High-frequency diffusion sheet

Abstract

Provided is a high-frequency diffusion sheet that enables good reception of electromagnetic waves by communication equipment over a wide area within a building, for example, by diffusing high-frequency range electromagnetic waves with excellent diffusion and uniformity. A high-frequency diffusion sheet 10 according to the present invention is used to diffuse high-frequency range electromagnetic waves, and includes an electromagnetic wave shielding layer 11 that has electromagnetic wave shielding properties, wherein: the electromagnetic wave shielding layer 11 is patterned as seen in a plan view of the high-frequency diffusion sheet 10 and has a plurality of openings 15 that penetrate in the thickness direction of the electromagnetic wave shielding layer 11; and if the separation distance between adjacent openings 15 is a distance P, the distance P includes a first distance P1 and a second distance P2 different from the first distance P1.

Description

High frequency diffusion sheet

[0001] The present invention relates to a radio frequency diffusion sheet.

[0002] In recent years, as communication devices such as mobile phones, smartphones, tablets, and mobile personal computers have become faster and have higher capacities, it has been proposed to use electromagnetic waves in the high-frequency range of 1 GHz or more and 80 GHz or less as the electromagnetic waves (electromagnetic signals) received by these communication devices (see, for example, Patent Document 1).

[0003] Electromagnetic waves in such high-frequency ranges have a higher degree of directivity (directionality) than those in low-frequency ranges. Therefore, when electromagnetic waves are received by communication devices inside a building, the reception strength decreases in places where the electromagnetic wave source cannot be seen. In other words, there is a problem in that electromagnetic waves cannot be received well in areas where electromagnetic waves are difficult to penetrate (shielding areas), such as walls, rather than areas where electromagnetic waves are permissible (transmission areas), such as windows.

[0004] JP 2012-190920 A

[0005] To solve these problems, it is necessary to diffuse high-frequency electromagnetic waves with excellent diffusion properties, thereby enabling reception by communication devices over a wide area within a building. Another issue is how to improve the uniformity of the reception environment within the area where electromagnetic waves can be received by communication devices.

[0006] The object of the present invention is to provide a high-frequency diffusion sheet that diffuses electromagnetic waves in the high-frequency range with excellent diffusion and uniformity, thereby enabling good reception of electromagnetic waves by communication devices over a wide area, for example, within a building.

[0007] The above object is achieved by the present invention as set forth in the following (1) to (14): (1) A high-frequency diffusion sheet that is used to diffuse electromagnetic waves in the high-frequency region when the electromagnetic waves pass through the sheet, and that includes an electromagnetic wave shielding layer having electromagnetic wave shielding properties, the electromagnetic wave shielding layer being patterned in a plan view of the high-frequency diffusion sheet and having a plurality of openings that penetrate the electromagnetic wave shielding layer in a thickness direction, and wherein, when a separation distance between adjacent openings is defined as a distance P, the distance P includes a first distance P1 and a second distance P2 that is different from the first distance P1.

[0008] (2) The high-frequency diffusion sheet according to (1), wherein the openings have a rectangular shape in plan view with a first direction as the short side direction and a second direction intersecting the first direction as the long side direction, and the distance P is a distance between the openings in the short side direction of the openings.

[0009] (3) The high-frequency diffusion sheet according to (1) or (2), wherein Pave / λ satisfies 0.2≦Pave / λ≦3.0, where Pave [mm] is an average distance between adjacent openings and λ [mm] is a wavelength of the electromagnetic wave.

[0010] (4) The high frequency diffusion sheet according to (3), wherein, when the maximum value of the distance P is Pmax and the minimum value is Pmin, Pmax / λ-Pmin / λ is 0.1 or more and 2.8 or less.

[0011] (5) The radio frequency diffusion sheet according to any one of (2) to (4), wherein a plurality of the openings form an opening group arranged in the first direction, a plurality of the opening groups form an opening matrix arranged in the second direction, and the distances P are the same among the opening groups.

[0012] (6) The radio frequency diffusion sheet according to any one of (2) to (4), wherein the plurality of openings form an opening group arranged in the first direction, the plurality of opening groups form an opening matrix arranged in the second direction, and the positions of the openings in the first direction are aligned with each other among the opening groups.

[0013] (7) The high-frequency diffusion sheet according to any one of (1) to (6), wherein the electromagnetic wave shielding layer shields the electromagnetic waves by reflecting or absorbing the electromagnetic waves.

[0014] (8) The high-frequency diffusion sheet according to (7), wherein the electromagnetic wave shielding layer is a metal thin film layer or a metal powder-containing adhesive layer containing metal powder and a binder resin.

[0015] (9) The radio-frequency diffusion sheet according to any one of (1) to (8), wherein the radio-frequency diffusion sheet has a transparent resin film, and the electromagnetic wave shielding layer is bonded to the resin film.

[0016] (10) The high-frequency diffusion sheet according to any one of (1) to (9) above, wherein the high-frequency diffusion sheet is configured so that the electromagnetic waves are diffused by being diffracted by the openings when the electromagnetic waves pass through the high-frequency diffusion sheet.

[0017] (11) The high-frequency diffusion sheet according to any one of (1) to (10), wherein W / λ is 0.3 or more and 3.0 or less, where W [mm] is the average width of the openings and λ [mm] is the wavelength of the electromagnetic waves.

[0018] (12) The high-frequency diffusion sheet according to any one of (1) to (11) above, wherein the electromagnetic wave shielding layer has an average thickness T of 0.01 μm or more and 70.0 μm or less.

[0019] (13) The high-frequency diffusion sheet according to any one of (1) to (12) above, wherein the frequency of the electromagnetic waves is 1 GHz or more and 80 GHz or less.

[0020] (14) The high-frequency diffusion sheet according to any one of (1) to (13) above, which is attached to a transmission area of ​​a building where the transmission of the electromagnetic waves is permitted.

[0021] According to the present invention, a high-frequency diffusion sheet is obtained that reliably diffracts electromagnetic waves at openings in the high-frequency diffusion sheet when they pass through. Furthermore, in the present invention, the separation distance (distance P) between adjacent openings includes a first distance P1 and a second distance P2 different from the first distance, so that the electromagnetic waves diffused with excellent diffusion can be diffused with uniform intensity. Therefore, by attaching the high-frequency diffusion sheet to an electromagnetic wave transmission area, such as a window, the high-frequency diffusion sheet can diffract electromagnetic waves in the high-frequency range and diffuse them with excellent diffusion and uniformity. This enables communication devices to receive electromagnetic waves effectively over a wide area within a building.

[0022] FIG. 1 is a plan view showing a first embodiment of the radio-frequency diffusion sheet of the present invention. FIG. 2 is a cross-sectional view taken along line A-A in FIG. 1. FIG. 3 is a plan view showing another configuration of openings in the electromagnetic wave shielding layer of the radio-frequency diffusion sheet of FIG. 1. FIG. 4 is a plan view showing another arrangement of openings in the electromagnetic wave shielding layer of the radio-frequency diffusion sheet of FIG. 1. FIG. 5 is a plan view showing another arrangement of openings in the electromagnetic wave shielding layer of the radio-frequency diffusion sheet of FIG. 1. FIG. 6 is a diagram showing a second embodiment of the radio-frequency diffusion sheet of the present invention (FIG. 6(a) is an overall view of the radio-frequency diffusion sheet according to the second embodiment, and FIG. 6(b) is a partially enlarged view of the area [B] surrounded by the dotted line in FIG. 6(a)). FIG. 7 is a diagram showing a test object used to evaluate the diffraction of electromagnetic waves (FIG. 7(a) is a plan view, and FIG. 7(b) is a cross-sectional view taken along line B-B in FIG. 7(a)). FIG. 8 is a table showing five types of arrangement patterns (a) to (e) described in Tables 1 and 2. FIG. 9 is a conceptual diagram for explaining a method for measuring the received intensity at a predetermined deflection angle α of an electromagnetic wave diffracted and diffused by a subject.

[0023] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The radio frequency diffusion sheet of the present invention will be described in detail below with reference to preferred embodiments shown in the accompanying drawings.

[0024] <First Embodiment of Radio-Frequency Diffusion Sheet> Fig. 1 is a plan view showing a first embodiment of the radio-frequency diffusion sheet of the present invention. Fig. 2 is a cross-sectional view taken along line A-A in Fig. 1 . Fig. 3 is a plan view showing another configuration of openings in the electromagnetic wave shielding layer included in the radio-frequency diffusion sheet of Fig. 1 . Fig. 4 is a plan view showing another arrangement of openings in the electromagnetic wave shielding layer included in the radio-frequency diffusion sheet of Fig. 1 . Fig. 5 is a plan view showing another arrangement of openings in the electromagnetic wave shielding layer included in the radio-frequency diffusion sheet of Fig. 1 . In each figure, an X-axis, a Y-axis, and a Z-axis are defined as three mutually orthogonal axes, and each axis is represented by an arrow. The tip end of each arrow is referred to as the "plus side" of each axis, and the base end of each arrow is referred to as the "negative side" of each axis. In the following description, the direction parallel to the X-axis is also referred to as the "first direction," and the direction parallel to the Y-axis is also referred to as the "second direction." Furthermore, in the following description, the Z-axis direction may be referred to as the "thickness direction," the positive side of the Z-axis may be referred to as "upper," and the negative side of the Z-axis may be referred to as "lower." Furthermore, in each drawing referred to in this specification, the dimensional ratios of each part are exaggerated and may differ significantly from the actual dimensional ratios.

[0025] The high-frequency diffusion sheet 10 is used to diffuse electromagnetic waves in the high-frequency region and includes an electromagnetic wave shielding layer 11 that has electromagnetic wave shielding properties. The electromagnetic wave shielding layer 11 extends along the XY plane and is patterned in a plan view from the Z axis of the high-frequency diffusion sheet 10. As a result, the electromagnetic wave shielding layer 11 has openings 15 that penetrate through it in the thickness direction.

[0026] In the present invention, when the separation distance between adjacent openings 15 in this high-frequency diffusion sheet 10 is defined as distance P, distance P (separation distance) includes a first distance P1 and a second distance P2 that is different from this first distance.

[0027] By providing the openings 15 in the high-frequency diffusion sheet 10, electromagnetic waves in the high-frequency region can be reliably diffracted at the openings 15 when they pass through the high-frequency diffusion sheet 10. This allows the electromagnetic waves to be diffused with excellent diffusivity. Furthermore, in the present invention, when the separation distance between adjacent openings 15 is defined as a distance P, this distance P includes a first distance P1 and a second distance P2 that is different from the first distance. This allows the electromagnetic waves to be diffused with uniform intensity.

[0028] When such a high-frequency diffusion sheet 10 is attached to a transmission area that allows the transmission of electromagnetic waves, such as a window in a building, the sheet 10 diffracts the electromagnetic waves as they pass through the transmission area, diffusing them with excellent diffusion and uniformity. This allows communication devices to receive electromagnetic waves effectively over a wide area within the building.

[0029] The high-frequency diffusion sheet 10 may be attached directly to a window provided in a building, or may be attached to a curtain, blind, or the like that is arranged corresponding to the window. In this case, the high-frequency diffusion sheet 10 still provides the above-described effects.

[0030] The following provides a more detailed description of the radio frequency diffusion sheet 10. In this embodiment, the radio frequency diffusion sheet 10 includes an electromagnetic wave shielding layer 11 having electromagnetic wave shielding properties and a resin film 12 supporting the electromagnetic wave shielding layer 11, as shown in Figures 1 and 2 .

[0031] <<Resin Film>> The resin film 12 is bonded to the electromagnetic wave shielding layer 11, thereby supporting the electromagnetic wave shielding layer 11. This allows the shape of the radio frequency diffusion sheet 10 to be stably maintained. A transparent resin film is preferably used for the resin film 12. This allows the radio frequency diffusion sheet 10 to be applied to lighting sections such as windows.

[0032] Examples of resin film 12 include those primarily made of thermosetting resins such as polyimide resin, polyamide resin, and epoxy resin, polyester-based resins such as polyethylene terephthalate and polyethylene naphthalate, olefin-based resins such as polypropylene and cycloolefin polymer, acrylic resins such as polymethyl methacrylate, and thermoplastic resins such as polycarbonate-based resins. These are preferably used because of their transparency. The term "primary material" refers to the material with the highest mass fraction in resin film 12.

[0033] The average thickness of the resin film 12 is not particularly limited, but is preferably 0.01 mm or more and 0.40 mm or less, and more preferably 0.10 mm or more and 0.30 mm or less. By setting the average thickness of the resin film 12 within this range, the resin film 12 has appropriate rigidity, and can reliably support the electromagnetic wave shielding layer 11.

[0034] <<Electromagnetic Wave Shielding Layer>> The electromagnetic wave shielding layer 11 has openings 15 penetrating through it in the thickness direction. The electromagnetic wave shielding layer 11 has a layered overall shape. The electromagnetic wave shielding layer 11 has electromagnetic wave shielding properties that suppress or block the transmission of electromagnetic waves in areas where the openings 15 are not formed. On the other hand, the electromagnetic wave is allowed to pass through in areas where the openings 15 are formed.

[0035] The electromagnetic wave shielding layer 11 can be divided into several types depending on the mechanism by which it shields electromagnetic waves. For example, the electromagnetic wave shielding layer 11 may be a reflective layer that is primarily responsible for reflecting incident electromagnetic waves, or an absorbing layer that is primarily responsible for absorbing incident electromagnetic waves. Among these, the electromagnetic wave shielding layer 11 is preferably a reflective layer. This allows the electromagnetic waves incident on the electromagnetic wave shielding layer 11 to be shielded by reflecting them, thereby improving the transmittance of electromagnetic waves at the opening 15. Note that "predominantly" means that, for example, when the electromagnetic wave shielding layer 11 has both a function of reflecting electromagnetic waves and another function, the reflection function is more dominant in contributing to "shielding."

[0036] The reflective layer and the absorbing layer will be described below. As described above, the reflective layer has the function of blocking incident electromagnetic waves by reflecting them.

[0037] Examples of reflective layers include metal powder-containing adhesive layers, metal thin film layers, metal meshes, and layers made of conductive materials such as ITO. These layers may be used alone or in combination. Among these, metal powder-containing adhesive layers and metal thin film layers are preferably used. Metal powder-containing adhesive layers and metal thin film layers exhibit excellent electromagnetic wave shielding properties even when their film thicknesses are set relatively thin. For this reason, they are preferably used as reflective layers.

[0038] The metal powder-containing adhesive layer contains, for example, metal powder and a binder resin. The metal powder is a powder composed of a metal material such as gold, silver, copper, or nickel, either as a simple substance or as an alloy. It may also be a composite material or mixed material that combines two or more metal materials, such as silver-coated copper. Among these, it is preferable to use a metal powder composed of silver or its alloy because of its excellent electromagnetic wave shielding properties.

[0039] The ratio of the metal powder to the binder resin in the metal powder-containing adhesive layer is not particularly limited, but is preferably 40:60 to 95:5 by weight, and more preferably 50:50 to 90:10.

[0040] The metal powder-containing adhesive layer may further contain a flame retardant, a leveling agent, a viscosity adjuster, and the like in addition to the metal powder and binder resin.

[0041] Examples of the metal thin film layer include a vapor-deposited film or metal foil whose main material is the metal material contained in the metal powder.

[0042] As described above, the absorbing layer has the function of blocking incident electromagnetic waves by absorbing them, by converting the incident electromagnetic waves into thermal energy, for example.

[0043] Examples of the absorbing layer include a conductive absorbing layer containing a conductive absorbing material such as metal powder or a conductive polymer material, a dielectric absorbing layer containing a dielectric absorbing material such as a carbon-based material or a dielectric polymer material, and a magnetic absorbing layer containing a magnetic absorbing material such as a soft magnetic metal. Each of these layers preferably contains the aforementioned material as the main material. Each of these layers may be used alone or in combination. The absorbing layer preferably contains both the aforementioned material and a binder resin.

[0044] The conductive absorbing layer absorbs electromagnetic waves by converting electromagnetic energy into thermal energy through heat generation caused by current flowing inside the material when an electric field is applied. The dielectric absorbing layer absorbs electromagnetic waves by converting electromagnetic energy into thermal energy through dielectric loss. The magnetic absorbing layer absorbs electromagnetic waves by converting electromagnetic energy into thermal energy through magnetic loss such as eddy current loss, hysteresis loss, and magnetic resonance.

[0045] Examples of conductive absorbing materials include conductive polymer materials, metal oxides such as ATO, and conductive ceramics.

[0046] Examples of conductive polymer materials include polyacetylene, polypyrrole, PEDOT (poly-ethylenedioxythiophene), PEDOT / PSS, polythiophene, polyaniline, poly(p-phenylene), polyfluorene, polycarbazole, polysilane, and derivatives thereof, and one or more of these can be used in combination.

[0047] Examples of dielectric absorbing materials include carbon-based materials, dielectric polymer materials, and ceramic materials.

[0048] Examples of carbon-based materials include carbon nanotubes such as single-walled carbon nanotubes and multi-walled carbon nanotubes, carbon nanofibers, CN nanotubes, CN nanofibers, BCN nanotubes, BCN nanofibers, graphene, carbon microcoils, carbon nanocoils, carbon nanohorns, and carbon nanowalls, and these may be used alone or in combination of two or more.

[0049] Examples of ceramic materials include barium titanate, perovskite-type barium calcium titanate zirconate crystal particles, titania, alumina, zirconia, silicon carbide, and aluminum nitride, and one or more of these may be used in combination.

[0050] Examples of magnetic absorption materials include soft magnetic metals such as iron, silicon steel, magnetic stainless steel (Fe-Cr-Al-Si alloy), sendust (Fe-Si-Al alloy), permalloy (Fe-Ni alloy), silicon copper (Fe-Cu-Si alloy), Fe-Si alloy, and Fe-Si-B(-Cu-Nb) alloy, and ferrite.

[0051] As the binder resin, various resin materials can be used, and are not particularly limited. Examples include thermosetting resins such as epoxy resin, phenol resin, amino resin, unsaturated polyester resin, and thermosetting elastomer, and thermoplastic resins such as olefin resin, polyamide resin, polyimide resin, acrylic resin, polyester resin, vinyl chloride resin, styrene resin, styrene-based thermoplastic elastomer, and olefin-based thermoplastic elastomer, and these can be used alone or in combination of two or more.

[0052] The average thickness T of the electromagnetic wave shielding layer 11 is not particularly limited, but is preferably 0.01 μm or more and 70.0 μm or less, more preferably 1.0 μm or more and 70.0 μm or less, and even more preferably 10.0 μm or more and 40.0 μm or less. By setting the average thickness T of the electromagnetic wave shielding layer 11 within this range, it is possible to more reliably suppress or block the transmission of electromagnetic waves in areas where the openings 15 are not formed. This allows the electromagnetic waves that pass through the openings 15 to be reliably diffracted.

[0053] As shown in FIG. 2, the opening 15 is a through-hole that penetrates the electromagnetic wave shielding layer 11 in the thickness direction.

[0054] 2, when electromagnetic waves (plane waves WA) in the high frequency range (frequency: approximately 1 GHz or more and 80 GHz or less) are incident on the electromagnetic wave shielding layer 11, the electromagnetic waves are diffracted and diffused as they pass through the openings 15. Therefore, for example, when the high frequency diffusion sheet 10 is attached to a transmission area such as a window in a building, it becomes possible for communication devices to receive electromagnetic waves well over a wide area within the building.

[0055] In addition, in the high-frequency diffusion sheet 10, the distance P between adjacent openings 15 includes a first distance P1 and a second distance P2 that is different from the first distance.

[0056] With this configuration, the distance P varies, so that the intensity of the electromagnetic wave diffused at the opening 15 can be made uniform.

[0057] The planar shape of each opening 15 shown in Fig. 1 is a rectangle with the X-axis direction (first direction) as the short side direction and the Y-axis direction (second direction) as the long side direction. The multiple openings 15 shown in Fig. 1 have the same length (length in the Y-axis direction) and the same width (length in the X-axis direction). In Fig. 1, the separation distance between the openings 15 in the short side direction of the openings 15 is referred to as distance P.

[0058] The number of openings 15 is not limited as long as there are three or more openings 15 (the possible numbers of first distance P1 and second distance P2) provided in the electromagnetic wave shielding layer 11. In this embodiment, as shown in FIG. 1 , an opening group GR is configured in which a plurality of openings 15 are arranged at equal intervals in the X-axis direction (first direction). Also in FIG. 1 , an opening matrix MT is configured in which the opening groups GR are arranged at equal intervals in the Y-axis direction (second direction). In FIG. 1 , as an example, three opening groups GR are arranged in the Y-axis direction. In this specification, the opening group GR located furthest to the negative side of the Y axis in FIG. 1 is referred to as the "first row," the opening group GR located furthest to the positive side of the Y axis is referred to as the "third row," and the opening group GR located between the first and third rows is referred to as the "second row." In the first and third rows, the distance P between the openings 15 in the X-axis direction (the short-side direction of the openings 15) is a first distance P1, and in the second row, the distance P between the openings 15 in the X-axis direction is a second distance P2 that is greater than the first distance P1. In FIG. 1 , the first and third rows include nine openings 15, and the second row includes six openings 15. As a result, the opening matrix MT shown in FIG. 1 is composed of a total of 24 openings 15. The number of openings 15 in the opening matrix MT is not particularly limited and may be set appropriately depending on the size of the radio frequency diffusion sheet 10, etc.

[0059] 1, the distances P are the same for each of the opening groups GR. Specifically, in the first and third rows, the distance P is the same as the first distance P1, and in the second row, the distance P is the same as the second distance P2. With this configuration, the distance P includes the first distance P1 and the second distance P2, so that the electromagnetic waves can be diffused with more uniform intensity in the openings 15. Note that the distances P being the same for each of the opening groups GR means that the difference between the maximum and minimum values ​​of the distance P in each opening group GR is 5% or less of the minimum value.

[0060] The average value of the distance P is represented by the average value of the first distance P1 and the second distance P2 (=(P1+P2) / 2). This average value is defined as the average separation distance Pave [mm], and the wavelength λ [mm] of the electromagnetic wave incident on the high-frequency diffusion sheet 10. In this case, the relational expression Pave / λ, which represents the ratio of the average separation distance Pave to the wavelength λ, preferably satisfies the relationship 0.2≦Pave / λ≦3.0, more preferably the relationship 0.2≦Pave / λ≦1.3, and even more preferably the relationship 0.2≦Pave / λ≦1.0.

[0061] Furthermore, the average value of the width of the openings 15 is defined as an average width W [mm]. In this case, the relational expression W / λ representing the ratio of the average width W to the wavelength λ preferably satisfies the relationship 0.3≦W / λ≦3.0, more preferably the relationship 0.3≦W / λ≦1.5, and even more preferably the relationship 0.2≦W / λ≦1.0.

[0062] When the relationship between Pave / λ and the relationship between W / λ satisfy the above-mentioned relationships, the electromagnetic waves can be diffused with excellent diffusivity and with more uniform intensity at the openings 15. Furthermore, the electromagnetic wave transmittance of the high frequency diffusion sheet 10 can be further improved.

[0063] 1, two types of distances P (first distance P1 and second distance P2) are set in the entire opening matrix MT, but three or more types of distances P may be set. Specifically, the distances P set in the opening matrix MT may include distances P3, P4, ..., Pn (n is an integer of 3 or more) that are different from the first distance P1 and the second distance P2. When the distances P include distances P1, P2, ..., Pn, the average separation distance Pave is expressed as (P1 + P2 + ... + Pn) / n [mm].

[0064] Furthermore, the maximum value of the distance P in the high-frequency diffusion sheet 10 is defined as Pmax, and the minimum value is defined as Pmin. In this case, the relational expression (Pmax / λ-Pmin / λ) representing the difference between the ratio of the maximum value Pmax to the wavelength λ (Pmax / λ) and the ratio of the minimum value Pmin to the wavelength λ (Pmin / λ) preferably satisfies the relationship 0.1≦(Pmax / λ-Pmin / λ)≦2.8, and more preferably 0.5≦(Pmax / λ-Pmin / λ)≦2.0. When the relational expression (Pmax / λ-Pmin / λ) satisfies this relationship, a high-frequency diffusion sheet 10 can be realized that can diffuse electromagnetic waves with more uniform intensity.

[0065] Furthermore, the high frequency diffusion sheet 10 is preferably configured so that the diffused electromagnetic waves satisfy the following conditions.

[0066] First, the angle formed between the radiation direction of the electromagnetic wave diffused with the highest intensity at the openings 15 and the transmission direction of the electromagnetic wave traveling straight through the openings 15 is defined as the "radiation angle θ" shown in FIG. 2. The radiation angle θ is preferably greater than 30° and less than 90°, and more preferably greater than 60° and less than 90°. This allows for the realization of a high-frequency diffusion sheet 10 that can sufficiently diffuse electromagnetic waves. Note that, in this specification, "diffused electromagnetic waves" refers to electromagnetic waves excluding electromagnetic waves traveling straight through the openings 15 without being diffused (electromagnetic waves transmitting in a direction perpendicular to the incident surface of the high-frequency diffusion sheet 10).

[0067] Furthermore, the transmittance of the electromagnetic waves through the high frequency diffusion sheet 10 is preferably 30% or more, and more preferably 50% or more, thereby realizing a high frequency diffusion sheet 10 that has excellent transmittance in the high frequency range.

[0068] The planar shape of the openings 15 is not limited to the shape shown in FIG. 1 . Examples of the shape of the openings 15 include a circular shape as shown in FIG. 3 , as well as shapes with curved portions such as S-shape, U-shape, semicircular shape, and wavy shape, and shapes with corners such as V-shape, X-shape, L-shape, H-shape, T-shape, W-shape, and U-shape. When the planar shape of the openings 15 is a circular shape as shown in FIG. 3 , the diameter D of the circle corresponds to the width of the rectangular openings 15 described above. In the radio frequency diffusion sheet 10 shown in FIG. 3 , the circular openings 15 are arranged along a direction that obliquely intersects the X-axis and Y-axis within the X-Y plane. The distance P between adjacent openings 15 in this direction includes a first distance P1 and a second distance P2.

[0069] 1 , when the length and width of the shape in plan view are different (anisotropic shape), the ratio of length to width (aspect ratio) is not particularly limited, but is preferably 2.0 to 20.0, more preferably 3.0 to 10.0, and even more preferably 4.0 to 8.0. This allows for the realization of a high frequency diffusion sheet 10 that provides good diffusion and uniformity of electromagnetic wave intensity, particularly in the width direction of the opening 15 (X-axis direction).

[0070] The anisotropic shape may be a rectangular shape, an elliptical or oval circular shape, a polygonal shape, or any other shape.

[0071] 1, a plurality of openings 15 are arranged in the X-axis direction (first direction) to form an opening group GR. Furthermore, in FIG. 1, a plurality of opening groups GR are arranged in the Y-axis direction (second direction) to form an opening matrix MT. In FIG. 1, the distances P in the X-axis direction are the same for each opening group GR. In FIG. 1, the distance P in the first and third rows is a first distance P1, and the distance P in the second row is a second distance P2.

[0072] In contrast, in FIG. 4 , the distances P in the X-axis direction are not the same for each of the opening groups GR. That is, in FIG. 4 , the first to third rows each include a first distance P1 and a second distance P2. Also, in FIG. 4 , the arrangement patterns of the first distance P1 and the second distance P2 are the same for each of the first to third rows. That is, in FIG. 4 , the positions of the openings 15 in the X-axis direction are aligned with each other for each of the opening groups GR. Also, in FIG. 4 , the second distance P2 is set in the area surrounded by the dotted line, and the first distance P1 is set in the surrounding area. Even with the arrangement of the openings 15 shown in FIG. 4 , the same effect as the radio frequency diffusion sheet 10 shown in FIG. 1 can be obtained. Note that the positions of the openings 15 being aligned with each other means that the positional deviation of the openings 15 in the X-axis direction between the opening groups GR is less than 50% of the average width W of the openings 15.

[0073] 5, the distance P in the first and third rows is the first distance P1. Meanwhile, in Fig. 5, the distance P in the second row includes the first distance P1 and the second distance P2. Also, in Fig. 5, the second distance P2 is set in the area surrounded by the dotted line, and the first distance P1 is set in the surrounding area. Even with the arrangement of the openings 15 shown in Fig. 5, the same effect as that of the radio frequency diffusion sheet 10 shown in Fig. 1 can be obtained.

[0074] Although the openings 15 have the same shape in the above drawings, the openings 15 may have different shapes.

[0075] Furthermore, when one opening group GR includes a first distance P1 and a second distance P2, it is preferable that the ratio between these distances be optimized. Specifically, when P1<P2, the ratio P2 / P1 is preferably 1.20 or greater and 15.0 or less, and more preferably 1.50 or greater and 8.00 or less. This makes it possible to realize a high-frequency diffusion sheet 10 that provides good diffusion properties and uniformity in electromagnetic wave intensity in the extension direction (X-axis direction) of the opening group GR.

[0076] <<Adhesive Layer>> The radio frequency diffusion sheet 10 may have an adhesive layer laminated on the surface of the resin film 12 opposite to the electromagnetic wave shielding layer 11. This allows the radio frequency diffusion sheet 10 to be easily attached to a transparent area such as a window in a building.

[0077] The material of the adhesive layer is not particularly limited, but is preferably an adhesive containing at least one of an acrylic adhesive, a rubber adhesive, a silicone adhesive, and the like.

[0078] Examples of acrylic adhesives include resins composed of (meth)acrylic acid and esters thereof, copolymers of (meth)acrylic acid and esters thereof with unsaturated monomers copolymerizable therewith (meth)acrylic acid and esters thereof (e.g., vinyl acetate, styrene, acrylonitrile, etc.), etc. Mixtures of two or more of these resins may also be used.

[0079] Examples of rubber-based adhesives include natural rubber-based, isoprene rubber-based, styrene-butadiene-based, reclaimed rubber-based, and polyisobutylene-based adhesives, as well as block copolymers containing rubber such as styrene-isoprene-styrene and styrene-butadiene-styrene.

[0080] Examples of silicone-based adhesives include dimethylsiloxane-based and diphenylsiloxane-based adhesives.

[0081] The adhesive layer may contain various additives such as a plasticizer, a tackifier, a thickener, a filler, an antioxidant, an antiseptic, an anti-mold agent, a dye, and a pigment.

[0082] The high-frequency diffusion sheet 10 may be a laminate in which one side of the electromagnetic wave shielding layer 11 is supported by a resin film 12, or may be a laminate in which both sides of the electromagnetic wave shielding layer 11 are supported by a resin film 12, or may be a form in which the resin film 12 is omitted.

[0083] The high frequency diffusion sheet 10 may further include an intermediate layer or the like between the electromagnetic wave shielding layer 11 and the resin film 12 and / or between the resin film 12 and the adhesive layer.

[0084] Second Embodiment Next, a second embodiment of the radio frequency diffusion sheet of the present invention will be described.

[0085] 6A and 6B are diagrams showing a second embodiment of the radio frequency diffusion sheet of the present invention, in which Fig. 6A is an overall view of the radio frequency diffusion sheet according to the second embodiment, and Fig. 6B is a partially enlarged view of an area [B] surrounded by a dotted line in Fig. 6A.

[0086] The second embodiment will be described below, but the following description will focus on the differences from the first embodiment, and a description of similar points will be omitted.

[0087] The radio frequency diffusion sheet 10 shown in FIG. 6 is the same as the radio frequency diffusion sheet 10 shown in FIG. 1 except that the configuration of the electromagnetic wave shielding layer 11 is different.

[0088] 6 has a plurality of through holes 16 that are provided in an area where no openings 15 are formed and are smaller than the openings 15. The through holes 16 penetrate the electromagnetic wave shielding layer 11 in the thickness direction, similar to the openings 15. This configuration can solve the following problems.

[0089] As described above, the high frequency diffusion sheet 10 is used by being attached to a transparent area such as a window in a building. Such a transparent area may be required to be transparent. In this case, "transparency" refers to high transmittance, particularly for visible light. Visible light is defined as light having a wavelength of 300 nm or more and 800 nm or less.

[0090] The area of ​​the electromagnetic wave shielding layer 11 where the openings 15 are not formed contains a material that exhibits electromagnetic wave blocking properties in order to suppress or block the transmission of electromagnetic waves. Such a material may cause translucency or opacity to visible light.

[0091] Therefore, in this embodiment, a plurality of through holes 16 are provided in the electromagnetic wave shielding layer 11. This makes it possible to impart transparency to the electromagnetic wave shielding layer 11 even when the electromagnetic wave shielding layer 11 contains a material that exhibits electromagnetic wave blocking properties. As a result, it is possible to realize a high frequency diffusion sheet 10 that does not obstruct lighting, views, etc., even when attached to a transparent area such as a window.

[0092] The through holes 16 are formed to be smaller in size than the openings 15 so as to suppress the transmission of electromagnetic waves while allowing the transmission of visible light. As shown in FIG. 6B , when the width of the through holes 16 is Wh, the width Wh of the through holes 16 is preferably approximately 50 μm or more but less than 1000 μm, and more preferably approximately 100 μm or more but 250 μm or less. In this case, the separation distance Ph between the through holes 16 is preferably approximately 10 μm or more but 150 μm or less, and more preferably approximately 30 μm or more but 75 μm or less. By setting the width Wh and separation distance Ph of the through holes 16 within the above ranges, the electromagnetic wave shielding layer 11 can effectively shield electromagnetic waves in the high-frequency range and effectively transmit visible light. The width Wh refers to the maximum length in the direction in which the through holes 16 are closest to each other, and the separation distance Ph refers to the minimum distance in that direction. For example, in the case of the square-shaped through holes 16 shown in Fig. 6(b), the through holes 16 are arranged so as to be closest to each other in the X-axis direction. Therefore, the width Wh of the through holes 16 shown in Fig. 6(b) is the length of the side of the through holes 16 extending in the X-axis direction.

[0093] The planar shape of the through hole 16 is not limited to the shape shown in Fig. 6(b) . The planar shape of the through hole 16 may be, for example, an S-shape, a U-shape, a circle, a semicircle, or a wave-like shape having a curved portion, or may be a linear shape, a V-shape, an X-shape, an L-shape, an H-shape, a T-shape, a W-shape, or a U-shape having an angled portion.

[0094] 6(b), the through holes 16 all have the same shape, but they may have different shapes. Also, in FIG. 6(b), the through holes 16 are arranged at equal intervals, but the arrangement pattern of the through holes 16 is not limited to this, and the through holes 16 may be arranged randomly, for example.

[0095] The high frequency diffusion sheet 10 according to the second embodiment as described above also provides the same effects as those of the first embodiment.

[0096] The visible light transmittance of the radio frequency diffusion sheet 10 according to the second embodiment is preferably 70% or more and 100% or less, and more preferably 90% or more and 100% or less. This allows for a radio frequency diffusion sheet 10 with excellent light transmissivity. As a result, even when attached to a transparent area such as a window, the radio frequency diffusion sheet 10 does not particularly obstruct natural lighting or the view. The light transmittance can be measured, for example, using an ultraviolet-visible spectrophotometer.

[0097] Although the high frequency diffusion sheet of the present invention has been described above, the present invention is not limited to the above-described embodiment.

[0098] For example, the high-frequency diffusion sheet of the present invention may be one in which each component of the above-described embodiment is replaced with any component that can perform the same function, or one in which any component is added to the above-described embodiment.

[0099] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples in any way.

[0100] 1. Preparation of Films, etc. <Metal Foil Laminated Resin Film> An aluminum foil-PET substrate laminate was prepared as a metal foil laminated resin film by bonding an aluminum foil having an average thickness of 12 μm onto a PET substrate (resin film 12) having an average thickness of 0.1 mm via an acrylic adhesive.

[0101] <Frame> Figure 7 is a diagram showing an object 150 used for evaluating the diffraction of electromagnetic waves. Figure 7(a) is a plan view of the object 150, and Figure 7(b) is a cross-sectional view taken along line BB in Figure 7(a).

[0102] 7 includes a frame 100 that does not allow electromagnetic waves to pass through. The frame 100 is made of an aluminum plate whose outer shape and inner opening are both square, and has an outer shape of 200 mm x 200 mm and an inner opening size of 100 mm x 100 mm.

[0103] 2. Preparation of Radio Frequency Diffusion Sheet The prepared metal foil laminated resin film (aluminum foil-PET substrate laminate) was cut into a size of 100 mm x 100 mm. Next, laser light was irradiated onto the aluminum foil provided in the cut metal foil laminated resin film to form openings (slits) satisfying the conditions such as the shape and arrangement shown in Table 1 or Table 2. In this way, radio frequency diffusion sheets of Samples No. 1 to 11 were prepared, each comprising a resin film having a patterned electromagnetic wave shielding layer provided thereon.

[0104] The "arrangement patterns" listed in Tables 1 and 2 correspond to the five arrangement patterns (a) to (e) shown in Fig. 8. Furthermore, "upper left," "lower left," "upper right," and "lower right" in Tables 1 and 2 refer to the four areas obtained when the arrangement patterns (a), (b), (d), and (e) shown in Fig. 8 are divided horizontally in half and vertically in half, respectively. Furthermore, "center" in Tables 1 and 2 refers to the center of the three areas obtained when the arrangement pattern (c) shown in Fig. 8 is divided horizontally into thirds, and "edges" refer to both ends of the three areas.

[0105] Furthermore, if the arrangement pattern has different distances P within the opening group, it is marked with an "O" in Tables 1 and 2, and if the arrangement pattern has the same distance P within the opening group, it is marked with an "X" in Tables 1 and 2.

[0106] 3. Evaluation <Measurement of Radiation Angle θ> First, the high frequency diffusion sheet of each sample number was attached to the frame 100 to obtain a test object 150 for checking the diffraction and diffusion of electromagnetic waves.

[0107] Next, as shown in Fig. 9, a receiver 20 was placed to measure the electromagnetic wave transmitted through the subject 150. Fig. 9 is a conceptual diagram for explaining a method for measuring the reception intensity at a predetermined deflection angle α of the electromagnetic wave diffracted and diffused by the subject 150. In the method shown in Fig. 9, an electromagnetic wave (plane wave WA) having a frequency shown in Table 1 or Table 2 was incident on the high-frequency diffusion sheet of each sample number. Then, the receiver 20 was placed at a position 200 mm away from the center position of the high-frequency diffusion sheet 10, and the reception intensity was measured while changing the deflection angle α of the electromagnetic wave (the angle of the receiver 20 from the linear direction of the electromagnetic wave) from 0° to 90°.

[0108] <Evaluation of Electromagnetic Wave Reception Stability> The reception stability of electromagnetic waves transmitted through the high-frequency diffusion sheet was evaluated by evaluating the diffusion of electromagnetic waves by the high-frequency diffusion sheet (a characteristic indicating whether a uniform reception strength can be obtained regardless of the deflection angle α). Specifically, the reception stability was relatively evaluated by comparing the measurement results of the reception strength obtained for each deflection angle α shown in Figure 9 with the following evaluation criteria. The evaluation results are shown in Tables 1 and 2.

[0109] A: Electromagnetic waves can be received clearly and stably at any angle. B: Electromagnetic waves can be received clearly at any angle. C: Although there are some angles where reception is not clear, reception is sufficient overall. D: Reception is only possible at limited angles.

[0110]

[0111]

[0112] As shown in Tables 1 and 2, the results of the evaluation tests using the high-frequency diffusion sheets of each example demonstrated that the electromagnetic waves could be diffused well and that the diffused electromagnetic waves could be received stably regardless of the angle. Therefore, it was confirmed that the present invention can realize a high-frequency diffusion sheet that can diffuse high-frequency electromagnetic waves with excellent diffusion and uniformity.

[0113] According to the present invention, it is possible to provide a high frequency diffusion sheet that can diffuse high frequency electromagnetic waves with excellent diffusion properties and uniformity, thereby enabling good reception of electromagnetic waves by communication devices over a wide area, for example, within a building. Therefore, the present invention has industrial applicability.

[0114] 10 High frequency diffusion sheet 11 Electromagnetic wave shielding layer 12 Resin film 15 Opening 16 Through hole 20 Receiver 100 Frame 150 Object B Area D Diameter GR Aperture group MT Aperture matrix P Distance P1 First distance P2 Second distance Ph Separation distance T Average thickness W Average width Wh Width WA Plane wave α Deflection angle θ Radiation angle

Claims

1. A high-frequency diffusion sheet that is used to diffuse electromagnetic waves in the high-frequency range when the electromagnetic waves pass through, and that has an electromagnetic wave shielding layer with electromagnetic wave shielding properties, wherein the electromagnetic wave shielding layer is patterned in a plan view of the high-frequency diffusion sheet, and has a plurality of openings that penetrate the electromagnetic wave shielding layer in the thickness direction, and wherein when the separation distance between adjacent openings is distance P, distance P includes a first distance P1 and a second distance P2 that is different from first distance P1.

2. A radio frequency diffusion sheet according to claim 1, wherein the openings have a rectangular shape in plan view with a first direction as the short side and a second direction intersecting the first direction as the long side, and the distance P is the separation distance between the openings in the short side direction of the openings.

3. The high-frequency diffusion sheet according to claim 2, wherein Pave / λ satisfies 0.2≦Pave / λ≦3.0, where Pave is the average distance between adjacent openings and λ is the wavelength of the electromagnetic waves.

4. The high frequency diffusion sheet according to claim 3, wherein, when the maximum value of the distance P is Pmax and the minimum value is Pmin, Pmax / λ-Pmin / λ is 0.1 or more and 2.8 or less.

5. A radio frequency diffusion sheet according to claim 2, wherein a plurality of the openings form an opening group arranged in the first direction, a plurality of the opening groups form an opening matrix arranged in the second direction, and the distances P are the same among the opening groups.

6. The radio frequency diffusion sheet according to claim 2, wherein the plurality of openings form an opening group arranged in the first direction, and the plurality of opening groups form an opening matrix arranged in the second direction, and the positions of the openings in the first direction are aligned with each other between the opening groups.

7. The high frequency diffusion sheet according to claim 1, wherein the electromagnetic wave shielding layer shields the electromagnetic waves by reflecting or absorbing the electromagnetic waves.

8. The high frequency diffusion sheet according to claim 7, wherein the electromagnetic wave shielding layer is a metal thin film layer or a metal powder-containing adhesive layer comprising metal powder and a binder resin.

9. The radio frequency diffusion sheet according to claim 1, wherein the radio frequency diffusion sheet has a transparent resin film, and the electromagnetic wave shielding layer is bonded to the resin film.

10. The high frequency diffusion sheet according to claim 1, wherein the high frequency diffusion sheet is configured so that when the electromagnetic waves pass through the sheet, the electromagnetic waves are diffracted by the openings, thereby diffusing the waves.

11. A high frequency diffusion sheet according to claim 1, wherein W / λ is 0.3 or more and 3.0 or less, where W [mm] is the average width of the openings and λ [mm] is the wavelength of the electromagnetic waves.

12. The radio frequency diffusion sheet according to claim 1, wherein the electromagnetic wave shielding layer has an average thickness T of 0.01 μm or more and 70.0 μm or less.

13. The high frequency diffusion sheet according to claim 1, wherein the frequency of the electromagnetic waves is 1 GHz or more and 80 GHz or less.

14. The high frequency diffusion sheet according to claim 1, which is attached to a transparent area of ​​a building where the transmission of electromagnetic waves is permitted.

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