Reflective panel, electromagnetic wave reflection device, and electromagnetic wave reflection fence

Abstract

Provided are a reflective panel that has improved weather resistance, and an electromagnetic wave reflection device and an electromagnetic wave reflection fence in which said reflective panel is used. A reflective panel (10) has: a conductive layer (11) having a conductive pattern that reflects electromagnetic waves in a prescribed frequency band of 1 MHz to 300 GHz; a dielectric layer (14) bonded to at least one surface of the conductive layer (11) with an adhesive layer (12) interposed therebetween; and a protective layer (16) provided on the surface of the dielectric layer (14) opposite from the adhesive layer (12). After being subjected to a weather resistance test described in JIS K 7350-4, the reflective panel has a light transmittance of at least 60% at a wavelength of 350-800 nm.

Description

Reflection panel, electromagnetic wave reflection device, and electromagnetic wave reflection fence

[0001] The present invention relates to a reflection panel, an electromagnetic wave reflection device, and an electromagnetic wave reflection fence.

[0002] For the purpose of realizing manufacturing processes, office work automation, remote operation, control and management by AI (Artificial Intelligence), and autonomous driving, the introduction of wireless base stations is progressing both indoors and outdoors. Wireless base stations have been introduced not only indoors such as factories, plants, offices, and commercial facilities, but also outdoors such as highways and railway lines, and in scenarios regardless of indoors or outdoors such as medical sites and event venues.

[0003] In the fifth-generation mobile communication standard (hereinafter referred to as "5G"), a frequency band of 6 GHz or less called "sub-6" and a 28 GHz band classified as a millimeter wave band are provided. In the next-generation 6G mobile communication standard, an expansion to the sub-terahertz band is expected. By using such a high-frequency band, the communication bandwidth can be significantly expanded, and a large amount of data communication can be performed with low latency. A configuration in which an electromagnetic reflection device is arranged along at least a part of a manufacturing line has been proposed (see, for example, Patent Document 1).

[0004] Further, there is a radio wave reflector including a conductor for reflecting radio waves, and when measured according to the measurement method described in JIS R 1679:2007, there is at least one frequency at which the intensity of the reflected wave when an incident wave having a frequency of 3 GHz or more and 300 GHz or less is specularly reflected is -3 dB or more with respect to the incident wave, and the total light transmittance in a D65 standard light source is 65% or more (see, for example, Patent Document 2).

[0005] International Publication No. 2021 / 199504 Japanese Unexamined Patent Application Publication No. 2023-099,422

[0006] By using electromagnetic wave reflectors, communication environments can be improved in wireless communication systems that use highly directional radio waves. 5G use cases extend both indoors and outdoors. When electromagnetic wave reflectors are used in outdoor environments or indoor environments close to outdoors, the reflective panels tend to deform or discolor due to ultraviolet rays, temperature changes, humidity, etc., and their reflective properties deteriorate. When electromagnetic wave reflectors are used as safety fences or sound barriers, a decrease in transmittance to visible light reduces visibility and safety, deviating from the original specifications. Experiments have confirmed that a deformation of about 10% in a reflective panel with a conductive layer sandwiched between resin substrates adversely affects the reflection direction and reflection efficiency. Furthermore, it has been confirmed that irradiation with ultraviolet rays changes the relative permittivity of the resin substrate, making it impossible to obtain the designed reflection direction and reflection efficiency. To use electromagnetic wave reflectors in outdoor or near-outdoor environments, the weather resistance of the reflective panels needs to be improved.

[0007] Furthermore, the aforementioned radio wave reflectors are intended for indoor use, and there is no mention of their use in outdoor or near-outdoor indoor environments. When using radio wave reflectors (reflective panels) in outdoor or near-outdoor indoor environments, weather resistance is required to suppress the degradation described above.

[0008] One objective of this disclosure is to provide a reflective panel with improved weather resistance, an electromagnetic wave reflecting device using the same, and an electromagnetic wave reflecting system.

[0009] In one embodiment, the reflective panel comprises a conductive layer having a conductive pattern that reflects electromagnetic waves in a predetermined frequency band of 1 MHz to 300 GHz, a dielectric layer bonded to at least one surface of the conductive layer via an adhesive layer, and a protective layer provided on the surface of the dielectric layer opposite to the adhesive layer, wherein the light transmittance at wavelengths of 350-800 nm after a weathering test as described in JIS K 7350-4 is 60% or more.

[0010] A weather-resistant reflective panel, an electromagnetic wave reflecting device using the same, and an electromagnetic wave reflecting system will be realized.

[0011] This is a schematic diagram of a wireless transmission system according to an embodiment. This is a schematic diagram of an electromagnetic wave reflective fence formed by connecting multiple electromagnetic wave reflectors. This is a schematic diagram of a modified example of an electromagnetic wave reflector and an electromagnetic wave reflective fence. This is an example of the configuration of a horizontal cross-section of a frame along the A-A line in Figure 2A. This is a diagram showing an example of the layer configuration of a reflective panel.

[0012] The embodiment provides a wireless transmission system used in an outdoor or near-outdoor environment, and an electromagnetic wave reflective panel used in this wireless transmission system. An "environment near the outdoors" refers to a space that connects indoors and outdoors, such as a terrace, arcade, or balcony, or an indoor space located near glass, plastic, or other materials that transmit electromagnetic waves. When constructing a wireless transmission system that utilizes local 5G radio waves in an outdoor or near-outdoor environment, it is necessary to achieve both improved radio wave propagation conditions and prevention of radio wave leakage to the outside. In addition, there is a need to improve the weather resistance of the electromagnetic wave reflective panel so that it can maintain its reflection efficiency even after a long period of time. Weather resistance refers to the property of being resistant to deformation, discoloration, deterioration, and other forms of alteration when used in an outdoor or near-outdoor environment.

[0013] If we focus solely on suppressing the emission of radio waves to the outside, one might consider covering the interior with an electromagnetic wave absorber, similar to the gantry of an ETC (Electronic Toll Collection) system on a toll road. However, covering the entire wall surface of a road or facility with an electromagnetic wave absorber is impractical, and electromagnetic wave absorbers alone do not reduce dead zones or improve the radio wave propagation environment. To reduce dead zones and improve the radio wave propagation environment, electromagnetic wave reflectors are effective. However, considering the reality of use in outdoor or near-outdoor environments and the need to prevent radio wave emission, it is necessary to position the electromagnetic wave reflectors in an optimal position relative to the base station antenna. On the other hand, it is necessary to increase the mechanical strength and weather resistance of the reflective panels used in electromagnetic wave reflectors.

[0014] The embodiments provide a reflective panel, an electromagnetic wave reflector, and an electromagnetic wave reflector fence that satisfy these requirements. The configurations of the reflective panel, electromagnetic wave reflector, and electromagnetic wave reflector fence of the embodiments are described below with reference to the drawings. The embodiments shown below are examples for realizing the technical concept of this disclosure and do not limit the disclosure. The size, positional relationships, etc., of each component shown in each drawing may be exaggerated to facilitate understanding of the invention. In the following description, the same components or functions may be given the same name or reference numerals, and redundant explanations may be omitted.

[0015] <Wireless Transmission System> Figure 1 is a schematic diagram of a wireless transmission system 1 according to an embodiment. The wireless transmission system 1 includes a base station 33 installed outdoors or in an environment close to outdoors, which transmits wireless communications at frequencies included in the frequency band of 1 MHz to 300 GHz, and an electromagnetic wave reflector 60 which has a reflective panel that reflects electromagnetic waves of the base station's frequency and is installed along the longitudinal direction of an area that extends in a certain direction within the communication area of ​​the base station 33. In Figure 1, as an example of an outdoor environment, a wireless environment with a road 32 as the communication area is considered. In the coordinate system of Figure 1, the length direction of the road 32 is the X direction, the width direction is the Y direction, and the direction perpendicular to the road surface is the Z direction. Numerous vehicles 31 travel on the road 32. The vehicles 31 may be vehicles equipped with an automatic driving function or a semi-automatic driving function, or they may be vehicles without an automatic driving function. In any case, not only are there portable terminals held by the driver or passengers, but the vehicles 31 themselves have wireless communication functions, and a large amount of data is transmitted and received between the vehicles 31 and the control / management system.

[0016] To enable wireless communication between a mobile object such as a vehicle 31 and the network, a base station 33 is positioned along the road 32. The base station 33 transmits and receives signals or data to and from the vehicle 31 at a predetermined frequency within the frequency band of 1 MHz to 300 GHz. Due to the topography of the road 32, the surrounding environment, and the presence of numerous vehicles 31, it is difficult to deliver high-frequency radio waves, which have poor directivity, directly from the base station 33 to each vehicle 31. Therefore, an electromagnetic wave reflector 60 is positioned along at least one side of the road 32. Radio waves are a type of electromagnetic wave, and generally, electromagnetic waves below 3 THz are called radio waves. Here, the communication waves transmitted from the base station 33 are called "radio waves," and electromagnetic waves in general are called "electromagnetic waves." As will be described later, multiple electromagnetic wave reflectors 60 may be linked together and installed on the shoulder of the road 32 as an electromagnetic wave reflecting fence.

[0017] The uppermost part of the electromagnetic wave reflector 60 is installed at a higher position than the base station 33. It is desirable that the base station 33 has a directional antenna that forms a beam toward the road. In addition to the directional antenna of the base station 33, by placing the electromagnetic wave reflector 60 along at least one side of the road 32, the radio waves from the base station 33 are efficiently concentrated on the road 32, suppressing radio waves that escape outside the road 32. As a result, the received power outside the road 32 is lower than the average or median received power on the road 32.

[0018] Even if the beam shape is controlled at the base station 33, other vehicles 31 may interfere with the LOS (Line of Sight). In that case, the radio waves from the base station 33 can be reflected by the electromagnetic wave reflector 60 and delivered to the vehicles 31. Depending on the positional relationship between the road 32 and the base station 33, the shortest distance from the antenna of the base station 33 to the electromagnetic wave reflector 60 may be between 5.0m and 300.0m, and the maximum gain of the antenna of the base station 33 may be between 5dBi and 30dBi. If the shortest distance from the antenna of the base station 33 to the electromagnetic wave reflector 60 is less than 5.0m, it becomes difficult to efficiently deliver the radio waves from the base station 33 to the vehicles 31 via the electromagnetic wave reflector 60. If the shortest distance from the base station 33 to the electromagnetic wave reflector 60 exceeds 300.0m, it also becomes difficult to deliver the radio waves to the vehicles 31 via the electromagnetic wave reflector 60 from the standpoint of the maximum gain of the antenna and the straightness of radio wave propagation.

[0019] The size of the reflective surface of the electromagnetic wave reflector 60 should be such that it can cover at least the area determined by the radius R of the first Fresnel zone. The radius R of the first Fresnel zone when the radio waves radiated from the antenna of the base station 33 and reflected by the electromagnetic wave reflector 60 reach the vehicle 31 in phase is defined by the following equation.

[0020] R=[λd1d2 / (d1+d2)] １ / ２ Here, λ is the wavelength used, d1 is the distance from the base station 33 antenna to the electromagnetic wave reflector 60, and d2 is the distance from the electromagnetic wave reflector 60 to the vehicle 31 antenna.

[0021] If, in the 28 GHz band (wavelength approximately 10.7 mm), the distance d1 from the base station 33 antenna to the electromagnetic wave reflector 60 is 20.0 mm, and the distance d2 from the electromagnetic wave reflector 60 to the vehicle 31 is 10.0 m, then the size of the reflective surface of the electromagnetic wave reflector 60 only needs to be several tens of centimeters on each side. On the other hand, from the viewpoint of forming an electromagnetic wave reflection fence that covers a wide reflection area with a small number of electromagnetic wave reflectors 60, the width × length of the reflective surface of the electromagnetic wave reflector 60 may be about 2.0 m × 4.0 m. In this embodiment, the electromagnetic wave reflectors 60 are arranged along the road 32 such that the received power on the back side of the reflective surface of the electromagnetic wave reflector 60, i.e., in the area outside the road 32, is lower than the average or median value of the received power on the road 32.

[0022] <Electromagnetic Wave Reflectors and Electromagnetic Wave Reflecting Fences> Figure 2A is a schematic diagram of an electromagnetic wave reflecting fence 100A. The electromagnetic wave reflecting fence 100A consists of electromagnetic wave reflectors 60A-1, 60A-2, and 60A-3 (hereinafter sometimes collectively referred to as "electromagnetic wave reflectors 60A"), each having reflective panels 10A-1, 10A-2, and 10A-3 (hereinafter sometimes collectively referred to as "reflective panels 10A"), connected by a frame 50A. The coordinate system in Figure 2A is consistent with the coordinate system in Figure 1, with the width or lateral direction of the reflective panel 10 being the X direction, the thickness direction being the Y direction, and the height direction being the Z direction. In Figure 2A, three electromagnetic wave reflectors 60A are connected to constitute the electromagnetic wave reflecting fence 100A, but the number of electromagnetic wave reflectors 60A to be connected is determined as appropriate according to the conditions of the road 32.

[0023] The reflective panel 10A used in the electromagnetic wave reflector 60A reflects electromagnetic waves in the range of 1 MHz to 300 GHz, preferably 1 GHz to 100 GHz, and more preferably 1 GHz to 80 GHz. The reflective panel 10A has a layer containing a conductive film as a reflective film. The conductive film has a predetermined conductive pattern designed according to the desired reflection angle, frequency band, etc. The conductive pattern may include periodic patterns, mesh patterns, geometric patterns, etc., and may be formed of a transparent conductive film. The reflective panel 10A has a protective layer with ultraviolet protection on its outermost layer.

[0024] At least a portion of the reflective panel 10A may be a non-specular reflective surface with different incident and reflection angles for electromagnetic waves. Non-specular reflective surfaces include diffusing and scattering surfaces, as well as metasurfaces, which are artificial reflective surfaces designed to reflect radio waves in a desired direction. Reflective panels 10A-1, 10A-2, and 10A-3 may be electrically connected to each other from the viewpoint of maintaining the continuity of the reflected potential, but if metasurfaces are included, electrical connection between adjacent reflective panels 10A is not required. By holding adjacent reflective panels 10A together with a frame 50A, an electromagnetic wave reflective fence 100A connected in the X direction can be obtained.

[0025] The electromagnetic wave reflector 60A may have legs 56 to support the frame 50A, in addition to the reflector panel 10A and the frame 50A. The legs 56 may allow the electromagnetic wave reflector 60 or electromagnetic wave reflector fence 100 to stand on its own on the road surface. The legs 56 may be configured to be fixed to the road surface with screws, bolts, etc. Conversely, the electromagnetic wave reflector 60 or electromagnetic wave reflector fence 100 may stand on its own on the road surface and also have parts such as casters to make it movable. In addition to the frame 50A, a top frame 57 that holds the upper end of the reflector panel 10 and a bottom frame 58 that holds the lower end may be used. In this case, the frame 50A, the top frame 57 and the bottom frame 58 constitute a frame that holds the entire circumference of the reflector panel 10A. The frame 50A may be called a "side frame" due to its positional relationship with the top frame 57 and the bottom frame 58. By providing the top frame 57 and the bottom frame 58, mechanical strength and safety are ensured during the transport and assembly of the reflector panel 10. The top frame 57 may be configured to allow connection of another reflective panel or another component such as an electromagnetic wave absorbing panel to the upper end of the reflective panel 10A. This increases the flexibility in the size and function of the electromagnetic wave reflective fence 100A.

[0026] Figure 2B is a schematic diagram of an electromagnetic wave reflective fence 100B as a modified example. The electromagnetic wave reflective fence 100B consists of electromagnetic wave reflecting devices 60B-1, 60B-2, and 60B-3 (hereinafter sometimes collectively referred to as "electromagnetic wave reflecting devices 60A"), each having reflective panels 10B-1, 10B-2, and 10B-3 (hereinafter sometimes collectively referred to as "reflective panels 10B"), connected by a frame 50B. Each reflective panel 10B includes a curved surface in at least part of it. In this example, each reflective panel 10B is curved at its upper end in the Z direction. To hold and connect the reflective panels 10B that include the curved surface, the frame 50B has a curvature corresponding to the curvature of the reflective panels 10B. The radius of curvature of the reflective panels 10B is determined according to the width of the road 32 to which the electromagnetic wave reflecting devices 60B are applied, the surrounding conditions, the thickness of the reflective panels 10B, the height of the electromagnetic wave reflecting devices 60B, etc.

[0027] For example, if the thickness of the reflective panel 10B is 5.0 mm or more and 17.0 mm or less, and there are almost no obstacles above the road 32, the radius of curvature of the reflective panel 10B may be set to 1500 mm or more and 2500 mm or less, preferably 2000 mm or more and 2500 mm or less. Like the reflective panel 10A, it is desirable that the reflective panel 10B has a layer containing an ultraviolet-blocking agent in its outermost layer. Instead of a configuration in which the reflective panel 10B has a curved surface, a configuration in which another flat reflective panel 10 or another component such as an electromagnetic wave absorbing panel is connected at a predetermined inclination angle by the top frame 57 may be used.

[0028] Figure 2C shows an example of the configuration of frame 50A along the A-A line in Figure 2A, in a cross-sectional view parallel to the XY plane. Frame 50B has the same cross-sectional configuration as frame 50A, except that its upper part is curved along the curvature of the reflective panel 10B, and will therefore be collectively referred to as "frame 50" in the following description. Frame 50 has a conductive body 500 and slits 51-1 and 51-2 formed on both sides of the body 500 in the width direction. The edges of the reflective panels 10-1 and 10-2 are inserted into slits 51-1 and 51-2, respectively, and held within space 52. Space 52 is not essential, but by providing space 52, the body 500 of frame 50 can be made lighter, and the holding angle of the reflective panel 10 can be made more flexible.

[0029] By inserting the reflective panels 10-1 and 10-2 into the slits 51-1 and 51-2 respectively, adjacent reflective panels 10-1 and 10-2 can be stably held. Even when a part of the reflective panel 10B is curved, as shown in Figure 2B, the edge of the curved reflective panel 10B is inserted into the slit 51 of the curved frame and held in place. Part of the main body 500 may be made of a non-conductive material. A non-conductive cover 501, such as resin, may be provided on the outer surface of the main body 500, but if a cover 501 is provided, the cover 501 may be made of a resin material with good weather resistance.

[0030] <Configuration of the Reflective Panel> Figure 3 shows an example of the layer configuration of the reflective panel 10. The layer configuration in Figure 3 is the configuration in the thickness (Y) direction of the reflective panel 10. The reflective panel 10 includes a conductive layer 11, a dielectric layer 14 or 15 bonded to at least one surface of the conductive layer 11 via an adhesive layer 12 or 13, and a protective layer 16 or 17 provided on the surface of the dielectric layer 14 or 15. In the example in Figure 3, the conductive layer 11 is sandwiched between the dielectric layers 14 and 15 via adhesive layers 12 and 13, and protective layers 16 and 17 are provided on both surfaces of the dielectric layers 14 and 15. The protective layers 16 and 17 have an ultraviolet protection function. When using a reflective panel 10B that includes a curved surface as shown in Figure 2B, the protective layer may be provided only on the outer surface of the curved surface of the reflective panel 10B.

[0031] When the electromagnetic wave reflector 60 is used outdoors or in indoor facilities close to an outdoor environment, it is desirable that the reflective panel 10 be weather-resistant. The reflective panel 10 of this embodiment has mechanical strength and weather resistance that can withstand outdoor environments. When a typical electromagnetic wave reflector is placed in an outdoor environment, the surface substrate of the electromagnetic wave reflector tends to undergo deterioration such as deformation, discoloration, and degradation due to the effects of visible light and ultraviolet rays contained in sunlight, or due to temperature changes. When an electromagnetic wave reflecting fence 100, to which electromagnetic wave reflectors 60 are connected, is also used as an outdoor safety fence or sound barrier, a decrease in transmittance due to discoloration of the reflective panel 10 leads to a decrease in visibility. If the surface substrate of the reflective panel 10 is a resin substrate, the direction of reflection or reflection efficiency may change when deformation of about 1 / 100 of the original dimensions occurs due to the effects of temperature changes, etc. In addition, irradiation with ultraviolet rays may change the relative permittivity of the resin material or dielectric material, which may deviate from the designed reflection direction and reflection efficiency. The reflective panel 10 of this embodiment suppresses or reduces these problems.

[0032] The conductive layer 11 is a surface that forms the reflective surface of the reflective panel 10, and may be formed of a metal mesh, a periodic pattern, a geometric pattern, a transparent conductive film, etc. As an example, the conductive layer 11 includes a metal mesh formed of a good conductor such as Cu, Ni, SUS, Ag, etc. If a metasurface is included in part of the reflective panel 10, the conductive layer 11 may include a pattern that includes a periodic arrangement of multiple metal elements. The conductive layer 11 has a thickness of 10 μm to 200 μm, preferably 50 μm to 150 μm, so that it functions sufficiently as a reflective surface that reflects electromagnetic waves of the target frequency in the designed direction.

[0033] The adhesive layers 12 and 13 have a transmittance of 60% or more, preferably 70% or more, and more preferably 80% or more, with respect to the operating frequency, so as to guide the incident electromagnetic waves to the conductive layer 11. The adhesive layers 12 and 13 may be formed from vinyl acetate resin, acrylic resin, cellulose resin, aniline resin, ethylene resin, silicone resin, or other resin materials. If the adhesive layers 12 and 13 are to have durability and moisture resistance suitable for outdoor use, ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP) may be used. The thickness of the adhesive layers 12 and 13 is such that the dielectric layers 14 and 15 can be reliably adhered to and held in place by the conductive layer 11, for example, between 10 μm and 400 μm. The adhesive layers 12 and 13 have a relative permittivity and dielectric loss tangent suitable for achieving the target reflection characteristics of the conductive layer 11.

[0034] The dielectric layers 14 and 15 are insulating polymer films such as polycarbonate, cycloolefin polymer (COP), polyethylene terephthalate (PET), and fluororesin. In order to maintain the strength of the reflective panel 10 while keeping the total weight of the reflective panel 10 as light as possible, the thickness of the dielectric layers 14 and 15 is selected to be greater than 1.0 mm and within the range of 8.0 mm or less. The basis for this thickness range will be explained later. If the thickness of the conductive layer 11 is 100.0 μm, the ratio of the thickness of the dielectric layers 14 and 15 to the thickness of the conductive layer 11 is greater than 10 and 80 or less. The dielectric layers 14 and 15 have mechanical strength that can withstand outdoor use and have relative permittivity and dielectric loss tangent suitable for achieving the target reflective characteristics.

[0035] The protective layers 16 and 17 are, for example, resin layers containing an ultraviolet absorber. While ultraviolet shielding agents include ultraviolet absorbers and ultraviolet scatterers, using an ultraviolet scatterer may cause ultraviolet rays scattered by the reflective panel 10 to affect other electromagnetic wave reflectors 60. Therefore, ultraviolet rays are blocked by an ultraviolet absorber. As the ultraviolet absorber, benzotriazole-based, benzophenone-based, triazine-based, hydroxyphenyltriazine-based ultraviolet absorbers may be used. These ultraviolet absorbers may be blended into a resin and coated onto the surfaces of the dielectric layers 14 and 15 to form the protective layers 16 and 17 as coated films.

[0036] The thicknesses of the protective layers 16 and 17 are such that they sufficiently absorb ultraviolet rays while transmitting visible light and do not impair the transparency of the reflection panel 10, for example, 5 μm or more and 15 μm or less, preferably 10 μm ± several microns. From the viewpoint of maintaining transparency while ensuring the strength of the reflection panel, the ratio of the thicknesses of the dielectric layers 14 and 15 to the protective layers 16 and 17 is 66 or more and 1600 or less. When the thickness of the conductive layer 11 is 100.0 μm, the ratio of the thicknesses of the protective layers 16 and 17 to the thickness of the conductive layer 11 is 0.05 or more and 0.15 or less. From the viewpoint of maintaining the strength, reflection characteristics, and transparency of the reflection panel 10, the ratio of the thickness of the entire reflection panel 10 to the protective layer 16 or 17 is preferably 350 or more and 1000 or less.

[0037] The overall thickness of the reflection panel 10 having such a configuration is 5.0 mm or more and 17.0 mm or less. When the thickness of the conductive layer 11 is 100 μm, the ratio of the overall thickness of the reflection panel 10 to the conductive layer 11 is 50 or more and 170 or less. From the viewpoint of ensuring mechanical strength, since the ratio of the thickness of the dielectric material to the conductive layer 11 increases, when the reflection panel 10 includes a metasurface, it is desirable to appropriately design the relative permittivity and dielectric tangent of the entire dielectric portion including the adhesive layer 12, the dielectric layer 14, and the protective layer 16.

[0038] <Experimental Results> For the reflection panels 10A of Example 1 and Example ₂ below, a weather resistance test described in JIS K 7350-4 was conducted.

[0039] For the reflection panels 10A of Example 1 and Example ₂, a weather resistance test was conducted, and the light transmittance, contact angle, water vapor permeability of the protective layer, and surface energy were measured. Note that the light transmittance is synonymous with the visible light transmittance.

[0040] The light transmittance was measured in accordance with JIS K 7361-1:1997.

[0041] The contact angle was measured using a contact angle meter DMo-9₀₂ manufactured by Kyowa Interface Science Co., Ltd. and using the contact angle θ / ₂.

[0042] The water vapor permeability of the protective layer was measured in accordance with the procedure of A.3 in JIS K 7129.

[0043] <Example 1> Example 1 is an embodiment. The reflective panel 10A of Example 1 includes a conductive layer 11 made of a stainless steel mesh with a thickness of 100 μm, adhesive layers 12 and 13 made of ethylene vinyl acetate with a thickness of 400 μm, dielectric layers 14 and 15 made of a polycarbonate sheet with a thickness of 2.0 mm, and protective layers 16 and 17 made of a urethane acrylate-based hard coat layer. The above thicknesses are the thicknesses of each one layer of the adhesive layers 12 and 13, the dielectric layers 14 and 15, and the protective layers 16 and 17. The polycarbonate sheet was produced by injection molding a resin softened by heating into a mold and then cooling it with water or air to form the product, and then a coating containing a benzophenone-based ultraviolet absorber with a thickness of 20 μm was formed on the surface.

[0044] For the reflective panel 10A of Example 1, after performing the weather resistance test described in JIS K 7350-4, when the light transmittance of the reflective panel 10A at wavelengths of 350 to 800 nm was measured, it was 60.5%, and it was confirmed that it decreased by only 0.1% compared to before performing the weather resistance test described in JIS K 7350-4.

[0045] Also, for the reflective panel 10A of Example 1, after performing the weather resistance test described in JIS K 7350-4, when the contact angle, water vapor permeability, and surface energy were measured, the water contact angle was 85°, the n-hexadecane contact angle was 82°, and the water vapor permeability was 80 g / m ２ , 24 hr was confirmed. Also, the reflection efficiency was 72.3%, the reflection direction was such that the reflection peak angle was within ±5.0° of the desired angle, and it was confirmed that the allowable range of deviation of the reflection peak angle was 7.5° or less. The reflection efficiency is preferably 60% or more, and still more preferably 70% or more.

[0046] <Example 2> Example 2 is an embodiment. The reflective panel 10A of Example 1 includes a conductive layer 11 made of a stainless steel mesh with a thickness of 100 μm, adhesive layers 12 and 13 made of ethylene vinyl acetate with a thickness of 400 μm, dielectric layers 14 and 15 made of a polycarbonate sheet with a thickness of 2.0 mm, and protective layers 16 and 17 made of a urethane acrylate hard coat layer. The above thicknesses are the thickness of one layer each of the adhesive layers 12 and 13, dielectric layers 14 and 15, and protective layers 16 and 17. The polycarbonate sheet was extruded by injecting heated resin into a mold under pressure, and then cooling it. The resin contained a benzotriazole-based ultraviolet absorber, and was molded so that there was a large amount of the ultraviolet absorber on the surface layer.

[0047] Regarding the reflective panel 10A in Example 2, after conducting the weather resistance test described in JIS K 7350-4, the light transmittance of the reflective panel 10A at wavelengths of 350 to 800 nm was measured and found to be 60.3%, confirming that it decreased by only 0.1% compared to before the weather resistance test described in JIS K 7350-4.

[0048] Furthermore, after conducting a weather resistance test on the reflective panel 10A in Example 2 as described in JIS K 7350-4, the contact angle, water vapor transmission rate, and surface energy were measured. The water contact angle was 85°, the n-hexadecane contact angle was 81°, and the water vapor transmission rate was 80 g / m³. ２ It was confirmed that the reflection rate was 24 hours. Furthermore, the reflectivity was 72.4%, the reflection direction was such that the reflection peak angle was ±5.0° of the desired angle, and the allowable range of deviation in the reflection peak angle was 7.5° or less. A reflectivity of 60% or higher is preferable, and 70% or higher is even preferable.

[0049] <Example 3> Example 3 is a comparative example. The reflective panel 10A of Example 3 includes a conductive layer 11 made of a stainless steel mesh with a thickness of 100 μm, adhesive layers 12 and 13 made of ethylene vinyl acetate with a thickness of 400 μm, dielectric layers 14 and 15 made of a polycarbonate sheet with a thickness of 2.0 mm, and protective layers 16 and 17 made of a silicone-based hard coat layer. The thicknesses mentioned above are the thickness of one layer each of the adhesive layers 12 and 13, dielectric layers 14 and 15, and protective layers 16 and 17. The reflective panel 10A of Example 3 differs from the reflective panel 10A of Example 1 in that the protective layers 16 and 17 are replaced with a silicone-based hard coat layer. The polycarbonate sheet was manufactured by extrusion molding, in which heated and softened resin is injected into a mold, and then cooled with water or air to form the product. No surface coating was applied.

[0050] Regarding the reflective panel 10A in Example 3, after performing the weather resistance test described in JIS K 7350-4, the light transmittance of the reflective panel 10A at wavelengths of 350 to 800 nm was measured and found to be 60.5%, which is a decrease of 0.7% compared to before performing the weather resistance test described in JIS K 7350-4, JIS K 7373, or JIS Z8730.

[0051] Furthermore, regarding the reflective panel 10A in Example 3, after conducting a weather resistance test as described in JIS K 7350-4, JIS K 7373, or JIS Z 8730, the contact angle, water vapor transmission rate, and surface energy were measured. The results showed a contact angle of 80°, an n-hexadecane contact angle of 80°, and a water vapor transmission rate of 100 g / m³. ２ It was confirmed that the reflection time was 24 hours. Furthermore, the reflection efficiency was 75.6%, the reflection direction and the reflection peak angle were within ±3.0° of the desired angle, and it was confirmed that the allowable range for deviation of the reflection peak angle was 5.5° or less.

[0052] <Example 4> Example 4 is a comparative example. The reflective panel 10A of Example 4 includes a conductive layer 11 made of a stainless steel mesh with a thickness of 100 μm, adhesive layers 12 and 13 made of ethylene vinyl acetate with a thickness of 400 μm, dielectric layers 14 and 15 made of a polycarbonate sheet with a thickness of 2.0 mm, and protective layers 16 and 17 made of a silicone-based hard coat layer. The thicknesses mentioned above are the thickness of one layer each of the adhesive layers 12 and 13, dielectric layers 14 and 15, and protective layers 16 and 17. The reflective panel 10A of Example 4 differs from the reflective panel 10A of Example 1 in that the protective layers 16 and 17 are replaced with a silicone-based hard coat layer. The polycarbonate sheet was extruded by injecting heated resin into a mold under pressure, and then cooling it. The resin does not contain an ultraviolet absorber.

[0053] Regarding the reflective panel 10A in Example 4, after performing the weather resistance test described in JIS K 7350-4, the light transmittance of the reflective panel 10A at wavelengths of 350 to 800 nm was measured and found to be 60.5%, which is a decrease of 0.6% compared to before performing the weather resistance test described in JIS K 7350-4, JIS K 7373, or JIS Z8730.

[0054] Furthermore, regarding the reflective panel 10A in Example 4, after conducting a weather resistance test according to JIS K 7350-4, JIS K 7373, or JIS Z 8730, the contact angle, water vapor transmission rate, and surface energy were measured. The results showed a contact angle of 80°, an n-hexadecane contact angle of 80°, and a water vapor transmission rate of 100 g / m³. ２ It was confirmed that the reflection time was 24 hours. Furthermore, the reflection efficiency was 75.6%, the reflection direction and the reflection peak angle were within ±3.0° of the desired angle, and it was confirmed that the allowable range for deviation of the reflection peak angle was 5.5° or less.

[0055] <Effects> The reflective panel 10A of this disclosure has a conductive layer 11 having a conductive pattern that reflects electromagnetic waves in a predetermined frequency band of 1 MHz to 300 GHz, dielectric layers (14, 15) bonded to at least one surface of the conductive layer 11 via an adhesive layer, and protective layers (16, 17) provided on the surface of the dielectric layers (14, 15) opposite to the adhesive layer, and has a light transmittance of 60% or more at wavelengths of 350-800 nm after a weather resistance test as described in JIS K 7350-4. Therefore, even when used in an outdoor environment or an indoor environment close to the outdoors, it can maintain transparency and the designed reflection direction and reflection efficiency, and has good weather resistance.

[0056] Therefore, a reflective panel 10A with improved weather resistance can be provided.

[0057] Furthermore, the protective layers (16, 17) may be resin layers containing an acrylic water-repellent agent. This provides a reflective panel 10A with better weather resistance and improved weather resistance.

[0058] Furthermore, the outermost surface of the protective layer (16, 17) may have a water contact angle of 80° or more, and an n-hexadecane contact angle of 80° or more. This provides a reflective panel 10A with better weather resistance and improved weather resistance.

[0059] Furthermore, the water vapor transmission rate of the protective layers (16, 17) may be 50 to 100 g / m², 24hr, in accordance with JIS K 7129. This provides a reflective panel 10A with better weather resistance and improved weather resistance.

[0060] The electromagnetic wave reflecting device 60 of this disclosure comprises the above-described reflective panel 10A and a frame 50 that holds the reflective panel 10A. Therefore, even when used in an outdoor environment or an indoor environment close to the outdoors, transparency can be maintained, and the designed reflection direction and reflection efficiency can be maintained, and weather resistance is good.

[0061] Therefore, an electromagnetic wave reflector 60 using a reflective panel 10A with improved weather resistance can be provided.

[0062] Furthermore, the frame 50 may include a top frame 50 that holds the upper end of the reflective panel 10A, side frames 50 that hold the side ends of the reflective panel 10A, and a frame 50 (bottom frame) that holds the lower end of the reflective panel 10A. By holding the upper, side, and lower ends of the reflective panel 10A with the frame 50, the strength is increased and durability is improved. Therefore, an electromagnetic wave reflecting device 60 using a reflective panel 10A with high durability and improved weather resistance can be provided.

[0063] The electromagnetic wave reflective fence 100 of this disclosure has a configuration in which multiple reflective panels 10A are connected by a frame 50 using multiple electromagnetic wave reflective devices 60 as described above. Therefore, even when used in an outdoor environment or an indoor environment close to the outdoors, transparency can be maintained, and the designed reflection direction and reflection efficiency can be maintained, and weather resistance is good.

[0064] Therefore, an electromagnetic wave reflective fence 100 using a reflective panel 10A with improved weather resistance can be provided.

[0065] Furthermore, by using the reflective panel, electromagnetic wave reflector, and electromagnetic wave reflecting fence of the embodiment, it is possible to achieve both improvement of the radio wave propagation environment and suppression of radio wave leakage outside the necessary space in outdoor environments. The wireless transmission system 1 of the embodiment can also be applied to equipment that extends for a long distance in a certain direction in environments such as general roads, expressways, and railway lines. In particular, it can reduce dead zones on expressways equipped with sound barriers or safety fences on both sides, improve the radio wave propagation environment, and suppress radio wave leakage outside the expressway.

[0066] The size of the reflective surface of the electromagnetic wave reflector 60 can be appropriately designed depending on the application, and as an example, a size from 10 cm x 10 cm to 2.0 m x 4.0 m may be used. The height of the base station 33 antenna is not limited to 3.0 m, and may be lower than the upper end of the electromagnetic wave reflector 60. The ultraviolet absorber used in the outermost protective layer of the reflective panel and the material of the electromagnetic wave absorbing panel used in combination with the electromagnetic wave reflector can be appropriately selected depending on the application environment. The electromagnetic wave reflector 60B having a reflective panel 10B including a curved surface as shown in Figure 2B may be connected to constitute the wireless transmission system 1. The frequencies used in the wireless transmission system are not limited to the 4.7 GHz and 28 GHz bands. By controlling the pattern of the conductive layer 11 of the reflective panel 10, electromagnetic waves of the target frequency can be reflected in the range of 1 MHz to 300 GHz, preferably 1 GHz to 100 GHz, and more preferably 1 GHz to 80 GHz.

[0067] The embodiments of the present disclosure have been described above, but the present disclosure may include the following configurations: (Note 1) A reflective panel having: a conductive layer having a conductive pattern that reflects electromagnetic waves in a predetermined frequency band of 1 MHz to 300 GHz; a dielectric layer bonded to at least one surface of the conductive layer via an adhesive layer; and a protective layer provided on the surface of the dielectric layer opposite to the adhesive layer, wherein the light transmittance at wavelengths of 350-800 nm after a weathering test as described in JIS K 7350-4 is 60% or more. (Note 2) The reflective panel according to Note 1, wherein the protective layer is a resin layer containing an acrylic water repellent. (Note 3) The reflective panel according to Note 1 or 2, wherein the outermost surface of the protective layer has a water contact angle of 80 to 100° and an n-hexadecane contact angle of 80° or more. (Note 4) The water vapor transmittance of the protective layer is 50 to 100 g / m² in accordance with JIS K 7129. ２, a reflective panel as described in any one of Appendix 1 to Appendix 3, wherein the reflective panel is 24hr. (Appendix 5) An electromagnetic wave reflecting device having a reflective panel as described in any one of Appendix 1 to Appendix 4, and a frame that holds the reflective panel. (Appendix 6) An electromagnetic wave reflecting device as described in Appendix 5, wherein the frame includes a top frame that holds the upper end of the reflective panel, a side frame that holds the side end of the reflective panel, and a bottom frame that holds the lower end of the reflective panel. (Appendix 7) An electromagnetic wave reflecting fence in which a plurality of electromagnetic wave reflecting devices as described in Appendix 5 or 6 are used to connect a plurality of the reflective panels with the frame.

[0068] This application claims priority based on Japanese Patent Application No. 2025-024121, filed on 18 February 2025, and incorporates all of its disclosures herein.

[0069] 1. Wireless transmission system 10, 10A Reflective panel 11 Conductive layer 12, 13 Adhesive layer 14, 15 Dielectric layer 16, 17 Protective layer 31 Vehicle 32 Road 33 Base station 35 Electromagnetic wave absorber 50, 50A, 50B Frame 57 Top frame 58 Bottom frame 60, 60A, 60B Electromagnetic wave reflector 100A, 100B Electromagnetic wave reflecting fence

Claims

1. A reflective panel comprising: a conductive layer having a conductive pattern that reflects electromagnetic waves in a predetermined frequency band of 1 MHz to 300 GHz; a dielectric layer bonded to at least one surface of the conductive layer via an adhesive layer; and a protective layer provided on the surface of the dielectric layer opposite to the adhesive layer, wherein the light transmittance at wavelengths of 350-800 nm is 60% or more after undergoing a weather resistance test as described in JIS K 7350-4.

2. The reflective panel according to claim 1, wherein the protective layer is a resin layer containing an acrylic water-repellent agent.

3. The reflective panel according to claim 1 or 2, wherein the outermost surface of the protective layer has a water contact angle of 80° or more and 100° or less, and an n-hexadecane contact angle of 80° or more.

4. The water vapor permeability of the protective layer shall be 50 to 100 g / m² in accordance with JIS K 7129. ２ The reflective panel according to claim 1, wherein the reflective surface is 24hr.

5. An electromagnetic wave reflecting device comprising: a reflective panel as described in claim 1; and a frame for holding the reflective panel.

6. The electromagnetic wave reflecting device according to claim 5, wherein the frame includes a top frame that holds the upper end of the reflecting panel, a side frame that holds the side end of the reflecting panel, and a bottom frame that holds the lower end of the reflecting panel.

7. An electromagnetic wave reflective fence comprising a plurality of electromagnetic wave reflective devices as described in claim 5, wherein a plurality of reflective panels are connected by the frame.

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