Radio wave transmission structure

Abstract

The present invention improves the far field radio wave intensity of a radio wave transmission structure. This radio wave transmission structure 1 has both a difficult-to-transmit portion 1a through which radio waves are transmitted with difficulty and an easy-to-transmit portion 1b through which radio waves can be transmitted more easily than the difficult-to-transmit portion 1a. At least a portion of the difficult-to-transmit portion 1a is covered with a shielding layer 2 for shielding radio waves.

Description

Radio wave transparent structure

[0001] The present invention relates to a radio wave transparent structure having both a poorly transmitting portion that does not easily transmit radio waves and an easily transmitting portion that allows radio waves to easily transmit.

[0002] Like light, radio waves used in communications are known to refract and scatter at interfaces with different permittivity and permeability. In communications, all objects, such as concrete walls, display panels, and glass, have different permittivity and permeability from air, so the presence of an object (structure) in the path of the radio waves can cause poor communication.

[0003] In response to this, a technique for increasing the radio wave transmittance of a structure is disclosed, for example, in Patent Document 1. In Patent Document 1, a dielectric structure is bonded to the structure and the dielectric constant of the dielectric structure is adjusted to increase the radio wave transmittance of the structure.

[0004] Special Publication No. 2022-511466

[0005] However, the technique of Patent Document 1 has a problem in that when the radio wave transmittance of a part of the structure is improved, the communication state becomes worse the further away from the improved part.

[0006] The present invention has been made in view of the above problems, and an object of the present invention is to improve the radio wave intensity in the far field of a radio wave transparent structure.

[0007] After extensive research, the inventors of the present application have discovered that the cause of the above problem is that radio waves that have passed through the easy-to-permeate parts of the structure where radio wave permeability has been improved (scattered radio waves) cancel each other out due to a phase difference between the radio waves that have passed through the other difficult-to-permeate parts (transmitted radio waves).Based on this principle, the inventors have discovered that by blocking radio waves that enter the difficult-to-permeate parts, it is possible to prevent the scattered radio waves from being canceled out by the transmitted radio waves, and improve the radio wave intensity in the far field of the structure.

[0008] In order to solve the above problems, the present invention includes the following aspects. Item 1: A radio wave transparent structure having both a difficult-to-transmit portion that does not easily transmit radio waves and an easy-to-transmit portion that transmits radio waves more easily than the difficult-to-transmit portion, wherein at least a portion of the difficult-to-transmit portion is covered with a shielding layer that blocks radio waves. Item 2: A radio wave transparent structure according to Item 1, wherein the difficult-to-transmit portion is entirely covered with the shielding layer. Item 3: A radio wave transparent structure according to Item 1 or 2, wherein the shielding layer is a radio wave reflector that reflects incident radio waves. Item 4: The shielding layer has a conductive layer containing a conductor, a protective layer that holds the conductive layer, and an adhesive layer that bonds the conductive layer and the protective layer, and the radio wave transparent structure, the conductive layer, the adhesive layer, and the protective layer are laminated in this order, and the conductive layer has conductor-free regions surrounded by one or more linear conductors that are periodically arranged at predetermined intervals.

[0009] According to the present invention, it is possible to improve the radio wave intensity in the far field of a radio wave transparent structure.

[0010] (A) is a plan view of a radio wave transparent structure according to this embodiment, and (B) is a cross-sectional view taken along the line A-A in Fig. 1(A). (A) is a schematic cross-sectional view of a structure without a shielding layer, and (B) is a schematic cross-sectional view of a structure with a shielding layer. (A) and (B) are a schematic front view and a schematic cross-sectional view of an easy-to-transmit portion, respectively. A cross-sectional view showing the schematic configuration of a difficult-to-transmit portion. (A) is a plan view of a difficult-to-transmit portion, and (B) is an enlarged view of part A in Fig. 5(A).

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the accompanying drawings. Note that the present invention is not limited to the following embodiment, and various modifications are possible without departing from the spirit of the present invention.

[0012] [Structure] Fig. 1(A) is a plan view of a radio wave transparent structure (hereinafter referred to as structure) 1 according to this embodiment, and Fig. 1(B) is a cross-sectional view taken along line A-A in Fig. 1(A). The shape of the structure 1 is rectangular in plan view, but the shape and size of the structure 1 are not particularly limited.

[0013] As shown in Figure 1 (A), the structure 1 has both a difficult-to-permeate region 1a that does not easily transmit radio waves and an easy-to-permeate region 1b that allows radio waves to pass through more easily than the difficult-to-permeate region 1a. In other words, from the perspective of radio wave permeability, the structure 1 is divided into the difficult-to-permeate region 1a and the easy-to-permeate region 1b. Note that the difficult-to-permeate region 1a and the easy-to-permeate region 1b are located on the same plane, but they do not have to be located on the same plane.

[0014] As shown in FIG. 1B , the structure 1 includes a substrate 11 and a metamaterial structure 12 .

[0015] The substrate 11 is an object that divides a building, such as a concrete wall, glass, etc. The thickness and size of the substrate 11 are not particularly limited.

[0016] The metamaterial structures 12 are components that increase the radio wave transmittance of the structure 1, and a plurality of them are provided at intervals on the substrate 11. As a result, the portions of the structure 1 where the metamaterial structures 12 are provided become easy-to-transmit portions 1b, and the portions where the metamaterial structures 12 are not provided become difficult-to-transmit portions 1a. Furthermore, the difficult-to-transmit portions 1a are covered with a shielding layer 2 that blocks radio waves.

[0017] [Intensity of transmitted radio waves] By providing the shielding layer 2, it is possible to improve the intensity of radio waves transmitted through the structure 1 compared to when the shielding layer 2 is not provided. The reason for this will be explained below.

[0018] FIG. 2A is a schematic cross-sectional view of the structure 1 without the shielding layer 2, and FIG. 2B is a schematic cross-sectional view of the structure 1 with the shielding layer 2.

[0019] As shown in Figure 2(A), radio waves R1 incident on the poorly permeable region 1a of the structure 1 are attenuated and pass through the poorly permeable region 1a. On the other hand, radio waves R2 incident on the easily permeable region 1b of the structure 1 pass through the poorly permeable region 1a while being repeatedly scattered and reflected inside the metamaterial structure 12 and the substrate 11. In other words, radio waves R2 are a combination of scattered radio waves R21, R22, etc. Radio waves R2 that pass through the easy-to-permeable region 1b are attenuated less than radio waves R1 that pass through the poorly permeable region 1a.

[0020] Here, because radio waves undergo a phase shift when reflected at an interface between elements having different dielectric constants and magnetic permeabilities, the phase of radio wave R1 and the phase of radio wave R2 generally differ. The inventors of the present application have discovered that the phase difference between radio waves R1 and R2 causes radio waves R1 and R2 to cancel each other out, and that the closer the phase difference is to 180°, the greater the amount of cancellation between radio waves R1 and R2. Therefore, even if the intensity of the transmitted radio waves R2 is high near the easy-to-transmit portion 1b of the structure 1, in the far field where radio waves R1 and R2 are mixed, radio waves R1 and R2 may cancel each other out, resulting in poor communication conditions.

[0021] Therefore, in this embodiment, as shown in Fig. 2(B), the poorly permeable portion 1a of the structure 1 is covered with a shielding layer 2. As a result, the radio wave R1 does not pass through the poorly permeable portion 1a, and the radio wave R2 that has passed through the easily permeable portion 1b is not canceled out by the radio wave R1, and good communication conditions can be maintained even in the far field.

[0022] [Easy-to-Permeate Region] First, the structure of the easy-to-permeate region 1b provided with the metamaterial structure 12 will be described. Figures 3(A) and 3(B) are a schematic front view and a schematic cross-sectional view, respectively, of the easy-to-permeate region 1b. The easy-to-permeate region 1b is configured by laminating a substrate 11, a plurality of metal patterns 3 provided on the substrate 11, and a protective film 14 covering the plurality of metal patterns 3. The protective film 14 is adhered to the substrate 11 via an adhesive layer 13. The metal patterns 3, the adhesive layer 13, and the protective film 14 constitute the metamaterial structure 12.

[0023] 3A, each metal pattern 3 includes a split ring resonator 4 and an enclosing portion 5 surrounding the split ring resonator 4. The split ring resonator 4 and the enclosing portion 5 are made of a conductor. The enclosing portion 5 is separated from the split ring resonator 4 and is not in contact with the split ring resonator 4.

[0024] With this configuration, the easily permeable portion 1b can have resonance points for radio waves in multiple frequency bands, which is advantageous in that it is possible to have resonance points for radio waves in multiple frequency bands without stacking multiple structures 1, allowing radio waves in multiple frequency bands to pass through a single structure 1, and there are fewer restrictions on the installation location.

[0025] For example, radio waves transmitted from a transmitter are incident on the structure 1. The transmitter is a communication device having a transmitting antenna capable of outputting a radio signal using radio waves as a medium. Examples of transmitters include a fixed base station, a mobile base station, a radio wave transmitter, a wireless terminal, and a local 5G base station.

[0026] The radio waves that have passed through the structure 1 are transmitted to, for example, a receiver inside the building. The receiver is a communication device with a receiving antenna. Examples of receivers include smartphones, mobile phones, tablet devices, laptop computers, portable game consoles, repeaters, radios, and televisions.

[0027] The radio waves that can be transmitted through the structure 1 according to this embodiment are, for example, radio waves in a specific frequency band in which the frequency of the incident wave belongs to any of the ranges of 3 GHz to 5 GHz, 25 GHz to 30 GHz, and 100 GHz to 300 GHz. Among these, it is preferable that the transmission efficiency is set high in the 5 GHz frequency band (3 GHz to 5 GHz, 25 GHz to 30 GHz).

[0028] (Metal Pattern 3) The multiple metal patterns 3 are made of conductors. The multiple metal patterns 3 are formed on the substrate 11. All of the multiple metal patterns 3 are formed in the same shape and have a periodic structure. In other words, one metal pattern 3 represents the smallest unit in the metasurface.

[0029] Examples of methods for forming the metal pattern 3 on the substrate 11 include a method of laminating a thin film, in which the metal pattern 3 is embedded in a thin-film dielectric, on the substrate 11, and a method of forming the metal pattern 3 on the substrate 11 without using a dielectric. Examples of methods for forming the metal pattern 3 on the substrate 11 include the following.

[0030] Photoresist is applied to the substrate 11, covered with a photomask on which the metal pattern 3 is formed, and exposed to ultraviolet light, and the exposed portions are removed with a developer. Next, metal is vapor-deposited on the portions from which the photoresist has been removed, and then the photoresist is removed, thereby forming the metal pattern 3 on the substrate 11. Note that although an example using positive photolithography has been described here, negative photolithography may also be used.

[0031] The dielectric used here preferably has a relative dielectric constant of 1.5 or more, more preferably 2.5 or more, and even more preferably 3 or more. Examples of the dielectric include acrylic resin, PET (polyethylene terephthalate), and a mixture of acrylic and air.

[0032] Examples of conductors include one or more of silver, gold, copper, platinum, aluminum, titanium, silicone, indium tin oxide, and alloys (e.g., alloys containing nickel, chromium, and molybdenum). Examples of alloys containing nickel, chromium, and molybdenum include various grades of Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X.

[0033] The thickness of the metal pattern 3 is preferably 10 nm or more, more preferably 30 nm or more, and even more preferably 100 nm or more. On the other hand, the upper limit of the thickness of the metal pattern 3 is preferably 10 μm or less, more preferably 5 μm or less, and even more preferably 4 μm or less. When the thickness of the metal pattern 3 is 10 nm or more, appropriate radio wave intensity can be ensured.

[0034] Each metal pattern 3 preferably has a side of 15 mm or more, more preferably 20 mm or more, and even more preferably 25 mm or more, while each metal pattern 3 preferably has a side of 50 mm or less, more preferably 40 mm or less, and even more preferably 30 mm or less.

[0035] The distance between adjacent metal patterns 3 is preferably equal to or less than the wavelength of the radio waves to be transmitted. Specifically, it is preferably 20 mm or less, and more preferably 15 mm or less. On the other hand, the distance between adjacent metal patterns 3 may be 0 mm or more, and is preferably 5 mm or more, and more preferably 10 mm or more.

[0036] The metal pattern 3 preferably has a relative dielectric constant of 7 or more. On the other hand, the upper limit of the relative dielectric constant is preferably 10,000 or less.

[0037] As shown in Fig. 3A, each metal pattern 3 includes a split-ring resonator 4 and an enclosing portion 5 that surrounds each of the split-ring resonators 4 in a one-to-one relationship. The metal pattern 3 may have various shapes depending on the desired frequency band of radio waves for which radio wave permeability is to be increased. Here, the pattern shown in Fig. 3A will be described as an example. The metal pattern 3 of this embodiment can increase radio wave permeability in three frequency bands: a frequency band near 2 GHz, a frequency band near 3.4 GHz, and a frequency band near 5.1 GHz.

[0038] (Split-ring resonator 4) The split-ring resonator 4 is a metal microstructure having a structure finer than the wavelength of the target radio waves (electromagnetic waves). The split-ring resonator 4 corresponds to the split-ring resonator in a metasurface (metamaterial) and is also called a split-ring resonator (SRR).

[0039] The split ring resonator 4 according to this embodiment is composed of multiple linear bodies. Each linear body extends thinly. In this embodiment, each linear body is linear. Preferably, each split ring resonator 4 is formed rotationally symmetrically about the center of gravity G1 of the split ring resonator 4. The split ring resonator 4 according to this embodiment has a shape obtained by rotating a figure (a substantially T-shaped figure) consisting of a first linear body 41 extending horizontally from the center of gravity G1 and a second linear body 42 extending vertically from the middle of the first linear body 41 by 90 degrees about the center of gravity G1. In other words, the split ring resonator 4 according to this embodiment has a four-fold symmetry figure.

[0040] The multiple linear bodies are all formed with the same width in the longitudinal direction (same width). The line width is, for example, preferably 10 μm or more, more preferably 1 mm or more, and even more preferably 1.8 mm or more. On the other hand, the line width is preferably 2 mm or less. When the line width of the linear bodies is 2 mm or less, the degree of freedom in designing the metal pattern 3 can be improved. When the line width of the linear bodies is 10 μm or more, the productivity of the metal pattern can be maintained while suppressing costs.

[0041] (Enclosing portion 5) The surrounding portion 5 is provided on the substrate 11 and surrounds the split-ring resonator 4. The surrounding portion 5 is spaced apart from the split-ring resonator 4. The minimum distance L1 from the split-ring resonator 4 to the surrounding portion 5 is preferably 50% or more, more preferably 80% or more, and even more preferably 100% or more of the width (line width) of the linear body of the split-ring resonator 4. The maximum distance L2 from the split-ring resonator 4 to the surrounding portion 5 is preferably less than the wavelength of radio waves in the frequency band for which radio wave transmittance is to be increased.

[0042] The surrounding portion 5 is formed in a quadrangular shape. However, the surrounding portion 5 may be, for example, a triangular shape, a pentagonal shape, a hexagonal shape, a circular shape, an elliptical shape, etc. It is preferable that the surrounding portion 5 is continuous in the circumferential direction.

[0043] In this specification, "continuous" includes not only an embodiment in which the wire is continuous without being divided in the circumferential direction, but also an embodiment in which the wire is mostly continuous (with a slight separation in one portion). A slight separation is considered to be continuous if it is 5% or less of the circumferential length.

[0044] The line width of the surrounding portion 5 is preferably the same over the entire length. In this embodiment, the line width of the surrounding portion 5 is the same as the width of the linear members of the split-ring resonator 4, but may be smaller than the width of the linear members of the split-ring resonator 4.

[0045] (Protective Film 14) The protective film 14 can protect the metal patterns 3 by covering the multiple metal patterns 3. The protective film 14 has a size corresponding to the substrate 11 in a plan view. Examples of the protective film 14 include films made of synthetic resins. Examples of synthetic resins include one or more selected from the group consisting of PET (polyethylene terephthalate), COP (cycloolefin polymer), polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin.

[0046] The protective film 14 preferably contains fluorine. The protective film 14 containing fluorine can prevent transmission of ultraviolet rays, and therefore can protect the plurality of metal patterns 3 from ultraviolet rays.

[0047] The thickness of the protective film 14 is preferably 5 μm or more, more preferably 10 μm or more, and even more preferably 15 μm or more, while the upper limit of the thickness of the protective film 14 is preferably 100 μm or less, more preferably 50 μm or less, and even more preferably 25 μm or less.

[0048] The protective film 14 is adhered to the substrate 11 via an adhesive layer 13. The adhesive layer 13 may be made of, for example, a synthetic resin or a rubber adhesive sheet. Examples of synthetic resins include acrylic resin, silicone resin, and polyvinyl alcohol resin.

[0049] [Hard-to-permeate portion] Next, a description will be given of the hard-to-permeate portion 1a of the structure 1. As described above, the hard-to-permeate portion 1a is covered with the shielding layer 2 that blocks radio waves.

[0050] Fig. 4 is a cross-sectional view showing a schematic configuration of the difficult-to-penetrate portion 1a, taken along line B-B in Fig. 5(B). Fig. 5(A) is a plan view of the difficult-to-penetrate portion 1a, and Fig. 5(B) is an enlarged view of portion A in Fig. 5(A). The shielding layer 2 in this embodiment is a radio wave reflector that reflects radio waves. The shielding layer 2 has a conductive layer 22 containing a conductor 21, a protective layer 24 that holds the conductive layer 22, and an adhesive layer 23 that bonds the conductive layer 22 and the protective layer 24, and is laminated in the order of the substrate 11, the conductive layer 22, the adhesive layer 23, and the protective layer 24.

[0051] The shielding layer 2 includes a conductor 21 for blocking radio waves. The shielding layer 2 reflects radio waves having an incident frequency of 3 GHz to 5 GHz, 25 GHz to 30 GHz, or 100 GHz to 300 GHz.

[0052] The angle of incidence of the incident wave is at least a predetermined angle between 15 degrees and 75 degrees, preferably 45 degrees, and more preferably the entire range of angles between 15 degrees and 75 degrees. In this case, there is one frequency at which the intensity of the reflected wave when the incident wave is specularly reflected by the low-penetration region 1a is between -30 dB and 0 dB relative to the incident wave. Preferably, at a frequency of 28.5 GHz, the specular reflection intensity is between -30 dB and 0 dB relative to the incident wave. More preferably, the specular reflection intensity is between -30 dB and 0 dB relative to the incident wave over the entire frequency band from 20 GHz to 60 GHz, and even more preferably, the specular reflection intensity is between -30 dB and 0 dB relative to the incident wave over the entire frequency band from 3 GHz to 300 GHz. "Specular reflection intensity" refers to the reflection intensity at which radio waves are reflected, and refers to the intensity of the reflected wave when the incident wave is specularly reflected. "Flat" refers to a state without irregularities or curves.

[0053] The normal reflection intensity is preferably -25 dB or more and 0 dB or less relative to the incident wave, more preferably -22 dB or more and 0 dB or less, even more preferably -20 dB or more and 0 dB or less, and even more preferably -15 dB or more and 0 dB or less. When the normal reflection intensity is -30 dB or more relative to the incident wave, the difficult-to-penetrate portion 1a can reflect radio waves while maintaining a high reflection intensity. Note that in this embodiment, the normal reflection intensity and reflection intensity are values ​​when the distance between the reflection point of the difficult-to-penetrate portion 1a and the radio wave source and the distance between the reflection of the difficult-to-penetrate portion 1a and the receiving unit are 1 m.

[0054] (Configuration of each layer of the shielding layer 2) Each layer of the shielding layer 2 will be described in more detail below. In the following description, the direction in which each layer is stacked is defined as the vertical direction, and the vertical direction of the shielding layer 2 corresponds to the vertical direction in FIG. 4. The vertical and horizontal directions are also defined based on FIG. 5. The vertical and horizontal directions are used for the purpose of explanation, and do not define the vertical and horizontal directions when the structure 1 is used, such as when it is attached to a building or the like. The drawings are not drawn to scale. In FIG. 5(A), the adhesive layer 23 and protective layer 24 are omitted from the illustration of part of the structure 1.

[0055] (Conductive Layer 22) The conductive layer 22 is preferably one or more linear conductors 21 formed as a thin film on the upper surface of the substrate 11. All of the conductors 21 constituting the conductive layer 22 are formed on the upper surface of the substrate 11.

[0056] The conductor 21 is preferably made of silver (Ag), for example. The conductor 21 may be made of any metal, metal compound, or alloy having free electrons, and is not limited to silver. For example, the conductor 21 may be made of gold, copper, platinum, aluminum, titanium, silicone, indium tin oxide, or an alloy (for example, an alloy containing nickel, chromium, and molybdenum). Examples of alloys containing nickel, chromium, and molybdenum include various grades of Hastelloy B-2, B-3, C-4, C-2000, C-22, C-276, G-30, N, W, and X.

[0057] In this embodiment, as shown in FIG. 5B , one or more linear conductors 21 are arranged surrounding a plurality of regions 21a without conductors 21. That is, the conductive layer 22 includes conductors 21 and regions 21a without conductors 21 periodically arranged at predetermined intervals. The term "linear" means that the longitudinal length is 3000 times or more the length in the direction perpendicular to the longitudinal direction. In the example shown in FIG. 5B , a plurality of first linear conductors 21A and a plurality of second linear conductors 21B constituting the conductor 21 are arranged along the vertical and horizontal directions parallel to the edge of the square-shaped substrate 11. The first linear conductors 21A and the second linear conductors 21B are each arranged at equal intervals, and the region surrounded by two adjacent first linear conductors 21A and two adjacent second linear conductors 21B is the region 21a without conductors 21. The regions 21a without conductors 21 are squares of the same shape. In other words, a plurality of regions 21a without conductor 21 are arranged in the vertical and horizontal directions at intervals of the line width L6 of conductor 21. First linear body 21A and second linear body 21B are electrically connected at the intersections where they overlap.

[0058] The line width L6 of the conductor 21 is preferably set to 0.05 μm or more and 15 μm or less. The spacing L7 between adjacent conductors 21 in the vertical or horizontal direction (the length of one side of the square conductor-free region 12a) is set to be greater than the wavelength of visible light and less than the wavelength of radio waves reflected by the structure 1. In this example, it is set to 2 μm or more and 10 cm or less. More preferably, it is 20 μm or more and 1 cm or less, and even more preferably, it is 25 μm or more and 1 mm or less. Even more preferably, it is 30 μm or more and 250 μm or less. If the conductor-free region 21a is not square, the maximum length between any two points on the ends of the conductor-free region 21a is set to the above length. The conductor-free region 21a may also be filled with the adhesive of the adhesive layer 23.

[0059] The thickness (film thickness) L3 of the conductor 21 is preferably a thickness that allows visible light to pass through. The thickness L3 of the conductor 21 is preferably 0.05 μm or more and 10 μm or less. From the viewpoint of ensuring appropriate radio wave intensity, the thickness L3 is preferably 5 nm or more.

[0060] The conductive layer 22 preferably has a coverage of 1% or more and 50% or less, more preferably 1% or more and 10% or less. The coverage refers to the ratio of the area occupied by the conductor 21 per unit area in the region on the top surface of the substrate 11 where the conductive layer 22 is provided in a plan view. The region where the conductive layer 22 is provided is the region of the top surface of the substrate 11 excluding the peripheral edge of the substrate 11 (the portion between the edge of the substrate 11 and the conductive layer 22). The coverage is measured using a scanning electron microscope (SEM), a transmission electron microscope (TEM), an optical microscope, or the like.

[0061] In this way, since the coverage of the conductive layer 22 is small and the thickness L3 of the conductor 21 is thin, even if the substrate 11 is made of glass, a decrease in the visible light transmittance of the structure 1 can be suppressed.

[0062] 5(B), the shape of the region 21a where no conductor 21 is present is square, but the arrangement of the conductors 21 is not limited to this. For example, the spacing between adjacent first linear bodies 21A extending in the horizontal direction and the spacing between adjacent second linear bodies 21B extending in the vertical direction may be different, and the shape of the region 21a where no conductor 21 is present may be rectangular. Furthermore, the conductors 21 may be arranged so that the shape of the region 21a where no conductor 21 is present is a triangle, a circle, a polygon with pentagons or more sides, or the like.

[0063] (Adhesive Layer 23) The adhesive layer 23 adheres the protective layer 24 to the substrate 11 and the conductive layer 22 and is composed of an adhesive. The adhesive layer 23 has a size corresponding to the impermeability-impairing portion 1a in a planar view. A synthetic resin or rubber adhesive sheet is used as the adhesive for the adhesive layer 23. Examples of synthetic resins include acrylic resin, silicone resin, and polyvinyl alcohol resin. The thickness L4 of the adhesive layer 23 is the distance between the upper surface of the conductive layer 22 and the lower surface of the protective layer 24. In this embodiment, the thickness L4 is set to 150 μm, but is not limited thereto. The adhesive of the adhesive layer 23 may be filled in the region 12a of the conductive layer 22 where no conductor 21 is present or in the peripheral edge of the substrate 11 (the portion between the edge 13a of the substrate 11 and the conductive layer 22). The adhesive layer 23 may contain, in addition to the adhesive, any substance such as a synthetic resin or any other material.

[0064] (Protective Layer 24) The protective layer 24 has a size corresponding to the impermeable portion 1a in plan view, protects the conductor 21, and is composed of a protective material. A synthetic resin sheet (film) is used as the protective material of the protective layer 24. Examples of synthetic resins include one or more selected from the group consisting of PET (polyethylene terephthalate), COP (cycloolefin polymer), polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin. The thickness L5 of the protective layer 24 is preferably set to 0.02 mm or more and 0.30 mm or less. In addition to the protective material, the protective layer 24 may also contain any other substance such as a synthetic resin or any other material.

[0065] [Additional Notes] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and various modifications are possible without departing from the spirit of the present invention.

[0066] In the above embodiment, the entirety of the difficult-to-permeate portion 1a is covered with the shielding layer 2, but a configuration may be adopted in which only a portion of the difficult-to-permeate portion 1a is covered with the shielding layer 2. Even with this configuration, the amount of cancellation between the radio waves R1 and R2 can be reduced compared to the configuration shown in Fig. 2(A).

[0067] Furthermore, in the above embodiment, the shielding layer 2 is a radio wave reflector that reflects incident radio waves, but is not particularly limited as long as it has the function of blocking radio waves, and may be, for example, a radio wave absorber that absorbs radio waves.

[0068] In the above embodiment, the structure 1 has the easy-to-transmit region 1b formed by adding the metamaterial structure 12 to the substrate 11, but the structure is not particularly limited as long as it has both the difficult-to-transmit region 1a and the easy-to-transmit region 1b. For example, the easy-to-transmit region 1b may be a concrete wall with a glass window. In this case, the strength of the transmitted radio waves can be improved by covering at least a portion of the concrete wall with a shielding layer.

[0069] Examples of the present invention will be described below, but the present invention is not limited to the following examples.

[0070] In this example, the structure 1 shown in FIG. 1 was produced. The permeable region 1b was 200 mm × 200 mm = 40,000 mm ２ The shortest distance between the easy-to-permeate regions 1b was 200 mm. Furthermore, the difficult-to-permeate regions 1a were entirely covered with the shielding layer 2.

[0071] On the other hand, as a comparative example, a structure was produced in which the difficult-to-permeate portion 1 a was not covered with the shielding layer 2 (hereinafter referred to as a "non-shielding structure"). The non-shielding structure had the same configuration as the structure 1 according to this example, except that it did not have the shielding layer 2.

[0072] Millimeter waves with a frequency of 30 GHz (wavelength of 10 mm) were incident on the two structures 1 and the non-shielding structure, and the radio wave intensity (transmitted power) in the far field on the opposite side of the incident surface was measured. As a result, the intensity of the radio waves transmitted through structure 1 was 3.8 dB greater than the intensity of the radio waves transmitted through the non-shielding structure. In the non-shielding structure, the phase difference between the radio waves transmitted through the poorly penetrating portion and the radio waves transmitted through the easily penetrating portion was 190°.

[0073] In other words, in a non-shielding structure, the strength of radio waves that pass through the poorly permeable areas is reduced by the radio waves that pass through the easily permeable areas, but in structure 1, the strength of radio waves that pass through the easily permeable areas 1b is not reduced, and it was found that the radio wave strength in the far field can be improved.

[0074] REFERENCE SIGNS LIST 1 Structure (radio wave-transmitting structure) 1a Hardly-transmitting portion 1b Easy-transmitting portion 2 Shielding layer 3 Metal pattern 4 Split-ring resonator 11 Substrate 12 Metamaterial structure 12a Region 13 Adhesive layer 14 Protective film 21 Conductor 21A First linear body 21B Second linear body 21a Region 22 Conductive layer 23 Adhesive layer 24 Protective layer 41 First linear body 42 Second linear body R1 Radio wave R2 Radio wave

Claims

1. A radio wave transmission structure having a difficult-to-transmit portion that hardly transmits radio waves and an easy-to-transmit portion that transmits radio waves more easily than the difficult-to-transmit portion, wherein at least a part of the difficult-to-transmit portion is covered with a shielding layer that shields radio waves.

2. The radio wave transmission structure according to claim 1, wherein all of the difficult-to-transmit portion is covered with the shielding layer.

3. The radio wave transmission structure according to claim 1, wherein the shielding layer is a radio wave reflector that reflects incident radio waves.

4. The shielding layer has a conductive layer containing a conductor, a protective layer that holds the conductive layer, and an adhesive layer for adhering the conductive layer and the protective layer, and the radio wave transmission structure, the conductive layer, the adhesive layer, and the protective layer are laminated in this order. In the radio wave transmission structure according to claim 1, regions without a conductor surrounded by one or a plurality of linear conductors are periodically arranged at a predetermined interval.

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