Electromagnetic wave absorber

Abstract

To solve a problem in which a conventional electromagnetic wave absorber that has optical transparency and breathability has been unable to improve upon requirements for only the transparency characteristics as a shielding material while maintaining good reflection characteristics as an electromagnetic wave absorber.SOLUTION: A lance-shaped portion is added to a lattice-shaped or honeycomb-shaped plate, and the plate and the lance-shaped portion are integrally formed using a material that has a loss with respect to radio waves.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radio wave absorber suitable for use in millimeter wave band wireless application devices, the practical application of which has been progressing in recent years, and in particular to a technology for providing a radio wave absorber which has optical transparency and air permeability and is also used as a shielding material, and which can improve only the transmission characteristics as a shielding material according to requirements while maintaining good reflection characteristics as a radio wave absorber. [Background technology]

[0002] In recent years, the practical application of 5G communication devices using 28 GHz and millimeter-wave wireless devices such as radars using the 60 GHz, 76.5 GHz, and 79 GHz bands has progressed, and there is a demand for radio wave absorbers that can be used in the millimeter-wave bands. On the other hand, radio wave absorbers have internal loss and therefore also function as radio wave shielding materials. Here, the performance of radio wave absorbers is evaluated based on their reflection characteristics, and the performance of radio wave shielding materials is evaluated based on their transmission characteristics, but there are cases where materials with different performance in terms of reflection characteristics and transmission characteristics are required depending on the radio wave environment in which they are used. Furthermore, radio wave absorbers that also function as radio wave shielding materials are sometimes used outdoors, and so they require breathability from the standpoint of wind resistance, as well as optical transparency from the standpoint of visibility to prevent collisions with other moving objects. The following prior art documents show examples of radio wave absorbers that are breathable and light-transmitting. Patent Document 1 describes a radio wave absorber in which multiple composite wires, each of which is a metal wire coated with a magnetic loss material, are arranged orthogonally in a lattice pattern. Patent Document 2 describes a radio wave absorber made of a metal member coated with a radio wave absorbing material, similar to Patent Document 1, and is used between ETC lanes. Non-Patent Document 1 and Non-Patent Document 2 describe radio wave absorbers using a lattice of FRP mixed with glass fiber, and are used between ETC lanes. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 47-24253 [Patent Document 2] JP 2007-73773 A [Non-patent literature]

[0004] [Non-Patent Document 1] IEICE Transactions on Information and Communication Engineers, Vol. J106-C, No. 1, pp. 3-9, IEICE 2023. [Non-Patent Document 2] Proc. Asia-Pacific Microwave Conference 2006, vol.1, pp.63-66, 2006. Summary of the Invention [Problem to be solved by the invention]

[0005] Here, in the radio wave absorber in which coated wires, in which metal wires are coated with a material having radio wave absorbing properties, are arranged as described in the above Patent Documents 1 and 2, the reflection characteristics improve while the transmission characteristics deteriorate when the density of the coated wires is reduced, so it was not possible to improve only the transmission characteristics as a shielding material as required while maintaining good reflection characteristics as a radio wave absorber. Also, in the radio wave absorber using a lattice in which glass fiber is mixed into FRP as described in Non-Patent Documents 1 and 2, the reflection characteristics and transmission characteristics are determined simultaneously by the dielectric characteristics of the lattice material, the lattice dimensions, the lattice distance, and the lattice thickness, so it was not possible to improve only the transmission characteristics as a shielding material as required while maintaining good reflection characteristics as a radio wave absorber. [Means for solving the problem]

[0006] In order to solve the problems associated with the conventional radio wave absorbers, the radio wave absorber of the present invention has a tip shape added to the surface of a lattice- or honeycomb-shaped plate, and the plate and tip shape are integrally constructed using a material that has loss to radio waves, such as a resin containing carbon fiber. Furthermore, in the radio wave absorber of the present invention, instead of the pointed tip shape, a convex shape having a height of ¼ wavelength relative to the central frequency to be used is added and provided integrally, or a step in the thickness direction is added and provided integrally inside the plate shape, and the distance between the surface of the plate shape and the step is ¼ wavelength relative to the central frequency to be used. Effect of the Invention

[0007] As described above, the radio wave absorber of the present invention has a lattice-like or honeycomb-like plate shape, which provides light transmittance and air permeability. Furthermore, the reflection is reduced by the effect of the reflection loss being multiply accumulated between the pointed end shapes added to the surface of the plate shape, so that the reflection characteristics can be set only on the surface of the plate shape. Furthermore, by using a resin containing carbon fiber for the plate shape, the transmission loss increases when the thickness of the plate shape is increased, and the transmission characteristics can be improved. In other words, the transmission characteristics as a shielding material can be improved according to requirements while maintaining good reflection characteristics as a radio wave absorber. Furthermore, the same material can be used for the plate shape and the pointed end shape, so that the radio wave absorber can be easily manufactured by integral molding. Instead of the sword-tip shape, multiple convex shapes with a height of 1 / 4 wavelength relative to the center frequency being used can be added, or a step in the thickness direction can be added inside the plate shape and the distance between the surface of the plate shape and the step is set to 1 / 4 wavelength relative to the center frequency being used. This will cancel out reflections from surfaces with a height difference of 1 / 4 wavelength and reduce reflections, so the reflection characteristics can be set only on the surface of the plate shape. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a perspective view of a radio wave absorber having a tip-shaped surface on a plate-shaped surface according to a first embodiment; [Diagram 2] FIG. 13 is a diagram showing radio wave paths between the tip shapes of the first and fourth embodiments. [Diagram 3] FIG. 1 shows losses inside the plate shapes of the first to sixth embodiments. [Figure 4] FIG. 13 is a diagram showing reflection characteristics when the thickness of the plate shape is changed in the first embodiment. [Diagram 5]FIG. 13 is a diagram showing the transmission characteristics when the thickness of the plate shape is changed in the first embodiment. [Figure 6] FIG. 13 is a perspective view of a radio wave absorber having a convex shape on a plate-shaped surface in the second embodiment; [Figure 7] FIG. 13 shows cancellation of reflected waves on the surface of the radio wave absorber according to the second, third, fifth and sixth embodiments. [Figure 8] 13 is a perspective view of a plate-shaped radio wave absorber having a step inside in the third embodiment. [Figure 9] FIG. 13 is a perspective view of a radio wave absorber having a tip-shaped surface on a plate-shaped surface in the fourth embodiment; [Figure 10] FIG. 13 is a perspective view of a radio wave absorber having a convex shape on a plate-shaped surface in the fifth embodiment; [Figure 11] 13 is a perspective view of a plate-shaped radio wave absorber having a step inside in the sixth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, an embodiment of the present invention will be described. EXAMPLES

[0010] (Embodiment 1) Fig. 1 shows a first embodiment of the radio wave absorber of the present invention, which is a perspective view of the radio wave absorber having a tip shape on the surface of a lattice-like plate shape. In Fig. 1, 101 and 102 show the radio wave absorber of the first embodiment as viewed from different angles, 103 shows a radio wave absorber integrally formed using a material having loss for radio waves, 104 shows a lattice-like plate shape, 105 shows a tip shape additionally provided on the surface of the plate shape 104, and 106 shows a lattice hole shared by the tip shape 105 and the plate shape 104. Here, the radio wave absorber 103 ensures light transmittance and ventilation by the lattice holes 106. Here, the material constituting the radio wave absorber 103 is a resin containing 20% ​​carbon fiber in polylactic acid, which has a loss for radio waves. Separate measurements of this resin revealed that the relative dielectric constant was 6.5 and the dielectric loss tangent was 0.15. In order to maximize the transmission loss at the center frequency of 28 GHz used, the lattice period is 10 mm and the wall thickness of the lattice is 2.5 mm. In FIG. 1, reflection loss is accumulated due to multiple reflections between the tip shapes 105 additionally provided on the surface of the plate shape 104, thereby improving the reflection characteristics. FIG. 2 shows the path of radio waves reflected between the tip shapes when radio waves are incident from the side where the tip shape 105 of FIG. 1 is located. In FIG. 2, 201 shows a cross section of the tip shape, and 202 shows the path of the incident radio waves and the radio waves reflected on the surface of the tip shape. As shown in FIG. 2, the incident radio waves that arrive between the tip shapes also penetrate into the inside of the tip shape, while the incident radio waves are multiple-reflected on the surface of the tip shape along the path shown in 202 and return in the incident direction. In other words, the radio waves returning in the incident direction accumulate reflection losses on the surface of the tip shape, resulting in a large reflection loss, and the reflection characteristics of the radio wave absorber are improved. FIG. 3 shows how radio waves are lost inside the plate shape 104 in FIG. 1. 301 indicates the resin region of the plate shape 104 in FIG. 1 that has loss for radio waves, 302 indicates the air region of the lattice hole 106 in FIG. 1 that has no loss for radio waves, 303 indicates the propagating wave in the resin region, and 304 indicates the propagating wave in the air region. The incident radio waves arriving from the left side of FIG. 3 are divided into a component that enters the resin region 301 from the surface of the sword tip shape and a component that enters directly into the air region 302, and each component propagates inside the plate shape while exchanging energy through the boundary region 305. Since the wavelengths propagating in the resin region 301 and the air region 302 are different, each propagating wave that leaks into the other region through the boundary region 305 does not align with the wavefront of the original region and becomes an evanescent wave in the boundary region 305. Here, the propagating wave in the resin region 303 is attenuated due to loss, but energy continues to flow from the air region 304 to the resin region 303 via the evanescent wave in the boundary region 305. In other words, the longer the radio wave propagates inside the plate shape, the greater the transmission loss it undergoes, so by increasing the length of the plate shape, it is possible to improve only the transmission characteristics while maintaining the reflection characteristics. Fig. 4 shows the reflection characteristics calculated by an electromagnetic field simulator when the plate-shaped thickness 107 is 5 mm, 15 mm, and 25 mm in the first embodiment shown in Fig. 1, and the reflection characteristics manufactured and measured when the plate-shaped thickness 107 is 15 mm. 401 shows the calculation results when the plate-shaped thickness is 5 mm, 402 shows the calculation results when the plate-shaped thickness is 15 mm, and 403 shows the calculation results when the plate-shaped thickness is 25 mm, and 404 shows the manufacturing and measurement results. As shown in Fig. 4, it can be seen that at a center frequency of 28 GHz used, the reflection characteristics are maintained at -30 dB or less even when the plate-shaped thickness 107 is changed. FIG. 5 shows the transmission characteristics calculated by an electromagnetic field simulator when the plate-shaped thickness 107 is 5 mm, 15 mm, and 25 mm in the first embodiment shown in FIG. 1, and the transmission characteristics measured when the plate-shaped thickness 107 is 15 mm. 501 shows the calculation results when the plate-shaped thickness is 5 mm, 502 shows the calculation results when the plate-shaped thickness is 15 mm, and 503 shows the calculation results when the plate-shaped thickness is 25 mm, and 504 shows the production and measurement results. As shown in FIG. 5, the transmission characteristics are the best at the center frequency of 28 GHz used, and the transmission characteristics improve when the plate-shaped thickness 107 is increased. In other words, the effect of the present invention is supported as described above with reference to FIG. 3. Combined with the result of FIG. 4, it is possible to improve only the transmission characteristics while maintaining good reflection characteristics by increasing the plate-shaped thickness 107. Furthermore, in FIG. 5, when the plate-shaped thickness 107 is 15 mm, the calculation results are close to the manufacturing measurement results, which supports the principle of the effect of the present invention explained using FIG. 3 above. Therefore, if the plate-shaped thickness 107 is manufactured to be 25 mm, the transmission characteristics will be further improved. In the first embodiment, a design example and a production example have been shown in which the center frequency used is 28 GHz. However, if the radio wave absorber, which is a passive component, is produced with the same dielectric properties and the shape dimensions and wavelength being proportional to each other, similar reflection and transmission characteristics can be obtained even if it is designed and produced for other center frequencies, including fractional bandwidths, so that similar characteristics can be obtained in the 60 GHz band, 76.5 GHz band, or 79 GHz band. (Embodiment 2) Fig. 6 shows a second embodiment of the radio wave absorber of the present invention, which is a perspective view of a radio wave absorber having a convex shape with a height of 1 / 4 wavelength with respect to the center frequency used instead of the pointed shape on the surface of a plate shape. In Fig. 6, 601 and 602 show the state of the radio wave absorber of the second embodiment seen from different angles, 603 is a radio wave absorber integrally formed using a material having a loss for radio waves, 604 is a lattice-like plate shape, 605 is a convex shape with a height of 1 / 4 wavelength with respect to the center frequency used that is additionally provided on the surface of the plate shape 604, 606 is a lattice hole shared by the convex shape 605 and the plate shape 604, 607 is the thickness of the plate shape, and 608 is the height of the convex shape. Here, the radio wave absorber 603 ensures light transmittance and ventilation by the lattice hole 606. Here, for example, a resin containing 20% ​​carbon fiber in polylactic acid is used as the material forming the radio wave absorber 603. Furthermore, for example, if the center frequency used is 28 GHz, the lattice period is 10 mm, the thickness of the wall between the lattices is 2.5 mm, and the height 608 of the 1 / 4 wavelength convex shape is set to 2.7 mm. In Fig. 6, the convex shape added to the surface of the plate shape can reduce reflection at the surface at the center frequency used. Fig. 7 shows the path of radio waves reflected by the convex shape 605 when the radio waves are incident on the radio wave absorber in Fig. 6. In Fig. 7, 701 indicates the resin constituting the plate shape 604, 702 indicates the convex shape, 703 indicates the height of the convex shape, 704 indicates the path of the radio waves reflected at the tip of the convex shape 702, 705 indicates the path of the radio waves reflected at the bottom of the convex shape on the surface of the plate shape, and 706 indicates the synthesis surface of the paths 704 and 705. Here, the wave incident on the convex shape is reflected by the paths 704 and 705, but since there is a quarter-wave difference between the two paths, the reflected waves are in opposite phase at the synthesis surface 706 and cancel each other out, resulting in significant attenuation. In other words, the radio wave absorber 603 obtains a large amount of absorption centered on the frequency at which the height of the convex shape is a quarter-wavelength. On the other hand, the components that penetrate inside the convex shape undergo loss inside the radio wave absorber, but the principle by which radio waves are subjected to loss inside the plate shape 604 is the same as that explained in embodiment 1 using Figure 3, so explanation will be omitted here. In other words, combining the explanation with reference to FIG. 7 with the explanation with reference to FIG. 3, by increasing the thickness 607 of the plate shape, it is possible to improve only the transmission characteristics while maintaining favorable reflection characteristics. (Embodiment 3) Fig. 8 shows a third embodiment of the radio wave absorber of the present invention, which is a perspective view of a radio wave absorber in which a step in the thickness direction is additionally provided inside the plate shape, and the distance between the surface of the plate shape and the step is 1 / 4 wavelength with respect to the center frequency to be used. In Fig. 8, 801 and 802 show the radio wave absorber of the third embodiment as viewed from different angles, 803 is a radio wave absorber integrally formed using a material having loss for radio waves, 804 is a lattice-like plate shape, 805 is a step in the thickness direction additionally provided inside the plate shape with the distance from the surface of the plate shape being 1 / 4 wavelength with respect to the center frequency to be used, 806 is a lattice hole shared by the step 805 and the plate shape 804, 807 is the thickness of the plate shape, and 808 is the height of the step. Here, the radio wave absorber 803 ensures light transmission and ventilation by the lattice hole 806. Here, for example, a resin containing 20% ​​carbon fiber in polylactic acid is used as the material constituting the radio wave absorber 803. Furthermore, for example, if the center frequency used is 28 GHz, the lattice period is set to 10 mm, the thickness of the wall between the lattices is set to 2.5 mm, and the distance 808 between the plate-shaped surface and the step is set to 2.7 mm. In Fig. 8, the step provided on the plate-shaped surface can reduce reflection on the surface at the center frequency used. Fig. 7 shows the path of radio waves reflected by the step 805 when the radio waves are incident on the radio wave absorber in Fig. 8. In Fig. 7, 701 indicates the resin constituting the plate shape 804, 703 indicates the distance 808 between the plate-shaped surface and the step, 704 indicates the path of the radio waves reflected on the plate-shaped surface, 705 indicates the path of the radio waves reflected on the step 805, and 706 indicates the synthesis surface of the paths 704 and 705. Here, the wave incident on the radio wave absorber 803 is reflected by the paths 704 and 705, but since there is a quarter-wave difference between the two paths, the reflected waves are in opposite phase at the synthesis surface 706, and the reflected waves cancel each other out, resulting in significant attenuation. In other words, the radio wave absorber 803 obtains a large amount of absorption centered on the frequency at which the distance between the plate-shaped surface and the step is a quarter-wavelength. On the other hand, the components that penetrate inside the step are lost inside the radio wave absorber, but the principle by which radio waves are lost inside the plate shape 804 is the same as that explained in embodiment 1 using Figure 3, so explanation will be omitted here. In other words, similarly to the second embodiment, by combining the explanation in FIG. 7 with the explanation in FIG. 3, it becomes possible to improve only the transmission characteristics while maintaining favorable reflection characteristics by increasing the thickness 807 of the plate shape. (Embodiment 4) Fig. 9 shows a fourth embodiment of the radio wave absorber of the present invention, in which the lattice shape in the first embodiment is replaced with a honeycomb shape. In Fig. 9, 901 and 902 show the radio wave absorber of the fourth embodiment as viewed from different angles, 903 shows a radio wave absorber integrally formed using a material having loss for radio waves, 904 shows a honeycomb plate shape, 905 shows a pointed shape additionally provided to the plate shape 904, 906 shows honeycomb holes shared by the pointed shape 905 and the plate shape 904, and 907 shows the thickness of the plate shape. Here, the radio wave absorber 903 ensures light transmittance and breathability by the honeycomb holes 906. In Fig. 9, reflection loss accumulates between the pointed end shapes 905 that are added to the plate shape 904 due to multiple reflections, thereby improving the reflection characteristics. The principle by which the reflection characteristics are improved by multiple reflections between the pointed end shapes is the same as that explained in the first embodiment with reference to Fig. 2, and therefore a detailed explanation is omitted here. Also, the principle by which loss is given to radio waves inside the plate shape 904 is the same as that explained in the first embodiment with reference to Fig. 3, and therefore a detailed explanation is omitted here. In other words, similarly to the first embodiment, by combining the explanations in FIG. 2 and FIG. 3, it is possible to improve only the transmission characteristics while maintaining favorable reflection characteristics by increasing the thickness 907 of the plate shape. (Embodiment 5) Fig. 10 shows a fifth embodiment of the radio wave absorber of the present invention, in which the lattice shape in the second embodiment is replaced with a honeycomb shape. In Fig. 10, 111 and 112 show the radio wave absorber of the fifth embodiment as viewed from different angles, 113 shows a radio wave absorber integrally formed using a material having a loss for radio waves, 114 shows a honeycomb plate shape, 115 shows a convex shape having a height of 1 / 4 wavelength with respect to the center frequency to be used and additionally provided on the plate shape 114, 116 shows a honeycomb hole shared by the convex shape 115 and the plate shape 114, 117 shows the thickness of the plate shape, and 118 shows the height of the convex shape. Here, the radio wave absorber 113 ensures light transmittance and air permeability by the honeycomb holes 116. In Fig. 10, the convex shape provided in addition to the plate shape can reduce reflection on the surface at the center frequency used. The principle by which the convex shape improves the reflection characteristics is the same as that explained in the second embodiment with reference to Fig. 7, and therefore a description thereof will be omitted here. Also, the principle by which loss is given to radio waves inside the plate shape 114 is the same as that explained in the first embodiment with reference to Fig. 3, and therefore a description thereof will be omitted here. In other words, similarly to the second embodiment, by combining the explanation with reference to FIG. 7 with the explanation with reference to FIG. 3, it is possible to improve only the transmission characteristics while maintaining favorable reflection characteristics by increasing the thickness 117 of the plate shape. (Embodiment 6) Fig. 11 shows a sixth embodiment of the radio wave absorber of the present invention, in which the lattice shape in the third embodiment is changed to a honeycomb shape. In Fig. 11, 121 and 122 show the radio wave absorber of the sixth embodiment as viewed from different angles, 123 shows a radio wave absorber integrally formed using a material having a loss for radio waves, 124 shows a honeycomb-shaped plate shape, 125 shows a step in the thickness direction additionally provided inside the plate shape with a distance from the surface of the plate shape being 1 / 4 wavelength with respect to the center frequency to be used, 126 shows a honeycomb hole shared by the step 125 and the plate shape 124, 127 shows the thickness of the plate shape, and 128 shows the height of the step. Here, the radio wave absorber 123 ensures light transmission and ventilation by the honeycomb holes 126. In Fig. 11, the step added inside the plate shape can reduce reflection on the surface at the center frequency used. The principle by which the step improves the reflection characteristics is the same as that explained in the third embodiment with reference to Fig. 7, and therefore a description thereof will be omitted here. Also, the principle by which the radio wave is lost inside the plate shape 124 is the same as that explained in the first embodiment with reference to Fig. 3, and therefore a description thereof will be omitted here. In other words, similarly to the third embodiment, by combining the explanation with reference to FIG. 7 with the explanation with reference to FIG. 3, it is possible to improve only the transmission characteristics while maintaining favorable reflection characteristics by increasing the thickness 127 of the plate shape. Up to this point, the first to sixth embodiments of the present invention have been shown, but as the resin material having loss to radio waves, acrylonitrile, polycarbonate, or polyethylene terephthalate may be used instead of polylactic acid. [Industrial Applicability]

[0011] As described above, the radio wave absorber of the present invention has optical transparency and breathability, and can improve only the transmission characteristics as a shielding material according to requirements while maintaining good reflection characteristics as a radio wave absorber, so it can be expected to be used in environments requiring more complex communication conditions. In other words, it can be expected to be used in automatic manufacturing lines that operate remote-controlled robots that are placed in an overcrowded location using low-latency millimeter-wave communication, and as ceiling light covers and air conditioner covers in intelligent operating rooms that use remote-controlled robots that also use low-latency millimeter-wave communication. In addition, since the breathability improves wind resistance, it can be expected to be used in overcrowded communication systems such as millimeter-wave radar inspection equipment used outdoors and events using AI goggles used outdoors.

[0012] Furthermore, since the effects of the present invention can be similarly utilized in the microwave band, which has longer wavelengths than the millimeter wave band, by enlarging the dimensions of the radio wave absorber in proportion to the wavelength, it goes without saying that the present invention also applies to microwave band radio wave absorbers. Furthermore, it goes without saying that the effects of the present invention are maintained even if an insulating and light-reflecting paint is applied to the surface of the radio wave absorber of the present invention in order to improve the transmittance of lighting light, in a thickness that has a negligible effect on the wavelength of the central frequency to be used. [Explanation of symbols]

[0013] 101, 102: Wave absorber of the first embodiment viewed from different angles 601, 602: Wave absorber of the second embodiment viewed from different angles 801, 802: Wave absorber of the third embodiment viewed from different angles 901, 902: Wave absorber of the fourth embodiment viewed from different angles 111, 112 The radio wave absorber of the fifth embodiment viewed from different angles 121, 122 The radio wave absorber of the sixth embodiment seen from different angles 103, 603, 803, 903, 113, 123 Integrated radio wave absorber 104, 604, 804 Lattice plate shape 106, 606, 806 Lattice holes 904, 114, 124 Honeycomb plate shape 906, 116, 126 Honeycomb holes 105, 905 Sword tip shape 605, 115 Convex shape 805, 125 steps 107, 607, 807, 907, 117, 127 Plate thickness 608, 118 Height of convex shape 808, 128 Distance between the surface of the plate shape and the step 201 Sword-shaped cross section 202 Incident radio wave and the path of the radio wave reflected from the surface of the sword tip 301 Resin area with loss to radio waves 302 Lossless air region for radio waves 303 Propagating waves in resin regions 304 Propagating waves in the air domain 305 Boundary area 401, 501 Calculation results for plate thickness of 5mm 402, 502 Calculation results for plate thickness of 15mm 403, 503 Calculation results for plate thickness of 25mm 404, 504 Plate shape thickness 15mm 701 Resin that forms the plate shape 702 Convex and plate-shaped surfaces 703 Height of convex shape, height of step 704 Path of reflected radio waves 1 705 Path of reflected radio waves 2 706 Route synthesis surface

Claims

1. A radio wave absorber comprising: a lattice- or honeycomb-shaped plate-shaped surface on which a pointed end is added; and the plate-shaped surface and the pointed end are integrally formed using a material having a loss with respect to radio waves.

2. A radio wave absorber comprising: a lattice- or honeycomb-shaped plate-shaped surface on which a convex shape having a height of 1 / 4 wavelength with respect to a center frequency to be used is additionally provided; and the plate-shaped surface and the convex shape are integrally formed using a material having a loss with respect to radio waves.

3. A radio wave absorber comprising: a lattice- or honeycomb-shaped plate-like member having a step in the thickness direction, a distance between the surface of the plate-like member and the step being 1 / 4 wavelength of a center frequency to be used; and a material having a loss with respect to radio waves that is integrally formed with the plate-like member and the step.

4. 4. The radio wave absorber according to claim 1, wherein the material having a loss to radio waves is a resin containing carbon fiber.

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