TW202410553A - Reflective panel, electromagnetic wave reflection device, and electromagnetic wave reflection fence - Google Patents

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. The reflective panel comprises: an electrically conductive layer that has an electrically conductive pattern that reflects electromagnetic waves in a predetermined frequency band of 1-300 GHz; a dielectric layer that is bonded to at least one surface of the electrically conductive layer with an adhesive layer interposed therebetween; and a protective layer that includes an ultraviolet absorber, said protective layer being provided on the surface of the dielectric layer that is on the opposite side from the adhesive layer, wherein the ratio of the thickness of the dielectric layer to the thickness of the protective layer is 66-1600.

Description

Reflector, electromagnetic wave reflecting device and electromagnetic wave reflecting grid

The invention relates to a reflecting plate, an electromagnetic wave reflecting device and an electromagnetic wave reflecting grating.

The introduction of wireless base stations into indoor and outdoor environments is developing for the purpose of realizing automation of manufacturing processes or office work, remote operation, AI (Artificial Intelligence) control/management, and autonomous driving. In addition to indoor environments such as factories, workshops, offices, and commercial facilities, or outdoor environments such as highways and railway lines, wireless base stations are also introduced in settings that are not divided into indoor and outdoor environments, such as medical sites or event venues.

The fifth generation mobile communication standard (hereinafter referred to as "5G") provides a frequency band below 6 GHz, called "sub-6", and a 28 GHz band classified as a millimeter wave band. In the next generation 6G mobile communication standard, it is expected to be expanded to sub-THz. By using such a high-frequency bandwidth, the communication bandwidth is greatly expanded, and a large amount of data communication can be carried out with low latency. A structure in which an electromagnetic reflection device is arranged along at least a portion of a manufacturing line is proposed (for example, refer to patent document 1). [Prior art document] [Patent document]

Patent Document 1: International Publication No. 2021/199504

[The problem the invention is trying to solve]

By using electromagnetic reflection devices, the communication environment can be improved in wireless communication systems that use radio waves with strong linearity. 5G use cases are found both indoors and outdoors. When an electromagnetic wave reflection device is used in an outdoor environment or an indoor environment close to the outdoors, the reflection plate may be deformed or discolored due to ultraviolet rays, temperature changes, humidity, etc., and the reflection characteristics may deteriorate. When an electromagnetic wave reflection device is used as a safety barrier or soundproof wall, if the transmittance of visible light is reduced, visibility and safety will be reduced, and the device will deviate from the original specifications. The inventor confirmed that when the reflective plate with the conductive layer sandwiched between the resin substrate deforms by about 10%, it will adversely affect the reflection direction and reflection efficiency. It was further discovered that the relative dielectric constant of the resin substrate changes due to ultraviolet irradiation, and the designed reflection direction and reflection efficiency cannot be obtained. In order to use electromagnetic wave reflecting devices outdoors or in environments close to the outdoors, it is required to improve the weather resistance of the reflecting plates.

One object of the present invention is to provide a reflective plate with improved weather resistance, an electromagnetic wave reflection device and an electromagnetic wave reflection system using the same. [Technical means to solve problems]

In one embodiment, the reflective plate has: A conductive layer having a conductive pattern that reflects electromagnetic waves in a prescribed frequency band above 1 GHz and below 300 GHz; A dielectric layer bonded to at least one surface of the conductive layer via an adhesive layer; and A protective layer comprising an ultraviolet absorber disposed on the surface of the dielectric layer opposite to the adhesive layer; and The ratio of the thickness of the dielectric layer to the thickness of the protective layer is not less than 66 and not more than 1600. [Effects of the invention]

A reflector with improved weather resistance, an electromagnetic wave reflection device using the reflector, and an electromagnetic wave reflection system are provided.

In an implementation form, a wireless transmission system for use indoors and outdoors, and an electromagnetic wave reflecting plate used in the wireless transmission system are provided. When referred to as "indoors and outdoors", it includes indoor, outdoor, and close to outdoor environments. "Close to outdoor environments" means spaces connecting indoors and outdoors, such as terraces, arcades, balconies, or indoor spaces near glass, plastic, etc. that transmit electromagnetic waves. When constructing a wireless transmission system using local 5G radio waves in an outdoor or close to outdoor environment, it is necessary to consider both improving the radio wave propagation environment and preventing the radio waves from flying out. In addition, there is a demand to improve the weather resistance of the electromagnetic wave reflecting plate and maintain the reflection efficiency after a long time.

If the focus is only on suppressing radio waves from escaping to the outside, it may be considered to cover the inner surface with an electromagnetic wave absorber like the brackets of ETC (Electronic Toll Collection: Electronic Toll Collection) on toll roads. However, it is not practical to cover all the walls of roads or facilities with radio wave absorbers. Originally, electromagnetic wave absorbers alone cannot reduce dead zones and improve the radio wave propagation environment. In order to reduce dead zones and improve the radio wave propagation environment, electromagnetic wave reflection devices are more effective. However, considering the actual conditions of indoor and outdoor use and preventing radio waves from flying out, the electromagnetic wave reflection device needs to be arranged on the base station antenna in an optimal positional relationship. On the other hand, when used outdoors or in an environment close to the outdoors, it is especially necessary to increase the mechanical strength of the reflective plate used in the electromagnetic wave reflection device and improve the weather resistance.

In an embodiment, a wireless transmission system, a reflecting plate, and an electromagnetic wave reflecting device that meet these requirements are provided. Hereinafter, the structure of the wireless transmission system, the reflector plate, and the electromagnetic wave reflection device using the reflector plate according to the embodiment will be described with reference to the drawings. The forms shown below are examples for embodying the technical idea of the present invention and do not limit the present invention. In order to facilitate understanding of the invention, the sizes and positional relationships of the components shown in the drawings are sometimes exaggerated. In the following description, the same components or functions are given the same names or symbols, and repeated explanations are omitted.

<Wireless transmission system> FIG. 1 is a schematic diagram of a wireless transmission system 1 in an implementation form. The wireless transmission system 1 can be installed indoors or outdoors, but in the implementation form, the weather resistance in an outdoor or near-outdoor environment is particularly improved. The wireless transmission system 1 includes: a base station 33, which performs wireless communication in a specified frequency band of 1 GHz to 300 GHz, for example, 1 GHz to 170 GHz; and an electromagnetic wave reflecting device 60, which has a reflecting plate that reflects electromagnetic waves of the frequency of the base station 33, and is installed along the length direction of an area extending relatively long in a certain direction within the communication area of the base station 33. In FIG. 1, as an example of an outdoor environment, it is considered that the road 32 is set as the wireless environment of the communication area. In the coordinate system of Figure 1, the length direction of the road 32 is set as the X direction, the width direction is set as the Y direction, and the direction perpendicular to the road surface is set as the Z direction. Multiple vehicles 31 are traveling on the road 32. The vehicle 31 can be a vehicle with an automatic driving function or a semi-automatic driving function, or a vehicle without an automatic driving function. In either case, not only the mobile terminal held by the driver or the passenger also has a wireless communication function mounted on the vehicle 31 itself, but also a large amount of data is sent and received between the vehicle 31 and the control/management system.

In order to realize wireless communication between a mobile object such as a vehicle 31 and the network, a base station 33 is arranged along the road 32 . The base station 33 transmits and receives signals or data between the base station 33 and the vehicle 31 at a prescribed frequency in a frequency band ranging from 1 GHz to 170 GHz. Due to the terrain and surrounding environment of the road 32 and the presence of multiple vehicles 31 , it is difficult to directly transmit high-frequency radio waves lacking linearity from the base station 33 to each vehicle 31 . Therefore, the electromagnetic wave reflection device 60 is arranged along at least one side of the road 32 . Radio waves are a type of electromagnetic waves. Electromagnetic waves below 3 THz are generally called radio waves. Here, the communication wave transmitted from the base station 33 is called "radio wave", and the electromagnetic wave is generally called "electromagnetic wave". As will be described later, a plurality of electromagnetic wave reflection devices 60 may be connected and installed on the shoulder of the road 32 as an electromagnetic wave reflection grating.

The position of the antenna of the base station 33 may be higher or lower than the uppermost position of the electromagnetic wave reflection device 60 . When the uppermost part of the electromagnetic wave reflection device 60 is installed at a position higher than the antenna of the base station 33 , the leakage of radio waves to the outside of the road 32 can be effectively suppressed. When the uppermost position of the electromagnetic wave reflection device is lower than the antenna of the base station 33 , it is desirable that the base station 33 has an antenna with a directivity that forms a beam toward the road 32 . In addition to the directional antenna of the base station 33, by arranging the electromagnetic wave reflection device 60 along at least one side of the road 32, the radio waves from the base station 33 are effectively concentrated on the road 32, and the radio waves flying out of the road 32 are suppressed. Thereby, the received power outside the road 32 is lower than the average or median value of the received power on the road 32 .

Even if the base station 33 controls the beam shape, there are cases where other vehicles 31 interfere with LOS (Line of Sight). In this case, the electromagnetic wave reflection device 60 can reflect the radio waves from the base station 33 and transmit them to the vehicle 31 . According to 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 reflection device 60 can be set to 5.0 m or more and 300.0 m or less, and the maximum gain of the antenna of the base station 33 can be set to 5 dBi or more. Below 30 dBi. If the shortest distance from the antenna of the base station 33 to the electromagnetic wave reflection device 60 is less than 5.0 m, it will be difficult to effectively transmit the radio waves from the base station 33 to the vehicle 31 through the electromagnetic wave reflection device 60 . If it exceeds 300.0 m, which is the shortest distance from the base station 33 to the electromagnetic wave reflection device 60 , it is still difficult to transmit radio waves to the vehicle 31 via the electromagnetic wave reflection device 60 based on the maximum gain of the antenna and the linearity of the radio waves.

The size of the reflecting surface of the electromagnetic wave reflecting device 60 only needs to be a size that 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 reflection device 60 arrive at the vehicle 31 in the same phase is defined by the following equation.

Here, λ is the wavelength used, d1 is the distance from the antenna of the base station 33 to the electromagnetic wave reflecting device 60, and d2 is the distance from the electromagnetic wave reflecting device 60 to the antenna of the vehicle 31.

If the distance d1 from the antenna of the base station 33 to the electromagnetic wave reflection device 60 is 20.0 mm in the 28 GHz frequency band (wavelength is about 10.7 mm), and the distance d2 from the electromagnetic wave reflection device 60 to the vehicle 31 is 10.0 m, then the distance d2 of the electromagnetic wave reflection device 60 The size of the reflective surface only needs to be tens of centimeters on one side. On the other hand, from the perspective of using a smaller number of electromagnetic wave reflection devices 60 to form an electromagnetic wave reflection grating covering a wider reflection area, the width × length of the reflection surface of the electromagnetic wave reflection device 60 can be about 2.0 m × 4.0 m. In the embodiment, the electromagnetic wave reflecting device 60 is arranged along the road 32 such that the received power on the back side of the reflecting surface of the electromagnetic wave reflecting device 60 , that is, in the area outside the road 32 , is lower than the average or median value of the received power on the road 32 . 60.

<Electromagnetic wave reflection device and electromagnetic wave reflection grid> FIG2A is a schematic diagram of an electromagnetic wave reflection grid 100A. The electromagnetic wave reflection grid 100A is a device that connects electromagnetic wave reflection devices 60A-1, 60A-2 and 60A-3 (hereinafter collectively referred to as "electromagnetic wave reflection device 60A") having reflection plates 10A-1, 10A-2 and 10A-3 (hereinafter collectively referred to as "reflection plates 10A") with a frame 50A. The coordinate system of FIG2A is consistent with the coordinate system of FIG1, and the width or horizontal direction of the reflection plate 10 is set as the X direction, the thickness direction is set as the Y direction, and the height direction is set as the Z direction. In FIG. 2A , three electromagnetic wave reflection devices 60A are connected to form an electromagnetic wave reflection fence 100A, but the number of electromagnetic wave reflection devices 60A to be connected is appropriately determined according to the condition of the road 32.

The reflection plate 10A used in the electromagnetic wave reflection device 60A reflects electromagnetic waves between 1 GHz and below 300 GHz, for example, between 1 GHz and below 170 GHz, or between 1 GHz and below 100 GHz, or between 1 GHz and below 80 GHz. The reflective plate 10A has a layer including a conductive film as a reflective film. The conductive film has a specified conductive pattern designed according to the target reflection angle, bandwidth, etc. The conductive pattern can include periodic patterns, grid patterns, geometric patterns and other patterns, and is formed of a transparent conductive film. The reflective plate 10A has a protective layer with anti-ultraviolet function on the outermost layer.

At least a part of the reflective plate 10A may be a non-specular reflective surface with different incident angles and reflection angles of electromagnetic waves. In addition to diffusion surfaces or scattering surfaces, non-specular reflective surfaces also include artificial reflective surfaces (metasurfaces) designed to reflect radio waves in a desired direction. From the perspective of maintaining the continuity of the reflection potential, there are situations where it is desirable that the reflective plates 10A-1, 10A-2, and 10A-3 are electrically connected to each other. However, in the case of metasurfaces, adjacent reflective plates 10A may also be connected. Not electrically connected. By holding the adjacent reflection plates 10A with each other by the frame 50A, the electromagnetic wave reflection grating 100A connected in the X direction can be obtained.

In addition to the reflection plate 10A and the frame 50A, the electromagnetic wave reflection device 60A may also have legs 56 that support the frame 50A. The legs 56 allow the electromagnetic wave reflection device 60 or the electromagnetic wave reflection grid 100 to stand independently on the road surface. The leg 56 may be fixed to the road surface with screws, small screws, or the like. On the contrary, the electromagnetic wave reflection device 60 or the electromagnetic wave reflection grid 100 can also be made to stand on the road surface, and further have parts such as casters, so that it can be moved. In addition to the frame 50A, a top frame 57 for holding the upper end of the reflection plate 10 and a bottom frame 58 for holding the lower end of the reflection plate 10 may also be used. In this case, a frame is formed in which the entire circumference of the reflection plate 10A is held by the frame 50A, the top frame 57 and the bottom frame 58 . The frame 50A may also be called a "side frame" based on its positional relationship with the top frame 57 and the bottom frame 58 . By providing the top frame 57 and the bottom frame 58, the mechanical strength and safety during transportation and assembly of the reflective plate 10 are ensured. The top frame 57 may also be configured to be connected to other reflective plates, electromagnetic wave absorbing plates, and other other components at the upper end of the reflective plate 10A. Thereby, the degree of freedom in size and function of the electromagnetic wave reflection grating 100A becomes higher.

FIG. 2B is a schematic diagram of an electromagnetic wave reflection grid 100B as a variation. The electromagnetic wave reflection grid 100B is a device that connects electromagnetic wave reflection devices 60B-1, 60B-2, and 60B-3 (hereinafter collectively referred to as "electromagnetic wave reflection devices 60A") having reflection plates 10B-1, 10B-2, and 10B-3 (hereinafter collectively referred to as "reflection plates 10B") with a frame 50B. At least a portion of the reflection plate 10B includes a curved surface. In this example, the upper end side of the reflection plate 10B is bent in the Z direction. In order to hold and connect the reflection plate 10B including the curved surface, the frame 50B has a curvature corresponding to the curvature of the reflection plate 10B. The radius of curvature of the reflector 10B is determined by the width of the road 32 to which the electromagnetic wave reflecting device 60B is applied, the surrounding conditions, the thickness of the reflector 10B, the height of the electromagnetic wave reflecting device 60B, etc.

For example, when the thickness of the reflective plate 10B is 5.0 mm or more and 17.0 mm or less, and there are almost no obstacles above the road 32, the curvature radius of the reflective plate 10B can be set to 1500 mm or more and 2500 mm or less, preferably 2000 mm. mm above 2500 mm. Like the reflection plate 10A, it is desirable that the reflection plate 10B has a layer containing an ultraviolet protective agent as the outermost layer. Instead of having the reflection plate 10B have a curved surface, a structure may be used in which the top frame 57 is connected to other members such as other flat reflection plates 10 or electromagnetic wave absorbing plates at a predetermined inclination angle.

FIG2C shows an example of the structure of the frame 50A along the A-A line of FIG2A in a cross-sectional view parallel to the XY plane. Frame 50B has the same cross-sectional structure as frame 50A except that the upper portion is bent along the bend of the reflector 10B, so it is 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 reflectors 10-1 and 10-2 are inserted into the slits 51-1 and 51-2, respectively, and are held in the space 52. The space 52 is not essential, but by providing the space 52, the body 500 of the frame 50 can be made lighter and the holding angle of the reflector 10 can have a margin.

By inserting the reflectors 10-1 and 10-2 into the slits 51-1 and 51-2, the adjacent reflectors 10-1 and 10-2 can be stably held. Even when a portion of the reflector 10B is bent as shown in FIG. 2B , the edge of the bent reflector 10B is inserted into and held in the slit 51 of the bent frame 50. A portion of the body 500 can be formed of a non-conductive material. A non-conductive cover 501 such as resin can be provided on the outer surface of the body 500. When the cover 501 is provided, the cover 501 can be formed of a resin material with good weather resistance.

<Construction of reflector> FIG. 3 shows an example of the layer structure of the reflector 10. The layer structure of FIG. 3 is the structure of the reflector 10 in the thickness (Y) direction. The reflector 10 includes: a conductive layer 11; a dielectric layer 14 or 15, which is bonded to at least one side of the conductive layer 11 via a bonding layer 12 or 13; and a protective layer 16 or 17, which is disposed on the surface of the dielectric layer 14 or 15. In the example of FIG. 3, the conductive layer 11 is sandwiched between the dielectric layers 14 and 15 via bonding layers 12 and 13, and protective layers 16 and 17 are disposed on the surfaces of both dielectric layers 14 and 15. The protective layers 16 and 17 have an anti-ultraviolet function. When using a reflector 10B including a curved surface as shown in FIG. 2B , a protective layer may be provided only on the surface outside the curved surface of the reflector 10B.

When the electromagnetic wave reflection device 60 is used outdoors or in an indoor facility close to the outdoor environment, it is desirable that the reflection plate 10 has weather resistance. The reflective plate 10 of the embodiment has mechanical strength and weather resistance that can withstand outdoor environments. When a general electromagnetic wave reflection board is placed in an outdoor environment, the surface substrate of the electromagnetic wave reflection board may undergo deformation, discoloration, deterioration, etc. due to the influence of visible light or ultraviolet rays contained in sunlight, or the influence of temperature changes. tendency. When the electromagnetic wave reflection grating 100 connected to the electromagnetic wave reflection device 60 is also used as an outdoor safety fence or a soundproof wall, if the transmittance is reduced due to the influence of discoloration of the reflecting plate 10, visibility will be reduced. When the surface substrate of the reflective plate 10 is a resin substrate, if deformation occurs by approximately 1/100 of the original size due to temperature changes, etc., the direction of reflection or the reflection efficiency may change. In addition, due to the irradiation of ultraviolet rays, the relative dielectric constant of the resin material or dielectric material changes, which may deviate from the designed reflection direction and reflection efficiency. The reflective plate 10 of the embodiment suppresses or reduces these problems.

The conductive layer 11 forms the reflective surface of the reflective plate 10 and can be formed of a metal grid, a periodic pattern, a geometric pattern, a transparent conductive film, etc. As an example, the conductive layer 11 includes a metal mesh formed of good conductors such as Cu, Ni, SUS, and Ag. In the case where a portion of the reflective plate 10 includes a metasurface, the conductive layer 11 may include a periodically arranged pattern of a plurality of metal elements. The conductive layer 11 has a thickness of not less than 10 μm and not more than 200 μm, preferably not less than 50 μm and not more than 150 μm, so as to fully function as a reflective surface that reflects electromagnetic waves of a target frequency in a designed direction.

In order to guide the incident electromagnetic waves to the conductive layer 11, the transmittance of the bonding layers 12 and 13 for the use frequency is 60% or more, preferably 70% or more, and more preferably 80% or more. The bonding layers 12 and 13 can be formed of vinyl acetate resin, acrylic resin, cellulose resin, aniline resin, ethylene resin, silicone resin, or other resin materials. In order to make the bonding layers 12 and 13 durable and moisture-resistant for outdoor use, ethylene-vinyl acetate (EVA: ethylene-vinyl acetate) copolymer or cycloolefin polymer (COP: Cyclo Olefin Polymer) can also be used. The thickness of the connecting layers 12 and 13 is such that the dielectric layers 14 and 15 can be securely connected to the conductive layer 11, for example, 10 μm to 400 μm or less. The connecting layers 12 and 13 have relative dielectric constants and dielectric loss factors suitable for achieving the desired reflective characteristics of the conductive layer 11.

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 plate 10 and reduce the total weight of the reflective plate 10 as much as possible, the thickness of the dielectric layers 14 and 15 is selected within the range of thicker than 1.0 mm and less than 8.0 mm. The basis for this thickness range will be described later. If the thickness of the conductive layer 11 is set to 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 less than 80. The dielectric layers 14 and 15 have mechanical strength that can withstand outdoor use, and have a relative dielectric constant and a dielectric loss factor suitable for achieving the target reflection characteristics.

The protective layers 16 and 17 are, for example, resin layers containing ultraviolet absorbers. Ultraviolet preventers include ultraviolet absorbers and ultraviolet scatterers, but if ultraviolet scatterers are used, ultraviolet rays scattered by the reflector 10 may sometimes affect other electromagnetic wave reflection devices 60. Therefore, ultraviolet rays are prevented by ultraviolet absorbers. As ultraviolet absorbers, ultraviolet absorbers such as benzotriazole, benzophenone, triazine, and hydroxyphenyltriazine can be used. These ultraviolet absorbers can be mixed in resin and applied to the surfaces of the dielectric layers 14 and 15 to form protective layers 16 and 17 as coating films.

The thickness of the protective layers 16 and 17 is a thickness that fully absorbs ultraviolet rays and transmits visible light without obstructing the transparency of the reflector 10, for example, 5 μm or more and 15 μm or less, preferably 10 μm ± several micrometers. From the perspective of ensuring the strength of the reflector and maintaining transparency, the ratio of the thickness of the dielectric layers 14 and 15 to the thickness of the protective layers 16 and 17 is 66 or more and 1600 or less. When the thickness of the conductive layer 11 is set to 100.0 μm, the ratio of the thickness 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 perspective of maintaining the strength, reflection characteristics and transparency of the reflector 10, the thickness of the entire reflector 10 relative to the protective layer 16 or 17 is preferably 350 or more and 1000 or less.

The thickness of the entire reflector 10 of such a structure is not less than 5.0 mm and not more than 17.0 mm. When the thickness of the conductive layer 11 is 100 μm, the ratio of the thickness of the entire reflector 10 to the conductive layer 11 is not less than 50 and not more than 170. From the perspective of ensuring mechanical strength, since the ratio of the thickness of the dielectric material to the conductive layer 11 becomes larger, when the reflector 10 includes a metasurface, it is expected that the relative dielectric constant and dielectric loss factor of the entire dielectric part including the bonding layer 12, the dielectric layer 14 and the protective layer 16 are appropriately designed.

<Evaluation of reflector and wireless transmission system> Evaluate the changes in power reflection efficiency and transparency of the reflector 10 after long-term use. Also, evaluate the received power distribution of the wireless transmission system 1 using the electromagnetic wave reflection device 60 having the reflector 10.

FIG. 4 is a diagram of a model 20 of a conductive layer 11 used in the evaluation of reflection efficiency. The coordinate space of the model 20 used for evaluation is a space different from the coordinate space of the wireless transmission system of FIG. 1 , and the plane forming the conductive layer 11 is set as the ab plane, and the axis perpendicular to the ab plane is set as the c axis. The conductive layer 11 includes a repetition of a unit pattern 210 formed by a plurality of metal elements 151. The unit pattern 210 is also called a "supercell", and a plurality of metal elements 151 having a long axis in the b direction are arranged in the a direction at a predetermined interval. The a direction corresponds to the X direction of the reflector 10A of FIG. 2A .

FIG5 is an analysis space 101 of electromagnetic wave simulation, FIG6 is a schematic diagram of the ab surface of the analysis space 101, and FIG7 is a schematic diagram of the ac surface of the analysis space 101. The dimensions of the analysis space 101 indicated by the a-axis×b-axis×c-axis are 111.8 mm×32.1 mm×3.7 mm. The model 20 of the conductive layer 11 is arranged in the analysis space 101. The model 20 has an 8×6 unit pattern in which 8 unit patterns 210 are repeatedly arranged in the a direction and 6 unit patterns 210 are repeatedly arranged in the b direction. The boundary condition is a design in which an electromagnetic wave absorber 102 is arranged around the analysis space 101. The unit pattern 210 is designed to reflect a vertically incident electromagnetic wave of a specified frequency at an angle of 50°.

The evaluation method uses a model 20 of 8×6 unit patterns 210 in the analysis space 101 shown in FIGS. 5 , 6 and 7 . A plane wave of a specified frequency is incident on the model 20 at an incident angle of 0°, and the scattering cross-sectional area of the reflected wave is analyzed using general three-dimensional electromagnetic field simulation software. The scattering cross-section area, that is, the radar reflection cross section (RCS: Rader Cross Section), is used as an indicator of the ability to reflect incident electromagnetic waves, or the reflection characteristics. Calculate the power reflection efficiency based on the angle of the reflected wave and the gain (dB) value. When "reflection efficiency" is described in the following description, it means power reflection efficiency unless otherwise specified.

In the case of a metasurface that reflects at a reflection angle different from the incident angle, the calculated reflection efficiency needs to be corrected. An ideal conductive plate is a perfect mirror reflector, and for vertical incidence, it reflects electromagnetic waves in the same direction. In contrast, a metasurface formed by a unit pattern 210 reflects electromagnetic waves in a direction different from the incident angle. The reflection efficiency of the metasurface is the value obtained by dividing the electric reflection efficiency calculated based on the gain value by the correction value.

If the reflected electric field on the lossless metasurface determined by the simulation model 20 in Figure 4 or Figure 5 is set to E _MR , and the reflected electric field on the ideal conductive plate is set to E _PEC , then the correction value εp is set to | E _MR /E _PEC | ² . |E _MR /E _PEC | is expressed by the following formula.

[Number 1] or

[Number 2] Here, θ is the incident angle to the metasurface, and ϕ is the reflection angle corresponding to normal reflection. If the reflection angle of the metasurface is set to θ=50° or θr=50°, the incident angle is set to θi=0°, and the reflection angle of the normal reflection is set to ϕ=25°, the correction value εp is 0.7826.

<Evaluation of Weather Resistance> In the following Examples 1 and 2, the weather resistance of the reflective plate 10 was evaluated. Example 1 is an example, and Example 2 is a comparative example. The weather resistance evaluation items are set to changes in reflection efficiency, turbidity value and YI value after the reflective plate 10 is placed in a specified environment for a certain period of time. The turbidity value is the ratio (%) of scattered light to total transmitted light, and is an indicator of haze or transparency. The higher the turbidity value, the higher the haze. The YI value represents the degree of yellowing, and a positive value represents the change from transparent to yellow. Calculate the 3 stimulus values (X, Y, Z) by spectrophotometry, according to the formula Find the YI value.

[example 1] Example 1 shows the simulation results of the configuration of the embodiment. A dielectric layer 14 is disposed on at least one side of the conductive layer 11 in the layer structure shown in FIG. 3 , and a protective layer 16 covers the outermost surface of the dielectric layer 14 . The protective layer 16 contains an ultraviolet absorber. Through the above simulation, the effect of the protective layer 16 is evaluated. For the purpose of simulation, a polycarbonate film with a thickness of 0.7 mm is set as the supporting layer to support the conductive layer 11. On the opposite side of the polycarbonate film to the conductive layer 11, a base layer of an Ag-based multilayer film with a thickness of 0.36 mm was set. On the supporting surface of the polycarbonate film on the opposite side to the base layer, a conductive layer 11 is disposed with a bonding material with a thickness of 0.01 mm. The adhesive material is only suitable for carrying the portion of the metal element 151 constituting the unit pattern 210 of the conductive layer 11 . The material of the conductive layer 11 is copper foil with a thickness of 0.03 mm.

A bonding layer 12 with a thickness of 400 μm is provided to cover the conductive layer 11, and a polycarbonate sheet with a thickness of 2.0 mm is bonded to the bonding layer 12 as a dielectric layer 14. A protective layer 16 with a thickness of 8.0 μm is disposed on the surface of the polycarbonate sheet. The protective layer 16 is a resin coating layer mixed with an ultraviolet absorber. The width of the metal element 151 in the a-axis direction of the unit pattern 210 contained in the conductive layer 11 is uniformly 1.6 mm. The lengths of the metal element 151 in the b-axis direction are 2.5663 mm, 2.9113 mm, 4.0717 mm, 1.2521 mm, 1.8975 mm, and 2.5357 mm, respectively. At this time, the area occupancy rate of the metal element 151 relative to the dielectric layer 14 is 32.6%, and the transmittance of visible light is 43.1%.

When a 28.0 GHz electromagnetic wave incident at an incident angle of 0° is reflected at a reflection angle of 50°, the gain value at 50° of the RCS curve is -1.1087 dB, and the reflection efficiency after correction with εp=0.7826 is 85.1%.

Calculate again after placing the reflective plate in an environment of 60°C and 95% humidity for 500 hours. When an electromagnetic wave of 28.0 GHz is incident at an incident angle of 0° and reflected at a reflection angle of 50°, the gain value at 50° of the RCS curve is -1.4735dB, and the reflection efficiency after correction with εp=0.7826 is 78.2%. In addition, when the same reflective plate structure was exposed to a solar weathering tester for 5,000 hours, the change in turbidity value was 3.0%, and the change in YI value ΔYI was 2.0%.

In Example 1, by providing a protective layer 16 containing an ultraviolet absorber on the surface of the dielectric layer 14 covering the conductive layer 11, the decrease in reflection efficiency after being placed in a high temperature and high humidity environment for 500 hours was suppressed to about 7%. In addition, the increase in turbidity value was only 3.0%, and the change in ΔYI was 2.0%, indicating that the transparency of the reflector 10 was maintained.

[Example 2] Example 2 shows the simulation results of the comparative example. The conditions are the same as those of Example 1 except that no protective layer is provided on the surface of the dielectric layer 14. The layer structure of the reflector without the protective layer, the width and length of the metal element 151 of the unit pattern 210, and the area occupancy and transmittance of the metal element 151 relative to the dielectric layer are the same as those of Example 1.

When a 28.0 GHz electromagnetic wave incident at an incident angle of 0° is reflected at a reflection angle of 50°, the gain value at 50° of the RCS curve is -1.1087 dB, and the reflection efficiency corrected by εp=0.7826 is 85.1%. The same reflection efficiency as in Example 1 can be obtained.

After the reflector of Example 2 was placed in an environment of 60°C and 95% humidity for 500 hours, the calculation was repeated. The gain value at 50° of the RCS curve when the electromagnetic wave of 28.0 GHz incident at an angle of 0° was reflected at a reflection angle of 50° was -2.9630 dB, and the reflection efficiency corrected by εp=0.7826 was 55.5%. In addition, in the test of the same reflector structure exposed to the sunlight weathering tester for 3000 hours, the change in turbidity value was 10.0%, and the change in YI value indicating yellowing degree ΔYI was 18.0%.

In the case where no protective layer is provided on the surface of the dielectric layer 14, when placed in a high temperature and high humidity environment for the same time, the reflection efficiency is reduced to 55.0%, which is lower than the reflection efficiency of 60.0% which is a standard for the electromagnetic wave reflector to function. The turbidity value increases by 10%, and the ΔYI is as high as 18.0%, indicating that the reflector is significantly yellowed and the transparency is deteriorated.

<Evaluation of mechanical strength> In Examples 3 to 6, the evaluation results of the mechanical strength of the reflector 10 are shown. The mechanical strength of the reflector 10 is evaluated in accordance with the strength test and impact resistance test according to NEXCO (Nippon Expressway Company Limited) test methods 901 and 902. Examples 3 and 4 show the evaluation results of the configuration of the embodiment, and Examples 5 and 6 show the evaluation results of the comparative example.

[Example 3] Example 3 shows the evaluation results of the mechanical strength of the examples. In the layer structure of Figure 3, two flat polycarbonate sheets of dielectric layers 14 and 15 with a length of 1.0 m, a width of 2.0 m, and a thickness of 8.0 mm are set on both sides of the conductive layer 11. The conductive layer 11 is a stainless steel mesh with a thickness of 100.0 μm. Between the dielectric layers 14 and 15 of the polycarbonate sheet and the conductive layer 11, adhesive layers 12 and 13 of ethylene vinyl acetate with a thickness of 400 μm are set. On the surfaces of the dielectric layers 14 and 15, protective layers 16 and 17 containing ultraviolet absorbers with a thickness of 7.0 μm are set. The ratio of the thickness of the dielectric layer 14 or 15 and the protective layer 16 or 17 is 8.0 mm: 7.0 μm = 1143:1. The thickness ratio of the dielectric layer 14 or 15 to the conductive layer 11 is 8.0 m: 100.0 μm = 80:1.

Impact resistance test: Impact the reflective plate of Example 3 with an iron ball impact body of 300 kg, and measure the anti-scattering rate. The anti-scattering rate is based on Anti-scatter rate (%) = (weight of component - total weight of fragments)/weight of component × 100 express. The smaller the total weight of scattered fragments, the higher the scattering prevention rate. The anti-scattering rate of the reflective plate in Example 3 is as high as 99%, and only 1% of the light-transmitting part (i.e., dielectric layer and protective layer) is scattered as debris. In addition, the maximum weight of the fragments of the light-transmitting part is a light weight of 1.5 g or less. The strength test is evaluated by measuring the amount of bending at the center of the reflective plate and confirming that the ratio of the amount of bending to the short side (1.0 m) of the reflective plate is 1/15 or less. The deflection amount of the center of the reflective plate in Example 3 is less than 1/15 of the length of the short side, and the impact resistance and strength are both good.

[Example 4] Example 4 shows the evaluation results of the mechanical strength of the embodiment. The layer structure of the reflector of Example 4 is the same as that of the reflector of Example 3, except that the thickness of the polycarbonate sheet forming the dielectric layers 14 and 15 is changed to 5.0 mm. The conductive layer 11 is a stainless steel grid with a thickness of 100.0 μm, the following layers 12 and 13 are ethylene vinyl acetate with a thickness of 400 μm, and the protective layers 16 and 18 are resin layers with a thickness of 7.0 μm containing an ultraviolet absorber. The ratio of the thickness of the dielectric layer 14 or 15 to the protective layer 16 or 17 is 5.0 mm:7.0 μm=714:1. The thickness ratio of the dielectric layer 14 or 15 to the conductive layer 11 is 5.0 mm: 100.0 μm = 50:1.

The results of the strength test and impact resistance test show that the anti-scattering rate of the reflective plate in Example 4 using a polycarbonate sheet with a thickness of 5.0 mm as a dielectric layer and a protective layer of 7.0 μm is as high as 99% as in Example 3. The maximum weight of the fragments of the transparent part is 1.5 g or less. Confirm that the amount of curvature at the center of the reflector is less than 1/15 of the short side (1.0 m) of the reflector. The impact resistance and strength of the reflective plate in Example 4 are both good.

[Example 5] Example 5 shows the evaluation results of the mechanical strength of the reflective plate of the comparative example. In the layer composition of the reflective plate in Example 5, the thickness of the polycarbonate sheets forming the dielectric layers 14 and 15 is changed to 1.0 mm, and the thickness of the protective layers 16 and 17 on the surfaces of the dielectric layers 14 and 15 is changed to Except for 0.5 μm, the layer structure is the same as that of the reflective plates of Examples 3 and 4. The ratio of the thickness of the dielectric layer 14 or 15 and the protective layer 16 or 17 is 1.0 mm: 0.5 μm = 2000: 1. The ratio of the thickness of the dielectric layer 14 or 15 and the conductive layer 11 is 1.0 mm: 100.0 μm = 10:1.

The results of the strength test and impact resistance test showed that the anti-scattering rate of the reflector in Example 5, which used a dielectric layer of a polycarbonate sheet with a thickness of 1.0 mm and a protective layer with a thickness of 0.5 μm, did not reach 99%. This means that the scattered weight of the fragments in the light-transmitting part is larger. The maximum weight of the fragments in the light-transmitting part exceeded 1.5 g. It was confirmed that the bending amount at the center of the reflector in the strength test was greater than 1/15 of the short side (1.0 m) of the reflector, and the deformation of the reflector was large. The impact resistance and strength of the reflector in Example 5 were insufficient.

[Example 6] Example 6 shows the evaluation results of the mechanical strength of the reflective plate of another comparative example. The layer composition of the reflective plate in Example 6 is changed except that the thickness of the polycarbonate sheets forming the dielectric layers 14 and 15 is changed to 1.0 mm, and the thickness of the stainless steel grid that becomes the conductive layer 11 is changed to 5.0 μm. The layer composition of the reflective plates in Examples 3 and 4 is the same. The ratio of the thickness of the dielectric layer 14 or 15 and the protective layer 16 or 17 is 1.0 mm: 7.0 μm = 143:1. The ratio of the thickness of the dielectric layer 14 or 15 and the conductive layer 11 is 1.0 mm: 5.0 μm = 200:1.

The results of the strength test and the impact resistance test showed that the anti-scattering rate of the reflector of Example 6, which used a polycarbonate sheet with a thickness of 1.0 mm and a protective layer with a thickness of 7.0 μm, did not reach 99%. Although the thickness of the protective layer was the same as that of Examples 3 and 4, the anti-scattering rate did not reach 99.9%. This is believed to be because the dielectric layers 14 and 15 of the polycarbonate sheet became thinner, resulting in a decrease in mechanical strength. In addition, the maximum weight of the fragments in the light-transmitting portion exceeded 1.5 g. The polycarbonate sheet became thinner but the maximum weight of the fragments in the light-transmitting portion exceeded 1.5 g, indicating that the scattered fragments were larger. It was confirmed that the bending amount at the center of the reflector in the strength test was greater than 1/15 of the short side (1.0 m) of the reflector, and the deformation of the reflector was greater. The impact resistance and strength of the reflector of Example 6 were insufficient.

From the evaluation results of Examples 1 to 6, it can be seen that by providing a protective layer 16 or 17 containing an ultraviolet absorber on the surface of the dielectric layer 14 or 15, the yellowing and reduction in transparency of the reflector can be suppressed even after long-term outdoor use. In addition, by optimizing the thickness of the dielectric layer and the protective layer, the mechanical strength of the reflector is improved. Specifically, by setting the thickness of the dielectric layer 14 or 15 to 1.0 mm or more and 8.0 mm or less, and setting the thickness of the protective layer 16 or 17 to 5.0 μm or more and 15.0 μm or less, the strength and transparency of the reflector are maintained, and the reduction in reflection characteristics caused by the outdoor environment is suppressed. The ratio of the thickness of the dielectric layer 14 or 16 to the thickness of the protective layer 16 or 17 is expected to be in the range of 50:1 to 200:1. The thickness ratio of the dielectric layer 14 or 15 to the conductive layer 11 is preferably greater than 5 and less than 100.

<Receiving power distribution of wireless transmission system> Next, the receiving power distribution of the wireless transmission system 1 is evaluated. FIG8 is a top view of the simulation model 200 of the wireless transmission system, and FIG9 is a three-dimensional view of the simulation model 200 of the wireless transmission system. Model 200 is a road 32, in which there are vehicles 31a and 31b, a plate 38, and a column 39 supporting the plate 38. The width of the road 32 is 14.0 m and the length is 200.0 m. Transmitter station Tx1 is arranged on one side of the road 32, and transmitter station Tx2 is arranged on the other side in a staggered manner. Electromagnetic wave reflection devices 60 of the type shown in FIG2A are arranged on both sides of the road 32. A light-transmitting soundproof wall can also be provided along the electromagnetic wave reflection device 60 or integrally with the electromagnetic wave reflection device 60. The model 200 is used to calculate the received power distribution within the road 32.

FIG. 10 shows the materials and coordinates of the objects used in the model 200 of FIGS. 8 and 9 . In the model 200, two types of vehicles 31 are set. The body of the vehicle 31a is made of metal, and has a length of 4.1 m, a width of 1.7 m, and a height of 1.5 m. The body of the vehicle 31b is made of metal, with a length of 4.8 m, a width of 1.7 m, and a height of 1.5 m. Road 32 is a concrete lane with a width of 14.0 m and a length of 200.0 m as mentioned above. Board 38 is a base plate for 5 GHz wireless LAN of IТU (International Telecommunication Union), with a width of 8.0 m, a thickness of 0.075 m, and a height of 5.0 m. The column 39 is made of metal, has a diameter of 0.2 m, a height of 5.0 m, and a length in the Y direction of 14.0 m.

The electromagnetic wave reflection device 60 is arranged throughout the road 32 with a length of 200.0 m. Specifically, four layers of 100 reflecting plates with a width of 2.0 m and a height of 1.0 m are arranged in the height (Z) direction and are connected in the X direction to form a grid connecting a total of 400 pieces and a height of 4.0 m. Metal (stainless steel) is provided on the conductive layer 11 of the reflective plate 10 .

The transmitting antennas of the transmitting stations Tx1 and Tx2 are set at a height of 3.0 m. The beam width of the transmitting antennas is 28°. The antenna of the receiver Rx is a non-directional antenna with a height of 1.0 m and a maximum gain of 0 dBi. The receiver Rx measures the received power at all positions within a plane at a height of 1.0 m on the road 32 parallel to the XY plane.

Under the above conditions, the received power distribution is calculated in Examples 7 to 11. Examples 7, 9, 11, and 12 use the reflector structure of the embodiment, while Examples 8 and 10 are used as comparative examples using only the conventional light-transmitting soundproof wall structure.

[Example 7] Figure 11 shows the received power distribution of Example 7. In Example 7, electromagnetic wave reflectors with a height of 4.0 m and 400 reflectors 10 with a width of 2.0 m × a height of 1.0 m connected to one side are installed on both sides of the road 32 shown in Figures 8 and 9. The transmitting antennas of the transmitting stations Tx1 and Tx2 are installed at a height of 3.0 m on both sides of the road 32. The transmitting frequency of the transmitting stations Tx1 and Tx2 is 4.7 GHz, and the maximum gain of the transmitting antenna is 20 dBi. On the road 32 with a width of 14 m × a length of 200 m, the received power distribution in a plane with a height of 1.0 m parallel to the XY plane is measured using a non-directional receiving antenna. The total RSRP (Reference Signal Received Power) within the plane is -287.326 dBm, and the median value is -89 dBm. On the other hand, the radio wave intensity outside the road is less than -100 dBm. When the output of the uplink line is measured in the area behind the electromagnetic wave reflecting device 60, it is less than 50% of the transmission rate. This means that outside the electromagnetic wave reflecting device 60, the intensity of the communication radio waves from the transmitting station Tx is smaller, and fewer radio waves leak to the outside of the road 32. It can be seen that the radio waves radiated from the transmitting stations Tx1 and Tx2 are effectively directed toward the road 32 through the reflecting plate 10 of the electromagnetic wave reflecting device 60. The evaluation results of Example 7 are applicable to the frequency band below 6 GHz. The central value of the received power within road 32 is above -90 dBm, and the received power outside the road is lower than that within the road, and does not reach -100 dBm.

[Example 8] FIG. 12 shows the received power distribution of the configuration of Example 8. Example 8 is a comparative example in which light-transmitting soundproof walls made of polycarbonate with a height of 4.0 m are set on both sides of the road 32 in place of the electromagnetic wave reflection device 60 . The length of the translucent soundproof wall is 200 m on one side and 400 m on both sides. Other conditions are the same as Example 7. The transmitting stations Tx1 and Tx2 transmit 4.7 GHz reference signals on both sides of the road 32 from a height of 3.0 m. The maximum gain of the transmitting antenna is the same as Example 7, which is 20 dBi. In a plane with a height of 1.0 m parallel to the XY plane, the sum of RSRP is -372.833 dBm, and the central value is -107 dBm. The maximum received power of radio waves outside the road is as high as -80 dBm. When the output of the uplink line is measured in the area on the back side of the electromagnetic wave reflection device 60, the maximum transmission rate reaches 80%. This means that the radio waves emitted from the transmitting stations Tx1 and Tx2 leak to the outside of the light-transmitting sound insulation wall with relatively high electric power.

[Example 9] Figure 13 shows the received power distribution of Example 9. Example 9 is the same as Example 7 except that the transmission frequency of the transmitters Tx1 and Tx2 is changed to 28.3 GHz. On both sides of the road 32, an electromagnetic wave reflector with a height of 4.0 m and a width × height of 400 pieces of 2.0 m × 1.0 m reflectors 10 connected on one side is set. The transmitters Tx1 and Tx2 are set at a height of 3.0 m on both sides of the road 32, and transmit a reference signal of 28.3 GHz from a transmitting antenna with a maximum gain of 20 dBi. The total RSRP in the plane parallel to the XY plane at a height of 1.0 m is -399.424 dBm, and the central value is -125 dBm. The received power outside the road is lower than -125 dBm. When the output of the uplink line is measured in the area behind the electromagnetic wave reflection device 60, it is less than 50% of the transmission rate. It can be seen that the electromagnetic wave reflection device 60 can also improve the radio wave propagation environment on the road 32 for radio waves in the 28 GHz band and suppress the leakage of radio waves outside the road 32. The result of Example 9 is suitable for communication in the millimeter wave band of 28 GHz to 32 GHz. The central value of the received power in the road 32 is above -125 dBm, and the received power outside the road 32 does not reach -125 dBm.

[Example 10] Figure 14 shows the received power distribution of the configuration of Example 10. Example 10 is a configuration of the comparative example, where polycarbonate panels with a width of 4 m × a height of 2.0 m × 1.0 m are connected on both sides of the road 32, and a polycarbonate light-transmitting soundproof wall is set to replace the electromagnetic wave reflection device 60. The conditions are the same as those of Example 8, except that the transmission frequency of the transmitting stations Tx1 and Tx2 is changed to 28.3 GHz. The length of the light-transmitting soundproof wall with a height of 4.0 m is 200 m on one side and 400 m on both sides. Transmitting stations Tx1 and Tx2 transmit 28.3 GHz reference signals from a height of 3.0 m on both sides of the road 32. The maximum gain of the transmitting antenna is the same as that of Examples 7 to 9, which is 20 dBi. In a plane parallel to the XY plane at a height of 1.0 m, the total RSRP is -496.329 dBm, and the median value is -145 dBm. The maximum radio wave intensity outside the road is as high as -100 dBm. When the output of the uplink line is measured in the area behind the electromagnetic wave reflection device 60, the maximum transmission rate reaches 80%. It can be seen that the 28 GHz band radio waves radiated from the transmitters Tx1 and Tx2 cannot effectively cover the communication area on the road 32, but leak to the outside of the light-transmitting soundproof wall.

[Example 11] FIG. 15 shows the received power distribution of the configuration of Example 11. In Example 11, the electromagnetic wave absorber 35 is combined with the reflection plate 10 of the embodiment. On both sides of the road 32, 400 pieces of reflective panels 10 with a width × height of 2.0 m × 1.0 m are connected on one side, and a total of 800 pieces are connected on both sides. On the reflective surface 10, as the electromagnetic wave absorber 35, an electromagnetic wave absorbing plate with a height of 2.0 m made of polymer fibers is installed over 200 m on one side and 400 m on both sides. The total height is set to 6.0 m. The transmitting stations Tx1 and Tx2 are installed at a height of 3.0 m on both sides of the road 32, and transmit a 4.7 GHz reference signal from a transmitting antenna with a maximum gain of 20 dBi. The sum of RSRP in the plane with a height of 1.0 m parallel to the XY plane is -359.761 dBm, and the central value is -110 dBm. The radio wave intensity outside the road is lower than -110 dBm. When the output of the uplink line is measured in the area on the back side of the electromagnetic wave reflection device 60, it is less than 50% of the transmission rate. If the electromagnetic wave absorber 35 is connected to the upper end of the electromagnetic wave reflection device 60, the received power intensity on the road 32 will be slightly lower than in Example 7, but the electromagnetic wave can be effectively prevented from flying out of the road 32. The calculation results in Example 11 are suitable for frequency bands up to 6 GHz.

[Example 12] FIG. 16 shows the received power distribution of the configuration of Example 12. Example 12 is the same as Example 11 except that the maximum gain of transmitting stations Tx1 and Tx2 is changed to 10 dBi. Connect 400 pieces of reflective plates 10 with a width x height of 2.0 m x 1.0 m on one side and 800 reflective plates 10 with a width × height of 2.0 m 200 m and 400 m on both sides. The transmitting stations Tx1 and Tx2 are installed at a height of 3.0 m on both sides of the road 32, and transmit a 4.7 GHz reference signal from a transmitting antenna with a maximum gain of 10 dBi. The sum of RSRP in the plane with a height of 1.0 m parallel to the XY plane is -359.759 dBm, and the central value is -110 dBm. The radio wave intensity outside the road is lower than -110 dBm. When the output of the uplink line is measured in the area on the back side of the electromagnetic wave reflection device 60, it is less than 50% of the transmission rate. If the electromagnetic wave absorber 35 is connected to the upper end of the electromagnetic wave reflection device 60, the received power intensity on the road 32 will be slightly lower than in Example 7, but the electromagnetic wave can be effectively prevented from flying out of the road 32. It can be seen that the maximum gain of the transmitting antenna of the transmitting station Tx is 5 dBi or more and 30 dBi or less, preferably 10 dBi or more and 20 dBi or less, when the received power is distributed on the road 32 in a plane with a height of 1 m parallel to the XY plane. The range is not affected. The calculation results in Example 12 are suitable for frequency bands up to 6 GHz.

As described above, by using the wireless transmission system or reflector of the embodiment, the radio wave propagation environment can be improved and the radio waves can be suppressed from flying out of the necessary space in the indoor facilities in the outdoor environment or the environment close to the outdoor environment. The wireless transmission system 1 of the embodiment is applicable not only to general roads, highways, and railway lines, but also to the terraces and arcades of commercial facilities or public facilities that extend in a certain direction in the environment close to the outdoor environment. In particular, the dead zone can be reduced on the highway with soundproof walls or safety fences on both sides, the radio wave propagation environment can be improved, and the radio waves can be suppressed from flying out of the highway.

The size of the reflecting surface of the electromagnetic wave reflecting device 60 can be appropriately designed according to the application site. As an example, the size of 10 cm×10 cm to 2.0 m×4.0 m can be used. The height of the antenna of the base station 33 is not limited to 3.0 m, as long as it is lower than the upper end of the electromagnetic wave reflection device 60 . The ultraviolet absorber used in the outermost protective layer of the reflective plate or the material of the electromagnetic wave absorbing plate used in combination with the electromagnetic wave reflecting device can be appropriately selected according to the application environment. It is also possible to connect an electromagnetic wave reflection device 60B having a reflection plate 10B including a curved surface as shown in FIG. 2B to form a wireless transmission system 1 . The frequencies used by wireless transmission systems are not limited to the 4.7 GHz and 28 GHz frequency bands. By controlling the pattern of the conductive layer 11 of the reflective plate 10, it can reflect in a specified frequency band above 1 GHz and below 300 GHz, such as above 1 GHz and below 170 GHz, or above 1 GHz and below 100 GHz, or above 1 GHz and below 80 GHz. Electromagnetic waves of target frequency.

The above has described the implementation form of the present disclosure, but the present disclosure may include the following structures. (Item 1) A reflector having: A conductive layer having a conductive pattern that reflects electromagnetic waves in a specified frequency band of 1 GHz or more and 300 GHz or less; A dielectric layer that is bonded to at least one surface of the conductive layer via a bonding layer; and A protective layer that includes an ultraviolet absorber disposed on the surface of the dielectric layer on the opposite side of the bonding layer; and The ratio of the thickness of the dielectric layer to the thickness of the protective layer is 66 or more and 1600 or less. (Item 2) A reflector as in Item 1, wherein the protective layer is a resin layer including the ultraviolet absorber. (Item 3) A reflector as in item 1 or 2, wherein the protective layer is a coating film coated on the surface of the dielectric layer. (Item 4) A reflector as in any one of items 1 to 3, wherein the conductive layer is formed of a metal grid; and the ratio of the thickness of the dielectric layer to the thickness of the metal grid is greater than 10 and less than 80. (Item 5) A reflector as in any one of items 1 to 4, wherein the dielectric layer is formed of polycarbonate having a thickness of greater than 1.0 mm and less than 8.0 mm. (Item 6) A reflector as in any one of items 1 to 5, wherein the first dielectric layer and the second dielectric layer are bonded to both surfaces of the conductive layer via a bonding layer, and the protective layer containing the ultraviolet absorber is disposed on the surface of the first dielectric layer and the second dielectric layer. (Item 7) A reflector as in any one of items 1 to 6, wherein the reflector has a curved surface. (Item 8) An electromagnetic wave reflecting device, comprising: a reflector as in any one of items 1 to 7; and a frame for holding the reflector. (Item 9) An electromagnetic wave reflecting device as in item 8, wherein the frame includes a top frame for holding the upper end of the reflector, a side frame for holding the side end of the reflector, and a bottom frame for holding the lower end of the reflector. (Item 10) An electromagnetic wave reflection grid, which uses a plurality of electromagnetic wave reflection devices such as item 8 or 9, and connects a plurality of the above reflection plates with the above frame.

This application is based on Japanese Patent Application No. 2022-130006 filed on August 17, 2022 and claims priority thereon, and includes all the contents of the Japanese patent application.

1: Wireless transmission system 10: Reflective plate 10-1: Reflective plate 10-2: Reflective plate 10A: Reflective plate 10A-1: Reflective plate 10A-2: Reflective plate 10A-3: Reflective plate 10B: Reflective plate 10B-1: Reflective plate 10B-2: Reflective plate 10B-3: Reflective plate 11:Conductive layer 12: Next layer 13: Next layer 14: Dielectric layer 15: Dielectric layer 16:Protective layer 17:Protective layer 20:Model 31:Vehicle 31a:Vehicle 31b: Vehicle 32:Road 33:Base station 35:Electromagnetic wave absorber 38: Board 39: column 50: Frame (side frame) 50A: Frame (side frame) 50B: Frame (side frame) 51-1:Slit 51-2:Slit 52:Space 56:Feet 57:Top frame 58: Bottom frame 60:Electromagnetic wave reflection device 60A: Electromagnetic wave reflection device 60A-1: Electromagnetic wave reflection device 60A-2: Electromagnetic wave reflection device 60A-3: Electromagnetic wave reflection device 60B: Electromagnetic wave reflection device 60B-1: Electromagnetic wave reflection device 60B-2: Electromagnetic wave reflection device 60B-3: Electromagnetic wave reflection device 100A: Electromagnetic wave reflection grating 100B: Electromagnetic wave reflection grating 101: Analysis space 102:Electromagnetic wave absorber 151:Metal components 200:Model 210:Unit pattern 500:Ontology 501: cover d1: distance d2: distance Rx: receiver Tx: sending station Tx1: sending station Tx2: sending station

FIG. 1 is a schematic diagram of the wireless transmission system according to the embodiment. Figure 2A is a schematic diagram of an electromagnetic wave reflection grating connected with a plurality of electromagnetic wave reflection devices. FIG. 2B is a schematic diagram of a modified example of the electromagnetic wave reflection device and the electromagnetic wave reflection grating. Fig. 2C is a structural example of a horizontal cross-section along the line A-A in Fig. 2A. FIG. 3 is a diagram showing an example of the layer structure of the reflective plate. Figure 4 is a diagram showing a model of the conductive layer used for evaluation. Figure 5 is a diagram showing the analysis space. Figure 6 is a schematic diagram of the ab surface of the analytical space. Figure 7 is a schematic diagram of the ac plane of the analytical space. Figure 8 is a top view of the simulation model of the wireless transmission system. Figure 9 is a three-dimensional view of a simulation model of a wireless transmission system. Figure 10 is a diagram showing the materials and coordinates of objects used in the models of Figures 8 and 9. FIG. 11 is a diagram showing the received power distribution in Example 7. FIG. 12 is a diagram showing the received power distribution in Example 8. Fig. 13 is a diagram showing the received power distribution in Example 9. FIG. 14 is a diagram showing the distribution of received power in Example 10. FIG. 15 is a diagram showing the received power distribution in Example 11. Fig. 16 is a diagram showing the received power distribution in Example 12.

10: Reflective plate

11:Conductive layer

12: Next layer

13: Next layer

14: Dielectric layer

15: Dielectric layer

16: Protective layer

17: Protective layer

Claims (10)

A reflective plate having: A conductive layer having a conductive pattern that reflects electromagnetic waves in a specified frequency band above 1 GHz and below 300 GHz; A dielectric layer bonded to at least one surface of the conductive layer via an adhesive layer; and A protective layer comprising an ultraviolet absorber disposed on the surface of the dielectric layer opposite to the adhesive layer; and The ratio of the thickness of the dielectric layer to the thickness of the protective layer is not less than 66 and not more than 1600. As in the reflective plate of claim 1, wherein the protective layer is a resin layer containing the ultraviolet absorber. As in the reflector of claim 1, wherein the protective layer is a coating film coated on the surface of the dielectric layer. A reflector as claimed in claim 1, wherein the conductive layer is formed by a metal grid; and the ratio of the thickness of the dielectric layer to the thickness of the metal grid is greater than 10 and less than 80. As the reflector of claim 1, wherein the dielectric layer is formed of polycarbonate having a thickness of not less than 1.0 mm and not more than 8.0 mm. Such as the reflector of claim 1, wherein The first dielectric layer and the second dielectric layer are bonded to both surfaces of the conductive layer via an adhesive layer, and the protective layer including the ultraviolet absorber is provided on the surfaces of the first dielectric layer and the second dielectric layer. Such as the reflector of claim 1, wherein The above-mentioned reflecting plate has a curved surface. An electromagnetic wave reflection device, which has: Such as requesting any one of the reflector items 1 to 7; and Keep the reflector framed above. The electromagnetic wave reflection device of claim 8, wherein The frame includes a top frame that holds the upper end of the reflective plate, a side frame that holds the side ends of the reflective plate, and a bottom frame that holds the lower end of the reflective plate. An electromagnetic wave reflection grating, which uses a plurality of electromagnetic wave reflection devices as claimed in claim 8, and connects a plurality of the above-mentioned reflection plates with the above-mentioned frame.