Electromagnetic wave absorber

Abstract

In this electromagnetic wave absorber, incident electromagnetic waves that have entered a plurality of openings (11) in a first metal layer (10) pass through a dielectric (30). The plurality of inclined surfaces (22a, 22b) retroreflect an incident electromagnetic wave (D1) that has passed through the dielectric. Reflected electromagnetic waves (D3) retroreflected by the plurality of inclined surfaces are reflected by the first metal layer after passing through the dielectric. The reflected electromagnetic wave (D4) is retroreflected by the plurality of inclined surfaces after passing through the dielectric. The retro-reflected electromagnetic wave (D6) is reflected by the first metal layer after passing through the dielectric. The wavefront of the reflected electromagnetic wave (D7) coincides with the wavefront of the incident electromagnetic wave, whereby the electromagnetic wave resonates. The dielectric absorbs an electromagnetic wave by converting the electromagnetic wave into heat by dielectric loss in a state in which the electromagnetic wave resonates.

Description

Technical Field

[0001] This disclosure relates to electromagnetic wave absorbers. Background Technology

[0002] Previously, several basic types of electromagnetic wave absorbers were known. One type, the quarter-λ type, involved a wave absorber comprising a first component that allows a portion of an incident electromagnetic wave incident from one side of a predetermined direction to pass through, and a second component disposed on the other side of the predetermined direction relative to the first component (see, for example, Patent Document 1). λ is the wavelength of the electromagnetic wave. An intermediate material, serving as a dielectric, is disposed between the first and second components. The second component reflects the electromagnetic wave that has passed through the intermediate material. In this electromagnetic wave absorber, due to multiple reflections of the electromagnetic wave between the second and first components, the electromagnetic wave is attenuated by the resistive component of the first component, the dielectric loss caused by the intermediate material, and the magnetic loss caused by the intermediate material.

[0003] Existing technical documents

[0004] Patent documents

[0005] Patent Document 1: Japanese Patent Application Publication No. 2000-091782 Summary of the Invention

[0006] The inventors have investigated the attenuation of unwanted electromagnetic waves emitted from an automotive radar device that interfere with electromagnetic waves originally used for detecting the vehicle's surroundings, using the aforementioned electromagnetic wave absorber. The automotive radar device uses electromagnetic waves within a predetermined frequency range to detect the vehicle's surroundings. For example, when unwanted electromagnetic waves within the predetermined frequency range are incident on the aforementioned electromagnetic wave absorber, if the electromagnetic waves resonate at frequencies within the predetermined frequency range, the unwanted electromagnetic waves can be efficiently attenuated using the resistive component of the first component, the dielectric loss caused by the intermediate material, and the magnetic loss caused by the intermediate material.

[0007] Here, the incident electromagnetic wave that has passed through the first component is reflected by the second component. When the reflected electromagnetic wave is reflected by the first component, if the wavefront of the reflected electromagnetic wave coincides with the wavefront of the incident electromagnetic wave that has passed through the first component, the electromagnetic wave can be made to resonate through the electromagnetic wave absorber.

[0008] In this case, the resonant frequency of the electromagnetic wave is determined by the positional relationship between the wavefront of the reflected electromagnetic wave reflected by the first component and the wavefront of the incident electromagnetic wave that has passed through the first component. Therefore, if the incident angle of the incident electromagnetic wave relative to the electromagnetic wave absorber changes, the positional relationship between the wavefront of the reflected electromagnetic wave and the wavefront of the incident electromagnetic wave that has passed through the first component changes.

[0009] Therefore, if the incident angle of the electromagnetic wave changes, the resonant frequency will change, potentially causing the resonant frequency to deviate from the aforementioned predetermined frequency range. In this case, it is impossible to efficiently attenuate unwanted electromagnetic waves within the aforementioned predetermined frequency range.

[0010] The purpose of this disclosure is to provide an electromagnetic wave absorber that can suppress changes in resonant frequency even when the incident angle of the electromagnetic wave changes.

[0011] According to one aspect of this disclosure, an electromagnetic wave absorber possesses:

[0012] The first component allows electromagnetic waves incident from one side in a predetermined direction to pass through;

[0013] The dielectric, which is disposed on the opposite side of the first component in a predetermined direction; and

[0014] The second component is positioned on the opposite side of the dielectric in a predetermined direction and has multiple inclined surfaces whose normal direction is inclined relative to the predetermined direction to retroreflect electromagnetic waves that have passed through the dielectric.

[0015] When electromagnetic waves that have passed through the first component resonate due to multiple reflections between the first component and multiple inclined surfaces, the electromagnetic waves are attenuated by using a dielectric.

[0016] Therefore, the second component retroreflects electromagnetic waves through multiple inclined surfaces. Thus, when the incident angle of the electromagnetic wave changes, changes in the positional relationship between the electromagnetic wave transmitted through the first component and the electromagnetic wave after multiple reflections can be suppressed. Therefore, changes in the positional relationship between the wavefront of the electromagnetic wave transmitted through the first component and the wavefront of the electromagnetic wave after multiple reflections can be suppressed. Therefore, an electromagnetic wave absorber that can suppress changes in resonant frequency even when the incident angle of the electromagnetic wave changes can be provided. Attached Figure Description

[0017] Figure 1 This is a perspective view of the electromagnetic wave absorber in the first embodiment, illustrating the plurality of openings formed in the first metal layer, the plurality of triangular prisms formed in the second metal layer, and the dielectric disposed between the first metal layer and the second metal layer.

[0018] Figure 2 yes Figure 1 The perspective view of the electromagnetic wave absorber in the first embodiment is a diagram used to illustrate the positional relationship between the plurality of openings formed in the first metal layer and the plurality of triangular prisms formed in the second metal layer.

[0019] Figure 3 It means Figure 1A diagram of a portion of the electromagnetic wave absorber in the first embodiment is used to illustrate the shape of the side surface of a triangular prism formed in the second metal layer and the two angles constituting the side surface.

[0020] Figure 4 It means in Figure 1 A schematic diagram illustrating a specific example of electromagnetic wave absorption in the first embodiment, in which electromagnetic waves incident from one side of the stacking direction through an opening are subjected to multiple reflections between the first metal layer and the second metal layer.

[0021] Figure 5 This is a schematic diagram showing the positional relationship between the wavefront of the incident electromagnetic wave outside the dielectric, the wavefront of the incident electromagnetic wave inside the dielectric, and the wavefront of the reflected electromagnetic wave in the electromagnetic wave absorber of the comparative embodiment of the first embodiment.

[0022] Figure 6 This is a schematic diagram illustrating a specific example of electromagnetic wave absorption in the comparative embodiment of the first embodiment, where electromagnetic waves incident through an opening between the first and second metal layers undergo multiple reflections.

[0023] Figure 7 It means in Figure 1 A schematic diagram showing the positional relationship between the wavefront of the incident electromagnetic wave outside the dielectric, the wavefront of the incident electromagnetic wave inside the dielectric, and the wavefront of the reflected electromagnetic wave in the electromagnetic wave absorber of the first embodiment when the incident angle changes.

[0024] Figure 8 This is a schematic diagram illustrating a specific example of multiple reflections of electromagnetic waves between the first and second metal layers in a comparative electromagnetic wave absorber according to the first embodiment, before the incident angle changes.

[0025] Figure 9 This is a schematic diagram illustrating a specific example of multiple reflections of electromagnetic waves between the first and second metal layers in a comparative electromagnetic wave absorber according to the first embodiment, after a change in the incident angle.

[0026] Figure 10 This is a schematic diagram illustrating a specific example in which, in the electromagnetic wave absorber of the first embodiment, when the incident angle is 0°, the incident electromagnetic wave is retroreflected by a pair of inclined surfaces of the second metal layer.

[0027] Figure 11 This is a schematic diagram illustrating a specific example in the electromagnetic wave absorber of the first embodiment, where, when the incident angle is 0°, the incident electromagnetic wave is retroreflected by an effective reflecting surface formed by a pair of inclined surfaces of the second metal layer.

[0028] Figure 12This is a schematic diagram illustrating a specific example in which, in the electromagnetic wave absorber of the first embodiment, when the incident angle is 5°, the incident electromagnetic wave is retroreflected by a pair of inclined surfaces of the second metal layer.

[0029] Figure 13 This is a schematic diagram illustrating a specific example in the electromagnetic wave absorber of the first embodiment, where, at an incident angle of 5°, the incident electromagnetic wave is retroreflected by an effective reflecting surface formed by a pair of inclined surfaces of the second metal layer.

[0030] Figure 14 This is a schematic diagram illustrating a specific example of multiple reflections of electromagnetic waves between a pair of inclined surfaces of the second metal layer and the first metal layer when the incident angle is 0° in the electromagnetic wave absorber of the first embodiment.

[0031] Figure 15 This is a schematic diagram illustrating a specific example of multiple reflections of electromagnetic waves between a pair of inclined surfaces of the second metal layer and the first metal layer when the incident angle is 5° in the electromagnetic wave absorber of the first embodiment.

[0032] Figure 16 This is a schematic diagram showing the wavefront of the incident electromagnetic wave and the wavefront of the reflected electromagnetic wave when there is multiple reflection between a pair of inclined surfaces of the second metal layer and the first metal layer in the electromagnetic wave absorber of the first embodiment, when the incident angle is 5°.

[0033] Figure 17 This is a schematic diagram illustrating a specific example of an effective reflecting surface formed by two adjacent pairs of inclined surfaces in the second metal layer in the electromagnetic wave absorber of the first embodiment.

[0034] Figure 18 This is a schematic diagram showing the wavefront of the incident electromagnetic wave and the wavefront of the reflected electromagnetic wave when the incident angle is 10° in the electromagnetic wave absorber of the first embodiment, during multiple reflections of the electromagnetic wave between a pair of inclined surfaces of the second metal layer and the first metal layer.

[0035] Figure 19 This is a graph showing the relationship between the reflection loss of electromagnetic waves and the resonant frequency of electromagnetic waves when the incident angle of electromagnetic waves is 0°, 20°, 40°, and 60° in the electromagnetic wave absorber of the comparative embodiment of the first embodiment.

[0036] Figure 20 This is a graph showing the relationship between the reflection loss of electromagnetic waves and the resonant frequency of electromagnetic waves when the incident angle of electromagnetic waves is 0°, 20°, 40°, and 60° in the electromagnetic wave absorber of the first embodiment.

[0037] Figure 21This is a graph showing the relationship between the reflection loss of electromagnetic waves and the incident angle of electromagnetic waves when the frequencies of electromagnetic waves are 75.5 GHz, 76.0 GHz, 76.5 GHz, and 77.0 GHz in the electromagnetic wave absorber of the comparative embodiment of the first embodiment.

[0038] Figure 22 This is a graph showing the relationship between the reflection loss of electromagnetic waves and the incident angle of electromagnetic waves when the frequencies of electromagnetic waves are 75.5 GHz, 76.0 GHz, 76.5 GHz, and 77.0 GHz in the electromagnetic wave absorber of the first embodiment.

[0039] Figure 23 This is a graph showing the relationship between the absorption frequency and the height of the triangular prisms, expressed in units of λ, when the bottom surface between the two triangular prisms is not provided in the electromagnetic wave absorber of the first embodiment at incident angles of 0° and 40°.

[0040] Figure 24 This is a diagram illustrating a plurality of triangular prisms with a height of 0.15λ, in which the wavelength of the electromagnetic wave traveling within the dielectric is set to λ in the electromagnetic wave absorber of the first embodiment, without the bottom surface between the two triangular prisms being provided.

[0041] Figure 25 This is a diagram illustrating the plurality of triangular prisms with a height of 0.55λ in the electromagnetic wave absorber of the first embodiment, without the bottom surface between the two triangular prisms being provided.

[0042] Figure 26 This is a graph showing the relationship between the absorption frequency and the height of the triangular prism, expressed in units of λ, when the base surface between two triangular prisms is provided in the electromagnetic wave absorber of the first embodiment, at incident angles of 0° and 40°.

[0043] Figure 27 This is a diagram illustrating a plurality of triangular prisms with a height of 0.15λ, in which the wavelength of the electromagnetic wave traveling within the dielectric is set to λ, and a base is provided between two triangular prisms in the electromagnetic wave absorber of the first embodiment.

[0044] Figure 28 This is a diagram illustrating a plurality of triangular prisms with a height of 0.5λ, in which the wavelength of the electromagnetic wave traveling within the dielectric is set to λ, and a base is provided between two triangular prisms in the electromagnetic wave absorber of the first embodiment.

[0045] Figure 29 This is a side view of the electromagnetic wave absorber according to the second embodiment, and is a diagram used to illustrate the positional relationship between the plurality of openings formed in the first metal layer and the plurality of triangular prisms formed in the second metal layer.

[0046] Figure 30 This is a perspective view of the electromagnetic wave absorber according to the third embodiment, which is a perspective view used to illustrate the opening formed in the first metal layer and the inclined surface of the quadrangular prism formed in the second metal layer.

[0047] Figure 31 This is a perspective view of the electromagnetic wave absorber according to the fourth embodiment, which is a perspective view used to illustrate the opening formed in the first metal layer and the inclined surface of the quadrangular prism formed in the second metal layer.

[0048] Figure 32 This is a perspective view of the electromagnetic wave absorber according to the fourth embodiment, and is a diagram used to illustrate the opening formed in the first metal layer and the inclined surfaces of the three triangular prisms formed in the second metal layer.

[0049] Figure 33 This is a front view of the electromagnetic wave absorber according to the fourth embodiment, and is a diagram used to illustrate the two inclined surfaces of the triangular prism of the second metal layer and the two inclined surfaces arranged longitudinally relative to the triangular prism when the first metal layer is removed.

[0050] Figure 34 This is a perspective view of the electromagnetic wave absorber according to the fourth embodiment. It is a diagram used to illustrate the two inclined surfaces of a triangular prism of the second metal layer and the two triangular prisms arranged longitudinally in the state where the first metal layer has been removed.

[0051] Figure 35 This is a perspective view of the electromagnetic wave absorber according to the fifth embodiment, illustrating the opening formed in the first metal layer, the two inclined surfaces of the quadrangular prism formed in the second metal layer, and the two quadrangular prisms arranged longitudinally relative to the quadrangular prism.

[0052] Figure 36 This is a front view of the electromagnetic wave absorber according to the fifth embodiment, and is a diagram used to illustrate the opening formed in the first metal layer and the two inclined surfaces of the quadrangular prism formed in the second metal layer.

[0053] Figure 37 This is a side view of the electromagnetic wave absorber according to the fifth embodiment, and is a diagram used to illustrate the inclined surface of the quadrangular prism formed in the second metal layer and the two inclined surfaces arranged longitudinally relative to the quadrangular prism.

[0054] Figure 38 This is a perspective view of the electromagnetic wave absorber according to the fifth embodiment, and is a diagram used to illustrate the inclined surface of the quadrangular prism formed in the second metal layer and the two quadrangular prisms arranged longitudinally relative to the quadrangular prism.

[0055] Figure 39This is a perspective view of the electromagnetic wave absorber according to the sixth embodiment, and is a diagram used to illustrate two reflecting surfaces formed by the curved surfaces of a triangular prism formed in the second metal layer.

[0056] Figure 40 This is a diagram of the electromagnetic wave absorber according to the sixth embodiment, illustrating two reflecting surfaces formed by the curved surfaces of a triangular prism formed in the second metal layer.

[0057] Figure 41 This is a diagram of the electromagnetic wave absorber according to the seventh embodiment, and is a side view for illustrating the two reflecting surfaces formed by the curved surfaces of the triangular prism formed in the second metal layer.

[0058] Figure 42 This is a perspective view of the electromagnetic wave absorber according to the seventh embodiment, and is a diagram used to illustrate two reflecting surfaces formed by the curved surfaces of a triangular prism formed in the second metal layer.

[0059] Figure 43 This is a front view of the electromagnetic wave absorber according to the seventh embodiment, and is a diagram used to illustrate the inclined surfaces that respectively constitute multiple recesses formed in the second metal layer.

[0060] Figure 44 This is a side view of the electromagnetic wave absorber according to the seventh embodiment, and is a diagram used to illustrate the inclined surfaces that respectively constitute the plurality of recesses formed in the second metal layer.

[0061] Figure 45 This is a front view of the second metal layer of the electromagnetic wave absorber in the seventh embodiment, and is a front view used to illustrate the inclined surfaces that form multiple recesses in the second metal layer when the first metal layer is removed.

[0062] Figure 46 This is a schematic diagram showing the three inclined surfaces of the triangular pyramid-shaped recessed unit of the second metal layer of the electromagnetic wave absorber formed in the seventh embodiment, and a diagram showing the recessed part formed with the opening facing the obliquely upward side. Detailed Implementation

[0063] Hereinafter, embodiments of the present disclosure will be described based on the accompanying drawings. Furthermore, in order to simplify the description of each of the following embodiments, identical or equivalent parts will be labeled with the same reference numerals in the drawings.

[0064] (First Implementation)

[0065] use Figure 1 , Figure 2 , Figure 3The first embodiment of the electromagnetic wave absorber 1 disclosed herein will be described. The electromagnetic wave absorber 1 of this embodiment attenuates useless electromagnetic waves in the electromagnetic waves emitted from the vehicle-mounted radar device that interfere with the electromagnetic waves used to detect the vicinity of the vehicle.

[0066] Figure 1 This is a three-dimensional diagram showing the overall structure of the electromagnetic wave absorber 1. Figure 2 This is a three-dimensional diagram of electromagnetic wave absorber 1. (See diagram below.) Figure 1 and Figure 2 As shown, the electromagnetic wave absorber 1 includes a first metal layer 10, a second metal layer 20, and a dielectric 30. The first metal layer 10 is a first component formed as a thin film with the stacking direction (i.e., a predetermined direction) Ya as its thickness direction, in a manner that it is formed along the transverse direction Yb and the longitudinal direction Yc, respectively. The transverse direction Yb is a second direction orthogonal to the stacking direction Ya, and the longitudinal direction Yc is a direction orthogonal to both the transverse direction Yb and the stacking direction Ya.

[0067] The first metal layer 10 is made of a conductive metallic material such as copper or silver. A plurality of openings 11 are provided in the first metal layer 10. Each of the plurality of openings 11 is formed, for example, elliptical. The plurality of openings 11 are arranged in the longitudinal direction Yc and the transverse direction Yb. Thus, the first metal layer 10 constitutes an opening pattern having a plurality of openings 11 arranged in the longitudinal direction Yc and the transverse direction Yb. Figure 1 An example is shown where, for example, eight openings 11 are provided in the first metal layer 10.

[0068] like Figure 1 and Figure 2 As shown, the second metal layer 20 is a second component disposed on the opposite side of the first metal layer 10 in the lamination direction Ya. The second metal layer 20 is made of a conductive metal material such as copper or silver. The second metal layer 20 includes a base layer 21 and a plurality of triangular prisms 22. The base layer 21 is formed into a thin film with the lamination direction Ya as its thickness direction, formed along both the transverse direction Yb and the longitudinal direction Yc. The plurality of triangular prisms 22 are reflectors disposed between the base layer 21 and the first metal layer 10. Figure 1 As shown, multiple triangular prisms 22 are formed into triangular prisms, each having an axis Sa extending along the longitudinal direction Yc.

[0069] Multiple triangular prisms 22 are arranged at equal intervals along the transverse direction Yb. Each of the multiple triangular prisms 22 is formed to protrude from the base layer 21 towards one side in the stacking direction Ya. Each of the multiple triangular prisms 22 is arranged opposite to one of the multiple openings 11. For example... Figure 2 and Figure 3As shown, the plurality of triangular prisms 22 each have inclined surfaces 22a and 22b. Among the plurality of triangular prisms 22, the inclined surface 22a is a first inclined surface disposed on the opposite side of the transverse Yb relative to the inclined surface 22b. Thus, the second metal layer 20 forms a pattern structure having a plurality of inclined surfaces 22a and 22b.

[0070] like Figure 3 As shown, the inclined surface 22a is arranged such that its normal direction hs1 intersects the stacking direction Ya. The inclined surface 22a is formed such that the closer it is to the side facing the transverse Yb, the further it advances towards the side facing the stacking direction Ya. Conversely, the inclined surface 22b is arranged such that its normal direction hs2 intersects the stacking direction Ya. The inclined surface 22b is a second inclined surface formed such that the closer it is to the side facing the transverse Yb, the further it advances towards the side facing the stacking direction Ya.

[0071] The inclined surface 22b is formed such that the closer it is to the other side of the transverse direction Yb, the further it is to the side of the stacking direction Ya. Thus, multiple triangular prisms 22 are arranged in the transverse direction Yb, and multiple inclined surfaces 22a and multiple inclined surfaces 22b are arranged alternately in the transverse direction Yb. For example... Figure 3 As shown, a triangular side surface 23 is provided on one side of the longitudinal direction Yc of each of the plurality of triangular prisms 22. The base edge 23a of the side surface 23 is formed along the transverse direction Yb. The side edges 23b and 23c of the side surface 23 are respectively arranged on one side of the stacking direction Ya relative to the base edge 23a. In this embodiment, the angle θa formed between the base edge 23a and the side edge 23b and the angle θb formed between the base edge 23a and the side edge 23c are set to the same angle.

[0072] Side 23b forms one side of the longitudinal direction Yc in the inclined surface 22a. Side 23c forms one side of the longitudinal direction Yc in the inclined surface 22b. Furthermore, in Figure 1 , Figure 2 In the base layer 21, a bottom surface 21a is provided between two adjacent triangular prisms 22. The multiple bottom surfaces 21a are formed along the transverse Yb and longitudinal Yc, respectively. Thus, the second metal layer 20 is provided with multiple inclined surfaces 22a, multiple inclined surfaces 22b, and multiple bottom surfaces 21a.

[0073] Furthermore, for ease of explanation, the plurality of inclined surfaces 22a and 22b will be collectively referred to as the plurality of inclined surfaces 22a and 22b. In this embodiment, a pair of inclined surfaces 22a and 22b are arranged between adjacent triangular prisms 22, separated by a dielectric 30. Thus, a plurality of pairs of inclined surfaces 22a and 22b are provided between the plurality of triangular prisms 22, separated by a dielectric 30. As will be described later, the plurality of pairs of inclined surfaces 22a and 22b in this embodiment retroreflect electromagnetic waves passing through the dielectric 30.

[0074] A dielectric 30 is disposed between the first metal layer 10 and the second metal layer 20. Specifically, the dielectric 30 is disposed between the plurality of inclined surfaces 22a, 22b and the plurality of bottom surfaces 21a of the second metal layer 20 and the first metal layer 10. As described later, the dielectric 30 attenuates electromagnetic waves incident through the plurality of openings 11 by converting them into heat through dielectric loss. In this embodiment, PPS, or polyphenylene sulfide, is used as the dielectric 30, for example.

[0075] Next, refer to Figure 2 , Figure 4 , Figure 5 The operation of the electromagnetic wave absorber 1 in this embodiment will be explained. Figure 4 This is a schematic diagram illustrating the multiple reflections of electromagnetic waves between the first metal layer 10 and the second metal layer 20. Figure 5 This is a schematic diagram showing the positional relationship between the wavefronts of incident electromagnetic waves D0 and D1, and the wavefronts of reflected electromagnetic waves D3, D4, and D5. First, an incident electromagnetic wave D0 (i.e., a useless electromagnetic wave) of a frequency within a predetermined frequency range arrives at the first metal layer 10 from one side of the stacking direction Ya. This arriving incident electromagnetic wave D0 passes through multiple openings 11 in the first metal layer 10 and is incident as electromagnetic wave D1 into the dielectric 30. After traveling within the dielectric 30 as incident electromagnetic wave D1, the incident electromagnetic wave D0 is retroreflected by multiple pairs of inclined surfaces 22a and 22b of the second metal layer 20.

[0076] Here, adjacent inclined surfaces 22a and 22b are positioned opposite each other, separated by a dielectric 30. For example, one of the inclined surfaces 22a and 22b reflects the incident electromagnetic wave D1 into a reflected electromagnetic wave D2. The other inclined surface, other than one of the inclined surfaces 22a and 22b, reflects the reflected electromagnetic wave D2 into a reflected electromagnetic wave D3 (i.e., the first reflected electromagnetic wave). At this time, the reflected electromagnetic wave D3 travels in a direction parallel to and opposite to the direction of travel of the incident electromagnetic wave D1. That is, the reflected electromagnetic wave D3 travels along the direction of travel of the incident electromagnetic wave D1 and in a direction opposite to the direction of travel of the incident electromagnetic wave D1.

[0077] Thus, the incident electromagnetic wave D1 is retroreflected by a pair of inclined surfaces 22a and 22b. The reflected electromagnetic wave D3, traveling in a direction parallel to and opposite to the direction of travel of the incident electromagnetic wave D1, is then reflected by the first metal layer 10 after traveling within the dielectric 30. This reflected electromagnetic wave D3, as reflected electromagnetic wave D4 (i.e., the second reflected electromagnetic wave), travels within the dielectric 30 and is again retroreflected by multiple pairs of inclined surfaces 22a and 22b of the second metal layer 20. For example, one of the inclined surfaces 22a and 22b reflects the reflected electromagnetic wave D4 as reflected electromagnetic wave D5.

[0078] The other inclined surface, other than one of the inclined surfaces 22a and 22b, reflects the reflected electromagnetic wave D5 into a reflected electromagnetic wave D6. This incident reflected electromagnetic wave D6 (i.e., the third reflected electromagnetic wave) travels in a direction parallel to and opposite to the direction of travel of the reflected electromagnetic wave D4. That is, the reflected electromagnetic wave D6 travels along the direction of travel of the reflected electromagnetic wave D4 and in the opposite direction. After traveling within the dielectric 30, the traveling reflected electromagnetic wave D6 is reflected by the first metal layer 10. At this time, the wavefront of the reflected electromagnetic wave D4 and the wavefront of the reflected electromagnetic wave D6 are as follows: Figure 5 Intersect as shown.

[0079] The reflected electromagnetic wave D6 is reflected by the first metal layer 10 as reflected electromagnetic wave D7 (i.e., the fourth reflected electromagnetic wave). Thus, the incident electromagnetic wave D1, which has passed through the first metal layer 10 and the dielectric 30, undergoes multiple reflections between the first metal layer 10 and the plurality of inclined surfaces 22a, 22b. At this time, as described later, if the wavefront of the reflected electromagnetic wave D4 coincides with the wavefront of the incident electromagnetic wave D1, the electromagnetic wave becomes resonant. On the other hand, if the wavefront of the reflected electromagnetic wave D7 coincides with the wavefront of the incident electromagnetic wave D1, the electromagnetic wave also becomes resonant between the plurality of inclined surfaces 22a, 22b and the first metal layer 10. At this time, if the dielectric 30 generates electromagnetic wave resonance at a frequency within a predetermined frequency range, the dielectric 30 attenuates the useless electromagnetic wave by converting it into heat through dielectric loss.

[0080] Next, refer to Figure 6 , Figure 7 A specific example of electromagnetic wave resonance in electromagnetic wave absorber 1A in the comparative example of this embodiment will be described. Figure 7 This is a schematic diagram showing the general structure of the electromagnetic wave absorber 1A. In the comparative example, the electromagnetic wave absorber 1A has a flat surface formed in the second metal layer 20 of the electromagnetic wave absorber 1 in this embodiment, instead of multiple inclined surfaces 22a and 22b. The flat surface is a surface formed parallel to the transverse direction Yb and parallel to the longitudinal direction Yc. Figure 7The diagram of the first metal layer 10 of the electromagnetic wave absorber 1A omits the multiple openings 11.

[0081] Figure 7 This illustrates an example of multiple reflections of an electromagnetic wave incident on an electromagnetic wave absorber 1A between the first metal layer 10 and the second metal layer 20. Figure 7 This indicates the positional relationship between the wavefront of the incident electromagnetic wave Da1 and the wavefront of the reflected electromagnetic wave Da2 between the first metal layer 10 and the second metal layer 20. Firstly, in... Figure 7 In the electromagnetic wave absorber 1A, the incident electromagnetic wave Da0 arrives from one side of the stacking direction Ya toward the first metal layer 10, and the arriving incident electromagnetic wave Da0 enters the dielectric 30 through the multiple openings 11 of the first metal layer 10.

[0082] The incident electromagnetic wave Da0, acting as incident electromagnetic wave Da1, travels within dielectric 30 and is reflected by the second metal layer 20. The incident electromagnetic wave Da1, reflected by the second metal layer 20, becomes reflected electromagnetic wave Da2 and passes through dielectric 30 before being reflected by the first metal layer 10. The reflected electromagnetic wave Da2, reflected by the first metal layer 10, becomes reflected electromagnetic wave Da3 and passes through dielectric 30 towards the second metal layer 20. If the wavefront of the reflected electromagnetic wave Da3 coincides with the wavefront of the incident electromagnetic wave Da1, then the electromagnetic waves are in a state of resonance within dielectric 30.

[0083] Here, the dimension of the stacking direction Ya between the first metal layer 10 and the second metal layer 20 in the electromagnetic wave absorber 1A is defined as the thickness dimension a. The intersection point closest to the stacking direction Ya among multiple intersection points where the wavefront of the reflected electromagnetic wave Da2 coincides with the wavefront of the incident electromagnetic wave Da1 is designated as intersection point Ka. The intersection point on the other side of the stacking direction Ya among multiple intersection points where the wavefront of the reflected electromagnetic wave Da2 coincides with the wavefront of the incident electromagnetic wave Da1 is designated as intersection point Kb. Between intersection points Ka and Kb, there exists an intersection point Kc where the wavefront of the reflected electromagnetic wave Da2 coincides with the wavefront of the incident electromagnetic wave Da1.

[0084] Let distance X be the distance between one side of the stacking direction Ya in the comparative electromagnetic wave absorber 1A and the intersection point Ka, and let distance X be the distance between the other side of the stacking direction Ya in the electromagnetic wave absorber 1A and the intersection point Kb. Furthermore, let the angle of incidence of the incident electromagnetic wave Da0 relative to the dielectric 30 be the angle of incidence θ1. The angle of incidence θ1 is a narrow angle formed between the wavefront of the incident electromagnetic wave Da0 and the transverse Yb. Let the angle of refraction of the incident electromagnetic wave Da0 relative to the dielectric 30 be the angle of refraction θ2. The angle of refraction θ2 is a narrow angle formed between the wavefront of the incident electromagnetic wave Da1 and the transverse Yb. Here, if the relative permittivity of the dielectric 30 is set to εr, then the angle of refraction θ2 is approximately θ1 / √εr.

[0085] Let the wavelength of the incident electromagnetic wave Da0 in the atmosphere be λ0, and the wavelength of the incident electromagnetic wave Da1 in the transverse Yb of dielectric 30 be λg. Here, if the frequency is set as f0 and the speed of light in the atmosphere is set as c0, then the incident angle θ1, wavelength λg, wavelength λ0, frequency f0, and speed of light c0 have the following relationship as shown in Equation 1.

[0086] λg·sinθ=λ0=f0·c0…(Formula 1)

[0087] Within the dielectric 30 of the electromagnetic wave absorber 1A, when the wavefront of the incident electromagnetic wave Da1 coincides with the wavefront of the reflected electromagnetic wave Da3, an electromagnetic wave resonance state is achieved. In this case, the wavelength λg, thickness a, distance X, and refraction angle θ2 have the following numerical relationship: Equation 2.

[0088] (a-2·X) / λg=tan(θ2)…(Formula 2)

[0089] Next, based on equations 1 and 2, the frequency f0 shown in equation 3 can be obtained. That is, the frequency f0 can be obtained from the speed of light c0, the angle of refraction θ2, the angle of incidence θ1, the thickness a, and the distance X. Thus, the resonant frequency of the electromagnetic wave in the electromagnetic wave absorber 1A is determined to be the frequency f0.

[0090] f0=c0·tan(θ2) / {(a-2·X)·sinθ}…(Formula 3)

[0091] Here, if the incident angle θ1 of the incident electromagnetic wave Da0 relative to the electromagnetic wave absorber 1A changes, the refraction angle θ2 changes. Accompanying this, the distance X changes, and therefore (a-2·X) changes. Thus, if the incident angle θ1 changes, the frequency f0, which is the resonant frequency, changes. For example, if the incident angle θ1 increases, (a-2·X) decreases, and therefore the frequency f0, which is the resonant frequency, increases. However, in the comparative electromagnetic wave absorber 1A, the distance X is determined by the positional relationship between the incident electromagnetic wave Da1 and the reflected electromagnetic wave Da2.

[0092] Therefore, if the incident angle θ1 increases, then as Figure 8 , Figure 9 As shown, the reflected electromagnetic wave Da3 shifts significantly to the right relative to the incident electromagnetic wave Da1. Therefore, if the incident angle θ1 changes, the positional relationship between the wavefronts of the incident electromagnetic wave Da1 and the reflected electromagnetic wave Da3 changes significantly, thus (a-2·X) changes significantly. Consequently, the change in frequency f0 when the incident angle θ1 changes becomes larger. Figure 8 It is a diagram showing the positional relationship between the wavefront of the incident electromagnetic wave Da1 and the wavefront of the reflected electromagnetic wave Da2 before the incident angle θ1 changes. Figure 9It is a diagram showing the positional relationship between the wavefront of the incident electromagnetic wave Da1 and the wavefront of the reflected electromagnetic wave Da2 after the incident angle θ1 changes.

[0093] In the electromagnetic wave absorber 1 of this embodiment, when the incident angle θ1 changes, the change in the positional relationship between the incident electromagnetic wave D1 and the reflected electromagnetic wave D3 can be suppressed, as described below. First, in this embodiment, as... Figure 10 , Figure 11 , Figure 12 , Figure 13 As shown, a pair of inclined surfaces 22a and 22b retroreflect the incident electromagnetic wave D1, which has passed through multiple openings 11 of the first metal layer 10 and the dielectric 30, as a reflected electromagnetic wave D3. At this time, as... Figure 11 , Figure 13 As shown, the incident electromagnetic wave D1 is retroreflected by the effective reflecting surface 25. The effective reflecting surface 25 is an imaginary reflecting surface formed by a pair of adjacent inclined surfaces 22a and 22b. The effective reflecting surface 25 is provided for ease of explanation. Here, the angle formed between the wavefront of the incident electromagnetic wave D1 and the transverse direction Yb is defined as the refraction angle θ2.

[0094] like Figure 14 As shown, when the incident electromagnetic wave D1 travels along the stacking direction Ya within the dielectric 30 and the refraction angle θ2 is 0°, if the wavefront K1 of the incident electromagnetic wave D1 coincides with the wavefront K4 of the reflected electromagnetic wave D4, then it becomes a state of electromagnetic wave resonance. Figure 14 The text illustrates a specific example of four electromagnetic waves, G1 to G4, acting in parallel. For instance... Figure 15 , Figure 16 As shown, when the refraction angle θ2 of the incident electromagnetic wave D1 is 5°, if the wavefront K1 of the incident electromagnetic wave D1 and the wavefront K4 of the reflected electromagnetic wave D4 are locally coincident, then the electromagnetic wave is in a state of resonance. Electromagnetic waves G1 to G4 represent the propagation path and direction of the electromagnetic waves. Figure 10 , Figure 12 The solid lines G1, G2, and G3 represent the states where electromagnetic waves are reflected in the order of inclined surfaces 22a and 22b. The dashed lines G1, G2, and G3 represent the states where electromagnetic waves are reflected in the order of inclined surfaces 22b and 22a. The solid lines G1, G2, and G3 and the dashed lines G1, G2, and G3 represent examples where electromagnetic waves propagate in opposite directions.

[0095] Figure 15 Examples are given of locations in the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 where wavefronts K1 and K4 are completely aligned, and where wavefronts K1 and K4 are staggered. Figure 16The diagram shows a wavefront K1 formed by connecting the wavefronts of four electromagnetic waves G1, and a wavefront K4 formed by connecting the wavefronts of four electromagnetic waves G4. There are two specific examples where wavefronts K1 and K4 coincide. In this case, the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 are retroreflected by the effective reflecting surface 25. On the other hand, if the refraction angle θ2 of the incident electromagnetic wave D1 is greater than 5°, then... Figure 17 As shown, the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 are retroreflected by the effective reflecting surface 25a, respectively.

[0096] The effective reflecting surface 25a is an imaginary reflecting surface formed by two adjacent pairs of inclined surfaces 22a and 22b. The effective reflecting surface 25a is provided for ease of explanation. (For example...) Figure 18 As shown, when the refraction angle θ2 of the incident electromagnetic wave D1 is 10°, the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 are both retroreflected by the effective reflecting surface 25a. If the wavefront K1 of the incident electromagnetic wave D1 and the wavefront K4 of the reflected electromagnetic wave D4 are locally coincident, then it is a state of electromagnetic wave resonance. Figure 18 The diagram shows a specific example where the wavefronts of two electromagnetic waves G1 are connected to each other to form a wavefront K1, and the wavefronts of two electromagnetic waves G4 are connected to each other to form a wavefront K4. There are five specific examples where wavefront K1 and wavefront K4 coincide. Figure 18 Specific examples illustrating the parallel action of electromagnetic waves G1, G3, G4, and G6.

[0097] Thus, even if the incident angle θ1 of the incident electromagnetic wave D1 changes and the refraction angle θ2 changes, the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 are retroreflected by the effective reflecting surface 25 or the effective reflecting surface 25a, respectively. Therefore, when the refraction angle θ2 changes, the change in the positional relationship between the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 is suppressed. That is, when the refraction angle θ2 changes, the change in the positional relationship between the wavefront of the incident electromagnetic wave D1 and the wavefront of the reflected electromagnetic wave D4 is suppressed. Therefore, when the incident angle θ1 changes, the change in the resonant frequency caused by the coincidence of the wavefronts of the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 can be suppressed.

[0098] Furthermore, when the incident angle θ1 of the incident electromagnetic wave D1 changes and the refraction angle θ2 changes, the change in the positional relationship between the incident electromagnetic wave D1 and the reflected electromagnetic wave D7 is suppressed. That is, when the refraction angle θ2 changes, the change in the positional relationship between the wavefront of the incident electromagnetic wave D1 and the wavefront of the reflected electromagnetic wave D7 is suppressed. Therefore, when the incident angle θ1 changes, the change in the resonant frequency caused by the coincidence of the wavefronts of the incident electromagnetic wave D1 and the reflected electromagnetic wave D7 can be suppressed. Thus, in this embodiment, in the electromagnetic wave absorber 1, the change in the resonant frequency when the incident angle θ1 of the incident electromagnetic wave arriving from one side of the stacking direction Ya changes can be suppressed. That is, when the incident angle θ1 changes, frequencies whose resonant frequency deviates from the predetermined frequency range can be suppressed. Next, referring to... Figure 19 , Figure 20 , Figure 21 , Figure 22 The electromagnetic wave attenuation of the electromagnetic wave absorber 1 in this embodiment will be explained.

[0099] Figure 19 This is a graph showing the electromagnetic wave reflection loss [dB] of the electromagnetic wave in electromagnetic wave absorber 1A when an electromagnetic wave of 76 GHz is incident on it. The vertical axis is set to the electromagnetic wave reflection loss [dB] of the electromagnetic wave in electromagnetic wave absorber 1A, and the horizontal axis is set to the electromagnetic wave frequency [GHz]. Figure 20 This is a graph showing the electromagnetic wave reflection loss [dB] of the electromagnetic wave absorber 1 of this embodiment when a 76GHz electromagnetic wave is incident on it, with the horizontal axis representing the electromagnetic wave reflection loss [GHz] of the electromagnetic wave absorber 1 of this embodiment. Figure 19 , Figure 20 In the diagram, curve NK1 represents the reflection loss of the electromagnetic wave when the incident angle θ1 is 0°. Curve NK2 represents the reflection loss of the electromagnetic wave when the incident angle θ1 is 20°. Curve NK3 represents the reflection loss of the electromagnetic wave when the incident angle θ1 is 40°. Curve NK4 represents the reflection loss of the electromagnetic wave when the incident angle θ1 is 60°.

[0100] In the comparative electromagnetic wave absorber 1A, the electromagnetic wave reflection loss is the loss expressed in dB, representing the ratio of the emitted electromagnetic wave to the incident electromagnetic wave in the electromagnetic wave absorber 1A. A larger absolute value of the electromagnetic wave reflection loss means a greater attenuation of the electromagnetic wave caused by the electromagnetic wave absorber 1A. The incident electromagnetic wave is the electromagnetic wave incident on the electromagnetic wave absorber 1A, and the emitted electromagnetic wave is the electromagnetic wave emitted from the electromagnetic wave absorber 1A. In the electromagnetic wave absorber 1 of this embodiment, the electromagnetic wave reflection loss is the loss expressed in dB, representing the ratio of the emitted electromagnetic wave to the incident electromagnetic wave. The incident electromagnetic wave is the electromagnetic wave incident on the electromagnetic wave absorber 1, and the emitted electromagnetic wave is the electromagnetic wave emitted from the electromagnetic wave absorber 1. A larger absolute value of the electromagnetic wave reflection loss means a greater attenuation of the electromagnetic wave caused by the electromagnetic wave absorber 1.

[0101] exist Figure 19 , Figure 20 In the graphs NK1, NK2, NK3, and NK4, the frequency at which the absolute value of the electromagnetic wave reflection loss is maximum is called the resonant frequency. Figure 19 , Figure 20 In the above, the resonant frequency at an incident angle θ1 of 20° is higher than the resonant frequency at an incident angle θ1 of 0°. The resonant frequency at an incident angle θ1 of 40° is higher than the resonant frequency at an incident angle θ1 of 20°. The resonant frequency at an incident angle θ1 of 60° is higher than the resonant frequency at an incident angle θ1 of 40°.

[0102] In the comparative electromagnetic wave absorber 1A, if the resonant frequency at an incident angle θ1 of 0° is set as the reference resonant frequency, then if the incident angle θ1 is greater than 0°, the resonant frequency changes significantly relative to the reference resonant frequency. On the other hand, in the electromagnetic wave absorber 1 of this embodiment, the resonant frequency also increases relative to the reference resonant frequency if the incident angle θ1 is greater than 0°. However, in this embodiment, when the incident angle θ1 is greater than 0°, the amount of change in the resonant frequency relative to the reference resonant frequency is suppressed compared to the comparative electromagnetic wave absorber 1A.

[0103] Therefore, in this embodiment, changes in the resonant frequency can be suppressed when the incident angle θ1 changes. Thus, frequencies deviating from the predetermined frequency range can be suppressed when the incident angle θ1 changes. Figure 21 It is a graph with the vertical axis set as the electromagnetic wave reflection loss [dB] of the electromagnetic wave absorber 1A as a scale and the horizontal axis set as the incident angle of the electromagnetic wave [°]. Figure 22 This is a graph with the vertical axis set to the electromagnetic wave reflection loss [dB] of the electromagnetic wave absorber 1 in this embodiment, and the horizontal axis set to the incident angle of the electromagnetic wave [°]. Figure 21 , Figure 22 In the diagram, curve FN1 represents the reflection loss of electromagnetic waves at a frequency of 75.5 GHz. Curve FN2 represents the reflection loss of electromagnetic waves at a frequency of 76.0 GHz.

[0104] Curve FN3 represents the reflection loss of electromagnetic waves at a frequency of 76.5 GHz. Curve FN4 represents the reflection loss of electromagnetic waves at a frequency of 77.0 GHz. Figure 21 As shown, in the comparative electromagnetic wave absorber 1A, curves FN1, FN2, FN3, and FN4 show that the electromagnetic wave reflection loss varies significantly with the incident angle θ1. On the other hand, as... Figure 22As shown in the figure, in this embodiment, according to the curves FN1, FN2, FN3, and FN4, the change in electromagnetic wave reflection loss caused by each incident angle θ1 is small.

[0105] Next, refer to Figure 23 , Figure 24 , Figure 25 , Figure 26 , Figure 27 , Figure 28 A specific example of the plurality of triangular prisms 22 in the second metal layer 20 of this embodiment will be described. Figure 23 The vertical axis represents the absorption frequency of electromagnetic wave absorber 1, and the horizontal axis represents the frequency of electromagnetic wave absorption. Figure 3 The graph shows the division value (Tk / λ) obtained by dividing the dimension Tk of the stacking direction Ya of the inclined faces 22a and 22b of the triangular prism 22 by λ. The absorption frequency is the frequency at which the electromagnetic wave can be attenuated by more than -10dB using the electromagnetic wave absorber 1 (e.g., the resonant frequency). The horizontal axis represents the height of the triangular prism 22 in units of λ when the wavelength of the electromagnetic wave traveling within the dielectric 30 is set to λ, and therefore can be expressed as "the height of the triangular prism 22 [λ]". The height [λ] of the triangular prism 22 represents the dimension Tk of the stacking direction Ya of the inclined faces 22a and 22b.

[0106] Figure 23 It means as Figure 24 and Figure 25 The graph shows the relationship between the absorption frequency of the electromagnetic wave absorber 1 without a bottom surface 21a and the division value Tk / λ. Figure 23 The curve Ta represents the relationship between the absorption frequency and the division value Tk / λ when the incident angle θ is 0°. The curve Tb represents the relationship between the absorption frequency and the height of the triangular prism 22 when the incident angle θ is 40°. Here, the absolute value of the difference between the absorption frequency of curve Ta and the absorption frequency of curve Tb is set as |ΔF|. According to curves Ta and Tb, when the division value Tk / λ, i.e., the height [λ] of the triangular prism 22, is above 0.15 and below 0.55, |ΔF| can be below 1 GHz.

[0107] Therefore, in the electromagnetic wave absorber 1, if the dimension Tk of the stacking direction Ya of the inclined surfaces 22a and 22b is 0.15·λ or more and 0.55·λ or less, the electromagnetic wave can be attenuated by more than -10dB when the change in absorption frequency is less than 1GHz. Figure 24 The triangular prism 22 represents the electromagnetic wave absorber 1 with the height [λ] of the triangular prism 22 being 0.15, and the angles θa and θb of the inclined surfaces 22a and 22b being 20°. Figure 25The triangular prism 22 represents the electromagnetic wave absorber 1 with the height [λ] of the triangular prism 22 being 0.55, and the angles θa and θb of the inclined surfaces 22a and 22b being 60°.

[0108] Figure 26 This is a graph where the vertical axis represents the frequency at which the electromagnetic wave absorber 1 can attenuate the electromagnetic wave by more than -10 dB (i.e., the absorption frequency), and the horizontal axis represents the height [λ] of the triangular prism 22. Here, when the wavelength of the electromagnetic wave traveling within the dielectric 30 is set to λ, Figure 26 The height [λ] of the triangular prism 22 in the middle is Figure 3 The division value is obtained by dividing the dimension Tk of the stacking direction Ya of the inclined surfaces 22a and 22b of the triangular prism 22 by λ. Figure 26 It means as Figure 27 and Figure 28 The graph shows the relationship between the absorption frequency of the electromagnetic wave absorber 1 with bottom surface 21a and the height [λ] of the triangular prism 22.

[0109] Figure 26 The curve Tc represents the relationship between the absorption frequency and the height [λ] of the triangular prism 22 when the incident angle θ is 0°. The curve Td represents the relationship between the absorption frequency and the height [λ] of the triangular prism 22 when the incident angle θ is 40°. Here, the absolute value of the difference between the absorption frequency of curve Tc and the absorption frequency of curve Td is set as |ΔF|. From curves Tc and Td, it can be seen that when the height [λ] of the triangular prism 22 is above 0.15 and below 0.5, |ΔF| can be below 2GHz.

[0110] Therefore, in the electromagnetic wave absorber 1, if the height Tk of the triangular prism 22 is 0.15λ or more and 0.5λ or less, the electromagnetic wave can be attenuated by more than -10dB when the change in absorption frequency is less than 2GHz. Figure 27 The triangular prism 22 represents the electromagnetic wave absorber 1 with the height [λ] of the triangular prism 22 being 0.15, and the angles θa and θb of the inclined surfaces 22a and 22b being 20°. Figure 28 The triangular prism 22 represents the electromagnetic wave absorber 1 with the height [λ] of the triangular prism 22 being 0.5, and the angles θa and θb of the inclined surfaces 22a and 22b being 60°.

[0111] However, in recent years, radar devices mounted on automobiles have been known as obstacle sensors. When radar is mounted on a vehicle, multiple reflections of electromagnetic waves between the radar substrate and the bumper, and between the radome and the bumper, interfere with the radar's original transmission and reception signals, degrading its performance (e.g., maximum sensing range and azimuth estimation accuracy). There is a need to address these multiple reflections of electromagnetic waves in a low-cost and compact manner. In particular, in recent years, due to advancements in manufacturing technology, the use of waveguides made of resin covered with metal to form antenna sections has increased, further emphasizing the need for countermeasures to absorb reflected electromagnetic waves (i.e., unwanted electromagnetic waves) from the radar substrate surface.

[0112] In contrast, as an electromagnetic wave absorber that absorbs reflected electromagnetic waves from the surface of a radar substrate, a method is considered where a virtual antenna is placed on the surface of the radar substrate, and resonance is generated through a resonant element on the substrate while thermal conversion is performed through a resistor. This method is useful in principle, but if it is to be implemented using an antenna made of resin with a metal-coated waveguide, there are problems such as longer waveguide traces and larger electromagnetic wave absorber volume.

[0113] Furthermore, as an electromagnetic wave absorber for absorbing reflected electromagnetic waves from the surface of a radar substrate, an electromagnetic wave absorber with a structure consisting of sequentially stacked full-surface conductor layers, dielectric layers composed of one or more layers of dielectric, and patterned layers having multiple patterns composed of conductors is considered. In this electromagnetic wave absorber, each pattern in the patterned layer differs from adjacent patterns in at least one of size and shape. While this allows for broadband and wide-angle absorption of incident electromagnetic waves, the high cost arises from the requirement of a multi-layered resin structure when applying the electromagnetic wave absorber to the construction of a resin waveguide covered by metal.

[0114] Furthermore, in electromagnetic wave absorbers, a sheet-shaped electromagnetic wave absorber has been proposed that, if the wave is tilted within a certain range, absorbs tilted electromagnetic waves (i.e., electromagnetic waves incident from a direction tilted relative to the direction perpendicular to the sheet surface) in the same way as perpendicularly incident waves. In such an electromagnetic wave absorber, there is a need to control the particle shape, filling rate, and sheet thickness of the soft magnetic metal powder.

[0115] In contrast, this embodiment avoids the problems associated with electromagnetic wave absorbers. An electromagnetic wave absorber 1 can be provided that is easily disposed around an antenna using a resin waveguide covered with metal, can be implemented at low cost, and attenuates electromagnetic waves of a predetermined frequency range even when the incident angle θ changes. According to this embodiment, the electromagnetic wave absorber 1 includes a first metal layer 10, a second metal layer 20, and a dielectric 30. The first metal layer 10 has a plurality of openings 11 that open in the stacking direction Ya, allowing incident electromagnetic waves D0 of a predetermined frequency range arriving from one side of the stacking direction Ya to pass through. The dielectric 30 is disposed on the other side of the stacking direction Ya relative to the first metal layer 10, allowing incident electromagnetic waves D1 that have passed through the plurality of openings 11 to pass through. The second metal layer 20 is disposed on the other side of the stacking direction Ya relative to the dielectric 30 and has a plurality of inclined surfaces 22a, 22b that back-reflect the incident electromagnetic waves D1 that have passed through the dielectric 30.

[0116] Here, the incident electromagnetic wave D1, passing through the dielectric 30, is reflected multiple times between the plurality of inclined surfaces 22a, 22b and the first metal layer 10, causing the electromagnetic wave to resonate at a frequency within a predetermined frequency range, thereby attenuating the electromagnetic wave due to the dielectric 30. Specifically, the plurality of inclined surfaces 22a, 22b reflect the incident electromagnetic wave D1, which has passed through the plurality of openings 11 of the first metal layer 10 and the dielectric 30, as a reflected electromagnetic wave D3. After passing through the dielectric 30, the reflected electromagnetic wave D3 is reflected by the first metal layer 10 as a reflected electromagnetic wave D4. The reflected electromagnetic wave D4 travels within the dielectric 30. At this time, the wavefront of the reflected electromagnetic wave D4 coincides with the wavefront of the incident electromagnetic wave D1, thereby causing the electromagnetic wave to resonate. Therefore, in the state of electromagnetic wave resonance, the dielectric 30 converts the electromagnetic wave into heat through dielectric loss, thereby attenuating the electromagnetic wave.

[0117] Therefore, in this embodiment, as described above, the incident electromagnetic wave D1 is retroreflected by multiple inclined surfaces 22a and 22b. Thus, when the incident angle θ changes, changes in the positional relationship between the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 can be suppressed. Consequently, when the incident angle θ changes, changes in the positional relationship between the wavefront of the incident electromagnetic wave D1 and the wavefront of the reflected electromagnetic wave D4 can be suppressed. Therefore, even when the incident angle θ changes, changes in the resonant frequency of the electromagnetic wave can be suppressed.

[0118] Therefore, even if the incident angle θ changes, by causing the electromagnetic wave to resonate at a frequency within a predetermined frequency range, it is possible to convert electromagnetic waves within the predetermined frequency range into heat. Thus, an electromagnetic wave absorber 1 can be provided that effectively attenuates electromagnetic waves within a predetermined frequency range even if the incident angle θ changes. In the electromagnetic wave absorber of this embodiment configured in this way, the following effects (a)(b)(c)(d)(e) can be obtained.

[0119] (a) The second metal layer 20 has an inclined surface 22a, which is formed such that the normal direction hs1 is inclined relative to the stacking direction Ya, and the further it advances towards the side of the transverse Yb, the further it advances towards the side of the stacking direction Ya. The second metal layer 20 has an inclined surface 22b, which is disposed on the side of the transverse Yb relative to the inclined surface 22a, and is formed such that the normal direction hs2 is inclined relative to the stacking direction Ya, and the further it advances towards the other side of the transverse Yb, the further it advances towards the side of the stacking direction Ya. When one of the inclined surfaces 22a and 22b reflects the incident electromagnetic wave D1, the other inclined surface, other than one of the inclined surfaces 22a and 22b, will reflect the incident electromagnetic wave D1 reflected by one inclined surface into a reflected electromagnetic wave D2. At this time, the other inclined surface will reflect the reflected electromagnetic wave D2 along the direction of travel of the incident electromagnetic wave D1 and in the opposite direction to the incident electromagnetic wave D1, thereby retroreflecting the incident electromagnetic wave D1.

[0120] When one of the inclined surfaces 22a and 22b reflects the electromagnetic wave D4, the other inclined surface will reflect the reflected electromagnetic wave D4 as a reflected electromagnetic wave D5. At this time, the other inclined surface will reflect the reflected electromagnetic wave D5 along the direction of travel of the reflected electromagnetic wave D4 and in the opposite direction to the reflected electromagnetic wave D4, thus retroreflecting the reflected electromagnetic wave D4. Therefore, with this simple configuration of inclined surfaces 22a and 22b, it is possible to appropriately retroreflect the incident electromagnetic wave D1 and the reflected electromagnetic wave D4.

[0121] (b) A plurality of inclined surfaces 22a and 22b are provided in the second metal layer 20, and the plurality of inclined surfaces 22a and 22b are arranged alternately in the transverse Yb. Therefore, the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 can be retroreflected appropriately.

[0122] (c) The plurality of triangular prisms 22 are arranged opposite to one of the plurality of openings 11. Thus, the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 can be retroreflected appropriately.

[0123] (d) In the electromagnetic wave absorber 1, when the wavelength of the electromagnetic wave traveling within the dielectric 30 of the electromagnetic wave absorber 1 is set to λ, the dimension Tk of the stacking direction Ya of the inclined surfaces 22a and 22b is set to a dimension of 0.15·λ or more and 0.55·λ or less.

[0124] Therefore, even if the incident angle θ1 of the electromagnetic wave changes from 0° to 40°, attenuation of more than -10dB can be achieved while keeping the change in absorption frequency below 1GHz. The absorption frequency is the frequency (e.g., resonant frequency) of the electromagnetic wave resonating in the electromagnetic wave absorber 1. Thus, even if the incident angle θ1 of the electromagnetic wave changes from 0° to 40°, the change in resonant frequency can be suppressed, and the resonant frequency can be made to converge within a predetermined frequency range. Therefore, sufficient attenuation of the electromagnetic wave can be ensured in the electromagnetic wave absorber 1.

[0125] (e) A plurality of triangular prisms 22 having inclined surfaces 22a and 22b are provided in the second metal layer 20 as a plurality of reflectors of this disclosure. In the second metal layer 20, the plurality of triangular prisms 22 are arranged in the transverse direction Yb, thereby the inclined surfaces 22a and 22b are arranged alternately in the transverse direction Yb. Therefore, in the second metal layer 20, a plurality of reflectors capable of retroreflecting the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 can be appropriately constructed.

[0126] (Second Implementation)

[0127] In the aforementioned first embodiment, in the electromagnetic wave absorber 1, a plurality of triangular prisms 22 are arranged such that they are respectively opposed to one of the plurality of openings 11. However, instead, in this second embodiment, in the electromagnetic wave absorber 1, as... Figure 29 As shown, the plurality of triangular prisms 22 are respectively arranged opposite to two adjacent openings 11 of the plurality of openings 11.

[0128] Specifically, a plurality of triangular prisms 22 are arranged such that their respective vertices 22c are opposite the middle portion 11a between the two adjacent openings 11. A plurality of triangular prisms 22 are arranged such that their respective inclined surfaces 22b are opposite one side of the two adjacent openings 11. A plurality of triangular prisms 22 are arranged such that their respective inclined surfaces 22a are opposite the other side of the two adjacent openings 11. Thus, each plurality of triangular prisms 22 is arranged opposite to two adjacent openings 11. That is, each plurality of triangular prisms 22 is arranged opposite to an integer number (e.g., two) of openings 11. In this embodiment, the number of openings 11 is an integer multiple (e.g., twice the number) of the number of triangular prisms 22.

[0129] (Third Implementation)

[0130] In the aforementioned first and second embodiments, examples were described where triangular prisms 22 having inclined surfaces 22a and 22b were used as the multiple reflectors of this disclosure. However, instead, in this third embodiment, as... Figure 30 , Figure 31 As shown, as multiple reflectors of this disclosure, a quadrangular prism 22A having inclined surfaces 22a and 22b and formed into a quadrangular prism shape can also be used respectively. Figure 30 This is a perspective view of the quadrangular prism 22A of the electromagnetic wave absorber 1 in this embodiment. Figure 31 This is a perspective view of one side of the longitudinal Yc of the quadrangular prism 22A of the electromagnetic wave absorber 1 in this embodiment.

[0131] The quadrangular prism 22A of this embodiment is formed into a quadrilateral by a cross-sectional view cut by an imaginary plane parallel to the stacking direction Ya and parallel to the transverse direction Yb. The quadrangular prism 22A is arranged opposite to one of the plurality of openings 11. An upper surface 22d, parallel to the transverse direction Yb and extending along the longitudinal direction Yc, is formed between the inclined surfaces 22a and 22b in the quadrangular prism 22A. The upper surface 22d is arranged opposite to the opening 11 in the first metal layer 110.

[0132] (Fourth Implementation)

[0133] In the electromagnetic wave absorber 1 of this fourth embodiment, reference is made to... Figure 32 , Figure 33 , Figure 34 An example will be described in which, in the electromagnetic wave absorber 1 of the first embodiment described above, triangular prisms 22X and 22Y arranged along the longitudinal direction Yc are used for each triangular prism 22 to reflect electromagnetic waves. Figure 32 This is a perspective view showing the triangular prisms 22, 22X, 22Y of the electromagnetic wave absorber 1 of this embodiment, and is an enlarged perspective view of a portion of the electromagnetic wave absorber 1 of this embodiment.

[0134] Figure 33 This is a front view of the triangular prisms 22, 22X, and 22Y with the first metal layer 10 in the electromagnetic wave absorber 1 of this embodiment removed. Figure 34 This is a perspective view of the electromagnetic wave absorber 1 according to this embodiment. Figure 32 , Figure 33 and Figure 34 As shown, in the second metal layer 20 of the electromagnetic wave absorber 1 in this embodiment, triangular prisms 22X and 22Y are provided for each triangular prism 22. Triangular prism 22X is a first reflector disposed on one side of the longitudinal direction Yc (i.e., the third direction) relative to each triangular prism 22.

[0135] Triangular prism 22X is a reflector formed in the shape of a triangular prism. Triangular prism 22X is formed such that its axis Sb extends along the transverse Yb. Triangular prism 22X is connected to one side of the longitudinal Yc of triangular prism 22. Triangular prism 22X is disposed on one side of the stacking direction Ya relative to the base layer 21. Triangular prism 22X has an inclined surface 22e and an upper surface 22f. Inclined surface 22e is disposed on one side of the longitudinal Yc relative to inclined surfaces 22a and 22b. The longitudinal Yc is a direction orthogonal to the stacking direction Ya and the transverse Yb, and is the direction connecting inclined surfaces 22a and 22b. Inclined surface 22e is a third inclined surface disposed such that its normal direction ks1 is inclined relative to the stacking direction Ya.

[0136] The inclined surface 22e is formed such that it advances towards the side of the longitudinal direction Yc and towards the side of the stacking direction Ya. The inclined surface 22e is formed in such a manner that it advances towards the other side of the longitudinal direction Yc and towards the other side of the stacking direction Ya. The upper surface 22f is disposed on one side of the longitudinal direction Yc relative to the inclined surface 22e. The upper surface 22f is formed to be parallel to the stacking direction Ya and parallel to the transverse direction Yb. The triangular prism 22Y is a second reflector disposed on the other side of the longitudinal direction Yc relative to each triangular prism 22. The triangular prism 22Y is connected to the other side of the longitudinal direction Yc (i.e., the third direction) of the triangular prism 22.

[0137] Triangular prism 22Y is disposed on one side of the stacking direction Ya relative to the base layer 21. Triangular prism 22Y has an inclined surface 22g and a lower surface 22h. Triangular prism 22Y is a reflector formed in the shape of a triangular prism. Triangular prism 22Y is formed such that its axis Sc extends along the transverse direction Yb. Inclined surface 22g is a fourth inclined surface disposed in such a way that its normal direction ks2 is inclined relative to the stacking direction Ya. Inclined surface 22g is disposed on the other side of the longitudinal direction Yc relative to inclined surfaces 22a and 22b. Inclined surface 22g is formed in such a way that the closer it is to the other side of the longitudinal direction Yc, the closer it is to the side of the stacking direction Ya.

[0138] The inclined surface 22g is formed such that as it advances towards the longitudinal direction Yc, it advances towards the opposite side of the stacking direction Ya. The lower surface 22h is positioned on the opposite side of the longitudinal direction Yc relative to the inclined surface 22g. The lower surface 22h is formed to be parallel to the stacking direction Ya and parallel to the transverse direction Yb. In this embodiment, the inclined surface 22e of the triangular prism 22X and the inclined surface 22g of the triangular prism 22Y are positioned opposite each other across the dielectric 30. The inclined surfaces 22e, 22g, and 22a, 22b, similarly reflect the incident electromagnetic wave D1 and the reflected electromagnetic wave D4 as described later.

[0139] Next, the operation of the electromagnetic wave absorber 1 in this embodiment will be explained. In this embodiment, if one of the inclined surfaces 22e and 22g reflects the incident electromagnetic wave D1, the other inclined surface (other than one of the inclined surfaces 22e and 22g) will reflect the incident electromagnetic wave D1 reflected by the other inclined surface as a reflected electromagnetic wave D2. The other inclined surface will reflect the reflected electromagnetic wave D2 as a reflected electromagnetic wave D3 in a direction parallel to the direction of travel of the incident electromagnetic wave D1 and opposite to the direction of travel of the incident electromagnetic wave D1. That is, the other inclined surface will reflect the reflected electromagnetic wave D2 as a reflected electromagnetic wave D3 in the opposite direction to the direction of travel of the incident electromagnetic wave D1. Thus, the inclined surfaces 22e and 22g perform retroreflection of the incident electromagnetic wave D1.

[0140] Furthermore, if one of the inclined surfaces 22e and 22g reflects the electromagnetic wave D4, then the other inclined surface (other than one of the inclined surfaces 22e and 22g) will reflect the reflected electromagnetic wave D4 as reflected electromagnetic wave D5. The other inclined surface will then reflect the reflected electromagnetic wave D5 as reflected electromagnetic wave D6 in a direction parallel to and opposite to the direction of travel of the reflected electromagnetic wave D4. That is, the other inclined surface will reflect the reflected electromagnetic wave D5 as reflected electromagnetic wave D6 along the direction of travel of the reflected electromagnetic wave D4 and in the opposite direction to the reflected electromagnetic wave D4. Thus, inclined surfaces 22e and 22g perform retroreflection of the reflected electromagnetic wave D4.

[0141] According to the embodiment described above, the second metal layer 20 has an inclined surface 22e disposed on one side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b. The inclined surface 22e is formed such that the normal direction ks1 is inclined relative to the stacking direction Ya, and it advances towards the stacking direction Ya as it moves towards the side of the longitudinal direction Yc. The second metal layer 20 has an inclined surface 22g disposed on the other side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b. The inclined surface 22g is formed such that the normal direction ks2 is inclined relative to the stacking direction Ya, and it advances towards the side of the stacking direction Ya as it moves towards the other side of the longitudinal direction Yc. Thus, the inclined surfaces 22e and 22g can appropriately retroreflect the incident electromagnetic wave D1 or the reflected electromagnetic wave D4.

[0142] In this embodiment with such a configuration, the second metal layer 20 includes a triangular prism 22X, which is disposed on one side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b, and is formed into a triangular prism shape by having an inclined surface 22e. The second metal layer 20 also includes a triangular prism 22Y, which is disposed on the other side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b, and is formed into a triangular prism shape by having an inclined surface 22g. In the second metal layer 20, triangular prisms 22X and 22Y are provided for each triangular prism 22. Therefore, by means of triangular prisms 22X and 22Y, the inclined surfaces 22e and 22g that retroreflect the incident electromagnetic wave D1 or the reflected electromagnetic wave D4 can be easily and appropriately arranged according to each triangular prism 22.

[0143] (Fifth Implementation)

[0144] In the aforementioned fourth embodiment, an example was described in which triangular prisms 22X and 22Y were used in the electromagnetic wave absorber 1 to retroreflect the incident electromagnetic wave D1 or the reflected electromagnetic wave D4. However, referring to... Figure 35 , Figure 36 , Figure 37 , Figure 38 This fifth embodiment describes an electromagnetic wave absorber 1 that uses quadrangular prisms 22S and 22T instead of triangular prisms 22X and 22Y for retroreflection of incident electromagnetic wave D1 or reflected electromagnetic wave D4.

[0145] Figure 35 This is a perspective view showing the structure of a portion of the electromagnetic wave absorber 1 according to this embodiment. Figure 36 This is a front view showing the structure of a portion of the electromagnetic wave absorber 1 according to this embodiment. Figure 37 This is a side view showing the structure of a portion of the electromagnetic wave absorber 1 according to this embodiment. Figure 38 This is a perspective view showing the structure of a portion of the electromagnetic wave absorber 1 according to this embodiment. Figure 35 , Figure 36 , Figure 37 , Figure 38 As shown, in the second metal layer 20 of the electromagnetic wave absorber 1 in this embodiment, quadrangular prisms 22S and 22T are provided for each quadrangular prism 22A. Quadrilateral prism 22S is a first reflector disposed on one side of the longitudinal (i.e., third direction) Yc relative to each quadrangular prism 22A.

[0146] The quadrangular prism 22S is connected to one side of the longitudinal direction Yc of the quadrangular prism 22A. The quadrangular prism 22S is disposed on one side of the stacking direction Ya relative to the base layer 21. The quadrangular prism 22S is a reflector formed in the shape of a quadrangular prism. The quadrangular prism 22S is formed such that its axis Sd extends along the transverse direction Yb. The quadrangular prism 22S has an inclined surface 22e. The inclined surface 22e is disposed in a manner in which its normal direction ks1 is inclined relative to the stacking direction Ya. The inclined surface 22e is formed such that the closer it is to the side of the longitudinal direction Yc, the closer it is to the side of the stacking direction Ya. The inclined surface 22e is formed in a manner in which the closer it is to the other side of the longitudinal direction Yc, the closer it is to the other side of the stacking direction Ya.

[0147] The quadrangular prism 22T is a second reflector disposed on the opposite side of the longitudinal (i.e., third direction) Yc of each quadrangular prism 22A. The quadrangular prism 22T is connected to the opposite side of the longitudinal Yc of the quadrangular prism 22A. The quadrangular prism 22T is disposed on one side of the stacking direction Ya relative to the base layer 21. The quadrangular prism 22T is a reflector formed in the shape of a quadrangular prism. The quadrangular prism 22T is formed such that its axis Se extends along the transverse Yb. The quadrangular prism 22T has an inclined surface 22g. The inclined surface 22g is disposed in a manner in which its normal direction ks2 is inclined relative to the stacking direction Ya. The inclined surface 22g is formed such that the closer it is to the opposite side of the longitudinal Yc, the closer it is to the opposite side of the stacking direction Ya.

[0148] In this embodiment, the inclined surfaces 22e and 22g of the quadrangular prism 22S and quadrangular prism 22T are positioned opposite each other across the quadrangular prism 22A, separated by a dielectric 30. The inclined surfaces 22e and 22g, like the inclined surfaces 22a and 22b, retroreflect the incident electromagnetic wave D1 and the reflected electromagnetic wave D4, as described later. Next, the operation of the electromagnetic wave absorber 1 of this embodiment will be explained. In this embodiment, if one of the inclined surfaces 22e and 22g reflects the incident electromagnetic wave D1, then the other inclined surface (other than one of the inclined surfaces 22e and 22g) will reflect the incident electromagnetic wave D1 reflected by one of the inclined surfaces into a reflected electromagnetic wave D2.

[0149] Another inclined surface reflects the reflected electromagnetic wave D2, which was reflected by one inclined surface, as reflected electromagnetic wave D3 in a direction parallel to and opposite to the direction of travel of the incident electromagnetic wave D1. That is, the other inclined surface reflects the reflected electromagnetic wave D2, which was reflected by one inclined surface, as reflected electromagnetic wave D3 in the opposite direction to the direction of travel of the incident electromagnetic wave D1. Thus, inclined surfaces 22e and 22g perform retroreflection of the incident electromagnetic wave D1.

[0150] Furthermore, if one of the inclined surfaces 22e and 22g reflects the electromagnetic wave D4, then the other inclined surface (other than one of the inclined surfaces 22e and 22g) will reflect the reflected electromagnetic wave D4 as reflected electromagnetic wave D5. The other inclined surface will then reflect the reflected electromagnetic wave D5 as reflected electromagnetic wave D6 in a direction parallel to and opposite to the direction of travel of reflected electromagnetic wave D4. That is, the other inclined surface will reflect the reflected electromagnetic wave D5 as reflected electromagnetic wave D6 in the opposite direction to the direction of travel of reflected electromagnetic wave D4. Thus, inclined surfaces 22e and 22g perform retroreflection of the reflected electromagnetic wave D4.

[0151] According to the embodiment described above, the second metal layer 20 has an inclined surface 22e, which is disposed on one side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b. The normal direction of this inclined surface is inclined relative to the stacking direction, and it is formed such that the closer it is to the longitudinal direction Yc, the further it advances towards the stacking direction Ya. The second metal layer 20 also has an inclined surface 22g, which is disposed on the other side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b. The normal direction of this inclined surface is inclined relative to the stacking direction, and it is formed such that the closer it is to the longitudinal direction Yc, the further it advances towards the stacking direction Ya. Therefore, the inclined surfaces 22e and 22g can appropriately retroreflect the incident electromagnetic wave D1 or the reflected electromagnetic wave D4.

[0152] In this embodiment with such a configuration, the second metal layer 20 includes a quadrangular prism 22S, which is disposed on one side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b, and is formed into a quadrangular prism shape by having an inclined surface 22e. The second metal layer 20 also includes a quadrangular prism 22T, which is disposed on the other side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b, and is formed into a quadrangular prism shape by having an inclined surface 22g. In the second metal layer 20, the quadrangular prisms 22S and 22T are provided for each of the triangular prisms 22. Therefore, the inclined surfaces 22e and 22g that can appropriately retroreflect the incident electromagnetic wave D1 or the reflected electromagnetic wave D4 can be easily achieved by the quadrangular prisms 22S and 22T.

[0153] (Sixth Implementation Method)

[0154] In the aforementioned first embodiment, an example was described where the second reflective surface of the second metal layer 20 of the electromagnetic wave absorber 1 is formed by the inclined surfaces 22a and 22b of the triangular prism 22. However, referring to... Figure 39 , Figure 40 , Figure 41 , Figure 42The fifth embodiment will be described in which inclined surfaces 22i and 22j of a triangular prism 22 formed by curved surfaces replace the inclined surfaces 22a and 22b of the triangular prism 22 in the second metal layer 20 of the electromagnetic wave absorber 1.

[0155] Figure 39 This is a perspective view showing the inclined surfaces 22i and 22j of the triangular prism 22 of the electromagnetic wave absorber 1 in this embodiment. Figure 40 This is a front view showing the inclined surfaces 22i and 22j of the triangular prism 22 of the electromagnetic wave absorber 1 in this embodiment. Figure 41 This is a side view showing the inclined surfaces 22i and 22j of the triangular prism 22 of the electromagnetic wave absorber 1 in this embodiment. Figure 42 This is a perspective view showing the inclined surfaces 22i and 22j of the triangular prism 22 of the electromagnetic wave absorber 1 according to this embodiment. The triangular prism 22 of this embodiment is formed similarly to the triangular prism 22 of the first embodiment, with its axis Sa extending along the longitudinal direction Yc. The inclined surface 22i is formed as a curved surface concave towards the other side of the stacking direction Ya. The inclined surface 22i is positioned relative to the inclined surface 22j on one side of the transverse direction Yb.

[0156] Inclined surface 22i is a first inclined surface formed such that the further it moves towards the side of the horizontal direction Yb, the further it moves towards the side of the stacking direction Ya. Inclined surface 22i is formed such that the further it moves towards the side of the horizontal direction Yb, the further it moves towards the side of the stacking direction Ya. Inclined surface 22j is a first inclined surface formed as a curved surface recessed towards the side of the stacking direction Ya. Inclined surface 22j is disposed on the side of the horizontal direction Yb relative to inclined surface 22i. Inclined surface 22j is formed such that the further it moves towards the side of the horizontal direction Yb, the further it moves towards the side of the stacking direction Ya. Inclined surface 22i and 22j reflect incident electromagnetic wave D1 and reflected electromagnetic wave D4 in the same manner as inclined surfaces 22a and 22b of the first embodiment described above.

[0157] (Seventh Implementation)

[0158] In the aforementioned first embodiment, an example of retroreflection by two inclined surfaces 22a and 22b in the second metal layer 20 of the electromagnetic wave absorber 1 was described. However, referring to... Figure 43 , Figure 44 , Figure 45 , Figure 46 The seventh embodiment of the electromagnetic wave absorber 1, in which three inclined surfaces 24a, 24b, and 24c replace two inclined surfaces 22a and 22b for retroreflection in the second metal layer 20, will be described. Figure 43 This is a front view of the electromagnetic wave absorber 1 according to this embodiment. Figure 44 This is a side view of the electromagnetic wave absorber 1 of this embodiment. Figure 45 It is Figure 37 The image shows the first metal layer 10 and dielectric 30 removed from the electromagnetic wave absorber 1. It is a front view of the second metal layer 20. Figure 46 It is a three-dimensional diagram showing the positional relationship of the three inclined surfaces 24a, 24b, and 24c.

[0159] The electromagnetic wave absorber 1 of this embodiment differs from the second metal layer 20 of the electromagnetic wave absorber 1 of the first embodiment described above. The second metal layer 20 of the electromagnetic wave absorber 1 of this embodiment will be described below. A reflective layer 24, replacing the plurality of triangular prisms 22, is provided in the second metal layer 20. The reflective layer 24 is disposed on one side of the stacking direction Ya relative to the base layer 21. The reflective layer 24 is formed as a film extending in the transverse direction Yb and the longitudinal direction Yc, with the stacking direction Ya as the thickness direction. The reflective layer 24 is made of, for example, a conductive metal material such as copper or silver.

[0160] In this embodiment, a plurality of recesses 24U are provided on one side of the stacking direction Ya in the reflective layer 24. Each of the plurality of recesses 24U is formed such that it opens to one side of the stacking direction Ya and is recessed to the other side of the stacking direction Ya. Figure 46 The diagram shows the recess 24U opening obliquely upwards. Multiple recesses 24U are formed into triangular pyramidal shapes by inclined surfaces 24a, 24b, and 24c. Inclined surface 24a is a reflecting surface whose normal direction hsa is inclined relative to the stacking direction Ya. Inclined surface 24b is a reflecting surface whose normal direction hsb is inclined relative to the stacking direction Ya. Inclined surface 24c is a reflecting surface whose normal direction hsc is inclined relative to the stacking direction Ya. Inclined surfaces 24a, 24b, and 24c are three reflecting surfaces having a first reflecting surface, a second reflecting surface, and a third reflecting surface.

[0161] Next, the operation of the electromagnetic wave absorber 1 in this embodiment will be explained. First, for example, the first inclined surface among the inclined surfaces 24a, 24b, and 24c reflects the incident electromagnetic wave D1. Then, the second inclined surface among the inclined surfaces 24a, 24b, and 24c, other than the first inclined surface, reflects the incident electromagnetic wave D1 reflected by the first inclined surface as a reflected electromagnetic wave D2. In this case, the third inclined surface among the inclined surfaces 24a, 24b, and 24c, other than the first and second inclined surfaces, reflects the reflected electromagnetic wave D2 reflected by the second inclined surface as a reflected electromagnetic wave D3 in a direction parallel to and opposite to the incident electromagnetic wave D1. That is, the third inclined surface reflects the reflected electromagnetic wave D2 reflected by the second inclined surface as a reflected electromagnetic wave D3 along the incident electromagnetic wave D1 in the opposite direction to the incident electromagnetic wave D1. Thus, the incident electromagnetic wave D1 is retroreflected by the inclined surfaces 24a, 24b, and 24c.

[0162] Furthermore, for example, the first inclined surface among the inclined surfaces 24a, 24b, and 24c reflects the reflected electromagnetic wave D4. Therefore, the second inclined surface among the inclined surfaces 24a, 24b, and 24c, other than the first inclined surface, will reflect the reflected electromagnetic wave D4 from the first inclined surface as reflected electromagnetic wave D5. In this case, the third inclined surface among the inclined surfaces 24a, 24b, and 24c, other than the first and second inclined surfaces, will reflect the reflected electromagnetic wave D5 from the second inclined surface as reflected electromagnetic wave D6 in a direction parallel to and opposite to reflected electromagnetic wave D4. That is, the third inclined surface will reflect the reflected electromagnetic wave D5 from the second inclined surface as reflected electromagnetic wave D6 along the direction opposite to reflected electromagnetic wave D4. Thus, the reflected electromagnetic wave D4 is retroreflected by the inclined surfaces 24a, 24b, and 24c.

[0163] According to the embodiment described above, the second metal layer 20 has inclined surfaces 24a, 24b, and 24c in the reflective layer 24, forming a concave portion 24U in a triangular pyramid shape extending from one side to the other in the stacking direction Ya. The inclined surfaces 24a, 24b, and 24c are capable of appropriately retroreflecting the incident electromagnetic wave D1 and the reflected electromagnetic wave D4.

[0164] (Other implementation methods)

[0165] (1) In the first embodiment described above, an example of retroreflection in the electromagnetic wave absorber 1 using two inclined surfaces 22a and 22b was explained. Furthermore, in the seventh embodiment described above, an example of retroreflection in the electromagnetic wave absorber 1 using three inclined surfaces 24a, 24b, and 24c was explained. Alternatively, in the first to seventh embodiments described above, retroreflection in the electromagnetic wave absorber 1 may be performed using four or more inclined surfaces.

[0166] (2) In the aforementioned second embodiment, an example was described in which the plurality of openings 11 are respectively arranged opposite to two adjacent openings 11 of the plurality of triangular prisms 22. However, it is also possible to arrange the plurality of openings 11 opposite to three or more adjacent triangular prisms 22 instead. Here, the number of openings 11 is an integer multiple of the number of triangular prisms 22.

[0167] (3) In the second embodiment described above, an example of using a triangular prism 22 formed in the shape of a triangular prism was described as the reflector of this disclosure. However, it is not limited to this; as multiple reflectors of this disclosure, a tetragonal prism 22A described in the third embodiment described above can also be used. The tetragonal prism 22A is a reflector formed in the shape of a tetragonal prism, and multiple tetragonal prisms 22A are arranged along the transverse direction Yb. In this case, multiple openings 11 are respectively configured to face two or more adjacent tetragonal prisms 22A. Here, the number of openings 11 is an integer multiple of the number of tetragonal prisms 22A.

[0168] (4) In the aforementioned first to seventh embodiments, an example of using a first metal layer 10 having a plurality of openings 11 as the first component of this disclosure has been described. However, alternatively, a semi-reflective component disposed on one side of the stacking direction Ya relative to the dielectric 30 may be used as the first component of this disclosure. In this case, if an electromagnetic wave is incident on the semi-reflective component from one side of the stacking direction Ya, a portion of the incident electromagnetic wave will pass through the semi-reflective component.

[0169] The transmitted electromagnetic wave passes through dielectric 30 and is retroreflected by multiple inclined surfaces 22a and 22b. This retroreflected electromagnetic wave then passes through dielectric 30 and is incident on the semi-reflective component. A portion of this incident electromagnetic wave is reflected by the semi-reflective component and exits from the semi-reflective component to the other side of the stacking direction Ya. Thus, the electromagnetic wave undergoes multiple reflections between the semi-reflective component and the multiple inclined surfaces 22a and 22b.

[0170] (5) In the aforementioned first to seventh embodiments, an example of using a first metal layer 10 having multiple openings 11 as the first component of this disclosure has been described. However, alternatively, multiple metal patches arranged on one side of the stacking direction Ya relative to the dielectric 30 may be used as the first component of this disclosure. The multiple metal patches may be formed into a plate shape, for example, from a conductive metal material. The multiple metal patches function as antennas that absorb electromagnetic waves arriving from one side of the stacking direction Ya and re-radiate the electromagnetic waves to the other side of the stacking direction Ya.

[0171] Thus, the multiple metal patches allow a portion of the electromagnetic waves arriving from one side of the stacking direction Ya to pass through the multiple electrodes. On the other hand, when electromagnetic waves that have passed through the dielectric 30 are incident, the multiple metal patches absorb the incident electromagnetic waves and radiate them back to the other side of the stacking direction Ya. Thus, the multiple metal patches reflect a portion of the electromagnetic waves arriving from the other side of the stacking direction Ya. As a first component of this disclosure, multiple conductive rings may also be used instead of multiple metal patches. Circular rings and square rings may also be used as multiple conductive rings.

[0172] (6) In the aforementioned sixth embodiment, an example was described where inclined surfaces 22i and 22j were respectively set as curved surfaces. However, in addition, they can also be set as follows: In the aforementioned second embodiment, inclined surfaces 22a and 22b are respectively set as curved surfaces. Similarly, in the aforementioned third embodiment, inclined surfaces 22a and 22b of the quadrangular prism 22A are respectively set as curved surfaces. In the aforementioned fourth embodiment, inclined surfaces 22e of the triangular prism 22X and 22g of the triangular prism 22Y are respectively set as curved surfaces. In the aforementioned fifth embodiment, inclined surfaces 22e of the quadrangular prism 22S and 22g of the quadrangular prism 22T are respectively set as curved surfaces.

[0173] (7) In the aforementioned fourth embodiment, an example of using a triangular prism 22X as a first reflector disposed on one side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b was described. An example of using a triangular prism 22Y as a second reflector disposed on the other side of the longitudinal direction Yc relative to the inclined surfaces 22a and 22b was also described. However, instead of using a first reflector or a second reflector, a quadrangular prism formed in the shape of a quadrangular prism may also be used as at least one of the first reflector and the second reflector.

[0174] (8) In the aforementioned fifth embodiment, an example of using a quadrangular prism 22S as a first reflector disposed on one side of the longitudinal direction Yc relative to the inclined surfaces 22a, 22b was described. An example of using a quadrangular prism 22T as a second reflector disposed on the other side of the longitudinal direction Yc relative to the inclined surfaces 22a, 22b was described. However, instead, a triangular prism formed in the shape of a triangular prism may also be used as at least one of the first and second reflectors.

[0175] (9) Furthermore, this disclosure is not limited to the foregoing embodiments and can be appropriately modified within the scope described in the claims. Additionally, the foregoing embodiments are not mutually exclusive and can be appropriately combined except in cases where they are clearly incompatible. Furthermore, in the foregoing embodiments, the elements constituting the embodiments are not necessarily essential, except where they are specifically stated to be necessary or are generally considered necessary. Furthermore, in the foregoing embodiments, when referring to the number, value, quantity, range, etc., of the constituent elements of the embodiments, the number is not limited to that specific number, except where it is specifically stated to be necessary or is generally limited to that specific number. Furthermore, in the foregoing embodiments, when referring to the shape, positional relationship, etc., of the constituent elements, the shape, positional relationship, etc., is not limited to that shape, positional relationship, etc., except where it is specifically stated or is generally limited to that specific shape, positional relationship.

Claims

1. An electromagnetic wave absorber, characterized in that, have: The first component allows electromagnetic waves incident from one side in a predetermined direction to pass through; A dielectric material, which is disposed on the opposite side of the predetermined direction relative to the first component; as well as The second component, disposed on the opposite side of the predetermined direction relative to the dielectric, has multiple inclined surfaces whose normal direction is inclined relative to the predetermined direction to retroreflect the electromagnetic waves that have passed through the dielectric. When the electromagnetic wave that has passed through the first component resonates due to multiple reflections between the plurality of inclined surfaces and the first component, the dielectric attenuates the electromagnetic wave.

2. The electromagnetic wave absorber according to claim 1, characterized in that, The electromagnetic wave that has passed through the first component and the dielectric, i.e., the incident electromagnetic wave, is retroreflected by the plurality of inclined surfaces. The incident electromagnetic wave, which is retroreflected, passes through the dielectric as a first reflected electromagnetic wave. The first reflected electromagnetic wave, which has passed through the dielectric, is reflected by the first component as a second reflected electromagnetic wave. If the wavefront of the second reflected electromagnetic wave reflected by the first component coincides with the wavefront of the incident electromagnetic wave that has passed through the dielectric, then the electromagnetic wave resonates.

3. The electromagnetic wave absorber according to claim 1, characterized in that, When the predetermined direction is set as the first direction, and the direction orthogonal to the first direction is set as the second direction, The plurality of inclined surfaces include: a first inclined surface, configured such that the closer one moves towards the second direction, the closer one moves towards the first direction; and a second inclined surface, disposed on the opposite side of the second direction relative to the first inclined surface, configured such that the closer one moves towards the opposite side of the second direction, the closer one moves towards the first direction. When one of the first and second inclined surfaces reflects electromagnetic waves that have passed through the dielectric, the other inclined surface of the first and second inclined surfaces will reflect the electromagnetic waves reflected by the first inclined surface in the opposite direction to the electromagnetic waves that have passed through the dielectric, thereby performing retroreflection on the electromagnetic waves that have passed through the dielectric.

4. The electromagnetic wave absorber according to claim 3, characterized in that, The plurality of inclined surfaces includes a plurality of first inclined surfaces and a plurality of second inclined surfaces. Multiple first inclined surfaces and multiple second inclined surfaces are arranged alternately in the second direction.

5. The electromagnetic wave absorber according to claim 4, characterized in that, The second component is provided with a plurality of reflectors, each reflector having a first inclined surface and a second inclined surface disposed on the opposite side of the second direction relative to the first inclined surface, and is formed in a prism shape. The plurality of reflectors are arranged in the second direction, thereby the plurality of first inclined surfaces and the plurality of second inclined surfaces are arranged alternately in the second direction.

6. The electromagnetic wave absorber according to claim 5, characterized in that, The first component is provided with multiple openings for electromagnetic waves incident from one side in a predetermined direction to pass through. The plurality of reflectors are respectively configured to face one of the plurality of openings.

7. The electromagnetic wave absorber according to claim 5, characterized in that, The first component is provided with multiple openings for electromagnetic waves incident from one side in a predetermined direction to pass through. The plurality of reflectors are respectively configured to face two or more of the plurality of openings. The number of openings is an integer multiple of the number of reflectors.

8. The electromagnetic wave absorber according to claim 5, characterized in that, The reflector has a first inclined surface and a second inclined surface and is formed into a triangular prism shape.

9. The electromagnetic wave absorber according to claim 5, characterized in that, The reflector has a first inclined surface and a second inclined surface and is formed into a quadrangular prism shape.

10. The electromagnetic wave absorber according to claim 3, characterized in that, When the direction orthogonal to the first direction and orthogonal to the second direction is designated as the third direction... The plurality of inclined surfaces have: A third inclined surface is disposed on one side of the third direction relative to the first and second inclined surfaces. The normal direction of the third inclined surface is inclined relative to the first direction, and the third inclined surface is formed such that the further it moves towards the third direction, the more it moves towards the first direction. as well as A fourth inclined surface is disposed on the opposite side of the third direction relative to the first and second inclined surfaces. The normal direction of the fourth inclined surface is inclined relative to the first direction, and the fourth inclined surface is formed such that the further it moves towards the opposite side of the third direction, the more it faces the first direction. When one of the third and fourth inclined surfaces reflects electromagnetic waves that have passed through the dielectric, the other inclined surface of the third and fourth inclined surfaces will reflect the electromagnetic waves reflected by the first inclined surface in the opposite direction to the direction of travel of the electromagnetic waves that have passed through the dielectric, thereby performing retroreflection on the electromagnetic waves that have passed through the dielectric.

11. The electromagnetic wave absorber according to claim 10, characterized in that, The second component includes: A first reflector, disposed on one side of the third inclined surface relative to the first and second inclined surfaces, is formed into a prism shape by having the third inclined surface; and The second reflector is disposed on the other side of the third direction relative to the first and second inclined surfaces, and is formed into a prism shape by having the fourth inclined surface.

12. The electromagnetic wave absorber according to claim 11, characterized in that, The reflector of at least one of the first reflector and the second reflector is formed in the shape of a triangular prism.

13. The electromagnetic wave absorber according to claim 11, characterized in that, The reflector of at least one of the first reflector and the second reflector is formed in the shape of a quadrangular prism.

14. The electromagnetic wave absorber according to claim 3, characterized in that, If the wavelength of the electromagnetic wave traveling within the dielectric is set to λ, then the dimensions of the first inclined surface and the second inclined surface in the first direction are set to be greater than 0.15·λ and less than 0.55·λ.

15. The electromagnetic wave absorber according to claim 1, characterized in that, The second component has three reflective surfaces that form a concave portion in the shape of a triangular pyramid extending from one side to the other in the predetermined direction. When the first reflecting surface of the three reflecting surfaces reflects the electromagnetic waves that have passed through the dielectric, and the second reflecting surface of the three reflecting surfaces (excluding the first reflecting surface) reflects the electromagnetic waves reflected by the first reflecting surface, the third reflecting surface of the three reflecting surfaces (excluding the first and second reflecting surfaces) reflects the electromagnetic waves reflected by the second reflecting surface in the opposite direction to the electromagnetic waves that have passed through the dielectric, thereby performing retroreflection on the electromagnetic waves that have passed through the dielectric.

16. The electromagnetic wave absorber according to any one of claims 1 to 15, characterized in that, The plurality of inclined surfaces are curved surfaces.

Images