Radio wave absorber

Abstract

A radio wave absorber according to the present invention comprises: a substrate made of a dielectric; a conductor thin film formed on the entire rear surface of the substrate; and a ring body made of three or more annular conductor thin films arranged concentrically on the front surface. When the wavelength of a to-be-absorbed radio wave is λ (m) and the relationship between the frequency f (Hz) of the radio wave and λ is (λ = c／f: c is the speed of light), if the width of the outermost annular first ring body is defined as R1, the width of the second ring body is defined as R2, the width of the third ring body is defined as R3, the interval between the first ring body and the second ring body is defined as S1, and the interval between the second ring body and the third ring body is defined as S2, it is preferable to satisfy the following relationship. ０.０００８×λ≦Ｒ１≦０.０６０８×λ、０.１１２×λ≦Ｒ２≦０.１４２４×λ、Ｒ３=optional、０.０８×λ≦Ｓ１≦０.１６×λ、Ｓ２=optional

Description

Radio wave absorber

[0001] This invention relates to a radio wave absorber. This application claims priority based on Japanese Patent Application No. 2025-031085, filed in Japan on February 28, 2025, the contents of which are incorporated herein by reference.

[0002] Radio wave absorbing materials, especially those with high performance exceeding 10 dB absorption, tend to be heavier and thicker because they contain larger amounts of ferrite or metal powder that act as radio wave absorbing materials. For example, Patent Document 1 below describes a material with the composition formula Co ｘ Zn ２-ｘ BaFe １６ O ２７ A radio wave absorber is disclosed having a radio wave absorbing layer made of a radio wave absorbing material in which an appropriate amount of W-type hexagonal ferrite powder is mixed into the matrix.

[0003] Japanese Patent Application Publication No. 2009-059728

[0004] According to conventional radio wave absorbers described in Patent Document 1 and others, the radio wave absorption rate of the material itself cannot be changed, and in order to increase the amount of radio wave absorption, there is no other measure than to increase the thickness according to the Lambert-Beer law. Therefore, in the case of conventional radio wave absorbers, in order to improve the radio wave absorption performance, the material had to be thick and heavy.

[0005] In view of the circumstances described above, the present invention aims to provide a radio wave absorber that can obtain sufficient radio wave absorption characteristics even with a lightweight and thin structure by introducing a novel structure unlike any other.

[0006] To solve the aforementioned problems, the present invention proposes the following embodiments. <1> An electromagnetic wave absorber according to one embodiment of the present invention comprises a substrate made of a dielectric, a reflective film made of a conductive thin film formed on the entire back surface of the substrate, and a ring body made of three or more annular conductive thin films arranged concentrically on the surface of the substrate, or a ring body made of two or more annular conductive thin films arranged concentrically and a central body made of a circular conductive thin film positioned in the center of the concentric arrangement.

[0007] With this configuration, three or more annular ring bodies exhibit a lens effect that scatters radio waves attempting to enter the base body from the surface side of the base body, and function to re-reflect radio waves that pass through the base body and attempt to exit from the surface side thereof. The same function is also achieved in a configuration including a ring body formed of two or more concentrically arranged annular conductor thin films and a central body formed of a circular conductor thin film arranged at the center of the concentric arrangement. Part of the radio waves incident on the base body is reflected by the reflective film on the back surface side of the base body, while part of the radio waves inside the base body is converted into heat and dissipated inside the dielectric constituting the base body, thereby exhibiting a radio wave absorbing effect.

[0008] <2> In the radio wave absorber according to one aspect of the present invention, when the wavelength of the radio wave to be absorbed is defined as λ (m), and the relationship between the frequency f (Hz) of the radio wave to be absorbed and λ is (λ = c / f, where c is the speed of light), among the three or more annular ring bodies, the width of the outermost annular first ring body is R １ , the width of the second annular second ring body positioned inside thereof is defined as R ２ , the width of the third annular third ring body positioned inside thereof is defined as R ３ , the interval between the first ring body and the second ring body is defined as S １ , and the interval between the second ring body and the third ring body is defined as S ２ , it is preferable that the following relational expressions and the following relationships are satisfied. 0.0008×λ≦R １ ≦0.0608×λ...Expression (1) 0.112×λ≦R ２ ≦0.1424×λ...Expression (2) R ３ = arbitrary 0.08×λ≦S １ ≦0.16×λ ...Expression (3) S ２ = arbitrary

[0009] <3> In the radio wave absorber according to one aspect of the present invention, it is preferable that the plurality of concentrically arranged ring bodies exhibit a lens effect that scatters radio waves attempting to enter the base body from the surface side of the base body, and function to re-reflect radio waves that pass through the base body and attempt to exit to the surface side of the base body.

[0010] In the radio wave absorber according to the present invention, a plurality of concentrically arranged ring bodies exhibit a lens effect that scatters radio waves attempting to enter the dielectric substrate from the surface side, and re-reflects radio waves attempting to exit the substrate to the surface side. The conductive thin film on the back side of the substrate reflects radio waves attempting to exit from the back side of the substrate to the outside. These effects work together to confine radio waves that enter the substrate, and a portion of these radio waves can be converted into heat and dissipated within the dielectric substrate. Therefore, a thin, lightweight radio wave absorber with excellent absorption can be provided.

[0011] A perspective view showing the front side of the radio wave absorber according to the first embodiment of the present invention. A perspective view showing the back side of the radio wave absorber according to the first embodiment. A front view showing the front side of the radio wave absorber according to the first embodiment. The width (R) of the first ring body in the radio wave absorber according to the first embodiment. １ A graph showing the results of a simulation of the relationship between the width (R) of the second ring body in the radio wave absorber according to the first embodiment. ２ A graph showing the results of a simulation of the relationship between the width (R) of the third ring body in the radio wave absorber according to the first embodiment. ３ A graph showing the results of a simulation of the relationship between the distance between the first ring body and the second ring body (S) in the radio wave absorber according to the first embodiment. １ A graph showing the results of a simulation of the relationship between the distance between the second ring body and the third ring body (S) in the radio wave absorber according to the first embodiment. ２ A graph showing the results of a simulation of the relationship between ( ) and the absorption rate.

[0012] <First Embodiment> Hereinafter, a radio wave absorber according to the first embodiment of the present invention will be described with reference to Figures 1 to 3. Note that in the drawings used in the following description, characteristic parts may be shown in enlargement. Figure 1 is a perspective view showing the front side of the radio wave absorber 1 according to the first embodiment, Figure 2 is a perspective view showing the back side of the radio wave absorber 1, and Figure 3 is a front view of the radio wave absorber 1. The radio wave absorber 1 according to this embodiment has a film-like substrate 2 made of a dielectric material that is square in plan view, a first ring body 5 on the outermost periphery, a second ring body 6 and a third ring body 7 inside it, arranged concentrically on the surface side of the substrate 2, and a reflective film 8 made of a conductive thin film that covers the entire back surface of the substrate 2.

[0013] The substrate 2 consists of a predetermined thickness of a square-shaped film or thin plate made of a dielectric material such as a synthetic resin. The planar shape of the substrate 2 is not particularly restricted. It may be a square shape as shown in Figure 1, or it may be a rectangular, circular, elliptical, sector-shaped, polygonal, or three-dimensional shape. As the synthetic resin constituting the substrate 2, one or more can be selected from the group consisting of PET (polyethylene terephthalate), polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin. In this embodiment, the thickness of the substrate 2 is set to about 50 μm, but it is not limited to this. The thickness of the substrate 2 can be selected to be about 20 to 2000 μm. The substrate 2 may have a configuration that includes any other material inside a dielectric such as a synthetic resin, or a laminated structure of multiple resin layers.

[0014] The first ring body 5, the second ring body 6, and the third ring body 7 are all annular in shape. In the first embodiment, the first ring body 5 is formed with the largest diameter, the second ring body 6 with the second largest diameter, and the third ring body 7 with the smallest diameter. The circles forming the outer or inner periphery of each of the first ring body 5, the second ring body 6, and the third ring body 7 must be perfect circles to obtain excellent radio wave absorption. The first ring body 5, the second ring body 6, and the third ring body 7 are all made of a conductive thin film such as a metal layer.

[0015] When the first ring body 5, the second ring body 6, and the third ring body 7 are formed from metal layers, the metal layers can be made from the metals listed below. The metal layers only need to be made from a metal that has free electrons, such as silver, and are not limited to silver. For example, they may be gold (Au), copper (Cu), platinum (Pt), zinc (Zn), iron (Fe), tin (Sn), lead (Pb), aluminum (Al), cobalt (Co), indium (In), nickel (Ni), chromium (Cr), titanium (Ti), altimon (Sb), bismuth (Bi), thallium (Tl), germanium (Ge), cadmium (Cd), silicon (Si), tungsten (W), molybdenum (Mo), indium tin oxide (ITO), and alloys (for example, alloys containing nickel, chromium, and molybdenum). Examples of alloys containing nickel, chromium, and molybdenum include various grades of Hastelloy® B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X. When applying these metal layers, the layer thickness can be selected to be 0.005 to 10 μm, for example, about 0.5 μm. A conductive thin film made of these listed metals may also be applied to the reflective film 8 provided on the entire back surface of the substrate 2.

[0016] In the structure of the first embodiment, the widths and spacing of the first ring body 5, the second ring body 6, and the third ring body 7 have a special relationship. The first ring body 5 is the largest diameter ring, the second ring body 6 is the second largest diameter ring, and the third ring body 7 is the smallest diameter ring, and these are arranged in concentric circles starting from the center of the base body 2.

[0017] In the radio wave absorber 1 of this embodiment, the wavelength of the radio wave to be absorbed is defined as λ (m), and the relationship with the frequency f (Hz) of the radio wave to be absorbed is defined as (λ = c / f: c = speed of light). Furthermore, the width of the first ring body 5 is R １ Defined as such, the width of the second ring body 6 is R ２ Defined as such, the width of the third ring body 7 is R ３ This is defined as follows. Also, the distance between the first ring body 5 and the second ring body 6 is defined as S. １ Defined as such, the distance between the second ring body 6 and the third ring body 7 is S ２ This is how it is defined. Based on the above definition, R １ and R ２ and R ３ and S １ and S ２ It is more preferable that the following relationships (1) to (3) and the relationship described below are satisfied: 0.0008 × λ ≤ R １ ≦0.0608×λ…(1) Formula 0.112×λ≦R ２ ≦0.1424×λ…(2) Formula R ３ = arbitrary 0.08×λ≦S １ ≦0.16×λ...Equation (3) S ２ =Optional Note: R ３ = any, S ２ = Since this is arbitrary, the third ring body 7 must be located inside the second ring body 6 at any width and interval in a concentric circle. ３ While not particularly limited, it is preferably 0 × λ or more and 0.0032 × λ ​​or less, and more preferably 0.008 × λ or more and 0.0224 × λ or less. ２While not particularly limited, it is preferable that the value is between 0.1408 × λ and 0.1504 × λ. Furthermore, the third ring body 7 can be replaced with a central body made of a circular conductive thin film. In this case, the configuration will consist of a first ring body 5 and a second ring body 6 made of two concentrically arranged annular conductive thin films, and a central body made of a circular conductive thin film (not shown) placed in the center of the concentric arrangement. There may be three or more ring bodies made of concentrically arranged annular conductive thin films.

[0018] In a configuration having a first ring body 5, a second ring body 6, and a third ring body 7, for example, in the case of a 48 GHz radio wave, the wavelength is 6.25 mm, so the following relationship holds: 0.005 ≤ R １ ≤0.38, 0.7 ≤R ２ ≤0.89, 0.5 ≤S １ ≤ 1

[0019] Also, R １ and R ２ and R ３ and S １ and S ２ It is more preferable that equations (4) to (6) below satisfy the relationship described below: 0.00128 × λ ≤ R １ ≦0.048×λ…Equation (4) 0.1152×λ≦R ２ ≦0.136×λ…(5) Formula R ３ = arbitrary 0.096×λ≦S １ ≦0.16×λ…(6) formula S ２ = any

[0020] In a configuration having a first ring body 5, a second ring body 6, and a third ring body 7, for example, in the case of a 48 GHz radio wave, the wavelength is 6.25 mm, so the following relationship holds: 0.008 ≤ R １ ≤0.3 0.72 ≤R ２ ≤0.85 0.6 ≤S １ ≤ 1

[0021] Also, R １ and R ２ and R ３ and S １ and S２ It is even more preferable that equations (7) to (9) below satisfy the relationship described below: 0.0016 × λ ≤ R １ ≦0.04×λ…Equation (7) 0.12×λ≦R ２ ≦0.1344×λ…(8) Formula R ３ = arbitrary 0.112×λ≦S １ ≦0.16×λ...Equation (9) S ２ = any

[0022] In a configuration having a first ring body 5, a second ring body 6, and a third ring body 7, for example, in the case of a 48 GHz radio wave, the wavelength is 6.25 mm, so the following relationship holds: 0.01 ≤ R １ ≤0.25 0.75 ≤R ２ ≤0.84 0.84≦S １ ≤ 1

[0023] By satisfying the relationships shown in equations (1) to (3) above, a radio wave absorber 1 exhibiting an absorption rate of 10 dB or more can be obtained. By satisfying equations (4) to (6), a radio wave absorber 1 with superior radio wave absorption rate can be obtained, and by satisfying equations (7) to (9), a radio wave absorber 1 with even better radio wave absorption rate can be obtained. These relationships are obtained from the R obtained in the simulation results described later. １ , R ２ , R ３ S １ S ２ This is proven by the relationship between the radio wave absorption rate and the material.

[0024] In the embodiments shown in Figures 1 and 3, the first ring body 5 is formed to be inscribed within the four sides of the base body 2, but it is not limited to this. It is sufficient that it is positioned on the surface side of the base body 2. In the embodiments shown in Figures 1 and 3, the width (R) of the second ring body 6 ２ ) is the width (R) of the first ring body 5. １ ) and the width (R) of the third ring body 7 ３Although it is formed larger than (2), it is sufficient that it is formed within the range shown by equation (2). Since the width of the third ring body 7 is arbitrary in the relationship of the equation, the width of the third ring body 7 may be smaller than the width of the second ring body 6, as shown in Figure 1, or it may be wider than the width of the second ring body 6. Also, as mentioned above, the third ring body 7 can be a circular central body.

[0025] In the radio wave absorber 1, a structure in which a first ring body 5, a second ring body 6, and a third ring body 7 are present on the surface side of the substrate 2, and a reflective film 8 is present on the back side of the substrate 2, can be obtained to obtain excellent radio wave absorption performance. With the above configuration, the three annular ring bodies 5, 6, and 7 exhibit a lens effect that scatters radio waves attempting to enter the substrate 2 from the surface side of the substrate 2, and also exhibit a re-reflection effect of radio waves attempting to exit the surface side of the substrate 2. A portion of the radio waves incident on the substrate 2 is reflected by the reflective film 8 on the back side of the substrate 2, but a portion of the radio waves inside the substrate 2 are converted into heat and disappear within the dielectric material constituting the substrate 2, resulting in an excellent radio wave absorption effect.

[0026] Furthermore, if the ring bodies 5, 6, and 7 in the radio wave absorber 1 satisfy the relationships described in equations (1) to (3) above, even better radio wave absorption performance, such as an absorption rate of 10 dB or more, can be achieved. When the relationships satisfy the relationships described in equations (1) to (3) above, the ring bodies 5, 6, and 7 can efficiently exert a lens effect that diffuses radio waves that are about to enter the substrate 2 from the surface side of the radio wave absorber 1. Moreover, the effect of confining radio waves that are about to exit from the inside of the substrate 2 to the surface side of the substrate 2 is efficiently exerted, resulting in an excellent radio wave absorption rate. The radio wave absorber 1 shown in Figure 1 can be applied, for example, as a component of the peripheral wall of an anechoic chamber. This makes it possible to provide an anechoic chamber that does not affect the surroundings with electromagnetic noise and is itself less susceptible to the influence of electromagnetic noise from the surroundings.

[0027] (Simulation results of radio wave absorption rate) A design space exploration simulation was performed using Dassault Systems K.K.'s software, CST studio suite 2024 (3D EM analysis software for electromagnetic field analysis, design, and optimization), in conjunction with Ilight 2024 Design Gateway, also from Dassault Systems K.K. Electromagnetic field analysis was performed using the FDTD (Finite Difference Time Domain Method), and the dimensions were optimized for the desired performance based on the results of the electromagnetic field analysis. A genetic algorithm (GA) was used for the optimization method.

[0028] The radio wave absorption rate when a 48 GHz (wavelength 6.25 mm) radio wave is incident on a resin substrate 2 with a dielectric constant of 2.9 having a first ring body, a second ring body, and a third ring body as shown in Figure 3 is determined by the parameter R of the width of the first ring body. １ , width R of the second ring body ２ , width R of the third ring body ３ The distance S between the first ring body and the second ring body. １ The distance S between the second ring body and the third ring body. ２ The values ​​were determined for each of the following cases. The film thickness of the first, second, and third ring bodies was set to 5 μm, and the thickness of the substrate 2 was set to 1000 μm, and the simulation was performed.

[0029] Width of the first ring body 5 (R １ Figure 4 shows the simulation results of the radio wave absorption rate when the width (R) of the second ring body 6 is changed. ２ Figure 5 shows the simulation results of the radio wave absorption rate when the width (R) of the third ring body 7 is changed. ３ Figure 6 shows the simulation results of the radio wave absorption rate when the distance between the first ring body 5 and the second ring body 6 (S １ Figure 7 shows the simulation results of the radio wave absorption rate when the distance between the second ring body 6 and the third ring body 7 (S) is changed. ２ Figure 8 shows the simulation results of the radio wave absorption rate when the ) is changed. In Figures 4 to 8, the region where the value on the vertical axis is 0.9 or higher corresponds to the region where the radio wave absorption rate is 10 dB or higher.

[0030] Further, the respective values of the calculation results underlying the simulation results shown in FIGS. 4 to 8 are shown in Tables 1 to 9 below.

[0031]

[0032]

[0033]

[0034]

[0035]

[0036]

[0037]

[0038]

[0039]

[0040] Looking at the results shown in FIG. 4, the index on the vertical axis (3D / Mix 0D) is a numerical value corresponding to radio wave absorptivity. The position of the rightmost plot among the plurality of plots with a numerical value of 0.9 or more is 0.38. Since a numerical value of 0.9 or more indicates an absorptivity of 10 dB or more, it can be determined that the position of the leftmost plot among the plurality of plots is 0.005. Each plot in FIG. 4 corresponds to R shown in Tables 1 to 2 １ with respect to which the numerical values of the simulation results shown in Nos. 1 to 198 are presented. From the graph collectively showing the simulation results shown in FIG. 4 and the results shown in Tables 1 and 2, R １ can be read to have a lower limit of 0.005 and an upper limit of 0.38. In this case, it can be mentioned that the relationship 0.005≦R １ ≦0.38, which is a specific example of 48 GHz band radio waves in the aforementioned formula (1), is satisfied.

[0041] Further, from the graph of the simulation results shown in FIG. 4 and the results shown in Tables 1 and 2, more preferable R １ can be read to have a lower limit of 0.008 and an upper limit of 0.3. In this case, 0.008≦R １it can be stated that the relationship of ≦0.3 is satisfied. Further, from the graph of simulation results shown in FIG. 4 and the results shown in Table 1 and Table 2, the most preferable R １ can be read to have a lower limit of 0.01 and an upper limit of 0.25. In this case, 0.01≦R, which is a specific example of radio waves in the 48 GHz band according to the above formula (7) １ it can be stated that the relationship of ≦0.25 is satisfied.

[0042] Looking at the results shown in FIG. 5, a plurality of plots with a numerical value of 0.9 or more are distributed in the range of 0.7 or more and 0.89 or less for the value of R ２ Similarly, from the graph summarizing the simulation results shown in FIG. 5 and the results shown in Tables 2 to 4, R ２ can be read to have a lower limit of 0.7 and an upper limit of 0.89. In this case, 0.7≦R, which is a specific example of radio waves in the 48 GHz band according to the above formula (2) ２ it can be stated that the relationship of ≦0.89 is satisfied. Further, from the graph of simulation results shown in FIG. 5 and the results shown in Tables 2 to 4, more preferable R ２ can be read to have a lower limit of 0.8 and an upper limit of 0.85. In this case, 0.72≦R, which is a specific example of radio waves in the 48 GHz band according to the above formula (5) ２ it can be stated that the relationship of ≦0.85 is satisfied. Further, from the graph of simulation results shown in FIG. 5 and the results shown in Tables 2 to 4, the most preferable R ２ can be read to have a lower limit of 0.82 and an upper limit of 0.84. In this case, 0.75≦R, which is a specific example of radio waves in the 48 GHz band according to the above formula (8) ２ it can be stated that the relationship of ≦0.84 is satisfied.

[0043] In FIG. 6, plots with a numerical value of 0.9 or more are dispersed over a wide range, and the lower limit and upper limit of R ３ have no particular tendency, so it is considered that any value may be adopted for R ３

[0044] Looking at the results shown in FIG. 7, a plurality of plots with a numerical value of 0.9 or more are distributed in the range of 0.5 or more and 1.0 or less for the value of S １ Looking at the results shown in FIG. 7, S １ ​Since the lower limit can be read as 0.5 and the upper limit as 1.0, it can be said that the relationship 0.08 × λ ≤ S1 ≤ 0.16 × λ ... (3) is satisfied. Similarly, from the results shown in Figure 7, S １ A more preferable lower limit can be read as 0.6 and an upper limit as 1, so the specific example of a 48 GHz band radio wave in equation (6) above is 0.6 ≤ S １ It can be said that the relationship ≤ 1 is satisfied. Similarly, from the results shown in Figure 7, S １ The most preferable lower limit can be read as 0.84 and the upper limit as 1, so the specific example of a 48 GHz band radio wave in equation (9) above is 0.84 ≤ S １ It can be stated that the relationship ≤ 1 is satisfied.

[0045] In Figure 8, plots with values ​​of 0.9 or higher are widely distributed, S ２ There is no particular trend in the lower and upper limits, S ２ It is considered that any value may be adopted for this. In this specification, "lens effect" refers to the first ring body 5, the second ring body 6, and the distance S between them, which are arranged on the surface side of the base body 2. １ This refers to a mechanism that spatially controls the phase of incident radio waves by forming a pseudo dielectric constant distribution, thereby focusing or spreading the radio waves to a specific region inside the substrate. Specifically, as shown in the simulation results in Figures 4, 5, and 7, the width R of the first ring body... １ , width R of the second ring body ２ , and the interval S １ set to a predetermined numerical range (for example, 0.005 ≤ R １ ≤0.38, 0.7 ≤R ２ ≤0.89, 0.5 ≤S １ By setting it to ≤1.0, the behavior of radio waves is optimized, and the electromagnetic wave control state that achieves a radio wave absorption rate of 0.9 (10 dB) or higher is defined as "a state in which the lens effect is efficiently exerted." This effect differs from attenuation due to the absorption characteristics of the material; it involves locally changing the effective refractive index by designing the dimensions of the ring structure, efficiently guiding radio waves to the absorption layer (or attenuation region) within the substrate, thereby maximizing absorption efficiency while suppressing reflection.

[0046] The embodiments and simulation results of the present invention have been described above, but the embodiments described above are presented as examples. These embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. The above embodiments are included in the scope and spirit of the invention, as well as in the claims of the invention and its equivalents.

[0047] According to the embodiments described above, the multiple concentrically arranged ring bodies exhibit a lens effect that scatters radio waves attempting to enter the dielectric substrate from the surface side, and re-reflects radio waves attempting to exit the substrate to the surface side. The conductive thin film on the back side of the substrate reflects radio waves attempting to exit from the back side of the substrate to the outside. These effects work together to confine radio waves that enter the substrate, and a portion of these radio waves can be converted into heat and dissipated within the dielectric substrate. As a result, a thin, lightweight radio wave absorber with excellent absorption can be provided.

[0048] 1...Radio wave absorber 2...Substrate 5...First ring 6...Second ring 7...Third ring 8...Reflective film R １ ...Width of the first ring body R ２ ...Width of the second ring body R ３ ...Width of the third ring body S １ ...the distance between the first ring and the second ring S ２ ...the distance between the second and third ring bodies

Claims

1. A radio wave absorber comprising a substrate made of a dielectric material, a reflective film made of a conductive thin film formed on the entire back surface of the substrate, and a ring body made of three or more annular conductive thin films arranged concentrically on the surface of the substrate, or a ring body made of two or more annular conductive thin films arranged concentrically and a central body made of a circular conductive thin film positioned in the center of the concentric arrangement.

2. Let λ (m) be the wavelength of a radio wave to be absorbed, and the relationship between the frequency f (Hz) of the radio wave to be absorbed and λ is (λ = c / f: c is the speed of light), wherein in the three or more annular ring bodies, the width of the outermost annular first ring body is defined as R １ , the width of the second annular second ring body located inside thereof is defined as R ２ , the width of the third annular third ring body located inside thereof is defined as R ３ , the interval between the first ring body and the second ring body is defined as S １ , and the interval between the second ring body and the third ring body is defined as S ２ , the radio wave absorber according to claim 1, which satisfies the following relational expression and the following relationship: 0.0008×λ≦R １ ≦0.0608×λ...Formula (1) 0.112×λ≦R ２ ≦0.1424×λ...Formula (2) R ３ = arbitrary 0.08×λ≦S １ ≦0.16×λ ...Formula (3) S ２ = arbitrary 3. The radio wave absorber according to claim 1 or 2, wherein a plurality of concentrically arranged ring bodies exhibit a lens effect that scatters radio waves attempting to enter the substrate from the surface side of the substrate, and re-reflects radio waves that are passing through the substrate and attempting to exit to the surface side of the substrate.

Images