Electromagnetic wave absorber, electromagnetic wave absorbing system, and electromagnetic wave attenuation method

Abstract

To provide an electromagnetic wave absorber having a simple structure, high electromagnetic wave absorption performance, a wide absorption band, and optical transparency.SOLUTION: An electromagnetic wave absorber 10 includes a dielectric layer 21 containing a light-transmitting dielectric material, a patch element 22 arranged on one main surface of the dielectric layer 21, and a reflective film 23 formed on the other main surface of the dielectric layer 21. The dielectric layer 21 has a thickness in the range of 1 / 100 to 1 / 10 of the wavelength in the dielectric layer of the electromagnetic wave to be attenuated.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an electromagnetic wave absorber, an electromagnetic wave absorbing system, and a method for attenuating electromagnetic waves. [Background technology]

[0002] The use of indoor wireless communication devices is expanding. Along with this, there is also growing concern that the communication environment will deteriorate due to electromagnetic interference caused by multiple reflections from indoor walls, etc. From this perspective, electromagnetic wave absorbers (panels) that are installed on the walls of a room and absorb (attenuate) electromagnetic waves have been developed.

[0003] For example, Patent Document 1 discloses an electromagnetic wave absorber that absorbs electromagnetic waves in a wide band in the GHz band, taking UWB communication and the like into consideration. This electromagnetic wave absorber is composed of a resistive film, patch materials (electrodes) arranged in a matrix on one surface of the resistive film, a dielectric layer arranged on the patch materials, and a metal foil arranged on the dielectric layer. This electromagnetic wave absorber has a wide absorption band, but a small absorption peak. In addition, since the resistive film and the dielectric layer are laminated, there is a risk that the whole absorber will become thick and heavy. In addition, adjustment of the resistive film is complicated. For this reason, it is desired to further simplify the structure and facilitate the manufacture. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-87980 A Summary of the Invention [Problem to be solved by the invention]

[0005] In UHF (Ultra High Frequency)-RFID (Radio Frequency IDentifier) ​​systems used in logistics and production management, the frequency used for communication is a specific frequency band, so broadband absorption across multiple frequency bands is not required. On the other hand, wide absorption characteristics are required to be able to accommodate variations in communication frequencies caused by variations in RFID quality, changes in environmental temperature, etc. Also, it is necessary to be able to handle oblique incidence caused by electromagnetic wave reflection, etc.

[0006] In addition, in logistics and production management sites, safety checks using visual inspections and surveillance cameras are also essential tasks. For this reason, it is undesirable for an electromagnetic wave absorber for improving the authentication accuracy of RFID tags to increase the blind spot of visibility. The electromagnetic wave absorber described in Patent Document 1 is made of a light-impermeable resistive film, a light-impermeable resin layer, a patch material, and a metal layer, and cannot contribute to such a purpose.

[0007] The present invention has been made in consideration of the above-mentioned circumstances, and has an object to provide an electromagnetic wave absorber and an electromagnetic wave absorption system that have a simple configuration, high electromagnetic wave absorption performance, a wide absorption band, and optical transparency. [Means for solving the problem]

[0008] [1] In order to achieve the above object, the electromagnetic wave absorber of the present invention comprises: a dielectric layer comprising an optically transparent dielectric material; A plurality of patch elements arranged on one main surface of the dielectric layer; a conductive reflective film arranged on a second main surface of the dielectric layer so as to face the patch element; Equipped with The dielectric layer has a thickness in the range of 1 / 100 to 1 / 10 of the wavelength within the dielectric layer of the electromagnetic wave to be attenuated.

[0009] [2] The dielectric layer desirably has a thickness in the range of 1 / 70 to 1 / 20 of the wavelength within the dielectric layer of the electromagnetic wave to be attenuated.

[0010] [3] The electromagnetic wave absorber according to [1] or [2], wherein the patch element, the dielectric layer, and the reflective film function, for example, as a cavity resonator for the electromagnetic wave to be attenuated, and generate an electric field concentration region within the dielectric layer.

[0011] [4] The electromagnetic wave absorber according to [1], [2] or [3], wherein it is desirable that the front surface of the patch element does not include a layer whose product t·εr2 of the thickness t and the relative dielectric constant εr2 is greater than the product T·εr1 of the thickness T of the dielectric layer and the relative dielectric constant εr1, where T is the thickness of the dielectric layer and εr1 is the relative dielectric constant of the dielectric layer.

[0012] [5] The electromagnetic wave absorber according to any one of [1] to [4], wherein it is desirable that no layer forming a frequency selective reflective / absorptive layer is disposed on the front surface of the patch element.

[0013] [6] The electromagnetic wave absorber according to any one of [1] to [5], wherein the patch element and the reflective film are desirably made of a light-transmitting metal.

[0014] [7] The electromagnetic wave absorber according to any one of [1] to [6], which may include a protective layer covering the plurality of patch elements.

[0015] [8] The electromagnetic wave absorber according to any one of [1] to [7], wherein, for example, at least one of the plurality of patch elements has a rectangular shape in plan view with notches formed at the corners.

[0016] [9] The electromagnetic wave absorber according to any one of [1] to [7], wherein, for example, the plurality of patch elements have a rectangular shape in a planar view, and a hole penetrating at least one of the patch elements is formed.

[10] The electromagnetic wave absorber according to [9], wherein the hole (including a notch) may penetrate at least one of the patch elements, the dielectric layer, and the reflective film.

[0017]

[11] For example, a plurality of the holes may be formed in each patch element. In this case, it is preferable that each patch element and the plurality of the holes are formed in a 90° rotational symmetry in a front view. The electromagnetic wave absorber according to any one of [8] to

[10] .

[0018]

[12] An electromagnetic wave absorbing system according to a second aspect of the present invention comprises a plurality of the above-mentioned electromagnetic wave absorbers, the plurality of electromagnetic wave absorbers being arranged opposite an electromagnetic wave source that radiates electromagnetic waves to be attenuated, and the cutout or hole of the patch element has a size corresponding to the angle of incidence of the electromagnetic waves from the electromagnetic wave source.

[0019]

[13] An electromagnetic wave absorption system according to a third aspect of the present invention comprises a plurality of the above-mentioned electromagnetic wave absorbers, the plurality of electromagnetic wave absorbers being arranged opposite an electromagnetic wave source that radiates electromagnetic waves to be attenuated, and the size of the cutout portion is formed so as to decrease as the incident angle of the electromagnetic waves from the electromagnetic wave source increases.

[0020]

[14] An electromagnetic wave absorbing system according to a fourth aspect of the present invention comprises a plurality of the above-mentioned electromagnetic wave absorbers, the plurality of electromagnetic wave absorbers being arranged opposite an electromagnetic wave source that radiates electromagnetic waves to be attenuated, and the hole has a diameter that increases as the angle of incidence of the electromagnetic waves from the electromagnetic wave source increases.

[0021]

[15] A method for attenuating electromagnetic waves according to a first aspect of the present invention comprises: A plurality of the electromagnetic wave absorbers are arranged facing an electromagnetic wave source, before or after the arrangement, forming cutout portions at corners of the patch elements each having a rectangular shape in a plan view of each of the electromagnetic wave absorbers; The size of the notch portion decreases as the incident angle of the electromagnetic wave from the electromagnetic wave source increases.

[0022]

[16] A method for attenuating electromagnetic waves according to a second aspect of the present invention comprises: A plurality of the electromagnetic wave absorbers are arranged facing an electromagnetic wave source, forming holes through the plurality of patch elements of each of the electromagnetic wave absorbers before or after the placement; The holes have a diameter that increases as the incident angle of the electromagnetic wave from the electromagnetic wave source increases. Effect of the Invention

[0023] According to the electromagnetic wave absorber of the present invention, it is possible to obtain high absorption characteristics for the target electromagnetic wave, even with a simple structure. In addition, since the width of the absorption band can be adjusted by adjusting the thickness of the dielectric layer, it is possible to set a wide absorption band according to the characteristics of the electromagnetic wave. In addition, since the dielectric layer is formed from a light-transmitting dielectric material, it is possible to suppress the occurrence of blind spots due to the electromagnetic wave absorber. Furthermore, when through holes are formed, it is possible to ensure ventilation.

[0024] The electromagnetic wave absorbing system of the present invention can provide the same effect. Furthermore, the electromagnetic wave attenuation method of the present invention makes it possible to appropriately attenuate the desired electromagnetic wave through simple steps. [Brief description of the drawings]

[0025] [Figure 1] 1A and 1B are perspective views of an electromagnetic wave absorber according to an embodiment of the present invention, where (a) is a view of the front side and (b) is a view of the back side. [Diagram 2] 2 is a cross-sectional view of the electromagnetic wave absorber shown in FIG. 1 taken along line II-II. [Diagram 3] FIG. 3 is a diagram for explaining an evaluation target region of the electromagnetic wave absorber shown in FIGS. 1 and 2. [Figure 4] 4A and 4B are diagrams for explaining the distribution of electric field strength in the evaluation target area shown in FIG. 3, in which (a) is a diagram showing the electric field strength distribution in the evaluation target area when an electromagnetic wave of a frequency near the target frequency is incident, and (b) is a diagram showing the electric field strength distribution in the evaluation target area when an electromagnetic wave of the target frequency is incident. [Diagram 5] 1A to 1C are diagrams illustrating a method for evaluating an electromagnetic wave absorber according to an embodiment. [Figure 6]3 is a graph showing (a) the absorption characteristics for TE waves and (b) the absorption characteristics for TM waves of the electromagnetic wave absorber shown in FIGS. 1 and 2 when the thickness of the dielectric layer is 5 mm. [Figure 7] 3 is a graph showing (a) the absorption characteristics for TE waves and (b) the absorption characteristics for TM waves of the electromagnetic wave absorber shown in FIGS. 1 and 2 when the thickness of the dielectric layer is 10 mm. [Figure 8] 8 is a graph showing the absorption characteristics for the TE wave shown in FIGS. 6 and 7 when θ=10°, with the peak frequency normalized. [Figure 9] 1A and 1B are diagrams of an electromagnetic wave absorber according to a comparative example, where (a) is an exploded perspective view and (b) is a cross-sectional view. [Figure 10] 10 is a graph showing (a) the absorption characteristics for TE waves and (b) the absorption characteristics for TM waves of the electromagnetic wave absorber shown in FIG. [Figure 11] FIG. 11 is a front view of an electromagnetic wave absorber according to a second embodiment. [Figure 12] FIG. 13 is a diagram showing an example of the arrangement of electromagnetic wave absorbers. [Figure 13] 13 is a graph showing the absorption characteristics of the electromagnetic wave absorber shown in FIG. 12 with respect to a TE wave. [Figure 14] 4(a) to 4(c) are diagrams illustrating the absorption peak frequency of the electromagnetic wave absorber according to the first embodiment. [Figure 15] 13(a) and 13(b) are diagrams for explaining the absorption peak frequency of an electromagnetic wave absorber according to the second embodiment. [Figure 16] FIG. 11 is a diagram showing an example of an absorption peak frequency table showing the relationship between the incidence angle θ, the radius R of the through hole, and the absorption peak frequency of the electromagnetic wave absorber according to the second embodiment. [Figure 17] FIG. 11 is a front view of an electromagnetic wave absorber according to a third embodiment. [Figure 18] 18 is a graph showing the absorption characteristics of the electromagnetic wave absorber shown in FIG. 17 with respect to a TE wave. [Figure 19] 13(a) and 13(b) are diagrams for explaining the absorption peak frequency of an electromagnetic wave absorber according to the third embodiment. [Figure 20]FIG. 11 is a diagram showing an example of an absorption peak frequency table showing the relationship between the incidence angle θ, the radius R of the through hole, and the absorption peak frequency of the electromagnetic wave absorber according to the third embodiment. [Figure 21] 13(a) to 13(d) are front views of electromagnetic wave absorbers according to modified examples. [Figure 22] FIG. 13 is an exploded perspective view of an electromagnetic wave absorber according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0026] An electromagnetic wave absorber according to an embodiment of the present invention will be described with reference to the drawings.

[0027] 1(a), (b) and 2, an electromagnetic wave absorber 10 according to this embodiment includes a dielectric layer 21, patch elements 22 arranged in a matrix on a first main surface (front surface) of the dielectric layer (plate) 21, a reflective film 23 formed on the entire second main surface (back surface) of the dielectric layer 21, and a protective layer 24 (shown in FIG. 2) covering the entirety. The electromagnetic wave absorbers 10 are arranged, for example, on a wall, ceiling, floor, etc. in a room, and absorb incident electromagnetic waves and convert them into thermal energy.

[0028] The dielectric layer 21 is formed of a dielectric material that is light-transmitting and has a high dielectric constant. The light transmittance does not need to be 100%, and it is sufficient to show a certain degree of light transmittance, for example, a transmittance of about 50 to 70%, depending on the purpose and conditions of use. From the viewpoint of absorbing and attenuating electromagnetic waves, it is desirable for the dielectric material to have a high dielectric constant and a large dielectric dissipation factor (tan δ). Examples of dielectric materials that satisfy these conditions include PET resin (polyethylene terephthalate), acrylic resin, and PVC (polyvinyl chloride). For example, the relative dielectric constant εr21 of PET resin (hereinafter, the relative dielectric constant will be simply referred to as the dielectric constant) is about 2.0 to 4.0.

[0029] The dielectric layer 21 is formed in a square shape, for example, with each side measuring 100 mm to 2000 mm, depending on the purpose and application of the use. The thickness T of the dielectric layer 21 will be described later.

[0030] Patch element 22 is a square electrode. Patch elements 22 are arranged in a matrix at regular intervals G on one principal surface (front surface) of dielectric layer 21. The maximum length Pmax of one side of patch element 22 and the maximum interval Gmax are expressed by equations (1) and (2) when the center frequency of the electromagnetic wave to be attenuated (absorbed) (target electromagnetic wave) (hereinafter, attenuation target frequency) is fc. Pmax≒0.45λc / √(εr21) ···(1) Gmax≒0.05λc / √(εr21) ···(2) Note that λc is the central wavelength of the target electromagnetic wave = C / fc, where C is the speed of light in air.

[0031] Patch element 22 is formed from a conductor that is a perfect reflector of electromagnetic waves, for example a metal such as copper, aluminum, or alloys thereof. Patch element 22 is formed, for example, by patterning a conductor film formed on one main surface of dielectric layer 21 by vacuum deposition, sputtering, or the like.

[0032] The surface of the dielectric layer 21 on which the patch element 22 is arranged functions as the incident surface of the electromagnetic wave into the electromagnetic wave absorber 10, and no conductive layer, resistive layer, etc. that reflects or blocks the electromagnetic wave is arranged on the front side of the patch element 22.

[0033] Reflective film 23 is formed on the rear surface of dielectric layer 21 so as to face patch element 22 . The reflective film 23 is made of a conductor that is a perfect reflector of electromagnetic waves, such as a metal such as copper, aluminum, or an alloy thereof. The reflective film 23 is formed of a conductive film formed on the other main surface of the dielectric layer 21 by vacuum deposition, sputtering, or the like.

[0034] 2 is formed from a thin film of an insulating transparent material having environmental resistance and contamination resistance, and covers the entire outer surface of the electromagnetic wave absorber 10. Possible materials of this type include glass and epoxy resin. The thickness t of the protective layer 24 on the patch element 22 is formed to be thin enough not to affect the absorption characteristics of the dielectric layer 21.

[0035] The electromagnetic wave absorber 10 having the above-mentioned configuration is arranged, for example, on a wall, floor, ceiling, etc. in a room, and absorbs electromagnetic waves of a specific frequency radiated from an electromagnetic wave source and attenuates reflected waves, thereby reducing interference, congestion, etc.

[0036] Next, the thickness T of the dielectric layer 21 will be described. The thickness T of the dielectric layer 21 is set to a thickness suitable for converting the incident electromagnetic wave into thermal energy. To explain in more detail, the wavelength λd of the target electromagnetic wave in the dielectric layer 21 is expressed by equation (3). λd=C / (fc*√εr21) (3) Here, C is the speed of light in the dielectric layer, and εr21 is the relative dielectric constant of the dielectric material constituting the dielectric layer 21.

[0037] Here, if the thickness T of the dielectric layer 21 is smaller than 1 / 00 ​​of the wavelength λd in the dielectric layer 21, the thickness T is too small, so that almost no dielectric loss σ occurs in the dielectric layer 21, and the target electromagnetic wave cannot be attenuated. On the other hand, if the thickness T of the dielectric layer 21 is larger than 1 / 10 of the wavelength λd, the patch element 22, the reflective film 23, and the dielectric layer 21 therebetween do not function as a kind of resonator, and the target electromagnetic wave cannot be attenuated. Also, if the thickness T is large, the dielectric layer 21 becomes heavy and voluminous, which makes it inconvenient to install. For this reason, it is desirable to set the thickness T to about 1 / 70 to 1 / 20 of the wavelength λd of the target electromagnetic wave in the dielectric layer 21. Also, from the viewpoints of weight, thinness, and ease of installation, it is desirable to set the thickness T to 15 mm or less.

[0038] Next, the mechanism by which the electromagnetic wave absorber 10 absorbs electromagnetic waves will be described. As shown in FIG. 3, an evaluation target area D of an evaluation target including one patch element 22, dielectric layer 21, and reflective film 23 (hereinafter, evaluation target area) is set.

[0039] The electric field distribution within the evaluation area D when a plane wave with main polarization parallel to z is incident is shown in Figure 4 (a) and (b). (a) shows the electric field strength distribution in the evaluation area D when the frequency of the incident wave is 0.8fc or 1.2fc, which are values ​​close to the target attenuation frequency fc. On the other hand, (b) shows the electric field strength distribution in the evaluation area D when the frequency of the incident wave is a value that matches the target attenuation frequency fc.

[0040] As shown in FIG. 4(a), when the frequency of the incident wave is close to the target attenuation frequency fc, the electric field concentration point hardly appears in the evaluation target region D of the electromagnetic wave absorber 10. In contrast, as shown in FIG. 4(b), when the frequency of the incident wave is equal to the target attenuation frequency fc, a significant electric field concentration is observed in the evaluation target region D, and an electric field concentration region in which the electric field is stronger than the surroundings is formed. Furthermore, it was confirmed that an electric field component in the y-axis direction that is not included in the incident wave is generated. The electric field component in the y-axis direction is generated only in the dielectric layer 21, and its intensity is about 100 times that in the case of FIG. 4(a). It is considered that this is generated by the patch element 22 and the reflective film 23 acting like a cavity resonator with respect to the incident wave, and the mode of the incident wave is converted into the eigenmode of the cavity resonator.

[0041] If the dielectric loss (tan δ) of the dielectric constituting the dielectric layer 21 in the cavity resonator is σ, the power loss EL is σE with respect to the electric field strength E in the cavity resonator. 2 is proportional to.

[0042] Therefore, even if the dielectric loss σ is small, the electric field strength E becomes 100 times, so the power loss EL at resonance equal to the target frequency fc of the incident wave is about 100 times the power loss EL at non-resonance when the frequency of the incident wave is other than the target frequency fc. 2 = about 10 4 The increase is about 40 dB.

[0043] Therefore, it is believed that the layer structure of patch element 22-dielectric layer 21-reflective film 23 induces power loss EL due to the change in the electric field direction and electric field concentration, making it possible to achieve high electromagnetic wave absorption even when using a dielectric with a relatively low dielectric constant and low loss, such as transparent PET resin, with a relative dielectric constant of about 2.5 to 3.

[0044] A sample of the electromagnetic wave absorber 10 having the above configuration was fabricated and its electromagnetic wave absorbing performance was evaluated. First, a sample of the electromagnetic wave absorber 10 was fabricated, in which the target attenuation frequency fc was 1.4mx1.4mx5mm in width x height x thickness, the size P of one side of the patch element 22 was 83mm, the spacing G of the patch elements 22 was 8mm, and the dielectric layer 21 was made of transparent PET resin with a dielectric constant εr21=2.9. As the samples, sample 1 with the thickness T of the dielectric layer 21 being 5mm and sample 2 with the thickness T being 10mm were fabricated.

[0045] Sample 1 and Sample 2 were placed in an electromagnetic anechoic chamber 101, as shown in Fig. 5. For the evaluation, two log-periodic antennas (Schwarzbeck, USLP9142) were used as transmitting and receiving antennas, and a vector network analyzer (Advantest, R3767CG) was used as a measuring device.

[0046] Electromagnetic waves RW were irradiated from the network analyzer 102 to the electromagnetic wave absorber 10 via the transmitting antenna SA while scanning the frequency, and the reflected waves were received by the receiving antenna RA, and the receiving strength for each frequency was measured by the network analyzer 102. Next, the reflection coefficient = receiving strength / transmitting strength was calculated for each frequency. In order to eliminate reflections from the antenna jig and the like and to measure only the reflections from the electromagnetic wave absorber 10, a time domain measurement function was used in the measurement. In addition, the measurement was performed by adjusting the position and orientation of the transmitting antenna SA and the receiving antenna RA to adjust the incident angle θ of the electromagnetic wave RW to the electromagnetic wave absorber 10 (the angle between the traveling direction of the electromagnetic wave RW and the normal to the surface (= incident surface) of the electromagnetic wave absorber 10).

[0047] The absorption characteristics of sample 1 (T=5 mm) are shown in FIG. Figure 6(a) shows the absorption characteristics of sample 1 for oblique incidence (θ ≠ 0) of TE waves. As shown in the figure, when TE waves are irradiated, there is no significant shift in the maximum absorption frequency or maximum absorption amount when the incidence angle θ is θ = 10° to 45°. Furthermore, in the frequency range including 920 MHz used in UHF-RFID, the reflection coefficient is below -20 dB, with a peak value of around -50 dB, confirming the occurrence of high return loss.

[0048] On the other hand, FIG. 6(b) shows the results of measuring and evaluating the absorption characteristics of the sample 1 for oblique incidence of TM waves. As shown in the figure, it was confirmed that when TM waves were incident, the absorption characteristics were more dependent on the incidence angle θ than the TE waves. The reason for such absorption characteristics is that the electromagnetic wave absorption phenomenon occurs due to the resonance phenomenon of the cavity resonator formed by the patch element 22-dielectric layer 21-reflective film 23. To explain in more detail, an electric field component parallel to the patch element 22 is required to excite this cavity resonator. In the TE wave, since the electric field E is parallel to the main surface of the patch element 22, the electric field component parallel to the main surface of the patch element 22 is maintained regardless of the incidence angle θ. In contrast, in the TM wave, the electric field component parallel to the main surface of the patch element 22 is the cosθ component of the electric field E. For this reason, as the incidence angle θ increases, the electric field component parallel to the main surface of the patch element 22 rapidly attenuates, making it difficult to excite the cavity resonator, and the frequency range in which the absorption performance is exhibited transitions to a higher frequency range.

[0049] The circularly polarized waves used in UHF-RFID communications are composite waves of TE and TM waves. Therefore, sample 1, which can provide sufficient attenuation to the TE waves, can adequately suppress the reflection of the entire circularly polarized waves transmitted and received by the RFID. However, in sample 1, the absorption band (attenuation frequency range) where the reflection coefficient shows sufficient attenuation of -20 dB or less within the frequency band centered on 920 MHz used by UHF-RFID is a relatively narrow range of about 10 MHz, and depending on frequency fluctuations due to RFID manufacturing errors, fluctuations in environmental temperature, etc., the frequency of the electromagnetic waves may deviate from the absorption band, resulting in insufficient attenuation of the reflected waves.

[0050] The absorption characteristics of sample 2 (T=10 mm) are shown in FIG. Figure 7(a) shows the absorption characteristics of Sample 2 for oblique incidence of TE waves, and Figure 7(b) shows the absorption characteristics of Sample 2 for oblique incidence of TM waves. As shown in the figure, in Sample 2 with T=10mm, the absorption center frequency shifts to the lower frequency side compared to the absorption characteristics of Sample 1 with T=5mm, but the absorption bandwidth is significantly expanded. In addition, with regard to the angle of incidence, almost no change was observed in the absorption characteristics up to θ=30°, confirming that stable absorption characteristics are exhibited over a wide angle.

[0051] FIG. 8 shows the results of comparing the frequency characteristics of electromagnetic wave absorption for Sample 1 and Sample 2, normalized by the absorption center frequency at the incidence angle θ=10° shown in FIG. 6(a) and FIG. 7(a). The absorption center frequency of Sample 1 is about 920 MHz, and the absorption center frequency of Sample 2 is about 800 MHz. When comparing the absorption band where the reflection coefficient is -10 dB or less, Sample 2 with a thickness of T=10 mm, which is twice as thick as Sample 1 with T=5 mm, has a bandwidth that is more than four times as large. Also, when comparing the absorption band where the reflection coefficient is -20 dB or less, it was confirmed that Sample 2 with T=10 mm has a bandwidth that is about three times as large as Sample 1 with T=5 mm. Thus, it can be seen that in the electromagnetic wave absorber 10, the thickness T of the dielectric layer 21 can be adjusted according to the required width of the absorption band. For example, the thickness T of the dielectric layer 21 can be increased as the absorption bandwidth becomes wider.

[0052] For example, if the target attenuation frequency fc is 920 MHz and the required absorption bandwidth at -20 dB is 30 MHz in accordance with UHF-RFID, the thickness T of the dielectric layer 21 is 10 mm or more. However, the required thickness T decreases as the target attenuation frequency fc increases, so when assuming an electromagnetic wave absorption band for the GHz band, for example, an absorber for electromagnetic waves for ETC in the 5.8 GHz band, or an absorber for suppressing side lobes for vehicle-mounted radar using the 5G band, it can be made into a thin plate with T = 1.5 mm or a sheet with T = 300 μm. This makes it possible to realize a high-performance electromagnetic wave absorbing sheet with a wide angle and wide band.

[0053] As described above, it has been confirmed that increasing the thickness of the dielectric layer that causes the dielectric loss σ is an effective method for broadening the absorption band of an electromagnetic wave absorber. In addition to increasing the thickness of the dielectric layer 21, another method for increasing the thickness of the dielectric layer is to set the thickness T of the dielectric layer 21 to a constant value and to increase the thickness of the entire dielectric by disposing a dielectric layer 25 in front of the patch element 22 as shown in Figures 9(a) and (b). Therefore, a comparative example having the configuration shown in Figures 9(a) and (b) was created and its absorption characteristics were measured.

[0054] First, the configurations of dielectric layer 21, patch element 22, and reflective film 23 were the same as those of sample 1. Next, dielectric layer 25 of the same material and configuration as dielectric layer 21 was laminated on patch element 22. As a result, the total thickness of the dielectric was set to 10 mm, the same as that of sample 2. Next, the absorption characteristics of the comparative example were measured in the same manner as for Samples 1 and 2.

[0055] FIG. 10 shows the absorption characteristics of the comparative example. As shown in the figure, although the total thickness of the dielectric is 10 mm in common, the width of the absorption band showing -10 dB or less is about 10 to 30 MHz, unlike the absorption characteristics of sample 2 shown in FIGS. 8(a) and (b), and a broadband is not realized. In addition, the absorption peak frequency shifts significantly according to the incident angle θ, and the incidence angle dependency of the absorption characteristics becomes high. This is considered to be because the layer of the front dielectric layer 25 and the patch element 22 functions as a kind of FSS layer (frequency-selective reflection-absorption layer), and inhibits the electromagnetic wave containment function of the patch element 22-reflection film 23 on the rear surface from being realized. The situation in which the front FSS layer (dielectric layer 25-patch element 22) and the rear absorption layer (patch element 22-reflection film 23) each exhibit different absorption characteristics can also be confirmed from the fact that the band showing the absorption characteristics is realized at two frequencies at the incident angle θ=10° in both FIGS. 10(a) and (b).

[0056] Therefore, it is desirable to place the dielectric layers, as dielectric layer 21, together between patch element 22 and reflective film 23, without placing a dielectric layer that can function as an FSS layer in front of patch element 22. For this reason, it is desirable to select the thickness T and material of protective layer 24 so that the product t·εr24 of its thickness t and relative dielectric constant εr24 is sufficiently smaller than the product T·εr21 of the thickness T of dielectric layer 21 and relative dielectric constant εr21, for example, t·εr24<(1 / 10)T·εr21.

[0057] As described above, the electromagnetic wave absorber 10 according to the embodiment of the present invention can obtain high electromagnetic wave absorption properties, even though it has a very simple configuration in which patch elements 22 are arranged in a matrix on one main surface of the dielectric layer 21 and the reflective film 23 is arranged on the other main surface of the dielectric layer 21. Furthermore, a required absorption bandwidth can be obtained by adjusting the thickness T of the dielectric layer 21.

[0058] Furthermore, by using a transparent resin as the resin that constitutes the dielectric layer 21, and further forming thin metal films by physical vapor deposition as the patch element 22 and the reflective film 23, it is possible to ensure light transparency and reduce optical blind spots.

[0059] The present invention is not limited to the above-described embodiment, but may be modified and applied in various ways. Although an example has been described in which a relatively low-loss transparent PET resin is mainly used as the material for the dielectric layer 21, other light-transmitting dielectric materials may also be used. The shape of the dielectric layer 21 is arbitrary, and may be, for example, a triangle, a hexagon, or the like. Alternatively, any design may be applied.

[0060] The size, gap, and the like of the patch element 22 can be changed as appropriate. Although the planar shape of the patch element 22 is a square, the planar shape and the method of forming the patch element 22 can be changed as appropriate. Although a conductor, particularly a metal, has been exemplified as the material of the patch element 22, any material can be used as long as it is a conductor. For example, conductive polymers such as ITO (Indium Tin Oxide) and PEDOT (Polyethylenedioxythiophene) may be used. Furthermore, when the light transmittance of the electromagnetic wave absorber 10 does not need to be relatively low, a light-impermeable metal foil or the like may be used for the patch element 22.

[0061] The shape and the like of the reflective film 23 are also arbitrary, and it is not necessary for it to be formed on the entire back surface of the dielectric layer 21. A plurality of reflective films 23 may be formed. The material thereof may be ITO, a conductive polymer, or the like. In addition, when the light transmittance of the electromagnetic wave absorber 10 is not required, a light-opaque metal foil or the like may be used.

[0062] Patch element 22 and reflective film 23 may be made of a resistive film. The material, thickness, and arrangement position of the protective layer 24 are not limited to those in the embodiment and can be changed as appropriate. However, as described above, it is preferable that the protective layer 24 is arranged in a form that does not form an FSS.

[0063] (Embodiment 2) When multiple electromagnetic wave absorbers 10 are arranged, the incidence angle θ of the electromagnetic wave to each electromagnetic wave absorber 10 differs for each electromagnetic wave absorber 10. For example, assuming a case in which three electromagnetic wave absorbers 10a to 10c are arranged facing an electromagnetic wave source WS to construct an electromagnetic wave absorbing system 11 as shown in Fig. 11, the incidence angles of the electromagnetic waves from the electromagnetic wave source WS to the electromagnetic wave absorbers 10a to 10c gradually decrease from θa to θb to θc.

[0064] 6(a) and 7(a), the absorption peak frequency of the electromagnetic wave absorbers 10a to 10c changes depending on the incident angle θ. For this reason, if the electromagnetic wave absorbers 10a to 10c have the same configuration, the absorption peak frequency fp of some of the electromagnetic wave absorbers 10a to 10c will deviate from the frequency fo of the electromagnetic wave radiated from the electromagnetic wave source WS, and will not be able to sufficiently absorb and attenuate the electromagnetic wave.

[0065] On the other hand, if electromagnetic wave absorbers 10 are designed for each incident angle θ taking into consideration the dependency of the absorption peak frequency fp on the incident angle θ, it will be necessary to prepare many types of electromagnetic wave absorbers 10, which will increase the design and manufacturing burden and inventory amount, resulting in a lack of efficiency.

[0066] Moreover, since the electromagnetic wave absorber 10 of the first embodiment has a completely closed plane, if it is placed in a space, particularly in the middle of a ventilation path, it will obstruct ventilation, which may obstruct heat dissipation from the electromagnetic wave source WS and its peripheral circuits.

[0067] In this embodiment, a method is described in which the absorption peak frequency fp of the electromagnetic wave absorber 10 is adjusted in accordance with changes in the incident angle θ to match the frequency fo of the electromagnetic wave to be attenuated, and further, the breathability of the electromagnetic wave absorber 10 is ensured.

[0068] The basic structure of the electromagnetic wave absorber 10 according to this embodiment is the same as that of the electromagnetic wave absorber 10 of the first embodiment shown in FIGS. 12, however, holes (hereinafter, through holes) 26 that penetrate electromagnetic wave absorber 10 are formed at each intersection of the gap regions between patch elements 22 arranged in a matrix. Through holes 26 are formed in a circular shape whose center coincides with the center of the intersection region of the gap area.

[0069] FIG. 13 is a graph illustrating the relationship between the radius R of the through-hole 26 and the TE wave absorption characteristics of the electromagnetic wave absorber 10. In FIG. These absorption characteristics show the relationship between the radius R of through-hole 26 and the absorption characteristics when patch element 22 is a rectangle made of copper foil with size P=12 mm×12 mm, gap size (width) G=2 mm, and dielectric layer 21 is made of PET resin with thickness T=2 mm. This electromagnetic wave absorber 10 is intended to absorb and attenuate electromagnetic waves in the 5 GHz band used, for example, in an ETC (Electronic Toll Collection system).

[0070] When radius R of through hole 26 is 0, that is, when through hole 26 is not formed, the absorption peak frequency is about 5.3 GHz. On the other hand, when radius R is 1 mm, the periphery of through hole 26 very slightly overlaps the corners of each patch element 22, and the corners of patch elements 22 are very slightly cut out. On the other hand, when radius R is 2 mm and 3 mm, the periphery of through hole 26 overlaps the corners of each patch element 22, and each corner of each patch element 22 is removed, and the size of the removal is larger when radius R is 3 mm.

[0071] 13, the frequency of the absorption peak shifts to the higher frequency side as radius R of through-hole 26 increases and the amount of loss at the corners of patch element 22 increases, without any significant difference in the amount of absorption at the peak.

[0072] The reason why the absorption peak frequency fp increases as the through-hole 26 becomes larger will be explained. As shown in Fig. 14(a), assume that the electric field E and magnetic field H of the incident electromagnetic wave are parallel to the z-axis and x-axis, respectively. In this case, when the resonator formed by each patch element 22 is in a state of resonance with the electromagnetic wave, a current I flows in each patch element 22 as shown in Fig. 14(b), and the half wavelength λ / 2 of current I is approximately equal to the length P of patch element 22 in the z-axis direction, with the amplitude as shown in Fig. 14(c).

[0073] On the other hand, when through-hole 26 is formed in the gap region, current I flows as shown in Fig. 15(a), with its amplitude as shown in Fig. 15(b). In the region where through-hole 26 is formed, the region through which current I can flow is limited, and half the wavelength λ / 2 of current I on both sides of patch element 22 is shorter than when through-hole 26 is not formed. As a result, the absorption peak frequency fp is higher than when through-hole 26 is not formed.

[0074] Next, a method for adjusting the absorption peak frequency of the electromagnetic wave absorber 10 according to the incident angle θ by using the through-hole 26 will be described. First, for the electromagnetic wave absorber 10, the absorption peak frequency fp is obtained in advance by experiment or simulation for each combination of the incident angle θ and the radius R of the through-hole 26, and a table of absorption peak frequencies shown in FIG. 16 is prepared.

[0075] Next, a plurality of electromagnetic wave absorbers 10 are arranged, for example, as shown in FIG. Next, the angles of incidence θa, θb, and θc of the electromagnetic waves from the electromagnetic wave source WS to each of the electromagnetic wave absorbers 10a, 10b, and 10c are obtained. This process may be performed at the design stage of the arrangement of the electromagnetic wave absorbers 10, or may be performed at the installation site.

[0076] Next, according to the absorption peak frequency table shown in Fig. 16, radii Ra, Rb, and Rc are obtained when the absorption peak frequencies fpa, fpb, and fpc are equal to the frequency fo of the electromagnetic wave from the electromagnetic wave source WS when the incident angles are θa, θb, and θc. For example, if the frequency of the electromagnetic wave radiated by the electromagnetic wave source WS is 5.7 GHz, it is found that a radius R of 1 mm is appropriate for making the absorption peak frequency fp of the electromagnetic wave absorber 10 with an incident angle θ of 5° 5.7 GHz. If the corresponding value does not exist in the table, it may be found by using a complementation method.

[0077] In general, as the incident angle θ increases, the absorption peak frequency fp tends to increase, so the required radius R decreases, whereas as the incident angle θ decreases, the absorption peak frequency fp tends to decrease, so the required radius R increases. For example, if the frequency of the electromagnetic wave radiated by the electromagnetic wave source WS is 7.4 GHz, the absorption peak frequency fp of the electromagnetic wave absorber 10 becomes 7.4 GHz when the incident angle θ is 0° and the radius R of the through hole 26 is 5 mm, whereas when the incident angle is 60° and the radius R is 0.5 mm.

[0078] Next, a through hole 26 is formed in electromagnetic wave absorber 10a using a drill with a diameter of 2·Ra, a through hole 26 is formed in electromagnetic wave absorber 10b using a drill with a diameter of 2·Rb, and a through hole 26 with a diameter of 2·Rc is formed in electromagnetic wave absorber 10c using a drill with a diameter of 2·Rc.

[0079] In this manner, all of the electromagnetic wave absorbers 10a, 10b, and 10c are ready to absorb the electromagnetic wave of frequency fo from the electromagnetic wave source WS, completing the electromagnetic wave absorbing system 11 that absorbs the electromagnetic wave from the electromagnetic wave source WS.

[0080] In addition, since air can flow through the through holes 26, air cooling of the enclosed space is possible even when the electromagnetic wave source WS and its peripheral circuits are enclosed by the electromagnetic wave absorber 10. To improve the cooling capacity, a blower such as a fan may be provided to increase the amount of air flow.

[0081] The through hole 26 may be formed in a factory or the like based on a design drawing or the like of the electromagnetic wave absorbing system 11, and the electromagnetic wave absorber 10 with the through hole 26 formed therein may be installed on site. Alternatively, after the electromagnetic wave absorber 10 without the through hole 26 formed therein is placed, the incident angle θ may be obtained on site and a through hole 26 of an appropriate diameter may be formed using a hand drill or the like.

[0082] According to this embodiment, if several types of electromagnetic wave absorbers 10 having basic absorption peak frequencies are prepared, the electromagnetic waves to be absorbed can be attenuated by adding the simple process of forming through holes 26 in accordance with the frequency of the electromagnetic waves to be absorbed and the arrangement configuration of the electromagnetic wave absorbers, and it is also possible to reduce the inventory amount of electromagnetic wave absorbers 10.

[0083] (Embodiment 3) In the second embodiment, an example has been shown in which the frequency of the electromagnetic wave to be absorbed is shifted to the higher frequency side by partially removing the corners of patch element 22. The present invention is not limited to this, and for example, as shown in Fig. 17, by forming through-hole 27 in patch element 22, it is also possible to shift the absorption peak frequency to the lower frequency side as shown in Fig. 18. The absorption characteristics shown in Fig. 18 were obtained when patch element 22 was a rectangle made of copper foil with a size P = 13 mm × 13 mm, a gap size (width) G = 1.45 mm, and dielectric layer 21 was made of PET resin with a thickness T = 5 mm.

[0084] In FIG. 18, the absorption peak frequency is approximately 5.3 GHz when no through-hole 27 is formed (radius cR=0), but when cR=1 mm, there is almost no change, when cR=2 mm, the absorption peak frequency drops, and when cR=3 mm, no clear peak appears in the absorption characteristics. This is believed to be because when cR=2 mm, as shown in FIG. 19(a), the current I flows around the through-hole 27, and the current path becomes longer, resulting in a half-wavelength λ / 2 increase. Also, the reason there is no effect when cR=1 mm is believed to be because the through-hole 27 is too small to affect the length of the current path of the current I. On the other hand, the reason no clear peak appears in the absorption characteristics when cR=3 mm is believed to be because the size of the through-hole 27 is too large compared to the size of the patch element 22 (13 mm×13 mm), and the patch element 22 cannot function sufficiently as a resonant electrode, resulting in a decrease in the Q value of resonance.

[0085] The through-holes 27 are formed in the electromagnetic wave absorber 10 in the following manner. Here, an example will be described in which an electromagnetic wave absorbing system 11 shown in FIG. 11 is constructed.

[0086] First, for each combination of the incident angle θ and the radius cR of the through-hole 27, the absorption peak frequency fp is obtained by experiment or simulation, and an absorption peak frequency table shown in Fig. 20 is prepared. In the absorption peak frequency table shown in Fig. 20, NG indicates that appropriate attenuation characteristics cannot be obtained.

[0087] Next, angles of incidence θa, θb, and θc of the electromagnetic waves to be attenuated from the electromagnetic wave source WS onto the electromagnetic wave absorbers 10a, 10b, and 10c are obtained.

[0088] Next, according to the absorption peak frequency table shown in Fig. 20, radii cRa, cRb, and cRc are obtained when the absorption peak frequencies fpa, fpb, and fpc are equal to the frequency fo of the electromagnetic wave from the electromagnetic wave source WS when the incident angles are θa, θb, and θc. For example, if the frequency of the electromagnetic wave emitted by the electromagnetic wave source WS is 4.7 GHz, it is found that a radius cR = 4 mm is appropriate to make the absorption peak frequency fp of the electromagnetic wave absorber 10 with an incident angle θ of 5° 4.7 GHz. If the corresponding value does not exist in the table, it may be found by using an interpolation method.

[0089] In general, as the incident angle θ increases, the absorption peak frequency fp tends to increase, and the required radius cR also increases, whereas as the incident angle θ decreases, the absorption peak frequency fp tends to decrease, and the required radius cR also decreases. For example, if the frequency of the electromagnetic wave emitted by the electromagnetic wave source WS is 6.4 GHz, then when the incident angle θ is 0°, the radius R of the through-hole 26 is 0 mm, whereas when the incident angle is 60°, the radius R is 4.0 mm.

[0090] Next, a through hole 27 is formed in electromagnetic wave absorber 10a using a drill with a diameter of 2·Ra, a through hole 27 is formed in electromagnetic wave absorber 10b using a drill with a diameter of 2·Rb, and a through hole 27 with a diameter of 2·Rc is formed in electromagnetic wave absorber 10c using a drill with a diameter of 2·Rc.

[0091] In this manner, all of the electromagnetic wave absorbers 10a, 10b, and 10c are ready to absorb the electromagnetic wave of frequency fo from the electromagnetic wave source WS, completing the electromagnetic wave absorbing system 11 that absorbs the electromagnetic wave from the electromagnetic wave source WS.

[0092] In this way, the absorption peak frequency of the electromagnetic wave absorber 10 can be adjusted in accordance with its arrangement position, and the reflection of unwanted electromagnetic waves can be suppressed.

[0093] In addition, since air can flow through the through holes 27, air cooling of the enclosed space is possible even when the electromagnetic wave source WS and its peripheral circuits are enclosed by the electromagnetic wave absorber 10. To improve the cooling capacity, a blower such as a fan may be provided to increase the amount of air flow.

[0094] The through-hole 27 may be formed in a factory or the like based on a design drawing or the like of the electromagnetic wave absorbing system 11, and the electromagnetic wave absorber 10 with the through-hole 27 formed therein may be installed on-site. Alternatively, after the electromagnetic wave absorber 10 without the through-hole 27 formed therein is placed, the incident angle θ may be obtained on-site and the through-hole 27 with an appropriate diameter may be formed using a hand drill or the like.

[0095] In this embodiment as well, if several types of electromagnetic wave absorbers 10 having basic absorption peak frequencies are prepared, the electromagnetic waves to be absorbed can be attenuated by adding the simple process of forming through holes 27 in accordance with the frequency of the electromagnetic waves to be absorbed and the arrangement configuration of the electromagnetic wave absorbers, and it is also possible to reduce the inventory amount of c.

[0096] (Modification) In the second and third embodiments, in order to shift the absorption peak frequency, circular through-holes 26, 27 are formed in the electromagnetic wave absorber 10. By simply selecting the diameter of the drill, it is possible to form a nearly perfect circular hole, and the circular through-hole is suitable for uniformly processing a large number of patch elements 22. It is particularly suitable for appropriate processing at the installation site of the electromagnetic wave absorber 10.

[0097] However, the present invention is not limited to this. As described above, the absorption spectrum distribution of the electromagnetic wave absorber 10 varies depending on physical parameters such as the shape and size of the patch element 22, the size of the gap G, and the shape, size, number, and position of the openings or notches formed in the patch element 22. Therefore, any physical parameters may be adjusted so as to obtain a desired absorption spectrum distribution.

[0098] 21(a) and (b) show, as an example, an example in which a plurality of rectangular apertures 28 are formed in a region other than the central portion of the patch element 22. FIG. 21(a) shows an example in which two elongated rectangular apertures 28 are formed in the patch element 22, and FIG. 21(b) shows an example in which four elongated rectangular apertures 28 are formed in the patch element 22. FIG. 21(c) shows an example in which two circular apertures 29 are formed in the patch element 22, and FIG. 21(d) shows an example in which five circular apertures 29 are formed in the central portion and around the patch element 22. As physical parameters such as the shape, size, number, and position of the apertures 28 and 29 change, the route and wavelength of the current I induced by the incident electromagnetic wave change. This causes a change in the absorption spectrum distribution.

[0099] However, since the relative positional relationship between the electromagnetic wave source and the electromagnetic wave absorber 10 is undetermined, it is desirable that the patch element 22 and the openings 28, 29 be formed with 90° rotational symmetry when viewed from the front, i.e., when viewed in the y-axis direction, as illustrated in, for example, Figures 21(a) to (d).

[0100] In the second and third embodiments, examples have been shown in which through holes 26 and 27 are formed, but in situations in which ventilation is not necessary, a similar function can be achieved simply by forming a cutout portion by partially removing patch element 22. For example, in the configuration of Fig. 1, patch element 22 may be partially removed and processed into a desired shape and size, as shown in Figs.

[0101] Furthermore, the shape of the removed portion (cutout portion) of patch element 22 and the shape of through hole 27 are arbitrary. For example, in the configuration of Fig. 1, a triangular or quadrangular cutout portion may be formed at the corner of patch element 22 which is rectangular in plan view. Similarly, through hole 27 may be elliptical, polygonal, etc. in plan view.

[0102] Furthermore, patch element 22 may be formed with a part cut out or removed at the stage of forming patch element 22. For example, the part of dielectric layer 21 corresponding to the cut out or through hole may be masked, a conductive material such as copper paste or silver paste may be applied, and the masking may be removed after application to form the cut out or through hole.

[0103] In the above embodiment, an example has been described in which patch element 22 is disposed on dielectric layer 21, but this is not limiting. For example, as shown in Fig. 22, patch element 22A may be formed on optically transparent dielectric sheet 31, which may then be attached to dielectric layer 21. In this case as well, patch element 22A may be formed having, for example, cutout portion 32 or through-hole 33.

[0104] In the second and third embodiments, the through-holes 26 or 27 are formed with a single diameter, but the through-holes 26, notches or 27 with different diameters may be formed in one electromagnetic wave absorber 10. This makes it possible to widen the band in the peak region of the attenuation characteristics, which contributes to achieving the object of the invention. Similarly, one electromagnetic wave absorber 10 may have a mixture of regions where the through-holes 26 or 27 are formed and regions where they are not formed.

[0105] In the embodiment, the electromagnetic wave absorber that absorbs electromagnetic waves in the UHF band and the 5 GHz band has been exemplified, but the frequency band of the electromagnetic waves to be absorbed is arbitrary. [Explanation of symbols]

[0106] 10, 10a to 10c Electromagnetic wave absorber 21 Dielectric layer 22 Patch element 23 Reflective film 24 Protective layer 25 Dielectric Layer 26,27 Through holes 31 Dielectric sheet 32 Cutout 33 Through hole 102 Network Analyzer SA,RA antenna WS electromagnetic wave source

Claims

1. a dielectric layer comprising an optically transparent dielectric material; A plurality of patch elements arranged on one main surface of the dielectric layer; a conductive reflective film arranged on a second main surface of the dielectric layer so as to face the patch element; Equipped with the dielectric layer has a thickness in the range of 1 / 100 to 1 / 10 of the wavelength within the dielectric layer of the electromagnetic wave to be attenuated; Electromagnetic wave absorber.

2. the dielectric layer has a thickness in the range of 1 / 70 to 1 / 20 of the wavelength within the dielectric layer of the electromagnetic wave to be attenuated; 2. The electromagnetic wave absorber according to claim 1.

3. the patch element, the dielectric layer, and the reflective film function as a cavity resonator for the electromagnetic wave to be attenuated, and generate an electric field concentration region within the dielectric layer.

3. The electromagnetic wave absorber according to claim 1 or 2.

4. When the thickness of the dielectric layer is T and the relative dielectric constant is εr1, the front surface of the patch element is not provided with a layer whose product t·εr2 of the thickness t and the relative dielectric constant εr2 is larger than the product T·εr1 of the thickness of the dielectric layer and the relative dielectric constant εr1.

3. The electromagnetic wave absorber according to claim 1 or 2.

5. A layer forming a frequency selective reflection-absorption layer is not disposed on the front surface of the patch element.

3. The electromagnetic wave absorber according to claim 1 or 2.

6. the patch element and the reflective film are made of a light-transmitting metal.

3. The electromagnetic wave absorber according to claim 1 or 2.

7. a protective layer covering the plurality of patch elements; 3. The electromagnetic wave absorber according to claim 1 or 2.

8. The electromagnetic wave absorber according to claim 1 , wherein at least one of the plurality of patch elements has a rectangular shape in plan view with notches formed at corners thereof.

9. The electromagnetic wave absorber according to claim 1 , wherein the plurality of patch elements have a rectangular shape in a plan view, and at least one of the patch elements has a hole formed therethrough.

10. 10. The electromagnetic wave absorber of claim 9, wherein the hole penetrates at least one of the patch element, the dielectric layer, and the reflective film.

11. A plurality of holes are formed in each patch element, Each of the patch elements and the plurality of holes are formed in a rotationally symmetrical manner by 90° when viewed from the front. The electromagnetic wave absorber according to claim 10 .

12. A plurality of electromagnetic wave absorbers according to any one of claims 8 to 11, the plurality of electromagnetic wave absorbers are disposed opposite to an electromagnetic wave source that radiates electromagnetic waves to be attenuated; The cutout or hole of the patch element has a size according to an incident angle of an electromagnetic wave from an electromagnetic wave source. Electromagnetic wave absorbing system.

13. A plurality of the electromagnetic wave absorbers according to claim 8 are provided, the plurality of electromagnetic wave absorbers are disposed opposite to an electromagnetic wave source that radiates electromagnetic waves to be attenuated; The size of the notch portion decreases as the incident angle of the electromagnetic wave from the electromagnetic wave source increases. Electromagnetic wave absorbing system.

14. A plurality of the electromagnetic wave absorbers according to claim 9, 10 or 11 are provided, the plurality of electromagnetic wave absorbers are disposed opposite to an electromagnetic wave source that radiates electromagnetic waves to be attenuated; The hole has a diameter that increases as the incident angle of the electromagnetic wave from the electromagnetic wave source increases. Electromagnetic wave absorbing system.

15. A plurality of electromagnetic wave absorbers according to claim 1 or 2 are arranged facing an electromagnetic wave source, before or after the arrangement, forming cutout portions at corners of the patch elements each having a rectangular shape in a plan view of each of the electromagnetic wave absorbers; The size of the notch portion decreases as the incident angle of the electromagnetic wave from the electromagnetic wave source increases. Electromagnetic wave attenuation method.

16. A plurality of electromagnetic wave absorbers according to claim 1 or 2 are arranged facing an electromagnetic wave source, forming holes through the plurality of patch elements of each of the electromagnetic wave absorbers before or after the placement; the plurality of holes have diameters which increase as the incident angle of the electromagnetic wave from the electromagnetic wave source increases; Electromagnetic wave attenuation method.

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