Radio wave scattering sheet with protective layer

Abstract

To provide a radio wave scattering sheet with a protective layer that is provided with the protective layer which does not retard radio wave scattering characteristics as much as possible while improving the appearance and durability of the radio wave scattering sheet.SOLUTION: A radio wave scattering sheet 11 with a protective layer that has a surface metal processing layer 1c protected by coating a radio wave scattering surface 1d of a radio wave scattering sheet 1 with a dielectric layer 2 improves the appearance and durability of the radio wave scattering sheet 1 with the dielectric layer 2. In addition, the dielectric layer 2 covering the radio wave scattering surface 1d is 0.25 to 3.0 mm thick and the dielectric layer 2 has a specific inductive capacity of 2.0 to 4.0, so that a decrease in directional diffusion power is suppressed to 10% or less.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a radio wave scattering sheet with a protective layer that improves appearance and durability by covering a metal pattern exposed as a radio wave scattering surface of a radio wave scattering sheet with a metamaterial structure. [Background technology]

[0002] In recent years, the fifth generation wireless communication (so-called 5G) service has been launched, and radio waves in the 28 GHz frequency band are being used. In this frequency band, radio waves have a large propagation attenuation and a high degree of directivity, so if there is an obstruction between the transmitting antenna and the receiving antenna, the radio waves from the transmitting antenna do not reach the receiving antenna, resulting in a significant deterioration in communication quality. To address this issue, a radio wave scattering sheet with a metamaterial structure that scatters reflected radio waves over a wide angle has been developed.

[0003] As a radio wave scattering sheet with a metamaterial structure, there is a radio wave scattering sheet designed to obtain a desired scattering pattern by processing a specific metal pattern on a dielectric substrate (for example, see Non-Patent Document 1). In addition, a reflectarray has been developed that controls the reflection phase of the electromagnetic wave by changing the size and shape of the reflecting element to change the resonance frequency of each reflecting element, thereby controlling the incident direction and reflection direction of the electromagnetic wave (for example, see Patent Document 1). These radio wave scattering sheets and reflectarrays are used by attaching them to the walls and ceilings of a room, and by scattering the scattered waves on the surface (radio wave scattering surface) over a wide angle, it becomes possible for radio waves to reach areas that cannot be reached by ordinary metal plates, and the quality of wireless communication can be improved for multiple terminals and moving terminals. [Prior art documents] [Non-patent literature]

[0004] [Non-Patent Document 1] Y.Murakami, J.Chakarothai and K.Fujii, “Design of electromagnetic scattering wall using genetic algorithm,” IEICE Commun.Express, vol.9, pp.282-287, 2020. [Patent documents]

[0005] [Patent Document 1] International Publication No. 2022 / 186385 Summary of the Invention [Problem to be solved by the invention]

[0006] However, conventional radio wave scattering sheets and reflectarrays have exposed metal patterns on the radio wave scattering surface, so there is concern that rust or dirt will cause deterioration of their characteristics (so-called aging deterioration). In addition, when radio wave scattering sheets are placed and used indoors, the exposed metal patterns on the radio wave scattering surface do not necessarily look good, and when used outdoors, there are concerns about adverse effects on the surrounding scenery. Furthermore, regardless of whether they are used indoors or outdoors, there is a risk of fire occurring when sunlight that hits the radio wave scattering surface of a radio wave scattering sheet or the like is reflected and concentrated by the metal patterns.

[0007] One possible solution to the problems caused by the exposed metal patterns on these radio wave scattering surfaces is to cover the radio wave scattering surface of the radio wave scattering sheet with a non-metallic material so that the metal patterns are not exposed. However, if the radio wave scattering surface of the radio wave scattering sheet is covered with another material, there is a risk that the essential radio wave scattering characteristics will be deteriorated or significantly impaired, so it is important to consider what conditions the material that covers the radio wave scattering surface of the radio wave scattering sheet will meet.

[0008] Therefore, an object of the present invention is to provide a radio wave scattering sheet with a protective layer, which improves the appearance and durability of the radio wave scattering sheet while providing a protective layer that does not impair the radio wave scattering characteristics as much as possible. [Means for solving the problem]

[0009] In order to solve the above problems, the present invention provides a radio wave scattering sheet with a protective layer, comprising: a radio wave scattering sheet having a metamaterial structure that scatters electromagnetic waves in multiple directions when electromagnetic waves of a specific frequency band are received on a radio wave scattering surface having a specific metal pattern formed on a dielectric substrate; and a protective layer that covers the radio wave scattering surface of the radio wave scattering sheet to protect the metal pattern and has at least an outer surface that is opaque, wherein the protective layer covers the radio wave scattering surface to a thickness in the range of 0.25 mm to 3.0 mm and has a relative dielectric constant in the range of 2.0 to 4.0.

[0010] In the above configuration, the protective layer may be made of a single material that covers the radio wave scattering surface to a thickness in the range of 0.25 mm to 2.0 mm and has a relative dielectric constant in the range of 2.0 to 3.0.

[0011] In addition, in the above configuration, the protective layer may be a two-layer structure consisting of a lower protective layer placed on the radio wave scattering surface and an upper protective layer placed on the lower protective layer, the total thickness of the lower protective layer and the upper protective layer may be in the range of 0.5 to 1.0 mm, and the overall relative dielectric constant of the lower protective layer and the upper protective layer combined may be in the range of 2.0 to 3.0. Effect of the Invention

[0012] According to the radio wave scattering sheet with a protective layer of the present invention, the protective layer improves the appearance and durability of the radio wave scattering sheet, while suppressing the decrease in the directional diffusion degree of the radio wave scattering sheet to within 10%. [Brief description of the drawings]

[0013] [Figure 1]Fig. 1(A) is a schematic vertical cross-sectional view of a radio wave scattering sheet with a protective layer according to a first embodiment, and Fig. 1(B) is a schematic vertical cross-sectional view of a radio wave scattering sheet with a protective layer according to a second embodiment. [Diagram 2] FIG. 2 is a scattering characteristic diagram showing the scattering characteristics of a radio wave scattering sheet to which a commercially available wallpaper is attached as a protective layer. [Diagram 3] Fig. 3(A) is an explanatory diagram showing an example of using a radio wave scattering sheet with a protective layer in an office, and Fig. 3(B) is an explanatory diagram showing an example of using a radio wave scattering sheet with a protective layer outdoors. [Figure 4] FIG. 4 is a list showing the first examples (Examples 1-01 to 1-12) performed for Evaluation 1. [Diagram 5] FIG. 5 is a list showing first comparative examples (Comparative Examples 1-01 to 1-10) performed for Evaluation 1. As shown in FIG. [Figure 6] FIG. 6 is a list showing the second examples (Examples 2-01 to 2-09) performed for Evaluation 2. [Figure 7] FIG. 7 is a list showing Examples 2-10 to 2-19 among the second comparative examples (Comparative Examples 2-01 to 2-10) carried out for Evaluation 2. As shown in FIG. [Figure 8] FIG. 8 is a list showing Examples 3-01 to 3-08 out of the third examples carried out for Evaluation 3. As shown in FIG. [Figure 9] FIG. 9 is a list showing Examples 3-09 to 3-15 out of the third examples carried out for Evaluation 3. As shown in FIG. [Figure 10] FIG. 10 is a list showing Comparative Examples 3-01 to 3-07 out of the third comparative examples performed for Evaluation 3. [Figure 11] FIG. 11 is a list showing Comparative Examples 3-08 to 3-14 among the third comparative examples performed for Evaluation 3. As shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, embodiments of the radio wave scattering sheet with a protective layer of the present invention will be described in detail with reference to the accompanying drawings. Fig. 1(A) shows a schematic vertical cross-sectional view of a radio wave scattering sheet with a protective layer 11 of a first embodiment, and Fig. 1(B) shows a schematic vertical cross-sectional view of a radio wave scattering sheet with a protective layer 12 of a second embodiment.

[0015] The radio wave scattering sheet 11 with a protective layer of the first embodiment comprises a radio wave scattering sheet 1 comprising a dielectric substrate 1a having a back metal plate 1b and a front metalized layer 1c on both sides thereof, a dielectric layer 2 as a protective layer covering a radio wave scattering surface 1d corresponding to the surface of the front metalized layer 1c of the radio wave scattering sheet 1, and an adhesive layer 3 provided on the outer surface (lower surface) of the back metal plate 1b for attaching the radio wave scattering sheet 1 to a wall, ceiling, etc.

[0016] The radio wave scattering sheet 1 uses a glass epoxy board (grade FR4) with a thickness of about 0.68 [mm] and a relative dielectric constant of 4.5 as the dielectric board 1a, a metal film (for example, copper foil) of about 60 [μm] formed on one side of the dielectric board 1a as the back metal plate 1b, and a surface metal processing layer 1c in which a specific metal pattern is formed by processing the metal film (for example, copper foil) of about 60 [μm] formed on the other side of the dielectric board 1a by etching or the like. This radio wave scattering sheet 1 has a metamaterial structure that can scatter radio waves arriving at the radio wave scattering surface 1d from multiple directions in a wide angle by forming a patch structure in the surface metal processing layer 1c that combines areas with reflection phases of 0° and 180° within a unit unit surface (for example, a surface of 180 [mm] x 180 [mm]). The radio wave scattering sheet 1 of this embodiment was designed to match electromagnetic waves in the 28 [GHz] band selected as a specific frequency band. The total thickness of the radio wave scattering sheet 1, which is made up of the dielectric substrate 1a, the rear metal plate 1b, and the front metalized layer 1c, is about 0.8 mm.

[0017] The dielectric layer 2 may be formed by applying a coating agent or the like to the radio wave scattering surface 1d of the radio wave scattering sheet 1 in a uniform thickness, or by attaching a plate-shaped material made of an adhesive material to the radio wave scattering surface 1d of the radio wave scattering sheet 1. However, if the material forming the dielectric layer 2 is opaque, the surface metal processing layer 1c is not visible, so that the appearance of the radio wave scattering sheet 11 with the protective layer can be improved. The surface of the dielectric layer 2 is not limited to a single color, and may be configured with multiple colors. For example, if multiple types of coating agents with the same relative dielectric constant but different colors are used, a multi-colored pattern can be expressed on the surface of the dielectric layer 2. The material of this dielectric layer 2 can be selected from various materials, but since the incoming radio waves enter the dielectric layer 2 and reach the radio wave scattering surface 1d, and the scattered waves from the radio wave scattering surface 1d are transmitted through the dielectric layer 2 and emitted to the outside, it is considered that the thickness and dielectric constant of the dielectric layer 2 (hereinafter, the relative dielectric constant expressed as the ratio to the dielectric constant of a vacuum is used) are not little involved in the scattering characteristics of the radio wave scattering sheet 11 with the protective layer.

[0018] On the other hand, the radio wave scattering sheet 12 with a protective layer of the second embodiment includes a dielectric layer 2' as a protective layer covering the radio wave scattering surface 1d corresponding to the surface of the surface metal processing layer 1c of the radio wave scattering sheet 1, and an adhesive layer 3 provided on the outer surface of the back metal plate 1b in order to attach the radio wave scattering sheet 1 to a wall surface, a ceiling, or the like. The dielectric layer 2' has a two-layer structure in which an adhesive layer 2b as a lower protective layer is provided on the lower surface of a surface layer 2a as an upper protective layer, and is attached to the radio wave scattering surface 1d of the radio wave scattering sheet 1 by the viscosity of the adhesive layer 2b. Here, if the material forming the surface layer 2a of the dielectric layer 2' is opaque, the surface metal processing layer 1c becomes invisible, so that the appearance of the radio wave scattering sheet 12 with a protective layer can be improved. In addition, the materials of the surface layer 2a and the adhesive layer 2b can be selected in various ways, but it is considered that the thickness of the entire protective layer (dielectric layer 2') and the dielectric constant of the entire protective layer (dielectric layer 2') are not little involved in the scattering characteristics of the radio wave scattering sheet 12 with a protective layer. The protective layer is not limited to two layers, and may have a multi-layer structure of three or more layers including a printed layer and a surface coating layer.

[0019] FIG. 2 shows the scattering characteristics of the radio wave scattering sheet 12 with a protective layer, which is made by attaching a commercially available wallpaper, for example, a vinyl chloride resin sheet with a thickness of about 0.4 [mm] (estimated relative dielectric constant: 3.0), to the radio wave scattering sheet 1 as a protective layer. For comparison, the scattering characteristics of the radio wave scattering sheet 1 alone are shown by a broken line. Although the scattering pattern of the radio wave scattering sheet 12 with a protective layer does not completely match the scattering pattern of the radio wave scattering sheet 1 without wallpaper, the same results were obtained, and it was experimentally confirmed that the radio wave scattering sheet 1 can fully function as the radio wave scattering sheet 1 even if wallpaper is attached to the radio wave scattering surface 1d as a protective layer. Therefore, if the radio wave scattering sheets 11 and 12 with protective layers are attached to the walls and ceilings in an office as shown in FIG. 3(A), or if the radio wave scattering sheets 11 and 12 with protective layers are placed outdoors with a shield as shown in FIG. 3(B), radio waves in the 28 [GHz] band transmitted from a transmission source can be delivered over a wide area, improving communication quality. Moreover, the radio wave scattering sheets 11, 12 with protective layers can suppress deterioration over time by protecting the surface metal processed layer 1c of the radio wave scattering sheet 1 with the dielectric layers 2, 2', and can also improve their appearance so as to blend in with the surrounding environment.

[0020] Next, to obtain the radio wave scattering sheet 11 with a protective layer without significantly impairing the scattering characteristics of the radio wave scattering sheet 1, it is necessary to verify what conditions of the protective layer (dielectric layer 2) are effective. First, FIG. 4 shows a first example (Example 1-01 to Example 1-12) performed to evaluate the degree of change in the directional diffusion degree of the radio wave scattering sheet 11 with a protective layer. In the first example, the thickness and relative dielectric constant of the protective layer formed on the radio wave scattering surface 1d of the radio wave scattering sheet 1 with a thickness of 0.8 [mm] described above are changed, and it is evaluated whether the change is within -10% or worse than -10% with respect to the directional diffusion degree of the reference radio wave scattering sheet 1 (hereinafter referred to as Evaluation 1). Moreover, FIG. 5 shows the first comparative examples (Comparative Example 1-01 to Comparative Example 1-10) in which the change in directional diffusion degree is worse than -10%.

[0021] In Example 1-01, a 0.25 mm thick polyvinyl chloride (dielectric constant: 3.0) protective layer is provided so that the total thickness of the radio wave scattering sheet 11 with protective layer is 1.05 mm. The directional diffusion degree is +3.7%, which is higher than the directional diffusion degree of the reference radio wave scattering sheet 1, so that the evaluation 1 is within -10%. In this Example 1-01, the directional diffusion degree of the radio wave scattering sheet 11 with protective layer provided with protective layer (dielectric layer 2) is improved compared to the directional diffusion degree of the reference radio wave scattering sheet 1. Although the principle is unclear, by providing the radio wave scattering sheet 11 with protective layer provided with a protective layer of appropriate conditions, there is a possibility that the directional diffusion degree can be improved more than that of the radio wave scattering sheet 1 alone. This will be verified in Examples 2 and 3 described later.

[0022] In Example 1-02, a fluororesin (dielectric constant 4.0) having a thickness of 0.5 mm was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.3 mm. The change in directional diffusion degree was -8.3%, which was a decrease of less than -10% compared to the directional diffusion degree of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. In Example 1-03, a fluororesin (dielectric constant 4.0) having a thickness of 1.0 mm was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The change in directional diffusion degree was -8.7%, which was a decrease of less than -10% compared to the directional diffusion degree of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. The results of Examples 1-01 to 1-03 show that if the thickness of the protective layer is in the range of 0.25 mm to 1.0 mm and the relative dielectric constant of the protective layer is in the range of 3.0 to 4.0, the change in directional diffusion index of the reference radio wave scattering sheet 1 is within -10%.

[0023] In Example 1-04, a 1.5 mm thick nylon (dielectric constant 3.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 mm. The change in directional diffusion was -2.0%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. In Example 1-05, a 1.5 mm thick fluororesin (dielectric constant 4.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 mm. The change in directional diffusion was -1.1%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. From the results of Examples 1-04 to 1-05, it can be seen that if the thickness of the protective layer is 1.5 mm and the relative dielectric constant of the protective layer is within the range of 3.5 to 4.0, the change in directional diffusion index of the reference radio wave scattering sheet 1 is within -10%.

[0024] In Example 1-06, a 2.0 mm thick nylon (dielectric constant 3.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.8 mm. The change in directional diffusion was -2.8%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. In Example 1-07, a 2.0 mm thick fluororesin (dielectric constant 4.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.8 mm. The change in directional diffusion was -4.8%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. From the results of Examples 1-06 to 1-07, it can be seen that if the thickness of the protective layer is 2.0 mm and the relative dielectric constant of the protective layer is within the range of 3.5 to 4.0, the change in directional diffusion index of the reference radio wave scattering sheet 1 is within -10%.

[0025] In Example 1-08, a 2.5 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.3 mm. The change in directional diffusion was -4.5%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. In Example 1-09, a 2.5 mm thick epoxy resin (relative dielectric constant: 2.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.3 mm. The change in directional diffusion was -5.2%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. From the results of Examples 1-08 to 1-09, it can be seen that if the thickness of the protective layer is 2.5 mm and the relative dielectric constant of the protective layer is within the range of 2.0 to 2.5, the change in directional diffusion index of the reference radio wave scattering sheet 1 is within -10%.

[0026] In Example 1-10, a 3.0 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.8 mm. The change in directional diffusion was -9.1%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. In Example 1-11, a 3.0 mm thick polyvinyl chloride (relative dielectric constant: 3.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.8 mm. The change in directional diffusion was -5%, which was a decrease of less than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. In Example 1-12, a fluororesin (dielectric constant 4.0) having a thickness of 3.0 [mm] was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.8 [mm]. The change in directional diffusion index was -1%, which was a decrease of less than -10% compared to the directional diffusion index of the reference radio wave scattering sheet 1, so that the evaluation 1 was within -10%. From the results of Examples 1-10 to 12, it can be seen that if the thickness of the protective layer is 3.0 [mm] and the dielectric constant of the protective layer is within the range of 2.0 to 4.0, the change in directional diffusion index is within -10% compared to the reference radio wave scattering sheet 1.

[0027] In Comparative Example 1-01, a furan resin (dielectric constant 4.5) having a thickness of 0.5 mm was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.3 mm. The change in directional diffusion was -20%, which was a decrease of more than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. In Comparative Example 1-02, a polyurethane (dielectric constant 5.0) having a thickness of 0.5 mm was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.3 mm. The change in directional diffusion was -22%, which was a decrease of more than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. From the results of these comparative examples 1-01 to 1-02, it can be seen that even if the thickness of the protective layer is 0.5 mm, if the relative dielectric constant of the protective layer is in the range of 4.5 to 5.0, the change in directional diffusion index of the reference radio wave scattering sheet 1 is less than -10%.

[0028] In Comparative Example 1-03, a 1.0 mm thick glass epoxy (dielectric constant: 4.2) protective layer was provided so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The change in directional diffusion was -11.3%, which was a decrease of more than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. In Comparative Example 1-04, a 1.0 mm thick furan resin (dielectric constant: 4.5) protective layer was provided so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The directional diffusion was -12.1%, which was a decrease of more than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. In Comparative Example 1-05, a 1.0 mm thick polyurethane (dielectric constant: 5.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The change in directional diffusion index was -13.1%, which was a decrease of more than -10% compared to the directional diffusion index of the reference radio wave scattering sheet 1, and thus the evaluation 1 was outside the -10% range. From the results of Comparative Examples 1-03 to 1-05, it can be seen that even if the thickness of the protective layer is 1.0 mm, if the dielectric constant of the protective layer is in the range of 4.2 to 5.0, the change in directional diffusion index of the reference radio wave scattering sheet 1 is less than -10%.

[0029] In Comparative Example 1-06, gypsum (dielectric constant 5.5) having a thickness of 1.5 mm was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 [mm]. The change in directional diffusivity was -16.7%, which was a decrease of more than -10% compared to the directional diffusivity of the reference radio wave scattering sheet 1, so that Evaluation 1 was outside the -10% range. From the results of this Comparative Example 1-06, it can be seen that even if the thickness of the protective layer is 1.5 [mm], if the protective layer has a dielectric constant of 5.5, the change in directional diffusivity compared to the reference radio wave scattering sheet 1 will be less than -10%.

[0030] In Comparative Example 1-07, a 2.0 mm thick glass epoxy (dielectric constant: 4.2) protective layer was provided so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.8 mm. The change in directional diffusion was -10.9%, which was a decrease of more than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. In Comparative Example 1-08, a 2.0 mm thick furan resin (dielectric constant: 4.5) protective layer was provided so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.8 mm. The change in directional diffusion was -10.1%, which was a decrease of more than -10% compared to the directional diffusion of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. In Comparative Example 1-09, a 2.0 mm thick polyurethane (dielectric constant: 5.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.8 mm. The change in directional diffusivity was -13.5%, which was a decrease of more than -10% compared to the directional diffusivity of the reference radio wave scattering sheet 1, and thus the evaluation 1 was outside the -10% range. From the results of Comparative Examples 1-07 to 1-29, it can be seen that even if the thickness of the protective layer is 2.0 mm, if the dielectric constant of the protective layer is in the range of 4.2 to 5.0, the change in directional diffusivity compared to the reference radio wave scattering sheet 1 is less than -10%.

[0031] In Comparative Example 1-10, gypsum (dielectric constant 5.5) having a thickness of 3.0 [mm] was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.8 [mm]. The change in directional diffusivity was -14.7%, which was a decrease of more than -10% compared to the directional diffusivity of the reference radio wave scattering sheet 1, so that the evaluation 1 was outside the -10% range. From the results of Comparative Example 1-10, it can be seen that when the thickness of the protective layer is 3.0 [mm] and the dielectric constant of the protective layer is 5.5, the change in directional diffusivity compared to the reference radio wave scattering sheet 1 is less than -10%.

[0032] From the results of the first embodiment described above, if the thickness of the dielectric layer 2 as the protective layer covering the radio wave scattering surface 1d is in the range of 0.25 mm to 3.0 mm and the relative dielectric constant is in the range of 2.0 to 4.0, the change in the directional diffusion degree of the reference radio wave scattering sheet 1 is within -10%. Therefore, the radio wave scattering sheet 11 with the protective layer provided with the dielectric layer 2 that meets the above conditions as the protective layer can realize a directional diffusion degree close to that of the radio wave scattering sheet 1 used alone, and can contribute to improving the communication quality not only in the 28 [GHz] band but also in microwaves and millimeter waves. Moreover, the radio wave scattering sheet 11 with the protective layer can suppress deterioration over time by protecting the surface metal processing layer 1c of the radio wave scattering sheet 1 with the dielectric layer 2, and can improve the appearance so as to blend in with the surrounding environment. Although Example 1 only shows the radio wave scattering sheet with protective layer 11 using a single dielectric layer 2 as the protective layer, similarly, for the radio wave scattering sheet with protective layer 12 using two dielectric layers 2' as the protective layer, if the thickness covering the radio wave scattering surface 1d is in the range of 0.25 mm to 3.0 mm and the dielectric constant is in the range of 2.0 to 4.0, the change in directional diffusion degree is within -10% compared to the reference radio wave scattering sheet 1.

[0033] The upper limit of the thickness of the dielectric layer 2, which changes within -10% of the directional diffusion degree of the reference radio wave scattering sheet 1, is set to 3.0 [mm] because it is determined in consideration of the thickness of the coating agent used as the protective layer and the thickness of the actual wallpaper. If the thickness of the protective layer exceeds 3.0 [mm], the durability increases, but problems such as weight arise, making it inconvenient to handle the radio wave scattering sheets 11, 12 with protective layer, and in order to safely attach the radio wave scattering sheets 11, 12 with protective layer to a wall or ceiling, it becomes necessary to provide an adhesive layer 3 with very strong adhesive performance, which impairs practicality. Therefore, considering the realistic thickness range of the protective layer, it is judged that it is appropriate to set the upper limit of the thickness of the protective layer provided on the radio wave scattering sheet 1 to 3.0 [mm].

[0034] Next, Fig. 6 shows second examples (Examples 2-01 to 2-09) performed to evaluate the increase or decrease in directional diffusivity of the radio wave scattering sheet 11 with a protective layer. In the second examples, the thickness and relative dielectric constant of the protective layer formed on the radio wave scattering surface 1d of the radio wave scattering sheet 1 with a thickness of 0.8 [mm] described above are changed, and an evaluation is made as to whether a directional diffusivity equal to or greater than the directional diffusivity of the radio wave scattering sheet 1 (reference value 1.0) as a reference can be obtained (1.0 or more) or whether it does not reach the reference value (less than 1.0) (hereinafter referred to as Evaluation 2). Moreover, Fig. 7 shows second comparative examples (Comparative Example 2-01 to Comparative Example 2-10) with a decreased directional diffusivity.

[0035] In Example 2-01, a 0.25 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.05 mm. The change in directional diffusion degree was +11.1%, so that the evaluation 2 was 1.0 or more. In Example 2-02, a 0.25 mm thick polyvinyl chloride (relative dielectric constant: 3.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.05 mm. The directional diffusion degree was +3.7%, so that the evaluation 2 was 1.0 or more. In Example 2-03, a 0.5 mm thick epoxy resin (relative dielectric constant: 2.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.3 mm. The directional diffusion degree was +13.8%, so that the evaluation 2 was 1.0 or more. From the results of Examples 2-01 to 2-03, it can be seen that when the thickness of the protective layer is in the range of 0.25 mm to 0.5 mm and the relative dielectric constant of the protective layer is in the range of 2.0 to 3.0, the directional diffusion degree is increased to more than that of the reference radio wave scattering sheet 1, and the radio wave scattering characteristics are improved.

[0036] In Example 2-04, a 1.0 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The directional diffusion degree was +14.9%, so the evaluation 2 was 1.0 or more. In Example 2-05, a 1.0 mm thick epoxy resin (relative dielectric constant: 2.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The directional diffusion degree was +19.7%, so the evaluation 2 was 1.0 or more. In Example 2-06, a 1.0 mm thick polyvinyl chloride (relative dielectric constant: 3.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 1.8 mm. The directional diffusion degree was +12.0%, so the evaluation 2 was 1.0 or more. From the results of Examples 2-04 to 2-06, it can be seen that when the thickness of the protective layer is 1.0 mm and the relative dielectric constant of the protective layer is within the range of 2.0 to 3.0, the directional diffusion degree is increased to more than that of the reference radio wave scattering sheet 1, and the radio wave scattering characteristics are improved.

[0037] In Example 2-07, a 1.5 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 mm. The directional diffusion degree was +17.4%, so the evaluation 2 was 1.0 or more. In Example 2-08, a 1.5 mm thick epoxy resin (relative dielectric constant: 2.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 mm. The directional diffusion degree was +10.0%, so the evaluation 2 was 1.0 or more. In Example 2-09, a 2.0 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.8 mm. The directional diffusion degree was +10.4%, so the evaluation 2 was 1.0 or more. From the results of Examples 2-07 to 2-09, it can be seen that when the thickness of the protective layer is in the range of 1.5 mm to 2.0 mm and the relative dielectric constant of the protective layer is in the range of 2.0 to 2.5, the directional diffusion degree is increased to more than that of the reference radio wave scattering sheet 1, and the radio wave scattering characteristics are improved.

[0038] In Comparative Example 2-01, a fluororesin (dielectric constant: 4.0) having a thickness of 0.5 mm is provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer is 1.3 mm. The directional diffusion degree is -3.8%, so the evaluation 2 is less than 1.0. In Comparative Example 2-02, a soft PVC resin (dielectric constant: 3.3) having a thickness of 1.0 mm is provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer is 1.8 mm. The directional diffusion degree is -2.5%, so the evaluation 2 is less than 1.0. In Comparative Example 2-03, a nylon (dielectric constant: 3.5) having a thickness of 1.0 mm is provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer is 1.8 mm. The directional diffusion degree is -4.5%, so the evaluation 2 is less than 1.0. From the results of these comparative examples 2-01 to 2-03, it can be seen that even if the thickness of the protective layer is in the range of 0.5 mm to 1.0 mm, if the relative dielectric constant of the protective layer is in the range of 3.3 to 4.0, the directional diffusion degree is reduced compared to the reference radio wave scattering sheet 1, and the radio wave scattering characteristics are degraded.

[0039] In Comparative Example 2-04, a 1.5 mm thick soft PVC resin (dielectric constant: 3.3) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 mm. The directional diffusion degree was -0.8%, so that the evaluation 2 was less than 1.0. In Comparative Example 2-05, a 1.5 mm thick nylon (dielectric constant: 3.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 2.3 mm. The directional diffusion degree was -4.4%, so that the evaluation 2 was less than 1.0. From the results of Comparative Examples 2-04 to 2-05, it can be seen that even if the thickness of the protective layer is 1.5 mm, if the dielectric constant of the protective layer is in the range of 3.3 to 3.5, the directional diffusion degree is reduced compared to the radio wave scattering sheet 1 as the reference, and the radio wave scattering characteristics are degraded.

[0040] In Comparative Example 2-06, a 2.0 mm thick nylon (dielectric constant: 3.5) protective layer is provided so that the total thickness of the radio wave scattering sheet 11 with protective layer is 2.8 mm. The directional diffusion degree is -2.8%, so that the evaluation 2 is less than 1.0. In Comparative Example 2-07, a 2.0 mm thick fluororesin (dielectric constant: 4.0) protective layer is provided so that the total thickness of the radio wave scattering sheet 11 with protective layer is 2.8 mm. The directional diffusion degree is -4.8%, so that the evaluation 2 is less than 1.0. From the results of Comparative Examples 2-06 to 2-07, it can be seen that even if the thickness of the protective layer is 2.0 mm, if the dielectric constant of the protective layer is in the range of 3.5 to 4.0, the directional diffusion degree is reduced compared to the radio wave scattering sheet 1 as the reference, and the radio wave scattering characteristics are degraded.

[0041] In Comparative Example 2-08, a 2.5 mm thick paper (relative dielectric constant: 2.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.3 [mm]. The directional diffusion degree was -4.5%, so the evaluation 2 was less than 1.0. In Comparative Example 2-09, a 2.5 mm thick epoxy resin (relative dielectric constant: 2.5) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.3 [mm]. The directional diffusion degree was -5.2%, so the evaluation 2 was less than 1.0. In Comparative Example 2-10, a 2.5 mm thick polyvinyl chloride (relative dielectric constant: 3.0) was provided as a protective layer so that the total thickness of the radio wave scattering sheet 11 with protective layer was 3.3 [mm]. The directional diffusion degree was -6.1%, so the evaluation 2 was less than 1.0. The results of these comparative examples 2-08 to 10 show that when the thickness of the protective layer is 2.5 mm, even if the relative dielectric constant of the protective layer is in the range of 2.0 to 3.0, the directional diffusion degree is reduced compared to the reference radio wave scattering sheet 1, and the radio wave scattering characteristics are degraded.

[0042] From the results of the second embodiment described above, if the dielectric layer 2 as a protective layer has a thickness covering the radio wave scattering surface 1d in the range of 0.25 mm to 2.0 mm and a relative dielectric constant in the range of 2.0 to 3.0, a directional diffusion degree equal to or greater than that of the reference radio wave scattering sheet 1 can be obtained. Therefore, the radio wave scattering sheet 11 with a protective layer in which the dielectric layer 2 meeting the above conditions is provided as a protective layer can achieve a directional diffusion degree equal to or greater than that of the radio wave scattering sheet 1 used alone, and can therefore contribute greatly to improving communication quality not only in the 28 [GHz] band but also in microwaves and millimeter waves.

[0043] Next, in the radio wave scattering sheet 12 with a protective layer using the dielectric layer 2' as a protective layer consisting of two layers, the surface layer 2a and the adhesive layer 2b, a third example (Example 3-01 to Example 3-15) performed to evaluate the improvement rate of the directional diffusion degree is shown in Fig. 8 and Fig. 9. In the radio wave scattering sheet 12 with a protective layer of the second embodiment described above, the thickness of the entire protective layer and the relative dielectric constant of the entire protective layer can be finely changed by combining various materials of the surface layer 2a and the adhesive layer 2b. Therefore, in the third example, the thickness of the entire protective layer formed on the radio wave scattering surface 1d of the radio wave scattering sheet 1 with a thickness of 0.8 [mm] described above and the relative dielectric constant of the entire protective layer are changed, and it is evaluated whether an improvement rate of 10% or more is obtained (+10% or more) from the directional diffusion degree of the reference radio wave scattering sheet 1 (reference value ±0%) or whether the improvement rate remains less than 10% (less than +10%) (hereinafter referred to as Evaluation 3). Moreover, the third comparative examples (Comparative Example 3-01 to Comparative Example 3-14) in which the improvement rate of the directional diffusion degree is less than +10% are shown in FIG. 10 and FIG.

[0044] In Example 3-01, a 0.5 mm thick glue (dielectric constant: 2.0) is used as an adhesive layer, and a 0.5 mm thick paper (dielectric constant: 2.0) is used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 mm, the total thickness of the protective layer is 1.0 mm, and the total dielectric constant of the protective layer is 2.0. The improvement rate of the directional diffusion degree is +11.4%, so that the evaluation 3 is +10% or more. In Example 3-02, a 0.5 mm thick glue (dielectric constant: 2.0) is used as an adhesive layer, and a 0.5 mm thick epoxy resin (dielectric constant: 2.5) is used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 mm, the total thickness of the protective layer is 1.0 mm, and the total dielectric constant of the protective layer is 2.25. The improvement rate of the directional diffusion rate is +18.3%, so that the evaluation 3 is +10% or more. In Example 3-03, a starch paste (relative dielectric constant: 2.5) having a thickness of 0.25 [mm] is provided as an adhesive layer, and an epoxy resin (relative dielectric constant: 2.5) having a thickness of 0.75 [mm] is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 [mm], and the thickness of the entire protective layer is 1.0 [mm] and the relative dielectric constant of the entire protective layer is 2.5. The improvement rate of the directional diffusion rate is +19.7%, so that the evaluation 3 is +10% or more. From the results of Examples 3-01 to 3, if the thickness of the entire protective layer is 1.0 [mm] and the relative dielectric constant of the entire protective layer is within the range of 2.0 to 2.5, an improvement rate of 10% or more is obtained compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and it is found that the improvement rate of the radio wave scattering characteristics can be increased.

[0045] In Example 3-04, the radio wave scattering sheet 12 with protective layer is provided with an adhesive layer of 0.25 mm (relative dielectric constant: 3.0) and a surface layer of 0.75 mm (relative dielectric constant: 2.5), so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 mm, the total thickness of the protective layer is 1.0 mm, and the total dielectric constant of the protective layer is 2.625. The improvement rate of the directional diffusion degree is +17.9%, so that the evaluation 3 is +10% or more. In Example 3-05, the radio wave scattering sheet 12 with protective layer is provided with an adhesive layer of 0.5 mm (relative dielectric constant: 2.5) and a surface layer of 0.5 mm (relative dielectric constant: 3.0), so that the total thickness of the protective layer is 1.0 mm, and the total dielectric constant of the protective layer is 2.75. The improvement rate of the directional diffusion rate is +20.4%, so that the evaluation 3 is +10% or more. In Example 3-06, an acrylic resin (relative dielectric constant: 3.0) having a thickness of 0.5 [mm] is provided as an adhesive layer, and an epoxy resin (relative dielectric constant: 2.5) having a thickness of 0.5 [mm] is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 [mm], and the thickness of the entire protective layer is 1.0 [mm], and the relative dielectric constant of the entire protective layer is 2.75. The improvement rate of the directional diffusion rate is +16.8%, so that the evaluation 3 is +10% or more. In Example 3-07, a 0.25 mm thick starch paste (dielectric constant: 2.5) was used as an adhesive layer, and a 0.75 mm thick polyvinyl chloride (dielectric constant: 3.0) was used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer was 1.8 mm, and the total thickness of the protective layer was 1.0 mm, and the total dielectric constant of the protective layer was 2.875. The improvement rate of the directional diffusion degree was +19.0%, so that the evaluation 3 was +10% or more. In Example 3-08, a 0.25 mm thick acrylic resin (dielectric constant: 3.0) was used as an adhesive layer, and a 0.75 mm thick polyvinyl chloride (dielectric constant: 3.0) was used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer was 1.8 mm, and the total thickness of the protective layer was 1.0 mm, and the total dielectric constant of the protective layer was 3.0. The improvement in directional diffusion is +12.0%, so a rating of 3 is +10% or more.From the results of Examples 3-04 to 3-08, it can be seen that if the thickness of the entire protective layer is 1.0 mm and the relative dielectric constant of the entire protective layer is within the range of 2.625 to 3.0, an improvement of 10% or more is obtained compared to the directional diffusion degree of the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristics can be increased.

[0046] In Example 3-09, a 0.25 mm thick glue (dielectric constant: 2.0) is used as an adhesive layer, and a 0.25 mm thick paper (dielectric constant: 2.0) is used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the total thickness of the protective layer is 0.5 mm, and the total dielectric constant of the protective layer is 2.0. The improvement rate of the directional diffusion degree is +11.8%, so that the evaluation 3 is +10% or more. In Example 3-10, a 0.25 mm thick glue (dielectric constant: 2.0) is used as an adhesive layer, and a 0.25 mm thick epoxy resin (dielectric constant: 2.5) is used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the total thickness of the protective layer is 0.5 mm, and the total dielectric constant of the protective layer is 2.25. The improvement rate of the directional diffusion rate is +10.5%, so that the evaluation 3 is +10% or more. In Example 3-11, a 0.25 mm thick glue (relative dielectric constant: 2.0) is provided as an adhesive layer, and a 0.25 mm thick polyvinyl chloride (relative dielectric constant: 3.0) is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, and the total thickness of the protective layer is 0.5 mm and the total dielectric constant of the protective layer is 2.5. The improvement rate of the directional diffusion rate is +12.6%, so that the evaluation 3 is +10% or more. From the results of Examples 3-09 to 3-11 in which glue is commonly used as the material of the adhesive layer, if the total thickness of the protective layer is 0.5 mm and the relative dielectric constant of the protective layer is within the range of 2.0 to 2.5, an improvement rate of 10% or more is obtained compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and it is found that the improvement rate of the radio wave scattering characteristics can be increased.

[0047] In Example 3-12, a 0.25 mm thick starch paste (dielectric constant: 2.5) is used as an adhesive layer, and a 0.25 mm thick paper (dielectric constant: 2.5) is used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the total thickness of the protective layer is 0.5 mm, and the total dielectric constant of the protective layer is 2.5. The improvement rate of the directional diffusion degree is +11.4%, so that the evaluation 3 is +10% or more. In Example 3-13, a 0.25 mm thick starch paste (dielectric constant: 2.5) is used as an adhesive layer, and a 0.25 mm thick polyvinyl chloride (dielectric constant: 3.0) is used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the total thickness of the protective layer is 0.5 mm, and the total dielectric constant of the protective layer is 2.75. The improvement rate of the directional diffusion rate is +14.9%, so the evaluation 3 is +10% or more. From the results of Examples 3-12 to 3-13, which commonly used starch paste as the material of the adhesive layer, it is found that if the total thickness of the protective layer is 0.5 [mm] and the relative dielectric constant of the protective layer is within the range of 2.5 to 2.75, an improvement rate of 10% or more is obtained compared to the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristics can be increased.

[0048] In Example 3-14, the radio wave scattering sheet 12 with protective layer is provided with an adhesive layer of 0.25 mm (relative dielectric constant: 3.0) and a surface layer of 0.25 mm (relative dielectric constant: 2.5), so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the total thickness of the protective layer is 0.5 mm, and the total dielectric constant of the protective layer is 2.75. The improvement rate of the directional diffusion degree is +14.1%, so that the evaluation 3 is +10% or more. In Example 3-15, the radio wave scattering sheet 12 with protective layer is provided with an adhesive layer of 0.25 mm (relative dielectric constant: 3.0) and a surface layer of 0.25 mm (relative dielectric constant: 3.0), so that the total thickness of the protective layer is 1.3 mm, the total thickness of the protective layer is 0.5 mm, and the total dielectric constant of the protective layer is 3.0. The improvement rate of the directional diffusion rate is +11.6%, so the evaluation score is +10% or more. From the results of Examples 3-12 to 3-13, which commonly used acrylic resin as the material of the adhesive layer, it is found that if the total thickness of the protective layer is 0.5 [mm] and the relative dielectric constant of the protective layer is within the range of 2.5 to 2.75, an improvement rate of 10% or more is obtained compared to the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristics can be increased.

[0049] In Comparative Example 3-01, a 0.1 mm thick glue (dielectric constant: 2.0) was used as an adhesive layer, and a 0.15 mm thick epoxy resin (dielectric constant: 2.5) was used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer was 1.05 mm, the total thickness of the protective layer was 0.25 mm, and the total dielectric constant of the protective layer was 2.3. The improvement rate of the directional diffusion degree was +5.9%, so the evaluation 3 was less than +10%. In Comparative Example 3-02, a 0.1 mm thick starch glue (dielectric constant: 2.5) was used as an adhesive layer, and a 0.15 mm thick polyvinyl chloride (dielectric constant: 3.0) was used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer was 1.05 mm, the total thickness of the protective layer was 0.25 mm, and the total dielectric constant of the protective layer was 2.6. The improvement rate of the directional diffusion rate is +9.8%, so the evaluation score is less than +10%. From the results of these comparative examples 3-01 to 3-02, it is found that when the thickness of the entire protective layer is 0.25 mm, which is less than 0.5 mm, even if the relative dielectric constant of the entire protective layer is within the range of 2.3 to 2.6, it is not possible to obtain an improvement rate of 10% or more compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristics falls to less than 10%.

[0050] In Comparative Example 3-03, an acrylic resin (dielectric constant: 3.0) having a thickness of 0.25 mm is used as an adhesive layer, and a nylon (dielectric constant: 3.5) having a thickness of 0.25 mm is used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the thickness of the entire protective layer is 0.50 mm, and the dielectric constant of the entire protective layer is 3.25. The improvement rate of the directional diffusion degree is +8.3%, so that the evaluation 3 is less than +10%. In Comparative Example 3-04, an acrylic resin (dielectric constant: 3.5) having a thickness of 0.25 mm is used as an adhesive layer, and a nylon (dielectric constant: 3.5) having a thickness of 0.25 mm is used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 mm, the thickness of the entire protective layer is 0.50 mm, and the dielectric constant of the entire protective layer is 3.5. The improvement rate of the directional diffusion rate is +5.1%, so that the evaluation 3 is less than +10%. In Comparative Example 3-05, an acrylic resin (relative dielectric constant: 3.0) having a thickness of 0.25 [mm] is provided as an adhesive layer, and a furan resin (relative dielectric constant: 4.5) having a thickness of 0.25 [mm] is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.3 [mm], and the thickness of the entire protective layer is 0.50 [mm], and the relative dielectric constant of the entire protective layer is 3.75. The improvement rate of the directional diffusion rate is +7.3%, so that the evaluation 3 is less than +10%. From the results of these Comparative Examples 3-03 to 3-05, it is found that even if the thickness of the entire protective layer is 0.5 [mm], if the relative dielectric constant of the entire protective layer is in the range of 3.25 to 3.75, it is not possible to obtain an improvement rate of 10% or more compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristic is reduced to less than 10%.

[0051] In Comparative Example 3-06, a 0.5 mm thick starch paste (dielectric constant: 2.5) is provided as an adhesive layer, and a 0.5 mm thick fluororesin (dielectric constant: 4.0) is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 mm, the total thickness of the protective layer is 1.0 mm, and the total dielectric constant of the protective layer is 3.25. The improvement rate of the directional diffusion degree is +9.4%, so the evaluation 3 is less than +10%. In Comparative Example 3-07, a 0.25 mm thick starch paste (dielectric constant: 2.5) is provided as an adhesive layer, and a 0.75 mm thick quartz (dielectric constant: 3.7) is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 mm, the total thickness of the protective layer is 1.0 mm, and the total dielectric constant of the protective layer is 3.4. Since the improvement rate of the directional diffusion rate is +7.9%, the evaluation 3 is less than +10%. In the comparative example 3-08, an acrylic resin (relative dielectric constant 3.0) having a thickness of 0.5 [mm] is provided as an adhesive layer and a fluororesin (relative dielectric constant 4.0) having a thickness of 0.5 [mm] is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 [mm], and the thickness of the entire protective layer is 1.0 [mm] and the relative dielectric constant of the entire protective layer is 3.5. Since the improvement rate of the directional diffusion rate is +2.0%, the evaluation 3 is less than +10%. In Comparative Example 3-09, a 0.25 mm thick starch paste (dielectric constant: 2.5) is provided as an adhesive layer, and a 0.75 mm thick fluororesin (dielectric constant: 4.0) is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 1.8 mm, and the thickness of the entire protective layer is 1.0 mm and the dielectric constant of the entire protective layer is 3.625. Since the improvement rate of the directional diffusion rate is +2.5%, the evaluation 3 is less than +10%. From the results of these Comparative Examples 3-06 to 3-09, it is found that even if the thickness of the entire protective layer is 1.0 mm, if the dielectric constant of the entire protective layer is in the range of 3.25 to 3.625, it is not possible to obtain an improvement rate of 10% or more compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristic is reduced to less than 10%.

[0052] In Comparative Example 3-10, a 0.5 mm thick glue (dielectric constant: 2.0) is used as an adhesive layer, and a 1.0 mm thick polyvinyl chloride (dielectric constant: 3.0) is used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer is 2.3 mm, the total thickness of the protective layer is 1.5 mm, and the total dielectric constant of the protective layer is 2.75. The improvement rate of the directional diffusion degree is +5.6%, so the evaluation 3 is less than +10%. In Comparative Example 3-11, a 0.5 mm thick starch glue (dielectric constant: 2.5) is used as an adhesive layer, and a 1.0 mm thick polyvinyl chloride (dielectric constant: 3.0) is used as a surface layer, so that the total thickness of the radio wave scattering sheet 12 with protective layer is 2.3 mm, the total thickness of the protective layer is 1.5 mm, and the total dielectric constant of the protective layer is 2.875. The improvement rate of the directional diffusion rate is +5.1%, so that the evaluation 3 is less than +10%. In Comparative Example 3-12, a starch paste (relative dielectric constant: 2.5) having a thickness of 0.25 [mm] is provided as an adhesive layer, and a polyvinyl chloride (relative dielectric constant: 3.0) having a thickness of 1.25 [mm] is provided as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer is 2.3 [mm], so that the thickness of the entire protective layer is 1.5 [mm], and the relative dielectric constant of the entire protective layer is 2.9. The improvement rate of the directional diffusion rate is +3.6%, so that the evaluation 3 is less than +10%. From the results of Comparative Examples 3-11 to 3-12, it can be seen that when the thickness of the entire protective layer is 1.5 [mm], which is more than 1.0 [mm], even if the relative dielectric constant of the entire protective layer is in the range of 2.75 to 2.9, it is not possible to obtain an improvement rate of 10% or more compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristic is reduced to less than 10%.

[0053] In Comparative Example 3-13, a 0.5 mm thick glue (dielectric constant: 2.0) was used as an adhesive layer and a 1.5 mm thick polyvinyl chloride (dielectric constant: 3.0) was used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer was 2.8 mm, the total thickness of the protective layer was 2.0 mm, and the total dielectric constant of the protective layer was 2.75. The improvement rate of the directional diffusion degree was -5.8%, so the evaluation 3 was less than +10%. In Comparative Example 3-14, a 0.5 mm thick starch glue (dielectric constant: 2.5) was used as an adhesive layer and a 1.5 mm thick polyvinyl chloride (dielectric constant: 3.0) was used as a surface layer so that the total thickness of the radio wave scattering sheet 12 with protective layer was 2.8 mm, the total thickness of the protective layer was 2.0 mm, and the total dielectric constant of the protective layer was 2.875. The improvement rate of the directional diffusion rate is -1.9%, so the evaluation 3 is less than +10%. From the results of these comparative examples 3-13 to 3-14, it can be seen that when the thickness of the entire protective layer exceeds 1.0 [mm], that is, becomes 2.0 [mm], even if the relative dielectric constant of the entire protective layer is in the range of 2.75 to 2.875, it is not possible to obtain an improvement rate of 10% or more compared to the directional diffusion rate of the reference radio wave scattering sheet 1, and the improvement rate of the radio wave scattering characteristics falls to less than 10%.

[0054] From the results of the third embodiment described above, in the radio wave scattering sheet 12 with a protective layer that uses two layers, the surface layer 2a and the adhesive layer 2b, if the thickness of the entire protective layer covering the radio wave scattering surface 1d is in the range of 0.5 mm to 1.0 mm and the relative dielectric constant of the entire protective layer is in the range of 2.0 to 3.0, an improvement rate of 10% or more can be obtained from the directional diffusion degree of the reference radio wave scattering sheet 1. Therefore, the radio wave scattering sheet 11 with a protective layer provided with a dielectric layer 2' that meets the above conditions as a protective layer can achieve a directional diffusion degree equal to or greater than that of the radio wave scattering sheet 1 used alone, and can greatly contribute to improving communication quality not only in the 28 [GHz] band but also in microwaves and millimeter waves.

[0055] The above describes embodiments of the radio wave scattering sheet with a protective layer according to the present invention based on the attached drawings. However, the present invention is not limited to these embodiments, and may be implemented by reusing publicly known, existing equivalent technical means as long as the configuration described in the claims is not changed. [Explanation of symbols]

[0056] 11 Radio wave scattering sheet with protective layer (first embodiment) 1 Radio wave scattering sheet 1a Dielectric substrate 1b Back metal plate 1c Surface metal processing layer 1d Radio wave scattering surface 2. Dielectric Layer 3 Adhesive layer 12 Radio wave scattering sheet with protective layer (second embodiment) 2′ Dielectric layer 2a Surface layer 2b Adhesive layer

Claims

1. A radio wave scattering sheet with a metamaterial structure that scatters electromagnetic waves in multiple directions when it receives electromagnetic waves of a specific frequency band on a radio wave scattering surface formed with a specific metal pattern on a dielectric substrate; a protective layer that covers the radio wave scattering surface of the radio wave scattering sheet to protect the metal pattern and has at least an outer surface that is opaque; A radio wave scattering sheet with a protective layer comprising: The protective layer covers the radio wave scattering surface to a thickness in the range of 0.25 mm to 3.0 mm, and has a relative dielectric constant in the range of 2.0 to 4.

0.

2. The radio wave scattering sheet with protective layer as described in claim 1, characterized in that the protective layer is made of a single material having a thickness covering the radio wave scattering surface in the range of 0.25 mm to 2.0 mm and a relative dielectric constant in the range of 2.0 to 3.

0.

3. the protective layer has a two-layer structure including a lower protective layer disposed on the radio wave scattering surface and an upper protective layer disposed on the lower protective layer, The radio wave scattering sheet with protective layer as described in claim 1, characterized in that the total thickness of the lower protective layer and the upper protective layer is in the range of 0.5 to 1.0 mm, and the overall relative dielectric constant of the lower protective layer and the upper protective layer combined is in the range of 2.0 to 3.0.

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