is also high. In particular, according to the comparison between Examples 4 to 6 and Examples 2, 3 and 8, a more preferred transmittance can be obtained by providing a dielectric layer between the first substrate and the second substrate and separating the second structure layer from the third structure layer.

[0324] Furthermore, according to the comparison between Example 1 and Example 2, a more preferable transmittance can be obtained by setting the thickness of the metal cutting line to 500 nm or more.

[0325] In addition, the metasurface structure of the present invention is very thin compared to an optical lens having the same performance.

[0326] [Example 9]

[0327] A transmission-type refraction plate is manufactured using the metasurface structure of the present invention.

[0328] In the first to fourth structural body layers constituting the transmission-type refraction plate, the basic structure of each structural body layer is as follows.

[0329] like Fig.15 As conceptually shown in FIG. 1 , a rectangular section having a length (Y direction) of 0.400 mm and a width (X direction) of 0.140 mm is defined as a unit cell X. A unit in which eight unit cells X (unit cells X1 to X8) are arranged in the width direction (X direction) is defined as one unit.

[0330] In each unit cell X, the metal microstructure Z ( Z1 to Z8 ) is arranged at the center of the rectangular section in the X direction, and is arranged so that one end face of the metal microstructure is aligned with one end face of each unit cell X in the Y direction.

[0331] The metal microstructure Z1 is arranged in the unit cell X1, the metal microstructure Z2 is arranged in the unit cell X2, ..., the metal microstructure Z7 is arranged in the unit cell X7, and the metal microstructure Z8 is arranged in the unit cell X8. Metal cutting wires are used for the microstructures. The metal microstructures will be described later.

[0332] Each structural layer is formed by arranging the units composed of 8 unit cells X1 to X8 in a two-dimensional regular rectangular grid shape in the orthogonal X direction and Y direction. Therefore, in each structural layer, the unit cells X1 to X8 (metal microstructures Z1 to Z8) are repeatedly arranged in the X direction, and the same unit cells (metal microstructures Z) are arranged in the Y direction.

[0333] Change the photomask design so that Figure 6 , Fig. 9 and Fig.15 The length L and width W of the metal microstructures Z1 to Z8 shown in the figure, the spacing g in the length direction and the spacing y in the width direction between the metal microstructures, the offset a between the first metal microstructure and the second metal microstructure and the offset a between the third metal microstructure and the fourth metal microstructure, and the offset b between the second metal microstructure and the third metal microstructure respectively become the values ​​of the following Table 2.

[0334] In this way, using a photomask with a changed photomask design, in the same method as in Example 2, except that the first structural body layer is formed on one surface of the first substrate and the second structural body layer is formed on the other surface, and the third structural body layer is formed on one surface of the second substrate and the fourth structural body layer is formed on the other surface, thereby manufacturing a transmission type refraction plate 1 having four structural body layers of the first structural body layer to the fourth structural body layer.

[0335] Therefore, the thickness of all the metal microstructures is 100 nm.

[0336] As described above, in the manufactured metasurface structure, i.e., the transmission-type refraction plate, the first structure layer to the fourth structure layer are structures formed as follows: a unit in which eight unit cells X1 to X8 having metal microstructures Z1 to Z8 are arranged in the X direction, i.e., the width direction of the metal microstructure, is regarded as one unit, and the unit is regularly arranged in two dimensions in the X direction and the Y direction into a rectangular grid shape.

[0337] Regarding the transmission type refraction plate 1 formed by stacking the first to fourth structural body layers, the transmittance and transmission phase difference of electromagnetic waves with a frequency of 300 GHz (wavelength of 999 μm) were measured for the unit cells X1 to X8 constituting the units by numerical simulation simulating terahertz time domain spectroscopy (THz-TDS). In addition, the transmittance and transmission phase difference were measured in a state where four layers were stacked.

[0338] Furthermore, the transmission phase difference refers to, specifically, the phase difference given to the transmitted electromagnetic wave by the unit cell.

[0339] The results are collectively recorded in Table 2.

[0340] [Table 2]

[0341]

[0342] As a comparative example, a transmission type refraction plate formed only of the first substrate in Example 9, that is, a transmission type refraction plate having only two structure layers, the first structure layer and the second structure layer, was prepared, and the transmission phase difference was measured in the same manner.

[0343] As a result, in the comparative example, the phase difference of all the unit cells was smaller than the phase difference of Example 9.

[0344] [Example 10]

[0345] Change the photomask design so that Figure 6 , Fig. 9 and Fig.15The length L and width W of the metal microstructures Z1 to Z8 shown in the figure, the spacing g in the length direction and the spacing y in the width direction between the metal microstructures, the offset a between the first metal microstructure and the second metal microstructure, the offset a between the third metal microstructure and the fourth metal microstructure, and the offset b between the second metal microstructure and the third metal microstructure respectively become the values ​​of the following Table 3.

[0346] A transmission-type refraction plate 2 having four structural layers, namely, the first structural layer, the second structural layer, and the third structural layer were formed on one surface of the second substrate and the fourth structural layer were formed on the other surface, respectively, by the same method as in Example 9, i.e., Example 2, except that a photomask having a changed photomask design was used. Thus, a transmission-type refraction plate 2 having four structural layers, namely, the first structural layer, the fourth structural layer, and the second structural layer were formed on one surface of the second substrate and the fourth structural layer were formed on the other surface, was manufactured.

[0347] Regarding the transmission type refraction plate 2 formed by stacking the first to fourth structural body layers, the transmittance and transmission phase difference of electromagnetic waves with a frequency of 300 GHz (wavelength of 999 μm) were measured for the unit cells X1 to X8 constituting the units in the same manner as in Example 9. The results are collectively recorded in Table 3.

[0348] [Table 3]

[0349]

[0350] As a comparative example, a transmission type refraction plate formed only of the first substrate in Example 10, that is, a transmission type refraction plate having only two structure layers, the first structure layer and the second structure layer, was prepared, and the transmission phase difference was measured in the same manner.

[0351] As a result, in the comparative example, the phase difference of all the unit cells was smaller than the phase difference of Example 10.

[0352] [Measurement of refraction of electromagnetic waves]

[0353] The transmission and refraction waves of the produced transmission-type refraction plates 1 and 2 were measured by the following method.

[0354] The optical system was assembled by connecting a generator (terahertz generation module (TAS1120) manufactured by ADVANTEST CORPORATION) and a detector (terahertz detection module (TAS1230) manufactured by ADVANTEST CORPORATION) to the laser output port of a terahertz light sampling and analysis system (TAS7400TS manufactured by ADVANTEST CORPORATION).

[0355] In this optical system, a polarized wave parallel to the length direction of a metal microstructure (metal cutting line) is incident from the normal direction of a transmission-type refraction plate by a generator, and an electromagnetic wave refracted in the width direction of the metal microstructure is detected by a detector, and the intensity of the refracted wave is measured. In addition, the intensity of the transmitted wave measured by setting the generator and the detector in a transmission configuration with the transmission-type refraction plate removed is measured, and the intensity of the refracted wave relative to the intensity is taken as the diffraction efficiency.

[0356] As a result, at 300 GHz, the intensity measured by the transmissive refraction plate 1 at a position where the detector is tilted 63° relative to the incident wave is the maximum, and the diffraction efficiency is 45%. In addition, in the transmissive refraction plate 2, the intensity measured by the detector at a position where the detector is tilted 63° relative to the incident wave is the maximum, and the diffraction efficiency is 70%.

[0357] As described above, according to the transmission-type refraction plate formed of the metasurface structure of the present invention, it is shown that the incident electromagnetic wave is greatly refracted due to the large phase distribution formed by the four structural layers constituting the metasurface structure.

[0358] Furthermore, the transmission-type refraction plates of Examples 9 and 10 are metasurface structures having four structural layers, namely the first structural layer to the fourth structural layer, in which units each consisting of unit cells X1 to X8 having metal microstructures Z1 to Z8 are regularly arranged in a rectangular grid in two dimensions in the orthogonal X and Y directions.

[0359] As shown in Tables 2 and 3, in Examples 9 and 10, the phase difference of the unit cells in the unit increases from the unit cell X1 toward the unit cell X8. However, in Example 9, the phase difference of the unit cells in the unit increases linearly, that is, gradually, from the unit cell X1 toward the unit cell X8. In contrast, in Example 10, the phase difference of the unit cells in the unit has a portion where the phase difference decreases from the unit cell X1 toward the unit cell X8, that is, the change in the phase difference of the unit cell is nonlinear. According to the comparison between Example 9 and Example 10, in the transmission-type refraction plate composed of the metasurface structure, the diffraction efficiency of the nonlinearly changing phase difference of the unit cells constituting the unit is higher than that of the linearly changing phase difference.

[0360] [Example 11]

[0361] A sheet lens is produced using the metasurface structure of the present invention.

[0362] Similar to the above example, a sheet lens is produced by forming a first structural layer on one surface of a first substrate and a second structural layer on the other surface, forming a third structural layer on one surface of a second substrate and a fourth structural layer on the other surface, and combining the first substrate and the second substrate.

[0363] Each structural layer is constituted by arranging two types of units, namely, first units and second units.

[0364] like Fig.16 As conceptually shown in FIG. 1 , the first unit is composed of three metal microstructures in the Y direction (length direction), i.e., three unit cells, and two metal microstructures in the X direction (width direction), i.e., two unit cells (see FIG. 1 ). Fig.17 ) consists of a total of 6 unit cells.

[0365] On the other hand, Fig.17 As conceptually shown in FIG. 1 , the second unit is composed of two unit cells in total, namely, one unit cell which is one metal microstructure in the Y direction (length direction) and two unit cells which are two metal microstructures in the X direction (width direction).

[0366] In this example, all the metal microstructures are metal cutting lines, all of which have a width W of 0.054 mm and a thickness of 100 nm.

[0367] Furthermore, in this example, the intervals between adjacent metal microstructures in the width direction (X direction) were all set to 0.086 mm, the same as in the above example.

[0368] In this example, regardless of whether it is the first unit or the second unit, the intervals between the metal microstructures of adjacent units in the longitudinal direction (Y direction) are all set to 0.12 mm.

[0369] The above points are the same for all the metal microstructures and units provided in the first to fourth structure layers.

[0370] The first unit is composed of a first metal microstructure having a length of L1, a second metal microstructure having a length of L2 and disposed at a distance of 0.03 mm from the first metal microstructure, and a metal microstructure having a length of L3 and disposed at a distance of 0.03 mm from the second metal microstructure. Fig.16 As shown in FIG. 2 , the spacing distance between each metal microstructure is the distance in the longitudinal direction.

[0371] The second unit is composed of a metal microstructure having a length L1.

[0372] Furthermore, as described above, the interval between any one unit and the adjacent unit is 0.12 mm.

[0373] The selection of the unit to be used, i.e., the first unit or the second unit, and the length L of the metal microstructure constituting the unit and the offset (offset a and offset b) are selected in such a manner that the distance r between the center (optical axis) of the sheet lens and the center position of the unit is closest to the target phase difference φ (target phase difference φ) defined by the following formula x is allowed to be arbitrary between the target phase difference [°] shown in the following Table 4 and an integer multiple of 360°. In addition, as Fig.17 As shown in , the center position of the unit, that is, the calculated position of the distance r (r calculated position) is the center of the metal microstructure of each unit in the length direction and the center position of the two metal microstructures in the width direction.

[0374] Furthermore, in Table 4, the target phase difference is the total phase difference of the first structural body layer to the fourth structural body layer. In this example, all the units in the thickness direction overlapping the first structural body layer to the fourth structural body layer at the same position in the in-plane direction are regarded as one unit for the first unit and the second unit, and the first unit and the second unit do not overlap in the thickness direction at the same position in the in-plane direction.

[0375] In the following formula x, Rmax is the radius of the lens, f is the focal length of the lens, and λ is the wavelength of the incident electromagnetic wave. In this example, the radius Rmax of the lens is set to 4 mm, and the focal length f of the lens is set to 2.7 mm. In addition, the frequency of the electromagnetic wave is set to 300 GHz, and the wavelength λ is set to 0.999 mm.

[0376] φ[°]=[(Rmax 2 -r 2 ) / 2f]×(360° / λ)+178°…Formula x

[0377] In Table 4, the numerical values ​​of L1 to L3 are the numerical values ​​of the first structural layer.

[0378] The lengths of the first to third metal microstructures constituting the first unit in the second to fourth structure layers are as follows.

[0379] That is, in the second to fourth structural body layers, the first unit is as follows.

[0380] like Fig.16As shown in FIG. 1 , in the second structure layer, one end of the first metal microstructure is at the same position as the end on the same side in the first structure layer (not offset), and the length is L1 + offset a. The second metal microstructure is arranged at a distance of 0.03 mm from the first metal microstructure, and the length is L2. In addition, the third metal microstructure is arranged at a distance of 0.03 mm from the second metal microstructure, and the length is L3 - offset a.

[0381] And, if Fig.16 As shown in FIG. 1 , in the third structure layer, one end of the first metal microstructure is at the same position as the end on the same side in the first structure layer (no offset), and its length is L1 + offset amount a + offset amount b. The second metal microstructure is arranged at a distance of 0.03 mm from the first metal microstructure, and its length is L2. The third metal microstructure is arranged at a distance of 0.03 mm from the second metal microstructure, and its length is L3-offset amount a-offset amount b.

[0382] In addition, if Fig.16 As shown in FIG. 1 , in the fourth structure layer, one end of the first metal microstructure is at the same position as the end on the same side in the first structure layer (no offset), and the length is L1 + offset amount b. The second metal microstructure is arranged at a distance of 0.03 mm from the first metal microstructure, and its length is L2. The third metal microstructure constituting the first unit is arranged at a distance of 0.03 mm from the second metal microstructure, and its length is L3 - offset amount b.

[0383] However, in the first unit of the second to fourth structure layers, when the length of the third metal microstructure is negative, the third metal microstructure is not arranged.

[0384] On the other hand, in the first to fourth structural body layers, the length of the fine metal structure of the second unit is as follows: Fig.17 As shown in FIG. 1 , all are L1, and the offset amount a=the offset amount b=0.

[0385] [Table 4]

[0386]

[0387] So that the center position of the unit ( Fig.17 Each unit is configured in such a way that the "r calculation position" in the table becomes the position shown in Table 5.

[0388] Table 5 shows the distance r [mm] between the center (optical axis) of the sheet lens and the center position of the cell at each position of the structural body layer, the phase difference amount [°] calculated by the above formula x, and the target phase difference [°] in Table 4 corresponding to the phase difference amount calculated by the formula x. Based on the target phase difference at each position shown in Table 5, the cell (first cell or second cell) arranged at each position in the structural body layer is selected, and the photomask design is changed so that the metal microstructure (length) and the position (shift amount) of the metal microstructure become the structure shown in Table 4.

[0389] In Table 5, x [mm] is the position in the X direction from the center of the sheet lens, and y [mm] is the position in the Y direction from the center of the sheet lens.

[0390] A photomask with a changed photomask design is used. In addition, a first structural layer is formed on one surface of a first substrate, a second structural layer is formed on the other surface, and a third structural layer is formed on one surface of a second substrate, and a fourth structural layer is formed on the other surface in the same manner as in Example 2, thereby producing a sheet lens 1 having a structure of four layers, namely, a first structure to a fourth structure.

[0391] A schematic plan view of the produced sheet lens (first structural body layer) is shown in FIG. Fig.18 .

[0392] [Table 5]

[0393]

[0394] [Measurement of electromagnetic wave focusing ability]

[0395] The electromagnetic wave focusing capability of the manufactured sheet lens 1 was measured by the following method.

[0396] like Fig.19 As shown in FIG. 1 , the 300 GHz terahertz wave emitted from the wave source 50 is converted into a collimated beam (plane wave) in free space by the horn antenna 52 and the resin lens 54, and vertically incident on the sheet lens 1 (symbol S) with an effective diameter of 8 mm (radius Rmax = 4 mm). The polarization direction of the electromagnetic wave is set to be parallel to the length direction of the metal cutting line used as the metal microstructure, that is, to be set to the Y direction.

[0397] Next, the back side of the sheet lens 1 was scanned in the XYZ directions using a WR3.4 metal waveguide probe 56. The intensity of the electromagnetic wave incident on the probe was detected using a Schottky diode 58, and the voltage value was taken as the intensity at that point.

[0398] The intensity distribution of electromagnetic waves obtained on the XZ plane and YZ plane including the optical axis is shown in FIG. Fig. 20 In this example, the electromagnetic wave intensity is maximum at z = 1.3 mm. In this example, the back side of the lens is at Z = 0 mm, and the origin of the XYZ direction is offset by 0.22 mm from the back side of the lens.

[0399] The radio wave intensity distribution in the XY plane at Z = 1.3 mm is shown in Fig.21 The full width at half maximum of the focus is 0.6 mm in the X direction and 0.7 mm in the Y direction. The maximum radio wave intensity increases 17 times compared to the case where there is no sheet lens 1, indicating that the sheet lens 1 works as a convex lens.

[0400] Furthermore, the directivity improvement effect of the produced sheet lens 1 was measured by the following method.

[0401] like Fig. 22 As shown in FIG. 1 , the terahertz wave of 300 GHz emitted from the wave source 50 is focused by the resin lens 54 and the resin lens 56 via the horn antenna 52, and is incident on the metal pinhole 68 with a diameter of 0.6 mm. The polarization direction of the electromagnetic wave is set to be parallel to the length direction of the metal cutting wire used as the metal microstructure, that is, to be set to the Y direction.

[0402] A sheet lens 1 (symbol S) is disposed at a position 1.3 mm away from the pinhole 68 , and the sheet lens 1 is used to collimate (convert) the transmitted radiation having a large divergence angle into a parallel beam.

[0403] On a concentric circle centered on the incident surface of the sheet lens 1, the detector toward the rotation center was scanned in the angular direction to measure the directivity of the terahertz wave transmitted through the sheet lens 1. For detection, the electromagnetic wave was focused by the resin lens 70 and the horn antenna 72 set at a position 20 cm away from the sheet lens 1, and the intensity of the electromagnetic wave was detected by the Schottky diode 58 as a detector.

[0404] Fig.23 The results are obtained by changing the angle of the detector as shown in θ in the figure and scanning it in the H plane (orthogonal to the polarized wave of the (H-plane)) and the E plane (parallel to the polarized wave of the (E-plane)) containing the optical axis of the terahertz wave. The divergence angle of the collimated beam is about 7° in both the E plane and the H plane. Compared with the case where there is no sheet lens 1 (dashed line), the radio wave intensity at the center of the beam in the case where there is a sheet lens 1 (solid line) increases by 12 times, showing the effect of improving the directivity of the sheet lens 1. In addition, Fig.23In FIG. 1 , the value is magnified 10 times and displayed only when there is no sheet lens 1 (dashed line).

[0405] As a comparative example, a sheet lens 2 formed only of the first substrate in the sheet lens 1 produced in Example 11, that is, a sheet lens 2 formed only of two structural layers, namely, a first structural layer and a second structural layer, was produced.

[0406] Regarding each unit of the comparative example, for a unit arranged at the same position as a unit having each target phase difference shown in Table 4, the phase difference (transmission phase difference) of an electromagnetic wave with a frequency of 300 GHz (wavelength 999 μm) was measured by numerical simulation simulating terahertz time domain spectroscopy (THz-TDS) in the same manner as described above. In other words, for each unit of the comparative example, the phase difference of the electromagnetic wave was measured in the same manner as described above for a unit that was the same as the unit of Example 11 except that it did not have the third structural body layer and the fourth structural body layer.

[0407] The results are also shown in Table 4. As shown in Table 4, the phase difference of the comparative example is smaller than the phase difference of Example 11 in all the cells.

[0408] In addition, regarding the sheet lens 2 of the comparative example, the beam focusing capability and the directivity improvement effect were measured in the same manner as the sheet lens 1 of Example 11. Regarding beam focusing, since the phase difference was small, no focus was observed, and the operation as a convex lens was not observed. Regarding the directivity improvement effect, in the same manner, the intensity was reduced to less than 1 times compared to the case without the sheet lens 2, and the directivity improvement effect was not observed.

[0409] Industrial Applicability

[0410] The present invention can be preferably used in a communication system using a terahertz wave, and the like.

[0411] Explanation of symbols

[0412] 10-supersurface structure, 12-first substrate, 14-second substrate, 16-first structure layer, 16a-first metal microstructure, 18-second structure layer, 18a-second metal microstructure, 20-third structure layer, 20a-third metal microstructure, 24-fourth structure layer, 24a-fourth metal microstructure, 26-dielectric layer, 30-pillar, 32-spacer, 50-wave source, 52-horn antenna, 54, 62, 64, 70-resin lens, 56-metal waveguide probe, 58-Schottky diode, 68-pinhole, S-sheet lens.

Claims

1. A metasurface structure, which is a metasurface structure in which the following structural layers are stacked at intervals from each other and acts on electromagnetic waves with a frequency of 10 THz or less: a first structural body layer, wherein a plurality of first metal microstructures are arranged in an in-plane direction; a second structure layer, wherein a plurality of second metal microstructures are arranged in an in-plane direction; a third structure layer, wherein a plurality of third metal microstructures are arranged in an in-plane direction; and The fourth structure layer is formed by arranging a plurality of fourth metal microstructures in the in-plane direction.

2. The supersurface structure according to claim 1, wherein: In at least one of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, at least one metal microstructure is arranged to be offset in the in-plane direction with respect to the metal microstructures of the other structure layers.

3. The supersurface structure according to claim 2, wherein: In all of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, at least one metal microstructure is arranged to be offset in the in-plane direction with respect to the metal microstructures of the other structure layers.

4. The supersurface structure according to claim 1 or 2, wherein: A dielectric layer is provided in at least one of between the first structural body layer and the second structural body layer, between the second structural body layer and the third structural body layer, and between the third structural body layer and the fourth structural body layer.

5. The supersurface structure according to claim 1 or 2, wherein: A spacer is provided in at least one of between the first structural body layer and the second structural body layer, between the second structural body layer and the third structural body layer, and between the third structural body layer and the fourth structural body layer.

6. The supersurface structure according to claim 1, wherein: In at least one of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, at least one metal microstructure is a metal cutting wire.

7. The supersurface structure according to claim 6, wherein: In all of the first structure layer, the second structure layer, the third structure layer, and the fourth structure layer, all of the metal microstructures are the metal cutting wires.

8. The supersurface structure according to claim 6 or 7, wherein: The length of the metal cutting line is 0.1 to 1.0 times the wavelength of the electromagnetic wave of the frequency with the highest transmittance.

9. The supersurface structure according to claim 1 or 2, wherein: The thickness between the first structure layer and the second structure layer, between the second structure layer and the third structure layer, and between the third structure layer and the fourth structure layer is 30 nm to 30 mm.

10. The supersurface structure according to claim 1 or 2, wherein: The metasurface structure is a sheet-like lens.

11. The supersurface structure according to claim 1 or 2, wherein: The metasurface structure is a transmission-type refraction plate.

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