Electromagnetic wave shield

Abstract

An electromagnetic wave shield 1a is provided with a plate-shaped base portion 5, a plurality of first protrusion portions 31, and a plurality of second protrusion portions 32. The base portion 5 has a first surface 10 and a second surface 20. The second surface 20 extends along the first surface 10 at a position separated from the first surface 10. The plurality of first protrusion portions 31 protrude from the first surface 10. The plurality of second protrusion portions 32 protrude from the second surface 20. The electromagnetic wave shield 1a includes a dielectric. The plurality of first protrusion portions 31 are arranged spaced apart from each other such that centers C11 of the plurality of first protrusion portions 31 are positioned at vertices of a plurality of polygons arranged according to a predetermined rule in a plan view. The plurality of second protrusion portions 32 are arranged spaced apart from each other such that centers C21 of the plurality of second protrusion portions 32 are positioned at vertices of a plurality of polygons arranged according to a predetermined rule in a plan view.

Description

Electromagnetic shielding

[0001] This invention relates to electromagnetic shielding.

[0002] Systems that use radio waves for sensing have been known conventionally. For example, in the field of automotive technology, collision prevention systems equipped with radar that uses radio waves of a predetermined wavelength are being considered. In such collision prevention systems, for example, obstacle detection, measurement of the speed of surrounding vehicles, and measurement of the distance to surrounding vehicles are performed, and the vehicle speed and the distance to the vehicle are adjusted accordingly. For collision prevention systems to function properly, it is important to avoid receiving unwanted radio waves that would cause noise.

[0003] Patent Document 1 describes the use of an electromagnetic wave absorber for the purpose of absorbing unwanted electromagnetic waves that cause malfunctions in an automobile driving support system. In the electromagnetic wave absorber described in Patent Document 1, a plurality of scattering bodies of a certain shape made of a second dielectric material are periodically arranged in a matrix made of a first dielectric material.

[0004] Patent Document 2 describes a vehicle obstacle detection device that detects obstacles by transmitting radio waves from a radar device installed between the back surface of the bumper and the vehicle outward through the bumper. This vehicle obstacle detection device includes a false detection prevention member to prevent false detection by the radar device. The false detection prevention member includes, for example, a diffuse reflection structure with irregularities of a predetermined shape (see Figure 13). It is understood that the diffuse reflection structure diffusely reflects the incident waves from the radar device, dispersing their energy and preventing false detection.

[0005] Patent Document 3 describes a lateral shield for a radar transceiver. A non-uniform delay structure is arranged throughout this lateral shield. The non-uniform delay structure delays the radar signal propagating through the lateral shield by an amount of variation determined by the wavelength of the radar signal and the position of the radar signal on the lateral shield. This directs and diffuses the radar signal after it has propagated through the lateral shield.

[0006] Patent Document 4 describes an electromagnetic wave shield. This electromagnetic wave shield comprises a plate-shaped base, a plurality of first protrusions, and a plurality of second protrusions. The plate-shaped base has a first surface for receiving electromagnetic waves and a second surface that extends along the first surface at a position away from the first surface. The plurality of first protrusions protrude from the first surface in the direction opposite to the second surface. The plurality of second protrusions protrude from the second surface in the direction opposite to the first surface. Because the electromagnetic wave shield has a plurality of first protrusions and a plurality of second protrusions, the molded product can be easily removed from the fixed mold when the movable mold is removed after molding.

[0007] Patent Document 5 describes a vehicle obstacle detection device. As a vehicle obstacle detection device, an example configuration is given in which a radar device is attached to the rear end panel in front of the rear bumper via a bracket, and radio waves from the radar device are transmitted outward through the resin bumper to detect other vehicles. A portion of the transmitted waves from this radar device are reflected off the back surface of the rear bumper, and pass between the transmitting unit of the radar device and the back surface of the bumper to reach the rear wheels of the vehicle. Subsequently, when the reflected waves returning from the rear wheels are input to the receiving unit of the radar device, there is a problem in that the rear wheels of the vehicle, which are not the target vehicle, are mistakenly detected as the target vehicle. In view of this problem, a shielding plate is provided to block the path of the tire-reaching wave α.

[0008] Patent document 6 proposes a radar blanket for a vehicle radar system that reduces the amount of undesirable echo signals reaching the radar module. The radar blanket comprises a central portion and side walls. The central portion is configured to receive the radar module. The side walls surround the central portion and contain a non-conductive material. The side walls are covered with a radar-absorbing material having a predetermined dielectric constant. The thickness of the radar-absorbing material is determined such that the reduction in signal intensity passing through the material in one direction is at least 10 dB. As a result, if a signal that has passed through the radar-absorbing material is reflected by the vehicle before passing through the radar-absorbing material again, the side walls can reduce the signal intensity by 20 dB. This avoids interference with the radar receiver in many cases.

[0009] Japanese Patent Publication No. 2004-153135, Japanese Patent No. 5696781, International Publication No. 2021 / 058450, International Publication No. 2023 / 003034, International Publication No. 2012 / 144150, U.S. Patent Application Publication No. 2016 / 0370456, Specification

[0010] From the perspective of preventing the reception of unwanted radio waves, it is conceivable to adjust the transmission and reflection of electromagnetic waves. As described in Patent Documents 5 and 6, electromagnetic waves can arrive from various directions, and it is not easy to adjust the transmission and reflection of electromagnetic waves arriving from various directions.

[0011] In view of these circumstances, the present invention provides an electromagnetic shield that is advantageous in terms of adjusting the transmission and reflection of electromagnetic waves arriving from various directions.

[0012] The present invention provides an electromagnetic wave shield comprising: a plate-shaped base having a first surface and a second surface extending along the first surface at a position away from the first surface; a plurality of first protrusions projecting from the first surface in the direction opposite to the second surface; and a plurality of second protrusions projecting from the second surface in the direction opposite to the first surface, wherein the electromagnetic wave shield contains a dielectric, the plurality of first protrusions are arranged apart from each other such that in a plan view, the centers of the plurality of first protrusions are located at the vertices or inside of a plurality of polygons arranged according to a predetermined rule, and the plurality of second protrusions are arranged apart from each other such that in a plan view, the centers of the plurality of second protrusions are located at the vertices or inside of a plurality of polygons arranged according to a predetermined rule.

[0013] The electromagnetic shielding described above is advantageous in terms of adjusting the transmission and reflection of electromagnetic waves arriving from various directions.

[0014] Figure 1 is a plan view showing an example of an electromagnetic shield according to the present invention. Figure 2 is a plan view of the second surface of the electromagnetic shield shown in Figure 1. Figure 3 is a cross-sectional view of the electromagnetic shield shown in Figure 1, with line III-III as the cutting line. Figure 4A is a schematic diagram showing the relationship between the electromagnetic shield shown in Figure 1 and electromagnetic waves. Figure 4B is a schematic diagram showing the relationship between the electromagnetic shield shown in Figure 1 and electromagnetic waves. Figure 4C is a schematic diagram showing the relationship between the electromagnetic shield and electromagnetic waves according to a comparative example. Figure 4D is a schematic diagram showing the relationship between the electromagnetic shield and electromagnetic waves according to a comparative example. Figure 5A is a plan view showing another example of an electromagnetic shield according to the present invention. Figure 5B is a plan view showing yet another example of an electromagnetic shield according to the present invention. Figure 5C is a plan view showing yet another example of an electromagnetic shield according to the present invention. Figure 5D is a plan view showing yet another example of an electromagnetic shield according to the present invention. Figure 5E is a plan view showing yet another example of an electromagnetic shield according to the present invention. Figure 5F is a plan view showing yet another example of an electromagnetic shield according to the present invention. Figure 6A is a side view showing yet another example of the electromagnetic shield according to the present invention. Figure 6B is a side view showing the electromagnetic shield shown in Figure 6A. Figure 7A is a side view showing yet another example of the electromagnetic shield according to the present invention. Figure 7B is a side view showing the electromagnetic shield shown in Figure 7A. Figure 8A is a plan view showing yet another example of the electromagnetic shield according to the present invention. Figure 8B is a perspective view of the electromagnetic shield shown in Figure 8A. Figure 8C is a cross-sectional view of the electromagnetic shield shown in Figure 8A with the III-III line as the cutting line. Figure 8D is a diagram showing the relationship between regions Z1 and Z2 in the cross-sectional view of the electromagnetic shield shown in Figure 8C. Figure 9 is a plan view of the first surface of the electromagnetic shield shown in Figure 8A. Figure 10 is a plan view of the second surface of the electromagnetic shield shown in Figure 8A. Figure 11 is a plan view showing an example of a radar cover according to the present invention. Figure 12 is a cross-sectional view of the radar cover shown in Figure 11 with the XII-XII line as the cutting line. Figure 13A is a diagram schematically showing an example of a calculation model for electromagnetic field simulation. Figure 13B schematically shows an example of a calculation model for electromagnetic field simulation. Figure 13C schematically shows an example of a calculation model for electromagnetic field simulation.Figure 13D schematically shows an example of a calculation model for electromagnetic field simulation. Figure 13E schematically shows an example of a calculation model for electromagnetic field simulation. Figure 14A schematically shows an example of a calculation model for electromagnetic field simulation. Figure 14B schematically shows an example of a calculation model for electromagnetic field simulation. Figure 14C schematically shows an example of a calculation model for electromagnetic field simulation. Figure 14D schematically shows an example of a calculation model for electromagnetic field simulation. Figure 14E schematically shows an example of a calculation model for electromagnetic field simulation.

[0015] Embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited to the following embodiments.

[0016] As shown in Figures 1, 2, and 3, the electromagnetic shield 1a comprises a plate-shaped base 5, a plurality of first protrusions 31, and a plurality of second protrusions 32. The plate-shaped base 5 has a first surface 10 and a second surface 20. The second surface 20 extends along the first surface 10 at a position away from the first surface 10. The first surface 10 and the second surface 20 constitute, for example, the two main surfaces of the plate-shaped base 5. Each of the first surface 10 and the second surface 20 is, for example, a plane. The plurality of first protrusions 31 project from the first surface 10 in the direction opposite to the second surface 20. The plurality of second protrusions 32 project from the second surface 20 in the direction opposite to the first surface 10. In other words, the second protrusions 32 project in the direction opposite to the projection direction of the first protrusions 31. The electromagnetic shield 1a contains a dielectric material. As shown in Figure 1, the multiple first protrusions 31 are arranged such that, in a plan view, the centers C11 of the multiple first protrusions 31 are located at the vertices or inside of multiple polygons arranged according to a predetermined rule. The multiple first protrusions 31 are scattered such that, for example, in a plan view, the centers C11 of the multiple first protrusions 31 are located on the grid points of a two-dimensional grid. In Figure 1, the unit cell U1 of the two-dimensional grid is shown by a dashed line. The two-dimensional grid is an arrangement of points on a plane that is invariant with translation by a fixed distance in two independent directions. The multiple first protrusions 31 are arranged, for example, at predetermined intervals. As shown in Figure 2, the multiple second protrusions 32 are spaced apart from each other such that, in a plan view, the centers of the multiple second protrusions 32 are located at the vertices or inside of multiple polygons arranged according to a predetermined rule. The multiple second protrusions 32 are scattered such that, for example, in a plan view, the centers C21 of the second protrusions 32 are located on the grid points of a two-dimensional grid. In Figure 2, the unit cell U2 of the two-dimensional grid is shown by a dashed line. The multiple second protrusions 32 are arranged, for example, at predetermined intervals. The center C11 of the first protrusion 31 and the center C21 of the second protrusion 32 in a plan view are the centroids of the planar figures as seen from their plan views. In this specification, an electromagnetic shield is an article capable of attenuating the energy of electromagnetic waves. The principle by which an electromagnetic shield attenuates the energy of electromagnetic waves is not limited to a specific principle.The principle may utilize, for example, phenomena such as reflection, transmission, absorption, diffraction, and interference associated with the interaction between electromagnetic waves and the electromagnetic shield, as well as phenomena such as scattering and diffusion of electromagnetic waves resulting from these phenomena. When a predetermined electromagnetic wave is incident on the first surface 10 or the second surface 20 of the electromagnetic shield 1a, the energy of the electromagnetic wave is attenuated. The electromagnetic shield 1a shields electromagnetic waves in a specific area around the electromagnetic shield 1a.

[0017] Figure 4A schematically shows the relationship between the electromagnetic shield 1a and the electromagnetic wave E1 when the electromagnetic wave E1 is incident on the first surface 10. As shown in Figure 4A, when the electromagnetic wave E1 is incident perpendicularly on the first surface 10, a transmitted wave Et1 is generated due to the interaction between the electromagnetic wave E1 and the electromagnetic shield 1a. The transmitted wave Et1 travels in a direction different from the straight-line direction of the electromagnetic wave E1 and does not easily reach the region Z2 surrounding the electromagnetic shield 1a. Also, reflected waves originating from the electromagnetic wave E1 do not easily reach the region Z1 surrounding the electromagnetic shield 1a. For this reason, the influence of transmitted and reflected waves originating from the electromagnetic wave E1 is less pronounced in regions Z1 and Z2.

[0018] Figure 4B schematically shows the relationship between the electromagnetic shield 1a and the electromagnetic wave E2 when the electromagnetic wave E2 is incident on the second surface 20. As shown in Figure 4B, when the electromagnetic wave E2 is incident perpendicularly on the second surface 20, a transmitted wave Et2 is generated due to the interaction between the electromagnetic wave E2 and the electromagnetic shield 1a. The transmitted wave Et2 travels in a direction different from the straight-line direction of the electromagnetic wave E2 and does not easily reach the region Z1 surrounding the electromagnetic shield 1a. Also, reflected waves originating from the electromagnetic wave E2 do not easily reach the region Z2 surrounding the electromagnetic shield 1a. For this reason, the influence of transmitted and reflected waves originating from the electromagnetic wave E1 is less pronounced in regions Z1 and Z2.

[0019] Thus, with the electromagnetic wave shield 1a, regardless of whether electromagnetic waves are incident on the first surface 10 or the second surface 20, the influence of electromagnetic waves is less likely to occur in a specific area around the electromagnetic wave shield 1a. Therefore, electromagnetic waves are shielded in that specific area. The interaction between electromagnetic waves E1 and E2 and the electromagnetic wave shield 1a is adjusted so that electromagnetic waves are shielded in that specific area due to the arrangement of the multiple first protrusions 31 and the multiple second protrusions 32 as described above. For example, consider a case where the centers C11 of the multiple first protrusions 31 and the centers C21 of the multiple second protrusions 32 are not located at the vertices or inside of multiple polygons arranged according to a predetermined rule. In this case, it may become difficult to achieve a state in which electromagnetic waves are shielded in a specific area around the electromagnetic wave shield 1a over a wide area of ​​the electromagnetic wave shield.

[0020] Figures 4C and 4D schematically show the relationship between the electromagnetic wave shield 1x and electromagnetic waves in a comparative example. The electromagnetic wave shield 1x is configured similarly to the electromagnetic wave shield 1a, except that it does not have a plurality of first protrusions 31.

[0021] Figure 4C schematically shows the relationship between the electromagnetic shield 1x and the electromagnetic wave E1 when the electromagnetic wave E1 is incident on the first surface 10 of the electromagnetic shield 1x. As shown in Figure 4C, when the electromagnetic wave E1 is incident perpendicularly on the first surface 10, the interaction between the electromagnetic wave E1 and the electromagnetic shield 1a generates a transmitted wave Et1 and a reflected wave Er1. The transmitted wave Et1 does not easily reach the region Z2 surrounding the electromagnetic shield 1x. The reflected wave Er1 easily reaches the region Z1 surrounding the electromagnetic shield 1x, and the influence of the reflected wave Er1 originating from the electromagnetic wave E1 is easily felt in region Z1.

[0022] Figure 4D schematically shows the relationship between the electromagnetic shield 1x and the electromagnetic wave E2 when the electromagnetic wave E2 is incident on the second surface 20 of the electromagnetic shield 1x. As shown in Figure 4D, when the electromagnetic wave E2 is incident perpendicularly on the second surface 20, the interaction between the electromagnetic wave E2 and the electromagnetic shield 1x generates a transmitted wave Et2 and a reflected wave Er2. The transmitted wave Et2 and the reflected wave Er2 have difficulty reaching the surrounding regions Z1 and Z2 of the electromagnetic shield 1a.

[0023] Thus, with the electromagnetic wave shield 1x, when electromagnetic waves are incident on the second surface 20, the electromagnetic wave's influence is less likely to extend to specific areas around the electromagnetic wave shield 1x. On the other hand, when electromagnetic waves are incident on the first surface 10, the electromagnetic wave's influence is more likely to extend to specific areas. For this reason, the electromagnetic wave shield 1x is likely to be affected by electromagnetic waves in specific areas when electromagnetic waves arrive from various directions.

[0024] The two-dimensional lattices described above are not limited to any particular type of lattice. Examples of the two-dimensional lattices described above include square lattices, rectangular lattices, face-centered square lattices, face-centered rectangular lattices, rhombic lattices, hexagonal lattices, and heptagonal lattices.

[0025] As shown in Figures 1 and 2, the first protrusion 31 and the second protrusion 32 are similar to each other in a plan view. With this configuration, regardless of whether electromagnetic waves are incident on the first surface 10 or the second surface 20, the influence of electromagnetic waves is less likely to occur in a specific area around the electromagnetic wave shield 1a.

[0026] The shapes of the first protrusion 31 and the second protrusion 32 in plan view are not limited to any particular shape. Their shapes may be polygons such as triangles, quadrilaterals, hexagons, octagons, and star polygons, or they may be circles or ellipses.

[0027] As shown in Figure 3, the center C21 of the second projection 32 in plan view is, for example, located on the same straight line as the central axis A1 of the first projection 31. With this configuration, regardless of whether electromagnetic waves are incident on the first surface 10 or the second surface 20, the influence of electromagnetic waves is less likely to occur in a specific area around the electromagnetic wave shield 1a. The central axis A1 of the first projection 31 is a straight line passing through the center C12 of the interface between the plane containing the first surface 10 and the first projection 31, and the center C11 of the first projection 31 in plan view. The center C12 of that interface is the centroid of that interface.

[0028] As shown in FIG. 3, the protruding length P1 on the central axis A1 of the first protruding portion 31 is, for example, shorter than the protruding length P2 on the central axis A2 of the second protruding portion 32. According to such a configuration, when a specific member is arranged near the first surface 10 of the electromagnetic shield 1a, the first protruding portion 31 is less likely to contact the specific member. Therefore, there are fewer restrictions on the location where the electromagnetic shield 1a can be installed. The central axis A2 of the second protruding portion 32 is a straight line passing through the center C22 of the boundary surface between the plane including the second surface 20 and the second protruding portion 32 and the center C21 of the second protruding portion 32 in plan view. The center C22 of the boundary surface is the centroid of the boundary surface. The protruding length P1 may be the same as the protruding length P2.

[0029] The ratio P1 / P2 of the protruding length P1 to the protruding length P2 is not limited to a specific value. The ratio P1 / P2 is, for example, 0.05 to 1.0. In this case, even when electromagnetic waves are incident on either the first surface 10 or the second surface 20, the influence of the electromagnetic waves is less likely to reach a specific region around the electromagnetic shield 1a. The ratio P1 / P2 is preferably 0.1 to 0.8, more preferably 0.15 to 0.6, and even more preferably 0.15 to 0.5.

[0030] The protruding length P1 is not limited to a specific length. The electromagnetic shield 1a shields, for example, electromagnetic waves with a wavelength λ. The protruding length P1 is, for example, 0.55λ or less. According to such a configuration, the first protruding portion 31 is less likely to contact a specific member arranged near the first surface 10 of the electromagnetic shield 1a, and there are even fewer restrictions on the location where the electromagnetic shield 1a can be installed.

[0031] The protruding length P1 is preferably 0.51λ or less, and more preferably 0.50λ or less. The protruding length P1 is, for example, 0.06λ or more. In this case, even when electromagnetic waves are incident on the first surface 10, the influence of the electromagnetic waves is less likely to reach a specific region around the electromagnetic shield 1a. The protruding length P1 is preferably 0.10λ or more, and more preferably 0.15λ or more.

[0032] The sum (P1 + P2) of the protruding length P1 and the protruding length P2 is not limited to a specific value. The sum (P1 + P2) may be, for example, 0.75λ or more, and may be 0.79λ or more, or 0.83λ or more. The sum (P1 + P2) may be, for example, 1.5λ or less, 1.4λ or less, or 1.3λ or less. According to such a configuration, even when electromagnetic waves are incident on either the first surface 10 or the second surface 20, the influence of the electromagnetic waves is less likely to reach a specific region around the electromagnetic shield 1a.

[0033] The width W1 of the first protruding portion 31 and the width W2 of the second protruding portion 32 are not limited to specific values. Each of the width W1 and the width W2 is, for example, 0.53λ or more and 1.50λ or less. According to such a configuration, even when electromagnetic waves are incident on either the first surface 10 or the second surface 20, the influence of the electromagnetic waves is less likely to reach a specific region around the electromagnetic shield 1a. The width W1 is the minimum dimension of the first protruding portion 31 in a direction perpendicular to the central axis A1 of the first protruding portion 31 at the boundary surface between the plane including the first surface 10 and the first protruding portion 31. The width W2 is the minimum dimension of the second protruding portion 32 in a direction perpendicular to the central axis A2 of the second protruding portion 32 at the boundary surface between the plane including the second surface 20 and the second protruding portion 32.

[0034] Each of the width W1 and the width W2 is preferably 0.55λ or more and 1.4λ or less, and more preferably 0.60λ or more and 1.3λ or less.

[0035] The ratio W2 / W1 of the width W2 to the width W1 is not limited to a specific value. The ratio W2 / W1 is, for example, 0.9 to 1.2. According to such a configuration, even when electromagnetic waves are incident on either the first surface 10 or the second surface 20, the influence of the electromagnetic waves is less likely to reach a specific region around the electromagnetic shield 1a.

[0036] The distance D1 between adjacent first protrusions 31 in a specific direction and the distance D2 between adjacent second protrusions 32 in that specific direction are not limited to specific values. For example, each of distances D1 and D2 is between 1.01λ and 1.96λ. With this configuration, regardless of whether electromagnetic waves are incident on the first surface 10 or the second surface 20, the influence of electromagnetic waves is less likely to occur in a specific area around the electromagnetic wave shield 1a. The specific direction for determining distances D1 and D2 is a direction parallel to one of the multiple lines connecting the grid points of the two-dimensional grid with respect to the center C11 of the first protrusion 31.

[0037] The distances D1 and D2 are preferably between 1.1λ and 1.9λ, more preferably between 1.2λ and 1.8λ, and even more preferably between 1.3λ and 1.7λ.

[0038] The ratio of distance D2 to distance D1, D2 / D1, is not limited to a specific value. For example, the ratio D2 / D1 is between 0.9 and 1.2. With this configuration, regardless of whether the electromagnetic wave is incident on the first surface 10 or the second surface 20, the influence of the electromagnetic wave is less likely to occur in a specific area around the electromagnetic wave shield 1a.

[0039] The thickness t of the base 5 is not limited to a specific value. For example, the thickness t is 0.5 mm to 3 mm. The thickness of the base 5 may be 0.7 mm or more, or 0.8 mm or more. The thickness of the base 5 may be 2.5 mm or less, or 2 mm or less.

[0040] As shown in Figure 3, for example, the first protrusion 31 has a taper 31t, and the second protrusion 32 has a taper 32t. With such a configuration, when the electromagnetic wave shield 1a is manufactured by molding, the molded electromagnetic wave shield 1a can be easily removed from the fixed mold when the movable mold is removed after molding. The first protrusion 31 and the second protrusion 32 are each formed in the shape of a truncated pyramid, for example. The first protrusion 31 and the second protrusion 32 may each be formed in the shape of a truncated cone. The first protrusion 31 and the second protrusion 32 may each be formed in the shape of a prismatic column or a cylindrical column.

[0041] As shown in Figure 3, the first projection 31 has, for example, a first end face 31e, which is the end face in the projection direction. The first end face 31e extends, for example, perpendicular to the central axis A1 of the first projection 31. The second projection 32 has, for example, a second end face 32e, which is the end face in the projection direction. The second end face 32e extends perpendicular to the central axis A2 of the second projection 32. The first end face 31e and the second end face 32e extend, for example, parallel to each other.

[0042] The gradients of taper 31t and taper 32t are not limited to any specific value. For example, the gradient of taper 32t is 45° or less. The gradient of taper 32t may be 40° or less, 35° or less, 30° or less, 25° or less, or 20° or less. The gradient of taper 32t may be 1° or more, 2° or more, or 3° or more. The gradient of taper 31t is the angle of inclination of taper 31t with respect to the central axis A1 of the first projection 31. The gradient of taper 32t is the angle of inclination of taper 32t with respect to the central axis A2 of the second projection 32.

[0043] The electromagnetic shield 1a can be used as an electromagnetic shield for applications such as millimeter-wave radar, millimeter-wave wireless communication, and millimeter-wave sensing. Equipment to which the electromagnetic shield 1a is applied can be used, for example, in automobiles and wireless base stations. When the electromagnetic shield 1a is for millimeter-wave radar, it can be used for millimeter-wave radar in one frequency band selected from the group consisting of the 24 GHz band, 60 GHz band, 76 GHz band, and 79 GHz band. The electromagnetic shield 1a does not only shield electromagnetic waves of a specific wavelength, but may also shield electromagnetic waves in a wide wavelength range, although it can be considered as a "shielding target" for electromagnetic waves of a specific wavelength λ. For example, the wavelength λ of the electromagnetic waves to be shielded by an electromagnetic shield installed with an in-vehicle millimeter-wave radar where the frequency of the substantially irradiated electromagnetic waves is 76 to 77 GHz (wavelength of the electromagnetic waves is 3.89 to 3.94 mm) can be determined to be a wavelength of 3.92 mm corresponding to a center frequency of 76.5 GHz. For a vehicle-mounted millimeter-wave radar using electromagnetic waves with frequencies of 77–81 GHz (wavelengths of 3.70–3.89 mm), the wavelength λ of the electromagnetic waves to be shielded by the electromagnetic shield can be determined to be 3.79 mm, corresponding to a center frequency of 79 GHz. For a vehicle-mounted electromagnetic shield using electromagnetic waves with frequencies of 24.05–24.25 GHz (wavelengths of 12.36–12.47 mm), the wavelength λ of the electromagnetic waves to be shielded by the electromagnetic shield can be determined to be 12.41 mm, corresponding to a center frequency of 24.15 GHz. For a millimeter-wave radar using electromagnetic waves with frequencies of 60.0–60.1 GHz (wavelengths of 4.99–5.00 mm), the wavelength λ of the electromagnetic waves to be shielded by the electromagnetic shield can be determined to be 4.99 mm, corresponding to a center frequency of 60.05 GHz. For electromagnetic shielding used in millimeter-wave radio, where the frequency of the electromagnetic waves used is 27-29.5 GHz (wavelength of the electromagnetic waves used is 10.16-11.10 mm), the wavelength λ of the electromagnetic waves to be shielded can be determined to be 10.61 mm, corresponding to a center frequency of 28.25 GHz. For electromagnetic shielding that is stated to support frequencies of 70-90 GHz (corresponding wavelength is 3.33-4.28 mm), the wavelength λ of the electromagnetic waves to be shielded can be determined to be 3.75 mm, corresponding to a center frequency of 80 GHz.

[0044] As described above, the electromagnetic shield 1a contains a dielectric. The relative permittivity of the dielectric is not limited to a specific value. At least one frequency f included in the range of 10 GHz to 300 GHz g The imaginary part ε'' of the dielectric relative permittivity in this case is, for example, 0.1 or less. When attenuating electromagnetic waves using dielectric loss, it seems desirable for the value of the imaginary part ε'' of the dielectric to be large. On the other hand, with the electromagnetic wave shield 1a, even if the imaginary part ε'' of the dielectric relative permittivity is small, as 0.1 or less, the electromagnetic wave shield 1a can exhibit the desired performance by adjusting the phenomena that occur due to the interaction between the electromagnetic wave shield 1a and electromagnetic waves. The imaginary part ε'' may be 0.07 or less, 0.05 or less, or 0.01 or less.

[0045] The real part ε' of the relative permittivity of the dielectric material included in the electromagnetic wave shield 1a is not limited to a specific value. For example, the real part ε' of the relative permittivity of the dielectric material at at least one frequency in the range of 10 GHz to 300 GHz is 2.0 to 4.0. Even in such cases, the electromagnetic wave shield 1a can exhibit the desired performance by adjusting the phenomena that occur due to the interaction between the electromagnetic wave shield 1a and electromagnetic waves. The real part ε' may be 3.8 or less, 3.6 or less, 3.4 or less, 3.2 or less, 3.0 or less, 2.8 or less, 2.6 or less, or 2.4 or less. Preferably, the real part ε' is 2.1 to 3.5, and more preferably 2.2 to 3.0.

[0046] The electromagnetic wave shield 1a does not have any conductive parts, for example. To shield electromagnetic waves, it is conceivable to reflect electromagnetic waves using conductive parts such as a metal film. On the other hand, the electromagnetic wave shield 1a can shield electromagnetic waves even without having conductive parts. The electromagnetic wave shield 1a may be made only of dielectric material, or it may include conductive parts.

[0047] The electromagnetic shield 1a is, for example, a resin molded product. In this case, the manufacturing cost of the electromagnetic shield 1a is easily reduced. The resin used in the resin molded product is not limited to a specific resin.

[0048] The resin is, for example, a thermoplastic resin. Examples of resins include polyethylene, polypropylene, polyvinyl alcohol, polyethylene terephthalate, polybutylene terephthalate, ethylene-vinyl acetate copolymer, polystyrene, acrylonitrile styrene, acrylonitrile-butadiene-styrene copolymer, ASA resin, AES resin, acrylic resins such as PMMA, MS resin, MBS resin, cycloolefin resin, polyacetal resin, polyamide resin, polyester resin, polycarbonate resin, polyurethane resin, liquid crystal polymer, EPDM, PPS, PEEK, PPE, polysulfone resin, polyimide resin, fluororesin, thermoplastic elastomers such as olefin-based thermoplastic elastomer (TPO), or acrylic elastomer. The resin may also be a thermosetting resin. Examples of thermosetting resins include epoxy resin, acrylic resin, or silicone resin. The resin molded product may contain only one type of resin or may contain multiple types of resins.

[0049] The electromagnetic shield 1a may contain, for example, a filler. The filler may be a coloring agent such as carbon black, an inorganic reinforcing material such as talc, fiberglass, and minerals, or a softening agent. The electromagnetic shield 1a may also contain additives such as flame retardants and plasticizers. The electromagnetic shield 1a does not need to contain a filler. In this case, the electromagnetic shield 1a is easier to recycle.

[0050] If the electromagnetic shield 1a is a resin molded product, the molding method for the electromagnetic shield 1a is not limited to a specific method. The electromagnetic shield 1a may be manufactured by injection molding, press molding, blow molding, or vacuum molding.

[0051] In the electromagnetic shield 1a, the interaction between the electromagnetic shield and the electromagnetic waves that occurs for the purpose of shielding the electromagnetic waves is not limited to a specific interaction. For example, the electromagnetic shield 1a transmits at least a portion of the electromagnetic waves incident toward the first surface 10 or the second surface 20, and emits scattered electromagnetic waves from the second surface 20 or the first surface 10. In other words, the electromagnetic shield 1a can function as a radio wave transmitting scatterer. This makes it possible to achieve electromagnetic wave shielding with a simple configuration.

[0052] The electromagnetic shield 1a has a scattering rate of, for example, 0.1% or more. The scattering rate is the ratio of the intensity of a specific transmitted scattered wave to the intensity of a straight-propagating transmitted wave emitted from the second surface 20 or the first surface 10 when electromagnetic waves E1 or E2 are incident perpendicularly on the first surface 10 or the second surface 20. The scattering rate is determined, for example, according to the following equation (1). In equation (1), the intensity of the transmitted scattered wave is the sum of the intensities of transmitted scattered waves having scattering angles of, for example, 15°, 30°, 45°, 60°, and 75°. The scattering angle is the angle between the emission direction of the straight-propagating transmitted wave and the emission direction of the transmitted scattered wave. Scattering rate = Intensity of transmitted scattered wave / Intensity of straight-propagating transmitted wave Equation (1)

[0053] The intensity of transmitted scattered waves and the intensity of straight-propagated transmitted waves can be determined, for example, by measuring the transmission attenuation in the straight-propagation direction and the transmission attenuation at a predetermined scattering angle when electromagnetic waves E1 or E2 are incident perpendicularly on the first surface 10 or the second surface 20, referring to the Japanese Industrial Standard JIS R 1679:2007. The transmission attenuation is expressed by the following equation (2). In equation (2), P i P is the received power, and P0 is the transmitted power. i / P0| corresponds to the intensity of the transmitted wave. "Log" indicates the common logarithm. Transmission attenuation = |10Log(P i / P0) | Formula (2)

[0054] The scattering rate of the electromagnetic wave shield 1a may be 1% or more, 5% or more, 10% or more, 20% or more, 50% or more, 100% or more, 150% or more, or 200% or more.

[0055] In the electromagnetic shield 1a, the structure including the plurality of first protrusions 31 and the plurality of second protrusions 32 is considered to function as, for example, a diffraction grating. Regarding the diffraction of light, the zero-order light transmittance I0 in a diffraction grating having a rectangular cross-section is expressed by the following equation (3) according to the scalar diffraction theory. In equation (3), ε r is the real part of the relative permittivity of the material forming the diffraction grating, and sqrt(ε r ) is the square root of ε r . h is the height of the convex portion in the diffraction grating. λ is the wavelength of light. I0 = cos 2 (π・|sqrt(ε r )| - 1・(h / λ)) Equation (3)

[0056] According to Bragg's law, the direction (scattering angle) of the scattered transmitted wave due to diffraction is determined by the period of the convex portions in the diffraction grating. Interference fringes are formed by the constructive and destructive interference of the diffracted waves transmitted between the convex portions. In this case, it is considered that the transmitted scattered wave is observed due to the constructive interference of the diffracted waves. The constructive interference of the diffracted waves can be expressed by equation (4), and the destructive interference of the diffracted waves can be expressed by equation (5). In equations (4) and (5), d is the period of the convex portions in the diffraction grating, θ is the angle at which constructive or destructive interference of the diffracted waves occurs, m is an integer of 0 or more, and λ is the wavelength of the incident wave. It is understood that when λ is constant, the scattering angle of the transmitted scattered wave can vary depending on the period of the convex portions in the diffraction grating. Table 1 shows an example of the relationship between the scattering angle θ at which constructive interference of the diffracted waves occurs and the period d. d sin θ = mλ Equation (4) d sin θ = (m + 1 / 2)λ Equation (5)

[0057]

[0058] As shown in FIG. 3, the electromagnetic shield 1a includes a plurality of first protrusions 31 and a plurality of second protrusions 32. In this case, for example, referring to the above equation (3), it is understood that electromagnetic waves can be transmitted and scattered in a desired state by adjusting the protrusion length P1 and the protrusion length P2.

[0059] The electromagnetic shield 1a can be modified from various viewpoints. In the electromagnetic shield 1a, the arrangement of the multiple first protrusions 31 in a plan view is not limited to a specific arrangement, as long as their centers C11 are located at the vertices or inside of multiple polygons arranged according to a predetermined rule. In addition, the arrangement of the multiple second protrusions 32 in a plan view is not limited to a specific arrangement, as long as their centers C21 are located at the vertices or inside of multiple polygons arranged according to a predetermined rule. For example, examples of the predetermined rule include, as described above, that the center C11 or center C21 is located at a grid point of a two-dimensional grid, that multiple congruent polygons are arranged periodically, and that a particular polygon is surrounded by another polygon.

[0060] For example, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged in plan view as shown in Figures 5A, 5B, 5C, 5D, 5E, and 5F. In these figures, for the sake of explanation, the outlines of the first protrusions 31 and the second protrusions 32 are omitted, and only their centers C11 or C21 are shown.

[0061] As shown in Figure 5A, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, their centers C11 or C21 are located at the vertices of quadrilateral S1. The multiple first protrusions 31 or the multiple second protrusions 32 are arranged so that quadrilaterals S1 facing opposite directions appear alternately. Quadrilateral S1 has a predetermined relationship with a virtual triangle Q1. The virtual triangle Q1 is, for example, an equilateral triangle. The virtual triangle Q1 may also be an isosceles triangle or a right triangle. Three vertices of quadrilateral S1 are located inside the virtual triangle Q1. Each of these three vertices may be an equal distance from the nearest vertex of the virtual triangle Q1. A planar arrangement of multiple virtual triangles Q1 can be conceived so that virtual triangles Q1 facing opposite directions appear alternately. The remaining vertex of quadrilateral S1 is located between adjacent virtual triangles Q1.

[0062] As shown in Figure 5B, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, their centers C11 or C21 are located at the vertices of the hexagon S2. The multiple first protrusions 31 or the multiple second protrusions 32 are arranged so that multiple parallel hexagons S2 appear at equal intervals. The hexagon S2 has a predetermined relationship with a virtual quadrilateral Q2. The virtual quadrilateral Q2 is, for example, a square. The virtual quadrilateral Q2 may also be a rectangle or a parallelogram. The five vertices of the hexagon S2 are located inside the virtual quadrilateral Q2. Each of four of these five vertices may be an equal distance from the nearest vertex of the virtual quadrilateral Q2. The other vertex of these five vertices is located at the center of the virtual quadrilateral Q2. A planar arrangement of multiple parallel virtual quadrilaterals Q2 at equal intervals can be conceived. The remaining vertex of hexagon S2 is located between two adjacent virtual quadrilaterals Q2.

[0063] As shown in Figure 5C, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, their centers C11 or C21 are located at the vertices of the heptagon S3 or inside the heptagon S3. The multiple first protrusions 31 or the multiple second protrusions 32 are arranged so that multiple parallel heptagons S3 appear at equal intervals. The heptagon S3 has a predetermined relationship with a virtual hexagon Q3. The virtual hexagon Q3 is, for example, a regular hexagon. The four vertices of the heptagon S3 are located inside the virtual hexagon Q3. Also, inside the heptagon S3, there is, for example, a center C11 or center C21 located at the center of the virtual hexagon Q3. In addition, inside the heptagon S3, there are two centers C11 or C21 located equidistant from adjacent vertices of the virtual hexagon Q3. Each of the six specific centers C11 or C21 located at the vertices of the heptagon S3 or inside the heptagon S3 may be an equal distance from the nearest vertex of the virtual hexagon Q3. The six specific centers C11 or C21 include four centers C11 or C21 corresponding to four vertices of the heptagon S3 located inside the virtual hexagon Q3. In addition, the six specific centers C11 or C21 include two centers C11 or C21 located equidistant from adjacent vertices of the virtual hexagon Q3 inside the heptagon S3. A plane arrangement of multiple parallel virtual hexagons Q3 at equal intervals can be conceived. The remaining three vertices of the heptagon S3 are located between adjacent virtual hexagons Q3.

[0064] As shown in Figure 5D, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, their centers C11 or C21 are located at the vertices of multiple polygons inscribed in multiple concentric circles or inside those polygons. For example, the centers C11 or C21 are located at the vertices of or inside the hexagon S41. In addition, the multiple first protrusions 31 or the multiple second protrusions 32 are arranged such that, in a plan view, their centers C11 or C21 are located at the vertices of the dodecagon S42 or the octagon S43. The hexagon S41, dodecagon S42, and octagon S43 are each regular polygons. The hexagon S41 and dodecagon S42 are located inside the octagon S43, and the hexagon S41 is located inside the dodecagon S42. The center C11 or center C21 located inside hexagon S41 is located at the center of hexagon S41. Hexagon S41 is inscribed in virtual circle Q41. Dodecagon S42 is inscribed in virtual circle Q42. Octagon S43 is inscribed in virtual circle Q43. Virtual circles Q41, Q42, and Q43 are concentric.

[0065] As shown in Figure 5E, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, the center C11 or center C21 is located at the vertices of multiple polygons inscribed in multiple overlapping circles or inside those polygons. For example, the center C11 or center C21 is located at the vertices or inside of multiple dodecagons S5. The multiple dodecagons S5 are inscribed in multiple virtual circles Q5 that are arranged to overlap each other at equal intervals. The dodecagons S5 are, for example, regular polygons. The center C11 or center C21 located inside the dodecagon S5 is located at the center of the dodecagon S5.

[0066] As shown in Figure 5F, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, the center C11 or center C21 is located at the vertices of multiple polygons inscribed in multiple overlapping circles or inside those polygons. In addition, the multiple first protrusions 31 or the multiple second protrusions 32 may be arranged such that, in a plan view, the center C11 or center C21 is located at the vertices of or inside polygons other than those inscribed in circles. For example, the center C11 or center C21 is located at the vertices or inside multiple dodecagons S61. The multiple dodecagons S61 are inscribed in multiple virtual circles Q6 that are arranged to overlap each other at equal intervals. The dodecagons S61 are, for example, regular polygons. The center C11 or center C21 is located at the vertices or inside hexagons S62. The hexagons S62 are regular polygons. Hexagon S62 is located inside dodecagon S61.

[0067] For example, the electromagnetic shield 1a may be modified to be the electromagnetic shield 1b shown in Figure 6A, the electromagnetic shield 1c shown in Figure 7A, or the electromagnetic shield 1d shown in Figures 8A to 8C. The electromagnetic shields 1b, 1c, and 1d are configured similarly to the electromagnetic shield 1a, except for parts that are not specifically described. Components of the electromagnetic shields 1b, 1c, and 1d that are identical or corresponding to the components of the electromagnetic shield 1a are given the same reference numerals, and detailed descriptions are omitted. The description of the electromagnetic shield 1a also applies to the electromagnetic shields 1b, 1c, and 1d, to the extent that it does not technically contradict the description.

[0068] As shown in Figure 6A, in the electromagnetic wave shield 1b, the first end face 31e of the first protrusion 31 in the protruding direction is inclined with respect to a first plane p1 perpendicular to the central axis of the first protrusion 31. With this configuration, reflected waves originating from electromagnetic waves incident on the first surface 10 are less likely to reach region Z1, and the influence of reflected electromagnetic waves in region Z1 is less pronounced.

[0069] In the electromagnetic shield 1b, the magnitude of the inclination angle θ1 of the first end face 31e with respect to the first plane p1 is not limited to a specific value. The lower limit of the magnitude of the inclination angle θ1 is determined, for example, so that the straight line K1 does not come into contact with region Z1, as shown in Figure 6B. The straight line K1 is parallel to the normal N1 of the first end face 31e at the center C11 and is a straight line that is a predetermined distance L1 from the normal N1 in a direction perpendicular to the central axis A1. Region Z1 is the area surrounding the electromagnetic shield 1b, and the center of region Z1 is located on the same straight line as the central axis A1. Region Z1 has a predetermined dimension M1 in a direction perpendicular to the central axis A1. The center of region Z1 is a predetermined distance from the center C11. The upper limit of the magnitude of the inclination angle θ1 is determined, for example, so that the first projection 31 has a predetermined width W1 and the first end face 31e does not intersect with the first surface 10.

[0070] In the electromagnetic shield 1b, the first end faces 31e of the multiple first protrusions 31 are, for example, inclined in the same direction. In other words, lines perpendicular to the first end faces 31e of the multiple first protrusions 31 are parallel to each other.

[0071] As shown in Figure 7A, in the electromagnetic wave shield 1c, the first end face 31e of the first protrusion 31 in the protruding direction is inclined with respect to a first plane p1 perpendicular to the central axis A1 of the first protrusion 31. With this configuration, reflected waves originating from electromagnetic waves incident on the first surface 10 are less likely to reach region Z1, and the influence of reflected waves originating from electromagnetic waves in region Z1 is further reduced. Also, the second end face 32e of the second protrusion 32 in the protruding direction is inclined with respect to a second plane p2 perpendicular to the central axis A2 of the second protrusion 32. With this configuration, reflected waves originating from electromagnetic waves incident on the second surface 20 are less likely to reach region Z2, and the influence of reflected electromagnetic waves in region Z2 is further reduced.

[0072] In the electromagnetic shield 1c, the magnitude of the inclination angle θ1 of the first end face 31e with respect to the first plane p1 is not limited to a specific value. The lower limit of the magnitude of the inclination angle θ1 is determined, for example, so that the straight line K1 does not come into contact with region Z1, as shown in Figure 7B. The upper limit of the magnitude of the inclination angle θ1 is determined, for example, so that the first projection 31 has a predetermined width W1 while the first end face 31e does not intersect with the first surface 10.

[0073] In the electromagnetic shield 1c, the magnitude of the inclination angle θ2 of the second end face 32e with respect to the second plane p2 is not limited to a specific value. The lower limit of the magnitude of the inclination angle θ2 is determined, for example, so that the straight line K2 does not come into contact with region Z2, as shown in Figure 7B. The straight line K2 is parallel to the normal N2 of the second end face 32e at the center C21 and is a straight line that is a predetermined distance L2 from the normal N2 in a direction perpendicular to the central axis A2. Region Z2 is the area surrounding the electromagnetic shield 1c, and the center of region Z2 is located on the same straight line as the central axis A2. Region Z2 has a predetermined dimension M2 in a direction perpendicular to the central axis A2. Region Z2 is a predetermined distance from the center C21. The upper limit of the magnitude of the inclination angle θ2 is determined, for example, so that the second projection 32 has a predetermined width W2 and the second end face 32e does not intersect with the second surface 20.

[0074] In the electromagnetic shield 1c, the magnitudes of the inclination angles θ1 and θ2 may be the same or different. The ratio θ2 / θ1 is, for example, 0.8 to 1.2.

[0075] In the electromagnetic shield 1c, the first end faces 31e of the multiple first protrusions 31 are, for example, inclined in the same direction. In other words, lines perpendicular to the first end faces 31e of the multiple first protrusions 31 are parallel to each other. The second end faces 32e of the multiple second protrusions 32 are, for example, inclined in the same direction. In other words, lines perpendicular to the second end faces 32e of the multiple second protrusions 32 are parallel to each other. For example, in the electromagnetic shield 1c, the direction of the component of the normal vector of the second end face 32e parallel to the second plane p2 is opposite to the direction of the component of the normal vector of the first end face 31e parallel to the first plane p1. The first end faces 31e and the second end faces 32e may be parallel to each other.

[0076] As shown in Figures 8A to 8D, in the electromagnetic wave shield 1d, the first end face 31e of the first projection 31 in the projection direction is inclined with respect to a first plane p1 perpendicular to the central axis A1 of the first projection 31. In addition, the first end faces 31e of an adjacent pair of first projections 31 face different directions. With this configuration, reflected waves originating from electromagnetic waves incident on the first surface 10 are less likely to reach region Z1, and the influence of reflected electromagnetic waves in region Z1 is less pronounced.

[0077] Figure 9 shows the inclination direction of the first end faces 31e of each of the multiple first protrusions 31 in the electromagnetic shield 1d with respect to the first plane p1. In Figure 9, the symbols a, b, c, d, e, f, g, and h attached to each of the multiple first protrusions 31 indicate the direction of the component of the normal vector of the first end face 31e of the first protrusion 31 that is parallel to the first plane p1. The directions indicated by these symbols are shown by arrows in the figure. For example, in the multiple first protrusions 31 arranged in the above specific direction, the orientation of the first end faces 31e fluctuates periodically. The orientation of the first end faces 31e may fluctuate randomly.

[0078] As shown in Figures 8A to 8D, in the electromagnetic wave shield 1d, the second end face 32e of the second protrusion 32 in the protruding direction is inclined with respect to a second plane p2 perpendicular to the central axis A2 of the second protrusion 32. In addition, the second end faces 32e of adjacent pairs of second protrusions 32 face in different directions. With this configuration, reflected waves originating from electromagnetic waves incident on the second surface 20 are less likely to reach region Z2, and the influence of reflected electromagnetic waves in region Z2 is less pronounced.

[0079] Figure 10 shows the inclination direction of the second end faces 32e of each of the multiple second protrusions 32 with respect to the second plane p2 in the electromagnetic shield 1d. In Figure 10, the symbols a, b, c, d, e, f, g, and h attached to each of the multiple second protrusions 32 indicate the direction of the component of the normal vector of the second end face 32e of the second protrusion 32 that is parallel to the second plane p2. The directions indicated by these symbols are shown by arrows in the figure. For example, in the multiple second protrusions 32 arranged in the above specific direction, the direction of the second end face 32e fluctuates periodically. In the multiple second protrusions 32, the direction of the second end face 32e may fluctuate randomly. In the electromagnetic shield 1d, the center C21 of the second protrusion 32 is located, for example, on the same line as the central axis A1 of the first protrusion 31. In the first projection 31 and the second projection 32, where the center C21 is located on the same straight line as the central axis A1, the first end face 31e and the second end face 32e may be parallel to each other.

[0080] As shown in Figures 11 and 12, for example, a radar cover 50 equipped with an electromagnetic wave shield 1a can be provided.

[0081] The radar cover 50 is formed, for example, in the shape of a hollow truncated pyramid and has a first opening 52 and a second opening 54. The first opening 52 and the second opening 54 are each rectangular. The second opening 54 is larger than the first opening 52. A part of the radar (not shown), such as the antenna of the radar, is placed in the first opening 52. The inner surface of the radar cover 50 is formed by the first surface 10 of the electromagnetic shield 1a, and a plurality of first protrusions 31 are formed on its inner surface. On the other hand, the outer surface of the radar cover 50 is formed by the second surface 20 of the electromagnetic shield 1a, and a plurality of second protrusions 32 are formed on its outer surface.

[0082] Unwanted radio waves incident on the inner or outer surface of the radar cover 50 are shielded by the electromagnetic shield 1a. This prevents the radar from receiving unwanted radio waves.

[0083] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited to the following examples. First, the evaluation methods for the examples and comparative examples will be described.

[0084] Electromagnetic field analysis simulations were used to calculate the electromagnetic field strength when electromagnetic waves were incident perpendicularly to the first and second surfaces of the samples for each embodiment and comparative example. The transmission attenuation in the straight-line propagation direction and the reflection attenuation in the opposite direction were then calculated. Details of the parameters characterizing the shape of each sample are shown in Tables 2 and 3. Each parameter in Tables 2 and 3 corresponds to the projection length P1, projection length P2, width W1, width W2, distance D1, distance D2, inclination angle θ1, and inclination angle θ2 shown in Figures 3, 6A, 7A, and 8C. In the samples for each embodiment, multiple projections were arranged on the first and second surfaces, which are both surfaces of the plate-shaped base, to form a square grid in plan view. On the other hand, in the sample for the comparative example, multiple projections were arranged only on the second surface of the plate-shaped base to form a square grid in plan view, and no projections were provided on the first surface. Each projection was a frustoconical pyramidal shape in plan view. The side surface of the protrusion was inclined at 3° with respect to the central axis of the protrusion.

[0085] Figures 13A, 13B, 13C, 13D, and 13E schematically show the calculation models used to calculate the transmission attenuation and return attenuation when a 76.5 GHz electromagnetic wave EW is incident on the first surface of each sample S. Figures 13A and 13B schematically show the calculation model used to calculate the transmission attenuation. In this calculation model, each sample S was placed at a predetermined position in a rectangular parallelepiped calculation region VT1. The real part ε' of the relative permittivity of each sample S was 2.75, and the imaginary part ε'' of its relative permittivity was 0.02. These values ​​were determined by referring to the measured values ​​of the complex relative permittivity at 76.5 GHz obtained by dielectric property measurements for a predetermined polycarbonate (PC).

[0086] The region RI1, indicated by the dashed line in Figure 13E, is the region irradiated by the electromagnetic wave EW, and is a circle with a diameter of 30 mm centered at CE1. CE1 corresponds to the center of the electromagnetic wave EW. The amplitude direction of the electric field of the electromagnetic wave EW was parallel to the y-axis direction, parallel to a pair of opposite sides in the square contour of the sample S in plan view, and perpendicular to another pair of opposite sides. As described above, in the sample S, multiple protrusions on the first and second faces are arranged to form a square grid in plan view, and the diagonals of this square grid extend in directions parallel to the x-axis and y-axis. As shown in Figures 13A and 13B, the receiving surface FT1 was defined in the calculation region VT1. The receiving surface FT1 was perpendicular to the first surface of sample S and was formed by a collection of 91 circles with a diameter of 30 mm, each centered at 91 points spaced 2° apart, 120 mm away from the intersection of a line passing through the center CE1 with the second surface of sample S. The 91 points lay in a plane parallel to the zy plane, and one of the 91 points lay on the line perpendicular to the first surface of sample S and passing through the center CE1. The angle between the line segment connecting the intersection of the line perpendicular to the first surface of sample S and passing through the center CE1 with the second surface of sample S and the points at both ends of the 91 points, and the line itself, was -90° or 90°.

[0087] The calculations using this computational model were performed using Ansys Electronics Desktop HFSS 2021R1 software. The calculations were performed using the finite element method (FEM). In the FEM, the number of meshes in the computational domain VT1 was 500,000, and the number of meshes in sample S was 70,000.

[0088] In the above calculation model, when electromagnetic waves EW are incident on the sample S, the power P in the region including point QT1, which is located on a straight line perpendicular to the first surface of the sample S and passing through the center CE1, is among the 91 points on the receiving surface FT1. T1 Identify [W] and calculate the transmission attenuation L based on the following formula (6). T1 [%] was measured. In equation (6), P0 [W] is the transmitted power of the electromagnetic wave EW. The results are shown in Table 2. L T1[%]=100×(P0-P T1 ) / P0 formula (6)

[0089] Figures 13C and 13D schematically show the calculation model used to calculate the return loss. In this calculation model, each sample S was placed at a predetermined position in a rectangular calculation domain VR1. As shown in Figures 13C and 13D, a receiving surface FR1 was defined in the calculation domain VR1. The receiving surface FR1 was 120 mm away from the center CE1 and was formed by a collection of 91 circles with a diameter of 30 mm, each centered at 91 points spaced 2° apart. The 91 points were located in a plane parallel to the zy-plane, and one of the 91 points was located on a line perpendicular to the first surface of the sample S and passing through the center CE1. The angle between the line perpendicular to the first surface of the sample S and passing through the center CE and the line segments connecting the center CE of the sample S and the points located at both ends of the 91 points was -90° or 90°.

[0090] The calculations using this computational model were performed using Ansys Electronics Desktop HFSS 2021R1 software. The calculations were performed using the finite element method (FEM). In the FEM, the number of meshes in the computational domain VR1 was 500,000, and the number of meshes in sample S was 70,000.

[0091] In the above calculation model, when electromagnetic waves EW are incident on the sample S, the power P in the region including point QR1, which is located on a straight line perpendicular to the first surface of the sample S and passing through the center CE1, is among the 91 points on the receiving surface FT1. R1 [W] is identified, and the return loss L is calculated based on the following formula (7). R1 The percentage [%] was calculated. The results are shown in Table 2. L R1 [%]=100×(P0-P R1 ) / P0 formula (7)

[0092] Figures 14A, 14B, 14C, 14D, and 14E schematically show the calculation models used to calculate the transmission attenuation and return attenuation when a 76.5 GHz electromagnetic wave EW is incident on the second surface of each sample S. Figures 14A and 14B schematically show the calculation models used to calculate the transmission attenuation. In this calculation model, each sample S was placed at a predetermined position in a rectangular parallelepiped calculation region VT2.

[0093] The region RI2, indicated by the dashed line in Figure 14E, is the region irradiated by the electromagnetic wave EW, and is a circle with a diameter of 30 mm centered at the center CE2. The center CE2 corresponds to the center of the electromagnetic wave EW. The amplitude direction of the electric field of the electromagnetic wave EW was parallel to the y-axis direction, parallel to a pair of opposite sides in the square contour of the sample S in plan view, and perpendicular to another pair of opposite sides. As shown in Figures 14A and 14B, a receiving surface FT2 was defined in the calculation region VT2. The receiving surface FT2 was perpendicular to the second surface of the sample S, 120 mm away from the intersection of a line passing through the center CE2 and the first surface of the sample S, and was formed by a collection of 91 circles with a diameter of 30 mm, each centered at 91 points spaced 2° apart. The 91 points were located in a plane parallel to the zy-plane, and one of the 91 points lay on a line perpendicular to the first face of sample S and passing through the center CE2. The angle between the line segment connecting the intersection of the line perpendicular to the second face of sample S and passing through the center CE2 with the first face of sample S, and the points at both ends of the 91 points, and that line was -90° or 90°.

[0094] The calculations using this computational model were performed using Ansys Electronics Desktop HFSS 2021R1 software. The calculations were performed using the finite element method (FEM). In the FEM, the number of meshes in the computational domain VT2 was 500,000, and the number of meshes in sample S was 70,000.

[0095] In the above calculation model, when the electromagnetic wave EW is incident on the sample S, the power P in the region including point QT2, which is located on a straight line perpendicular to the second surface of the sample S and passing through the center CE2, is among the 91 points on the receiving surface FT2.T2 Identify [W] and calculate the transmission attenuation L based on the following formula (8). T2 The percentage [%] was calculated. The results are shown in Table 2. L T2 [%]=100×(P0-P T2 ) / P0 formula (8)

[0096] Figures 14C and 14D schematically show the calculation model used to calculate the return loss. In this calculation model, each sample S was placed at a predetermined position in a rectangular calculation domain VR2. As shown in Figures 14C and 14D, a receiving surface FR2 was defined in the calculation domain VR2. The receiving surface FR2 was 120 mm away from the center CE2 and was formed by a collection of 91 circles with a diameter of 30 mm, each centered at 91 points spaced 2° apart. The 91 points were located in a plane parallel to the zy plane, and one of the 91 points was located on a line perpendicular to the first surface of sample S and passing through the center CE2. The angle between the line perpendicular to the second surface of sample S and passing through the center CE2 and the line segments connecting the center CE2 of sample S and the points located at both ends of the 91 points was -90° or 90°.

[0097] The calculations using this computational model were performed using Ansys Electronics Desktop HFSS 2021R1 software. The calculations were performed using the finite element method (FEM). In the FEM, the number of meshes in the computational domain VR2 was 500,000, and the number of meshes in sample S was 70,000.

[0098] In the above calculation model, when the electromagnetic wave EW is incident on the sample S, the power P in the region including point QR2, which is located on a straight line perpendicular to the second surface of the sample S and passing through the center CE2, is among the 91 points on the receiving surface FT2. R2 [W] is identified, and the return loss L is calculated based on the following formula (9). R2 The percentage [%] was calculated. The results are shown in Table 2. L R2 [%]=100×(P0-P R2 ) / P0 Equation (9)

[0099] In the samples S according to Examples 1 to 4 and Examples 10 to 18, the end face of the protruding portion projecting from the first surface extended perpendicularly to the central axis of the protruding portion. In addition, the end face of the protruding portion projecting from the second surface extended perpendicularly to the central axis of the protruding portion.

[0100] In Sample S according to Example 5, the end face of the protruding portion projecting from the first surface was inclined with respect to a plane perpendicular to the central axis of the protruding portion. The component of the normal vector of this end face parallel to the plane perpendicular to the central axis of the protruding portion pointed in the positive y-axis direction. In addition, the end face of the protruding portion projecting from the second surface extended perpendicular to the central axis of that protruding portion.

[0101] In the samples according to Examples 6 to 9, the end face of the protrusion in the direction of projection of the protrusion protruding from the first surface was inclined with respect to a plane perpendicular to the central axis of the protrusion. In addition, the end face of the protrusion in the direction of projection of the protrusion protruding from the second surface was inclined with respect to a plane perpendicular to the central axis of the protrusion. In the sample according to Example 6, the component of the normal vector of the end face of the protrusion in the direction of projection of the protrusion protruding from the first surface that is parallel to the plane perpendicular to the central axis of the protrusion pointed in the positive y-axis direction. On the other hand, the component of the normal vector of the end face of the protrusion in the direction of projection of the protrusion protruding from the second surface that is parallel to the plane perpendicular to the central axis of the protrusion pointed in the negative y-axis direction. In the sample according to Example 7, the component of the normal vector of the end face of the protrusion in the direction of projection of the protrusion protruding from the first surface that is parallel to the plane perpendicular to the central axis of the protrusion pointed in the positive x-axis direction. On the other hand, the component of the normal vector of the end face of the protrusion in the direction of projection of the protrusion protruding from the second surface that is parallel to the plane perpendicular to the central axis of the protrusion pointed in the negative x-axis direction.

[0102] In the multiple protrusions projecting from the first surface of the samples in Examples 8 and 9, the end faces of adjacent pairs of protrusions in the projection direction were oriented in different directions, as shown in Figures 8B, 8C, and 9. In addition, in the multiple protrusions projecting from the second surface of these samples, the end faces of adjacent pairs of protrusions in the projection direction were oriented in different directions, as shown in Figures 8C and 10. In the multiple protrusions projecting from the first surface, the direction of the component of the normal vector of the end face in the projection direction that is parallel to the plane perpendicular to the central axis of the protrusion coincided with one of the eight directions obtained by dividing the space around the z-axis into eight equal angles. In the multiple protrusions projecting from the second surface, the direction of the component of the normal vector of the end face in the projection direction that is parallel to the plane perpendicular to the central axis of the protrusion coincided with one of the eight directions mentioned above.

[0103] As shown in Tables 2 and 3, the transmission attenuation L of the samples for each example. T1 , reflection loss L R1 , transmission attenuation L T2 , and the amount of return loss L R2 The percentage was over 90%, suggesting that regardless of whether the electromagnetic wave is incident on the first or second surface of the sample according to each embodiment, the influence of transmitted or reflected waves originating from the electromagnetic wave is less likely to affect a predetermined area around the sample according to each embodiment. On the other hand, in the sample according to Comparative Example 1, the return loss L R1 The percentage was less than 90%, suggesting that the influence of reflected waves originating from electromagnetic waves incident on the first surface could extend to a predetermined area around the sample.

[0104] A first aspect of the present invention provides an electromagnetic shield comprising: a plate-shaped base having a first surface and a second surface extending along the first surface at a position away from the first surface; a plurality of first protrusions projecting from the first surface in the direction opposite to the second surface; and a plurality of second protrusions projecting from the second surface in the direction opposite to the first surface, wherein the electromagnetic shield contains a dielectric, the plurality of first protrusions are spaced apart from each other such that in a plan view, the centers of the plurality of first protrusions are located at the vertices or inside of a plurality of polygons arranged according to a predetermined rule, and the plurality of second protrusions are spaced apart from each other such that in a plan view, the centers of the plurality of second protrusions are located at the vertices or inside of a plurality of polygons arranged according to a predetermined rule.

[0105] A second aspect of the present invention provides an electromagnetic shield in which, in the first aspect, the first projection and the second projection are similar to each other in a plan view.

[0106] A third aspect of the present invention provides an electromagnetic shield in which, in the first or second aspect, the protruding length of the first protrusion along its central axis is shorter than the protruding length of the second protrusion along its central axis.

[0107] A fourth aspect of the present invention provides an electromagnetic shield in which, in any one of the first to third aspects, the ratio of the protrusion length of the first protrusion on the central axis to the protrusion length of the second protrusion on the central axis is 0.1 to 1.0.

[0108] A fifth aspect of the present invention is to provide an electromagnetic wave shield in which, in any one of the first to fourth aspects, the electromagnetic wave shield shields electromagnetic waves of wavelength λ, and the protrusion length of the first protrusion at the central axis is 0.55λ or less.

[0109] The sixth aspect of the present invention provides an electromagnetic wave shield in which, in any one of the first to fifth aspects, the width of the first protrusion and the width of the second protrusion are 0.53λ or more and 1.50λ or less.

[0110] The seventh aspect of the present invention is to provide an electromagnetic shield in which, in any one of the first to sixth aspects, the electromagnetic shield shields electromagnetic waves of wavelength λ, and the distance between adjacent first protrusions and the distance between adjacent second protrusions is 1.01λ or more and 1.96λ or less.

[0111] The eighth aspect of the present invention provides an electromagnetic shield in which, in any one of the first to seventh aspects, the first end face in the protruding direction of the first protrusion is inclined with respect to a first plane perpendicular to the central axis of the first protrusion.

[0112] A ninth aspect of the present invention provides an electromagnetic shield in which, in the eighth aspect, the first end faces of a pair of adjacent first protrusions face in different directions.

[0113] The tenth aspect of the present invention provides an electromagnetic shield in which, in any one of the first to ninth aspects, the second end face of the second protrusion in the protruding direction is inclined with respect to a second plane perpendicular to the central axis of the second protrusion.

[0114] An eleventh aspect of the present invention provides an electromagnetic shield in which, in the tenth aspect, the second end faces of a pair of adjacent second protrusions face in different directions.

[0115] A twelfth aspect of the present invention is to provide an electromagnetic shield in which, in any one of the first to eleventh aspects, the electromagnetic shield does not have any conductive parts.

[0116] A thirteenth aspect of the present invention provides an electromagnetic shield in which, in any one of the first to twelfth aspects, the imaginary part ε'' of the relative permittivity of the dielectric at at least one frequency included in the range of 10 GHz to 300 GHz is 0.1 or less.

[0117] A fourteenth aspect of the present invention provides an electromagnetic shield in which, in any one of the first to thirteenth aspects, the real part ε' of the relative permittivity of the dielectric at at least one frequency in the range of 10 GHz to 300 GHz is 2.0 to 4.0.

[0118]

[0119]

Claims

1. An electromagnetic shield comprising: a plate-shaped base having a first surface and a second surface extending along the first surface at a position away from the first surface; a plurality of first protrusions projecting from the first surface in the direction opposite to the second surface; and a plurality of second protrusions projecting from the second surface in the direction opposite to the first surface, wherein the electromagnetic shield contains a dielectric, the plurality of first protrusions are spaced apart from each other such that in a plan view, the centers of the plurality of first protrusions are located at the vertices or inside of a plurality of polygons arranged according to a predetermined rule, and the plurality of second protrusions are spaced apart from each other such that in a plan view, the centers of the plurality of second protrusions are located at the vertices or inside of a plurality of polygons arranged according to a predetermined rule.

2. The electromagnetic shield according to claim 1, wherein the first projection and the second projection are similar to each other in a plan view.

3. The electromagnetic shield according to claim 1, wherein the projection length of the first projection along its central axis is shorter than the projection length of the second projection along its central axis.

4. The ratio of the protrusion length of the first protrusion to the protrusion length of the first protrusion on the central axis to the protrusion length of the second protrusion on the central axis is 0.05 to 1.0, the electromagnetic shield according to claim 1.

5. The electromagnetic shield according to claim 1, wherein the electromagnetic shield shields electromagnetic waves of wavelength λ, and the projection length of the first projection along the central axis is 0.55λ or less.

6. The electromagnetic shield according to claim 1, wherein the electromagnetic shield shields electromagnetic waves of wavelength λ, and the width of the first protrusion and the width of the second protrusion are 0.53λ or more and 1.50λ or less.

7. The electromagnetic shield according to claim 1, wherein the electromagnetic shield shields electromagnetic waves of wavelength λ, and the distance between adjacent first protrusions in a specific direction and the distance between adjacent second protrusions in a specific direction are 1.01λ or more and 1.96λ or less.

8. The electromagnetic shield according to claim 1, wherein the first end face of the first projection in the projection direction is inclined with respect to a first plane perpendicular to the central axis of the first projection.

9. The electromagnetic shield according to claim 8, wherein the first end faces of a pair of adjacent first protrusions are facing in different directions.

10. The electromagnetic shield according to claim 1, wherein the second end face of the second protrusion in the direction of protrusion is inclined with respect to a second plane perpendicular to the central axis of the second protrusion.

11. The electromagnetic shield according to claim 10, wherein the second end faces of a pair of adjacent second protrusions are facing in different directions.

12. The electromagnetic shield according to claim 1, wherein the electromagnetic shield does not have conductive parts.

13. The electromagnetic shield according to claim 1, wherein the imaginary part ε'' of the relative permittivity of the dielectric material at at least one frequency in the range of 10 GHz to 300 GHz is 0.1 or less.

14. The electromagnetic shield according to claim 1, wherein the real part ε' of the relative permittivity of the dielectric at at least one frequency in the range of 10 GHz to 300 GHz is 2.0 to 4.0.

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