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

Abstract

Provided are a reflection panel that reflects incident electromagnetic waves in multiple directions with a certain degree of reflection intensity, and an electromagnetic wave reflection device using the same. A reflection panel for reflecting radio waves of a predetermined band selected from a frequency band of 1-300 GHz inclusive comprises: a dielectric layer; a periodic conductive pattern that is provided on one surface of the dielectric layer; a ground layer that is provided on the other surface of the dielectric layer; and an adhesion layer that joins the conductive pattern to the one surface. The thickness of the conductive pattern is 0.1-10.0 μm exclusive. Alternatively, the thickness of the adhesion layer is 50-1500 μm exclusive.

Description

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

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

[0002] It is expected that mobile communication technologies such as the fifth-generation mobile communication system (hereinafter referred to as "5G"), which offer high speed, large capacity, low latency, and multiple simultaneous connections, will be introduced into the communication networks of the Internet of Things (IoT), which handles large amounts of data. In addition to the inherent mobility and flexibility of mobile communication technology, the low latency characteristics of 5G are said to be suitable for IoT. However, because 5G radio waves have a high degree of directionality, it is necessary to devise a propagation method, such as installing reflectors such as reflective panels, in order to deliver the radio waves to the required areas.

[0003] In recent years, artificial reflective surfaces known as "metasurfaces" have been developed. Metasurfaces are formed with periodic structures or patterns that are finer than the wavelength and are designed to reflect electromagnetic waves at a reflection angle different from the incident angle (see, for example, Non-Patent Document 1). Because metasurfaces can reflect incident electromagnetic waves in a designed direction while maintaining a planar configuration, they function effectively as reflectors even in environments where there is not enough space to install multiple specular reflective panels.

[0004] Diaz-Rubio et al., Sci. Adv. 2017: 3: e1602714 1

[0005] Metasurfaces are designed to reflect electromagnetic waves in a specific direction, and it is difficult to reflect incident electromagnetic waves in multiple directions with a consistent reflection intensity. Depending on the environment in which the reflective panel is installed, reflection in multiple directions may be required. The present invention aims to provide a reflective panel that reflects incident electromagnetic waves in multiple directions with a consistent reflection intensity, and an electromagnetic wave reflecting device using the same.

[0006] In one aspect, a reflective panel that reflects radio waves in a predetermined band selected from a frequency band of 1 GHz or more and 300 GHz or less has: a dielectric layer; a periodic conductive pattern provided on one surface of the dielectric layer; a ground layer provided on the other surface of the dielectric layer; and an adhesive layer that joins the conductive pattern to the one surface, wherein the adhesive layer that joins the conductive pattern is provided with the same area occupancy as the conductive pattern, and the thickness of the conductive pattern is greater than 0.1 μm and less than 10.0 μm.

[0007] In another aspect, a reflective panel that reflects radio waves in a predetermined band selected from a frequency band of 1 GHz or more and 300 GHz or less has: a dielectric layer; a periodic conductive pattern provided on one surface of the dielectric layer; a ground layer provided on the other surface of the dielectric layer; and an adhesive layer that joins the conductive pattern to the one surface of the dielectric layer, wherein the adhesive layer that joins the conductive pattern is provided with the same area occupancy as the conductive pattern, and the thickness of the adhesive layer is greater than 50 μm and less than 1500 μm.

[0008] A reflective panel that reflects incident electromagnetic waves in multiple directions with a certain degree of reflection intensity, and an electromagnetic wave reflecting device using the same, are realized.

[0009] Fig. 5 is a schematic diagram of an electromagnetic wave reflecting device using a reflective panel of an embodiment. Fig. 6 is a schematic diagram showing the mode of reflection at the reflective panel of an embodiment. Fig. 7 is a diagram showing a first example of a layer configuration of a reflective panel. Fig. 8 is a diagram showing a second example of a layer configuration of a reflective panel. Fig. 9 is a diagram showing a model of a conductive pattern used to evaluate reflection characteristics. Fig. 10 is a schematic diagram showing the configuration of a unit cell of the model of Fig. 5. Fig. 11 is a diagram showing an analysis space. Fig. 12 is a schematic diagram of an electromagnetic wave reflecting fence in which a plurality of electromagnetic wave reflecting devices are connected.

[0010] In an embodiment, a reflective panel is used to improve the radio wave environment by reflecting incident electromagnetic waves in two or more directions with a certain degree of reflection intensity. More specifically, a reflective panel is provided that simultaneously reflects electromagnetic waves in a first direction (specular reflection) and a second direction (non-specular reflection). Non-specular reflection refers to reflection at an angle different from the incident angle, including reflection by a metasurface with artificially controlled reflection characteristics.

[0011] In order to reflect incident electromagnetic waves in the direction of specular reflection and the direction of non-specular reflection with a certain degree of reflection intensity, the thickness of the conductive pattern of the conductive layer constituting the reflective surface and the thickness of the adhesive layer supporting the conductive pattern are controlled. Specifically, in a configuration in which the conductive pattern is adhered to the dielectric layer with an adhesive layer arranged with a shape or in-plane occupancy similar to that of the conductive pattern, the thickness of the adhesive layer is set to be greater than 50 μm and less than 1500 μm. Alternatively, the thickness of the conductive pattern is set to be greater than 0.1 μm and less than 10.0 μm. The shape or in-plane occupancy of the adhesive layer and the conductive pattern being "same" does not mean that they are exactly the same in every detail, but rather means that the shape or in-plane occupancy of the adhesive layer and the conductive pattern are the same within a range of ±5%, including allowable errors, process variations, etc.

[0012] The specific configuration of the reflective panel will be described below with reference to the drawings. The following embodiment is an example for embodying the technical concept of the present invention and is 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 redundant description may be omitted.

[0013] <Configuration of Reflective Panel and Electromagnetic Wave Reflecting Device> Fig. 1 is a schematic diagram of an electromagnetic wave reflecting device 60 using a reflective panel 10. The electromagnetic wave reflecting device 60 includes the reflective panel 10 and a frame 50 that holds the reflective panel. The width or horizontal direction of the reflective panel 10 is defined as the X direction, the height or vertical direction is defined as the Y direction, and the thickness direction is defined as the Z direction. The electromagnetic wave reflecting device 60 may be provided with legs 56 to allow the electromagnetic wave reflecting device 60 to stand on its own. The electromagnetic wave reflecting device 60 may have a top frame 57 that holds the upper end of the reflective panel 10 in the height (Y) direction, and a bottom frame 58 that holds the lower end.

[0014] The reflective panel 10, with a single panel, reflects electromagnetic waves in a predetermined frequency band selected from frequencies of 1 GHz to 300 GHz, for example, 1 GHz to 170 GHz, in both specular and non-specular directions with a certain degree of reflection intensity. As described below, the reflective panel 10 has a predetermined conductive pattern supported on a dielectric layer by an adhesive layer, and the conductive pattern forms a reflective surface. The conductive pattern is formed of a transparent conductive material or a good conductive metal material, and has a periodic pattern, mesh pattern, geometric pattern, or the like. The thickness of the conductive pattern is greater than 0.1 μm and less than 10.0 μm.

[0015] The frame 50 holds both ends of the reflective panel in the width (X) direction. The frame 50 may also be called a side frame due to the positional relationship between the top frame 57 and the bottom frame 58. The frame 50 not only stably holds the reflective panel 10 when the electromagnetic wave reflecting device 60 is assembled, but also contributes to the safety of transporting the reflective panel 10 and reinforcement of its mechanical strength. Furthermore, when multiple reflective panels 10 are connected for use, the frame 50 has the function and configuration of maintaining continuity of the reflected potential between adjacent reflective panels 10.

[0016] FIG. 2 schematically shows the reflection behavior of the reflective panel 10. Consider the case where electromagnetic waves EMi are incident on the reflective surface 105 of the reflective panel 10 from a direction perpendicular to the reflective surface 105. The angle of incidence for normal incidence is 0 degrees. In addition to the specular reflection component Rsp in the 0° direction, the reflective panel 10 generates at least one of a non-specular reflection component Rnsp that is reflected toward the +X side at a reflection angle different from 0°, and a non-specular reflection component −Rnsp that is reflected toward the −X side. The specular reflection component Rsp and the non-specular reflection component Rnsp or −Rnsp both have a reflection gain higher than −10 dB, and the difference in gain is within 8 dB, preferably within 5 dB.

[0017] In order to maintain a certain level of reflection intensity and realize reflection in multiple directions, the thickness of the conductive pattern that forms the reflecting surface 105 and the thickness of the adhesive layer that supports the conductive pattern are controlled.

[0018] <Layer Structure of Reflective Panel> Figure 3 shows the layer structure of the reflective panel 10A. This layer structure is the layer structure in the thickness (Z) direction of the reflective panel 10A. The reflective panel 10A has a dielectric layer 14, a conductive pattern 151 provided on one surface 141 of the dielectric layer 14, a ground plane 13 provided on the other surface 142 of the dielectric layer 14, and an adhesive layer 153 that joins the conductive pattern 151 to the dielectric layer 14. The adhesive layer 153 is provided on the surface 141 of the dielectric layer 14 with the same area occupancy as the conductive pattern 151.

[0019] The dielectric layer 14 is an insulating polymer film made of polycarbonate, cycloolefin polymer (COP), polyethylene terephthalate (PET), fluororesin, or the like, and has a thickness of approximately 0.3 mm to 1.0 mm. Generally, the thickness, dielectric constant, and dielectric loss tangent of the dielectric layer 14 greatly affect the reflective characteristics of the reflective panel 10. In this embodiment, the thicknesses of the adhesive layer 153 and the conductive pattern 151 are controlled to achieve reflection in multiple directions, so the dielectric layer 14 may be made of a material having a dielectric constant and dielectric loss tangent that do not inhibit the expression of the target reflective characteristics. As an example, an insulating polymer film having a dielectric constant of 3.0 or less and a dielectric loss tangent of 0.1 or less is used.

[0020] The conductive pattern 151 is a periodic pattern made of a good conductor such as Cu, Ni, or Ag, and has a thickness of more than 0.1 μm and less than 10.0 μm. The conductive pattern 151 forms the reflective surface 105 of the reflective panel 10 (see FIG. 2).

[0021] The ground plane 13 may be formed of the same material as the conductive patterns 151, or may be formed of a different conductive material. A capacitance is formed between the ground plane 13 and each conductive pattern 151, and the magnitude of the phase delay is controlled for each conductive pattern 151.

[0022] The adhesive layer 153 is formed to a thickness that can bond the conductive pattern 151 to the dielectric layer 14 and control the reflection characteristics of the reflective panel 10. Specifically, the thickness of the adhesive layer 153 is greater than 50 μm and less than 1500 μm. The adhesive layer 153 may be made of a resin such as vinyl acetate resin, acrylic resin, cellulose resin, aniline resin, ethylene resin, silicone resin, or the like.

[0023] Fig. 4 shows the layer structure of the reflective panel 10B. In addition to the structure shown in Fig. 3, the reflective panel 10B has an intermediate layer 16 that covers the conductive pattern 151 and the adhesive layer 153, and a dielectric substrate 17 that is joined to the conductive pattern 151 side by the intermediate layer 16. The reflective panel 10B may further have an intermediate layer 12 that covers the ground layer 13, and a dielectric substrate 11 that is joined to the ground layer 13 side by the intermediate layer 12.

[0024] The intermediate layer 16 protects the surface of the conductive pattern 151 and also adheres and holds the dielectric substrate 17. The intermediate layer 16 is preferably durable and moisture-resistant, and may be made of, for example, ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP). The thickness of the intermediate layer 16 is 10 μm to 400 μm.

[0025] The dielectric substrate 17 is preferably formed as the outermost layer of the reflective panel 10B from a material that is excellent in impact resistance, durability, and transparency. A dielectric sheet that is provided as the outermost layer of the reflective panel 10B for protection and durability and has a thickness greater than or equal to that of the dielectric layer 14 is called a "dielectric substrate" to distinguish it from the dielectric layer 14 that carries the conductive pattern 151. Polycarbonate, acrylic resin, PET, etc. can be used as the dielectric substrate 17. The thickness of the dielectric substrate 17 is, for example, 1.0 mm or more and 10.0 mm or less.

[0026] The intermediate layer 12 protects the surface of the ground layer 13 and also adhesively holds the dielectric substrate 11. The intermediate layer 12 is preferably durable and moisture-resistant, and may be made of, for example, ethylene-vinyl acetate (EVA) copolymer or cycloolefin polymer (COP). The thickness of the intermediate layer 12 is 10 μm to 400 μm.

[0027] The dielectric substrate 11 is preferably formed as the outermost layer of the reflective panel 10B from a material that is excellent in impact resistance, durability, and transparency. Polycarbonate, acrylic resin, PET, etc. can be used as the dielectric substrate 11. The thickness of the dielectric substrate 11 is, for example, 1.0 mm or more and 10.0 mm or less.

[0028] By covering the conductive pattern 151 with the intermediate layer 16 and then bonding the dielectric substrate 17, the intrusion of moisture and air into the surface of the conductive pattern 151 is suppressed, thereby suppressing deterioration of the reflective surface. By covering the ground plane 13 with the intermediate layer 12 and then bonding the dielectric substrate 11, the intrusion of moisture and air into the surface of the ground plane 13 is suppressed, thereby suppressing surface deterioration of the ground plane 13. This maintains the capacitance between the ground plane 13 and the conductive pattern 151 at a constant value, making it possible to maintain the magnitude of the designed phase delay.

[0029] In order for the reflective panel 10 to maintain a certain level of reflection intensity and reflect electromagnetic waves in two or more directions, the thickness of the conductive pattern 151 or the thickness of the adhesive layer 153 supporting the conductive pattern 151 is designed to be within an appropriate range.

[0030] 5 shows a model 21 of the conductive pattern 151 used to evaluate the reflective panel 10. The evaluation model 21 includes a periodic arrangement of unit cells (also called "supercells") 210. The unit cells 210 are arranged in six rows in the X direction and 36 rows in the Y direction.

[0031] FIG. 6 is a schematic diagram showing the configuration of a unit cell 210 of the model 21. The unit cell 210 is formed by six metal patches 211, 212, 213, 214, 215, and 216. The width (W) and length (L) of the metal patches 211-216 correspond to the width (X) and height (Y) directions of the reflective panel 10 in FIG. 1, respectively. The metal patches 211-216 have the same width W and different lengths L, but their central axes are aligned (the Y coordinate position of the central axis is constant). The pitch in the X direction is constant. The shape and size of the metal patches 211-216 control the phase of reflection, and the reflected waves are superimposed to form a reflected beam in the desired direction. In this example, the unit cell 210 is designed to reflect electromagnetic waves incident perpendicularly (with an incident angle of 0°) in a direction 50° from the normal.

[0032] 3 and 4, and are supported by an adhesive layer 153. The thickness of the adhesive layer 153 or the thickness of the conductive pattern 151 is changed to evaluate the reflection characteristics.

[0033] 5 is used, a plane wave of 28.0 GHz is incident at an incident angle of 0°, and the scattering cross section of the reflected wave is analyzed using general-purpose three-dimensional electromagnetic field simulation software. The scattering cross section, i.e., radar cross section (RCS), is used as an index indicating the ability to reflect incident electromagnetic waves.

[0034] Figure 7 shows an analysis space 101 for electromagnetic field simulation. The thickness direction of the layer structure of the reflective panel 10 is the Z direction, the width direction of the metal patch of the model 21 in Figure 5 is the X direction, and the length direction is the Y direction, and the analysis space is expressed as (size in the X direction) x (size in the Y direction) x (size in the Z direction). The size of the analysis space 101 when the frequency of the incident electromagnetic wave is 28.0 GHz is 83.9 mm x 192.6 mm x 3.7 mm. The boundary condition is a design in which electromagnetic wave absorbers 102 are arranged around the periphery of the analysis space 101. The layer structure of Figure 4 is used as the layer structure for evaluation.

[0035] Example 1 Example 1 is Example 1. Focusing on the thickness of the adhesive layer, a 0.7 mm-thick polycarbonate film is used as the dielectric layer 14. A 0.36 mm-thick Ag-based multilayer ground plane 13 is formed on one side of the polycarbonate film. A 0.03 mm-thick copper foil conductive pattern 151 is placed on the other side of the polycarbonate film. The conductive pattern 151 is supported by a 550 μm-thick adhesive layer 153 with the same area occupancy as the conductive pattern 151. The adhesive layer 153 is a commercially available adhesive with a relative permittivity of 2.4 and a dielectric dissipation factor of 0.05. The ground plane 13 and conductive pattern 151 are each covered with a 400 μm-thick layer of ethylene vinyl acetate and sandwiched between two 2.0 mm-thick polycarbonate sheets. The polycarbonate sheets are used as the outermost dielectric substrates 11 and 17.

[0036] In the RCS plot of a 28.0 GHz plane wave incident at an angle of incidence of 0°, the gain at 0° is −5.0616 dB, the gain at +50° is −2.9028 dB, and the gain at −50° is −14.6348 dB. A gain higher than −6 dB is obtained in the specular reflection direction of 0° and the designed +50° direction, and the difference in gain between these two directions is within 3 dB. By making the thickness of the adhesive layer 153 supporting the conductive pattern 151 550 μm, electromagnetic waves can be reflected in two directions: the specular reflection direction and the designed direction.

[0037] Example 2 Example 2 is Example 2. The conditions are the same as those of Example 1, except for the thickness of the adhesive layer. A conductive pattern 151 formed of copper foil with a thickness of 0.03 mm is supported by an adhesive layer 153 with a thickness of 750 μm and the same area occupancy as the conductive pattern 151. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −1.6845 dB, the gain at +50° is −5.5111 dB, and the gain at −50° is −12.9738 dB.

[0038] A gain of more than -6 dB is obtained in the direction of specular reflection 0° and the designed direction of +50°, and the difference in gain between these two directions is within 4 dB. By making the thickness of the adhesive layer 153 supporting the conductive pattern 151 750 μm, electromagnetic waves can be reflected in two directions: the direction of specular reflection and the designed direction.

[0039] Example 3 Example 3 is Example 3. The conditions are the same as those of Example 1, except for the thickness of the adhesive layer. A conductive pattern 151 formed of copper foil with a thickness of 0.03 mm is supported by an adhesive layer 153 with a thickness of 1000 μm and the same area occupancy as the conductive pattern 151. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −0.1677 dB, the gain at +50° is −8.1477 dB, and the gain at −50° is −14.1064 dB.

[0040] A gain of more than -10 dB is obtained in the 0° direction of specular reflection and the designed +50° direction, and the difference in gain between these two directions is within 8 dB. When the thickness of the adhesive layer 153 carrying the conductive pattern 151 is 1000 μm, electromagnetic waves can be reflected in two directions: the specular reflection direction and the designed direction.

[0041] Example 4 Example 4 is Example 4. The conditions are the same as those of Example 1, except for the thickness of the adhesive layer. A conductive pattern 151 formed of copper foil with a thickness of 0.03 mm is supported by an adhesive layer 153 with a thickness of 250 μm and the same area occupancy as the conductive pattern 151. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −6.6782 dB, the gain at +50° is −1.6853 dB, and the gain at −50° is −16.9408 dB.

[0042] A gain of more than -10 dB is obtained in the 0° direction of specular reflection and the designed +50° direction, and the difference in gain between these two directions is within 8 dB. When the thickness of the adhesive layer 153 carrying the conductive pattern 151 is 250 μm, electromagnetic waves can be reflected in two directions: the specular reflection direction and the designed direction.

[0043] Example 5 Example 5 is a fifth embodiment. Focus is placed on the thickness of the conductive pattern 151. A 0.7 mm thick polycarbonate film is used as the dielectric layer 14. A 0.36 mm thick Ag-based multilayer ground layer 13 is set on one side of the polycarbonate film. A 0.001 mm (1.0 μm) thick conductive pattern 151 made of copper foil is placed on the other side of the polycarbonate film. The conductive pattern 151 is supported by a 1000 μm thick adhesive layer 153 with the same area occupancy as the conductive pattern 151. The ground layer 13 and the conductive pattern 151 are each covered with a 400 μm thick ethylene vinyl acetate layer and sandwiched between two 2.0 mm thick polycarbonate sheets. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −9.0667 dB, the gain at +50° is −0.9954 dB, and the gain at −50° is −17.8861 dB.

[0044] A gain higher than -10 dB is obtained in the 0° direction of specular reflection and the designed +50° direction, and the difference in gain between these two directions is approximately 8 dB. When the thickness of conductive pattern 151 is 0.001 mm (1.0 μm), electromagnetic waves can be reflected in two directions: the specular reflection direction and the designed direction.

[0045] Example 6 Example 6 is Example 6. The conditions are the same as those of Example 5, except for the thickness of the conductive pattern 151. A ground layer 13 is formed of a 0.36 mm thick Ag-based multilayer film on one side of a 0.7 mm thick polycarbonate film serving as the dielectric layer 14. A conductive pattern 151 formed of a 0.005 mm (5.0 μm) thick copper foil is disposed on the other side of the polycarbonate film. The RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0° shows a gain of −2.8762 dB at 0°, a gain of −3.2452 dB at +50°, and a gain of −16.7852 dB at −50°.

[0046] A gain higher than -10 dB is obtained in the 0° direction of specular reflection and the designed +50° direction, and the difference in gain between these two directions is small at approximately 0.37 dB, so that the electromagnetic waves are reflected in the two directions with approximately the same intensity. When the thickness of the conductive pattern 151 is 0.005 mm (5.0 μm), the electromagnetic waves can be effectively reflected in two directions: the specular reflection direction and the designed direction.

[0047] Example 7 Example 7 is Comparative Example 1. In Comparative Example 1, the thickness of adhesive layer 153 supporting conductive pattern 151 with a thickness of 0.03 mm is set to 50 μm. The other configurations are the same as those of Example 1. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −16.3973 dB, the gain at +50° is −1.5362 dB, and the gain at −50° is −17.5759 dB.

[0048] If the thickness of the adhesive layer 153 carrying the conductive pattern 151 is reduced to 50 μm, the normally incident electromagnetic wave is reflected only in the designed 50° direction, and the gain does not exceed −10 dB in the 0° direction of specular reflection. It is desirable to make the thickness of the adhesive layer 153 thicker than 50 μm.

[0049] Example 8 Example 8 is Comparative Example 2. In Comparative Example 2, the thickness of adhesive layer 153 supporting conductive pattern 151 with a thickness of 0.03 mm is set to 1500 μm. The other configurations are the same as those of Example 1. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −0.9954 dB, the gain at +50° is −14.0880 dB, and the gain at −50° is −17.8861 dB.

[0050] If the thickness of the adhesive layer 153 supporting the conductive pattern 151 is increased to 1500 μm, the electromagnetic wave incident normally is reflected only in the direction of 0°, which is the direction of specular reflection, and a gain of more than −10 dB cannot be obtained in the designed direction. It is desirable to make the thickness of the adhesive layer 153 less than 1500 μm.

[0051] Example 9 Example 9 is Comparative Example 3. In Comparative Example 3, attention is focused on the thickness of conductive pattern 151. Conductive pattern 151 formed of copper foil with a thickness of 0.01 mm (10.0 μm) is supported by adhesive layer 153 with a thickness of 1000 μm and the same area occupancy as conductive pattern 151. The other conditions are the same as in Example 1. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −0.8865 dB, the gain at +50° is −15.1212 dB, and the gain at −50° is −14.134 dB.

[0052] If the thickness of the conductive pattern 151 is set to 0.01 mm, electromagnetic waves incident perpendicularly are reflected only in the direction of 0°, which is the direction of specular reflection, and a gain exceeding −10 dB cannot be obtained in the designed direction. It is desirable that the thickness of the conductive pattern 151 be less than 0.01 mm (10.0 μm).

[0053] Example 10 Example 10 is Comparative Example 4. In Comparative Example 4, the thickness of the conductive pattern 151 is reduced. The conductive pattern 151 is formed of copper foil with a thickness of 0.0001 mm (0.1 μm), and is supported by an adhesive layer 153 with a thickness of 1000 μm and the same area occupancy as the conductive pattern 151. The other conditions are the same as those of Example 1. In the RCS plot of a 28.0 GHz plane wave incident at an incident angle of 0°, the gain at 0° is −0.8865 dB, the gain at +50° is −15.1212 dB, and the gain at −50° is −14.134 dB.

[0054] If the thickness of the conductive pattern 151 is reduced to 0.0001 mm, the electromagnetic wave incident normally is reflected only in the direction of 0°, which is the direction of specular reflection, and no gain exceeding −10 dB can be obtained in the designed direction. It is desirable that the thickness of the conductive pattern 151 be thicker than 0.0001 mm (0.1 μm).

[0055] Based on Examples 1 to 10 (Examples 1 to 6 and Comparative Examples 1 to 4), the thickness of the adhesive layer 153 supporting the conductive pattern 151 at the same occupancy as the conductive pattern 151 is preferably greater than 50 μm and less than 1500 μm, more preferably 250 μm to 1000 μm, and even more preferably 250 μm to 750 μm. By setting the thickness of the adhesive layer 153 within this range, incident electromagnetic waves can be reflected in two directions, the direction of specular reflection and the designed direction, while maintaining a certain level of reflection intensity. Furthermore, the thickness of the conductive pattern 151 is preferably greater than 0.1 μm and less than 10.0 μm. By setting the thickness of the conductive pattern 151 within this range, incident electromagnetic waves can be reflected in two directions, the direction of specular reflection and the designed direction, while maintaining a certain level of reflection intensity.

[0056] The reflective panel and electromagnetic wave reflecting device of the embodiments are not limited to the above-described configuration examples. The results of Examples 1 to 9 are applicable to electromagnetic waves of 28 GHz ± 5 GHz. The in-plane size of the reflective panel 10 can be appropriately selected from a range of 10.0 cm × 10.0 cm to 3.0 m × 3.0 m. Furthermore, calculations have confirmed that results similar to those of Examples 1 to 6 can be obtained if the adhesive layer 153 that bonds the conductive pattern 151 to the dielectric layer 14 is at least partially separated or removed without covering the entire surface of the dielectric layer 14. The reflective panel 10 maintains a certain level of reflection intensity and reflects incident electromagnetic waves in the direction of specular reflection and the designed direction, so even a small reflective panel can effectively improve the radio wave environment. As shown in Figure 8, multiple reflective panels 10 may be connected together for use.

[0057] 8 is a schematic diagram of an electromagnetic wave reflective fence 100 in which multiple reflective panels 10-1, 10-2, and 10-3 are connected by a frame 50. Electromagnetic wave reflecting devices 60-1, 60-2, and 60-3 are formed by the reflective panels 10-1, 10-2, and 10-3 and the frames 50 that hold the side edges of these reflective panels, respectively. Each of the reflective panels 10-1, 10-2, and 10-3 reflects incident electromagnetic waves in a specular reflection direction and at least one non-specular reflection direction while maintaining a certain degree of reflection intensity.

[0058] The reflective panels 10-1, 10-2, and 10-3 (collectively referred to as "reflective panels 10" as appropriate) may be electrically connected to one another by a frame 50 in order to maintain continuity of the reflected potential. By forming at least a portion of the frame 50, for example, a portion connecting the adjacent side edges of two reflective panels 10, from a conductive material, the adjacent reflective panels 10 can be mechanically and electrically connected. As shown in FIG. 8 , the electromagnetic wave reflective fence 100 may be freestanding using legs 56, or may be installed on a wall or ceiling without legs 56. In this case, incident electromagnetic waves can be reflected in two or more directions while maintaining a certain level of reflection intensity.

[0059] The above disclosure may include the following aspects. (Item 1) A reflective panel that reflects radio waves in a predetermined band selected from a frequency band of 1 GHz or more and 300 GHz or less, comprising: a dielectric layer; a periodic conductive pattern provided on one surface of the dielectric layer; a ground layer provided on the other surface of the dielectric layer; and an adhesive layer that joins the conductive pattern to the one surface, wherein the adhesive layer that joins the conductive pattern is provided with the same area occupancy as the conductive pattern, and the conductive pattern has a thickness greater than 0.1 μm and less than 10.0 μm. (Item 2) The reflective panel according to item 1, further comprising: an intermediate layer that covers the adhesive layer and the conductive pattern. (Item 3) The reflective panel according to item 2, further comprising: a dielectric substrate joined onto the conductive pattern by the intermediate layer. (Item 4) The reflective panel according to any one of Items 1 to 3, wherein the conductive pattern forms a reflective surface of the reflective panel and reflects incident electromagnetic waves in a first direction for specular reflection and a second direction for non-specular reflection, the difference in reflection intensity between the first direction and the second direction being within 8 dB. (Item 5) A reflective panel that reflects radio waves in a predetermined band selected from a frequency band of 1 GHz or more and 300 GHz or less, comprising: a dielectric layer; a periodic conductive pattern provided on one surface of the dielectric layer; a ground layer provided on the other surface of the dielectric layer; and an adhesive layer that joins the conductive pattern to the one surface of the dielectric layer, wherein the adhesive layer that joins the conductive pattern is provided with the same area occupancy as the conductive pattern, and the thickness of the adhesive layer is greater than 50 μm and less than 1500 μm. (Item 6) The reflective panel according to Item 5, further comprising an intermediate layer that covers the adhesive layer and the conductive pattern. (Item 7) The reflective panel according to item 6, further comprising: a dielectric substrate joined onto the conductive pattern by the intermediate layer. (Item 8) The reflective panel according to any one of items 5 to 7, wherein the conductive pattern forms a reflective surface of the reflective panel, and reflects incident electromagnetic waves in a first direction for specular reflection and a second direction for non-specular reflection, and the difference between the reflection intensity in the first direction and the reflection intensity in the second direction is within 8 dB.(Item 9) An electromagnetic wave reflecting device comprising: a reflective panel according to any one of items 1 to 8; and a frame for holding the reflective panel. (Item 10) An electromagnetic wave reflective fence formed by connecting a plurality of reflective panels according to item 9.

[0060] This application claims priority based on Japanese Patent Application No. 2022-206475 filed on December 23, 2022, and includes the entire contents of this Japanese patent application.

[0061] 10, 10-1, 10-2, 10-3 Reflection panel 11, 17 Dielectric substrate 12, 16 Intermediate layer 13 Ground layer 14 Dielectric layer 151 Conductive pattern 153 Adhesive layer 50 Frame (side frame) 57 Top frame 58 Bottom frame 60, 60-1, 60-2, 60-3 Electromagnetic wave reflection device 100 Electromagnetic wave reflection fence 210 Unit cell

Claims

1. A reflective panel that reflects radio waves in a predetermined band selected from a frequency band of 1 GHz or more and 170 GHz or less, a dielectric layer; a periodic conductive pattern provided on one surface of the dielectric layer; a ground layer provided on the other surface of the dielectric layer; an adhesive layer that bonds the conductive pattern to the one surface; wherein the adhesive layer that adheres the conductive pattern is provided with the same area occupation rate as the conductive pattern, and the thickness of the conductive pattern is greater than 0.1 μm and less than 10.0 μm.

2. an intermediate layer covering the adhesive layer and the conductive pattern; The reflective panel of claim 1 further comprising:

3. a dielectric substrate bonded onto the conductive pattern by the intermediate layer; The reflective panel of claim 2 further comprising:

4. 2. The reflective panel of claim 1, wherein the conductive pattern forms a reflective surface of the reflective panel, reflecting incident electromagnetic waves in a first direction of specular reflection and a second direction of non-specular reflection, and the difference in reflection intensity between the first direction and the second direction is within 8 dB.

5. A reflective panel that reflects radio waves in a predetermined band selected from a frequency band of 1 GHz or more and 170 GHz or less, a dielectric layer; a periodic conductive pattern provided on one surface of the dielectric layer; a ground layer provided on the other surface of the dielectric layer; an adhesive layer that bonds the conductive pattern to the one surface of the dielectric layer; wherein the adhesive layer that adheres the conductive pattern is provided with the same area occupation rate as the conductive pattern, and the thickness of the adhesive layer is greater than 50 μm and less than 1500 μm.

6. an intermediate layer covering the adhesive layer and the conductive pattern; The reflective panel of claim 5 further comprising:

7. a dielectric substrate bonded onto the conductive pattern by the intermediate layer; The reflective panel of claim 6 further comprising:

8. 6. The reflective panel of claim 5, wherein the conductive pattern forms a reflective surface of the reflective panel, reflecting incident electromagnetic waves in a first direction of specular reflection and a second direction of non-specular reflection, and the difference between the reflection intensity in the first direction and the reflection intensity in the second direction is within 8 dB.

9. A reflective panel according to any one of claims 1 to 8; a frame for holding the reflective panel; An electromagnetic wave reflecting device having:

10. An electromagnetic wave reflecting fence comprising a plurality of electromagnetic wave reflecting devices according to claim 9 connected together.