Electromagnetic wave reflection / sound insulation device and radio transmission system

Abstract

Provided is an electromagnetic wave reflection / sound insulation device that achieves both improvement of a radio wave propagation environment and sound insulation or sound shielding.　This electromagnetic wave reflection / sound insulation device comprises: a panel in which a conductive layer for reflecting an electromagnetic wave in a predetermined frequency band of 1 GHz to 300 GHz inclusive is sandwiched between two dielectric substrates transparent to visible light; and a frame for holding at least both side ends of the panel. The total thickness of the two dielectric substrates is 10.0 mm or more. A radio transmission system can be constructed, for example, by attaching such electromagnetic wave reflection / sound insulation devices to supports installed at a fixed interval along a road having a base station incorporated thereinto.

Description

Electromagnetic wave reflection and sound insulation device and wireless transmission system

[0001] The present invention relates to an electromagnetic wave reflecting sound insulating device and a wireless transmission system.

[0002] Wireless base stations are being installed both indoors and outdoors for the purposes of automating manufacturing processes and office work, remote operation, control and management using AI (Artificial Intelligence), and realizing autonomous driving. Wireless base stations are being installed indoors in factories, plants, offices, commercial facilities, etc., and outdoors on highways, railway tracks, as well as in medical settings and event venues.

[0003] The fifth-generation mobile communication standard (hereinafter referred to as "5G") provides a frequency band below 6 GHz called "sub-6" and the 28 GHz band classified as the millimeter wave band. The next-generation 6G mobile communication standard is expected to expand into the sub-terahertz band. By using such high-frequency bands, communication bandwidth will be significantly expanded, enabling large-volume data communications with low latency. On expressways, large amounts of data related to maintenance, inspections, etc. are transmitted and received with the aim of preventing disasters and accidents. In order to accommodate such large volumes of data communications, the introduction of 5G mobile communications on expressways is expected.

[0004] On the other hand, 5G radio waves have the characteristics of being highly directional and not easily diffracted, which means that blind spots occur in various places, such as behind structures. A configuration has been proposed in which electromagnetic reflecting devices are placed along at least a portion of a production line in a factory (see, for example, Patent Document 1).

[0005] International Publication No. 2021 / 199504

[0006] In the case of expressways, it is necessary to create a wireless communication environment for linearly extending premises. While some expressways have soundproofing walls installed on the roadside shoulders, translucent soundproofing walls made of plastic or chemically strengthened glass do not eliminate blind zones, and 5G radio waves penetrate the soundproofing walls and leak outside the expressway. Metal soundproofing walls have numerous grooves for sound absorption, and the short-wavelength 5G radio waves are scattered by the groove structure, making it difficult to control reflected electromagnetic waves. One aspect of the present invention is to provide an electromagnetic wave reflective and soundproofing device that achieves both an improvement in the radio wave propagation environment and soundproofing or soundproofing.

[0007] In one embodiment, the electromagnetic wave reflective soundproofing device comprises a panel in which a conductive layer that reflects electromagnetic waves in a predetermined frequency band of 1 GHz or more and 300 GHz or less is sandwiched between two dielectric substrates that are transparent to visible light, and a frame that holds at least both side edges of the panel, wherein the total thickness of the two dielectric substrates is 10.0 mm or more.

[0008] An electromagnetic wave reflecting and soundproofing device is realized that achieves both an improvement in the radio wave propagation environment and sound insulation or soundproofing.

[0009] FIG. 10 is a schematic diagram of a wireless transmission system to which an electromagnetic wave reflecting sound insulating device of an embodiment is applied. FIG. 11 is a schematic diagram of a support installed on a road. FIG. 12 is a schematic diagram of an electromagnetic wave reflecting sound insulating device of an embodiment. FIG. 13 is a diagram showing an example of a configuration in which a top frame and a bottom frame are provided in the electromagnetic wave reflecting sound insulating device of FIG. 3. FIG. 14 is a diagram showing an example of the layer configuration of a panel. FIG. 15 is a cross-sectional view showing an example of a configuration of a frame used in an electromagnetic wave reflecting sound insulating device. FIG. 16 is a schematic diagram of an electromagnetic wave reflecting sound insulating device supported on a support. FIG. 17 is a cross-sectional view showing a modified example of the frame. FIG. 18 is a schematic diagram of an electromagnetic wave reflecting sound insulating device supported on a support using the frame of FIG. 7. FIG. 19 is a schematic diagram showing yet another modified example of the frame and its fixed state to the support.

[0010] In one embodiment, an electromagnetic wave reflecting and insulating device is provided that has both a reflector function for improving the radio wave environment and a sound-blocking or sound-proofing effect. For example, on elevated roads in urban areas where many buildings, residences, etc. are located nearby, sound-blocking walls are installed on both sides of the road to suppress noise generated by passing vehicles. While it is conceivable to increase the sound-blocking or sound-proofing effect while maintaining the reflector function, a taller metal sound-blocking wall would impair visibility for passing vehicles and reduce sunlight exposure to nearby buildings and residences. The electromagnetic wave reflecting and insulating device of the embodiment is transparent to visible light, reflects electromagnetic waves in a predetermined frequency band ranging from 1 GHz to 300 GHz, and has sound-blocking properties.

[0011] An electromagnetic wave reflecting soundproofing device and a wireless transmission system using the same according to an embodiment will be described below with reference to the drawings. The embodiments shown below are examples for embodying the technical concept of the present invention and are not intended to limit the present invention. The size, positional relationship, 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 names or symbols, and duplicate explanations may be omitted.

[0012] <Electromagnetic Wave Reflecting Soundproofing Device and Wireless Transmission System> FIG. 1 is a schematic diagram of a wireless transmission system 1 to which an electromagnetic wave reflecting soundproofing device 60 according to an embodiment is applied. FIG. 1 is a schematic plan view, showing a road 20 extending within an XZ plane. The length direction of the road 20 is the X direction, and the width direction is the Z direction. The Y direction, which is perpendicular to the XZ plane, is the height direction. A large number of vehicles 31 travel along the road 20. The vehicles 31 may be vehicles with automatic or semi-automatic driving functions, or vehicles without automatic driving functions. In either case, the vehicles 31 themselves have wireless communication devices installed in addition to mobile communication devices carried by drivers and passengers, and large amounts of data are communicated between the vehicles 31 and a control and management system on a network.

[0013] To improve the radio wave propagation environment on the road 20 and prevent noise and radio wave leakage outside the road 20, multiple electromagnetic wave reflective sound-proofing devices 60 are arranged along the length of the road 20. Each electromagnetic wave reflective sound-proofing device 60 includes a transparent panel 10 that reflects electromagnetic waves in a predetermined frequency band between 1 GHz and 300 GHz, and a frame 50 that holds at least both side edges of the panel. The term "transparent" used herein refers to light-transmitting properties, and transmits light with wavelengths shorter than those of far-infrared light, more specifically visible light. The panel 10 functions as a reflector for electromagnetic waves in a specific frequency band and also functions as a sound-insulating or soundproofing panel. The electromagnetic wave reflective sound-proofing devices 60 are supported by posts 25 installed at regular intervals along the roadside shoulder of the road. By installing the electromagnetic wave reflective sound-proofing devices 60 between adjacent posts 25, an electromagnetic wave reflective sound-proofing fence is constructed along the road 20.

[0014] To achieve wireless communication between a mobile object such as a vehicle 31 and a network, a base station 30 is installed at a predetermined distance L along the road 20. The base station 30 transmits and receives signals or data to and from the vehicle 31 in a predetermined frequency band of 1 GHz or more and 300 GHz or less. Due to factors such as the topography of the road 20, the surrounding environment, and the presence of traveling vehicles 31, it may be difficult for the antenna of the base station 30 to directly transmit high-frequency radio waves, which have poor linearity, to each vehicle 31. Furthermore, there is a demand for 5G radio waves to be prevented from leaking outside the road 20 so as not to conflict with commercial radio waves or emergency communication radio waves in other frequency bands. Therefore, an electromagnetic wave reflecting and soundproofing device 60 is installed along at least one side of the road 20. Radio waves are a type of electromagnetic wave, and electromagnetic waves of 3 THz or less are generally referred to as radio waves. Here, communication waves transmitted from the base station 30 are referred to as "radio waves," and electromagnetic waves in general are referred to as "electromagnetic waves."

[0015] It is desirable that the base station 30 has a directional antenna that forms a beam toward the road 20. In addition to the directional antenna of the base station 30, by placing an electromagnetic wave reflective soundproofing device 60 along at least one side of the road 20, radio waves from the base station 30 can be efficiently delivered to vehicles 31 traveling on the road 20, improving the wireless environment. The beam radiated from the base station 30 is incident on the reflecting surface of the panel 10 so that the cross section of the beam hits a position lower than the top edge of the reflecting surface of the electromagnetic wave reflective soundproofing device fence. This prevents electromagnetic waves in the frequency band used by the wireless transmission system 1 from escaping outside the road 20.

[0016] The electromagnetic wave reflecting sound insulation device 60 also prevents noise generated by traveling vehicles from reaching the road 20. The panel 10 of the electromagnetic wave reflecting sound insulation device 60 exhibits sound insulation (sound transmission loss) of 25 dB or more for 400 Hz sounds and sound insulation of 30 dB or more for 1000 Hz sounds. Road noise generated on the road surface by traveling vehicles 31 is said to be in the range of 100 Hz to 1000 Hz. Tire noise traveling on the road 20 and relatively low-pitched horns have frequencies of 400 Hz or thereabouts. High-pitched sounds such as electronic sirens and wind noise while traveling have frequencies of 1000 Hz or thereabouts. In the process of designing the thickness of the translucent dielectric substrate used in the panel 10, taking into account the flame resistance of the panel 10, the inventors discovered that the above-mentioned sound insulation effect can be achieved when the dielectric substrate has a certain thickness or greater. The thickness of the dielectric substrate will be described later.

[0017] 2 is a schematic diagram of support posts 25 installed on a road 20. The support posts 25 are generally installed at regular intervals on the roadside shoulder of the road 20. The support posts 25 are, for example, H-shaped steel beams, and are fixed to or embedded in a concrete base 23. The height, width, and installation intervals of the support posts 25 are appropriately selected depending on the application location. The electromagnetic wave reflecting soundproofing device 60 is supported between two adjacent support posts 25.

[0018] FIG. 3 is a schematic diagram of an electromagnetic wave reflective soundproofing device 60 according to an embodiment. The electromagnetic wave reflective soundproofing device 60 includes a transparent panel 10 that reflects electromagnetic waves in a predetermined frequency band between 1 GHz and 300 GHz, and a frame 50 that supports at least both side edges of the panel 10. The panel 10 may have a specular reflective surface that reflects incident electromagnetic waves at the same angle as the incident angle, or a non-specular reflective surface that reflects incident electromagnetic waves at an angle different from the incident angle. The non-specular reflective surface may include a metasurface, which is an artificial reflective surface that reflects incident electromagnetic waves in a controlled direction. When the panel 10 has a specular reflective surface, the frame 50 may be formed of a conductive material to maintain continuity of the reflected potential of adjacent panels via the support 25. When the panel 10 includes a metasurface, electrical connection between adjacent panels 10 is not required.

[0019] 4 shows a configuration example in which a top frame 57 and a bottom frame 58 are provided in the electromagnetic wave reflecting soundproofing device 60 of FIG. The frame 50, the top frame 57, and the bottom frame 58 form a frame that holds the entire periphery of the panel 10. The frame 50 may also be called a "side frame" because of its positional relationship with the top frame 57 and the bottom frame 58. The provision of the top frame 57 and the bottom frame 58 ensures mechanical strength and safety when the panel 10 is transported and assembled to the support 25.

[0020] When the entire periphery of the panel 10 is held by the frame 50, the top frame 57, and the bottom frame 58, the portion of the panel 10 exposed from the frame 50, the top frame 57, and the bottom frame 58 becomes an effective reflective surface. The top frame 57 may be configured so that another panel 10 can be connected to the top end of the panel 10. This increases the degree of freedom in the height of the electromagnetic wave reflecting soundproof fence. For example, if the posts 25 are installed at intervals of 2 m, a 3-m-tall electromagnetic wave reflecting soundproof fence can be constructed by arranging three panels each measuring 1 m long x 2 m wide in the height direction (Y direction).

[0021] <Layer Structure of Panel> Figure 5 shows an example of the layer structure of panel 10. The layer structure in Figure 5 is the structure in the thickness (Z) direction of panel 10. Panel 10 includes a conductive layer 11, a dielectric substrate 14 bonded to one surface of conductive layer 11 via adhesive layer 12, and a dielectric substrate 15 bonded to the other surface of conductive layer 11 via adhesive layer 13. Dielectric substrates 14 and 15 are transparent dielectric plates with low dielectric constants and dielectric loss tangents at high frequencies, such as polycarbonate, acrylic resin, cycloolefin polymer (COP), polyethylene terephthalate (PET), fluororesin, or chemically strengthened glass. Dielectric substrates 14 and 15 have a specific gravity of 1.10 or greater, preferably 1.20 or greater. If a resin plate is used, a glass filler may be added.

[0022] The dielectric substrates 14 and 15 may have the same thickness or different thicknesses, but to ensure sound insulation, the dielectric substrates 14 and 15 used in the panel 10 are designed to have a total thickness of 10.0 mm or more. When the dielectric substrates 14 and 15 have different thicknesses, the thinner one is used facing the road 20 (see FIG. 1 ). By facing the thinner dielectric substrate toward the road 20, electromagnetic waves are reflected toward vehicles 31 on the road 20 and noise on the road 20 is prevented from leaking outside the road 20.

[0023] The conductive layer 11 is a surface that forms the reflective surface of the panel 10 and is formed of a metal mesh, a periodic pattern, a geometric pattern, a transparent conductive film, or the like. As an example, the conductive layer 11 includes a metal mesh formed of a good conductor such as Cu, Ni, SUS, or Ag. When a metasurface is included as part of the panel 10, the conductive layer 11 may include a pattern including 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 as to function satisfactorily as a reflective surface that reflects electromagnetic waves of a target frequency in a designed direction.

[0024] The adhesive layer 12 has a transmittance of 60% or more, preferably 70% or more, and more preferably 80% or more for the operating frequency so that electromagnetic waves incident from the road 20 can reach the conductive layer 11 quickly. The adhesive layer 12 has a relative permittivity and dielectric loss tangent suitable for achieving the desired reflection characteristics of 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. To provide the adhesive layers 12 and 13 with durability and moisture resistance sufficient for outdoor use, ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP) may be used. When using EVA, the specific gravity may be increased by increasing the vinyl acetate (VA) content. The thickness of the adhesive layers 12 and 13 is sufficient to reliably adhere and hold the dielectric substrates 14 and 15 to the conductive layer 11, and is, for example, 10 μm or more and 500 μm or less.

[0025] A protective layer for UV protection, waterproofing, or water repellency may be provided on the outer surface of at least one of the dielectric substrates 14 and 15. In the case of a protective film for UV protection, a protective coating containing a UV absorber may be applied. Examples of UV absorbers that may be used include benzotriazole-based, benzophenone-based, triazine-based, and hydroxyphenyltriazine-based UV absorbers. In the case of a protective film for UV protection, the protective film may be provided at the interface between the dielectric substrate 14 or 15 and the adhesive layer 12 or 13 instead of on the outer surface of the dielectric substrate 14 or 15. The thickness of the protective layer is preferably such that it functions as a protective layer while not impairing the transparency of the panel 10, and is, for example, 5 μm to 15 μm, preferably 10 μm plus or minus several microns.

[0026] <Frame Configuration Example> FIG. 6 is a cross-sectional view of a frame 50A used in an electromagnetic wave reflecting soundproofing device 60. This cross-section is perpendicular to the longitudinal center axis of the frame 50A. The frame 50A has a conductive main body 51A, a space 53 formed in the main body 51A, and a slit 52 connecting to the space 53. The main body 51A is formed of a light metal such as aluminum, but if the panel 10 includes a metasurface, it may be formed of plastic, ceramics, or the like. The width of the slit 52 is determined according to the thickness of the panel 10. The side edges of the panel 10 are inserted into the slit 52 and held within the space 53. Providing the space 53 reduces the weight of the main body 51A of the frame 50A and allows for a more flexible holding angle for the panel 10. If the thickness of the frame 50A needs to be as close as possible to the thickness of the panel 10, the space 53 can be made smaller, or only the slit 52 can be formed in the main body 51A. As shown in FIG. 4, when the panel 10 is provided with a top frame 57 and a bottom frame 58, the top frame 57 and the bottom frame 58 may have the same cross-sectional configuration as the frame 50A.

[0027] FIG. 7 is a schematic diagram of an electromagnetic wave reflecting sound insulation device 60A supported by a support 25. The electromagnetic wave reflecting sound insulation device 60A includes a panel 10 and a frame 50A that supports the side edges of the panel 10. As described above, the panel 10 is a transparent panel that reflects electromagnetic waves in a predetermined frequency band between 1 GHz and 300 GHz and has a thickness sufficient to achieve a predetermined sound insulation performance. The thickness of the panel 10 is 10.0 mm or more and 20.0 mm or less, depending on the materials of the dielectric substrates 14 and 15 used. The dielectric substrate bonded to the surface of the conductive layer 11 opposite the road 20 side of the dielectric substrate 14 or 15 does not need to be a single plate, but may be a laminate of two or more dielectric sheets or plates. This increases the thickness and improves sound insulation. If necessary, the dielectric substrate on the side facing the road 20 may be a laminate of two or more dielectric sheets or plates.

[0028] A frame 50A that holds the panel 10 is fitted into one groove of a support 25 made of H-shaped steel. If the two dielectric substrates 14 and 15 (see FIG. 5 ) that sandwich the conductive layer 11 of the panel 10 have different thicknesses, an electromagnetic wave reflecting sound-insulating device 60A is attached to the support 25 so that the thinner dielectric substrate faces the road 20. A frame 50A of another electromagnetic wave reflecting sound-insulating device 60A is fitted into the other groove of the support 25. In this way, a continuous electromagnetic wave reflecting sound-insulating fence is constructed along the road 20.

[0029] FIG. 8 is a cross-sectional view of a frame 50B used in an electromagnetic wave reflecting soundproofing device 60. This cross-section is perpendicular to the longitudinal center axis of the frame 50B. The frame 50B has a conductive main body 51B, a space 53 formed in the main body 51B, a slit 52 connected to the space 53, and a groove 54 facing the slit 52 across the space 53. The widths of the slit 52 and the groove 54 are determined based on the thickness of the panel 10. The side edges of the panel 10 are inserted from the slit 52 through the space 53 to the groove 54 and held therein. The provision of the space 53 allows the weight of the main body 51B of the frame 50B to be reduced. The provision of the groove 54 allows the panel 10 to be held more stably. When a top frame 57 and a bottom frame 58 are provided on the panel 10 as shown in FIG. 4, the top frame 57 and the bottom frame 58 may have the same cross-sectional configuration as the frame 50B or the same cross-sectional configuration as the frame 50A shown in FIG. 6.

[0030] FIG. 9 is a schematic diagram of an electromagnetic wave reflecting sound-insulating device 60B supported by a support post 25. The electromagnetic wave reflecting sound-insulating device 60B includes a panel 10 and a frame 50B that holds the side edge of the panel 10. The panel 10 is the same panel as described with reference to FIG. 7. The frame 50B that holds the panel 10 is fitted into one groove of the support post 25, which is made of H-shaped steel. The electromagnetic wave reflecting sound-insulating device 60B is attached to the support post 25 so that the thinner sides of the two dielectric substrates 14 and 15 (see FIG. 5) that sandwich the conductive layer 11 of the panel 10 face toward the road 20. The frame 50B of another electromagnetic wave reflecting sound-insulating device 60B is fitted into the other groove of the support post 25, thereby constructing a continuous electromagnetic wave reflecting sound-insulating fence along the road 20.

[0031] 10 is a schematic diagram showing yet another modified example of the frame and how it is fixed to a support pole. The electromagnetic wave reflecting soundproofing device 60C includes a panel 10 and a frame 50C that holds the side edges of the panel 10. The frame 50C includes a main body 51C with a flange 55, a space 53 formed in the main body 51C, and a slit 52 that communicates with the space 53. The side edges of the panel 10 are inserted into and held in the slit 52 of the frame 50C. The electromagnetic wave reflecting soundproofing device 60 is attached to the support pole 25 so that the thinner of the two dielectric substrates that sandwich the conductive layer 11 of the panel faces the road.

[0032] Bolt holes are pre-formed in the flange 55 of the main body 51C of the frame 50C, and the frame 50C is fixed to the support posts 25 with bolts 26. This configuration is advantageous because it allows the electromagnetic wave reflecting and soundproofing device 60C to be assembled at the desired height from the road 20 side. In the configuration of Figure 10, the outer surface of the frame 50C protrudes outside the support posts 25. Therefore, if the frame 50C is made of metal, an insulating layer 56 may be provided on at least the outer surface facing the road 20. The insulating layer 56 can be formed by powder coating, solvent coating, anodizing, or the like. This prevents diffuse reflection of incident electromagnetic waves on the metal surface. The electromagnetic wave reflecting function and soundproofing function of the panel 10 are as described above.

[0033] In all of the frames 50A, 50B, and 50C, the edges of the panels 10 are inserted into the slits 52 and are not exposed, thereby suppressing scattering at the edges. Frames 50B and 50C may be combined to provide grooves 54 facing the slits 52 in the internal space of the frame with flanges 55. In this case, too, it is desirable to provide an insulating layer on at least the outer surface of the frame facing the road to prevent scattering.

[0034] Below, electromagnetic wave reflecting sound insulating devices 60 are designed under different conditions, and the radio wave environment improvement effect and sound insulating effect are confirmed. 28.2 GHz 5G base stations 30 (see FIG. 1 ) are installed at intervals of 200.0 m on a 15.0 m wide expressway. Support posts 25 are installed at 2.0 m intervals on the roadside shoulder of the road. Electromagnetic wave reflecting sound insulating devices 60 designed under different conditions are attached to the support posts 25, an electromagnetic wave reflecting sound insulating fence is installed, and the received power in the blind zone of the road 20 after the electromagnetic wave reflecting sound insulating fence is installed and the sound transmission loss specified in JIS A 1416 are measured in the space outside the electromagnetic wave reflecting sound insulating fence as viewed from the road 20.

[0035] Example 1 Example 1 is Example 1. Polycarbonate plates measuring 1.0 m in length and 2.0 m in width were used as dielectric substrates 14 and 15. The specific gravity of the polycarbonate used was 1.20. One polycarbonate plate was 2.0 mm thick, and the other was 8.0 mm thick, for a total polycarbonate thickness of 10.0 mm. A 100 μm thick stainless steel mesh was sandwiched between these two polycarbonate plates as conductive layer 11. Panel 10 was fabricated by bonding the polycarbonate plates to both sides of the stainless steel mesh using 400 μm thick ethylene vinyl acetate (EVA) adhesive layers 12 and 13. Both side edges and the top and bottom edges of panel 10 were held by frame 50A shown in FIG. 6 to fabricate electromagnetic wave reflecting soundproofing device 60A. This electromagnetic wave reflecting soundproofing device 60 is attached to a support 25 so that the 2.0 mm thick polycarbonate plate faces the road. Three layers of electromagnetic wave reflecting soundproofing devices 60A are stacked vertically to install an electromagnetic wave reflecting soundproofing fence 3.0 m high over a length of 200 m.

[0036] When the received power was measured in an area that had been a dead zone behind the equipment on road 20, it was found that the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, had improved to -100 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 29 dB at 400 Hz and 32 dB at 1000 Hz was confirmed.

[0037] Example 2 Example 2 is Example 2. The conditions are the same as Example 1, except that the thicknesses of the two dielectric substrates are different. Two polycarbonate plates, each 5.0 mm thick, 1.0 m long, and 2.0 m wide, are used as dielectric substrates 14 and 15. A 400 μm thick EVA sheet with a 100 μm thick stainless steel mesh sandwiched between the two polycarbonate plates forms a panel 10. The total thickness of the panel 10 is 10.9 mm, the same as in Example 1. The two side edges, top edge, and bottom edge of the panel 10 are held by the frame 50A shown in FIG. 6 to form an electromagnetic wave reflecting soundproofing device 60A. This electromagnetic wave reflecting soundproofing device 60 is attached to supports 25, and an electromagnetic wave reflecting soundproofing fence 3.0 m high and 200 m long is installed.

[0038] When the received power was measured in an area that had been a dead zone behind the equipment on road 20, it was found that the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, had improved to -105 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 28 dB at 400 Hz and 31 dB at 1000 Hz was confirmed.

[0039] Example 3 Example 3 is a third embodiment. In Example 3, a powder-coated frame 50C (see FIG. 10) is used. As in Example 1, a 2.0 mm thick, 1.0 m long, and 2.0 m wide polycarbonate plate and an 8.0 mm thick, 1.0 m long, and 2.0 m wide polycarbonate plate are used as dielectric substrates 14 and 15. A 100 μm thick stainless steel mesh is sandwiched between these two polycarbonate plates with a 400 μm thick EVA layer to produce a panel 10. The two side edges, top edge, and bottom edge of the panel 10 are held by a partially powder-coated frame 50C to produce an electromagnetic wave reflecting soundproofing device 60C. At least the outer surface of the frame 50C facing the road is powder-coated with an insulating material. The electromagnetic wave reflecting soundproofing device 60C is attached to the support 25 so that the flange 55 of the frame 50C and the thinner polycarbonate plate of the panel 10 face the road side, and an electromagnetic wave reflecting soundproofing fence 3.0 m high is installed over a length of 200 m.

[0040] When the received power was measured in an area behind equipment on road 20 that had been a dead zone, it was found to have improved from -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence to -95 dBm. By powder coating a portion of frame 50C with an insulating material, power loss due to scattering has been suppressed. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 30 dB at 400 Hz and 32 dB at 1000 Hz was confirmed.

[0041] Example 4 Example 4 is a fourth embodiment. In Example 4, an anodized aluminum frame 50C is used. As in Example 1, a 2.0 mm thick, 1.0 m long, and 2.0 m wide polycarbonate plate and an 8.0 mm thick, 1.0 m long, and 2.0 m wide polycarbonate plate are used as the dielectric substrates 14 and 15. A 100 μm thick stainless steel mesh is sandwiched between these two polycarbonate plates with a 400 μm thick EVA layer to produce a panel 10. The two side edges, top edge, and bottom edge of the panel 10 are held by a partially anodized aluminum frame 50C to produce an electromagnetic wave reflecting soundproofing device 60C. At least the outer surface of the frame 50C facing the road is anodized. The electromagnetic wave reflecting soundproofing device 60C is attached to the support 25 so that the flange 55 of the frame 50C and the thinner polycarbonate plate of the panel 10 face the road side, and an electromagnetic wave reflecting soundproofing fence 3.0 m high is installed over a length of 200 m.

[0042] When the received power was measured in an area behind equipment on road 20 that had been a dead zone, it was found to have improved from -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence to -95 dBm. By anodizing a portion of frame 50C, power loss due to scattering has been suppressed. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 30 dB at 400 Hz and 32 dB at 1000 Hz was confirmed.

[0043] Example 5 Example 5 is Example 5. Polycarbonate plates measuring 1.0 m in length and 2.0 m in width are used as dielectric substrates 14 and 15. One polycarbonate plate is 3.0 mm thick, and the other is 8.0 mm thick. A 100 μm thick stainless steel mesh is sandwiched between these two polycarbonate plates as the conductive layer 11. The polycarbonate plates are bonded to both sides of the stainless steel mesh using 400 μm thick ethylene vinyl acetate (EVA) adhesive layers 12 and 13 to produce a panel 10. The two side edges, top edge, and bottom edge of the panel 10 are held by the frame 50A shown in FIG. 6 to produce an electromagnetic wave reflecting soundproofing device 60A. This electromagnetic wave reflecting soundproofing device 60 is attached to a support 25 with the 3.0 mm thick polycarbonate plate facing the road. The electromagnetic wave reflecting sound insulating devices 60A are stacked in three stages in the height direction, and an electromagnetic wave reflecting sound insulating fence 3.0 m high is installed over a length of 200 m.

[0044] When the received power was measured in an area that had been a dead zone behind the equipment on road 20, it was found that the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, had improved to -100 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 30 dB at 400 Hz and 32 dB at 1000 Hz was confirmed.

[0045] Example 6 Example 6 is Example 6. Flame-retardant acrylic plates measuring 1.0 m in length and 2.0 m in width were used as dielectric substrates 14 and 15. The specific gravity of the acrylic plates used was 1.19. One acrylic plate was 3.0 mm thick, and the other was formed by laminating a 3.0 mm acrylic plate and a 5.0 mm acrylic plate. A 100 μm thick stainless steel mesh was sandwiched between the 3.0 mm thick acrylic plate and the 8.0 mm thick laminated acrylic plate as the conductive layer 11. Acrylic plates were bonded to both sides of the acrylic plate and both sides of the stainless steel mesh using 400 μm thick ethylene vinyl acetate (EVA) adhesive layers 12 and 13 to produce a panel 10. The two side edges, top and bottom edges of the panel 10 were held by the frame 50A shown in FIG. 6 to produce an electromagnetic wave reflecting soundproofing device 60A. This electromagnetic wave reflecting soundproofing device 60 is attached to the support 25 so that the 3.0 mm thick acrylic plate faces the road. Three layers of electromagnetic wave reflecting soundproofing devices 60A are stacked vertically to install a 3.0 m high electromagnetic wave reflecting soundproofing fence over a length of 200 m.

[0046] When the received power was measured in an area that had been a dead zone behind the equipment on road 20, it was found that the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, had improved to -100 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 29 dB at 400 Hz and 32 dB at 1000 Hz was confirmed.

[0047] Example 7 Example 7 is Example 7. Two chemically strengthened glass plates, each 1.0 m long, 2.0 m wide, and 6.0 mm thick, were used as dielectric substrates 14 and 15. The specific gravity of the chemically strengthened glass plates used was 2.50. A 100 μm thick stainless steel mesh was sandwiched between these two chemically strengthened glass plates as the conductive layer 11. The chemically strengthened plates were bonded to both sides of the stainless steel mesh using 400 μm thick ethylene vinyl acetate (EVA) adhesive layers 12 and 13 to produce a panel 10. The side edges, top edge, and bottom edge of the panel 10 were held by the frame 50A shown in FIG. 6 to produce an electromagnetic wave reflecting sound insulating device 60A. This electromagnetic wave reflecting sound insulating device 60A was attached to supports 25. Three layers of the electromagnetic wave reflecting sound insulating devices 60A were stacked vertically to install a 3.0 m high electromagnetic wave reflecting sound insulating fence spanning 200 m.

[0048] When the received power was measured in an area that had been a dead zone behind the equipment on road 20, it was found that the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, had improved to -100 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, sound insulation of 30 dB at 400 Hz and 32 dB at 1000 Hz was confirmed.

[0049] Example 8 Example 8 is Comparative Example 1. In Example 8, a single polycarbonate plate with a thickness of 10.0 mm, a length of 1.0 m, and a width of 2.0 m was used as the panel. This panel did not have a conductive layer 11 and did not have electromagnetic wave reflection functionality. The two side edges, top edge, and bottom edge of this panel were held by the frame 50A shown in FIG. 6 to prepare a sound insulation device. This sound insulation device was attached to supports 25, and a 3.0 m high sound insulation fence was installed over a length of 200 m.

[0050] When the received power was measured in an area behind the equipment on the road 20 that had been a blind zone, it was found to be the same received power of -120 dBm as the received power before the electromagnetic wave reflecting sound insulation fence was installed. When the sound transmission loss was measured in the space outside the electromagnetic wave reflecting sound insulation fence, sound insulation of 29 dB at 400 Hz and 32 dB at 1000 Hz was confirmed. The sound insulation fence of Example 8 transmits high-frequency electromagnetic waves used in the wireless transmission system 1. Not only does the sound insulation fence of Example 8 fail to improve the radio wave environment on the road 20, but it also causes electromagnetic waves from the base station 30 to leak outside the road 20, causing interference with radio waves in other frequency bands.

[0051] [Example 9] Example 9 is Comparative Example 2. In Example 9, a single polycarbonate plate with a thickness of 5.0 mm, a length of 1.0 m, and a width of 2.0 m is used as the panel. The thickness of the panel is half that of Example 8. In Example 9, the panel also does not have a conductive layer 11 and does not have an electromagnetic wave reflection function. A sound-insulating device is fabricated by holding both side edges, the top edge, and the bottom edge of the panel with the frame 50A shown in Figure 6. This sound-insulating device is attached to supports 25, and a 3.0 m high sound-insulating fence is installed over a length of 200 m.

[0052] When the received power was measured in an area behind the equipment on road 20 that had been a blind zone, it was found to be the same received power of -120 dBm as the received power before the electromagnetic wave reflecting sound insulation fence was installed. When the sound transmission loss was measured in the space outside the sound insulation fence, sound insulation of 20 dB at 400 Hz and 25 dB at 1000 Hz was confirmed. In the sound insulation fence of the comparative example, the high-frequency electromagnetic waves used in wireless transmission system 1 are transmitted through the sound insulation fence of Example 9. The sound insulation fence of Example 9 not only fails to improve the radio wave environment on road 20, but also fails to meet the sound insulation standards specified in JIS A 1416, which are 25 dB or more at 400 Hz and 30 dB or more at 1000 Hz.

[0053] Example 10 is Comparative Example 3. In Example 10, a 1.0 m long, 2.0 m wide panel made of aluminum angle iron welded together is used as the sound-insulating panel. The two side edges, top edge, and bottom edge of this panel are held by the frame 50A shown in FIG. 6 to prepare a sound-insulating device. This sound-insulating device is attached to the support posts 25, and a 3.0 m high sound-insulating fence is installed over a length of 200 m.

[0054] When the received power was measured in an area behind the equipment on the road 20 that had become a dead zone, it was -119 dBm, almost unchanged from the received power of -120 dBm before the installation of the electromagnetic wave reflective soundproof fence. The panel of Example 10 is a metal panel, and although some reflection occurs, most of it is scattered or diffused, resulting in a large loss of power and preventing radio waves emitted from the base station 30 from reaching the dead zone. When the sound transmission loss was measured in the space outside the soundproof fence, sound insulation of 29 dB at 400 Hz and 32 dB at 1000 Hz was confirmed. The soundproof fence of Example 10 meets the sound insulation standards specified in JIS A 1416, but is unable to improve the radio wave environment on the road 20. Furthermore, the panel is not transparent, resulting in poor visibility.

[0055] Example 11 Example 11 corresponds to Comparative Example 4. Polycarbonate plates measuring 1.0 m in length and 2.0 m in width were used as dielectric substrates 14 and 15. One polycarbonate plate was 3.0 mm thick, and the other was 6.0 mm thick. A 100 μm thick stainless steel mesh was sandwiched between these two polycarbonate plates as conductive layer 11. The polycarbonate plates were bonded to both sides of the stainless steel mesh using 400 μm thick ethylene vinyl acetate (EVA) adhesive layers 12 and 13 to produce panel 10. Both side edges and the top and bottom edges of panel 10 were held by frame 50A (see FIG. 6 ) to produce electromagnetic wave reflecting soundproofing device 60A. This electromagnetic wave reflecting soundproofing device 60 was attached to support posts 25 with the 3.0 mm thick polycarbonate plate facing the road. The electromagnetic wave reflecting sound insulating devices 60A are stacked in three stages in the height direction, and an electromagnetic wave reflecting sound insulating fence 3.0 m high is installed over a length of 200 m.

[0056] When the received power was measured in an area behind the equipment on road 20 that had been a dead zone, the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, improved to -100 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, it did not meet the sound insulation standards specified in JIS A 1416, which are 25 dB or more at 400 Hz and 30 dB or more at 1000 Hz. Compared to Examples 1 and 5, this is thought to be due to an insufficient total thickness of the polycarbonate plate.

[0057] Example 12 Example 12 corresponds to Comparative Example 5. Flame-retardant acrylic plates measuring 1.0 m in length and 2.0 m in width were used as dielectric substrates 14 and 15. One acrylic plate was 3.0 mm thick, and the other acrylic plate was formed by laminating two 3.0 mm-thick acrylic plates. A 100 μm-thick stainless steel mesh was sandwiched between the 3.0 mm-thick acrylic plate and the 6.0 mm-thick laminated acrylic plate as the conductive layer 11. Acrylic plates were bonded to both sides of the acrylic plate and both sides of the stainless steel mesh using 400 μm-thick ethylene vinyl acetate (EVA) adhesive layers 12 and 13 to produce a panel 10. Both side edges, top and bottom edges of the panel 10 were held by the frame 50A shown in FIG. 6 to produce an electromagnetic wave reflecting soundproofing device 60A. This electromagnetic wave reflecting soundproofing device 60 was attached to a support 25 with the 3.0 mm-thick acrylic plate facing the road. The electromagnetic wave reflecting sound insulating devices 60A are stacked in three stages in the height direction, and an electromagnetic wave reflecting sound insulating fence 3.0 m high is installed over a length of 200 m.

[0058] When the received power was measured in an area behind the equipment on road 20 that had been a dead zone, the received power, which was -120 dBm before the installation of the electromagnetic wave reflective sound insulation fence, improved to -100 dBm. When the sound transmission loss was measured in the space outside the electromagnetic wave reflective sound insulation fence, it did not meet the sound insulation standards specified in JIS A 1416, which are 25 dB or more at 400 Hz and 30 dB or more at 1000 Hz. Compared to Example 6, this is thought to be due to an insufficient total thickness of the acrylic plate.

[0059] The results of Examples 1 to 12 show that the electromagnetic wave reflective sound-insulating device 60, which includes a conductive layer 11 on the panel 10 that selectively reflects electromagnetic waves in a predetermined frequency band, improves received power by at least 20 dBm in blind zones. To provide the electromagnetic wave reflective sound-insulating device 60 with sound insulation of 25 dB or more at 400 Hz and 30 dB or more at 1000 Hz, the total thickness of the dielectric substrate used in the panel 10 must be 10.0 mm or more. Taking into account ease of transporting the electromagnetic wave reflective sound-insulating device 60 and attaching it to the support 25, the total thickness of the dielectric substrate may be 20.0 mm or less. This achieves an electromagnetic wave reflective sound-insulating device 60 that simultaneously improves the radio wave propagation environment and provides sound insulation or soundproofing. The wireless transmission system 1 using the electromagnetic wave reflective sound-insulating device 60 improves the radio wave environment on the road 20 and suppresses the emission of electromagnetic waves and noise outside the road 20.

[0060] The size of the panel 10 of the electromagnetic wave reflecting soundproofing device 60 can be designed according to the height and spacing of the support posts 25. To achieve a total thickness of 10.0 mm or more, one or both of the two dielectric substrates 14 and 15 may be formed by laminating two or more dielectric sheets or plates. The specific gravity of the dielectric sheet or plate is 1.10 or more, preferably 1.20 or more. By increasing the thickness of the dielectric substrate located outside the conductive layer 11 as viewed from the road 20, the soundproofing effect may be enhanced while maintaining the electromagnetic wave reflecting effect. The electromagnetic wave reflecting soundproofing device 60 of the embodiment can be installed not only on roads, but also on railway tracks, factory production lines, construction sites, outdoor concert halls, and the like.

[0061] The embodiments of the present disclosure have been described above, but the present disclosure may also include the following configurations. (Item 1) An electromagnetic wave reflecting sound-insulating device comprising: a panel in which a conductive layer that reflects electromagnetic waves in a predetermined frequency band of 1 GHz to 300 GHz is sandwiched between two dielectric substrates that are transparent to visible light; and a frame that holds at least both side edges of the panel, wherein the total thickness of the two dielectric substrates is 10.0 mm or more. (Item 2) The electromagnetic wave reflecting sound-insulating device according to Item 1, in which the frame holds both side edges, an upper edge, and a lower edge of the panel. (Item 3) The electromagnetic wave reflecting sound-insulating device according to claim 1 or 2, in which the two dielectric substrates have the same or different thicknesses. (Item 4) The electromagnetic wave reflecting sound-insulating device according to Item 3, in which one or both of the two dielectric substrates are formed by bonding two or more dielectric plates together. (Item 5) The electromagnetic wave reflecting sound insulating device according to any one of Items 1 to 4, wherein at least one of the two dielectric substrates has a protective layer containing an ultraviolet absorber provided on its surface. (Item 6) The electromagnetic wave reflecting sound insulating device according to any one of Items 1 to 5, wherein the frame has a main body, a space formed inside the main body, and a slit communicating with the space, and the panel is inserted into the slit. (Item 7) The electromagnetic wave reflecting sound insulating device according to Item 6, wherein the frame has a groove facing the slit across the space, and the panel is inserted from the slit to the groove. (Item 8) The electromagnetic wave reflecting sound insulating device according to Item 6 or 7, wherein the main body of the frame has a flange protruding in the opposite direction to the slit, and an insulating layer is provided covering at least a portion of the surface of the main body. (Item 9) A wireless transmission system comprising: posts installed at regular intervals along a linearly extending site; an electromagnetic wave reflective sound-proofing device according to any one of items 1 to 8 attached to the posts; and a base station that transmits the electromagnetic waves in the predetermined frequency band toward the site, wherein the frame of the electromagnetic wave reflective sound-proofing device is attached to the posts and the electromagnetic wave reflective sound-proofing device is supported between two adjacent posts.(Item 10) The wireless transmission system according to Item 9, wherein a plurality of electromagnetic wave reflective sound-proofing devices are arranged in the height direction between the two support pillars, and the electromagnetic waves transmitted from the base station are incident on the electromagnetic wave reflective sound-proofing devices at a position lower than the top of the effective reflection surface of the panel.

[0062] This international application claims priority based on Japanese Patent Application No. 2023-105882, filed on June 28, 2023, the entire contents of which are incorporated herein by reference.

[0063] REFERENCE SIGNS LIST 1 Wireless transmission system 10 Panel 11 Conductive layer 12, 13 Adhesive layer 14, 15 Dielectric substrate 20 Road 25 Support 30 Base station 31 Vehicle 50, 50A, 50B, 50C Frame 51A, 51B, 51C Body 52 Slit 53 Space 54 Groove 55 Flange 56 Insulating layer 60, 60A, 60B, 60C Electromagnetic wave reflecting sound insulating device

Claims

1. An electromagnetic wave reflecting and soundproofing device comprising: a panel in which a conductive layer that reflects electromagnetic waves in a specified frequency band of 1 GHz or more and 300 GHz or less is sandwiched between two dielectric substrates that are transparent to visible light; and a frame that holds at least both side edges of the panel, wherein the total thickness of the two dielectric substrates is 10.0 mm or more.

2. The electromagnetic wave reflecting soundproofing device according to claim 1, wherein the frame holds both side edges, an upper edge, and a lower edge of the panel.

3. The electromagnetic wave reflecting sound insulating device according to claim 1, wherein the thicknesses of the two dielectric substrates are the same or different.

4. The electromagnetic wave reflecting sound insulating device according to claim 3, wherein one or both of the two dielectric substrates are formed by bonding together two or more dielectric plates.

5. The electromagnetic wave reflecting sound insulating device according to claim 1, wherein at least one of the two dielectric substrates has a protective layer containing an ultraviolet absorbing agent provided on the surface.

6. The electromagnetic wave reflecting soundproofing device according to claim 1, wherein the frame has a main body, a space formed inside the main body, and a slit communicating with the space, and the panel is inserted into the slit.

7. The electromagnetic wave reflecting soundproofing device according to claim 6, wherein the frame has a groove facing the slit across the space, and the panel is inserted from the slit to the groove.

8. The electromagnetic wave reflecting soundproofing device according to claim 6, wherein the body of the frame has a flange that protrudes in the opposite direction to the slit, and an insulating layer is provided to cover at least a portion of the surface of the body.

9. A wireless transmission system comprising: pillars installed at regular intervals along a linearly extending site; an electromagnetic wave reflective sound-proofing device according to any one of claims 1 to 8 attached to the pillars; and a base station that transmits the electromagnetic waves in the specified frequency band toward the site, wherein the frame of the electromagnetic wave reflective sound-proofing device is attached to the pillars and the electromagnetic wave reflective sound-proofing device is supported between two adjacent pillars.

10. The wireless transmission system according to claim 9, wherein a plurality of electromagnetic wave reflective sound-proofing devices are arranged in the vertical direction between the two pillars, and the electromagnetic waves transmitted from the base station are incident on a position lower than the uppermost end of the effective reflective surface of the panel of the electromagnetic wave reflective sound-proofing device.