Electromagnetic wave absorber

Abstract

An electromagnetic wave absorber 500 comprises a frequency selective filter layer 400, a dielectric layer 200 positioned below the frequency selective filter layer 400, and a reflective layer 100 positioned below the dielectric layer 200. The reflective layer 100 includes a sheet-shaped first insulator 2 that has a first surface 3, and a first wiring pattern 11 that is provided on the upper surface of the first insulator 2 and is formed from fine metal wires 13. The first wiring pattern 11 has a first point 21, a first line 30 extending from the first point 21, and a second line 33 extending from the first point 21. The angle formed by the first line 30 and the second line 33 is greater than 0 degrees and less than 90 degrees, or is greater than 90 degrees and less than 180 degrees.

Description

Electromagnetic wave absorber

[0001] This disclosure relates to an electromagnetic wave absorber.

[0002] Conventionally, sheet-type electromagnetic wave absorbers such as those disclosed in Patent Documents 1 to 3 and Non-Patent Document 1 are known. For example, Patent Document 1 discloses an electromagnetic wave absorber formed in a sheet shape by sequentially laminating a resistive film, a dielectric layer, and a reflective layer. This reflective layer includes a closed-loop resonator in which a plurality of square grids made of a conductive material are arranged two-dimensionally within the main surface of the electromagnetic wave absorber. Furthermore, this electromagnetic wave absorber is a known quarter-wavelength type electromagnetic wave absorber, and the thickness of the dielectric layer is set to be 1 / 4 the effective wavelength of the electromagnetic wave to be absorbed.

[0003] Furthermore, Non-Patent Document 1 also discloses an electromagnetic wave absorber formed in a sheet shape by sequentially stacking a resistive layer, a dielectric layer, and a reflective layer. Rectangular patch elements are arranged in a two-dimensional pattern on the surface of the reflective layer, that is, on the surface facing the resistive layer. Because the reflective layer and the patch elements perform a function equivalent to an LC parallel resonant circuit, the thickness of the dielectric layer, which is the transmission path length of the electromagnetic wave, can be made thinner than 1 / 4 of the effective wavelength of the electromagnetic wave to be absorbed.

[0004] Japanese Patent Publication No. 2022-135025, International Publication No. 2022 / 156582, International Publication No. 2022 / 118719

[0005] Yoshinobu Okano, et al., "Development of an ultra-thin transparent electromagnetic wave absorber for suppressing false authentication in UHF-RFID systems," Transactions of the Institute of Electrical Engineers of Japan, March 1, 2013, Vol. 133, No. 3, pp. 431-440.

[0006] When electromagnetic waves to be absorbed are incident on an electromagnetic wave absorber, in both the electromagnetic wave absorbers disclosed in Patent Document 1 and Non-Patent Document 1, the electromagnetic waves are reflected by the reflective layer.

[0007] As mentioned above, the electromagnetic wave absorber disclosed in Patent Document 1 is a quarter-wavelength type electromagnetic wave absorber, and therefore the thickness of the dielectric layer needs to be changed according to the effective wavelength of the electromagnetic wave to be absorbed. In contrast, the electromagnetic wave absorber disclosed in Non-Patent Document 1 allows the thickness of the dielectric layer to be set regardless of the effective wavelength of the electromagnetic wave to be absorbed, but if the thickness of the dielectric layer becomes too thin, the attenuation of electromagnetic waves in the dielectric layer becomes insufficient. In other words, the electromagnetic wave absorption performance deteriorates.

[0008] This disclosure has been made in view of the foregoing, and its purpose is to provide an electromagnetic wave absorber with enhanced electromagnetic wave absorption performance.

[0009] To achieve the above objective, an electromagnetic wave absorber according to one aspect of the present disclosure comprises at least a frequency-selective filter layer, a dielectric layer located below the frequency-selective filter layer, and a reflective layer located below the dielectric layer. The reflective layer has a sheet-like first insulator having a first surface, and a first wiring pattern provided on the upper surface of the first insulator and formed of metal fine wires. The first wiring pattern has a first point, a first line extending from the first point, and a second line extending from the first point. The angle between the first line and the second line is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

[0010] According to this disclosure, the propagation distance of electromagnetic waves within the dielectric layer can be increased, thereby improving the electromagnetic wave absorption performance.

[0011] Figure 1 is a schematic diagram of an electromagnetic wave absorber according to an embodiment, viewed from above. Figure 2 is a schematic diagram of a unit cell of the electromagnetic wave absorber, viewed from above. Figure 3 is a cross-sectional view taken along line III-III in Figure 2. Figure 4 is a partially enlarged view of region IVA shown in Figure 2 and region IVB shown in Figure 3. Figure 5 is a cross-sectional view taken along line V-V in Figure 4. Figure 6 is an enlarged view of the first wiring pattern shown in Figure 4. Figure 7 is an enlarged view of region VII shown in Figure 6. Figure 8 is a graph showing the relationship between the frequency of the electromagnetic wave (in GHz) and the shielding performance (in dB) of each sample when a predetermined electromagnetic wave is incident on each of four reflective layer samples with different pitch values. Figure 9 is a partially enlarged view of a part of a reflective layer including a grid-like wiring pattern in the configuration of the prior art. Figure 10 is a schematic image showing the state of the reflected wave reflected upward from the top surface of the reflective layer when a predetermined electromagnetic wave is irradiated onto a reflective layer of the conventional configuration (see Figure 9). Figure 11 is a schematic diagram showing the state of reflected waves reflected upward from the first surface when a predetermined electromagnetic wave is irradiated onto the reflective layer according to the embodiment. Figure 12 is a schematic diagram showing the propagation state of reflected waves within the dielectric layer in an electromagnetic wave absorber using a conventionally configured reflective layer (see Figure 9). Figure 13 is a schematic diagram showing the propagation state of reflected waves within the dielectric layer in the electromagnetic wave absorber according to the embodiment. Figure 14 is a diagram showing the frequency dependence of reflection loss and transmission loss in the electromagnetic wave absorber according to the embodiment. Figure 15 is a partially enlarged view of a wiring pattern according to the first modified example, corresponding to Figure 4, showing a configuration where the first line in the wiring pattern is a sine curve. Figure 16 is a partially enlarged view of the first wiring pattern shown in Figure 15. Figure 17 is a partially enlarged view of region XVII shown in Figure 16. Figure 18 is a corresponding Figure 4 of another wiring pattern according to the first modified example. Figure 19 is a corresponding Figure 4 of yet another wiring pattern according to the first modified example. Figure 20A is a schematic diagram of a filter pattern according to the second modified example viewed from above. Figure 20B is a schematic diagram of another filter pattern relating to the second modification, viewed from above. Figure 20C is a schematic diagram of yet another filter pattern relating to the second modification, viewed from above.

[0012] The embodiments of this disclosure will be described in detail below with reference to the drawings. The following descriptions of embodiments are illustrative in nature and are not intended to limit this disclosure, its applications, or its uses.

[0013] (Embodiment) [1: Configuration of the electromagnetic wave absorber] Figure 1 is a schematic diagram of an electromagnetic wave absorber according to an embodiment, viewed from above. Figure 2 is a schematic diagram of a unit cell of the electromagnetic wave absorber, viewed from above. Figure 3 is a cross-sectional view taken along the line III-III in Figure 2.

[0014] As shown in Figures 1 to 3, the electromagnetic wave absorber 500 is made up of a plurality of unit cells 510 arranged two-dimensionally at a predetermined period. Each of the plurality of unit cells 510 has one filter pattern 400A. The plurality of unit cells 510 are arranged in a continuous manner, and the components other than the filter pattern 400A are common to the plurality of unit cells 510.

[0015] Furthermore, as shown in Figure 3, the electromagnetic wave absorber 500 is a sheet-like component in which a reflective layer 100, a dielectric layer 200, and a frequency-selective filter layer 400 are arranged in that order from bottom to top. In the example shown in this embodiment, the thickness t1 of the reflective layer 100 and the thickness t4 of the frequency-selective filter layer 400 are the same value (= 50 μm), but this is not limited to this and can be appropriately changed according to the required performance of the electromagnetic wave absorber 500. The configuration of the reflective layer 100 and the frequency-selective filter layer 400 will be described later.

[0016] The dielectric layer 200 consists of a first dielectric layer 210 and a second dielectric layer 220 positioned above the first dielectric layer 210. The first dielectric layer 210 and the second dielectric layer 220 are made of the same material, but their thicknesses are different. In the example shown in this embodiment, the thickness t21 (= 2.0 mm) of the first dielectric layer 210 is set to be thinner than the thickness t22 (= 3.0 mm) of the second dielectric layer 220. However, this is not limited to this, and depending on the required performance of the electromagnetic wave absorber 500, the thickness t21 may be thicker than the thickness t22, or the thickness t21 may be set to be the same as the thickness t22.

[0017] The upper surface of the first dielectric layer 210 and the lower surface of the second dielectric layer 220 are adhered to each other via an adhesive layer (third dielectric layer) 320. Also, the lower surface of the second dielectric layer 220 and the upper surface of the reflective layer 100 are adhered to each other via an adhesive layer 310. The upper surface of the second dielectric layer 220 and the lower surface of the frequency selection filter layer 400 are adhered to each other via an adhesive layer 330. The adhesive layers 310, 320, 330 are made of, for example, an acrylic resin. In the example shown in this embodiment, the adhesive layers 310, 320, 330 are made of the same material, and the thickness t3 is set to 50 μm, but it is not particularly limited thereto and can be appropriately changed. Since the first dielectric layer 210 and the second dielectric layer 220 are made of the same material, the relative dielectric constant (=ε1) is also the same, but the relative dielectric constant ε2 of the adhesive layer 330 is a value different from ε1. ε2 may be larger or smaller than ε1. It is preferable that the absolute value of the difference between ε2 and ε1 is 0.1 or more.

[0018] The total light transmittance of the electromagnetic wave absorber 500 (refer to JIS K 7375-2008) is 60% or more. Also, the sheet resistance of the metal fine wires 13, 413 (refer to FIG. 4) in the electromagnetic wave absorber 500 is 0.1 Ω / □ or more and 5.0 Ω / □ or less.

[0019] [2: Absorption process of electromagnetic wave] Next, the absorption process of electromagnetic wave by the electromagnetic wave absorber 500 will be described.

[0020] Among the electromagnetic waves incident from the upper surface of the frequency selection filter layer 400, only the electromagnetic waves of a predetermined frequency are propagated to the dielectric layer 200. The factors that determine the frequency band will be described later.

[0021] The electromagnetic wave propagated through the dielectric layer 200 is reflected upward by the region IVB provided on the upper surface of the reflective layer 100. The region IVB is a structure in which the wiring patterns 10 (refer to FIG. 4) are two-dimensionally arranged. Also, the filter pattern 400A of the frequency selection filter layer 400 has the same structure as the region IVB (region IVA in FIG. 2). These structures will be described in detail later.

[0022] Of the electromagnetic waves (reflected waves) reflected in region IVB, the reflected waves incident on the lower surface of the filter pattern 400A are reflected downward again at the lower surface.

[0023] In this way, when the electromagnetic wave propagates inside the dielectric layer 200 due to reflection in region IVB and multiple reflections inside the dielectric layer 200, the electromagnetic wave attenuates due to dielectric loss corresponding to the relative permittivity ε1. That is, the electromagnetic wave absorber 500 absorbs the electromagnetic wave by converting the energy of the electromagnetic wave transmitted through the frequency selection filter layer 400 into thermal energy by utilizing the attenuation phenomenon of the electromagnetic wave due to dielectric loss.

[0024] [3: Configuration of the reflection layer]FIG. 4 is a partially enlarged view of region IVA shown in FIG. 2 and region IVB shown in FIG. 3. FIG. 5 is a cross-sectional view taken along line V-V of FIG. 4.

[0025] As shown in FIG. 4, region IVB in the reflection layer 100 includes a plurality of wiring patterns 10. Each of the plurality of wiring patterns 10 is formed of a metal thin wire 13. Each of the plurality of wiring patterns 10 is formed in a closed shape by the metal thin wire 13. The shape of the base of the wiring pattern 10 is a regular polygon (see FIG. 6). In the present embodiment, a regular hexagon is exemplified as the regular polygon. The plurality of wiring patterns 10 are provided over the entire upper surface of the reflection layer 100 while maintaining the arrangement relationship shown in FIG. 4. That is, region IVB is provided over the entire upper surface of the reflection layer 100.

[0026] In the present embodiment, for convenience of explanation, any one of the plurality of wiring patterns 10 is referred to as the "first wiring pattern 11". Also, the wiring pattern 10 adjacent to the first wiring pattern 11 (the wiring pattern 10 located at the upper right of the paper surface of FIG. 4 of the first wiring pattern) is referred to as the "second wiring pattern 12".

[0027] The first wiring pattern 11 is provided on the first surface 3 of the first insulator 2 (see FIG. 5). The first wiring pattern 11 is formed of a metal thin wire 13. The line width of the metal thin wire 13 forming the first wiring pattern 11 (groove width dimension Lw; see FIG. 5) is 1.0 μm or more and 3.0 μm or less.

[0028] The second wiring pattern 12 is provided on the first surface 3 of the first insulator 2 (see Figure 5). The second wiring pattern 12 is formed of metal fine wires 13. The wire width of the metal fine wires 13 forming the second wiring pattern 12 is 1.0 μm or more and 3.0 μm or less.

[0029] Here, in Figure 4, the symbol Cg1 indicates the centroid of the first wiring pattern 11, and the symbol Cg2 indicates the centroid of the second wiring pattern 12.

[0030] <First Insulator> As shown in Figure 5, the reflective layer 100 includes a first insulator 2. The first insulator 2 is transparent.

[0031] The first insulator 2 is formed in sheet form. The thickness of the first insulator 2 is, for example, 25 μm or more and 200 μm or less.

[0032] As shown in Figure 5, the first insulator 2 has a first surface 3. The first surface 3 is the upper surface of the first insulator 2 and corresponds to the upper surface of the reflective layer 100.

[0033] As shown in Figure 5, the first insulator 2 has a first layer 4 and a second layer 5.

[0034] The first layer 4 is made of a transparent resin material. Examples of transparent resin materials include PET (polyethylene terephthalate), PEN (polyethylene naphthalate), PC (polycarbonate), COP (cycloolefin polymer), COC (cycloolefin copolymer), and PMMA (polymethyl methacrylate resin).

[0035] The second layer 5 is laminated on top of the first layer 4. The second layer 5 is made of a resin material that has insulating and permeable properties. The thickness of the second layer 5 is greater than the depth of the groove 6. The upper surface of the second layer 5 corresponds to the first surface 3.

[0036] <Grooves> As shown in Figure 5, the upper surface (first surface 3) of the first insulator 2 is provided with a plurality of grooves 6. The grooves 6 have a bottomed shape that is recessed from the first surface 3 toward the thickness direction of the second layer 5. The depth dimension Ld of the grooves 6 is set to, for example, 0.7 μm or more and 4.0 μm or less. The aspect ratio (Ld / Lw) of the grooves 6 is 0.3 or more.

[0037] <Metal wire> As shown in Figure 5, the metal wire 13 includes conductive metal embedded in the groove 6. This configuration makes it easy to form the curved first wire 30 and the second wire 33 (see Figure 6). The metal wire 13 is composed of an adhesion layer 14, a seed layer 15, a conductive layer 16, and a blackening layer 17.

[0038] The adhesion layer 14 is an element that ensures the adhesion of the seed layer 15 to the groove 6. The adhesion layer 14 is a metal layer composed of a metal nitride or metal oxide containing at least one metal selected from the group consisting of Ti, Ni, Al, V, W, Ta, Si, Cr, Ag, Mo, Cu, and Zn. The adhesion layer 14 may be a single layer or a laminate of multiple layers with different compositions. The adhesion layer 14 is laminated in a thin film form on the groove 6, for example, by vapor deposition or sputtering.

[0039] The seed layer 15 has the function of bonding the conductive layer 16 to the adhesion layer 14. Specifically, in this embodiment, the seed layer 15 functions as a cathode for depositing a plating solution containing copper (Cu) or the like onto the adhesion layer 14 during an electroplating process to form the conductive layer 16. The seed layer 15 is deposited on the adhesion layer 14 in a thin film form by, for example, vapor deposition or sputtering.

[0040] The conductive layer 16 is made of a conductive metal such as copper (Cu). The conductive layer 16 is formed, for example, by electroplating. When electroplating is performed, the conductive layer 16 is formed integrally with the seed layer 15 on its surface. As a result, the interface between the seed layer 15 and the conductive layer 16 becomes indistinguishable. Although copper (Cu) is suitable as the main component of the plating solution used in the electroplating process, other metals (e.g., silver, gold) may also be included.

[0041] The blackened layer 17 has the function of preventing the metal wire 13 from being visible when viewed from the first surface 3 of the first insulator 2. The blackened layer 17 is laminated on the surface of the conductive layer 16. The blackened layer 17 is formed by replacing (blackening) copper crystal grains located at the boundaries between copper crystal grains located on the surface of the conductive layer 16 with palladium. The thickness of the blackened layer 17 is, for example, 7 nm to 10 nm.

[0042] [4: Wiring Pattern Configuration] Figure 6 is an enlarged view of the first wiring pattern shown in Figure 4. Figure 7 is an enlarged view of region VII shown in Figure 6.

[0043] <Vertices> As shown in Figures 6 and 7, the first wiring pattern 11 has a plurality of vertices 20. The plurality of vertices 20 are positioned to form a regular polygon when connected to each other by a straight line VL. All of the plurality of vertices 20 are located on the first surface 3 of the first insulator 2. In addition, each vertex 20 is located at the intersection of the metal thin wires 13, 13 that form the wiring pattern 10.

[0044] The straight line VL corresponds to the imaginary line shown in Figures 6 and 7. In other words, the straight line VL is not formed by the metal thin wire 13.

[0045] As described above, in this embodiment, a regular hexagon is exemplified as the "regular polygon" that forms the base of the first wiring pattern 11 (wiring pattern 10). The multiple vertices 20 that form the regular hexagon of the first wiring pattern 11 are the six vertices 20 shown in Figure 6.

[0046] In this embodiment, for the sake of explanation, any one vertex 20 among the multiple vertices 20 will be referred to as the "first point 21". Furthermore, the vertex 20 located diagonally to the lower left of the first point 21 in Figure 6 will be referred to as the "second point 22". In addition, the vertex 20 located diagonally to the lower right of the first point 21 in Figure 6 will be referred to as the "third point 23".

[0047] As shown in Figure 6, the first wiring pattern 11 includes a first point 21 and a second point 22. The first wiring pattern 11 further includes a third point 23. The third point 23 is located at a position where the second point 22 is rotated 120 degrees around the first point 21. Specifically, the third point 23 is located at a position where the second point 22 is rotated 120 degrees counterclockwise around the first point 21.

[0048] The first wiring pattern 11, based on a regular hexagon, is isotropic. That is, the curved metal wires 13 can be arranged isotropically on each side of the first wiring pattern 11 based on a regular hexagon. As a result, when electromagnetic waves (incident waves) incident on the reflective layer 100 strike the curved metal wires 13, the reflected waves diffuse isotropically in all directions.

[0049] <First and Second Lines> As shown in Figure 6, the first wiring pattern 11 has a first line 30 connecting a first point 21 and a second point 22. The first line 30 intersects with the straight line VL connecting the first point 21 and the second point 22. The thin metal wire 13 connecting the first point 21 and the third point 23 is sometimes called the second line 33. The first line 30 and the second line 33 are both curved. When electromagnetic waves (incident waves) incident on the electromagnetic wave absorber 500 strike the curved thin metal wire 13, which includes the first line 30 and the second line 33, the reflected waves (see arrow Rw shown in Figure 7) can be diffused in all directions.

[0050] Furthermore, except for the extension direction, the shape of the second line 33 is the same as the shape of the first line 30. Therefore, the following explanation will use the first line 30 as an example.

[0051] The wavelength λ1 of the first line 30 (see Figure 7) is the length obtained by dividing the distance between the first point 21 and the second point 22 by a natural number of 1 or more. In this embodiment, the wavelength λ1 of the first line 30 is the length obtained by dividing the distance between the first point 21 and the second point 22 by "1". That is, a wavelength of a quantity corresponding to the above natural number is formed in the first line 30. Specifically, in this embodiment, the wavelength λ1 of the first line 30 is equal to the distance between the first point 21 and the second point 22. As a result, when an electromagnetic wave (incident wave) incident on the electromagnetic wave absorber 500 hits the first line 30, the reflected wave diffuses in all directions, and the generation of polarization at the reflection destination is suppressed.

[0052] Furthermore, since the first wiring pattern 11 in this embodiment is based on a regular hexagon, the wavelength λ1 of the first line 30 located on each side of the first wiring pattern 11 is equal to the length between the first point 21 and the second point 22. In other words, the wavelengths λ1 of the first line 30 located on each side of the first wiring pattern 11 do not have a phase difference with each other.

[0053] <First semicircle and second semicircle> As shown in Figures 6 and 7, the first line 30 in this embodiment includes the first semicircle 31 and the second semicircle 32.

[0054] Preferably, the first semicircle 31 has a diameter d1 (see Figure 6) that is less than or equal to half the length between the first point 21 and the second point 22. Similarly, the second semicircle 32 has a diameter d2 (see Figure 6) that is less than or equal to half the length between the first point 21 and the second point 22.

[0055] The two semicircles included in the second line 33 are sometimes referred to as the third semicircle 34 and the fourth semicircle 35. The third semicircle 34 corresponds to the first semicircle 31, and the fourth semicircle 35 corresponds to the second semicircle 32. Therefore, the following explanation will use the first semicircle 31 and the second semicircle 32 as examples.

[0056] In this embodiment, the diameter d1 of the first semicircle 31 is half the length between the first point 21 and the second point 22. The diameter d2 of the second semicircle 32 is half the length between the first point 21 and the second point 22. That is, the diameter d1 of the first semicircle 31 is the same size as the diameter d2 of the second semicircle 32.

[0057] The second semicircle 32 is connected to the first semicircle 31. The connection point between the first semicircle 31 and the second semicircle 32 is located at the midpoint M of the line VL.

[0058] The first semicircle 31 and the second semicircle 32 are located on opposite sides of the straight line VL connecting the first point 21 and the second point 22. In this embodiment, the first semicircle 31 is located inside the first wiring pattern 11, and the second semicircle 32 is located outside the first wiring pattern 11.

[0059] In this embodiment, when an electromagnetic wave (incident wave) incident on the reflective layer 100 strikes the first semicircle 31 and the second semicircle 32, the reflected wave can be diffused in all directions. Furthermore, since the first semicircle 31 and the second semicircle 32 are located on opposite sides of the straight line VL connecting the first point 21 and the second point 22, when the incident wave strikes the first semicircle 31 and the second semicircle 32, the reflected wave when the incident wave strikes the first semicircle 31 and the reflected wave when the incident wave strikes the second semicircle 32 are diffused isotropically in all directions (see arrow Rw shown in Figure 7). As a result, the reflected wave can be diffused isotropically in all directions across the entire first wiring pattern 11.

[0060] <Pitch> The symbol P shown in Figure 4 represents the distance (pitch) between the centroid Cg1 of the first wiring pattern 11 and the centroid Cg2 of the second wiring pattern 12. Preferably, the pitch P is 25 μm or more and 100 μm or less. If the pitch P is 25 μm or more and 100 μm or less, the transparency of the reflective layer 100 can be ensured while sufficient electromagnetic wave reflection performance, which is the main function of the reflective layer 100, can be obtained. In other words, the visibility of the metal wires 13 in the reflective layer 100 can be reduced. This point will be explained in detail later with reference to the drawings.

[0061] [5: Configuration of the Frequency Selective Filter Layer] As shown in Figure 2, the outer shape of the filter pattern 400A provided on the upper surface of the frequency selective filter layer 400 is ring-shaped, while the inside of the ring has a structure in which multiple wiring patterns 410 made of thin metal wires 413 are arranged periodically, as shown in Figure 4. The shape and dimensions of the wiring patterns 410 are the same as those of the wiring patterns 10 provided on the reflective layer 100. Taking this into consideration, in Figure 2 and the drawings shown thereafter, when the symbol for each part of the reflective layer 100 is X (where X is an integer between 1 and 99), the shape of the wiring pattern 410 of the frequency selective filter layer 400, in particular the filter pattern 400A, is denoted by the symbol 4X. In other words, in the frequency selective filter layer 400 as well, as shown in Figure 5, a groove 406 is provided in the second insulator 402, which consists of two insulating layers 404 and 405, and thin metal wires 413 are embedded in the groove 406. The metal wire 413 is composed of an adhesion layer 414, a seed layer 415, a conductive layer 416, and a blackening layer 417.

[0062] The upper surface of the frequency-selective filter layer 400 corresponding to the first surface 3 of the reflective layer 100 is referred to as the second surface 403. In addition, the first wiring pattern 11 and the second wiring pattern 12 are referred to as the third wiring pattern 411 and the fourth wiring pattern 412 in the frequency-selective filter layer 400.

[0063] The thin metal wires 413 corresponding to the first line 30, the second line 33, and the first to fourth semicircles 31, 32, 34, and 35 are referred to as the third line 430, the fourth line 433, and the fifth to eighth semicircles 431, 432, 434, and 435, respectively, in the wiring pattern 410 of the frequency-selective filter layer 400.

[0064] The first to third points 21, 22, and 23 included in the wiring pattern 10 are referred to as the fourth to sixth points 421, 422, and 423, respectively, in the wiring pattern 410 of the frequency-selective filter layer 400.

[0065] Also, in the frequency selection filter layer 400, the centers of gravity corresponding to the center of gravity Cg1 of the first wiring pattern 11 and the center of gravity Cg2 of the second wiring pattern 12 are referred to as the center of gravity Cg3 of the third wiring pattern 411 and the center of gravity Cg4 of the fourth wiring pattern 412, respectively.

[0066] As shown in FIGS. 1 and 2, the filter pattern 400A in the frequency selection filter layer 400 is two-dimensionally arranged with the same period as the unit cell 510. In the present embodiment, the period of the unit cell 510 in one direction within the plane of the second surface 403 is L Ｘ and the period in the direction orthogonal to the one direction is L Ｙ . Also, in the present embodiment, the period L Ｘ is equal to the period L Ｙ (L Ｘ = L Ｙ ).

[0067] The frequency f of the electromagnetic wave that passes through the frequency selection filter layer 400 and reaches the reflection layer 100 is determined by the period L Ｘ , the period L Ｙ , and the lengths L Ａ , L Ｂ that determine the size of the filter pattern 400A.

[0068] When the frequency of the electromagnetic wave is f and the wavelength is λ, the relationship fλ = c generally holds. Here, c is the speed of light in a vacuum. In the present embodiment, the period L Ｘ (= L Ｙ ) is set to 30% or more and 50% or less of the wavelength λ, the length L Ａ is set to 26% or more and 29% or less of the wavelength λ, and the length L Ｂ is set to 4% or more and 8% or less of the wavelength λ. At this time, only the electromagnetic wave in the frequency band having a predetermined frequency width with the frequency f (= c / λ) as the center frequency can pass through the frequency selection filter layer 400 and reach the reflection layer 100. In other words, only the electromagnetic wave in the frequency band having a predetermined frequency width with the frequency f (= c / λ) as the center frequency is absorbed by the electromagnetic wave absorber 500.

[0069] If the frequency band of the incident electromagnetic wave is approximately 0.01 GHz to 40 GHz, the wavelength of the electromagnetic wave will be approximately 7.5 mm to 30 m. Therefore, for example, if the center frequency of the electromagnetic wave to be absorbed is 0.925 GHz, the center wavelength of the electromagnetic wave that can be absorbed by the electromagnetic wave absorber 500 will be approximately 32.4 cm. Therefore, the period L of the filter pattern 400A Ｘ (=L Ｙ The length L shown in Figure 2 is set to approximately 13 cm. Ａ Let it be approximately 8.7 cm, and length L Ｂ If the width is approximately 1.9 cm, only electromagnetic waves in a predetermined frequency band with a center frequency of 0.925 GHz will be absorbed by the electromagnetic wave absorber 500. Note that 0.925 GHz is the center frequency of communication radio waves used in known UHF-RFID (Ultra High Frequency - Radio Frequency Identification) systems.

[0070] [6: Consideration of reflection of electromagnetic waves in the reflective layer] <Relationship between shielding performance and pitch P> Figure 8 is a graph showing the relationship between the frequency of electromagnetic waves (unit: GHz) and the shielding performance (unit: dB) of each sample when a predetermined electromagnetic wave is incident on each of four samples (first to fourth samples S1 to S4) with different pitch P values.

[0071] The horizontal axis of the graph shown in Figure 8 represents the frequency of electromagnetic waves (GHz). The vertical axis of the graph shown in Figure 8 represents the shielding performance (dB), that is, the transmission attenuation performance of electromagnetic waves. Generally, the value of shielding performance is a number that relatively expresses how much electromagnetic waves have been attenuated, and is expressed logarithmically as the ratio (attenuation amount) of the electric field strength before shielding to the electric field strength after shielding.

[0072] In the graph shown in Figure 8, the pitch P in the first sample S1 is 25 μm. This "25 μm" is assumed to be less than 1 / 10 of the wavelength in electromagnetic waves. The pitch P in the second sample S2 is 50 μm. This "50 μm" is assumed to be less than 1 / 5 of the wavelength in electromagnetic waves. The pitch P in the third sample S3 is 100 μm. This "100 μm" is assumed to be less than 1 / 2 of the wavelength in electromagnetic waves. The pitch P in the fourth sample S4 is 200 μm. In all four samples, the line width of the metal wire 13 is 2.4 μm.

[0073] Here, if the shielding performance (dB) is -20 dB or less, a transmission attenuation (shielding rate) of 99% or more can be obtained. Based on this premise, in the graph of Figure 6, for the sake of explanation, the region X in which a transmission attenuation of 99% or more (the shielding rate when each sample shields the electromagnetic waves incident on each sample) can be obtained is shown by a dashed line.

[0074] In samples S1 to S3, all portions were located within region X shown in Figure 8. Specifically, in samples S1 to S3, transmission attenuation of 99% or more was possible in any range of the horizontal frequency axis in the graph of Figure 8 from 0.01 GHz to 40 GHz. In other words, if the pitch P is between 25 μm and 100 μm, transmission attenuation of 99% or more is possible in any range of the frequency from 0.01 GHz to 40 GHz. Thus, sufficient shielding performance can be obtained if the pitch P is between 25 μm and 100 μm.

[0075] In contrast, as shown in the graph in Figure 8, when the pitch P value becomes larger than that of sample S3, transmission attenuation of 99% or more cannot be obtained in the frequency range of 0.01 GHz to 40 GHz. In other words, if the pitch P exceeds 101 μm, sufficient shielding performance cannot be obtained.

[0076] In particular, for the fourth sample S4 (pitch P of 200 μm), the value on the vertical axis of the graph in Figure 8 is greater than -20 dB in the entire frequency range from 0.01 GHz to 40 GHz. Thus, the fourth sample S4 is located outside the dashed line region shown in the graph in Figure 8, and a transmission reduction of 99% or more cannot be achieved.

[0077] On the other hand, considering the simulation results for samples S1 to S4 shown in the graph in Figure 8, it can be expected that if the pitch P is less than 25 μm, a transmission attenuation of 99% or more can be obtained in the frequency range of 0.01 GHz to 40 GHz. In other words, even if the pitch P is less than 25 μm, the shielding performance will improve.

[0078] However, if the pitch P is less than 25 μm, the spacing between the metal wires 13, 13 that constitute the wiring pattern 10 (first wiring pattern 11) becomes narrower. As a result, when the electromagnetic wave absorber 500 is viewed from the side where the first surface 3 is located, the multiple metal wires 13 provided on the first surface 3 become visually recognizable and conspicuous. This impairs the transparency of the electromagnetic wave absorber 500. Specifically, the total light transmittance of the electromagnetic wave absorber 500 may fall below 60%. From this perspective, in order to maintain a total light transmittance of 60% or more, it is necessary to set the pitch P to 25 μm or more.

[0079] As described above, if the pitch P is between 25 μm and 100 μm, the transparency of the electromagnetic wave absorber 500 can be ensured while sufficient shielding performance of the reflective layer 100 can be obtained.

[0080] Furthermore, the same argument applies to the filter pattern 400A of the frequency-selective filter layer 400 regarding transparency. In other words, if the pitch P is between 25 μm and 100 μm, the transparency of the electromagnetic wave absorber 500 can be ensured, meaning that the visibility of the metal wires 413 in the filter pattern 400A can be reduced. In addition, sufficient frequency selectivity of the frequency-selective filter layer 400 can be obtained.

[0081] Furthermore, sufficient shielding performance can be obtained against reflected waves incident on the lower surface of the filter pattern 400A. In other words, reflected waves incident on the lower surface of the filter pattern 400A can be reflected again inside the electromagnetic wave absorber 500. This makes it possible to increase the propagation distance of electromagnetic waves inside the dielectric layer 200.

[0082] <Relationship between reflected wave propagation state and wiring pattern shape> Next, referring to Figures 9 to 11, the state of the reflected wave Rw2 when an electromagnetic wave (incident wave Iw) incident on the reflective layer 100 according to this embodiment is reflected will be explained in comparison with the state of the reflected wave Rw1 when an electromagnetic wave (incident wave Iw) incident on the reflective layer 110 according to the conventional configuration (hereinafter referred to as "conventional configuration") is reflected.

[0083] Figure 9 is a magnified view of a portion of the reflective layer, including a grid-like wiring pattern, in the configuration of the prior art.

[0084] A prior art configuration includes, for example, a reflective layer 110 consisting of a grid-like wiring pattern 111 as shown in Figure 9. In the conventional configuration, the metal fine wires 112 of the wiring pattern 111 are formed in a straight line. In other words, the outer shape of the wiring pattern 111 when viewed from above is a simple rectangular grid. That is, the reflective layer 110 according to the conventional configuration has a different configuration from the reflective layer 100 according to this embodiment.

[0085] Figure 10 is a schematic diagram illustrating the state of the reflected wave reflected from the first surface 113 of the reflective layer 110 when a predetermined electromagnetic wave is irradiated onto the reflective layer 110 shown in Figure 9, using a simulation device (Ansys HFSS manufactured by Ansys). In Figure 9, the state of the reflected wave is represented by shades of black and white.

[0086] Figure 11 is a schematic diagram showing the state of the reflected wave reflected from the first surface 3 when a predetermined electromagnetic wave is irradiated onto the reflective layer 100 according to this embodiment using a simulation device (Ansys HFSS manufactured by Ansys). In Figure 11, as in Figure 10, the state of the reflected wave is represented by shades of black and white.

[0087] Referring to Figure 10, in the conventional reflective layer 110, electromagnetic waves (incident wave Iw) incident on a linear metal wire 112 (the metal wire 112 is not shown in Figure 10) are reflected in a certain direction. Specifically, the black and white shading shown in Figure 10 is almost uniformly dense across the entire upper surface of the reflective layer 110. That is, the reflected wave Rw1 is traveling upwards on the reflective layer 110 as shown in Figure 10. As a result, the degree of diffusion of the reflected wave is relatively low.

[0088] In contrast, referring to Figure 11, in the reflective layer 100 according to the embodiment of this disclosure, electromagnetic waves (incident wave Iw) that strike the wiring pattern 10 having a curved first line 30 (the wiring pattern 10 is not shown in Figure 11) are reflected in a way that diffuses in all directions. Specifically, the black and white shades shown in Figure 11 spread radially upward from the first surface 3 of the reflective layer 100. That is, the reflected wave Rw2 propagates radially upward from the first surface 3 of the reflective layer 100 shown in Figure 11. As a result, the degree of diffusion of the reflected wave is higher than in the case shown in Figure 10.

[0089] Furthermore, if we assume that the diffusion rate of reflected waves in the conventional reflective layer 110 is "1.0", then the diffusion rate of reflected waves in the reflective layer 100 according to this embodiment will be 1.5 or more and 3.0 or less.

[0090] Considering these points, it can be understood that the propagation state of reflected waves within the dielectric layer 200 differs significantly between the case where the conventional reflective layer 110 is used as the reflective layer of the electromagnetic wave absorber 500 and the case where the reflective layer 100 according to this embodiment is used. Further explanation will be given below with reference to the drawings.

[0091] Figure 12 is an illustrative diagram showing the propagation state of reflected waves within the dielectric layer in an electromagnetic wave absorber using a conventional reflective layer (see Figure 9). Figure 13 is an illustrative diagram showing the propagation state of reflected waves within the dielectric layer in an electromagnetic wave absorber according to an embodiment. Figure 14 is a diagram showing the frequency dependence of reflection loss and transmission loss in an electromagnetic wave absorber according to an embodiment.

[0092] For the sake of clarity, the metal wire 112 provided on the first surface 113 of the reflective layer 110 is omitted from the illustration in Figure 12. Similarly, the metal wire 13 provided on the first surface 3 of the reflective layer 100 is omitted from the illustration in Figure 13. Furthermore, the frequency-selective filter layer 400 is omitted from the illustration in Figures 12 and 13.

[0093] As shown in Figure 12, when a conventional reflective layer 110 is used, the metal wires 112 constituting the wiring pattern 111 are arranged in a simple grid. As a result, the degree of diffusion of reflected waves is low, as mentioned above, and the distance over which reflected waves propagate within the dielectric layer 200 cannot be increased. In other words, reflected waves are not sufficiently attenuated by dielectric loss occurring within the dielectric layer 200, and the electromagnetic wave absorption performance cannot be improved. In particular, if the thickness of the dielectric layer 200 is less than 1 / 4 of the wavelength of the incident electromagnetic wave, there is a risk that the electromagnetic wave absorber 500 will not be able to sufficiently absorb the electromagnetic wave.

[0094] On the other hand, as shown in Figure 13, when the reflective layer 100 according to this embodiment is used, the degree of diffusion of reflected waves can be increased compared to the case shown in Figure 12 because the metal thin wires 13 constituting the wiring pattern 10 are curved.

[0095] Therefore, in the electromagnetic wave absorber 500 of this embodiment that uses the reflective layer 100, the distance over which reflected waves propagate within the dielectric layer 200 can be increased compared to the case where the reflective layer 110 of the conventional configuration is used. As a result, in the electromagnetic wave absorber 500 using the reflective layer 100 of this embodiment, the amount of attenuation of electromagnetic waves within the dielectric layer 200 can be increased, and the electromagnetic wave absorption performance of the electromagnetic wave absorber 500 can be improved. Furthermore, even when the thickness of the dielectric layer 200 is thinner than 1 / 4 of the wavelength of the incident electromagnetic wave, the electromagnetic wave absorber 500 can sufficiently absorb the electromagnetic wave.Specific examples will be described below.

[0096] As shown in Figure 14, when the attenuation of the reflection in the electromagnetic wave absorber 500 becomes less than -10 dB, more than 90% of the electromagnetic waves incident on the electromagnetic wave absorber 500 and propagating inside it will be absorbed. For example, if the center frequency fc of the electromagnetic wave to be absorbed is 0.925 MHz and the period L of the filter pattern 400AＸ (=L Ｙ ) and the length L of the filter pattern 400A Ａ , L Ｂ The range is defined as described above. In this case, as shown in Figure 14, the transmission attenuation increased around the center frequency fc, while the reflection attenuation decreased. Furthermore, it was confirmed that the reflection attenuation was less than -10 dB in the frequency band from (fc - 0.015) GHz to (fc + 0.2) GHz.

[0097] In other words, for electromagnetic waves in the frequency band to be absorbed, the period L of the filter pattern 400A Ｘ (=L Ｙ ) and the length L of the filter pattern 400A Ａ , L Ｂ It was found that by setting the appropriate parameters, electromagnetic waves in that frequency band can be reliably absorbed.

[0098] [First Modified Example] Figure 15 is a partially enlarged view of the wiring pattern according to the first modified example, and is a corresponding figure to Figure 4, showing a configuration in which the first line in the wiring pattern is a sine curve. Figure 16 is a partially enlarged view of the first wiring pattern shown in Figure 15. Figure 17 is a partially enlarged view of region XVII shown in Figure 16.

[0099] Figure 18 is a diagram corresponding to Figure 4 of another wiring pattern relating to the first modification. Figure 19 is a diagram corresponding to Figure 4 of yet another wiring pattern relating to the first modification.

[0100] In the above embodiment, the first line 30 is shown to include the first semicircle 31 and the second semicircle 32, but the embodiment is not limited to this. For example, as shown in Figures 15 to 19, the first lines 30, 54, and 74 do not have to include the first semicircle 31 and the second semicircle 32.

[0101] Furthermore, the shape and arrangement of the wiring patterns 50 and 70 of the reflective layer 100 shown in this modified example also apply to the wiring patterns 450 and 470 of the frequency-selective filter layer 400. Therefore, in the following explanation, the wiring patterns 50 and 70 will be used as examples.

[0102] The reflective layer 100 shown in Figure 15 includes a first insulator 41. Although not shown in the figure, the first insulator 41 has the same configuration as the first insulator 2 in the above embodiment (first surface 3, first layer 4, second layer 5, and groove 6).

[0103] The reflective layer 100 comprises a plurality of wiring patterns 50. Each wiring pattern 50 is formed of a fine metal wire 42. Each wiring pattern 50 is formed in a closed manner by the fine metal wire 42. The line width of the fine metal wire 42 is 1.0 μm or more and 3.0 μm or less, as in the above embodiment.

[0104] In this modified example, any one of the multiple wiring patterns 50, 70 (see Figure 18) is referred to as the "first wiring pattern 51, 71". Furthermore, a wiring pattern 50 adjacent to the first wiring pattern 51, 71 is referred to as the "second wiring pattern 52, 72". In the example shown in Figures 15 and 18, the second wiring pattern 52 is located in the upper right corner of the first wiring pattern 51, and the second wiring pattern 72 is located in the upper right corner of the first wiring pattern 71.

[0105] Both the first wiring pattern 51 and the second wiring pattern 52 are based on a regular hexagon. The pitch P is 25 μm or more and 100 μm or less, as in the above embodiment.

[0106] As shown in Figure 16, the first wiring pattern 51 has a first line 54 connecting a first point 61 and a second point 62. The first line 54 intersects with the straight line VL connecting the first point 61 and the second point 62.

[0107] As shown in Figure 17, the first line 54 is a sinusoidal curve. The first line 54 contains one or more wavelengths λ2 in the straight line VL connecting the first point 61 and the second point 62. In this modified example, the first line 30 contains three wavelengths λ2. That is, in this modified example, each wavelength λ2 in the first line 54 is the length obtained by dividing the length between the first point 61 and the second point 62 by "3".

[0108] Each wavelength λ2 of the first line 54 is between 1 / (4√3) and 1 / √3 times the pitch P, which is the distance between the centroid Cg1 of the first wiring pattern 51 and the centroid Cg2 of the second wiring pattern 52. Furthermore, the amplitude A of the sinusoidal first line 54 is between 1 / 20 and 1 / 3 times the wavelength λ2. This makes it possible to appropriately form the first line 54 as a sinusoidal curve in the first wiring pattern 51, which is based on a regular hexagon. As a result, electromagnetic waves incident on the reflective layer 100 strike the first line 54, causing the reflected waves to be diffused in all directions. In addition, reflected waves incident on the lower surface of the filter pattern 400A strike the third line 454, causing the reflected waves to be diffused again in all directions towards the reflective layer 100.

[0109] The above-mentioned "amplitude" corresponds to the distance (dimension A shown in Figure 17) from the straight line VL connecting the first point 61 and the second point 62 to the highest point of the peak or the deepest point of the valley included in one wavelength λ2 in a direction perpendicular to the straight line VL.

[0110] Furthermore, the reflective layer 100 shown in Figure 18 includes a plurality of wiring patterns 70. Each wiring pattern 70 is formed of a fine metal wire 73. Each wiring pattern 70 is formed in a regular hexagonal shape using the fine metal wire 73. The wire width of the fine metal wire 73 is 1.0 μm or more and 3.0 μm or less, as in the above embodiment.

[0111] As shown in Figure 18, the thin metal wires 73 that make up the wiring pattern 70 are formed as straight lines connecting one vertex to an adjacent vertex. For example, the first line 74 coincides with the straight line VL connecting the first point 81 and the second point 82. Also, the second line 75 coincides with the straight line connecting the first point 81 and the third point 83. In this case, the angle θ pointed to by the first line 74 and the second line 75 is 120 degrees, which is different from 90 degrees. The conventional wiring pattern 111 shown in Figure 9 corresponds to the case where the angle θ is 90 degrees.

[0112] As shown in Figure 18, by making the wiring pattern 70 formed of metal wires 73 a regular hexagon, the degree of diffusion of reflected waves reflected by the metal wires 73 can be increased compared to the conventional wiring pattern 111 shown in Figure 9. Furthermore, not limited to the example shown in Figure 18, when the angle θ is different from 90 degrees, that is, when the angle θ is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees, the degree of diffusion of reflected waves reflected by the metal wires 73 can be increased. In this way, the propagation distance of electromagnetic waves inside the dielectric layer 200 can be increased compared to the electromagnetic absorber 500 using the conventional wiring pattern 111 shown in Figure 9. As a result, the attenuation of electromagnetic waves inside the dielectric layer 200 can be increased, and the electromagnetic wave absorption performance of the electromagnetic wave absorber 500 can be improved.

[0113] Furthermore, in the wiring pattern 470 of the frequency-selective filter layer 400, it is preferable that the angle θ between the third line 474 and the fourth line 475 satisfies the aforementioned range. By doing so, the reflected wave incident on the lower surface of the filter pattern 400A is reflected again inside the electromagnetic wave absorber 500, and the degree of diffusion of the reflected wave in this case can be increased. As a result, the propagation distance of the electromagnetic wave inside the dielectric layer 200 can be increased, and as a result, the attenuation of the electromagnetic wave can be increased. This improves the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. Note that if the angle θ satisfies the aforementioned range, the metal wires 73 and 473 may be curved.

[0114] Furthermore, the wiring pattern in the reflective layer 100 does not have to be a periodic structure as shown in Figures 4, 15, and 18; it may be a non-periodic structure. For example, as shown in Figure 19, the metal nanowires 91 formed in the reflective layer 100 and the metal nanowires 491 formed in the frequency-selective filter layer 400 may have a Voronoi structure.

[0115] A Voronoi structure is a structure in which, for multiple generator points (sites) placed at arbitrary positions in a given metric space, regions are divided according to how close other points in the same metric space are to each generator point. In particular, in the case of the two-dimensional Euclidean plane, the boundaries of the regions are parts of the angle bisectors of each generator point.

[0116] Even when the wiring pattern formed by the metal wires 91 and 491 is a Voronoi structure, the angle θ between two straight lines extending in different directions from a single point (the first point) generally satisfies the range described above. Therefore, the degree of diffusion of the reflected waves reflected by the metal wires 91 and 491 can be increased.

[0117] [Second Modification] Figure 20A is a schematic diagram of the filter pattern according to the second modification, viewed from above. Figure 20B is a schematic diagram of another filter pattern according to the second modification, viewed from above. Figure 20C is a schematic diagram of yet another filter pattern according to the second modification, viewed from above.

[0118] The shape of the filter pattern formed in the frequency-selective filter layer 400 is not limited to the shape of the filter pattern 400A shown in Figures 1 and 2, but can be changed as appropriate.

[0119] For example, as shown in Figure 20A, the outline of the filter pattern 400B may be rectangular. Similarly, as shown in Figure 20B, the outline of the filter pattern 400C may be cross-shaped, and as shown in Figure 20C, the outline of the filter pattern 400D may be a rectangular frame.

[0120] In this way, only electromagnetic waves in a frequency band with a predetermined frequency width and a center frequency f (= c / λ) are absorbed by the electromagnetic wave absorber 500.

[0121] Furthermore, the shape and arrangement of the wiring patterns inside each of the filter patterns 400B, 400C, and 400D can take the shapes and arrangements shown in the embodiment and the first modified example.

[0122] (Other Embodiments) In the above embodiments, the first lines 30, 54, the second lines 33, 55, the third lines 430, 454, and the fourth lines 433, 455 do not have to be formed as perfect curves due to design or manufacturing-related accuracy requirements. That is, the first lines 30, 54, the second lines 33, 55, the third lines 430, 454, and the fourth lines 433, 455 do not have to be formed as highly accurate curves in design or manufacturing. They just need to be formed as curves that can diffuse reflected waves isotropically in all directions.

[0123] In the above embodiment and the first modification, a "regular hexagon" was shown as an example of a regular polygon that forms the base of the wiring pattern, but it is not limited to this shape. That is, regular polygons include equilateral triangles, squares, regular pentagons, etc. Furthermore, the base of the wiring pattern is not limited to regular polygons, and may be any polygon other than a quadrilateral.

[0124] Furthermore, in the wiring pattern 50 shown in Figures 15-17 of the first modified example, the first line 54 and the second line 55 may be triangular wave shapes. The first line 54 should intersect with the straight line connecting the first point 61 and the second point 62. Similarly, the second line 55 should intersect with the straight line connecting the first point 61 and the third point 63. By doing so, the degree of diffusion of reflected waves in the reflective layer 100 can be increased, thereby increasing the propagation distance of electromagnetic waves inside the dielectric layer 200.

[0125] Furthermore, the dielectric layer 200 may be composed of three or more dielectric layers. In this case as well, the different dielectric layers are bonded together by adhesive layers. Preferably, the absolute value of the difference between the relative permittivity of the dielectric layer and the relative permittivity of the adhesive layer is 0.1 or more.

[0126] (Summary) As a first disclosure, the electromagnetic wave absorber 500 comprises at least a frequency-selective filter layer 400, a dielectric layer 200 located below the frequency-selective filter layer 400, and a reflective layer 100 located below the dielectric layer 200. The reflective layer 100 has a sheet-like first insulator 2 having a first surface 3, and a first wiring pattern 11 provided on the upper surface of the first insulator 2 and formed of metal fine wires 13. The first wiring pattern 11 has a first point 21, a first line 30 extending from the first point 21, and a second line 33 extending from the first point 21. The angle between the first line 30 and the second line 33 is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

[0127] In the first disclosure, the angle between the first line 30 and the second line 33, which extend from the first point 21 in the first wiring pattern 11 formed of the metal nanowire 13, is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees. In this way, the degree of diffusion of reflected waves reflected by the reflective layer 100 can be increased compared to when using a reflective layer 110 having a conventional wiring pattern 111 composed of a rectangular frame. This increases the attenuation of electromagnetic waves inside the dielectric layer 200, and improves the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. Furthermore, the same effects as in the first disclosure can be achieved in electromagnetic wave absorbers 500 using a reflective layer 100 having wiring patterns 50, 70 as shown in the first modified example and a reflective layer 100 having metal nanowire 91 as shown in Figure 19. In other words, the degree of diffusion of reflected waves in the reflective layer 100 can be increased, and the propagation distance of electromagnetic waves inside the dielectric layer 200 can be increased. This increases the attenuation of electromagnetic waves within the dielectric layer 200, thereby improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500.

[0128] Furthermore, in all of the embodiments, first and second modifications, even when the thickness of the dielectric layer 200 is less than 1 / 4 of the wavelength of the incident electromagnetic wave, the attenuation of the electromagnetic wave inside the dielectric layer 200 can be increased, thereby improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. Note that if the thickness of the dielectric layer 200 is increased, for example, to more than 1 / 4 of the wavelength of the incident electromagnetic wave, the attenuation of the electromagnetic wave inside the dielectric layer 200 can be increased even further.

[0129] As a second disclosure, the first wiring pattern 11 is positioned to form a polygon when connected to each other by straight lines, and further comprises a plurality of vertices 20 including a first point 21 and a second point 22.

[0130] The first line 30 connects the first point 21 and the second point 22, and intersects with the line connecting the first point 21 and the second point 22. The aforementioned polygon may also be a quadrilateral.

[0131] In the second disclosure, the first line 30 (metal thin wire 13) forming the first wiring pattern 11 intersects (and is formed in a curved shape with) a straight line VL connecting the first point 21 and the second point 22.

[0132] Furthermore, the first wiring pattern 11 is positioned to form a polygon when connected to each other by straight lines. As a result, in the reflective layer 100, the first line 30 (metal thin wire 13), which is curved and intersects with the straight line VL, is arranged to form the outer shape of the first wiring pattern 11. Due to these features, when electromagnetic waves incident on the reflective layer 100 strike the first line 30, the degree of diffusion of the reflected waves can be significantly increased compared to the conventional reflective layer 110 configuration shown in Figure 9. In addition, the attenuation of electromagnetic waves inside the dielectric layer 200 can be increased, improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. Furthermore, an electromagnetic wave absorber 500 using a reflective layer 100 having the wiring pattern 50 shown in the first modified example can also achieve the same effects as in the first disclosure. That is, the degree of diffusion of reflected waves in the reflective layer 100 can be increased, and the propagation distance of electromagnetic waves inside the dielectric layer 200 can be increased. This increases the attenuation of electromagnetic waves within the dielectric layer 200, thereby improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500.

[0133] As a third disclosure, the polygon formed by the multiple vertices 20 is a regular polygon.

[0134] In the third disclosure, the first wiring pattern 11, which is based on a regular polygon, isotropic. As a result, in the reflective layer 100, the first lines 30 (metal thin wires 13) are arranged isotropically in the first wiring pattern 11. Consequently, when electromagnetic waves incident on the reflective layer 100 strike the first lines 30, the reflected waves diffuse isotropically in all directions. This significantly increases the degree of diffusion of reflected waves compared to the conventional reflective layer 110 shown in Figure 9, as electromagnetic waves incident on the reflective layer 100 strike the first lines 30. Furthermore, the attenuation of electromagnetic waves inside the dielectric layer 200 can be increased, improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. In addition, an electromagnetic wave absorber 500 using a reflective layer 100 having the wiring patterns 50 and 70 shown in the first modified example can also achieve the same effects as in the first disclosure. In other words, the degree of diffusion of reflected waves in the reflective layer 100 can be increased, thereby increasing the propagation distance of electromagnetic waves inside the dielectric layer 200. This increases the attenuation of electromagnetic waves inside the dielectric layer 200, thereby improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500.

[0135] As a fourth disclosure, the plurality of vertices 20 further have a third point 23 located at a position obtained by rotating the second point 22 by 120 degrees around the first point 21.

[0136] In the fourth disclosure, since the multiple vertices 20 further have a third point 23 located at a position where the second point 22 is rotated 120 degrees around the first point 21, it becomes possible to make the base shape of the first wiring pattern 11 a "regular hexagon". The first wiring pattern 11 based on a regular hexagon is isotropic. That is, the first line 30 (metal thin wire 13) can be arranged isotropically on each side of the first wiring pattern 11 based on a regular hexagon. As a result, when electromagnetic waves incident on the reflective layer 100 strike the first line 30, the reflected waves diffuse isotropically in all directions. Therefore, in the fourth disclosure, it becomes possible to further increase the degree of diffusion of the reflected waves in the direction the reflected waves are heading. As a result, the propagation distance of electromagnetic waves inside the dielectric layer 200 can be increased. This makes it possible to increase the attenuation of electromagnetic waves inside the dielectric layer 200 and improve the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. Furthermore, an electromagnetic wave absorber 500 using the reflective layer 100 according to the first modified example can also achieve the same effects as those of the fourth disclosure.

[0137] As a fifth disclosure, the first line 30 includes a first semicircle 31 whose diameter d1 is less than or equal to half the length between the first point 21 and the second point 22, and a second semicircle 32 connected to the first semicircle 31, whose diameter d2 is less than or equal to half the length between the first point 21 and the second point 22. The first semicircle 31 and the second semicircle 32 are located on opposite sides of the straight line VL connecting the first point 21 and the second point 22.

[0138] In the fifth disclosure, when an electromagnetic wave (incident wave) incident on the reflective layer 100 strikes the first semicircle 31 and the second semicircle 32, the reflected wave can be diffused in all directions. Furthermore, since the first semicircle 31 and the second semicircle 32 are located on opposite sides of the straight line VL connecting the first point 21 and the second point 22, when the incident wave strikes the first semicircle 31 and the second semicircle 32, the reflected wave when the incident wave strikes the first semicircle 31 and the reflected wave when the incident wave strikes the second semicircle 32 are diffused isotropically in all directions (see arrow Rw shown in Figure 5). As a result, the reflected wave can be diffused isotropically in all directions as a whole in the first wiring pattern 11. Also, the electromagnetic wave absorber 500 using the reflective layer 100 according to the first modification can achieve the same effects as in the fifth disclosure.

[0139] As a sixth disclosure, in the electromagnetic wave absorber 500 according to the first modified example, the first line 54 is a sine curve. The wavelength of the first line 54 is the length obtained by dividing the length between the first point 61 and the second point 62 by a natural number of 1 or more.

[0140] In the sixth disclosure, wavelengths corresponding to the above-mentioned natural numbers are formed in the first line 54. As a result, when electromagnetic waves incident on the reflective layer 100 strike the first line 54, the reflected waves can be diffused in all directions, and the generation of polarization at the reflection destination can be suppressed. The first line 54 may also be triangular wave shaped.

[0141] Furthermore, the reflective layer 100 of the electromagnetic wave absorber 500 according to the first modified example is provided on the first surface 3 of the first insulator 41 and is formed of metal thin wires 42, and further comprises a second wiring pattern 52 adjacent to the first wiring pattern 51. The first line 54 is a sine curve. The wavelength λ2 of the first line 54 is between 1 / (4√3) and 1 / √3 times the pitch P, which is the distance between the centroid Cg1 of the first wiring pattern 51 and the centroid Cg2 of the second wiring pattern 52. The amplitude of the first line 54 is between 1 / 20 and 1 / 3 times the wavelength.

[0142] In this disclosure, in a first wiring pattern 51 based on a regular hexagon, the first line 54 can be appropriately formed as a sinusoidal curve. As a result, when electromagnetic waves incident on the reflective layer 100 strike the first line 54, the reflected waves can be diffused in all directions.

[0143] As a seventh disclosure, the dielectric layer 200 includes at least a first dielectric layer 210 and a second dielectric layer 220 located above the first dielectric layer 210.

[0144] In the seventh disclosure, the dielectric layer 200 includes at least a first dielectric layer 210, a second dielectric layer 220, and an adhesive layer (third dielectric layer) 320 interposed between the first dielectric layer 210 and the second dielectric layer 220.

[0145] In the seventh disclosure, the interposition of the adhesive layer 320 between the first dielectric layer 210 and the second dielectric layer 220 ensures that the propagation direction of incident and / or reflected waves changes reliably at the interface between the first dielectric layer 210 and the second dielectric layer 220. Furthermore, the propagation direction of incident and / or reflected waves also changes reliably at the interface between the first dielectric layer 210 and the adhesive layer 330, and at the interface between the adhesive layer 330 and the second dielectric layer 220. This allows for an increase in the propagation distance of electromagnetic waves within the dielectric layer 200.

[0146] As the eighth disclosure, the relative permittivity ε2 of the adhesive layer 320 is different from the relative permittivity ε1 of the first dielectric layer 210 and the second dielectric layer 220, and the difference between the relative permittivity ε1 and the relative permittivity ε2 is 0.1 or more.

[0147] In the eighth disclosure, the propagation direction of the incident wave and / or reflected wave is reliably and significantly changed at the interface between the first dielectric layer 210 and the adhesive layer 330, or at the interface between the adhesive layer 330 and the second dielectric layer 220. This makes it possible to increase the propagation distance of electromagnetic waves within the dielectric layer 200.

[0148] As the ninth disclosure, the frequency-selective filter layer 400 has a period L shorter than the wavelength λ of the electromagnetic wave in the frequency band to be absorbed. Ｘ (=L ＹIt has multiple filter patterns 400A arranged two-dimensionally in the direction of the frequency-selective filter layer 400. When viewed from a direction orthogonal to the frequency-selective filter layer 400, the size of the filter pattern 400A is the period L Ｘ (=L Ｙ It is smaller than ).

[0149] The ninth disclosure describes the arrangement period L of the filter pattern 400A. Ｘ (=L Ｙ The wavelength λ of the electromagnetic wave to be absorbed is made shorter than the wavelength λ, and the size of the filter pattern 400A is set to the period L. Ｘ (=L Ｙ This is made smaller than ). As a result, frequency dependence is imparted to the electromagnetic waves that can be transmitted through the frequency-selective filter layer 400.

[0150] As the tenth disclosure, period L Ｘ (=L Ｙ The wavelength λ is set to be between 30% and 50%.

[0151] In the tenth disclosure, period L Ｘ (=L Ｙ By setting the length L to 30% to 50% of the wavelength λ, only electromagnetic waves in a frequency band with a predetermined frequency width and a center frequency f (= c / λ) can pass through the frequency-selective filter layer 400 and reach the reflection layer 100. In other words, only electromagnetic waves in a frequency band with a predetermined frequency width and a center frequency f are absorbed by the electromagnetic wave absorber 500. Ａ The wavelength λ is set to be between 26% and 29%, and the length L Ｂ It is more preferable that the value be between 4% and 8% of the wavelength λ. Only electromagnetic waves in a frequency band with a predetermined frequency width and a center frequency f are reliably absorbed by the electromagnetic wave absorber 500.

[0152] Furthermore, an electromagnetic wave absorber 500 using a frequency-selective filter layer 400 having filter patterns 400B, 400C, and 400D according to the second modified example can also achieve the same effects as those of the tenth disclosure.

[0153] As an eleventh disclosure, each of the plurality of filter patterns 400A includes a third wiring pattern 411 formed of a metal fine wire 413. The third wiring pattern 411 has a fourth point 421, a third line 430 extending from the fourth point 421, and a fourth line 433 extending from the fourth point 421. The angle between the third line 430 and the fourth line 433 is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

[0154] In the eleventh disclosure, the angle between the third line 430 and the fourth line 433 is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees. This makes it possible to increase the degree of diffusion of reflected waves reflected from the lower surface of the frequency-selective filter layer 400 compared to when using a frequency-selective filter layer having a conventional wiring pattern composed of a rectangular frame. This makes it possible to increase the attenuation of electromagnetic waves inside the dielectric layer 200 and improve the electromagnetic wave absorption performance of the electromagnetic wave absorber 500. Furthermore, the same effects as in the eleventh disclosure can be achieved in the electromagnetic wave absorber 500 using the frequency-selective filter layer 400 having the wiring patterns 450 and 470 shown in the first modified example and the frequency-selective filter layer 400 having the metal nanowire 491 shown in Figure 19.

[0155] As a twelfth disclosure, the third wiring pattern 411 of the frequency-selective filter layer 400 has the same shape as the first wiring pattern 11 of the reflective layer 100.

[0156] In the twelfth disclosure, the third wiring pattern 411 and the first wiring pattern 11 are made to have the same shape. This makes it possible to make the pattern of the metal wires 413 in the frequency-selective filter layer 400 and the pattern of the metal wires 13 in the reflective layer 100 the same, and to unify the manufacturing process of the frequency-selective filter layer 400 and the reflective layer 100. This reduces the cost of the electromagnetic wave absorber 500.

[0157] Furthermore, the reflective layer 100 is provided on the first surface 3 of the first insulator 2 and is formed of metal wires 13, and further comprises a second wiring pattern 12 adjacent to the first wiring pattern 11. The centroid Cg1 of the first wiring pattern 11 and the centroid Cg2 of the second wiring pattern 12 are spaced apart by a predetermined distance (= pitch P). The frequency-selective filter layer 400 is provided on the second surface 403 of the second insulator 402 and is formed of metal wires 413, and further comprises a fourth wiring pattern 412 adjacent to the third wiring pattern 411. The centroid Cg3 of the third wiring pattern 411 and the centroid Cg4 of the fourth wiring pattern 412 are spaced apart by a predetermined distance (= pitch P).

[0158] The third wiring pattern 411 may have a different shape from the first wiring pattern 11. However, even in that case, the first wiring pattern 11 and the third wiring pattern 411 each have at least the features shown in the first and second disclosures, respectively.

[0159] Furthermore, if the third wiring pattern 411 and the first wiring pattern 11 have different shapes, the distance between the centroid Cg1 of the first wiring pattern 11 and the centroid Cg2 of the second wiring pattern 12 may be different from the distance between the centroid Cg3 of the third wiring pattern 411 and the centroid Cg4 of the fourth wiring pattern 412.

[0160] However, the distance between them (= pitch P) is preferably 25 μm or more and 100 μm or less. By doing so, the transparency of the electromagnetic wave absorber 500 can be ensured, that is, the visibility of the wiring pattern 10 in the reflective layer 100 and the metal fine wires 413 in the filter pattern 400A can be reduced.

[0161] As a thirteenth disclosure, the frequency-selective filter layer 400 is used in an electromagnetic wave absorber 500 that absorbs electromagnetic waves by utilizing dielectric loss. The frequency-selective filter layer 400 comprises a sheet-like second insulator 402 having a second surface 403, and a period L provided on the upper surface of the second insulator 402, which is shorter than the wavelength λ of the electromagnetic wave in the frequency band to be absorbed. Ｘ (=L ＹIt has multiple filter patterns 400A arranged two-dimensionally in the direction of the frequency-selective filter layer 400. When viewed from a direction orthogonal to the frequency-selective filter layer 400, the size of the filter pattern 400A is the period L Ｘ (=L Ｙ It is smaller than ).

[0162] The 13th disclosure describes the arrangement period L of the filter pattern 400A. Ｘ (=L Ｙ The wavelength λ of the electromagnetic wave to be absorbed is made shorter than the wavelength λ, and the size of the filter pattern 400A is set to the period L. Ｘ (=L Ｙ This is made smaller than ). As a result, frequency dependence is imparted to the electromagnetic waves that can be transmitted through the frequency-selective filter layer 400.

[0163] As the 14th disclosure, period L Ｘ (=L Ｙ The wavelength λ is set to be between 30% and 50%.

[0164] In the 14th disclosure, period L Ｘ (=L Ｙ By setting the frequency of the filter to 30% to 50% of the wavelength λ, only electromagnetic waves in a frequency band with a predetermined frequency width and a center frequency of frequency f (= c / λ) can pass through the frequency-selective filter layer 400 and reach the reflection layer 100. In other words, only electromagnetic waves in a frequency band with a predetermined frequency width and a center frequency of frequency f are absorbed by the electromagnetic wave absorber 500.

[0165] Furthermore, an electromagnetic wave absorber 500 using a frequency-selective filter layer 400 having filter patterns 400B, 400C, and 400D according to a second modified example can also achieve the same effects as those disclosed in the 13th and 14th disclosures.

[0166] As a fifteenth disclosure, each of the plurality of filter patterns 400A includes a third wiring pattern 411 formed of a metal fine wire 413. The third wiring pattern 411 has a fourth point 421, a third line 430 extending from the fourth point 421, and a fourth line 433 extending from the fourth point 421. The angle between the third line 430 and the fourth line 433 is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

[0167] In the 15th disclosure, the angle between the third line 430 and the fourth line 433, which extend from the fourth point 421 included in the third wiring pattern 411 formed of metal nanowires 413, is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees. By doing so, the degree of diffusion of reflected waves reflected again at the lower surface of the frequency-selective filter layer 400 can be increased compared to when using a frequency-selective filter layer having a conventional wiring pattern composed of a rectangular frame. As a result, the attenuation of electromagnetic waves inside the dielectric layer 200 can be increased, and the electromagnetic wave absorption performance of the electromagnetic wave absorber 500 can be improved. Furthermore, the same effects as in the 15th disclosure can be achieved in the electromagnetic wave absorber 500 using the frequency-selective filter layer 400 having wiring patterns 450 and 470 as shown in the first modified example and the frequency-selective filter layer 400 having metal nanowires 491 as shown in Figure 19. In other words, the degree of diffusion of reflected waves that are reflected again at the lower surface of the frequency-selective filter layer 400 is increased, thereby increasing the propagation distance of electromagnetic waves inside the dielectric layer 200. This increases the attenuation of electromagnetic waves inside the dielectric layer 200, thereby improving the electromagnetic wave absorption performance of the electromagnetic wave absorber 500.

[0168] The shape of the third line 430 may have the same characteristics as the shape of the first line 30 in the second disclosure. In this case as well, the frequency-selective filter layer 400 can achieve the same effects as in the fifteenth disclosure.

[0169] Furthermore, as a sixteenth disclosure, in the reflective layer 100, the wiring pattern composed of metal nanowires 91 has a plurality of vertices located at positions where they form polygons when connected to each other by straight lines. The polygons formed by the plurality of vertices are arranged two-dimensionally and aperiodically on the upper surface of the first insulator 2. In other words, the wiring pattern composed of metal nanowires 91 has a plurality of vertices located at positions where they form polygons when connected to each other by straight lines. The polygons formed by the plurality of vertices are arranged two-dimensionally on the upper surface of the first insulator 2, constituting a Voronoi structure.

[0170] In the sixteenth disclosure, the angle formed by the metal wires 91 extending in different directions from one vertex generally satisfies the range of angles formed by the first line 30 and the second line 33 in the first disclosure. Therefore, it can achieve the same effects as the first disclosure.

[0171] Furthermore, as a seventeenth disclosure, in the frequency-selective filter layer 400, the wiring pattern composed of metal nanowires 491 has a plurality of vertices located at positions where they form a polygon when connected to each other by straight lines. The polygon formed by the plurality of vertices is arranged two-dimensionally and aperiodically on the upper surface of the second insulator 402. In other words, the wiring pattern composed of metal nanowires 491 has a plurality of vertices located at positions where they form a polygon when connected to each other by straight lines. The polygon formed by the plurality of vertices is arranged two-dimensionally on the upper surface of the second insulator 402, forming a Voronoi structure.

[0172] In other words, in the seventeenth disclosure, in the frequency-selective filter layer 400, the angle formed by the metal nanowires 491 extending in different directions from one vertex generally satisfies the range of angles formed by the third wire 430 and the fourth wire 433 in the eleventh disclosure. Therefore, it is possible to achieve the same effects as in the eleventh disclosure.

[0173] The electromagnetic wave absorber of this disclosure is useful because it can increase the propagation distance of electromagnetic waves within the dielectric layer, thereby improving its electromagnetic wave absorption performance.

[0174] 2, 41 First insulator 3 First surface 4 First layer 5 Second layer 6 Groove 10, 50, 70 Wiring pattern 11, 51, 71 First wiring pattern 12, 52, 72 Second wiring pattern 13, 42, 73, 91 Fine metal wire 20, 60 Vertices 21, 61, 81 First point 22, 62, 82 Second point 23, 63, 83 Third point 30, 54, 74 First line 33, 55, 75 Second line 31 First semicircle 32 Second semicircle 34 Third semicircle 35 Fourth semicircle 100 Reflective layer 110 Reflective layer according to conventional configuration 111 Wiring pattern according to conventional configuration 112 Fine metal wire according to conventional configuration 113 First surface 200 Dielectric layer 210 First dielectric layer 220 Second dielectric layer 310 Adhesive layer 320 Adhesive layer (third dielectric layer) 330 Adhesive layer 400 Frequency select filter layer 400A-400D Filter pattern 402 Second insulator 403 Second surface 410, 450, 470 Wiring pattern 411, 451, 471 Third wiring pattern 412, 452, 472 Fourth wiring pattern 413, 442, 473, 491 Metal wire 420, 460 Vertices 421, 461, 481 Fourth point 422, 462, 482 Fifth point 423, 463, 483 Sixth point 430, 454, 474 Third line 433, 455, 475 Fourth line 431 Fifth semicircle 432 Sixth semicircle 434 Seventh semicircle 435 Eighth semicircle 500 Electromagnetic wave absorber 510 Unit cell d1: Diameter of the first (fifth) semicircle d2: Diameter of the second (sixth) semicircle VL Straight line P Pitch Cg1 Centroid of the first wiring pattern Cg2 Centroid of the second wiring pattern Cg3 Centroid of the third wiring pattern Cg4 Centroid of the fourth wiring pattern

Claims

1. An electromagnetic wave absorber comprising at least a frequency-selective filter layer, a dielectric layer located below the frequency-selective filter layer, and a reflective layer located below the dielectric layer, wherein the reflective layer comprises a sheet-like first insulator having a first surface, and a first wiring pattern provided on the upper surface of the first insulator and formed of thin metal wires, wherein the first wiring pattern comprises a first point, a first line extending from the first point, and a second line extending from the first point, and the angle between the first line and the second line is greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

2. The electromagnetic wave absorber according to claim 1, wherein the first wiring pattern is provided at positions that form a polygon when connected to each other by straight lines, and further comprises a plurality of vertices including the first point and the second point, and the first line connects the first point and the second point and intersects with the straight line connecting the first point and the second point.

3. The electromagnetic wave absorber according to claim 2, wherein the polygon formed by the plurality of vertices is a regular polygon.

4. The electromagnetic wave absorber according to claim 2, wherein the plurality of vertices further include a third point located at a position obtained by rotating the second point by 120 degrees around the first point.

5. The electromagnetic wave absorber according to claim 2, wherein the first line includes a first semicircle whose diameter is less than or equal to half the length between the first point and the second point, and a second semicircle whose diameter is less than or equal to half the length between the first point and the second point and is connected to the first semicircle, and the first semicircle and the second semicircle are located on opposite sides of the straight line connecting the first point and the second point.

6. The electromagnetic wave absorber according to claim 2, wherein the first line is a sine curve, and the wavelength of the first line is the length obtained by dividing the length between the first point and the second point by a natural number of 1 or more.

7. The electromagnetic wave absorber according to claim 1, wherein the dielectric layer comprises at least a first dielectric layer, a second dielectric layer located above the first dielectric layer, and a third dielectric layer between the first dielectric layer and the second dielectric layer.

8. The electromagnetic wave absorber according to claim 7, wherein the third dielectric layer has a relative permittivity different from that of the first dielectric layer and the second dielectric layer, and the absolute value of the difference between the relative permittivity of the third dielectric layer and the relative permittivity of the first dielectric layer and the second dielectric layer is 0.1 or more.

9. The electromagnetic wave absorber according to claim 1, wherein the frequency-selective filter layer has a plurality of filter patterns arranged two-dimensionally with a period shorter than the wavelength of the electromagnetic wave to be absorbed, and the size of the filter patterns, when viewed from a direction orthogonal to the frequency-selective filter layer, is smaller than the period.

10. The electromagnetic wave absorber according to claim 9, wherein the period is 30% or more and 50% or less of the wavelength.

11. The electromagnetic wave absorber according to claim 9, wherein each of the plurality of filter patterns includes a third wiring pattern formed of the metal fine wires, the third wiring pattern having a fourth point, a third line extending from the fourth point, and a fourth line extending from the fourth point, the angle between the third line and the fourth line being greater than 0 degrees and less than 90 degrees, or greater than 90 degrees and less than 180 degrees.

12. The electromagnetic wave absorber according to claim 11, wherein the third wiring pattern of the frequency-selective filter layer has the same shape as the first wiring pattern of the reflective layer.

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