EP-4742452-A1 - PROTECTIVE-LAYER-EQUIPPED RADIO WAVE SCATTERING SHEET

Abstract

Provided is a protective-layer-equipped radio-wave scattering sheet that is provided with a protective layer that does not inhibit radio-wave scattering characteristics as much as possible while improving the appearance and durability of the radio-wave scattering sheet. [Solution] In a protective-layer-equipped radio-wave scattering sheet 11, in which an radio-wave scattering surface 1d of an radio-wave scattering sheet 1 is covered with a dielectric layer 2 to protect a front metal processed layer 1c, the appearance and durability of the radio-wave scattering sheet 1 is improved by the dielectric layer 2. In addition, by making the dielectric layer 2 covering the radio-wave scattering surface 1d have a thickness in the range of 0.25 mm to 3.0 mm, and by making the dielectric layer 2 have a relative permittivity in the range of 2.0 to 4.0, a decrease in the diffusion coefficient is limited to 10% or less.

Inventors

• MURAKAMI, YASUTAKA
• HAMADA, Rira
• CHAKAROTHAI, Jerdvisanop
• FUJII, KATSUMI

Assignees

• National Institute of Information and Communications Technology

Dates

Publication Date

20260513

Application Date

20240701

Claims (3)

1. A protective-layer-equipped radio-wave scattering sheet comprising: a metamaterial-structured radio-wave scattering sheet that, when an radio-wave scattering surface having a specific metal pattern formed on a dielectric substrate receives radio- waves in a specific frequency band, scatters the radio-waves in multiple directions; and a protective layer that covers the radio-wave scattering surface of the radio-wave scattering sheet to protect the metal pattern, at least an outer surface of the protective layer being opaque, wherein the protective layer has a thickness in a range of 0.25 mm to 3.0 mm at a portion covering the radio-wave scattering surface and has a relative permittivity in a range of 2.0 to 4.0.
2. The protective-layer-equipped radio-wave scattering sheet according to claim 1, wherein the protective layer is made of a single material having a thickness in a range of 0.25 mm to 2.0 mm at a portion covering the radio-wave scattering surface and having a relative permittivity in a range of 2.0 to 3.0.
3. The protective-layer-equipped radio-wave scattering sheet according to claim 1, wherein 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, and a total thickness of the lower protective layer and the upper protective layer is in a range of 0.5 mm to 1.0 mm, and a relative permittivity of the entire protective layer including the lower protective layer and the upper protective layer is in a range of 2.0 to 3.0.

Description

Technical Field The present invention relates to a protective-layer-equipped radio-wave scattering sheet in which a metal pattern exposed as an radio-wave scattering surface of a metamaterial-structured radio-wave scattering sheet is covered to improve the appearance and the durability. Background Art In recent years, the fifth-generation wireless communication (so-called 5G) service has been started, in which radio-waves in a frequency band of 28 GHz are used. In this frequency band, the propagation attenuation of the radio-waves is large and the straightness is high. Thus, if there is a shielding object between a transmission antenna and a reception antenna, the radio- waves from the transmission antenna do not reach the reception antenna, leading to a problem in that the communication quality is greatly deteriorated. To address this problem, metamaterial-structured radio-wave scattering sheets that scatter reflected waves of radio- waves at wide angles have been developed. There is an radio-wave scattering sheet, serving as a metamaterial-structured radio-wave scattering sheet, that is designed to have a desired scattering pattern by processing a specific metal pattern on a dielectric substrate (for example, see NPL 1). In addition, a reflectarray has been developed in which the dimensions and shape of reflective elements are changed to vary the resonant frequency of each reflective element, whereby the reflection phase of radio-waves is controlled, and the incident direction and the reflection direction of radio-waves are controlled (for example, see PTL 1). Such radio-wave scattering sheet and reflectarray are used by being attached to a wall surface, a ceiling, or the like in a room. By scattering scattered waves on the surface (radio-wave scattering surface) at wide angles, it is possible to cause radio-waves to reach a region where radio- waves do not reach in a typical metal flat plate, and it is possible to improve the quality of wireless communication for multiple terminals or moving terminals. Citation List Non Patent Literature NPL 1: Y. Murakami, J. Chakarothai and K. Fujii, "Design of electromagnetic scattering wall using genetic algorithm," IEICE Commun. Express, vol. 9, pp. 282 to 287, 2020. Patent Literature PTL 1: International Publication No. 2022/186385 Summary of Invention Technical Problem However, in the conventional radio-wave scattering sheet and reflectarray, the metal pattern of the radio-wave scattering surface is exposed. Hence, there has been a concern that the characteristics may deteriorate due to rust or adhesion of dirt (so-called deterioration over time). In addition, when the radio-wave scattering sheet or the like is used indoors, the appearance is not necessarily good because the metal pattern of the radio-wave scattering surface is exposed, whereas when the radio-wave scattering sheet or the like is used outdoors, adverse effect on the surrounding landscape is a concern. Furthermore, regardless of whether indoors or outdoors, sunlight incident on an radio-wave scattering surface of an radio-wave scattering sheet or the like may be reflected and focused by the metal pattern, posing a risk of fire. These problems caused by the metal pattern exposed on the radio-wave scattering surface may be solved by covering the radio-wave scattering surface of the radio-wave scattering sheet with a non-metal material so that the metal pattern is not exposed. However, covering the radio-wave scattering surface of the radio-wave scattering sheet with another material may lead to a risk that the radio-wave scattering characteristics, which are most important, may be deteriorated or significantly impaired. The important point is what material satisfying certain conditions is to be used to cover the radio-wave scattering surface of the radio-wave scattering sheet. Accordingly, an object of the present invention is to provide a protective-layer-equipped radio-wave scattering sheet provided with a protective layer that does not impair the radio-wave scattering characteristics as much as possible while improving the appearance and durability of the radio-wave scattering sheet. Solution to Problem To overcome the above problem, the present invention provides a protective-layer-equipped radio-wave scattering sheet including: a metamaterial-structured radio-wave scattering sheet that, when an radio-wave scattering surface having a specific metal pattern formed on a dielectric substrate receives radio- waves in a specific frequency band, scatters the radio- waves in multiple directions; and a protective layer that covers the radio-wave scattering surface of the radio-wave scattering sheet to protect the metal pattern, at least an outer surface of the protective layer being opaque. The protective layer has a thickness in a range of 0.25 mm to 3.0 mm at a portion covering the radio-wave scattering surface and has a relative permittivity in a range of 2.0 to 4.0. In the above configuration, the pro