Reflectarray with functional layer

Abstract

To provide a reflect array with a functional layer, capable of suppressing generation of bubbles with a micro fable size.SOLUTION: A reflect array includes an additional functional layer covering at least an upper surface and a side surface of an element pattern. The thickness L (μm) of the element pattern satisfies the following expression (1): 1.0≤L (1). The side surface has a first end connected to the lower surface of the element pattern and a second end connected to the upper surface of the element pattern. In a cross section, an angle α (°) between a straight line connecting the first end and the second end and a perpendicular line from the second end to the lower surface satisfies the following expression (2): α≥10 (2). When the side surface is divided at N points at equal intervals in a thickness direction using N determined from the following expression (3), an angle βi between a straight line connecting an i-1th point and an i-th point and a perpendicular line from the second end to the lower surface in a cross section satisfies the following expression (4) with any i. N=[L] (3) βi≥0 (4) (where i is an integer satisfying 1≤i≤N+1).SELECTED DRAWING: Figure 6

Description

[Technical field]

[0001] The present invention relates to a reflectarray with a functional layer. [Background technology]

[0002] With the advancement of digitalization in society, data communication speeds in wireless communication have increased dramatically, and the frequency of electromagnetic waves has also increased accordingly. However, as the frequency of electromagnetic waves increases, they tend to travel in a more directional direction, meaning that electromagnetic waves cannot get around buildings and other obstacles, which can easily result in blind zones where communication is not possible. For these reasons, in order to realize 5G and 6G communications over a wide area, it is necessary to increase the number of base stations. However, since increasing the number of base stations requires a large amount of cost, it is difficult to increase the number of base stations quickly. In recent years, to solve these problems, reflectarrays have been proposed as a technology to control the direction of electromagnetic waves. A reflectarray (electromagnetic wave reflector) is a member that reflects electromagnetic waves, and includes not only those that perform symmetrical reflection with equal angles of incidence and reflection, but also those that perform asymmetrical reflection with different angles of incidence and reflection, those that scatter electromagnetic waves in multiple directions, and those that collect electromagnetic waves at a specific location. Reflectarrays are described in Patent Documents 1 to 3. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] International Publication No. 2022 / 163813 [Patent Document 2] Patent No. 7206571 [Patent Document 3] Patent Publication No. 2022-119212 Summary of the Invention [Problem to be solved by the invention]

[0004] A reflectarray generally has a structure in which an element pattern is formed of a conductive layer on a base layer, and an additional functional layer such as a protective layer is further laminated on the conductive layer to cover it. If bubbles are generated around the element pattern in the process of laminating the additional functional layer on the element pattern, the reflection phase in the cell in which the element pattern is located will change significantly from the design value. If the number of cells with such defects exceeds a certain percentage, adverse effects such as an increase in unwanted reflection and a decrease in reflection intensity in the desired direction will occur. In the reflectarrays of Patent Documents 1 and 2, the problem of bubbles being mixed into the element pattern and the issue of how to suppress them are not recognized in the first place.

[0005] Bubbles are particles that are formed by enclosing gas inside or on the surface of a liquid or solid, and are covered with a single surfactant layer. Foam is a collection of bubbles, and may be covered with a double surfactant layer. Foam is a general term that includes air bubbles and foam. Bubble particles can have various shapes, including spheres and ellipsoids. The size of a bubble (bubble diameter) is defined as the length of the longest line segment connecting two points on the bubble's outline (described below).

[0006] The inventors noticed that ultrafine bubbles, which have a diameter of less than 1 μm, are negatively charged in neutral water, so they repel each other and do not combine, whereas microfibers, which have a diameter of approximately 1 μm or more, come into contact with each other and coalesce to form a single larger bubble or foam, which has a more adverse effect on reflection properties.

[0007] Although Patent Document 3 is an antenna technology and is in a different technical field from reflectarrays, it describes providing an inclined or curved surface on the side shape of the conductive layer to suppress the occurrence of gaps between the conductive layer and the additional function layer. However, there is no recognition of the issue of the effect on reflection characteristics according to the size of the air bubbles, and it is not clear in particular about the side shape of the element pattern aimed at suppressing microfiber-sized air bubbles. Therefore, an object of the present invention is to provide a reflect array capable of suppressing microfiber-sized bubbles. [Means for solving the problem]

[0008] In order to solve the above problems, a representative reflectarray with a functional layer of the present invention includes a ground layer, a dielectric layer, and an element pattern, and includes an additional functional layer covering at least the upper surface and side surfaces of the element pattern, and the thickness L (μm) of the element pattern satisfies formula (1): 1.0≦L (1) the side surface has a first end connected to the bottom surface of the element pattern and a second end connected to the top surface, and an angle α (°) between a straight line connecting the first end and the second end in a cross section and a perpendicular line from the second end to the bottom surface satisfies formula (2); α≧10 (2) When the side surface is divided at N points at equal intervals in the thickness direction using N calculated from formula (3), the angle βi between the line connecting the (i-1) point and the i point in the cross section and the perpendicular line from the second end to the underside satisfies formula (4) for any i. N=[L] (3) βi≧0 (4) (i is an integer satisfying 1≦i≦N+1.) Effect of the Invention

[0009] According to the present invention, it is possible to provide a reflect array capable of suppressing microfiber-sized bubbles. Problems, configurations and effects other than those described above will become apparent from the description of the following embodiments. [Brief description of the drawings]

[0010] [Figure 1] FIG. 1 is an example of a schematic diagram showing an enlarged reflection control area portion. [Diagram 2] FIG. 2 is a diagram showing an example of an element pattern shape. [Figure 3A] FIG. 3A is a schematic diagram showing an example of a variation of the layer configuration of the reflect array. [Figure 3B] FIG. 3B is a schematic diagram showing an example of a variation of the layer configuration of the reflect array. [Figure 4] FIG. 4 is a photograph of a portion of the element pattern observed from above the functional layer using an optical microscope. [Diagram 5] FIG. 5 is a schematic cross-sectional view showing a part of a basic layer configuration of a reflect array including a side surface of an element pattern. [Figure 6] FIG. 6 is an enlarged schematic view of the vicinity of the first side surface of the element pattern. [Figure 7A] FIG. 7A is a schematic diagram showing an example of division of the side shape of an element pattern and inclination angles α and βi. [Figure 7B] FIG. 7B is a schematic diagram showing an example of division of the side shape of an element pattern and inclination angles α and βi. [Figure 8] FIG. 8 is a graph showing the reflection angle and reflection intensity (bistatic RCS) in the example and the comparative example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to the embodiment. In addition, in the description of the drawings, the same parts are denoted by the same reference numerals.

[0012] In the following description, the xyz coordinate system is applied, and the reflectarray is formed on the xy plane. The shape of the reflectarray on the xy plane is arbitrary, but in the following description, the reflectarray is assumed to be the simplest rectangle, and each side of the reflectarray is formed parallel to the x-axis and y-axis, respectively. In addition, the ground layer, dielectric layer, element pattern, and functional layer are laminated in this order along the positive direction of the z-axis.

[0013] "Surface" can refer not only to the surface of a plate-like member, but also to the interface of a layer contained in the plate-like member that is approximately parallel to the surface of the plate-like member. Additionally, "upper surface" and "lower surface" refer to the surface shown at the top or bottom of a drawing when a plate-like member or a layer contained in the plate-like member is illustrated. Up refers to the positive direction of the z-axis, and down refers to the negative direction. The "upper surface" and "lower surface" are sometimes referred to with numbers such as "first surface" and "second surface."

[0014] The "side surface" refers to the surface connecting the "upper surface" and "lower surface". When the shape of the side surface is described as tapered, it means that all the side surfaces of the structure are inclined. When the shape of the side surface is described as forward tapered, it means that all the side surfaces of the structure are inclined so as to displace outward from the upper surface to the lower surface.

[0015] A "cross section" refers to a part or all of a surface obtained by cutting the reflect array in the z-axis direction on any line along the x-axis or y-axis in an xyz coordinate system.

[0016] The distance in the z-axis direction in the xyz coordinate system is sometimes referred to as "thickness." The z-axis direction is also sometimes referred to as the thickness direction.

[0017] (Reflection control area) The reflection control area refers to a part of the area that constitutes the reflectarray. The reflection control area is the smallest area that can reflect the electromagnetic wave incident on that area in a specified direction. The reflectarray is composed of one or more reflection control areas. The reflection control area includes not only a two-dimensional area in which the electromagnetic wave is parallel to the incident area, but also a layer structure formed in a direction perpendicular to the area.

[0018] Moreover, a unit cell refers to an area obtained by dividing a reflection control area. A unit cell contains one element pattern. Two or more unit cells exist in one reflection control area. The size of the side of only one unit cell in the x-axis direction is defined as Ux, and the size of the side in the y-axis direction is defined as Uy. In one reflection control area, the size (length) of a side in which multiple unit cells are lined up in the x-axis direction is defined as Sx.

[0019] FIG. 1 is an example of a schematic diagram showing an enlarged reflection control region. FIG. 1(a) is a perspective view of the reflection control region, FIG. 1(b) is a cross-sectional view of the reflection control region in the xz plane cut in the y direction Uy / 2, and FIG. 1(c) is a cross-sectional view of an arbitrary unit cell of the reflection control region in the yz plane cut in the x direction Ux / 2. An element pattern 1 having an element side surface 5 is formed on one xy plane of the dielectric layer 2, and a ground layer 3 is formed on the other xy plane. An additional functional layer 4 is formed so as to cover the entire element pattern 1 including the element side surface 5. When the unit cell is obtained by dividing the reflection control area into n equal parts along a predetermined direction, Ux is Sx / n, where n is an integer equal to or greater than 2. (In the example of FIG. 1, the long side in the x-axis direction is divided into three parts, so that the unit cell is a square.) 1 , 1 2 , 1 3 The reflection control area is made up of.

[0020] (Reflectarray Design) The reflectarray is designed according to the following procedure. First, the length Sx of the long side of the reflection control area is determined by the following formula (5). Here, Sx is the length of the long side of the reflection control area, λ is the wavelength of the electromagnetic wave applied to the reflectarray (hereinafter also referred to as "wavelength at the operating (design) frequency"), θi is the angle of incidence, and θr is the angle of reflection. The angle of incidence θi and the angle of reflection θr are values ​​measured on the zx plane. Here, the direction parallel to the z axis is θi=θr=0°, the angle of rotation in the positive direction of the x axis is θi=0 to 90°, and the angle of rotation in the negative direction is θr=0 to 90°.

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[0021] Next, the reflection phase required in each reflection control area is calculated using the following equation (6).

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[0022] After the reflection phase is obtained by the above method, the shape of the element pattern is changed so as to satisfy the reflection phase in each unit cell, and a simulation is performed to optimize the shape of the element pattern. When an electromagnetic wave is incident on the element pattern, the relationship between the shape of the element pattern and the reflection phase can be obtained by a simulation using, for example, an electromagnetic analysis tool (High Frequency Structure Simulator: HFSS) or the like.

[0023] The components of the reflectarray will now be described in more detail. (element pattern) The element pattern is provided to asymmetrically reflect the incident electromagnetic wave in a direction different from the symmetric reflection. The thickness of the element pattern is, for example, 10 nm to 105 μm.

[0024] The element pattern preferably has a surface resistance of 100Ω / □ or less. The material used for the element pattern is, for example, a conductive material. The same material as that used for the ground layer can be used as the material. A conductive inorganic or organic material may be formed on the dielectric layer. From the viewpoints of flexibility, film formability, stability, sheet resistance value, and low cost, it is preferable to use a film formed by a deposition method as the formation method described later as the element pattern.

[0025] The shape of the element pattern includes, but is not limited to, a cross patch. FIG. 2 is a diagram showing an example of the shape of the element pattern. As shown in FIG. 2, the reflect array may be formed with an element pattern of any shape that reflects radio waves, such as a continuous film, a mesh shape, or a punching shape. For example, instead of the cross patch (FIG. 2(a)), a cube patch (FIG. 2(b)), a cylindrical patch (FIG. 2(c)), a triangular prism patch (FIG. 2(d)), a Jerusalem cross patch (FIG. 2(e)), a plurality of parallel conductive patterns (FIG. 2(f)), a ring-shaped conductive pattern (FIG. 2(g)), or an element pattern (FIG. 2(h)) that is a combination of a plurality of these may be used.

[0026] A case where the element pattern is a cross patch will be described. A cross patch refers to a shape in which two square patches are perpendicular to each other in the xy plane. The length of the element pattern of the cross patch is defined as the element length, and the width of the element pattern of the cross patch is defined as the element width. Either or both of the element length and element width are changed to control the reflection phase of the unit cell. When the element length is fixed, it is desirable to set the value of the element length as large as possible within the unit cell. By setting it large, it becomes easier to obtain the desired reflection phase characteristics. When the element width is fixed, it is desirable to set the value of the element width as large as possible within the unit cell. By setting the value of the element width large, the slope of the reflection phase becomes gentle, so that the processing accuracy during processing is expanded. Note that the element length is not limited to being set to the element pattern of the cross patch, but can also be set to element patterns having other shapes. In addition, the element length can be set to a common length in the reflection control area, and it is also possible to set different lengths for each element pattern included in the reflection control area.

[0027] Methods for forming the element pattern include a method in which a conductive material is formed over the entire surface of the dielectric layer to form a continuous film, and then the element pattern is formed by processing, or a method in which an element pattern layer is formed directly on the dielectric layer.

[0028] As a method for forming a conductive material as a continuous film over the entire surface of the dielectric layer, in the case of metal, it is possible to select from dry coating such as sputtering or vapor deposition, plating or gravure coating using metal ink, wet coating such as die coating, etc. Alternatively, a rolled metal plate can be attached to the dielectric layer. Similarly, a continuous film can be formed by dry coating in the case of inorganic oxide materials, or wet coating in the case of organic materials. Painting or spraying methods may also be used. The continuous film thus formed is subjected to a removal process such as dry etching, wet etching, or cutting to remove unnecessary portions, thereby forming an element pattern.

[0029] When removing the reflect array by etching, the edges of the element patterns constituting the reflect array may become rounded (in other words, may become rounded), pinholes may occur, the cross-sectional shape may become forward or reverse tapered, or undercut or overetching may occur. Although such shape changes are expected to occur during the etching process, as long as the direction of the main beam of the electromagnetic waves reflected in the basic configuration is within a range of about ±5° of the designed reflection angle, this is considered to be acceptable as a reflection phase characteristic. Formation by cutting, printing, dry coating, plating, painting, or spraying is also acceptable.

[0030] Methods for directly forming the element pattern on the dielectric layer include printing using letterpress printing, lithographic printing, intaglio printing, stencil printing, transfer printing, etc., or masking the dielectric layer except for the element pattern portion with masking tape or masking agent, etc., and then forming the element pattern using dry coating, plating, painting, or spraying.

[0031] The cross-sectional shape of the element pattern is preferably a forward tapered shape that widens from the top to the bottom. The forward tapered shape increases the surface area of ​​the element pattern, which increases the adhesion to the functional layer when the functional layer is laminated, as described below, and makes it possible to suppress the inclusion of air bubbles.

[0032] The material of the element pattern may be the same as that of the ground layer, or a different material may be used. For example, at least one of the ground layer and the element pattern may be formed of Cu or Al. Cu has excellent conductivity and can reduce conductor loss. Al has low density, is lightweight, and is low cost, so a lightweight and inexpensive reflect array can be formed.

[0033] When the element pattern is in the form of a mesh, the line width of the mesh is preferably 5 μm to 30 μm, more preferably 6 μm to 15 μm. The line spacing of the mesh is preferably 50 μm to 500 μm, more preferably 100 μm to 300 μm. In addition, when the wavelength at the operating frequency is λ, the line spacing of the mesh is preferably 0.5×λ or less, more preferably 0.1×λ or less, and even more preferably 0.01×λ or less. If the line spacing of the mesh is 0.5×λ or less, the performance can be guaranteed. In addition, the line spacing of the mesh may be 0.001×λ or more. When a metal mesh or a transparent conductive material is used, the reflect array exhibits visible light transparency, making it possible to maintain the appearance after installation. When the element pattern is mesh-shaped or when a transparent conductive material is used, the reflect array exhibits visible light transparency, making it possible to maintain the appearance after installation.

[0034] When the element pattern is in the form of a thin film, adhesion with the additional functional layer and the adhesion improving layer is improved, and the flexibility of the reflect array can be improved, making it possible to use it on curved surfaces and to implement a roll-to-roll production process.

[0035] When the element pattern is formed using a thin film, the thickness is preferably greater than the skin depth calculated from the following formula (10): where d is the skin depth, ω is the angular frequency, μ is the magnetic permeability of the material, and σ is the electrical conductivity of the material.

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[0036] In order to increase the reflection efficiency of radio waves, it is necessary to reduce radio wave loss due to the element, and therefore it is preferable that the surface roughness of the element is small.

[0037] (Dielectric) As the dielectric material, in addition to a simple resin, composite materials such as paper, glass fiber, or carbon fiber impregnated with resin can be used. Examples of single resins include polyethylene (εr = 2.2 to 2.4), polypropylene (εr = 2.0 to 2.6), polystyrene (εr = 2.4 to 2.6), polyvinyl chloride (εr = 2.8 to 8.0), AS resin (εr = 2.6 to 3.1), ABS resin (εr = 2.4 to 4.1), polyethylene terephthalate (εr = 2.9 to 3.0), acrylic resin (εr = 2.7 to 4.5), urethane resin (εr = 4.0 to 7.1), epoxy resin (εr = 2.5 to 6.0), nylon (εr =3.0-5.0), polyimide (εr=2.4-2.7), fluororesin (εr=2.0-2.6), polycarbonate (εr=2.9-8.9), polyphenylene ether (εr=2.8-8.2), polyphenylene sulfide (εr=3.2-4.6), polyvinylidene fluoride (εr=6.4-10.0), polyethylene naphthalate (εr=2.9), phenol resin (εr=3.0-12.0), cycloolefin polymer (εr=2.3-2.5), etc. are listed. Here, εr indicates the relative dielectric constant. In particular, it is preferable to use polyethylene (PS), polyethylene terephthalate (PET), cycloolefin polymer (COP), etc., because they are inexpensive and have excellent versatility. The dielectric layer can be a single layer or multiple layers. The dielectric layer can also be a foam obtained by foaming the above materials. As the foam, a foam having high flexibility is preferably used. Examples of composite materials include paper / phenol resin, paper / epoxy resin, glass / epoxy resin, and glass / fluororesin composite materials. In addition, from the viewpoint of adjusting the dielectric constant, a mixture containing resin components or a dielectric compound and a resin component can be used. The relative dielectric constant of the mixture can be adjusted depending on the selection and content of the dielectric compound.

[0038] The relative dielectric constant of a mixture can be predicted, for example, by using the Maxwell-Garnett law. In a mixture of a dielectric A with a relative dielectric constant εa and a dielectric B with a relative dielectric constant εb, when the volume fraction of the dielectric A is δa, the relative dielectric constant εm of the mixture is expressed by the following relational expression (11).

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[0039] Examples of the dielectric compound include barium titanate (εr=250 to 20000), titanium oxide (εr=83 to 183), lead zirconate titanate, strontium tantalate bismuthate, and bismuth ferrite.

[0040] When a transparent dielectric material is used, the reflect array exhibits visible light transmittance, making it possible to maintain the appearance after installation.

[0041] The relative dielectric constant of the dielectric layer is preferably in the range of 1 to 20, more preferably in the range of 1 to 10, and even more preferably in the range of 2 to 4. If the relative dielectric constant is within the above range, the desired reflection phase characteristics tend to be easily obtained in the reflectarray. In addition, the dielectric loss tangent is preferably in the range of 0.00005 to 0.01, and more preferably in the range of 0.00005 to 0.001. If it is within the above range, a reflectarray with low dielectric loss can be produced.

[0042] The dielectric layer can be formed by, for example, wet coating such as die coating, comma coating, or gravure coating, melt extrusion methods such as a T-die method or an inflation method, a calendar film forming method, a solution casting method, a heat press method, etc. Also, a co-extrusion method in which a film is formed by extruding a plurality of resins in multiple layers may be used.

[0043] The thickness of the dielectric layer is appropriately selected depending on the design frequency. When the design frequency is 28 GHz, it is preferably 40 μm or more and 250 μm or less, and more preferably 50 μm or more and 200 μm or less. If it is too thin, it becomes difficult to ensure the reflection phase, and it becomes difficult to design the reflectarray. On the other hand, if it is too thick, it tends to be difficult to ensure the reflection phase, to lose flexibility, and to increase the total thickness of the reflectarray, making it difficult to save space. For this reason, the thickness of the dielectric layer is preferably 250 μm or less. When the design frequency is 60 GHz, the thickness of the dielectric layer is preferably 10 μm or more and 250 μm or less. When the design frequency is 100 GHz or more, it is easy to design the reflectarray if the thickness of the dielectric layer is about several μm or more and 100 μm or less.

[0044] (Ground layer) The ground layer is provided to reflect the electromagnetic waves that reach the reflect array. It is also used to support and protect the dielectric layer. The ground layer is made of a conductive material such as an inorganic oxide material, a metal material, or a conductive organic material. The thickness of the ground layer is, for example, 10 nm or more and 105 μm or less.

[0045] For example, inorganic oxide materials and metal materials include indium tin oxide (ITO), indium zinc oxide (IZO), aluminum zinc oxide (AZO), gallium zinc oxide (GZO), antimony tin oxide, Ag, Al, Au, Pt, Pd, Cu, Co, Cr, In, Ag-Cu, Cu-Au, and Ni. Nanoparticles or nanowires containing at least one of these materials may also be used. Organic materials having electrical conductivity include polythiophene derivatives, polyacetylene derivatives, polyaniline derivatives, polypyrrole derivatives, carbon nanotubes, graphene, and the like. In particular, Cu and Al are preferred from the viewpoints of material cost, electrical conductivity, and film formability. In order to reflect electromagnetic waves, it is desirable for the surface resistance of the ground layer to be 100Ω / □ or less. If this condition can be met, a transparent reflect array can also be produced by using ITO or a mixture (PEDOT / PSS) of polyethylenedioxythiophene (PEDOT) and polystyrenesulfonic acid (PSS).

[0046] The above materials can be used in the form of a continuous film, mesh, punched shape, or periodic structure. Here, mesh refers to a state in which a conductor has a mesh-like opening (opening) on ​​its plane. When the conductor is formed in a mesh shape, the mesh may be rectangular or rhombic. When the mesh is formed in a rectangular shape, it is preferable that the mesh is square. Square meshes have good design properties. They may also be randomly shaped by a self-organizing method. Making the mesh random can prevent moire. When processing metal into a mesh shape, methods such as punching a metal plate or etching a metal plate can be used. When the ground layer is mesh-like or a transparent conductive material is used, the reflect array exhibits visible light transparency, making it possible to maintain the appearance after installation.

[0047] When the ground layer is in the form of a mesh, the line width of the mesh is preferably 5 μm to 30 μm, more preferably 6 μm to 15 μm. The line spacing of the mesh is preferably 50 μm to 500 μm, more preferably 100 μm to 300 μm. Furthermore, when the wavelength at the operating frequency is λ, the line spacing of the mesh is preferably 0.5×λ or less, more preferably 0.1×λ or less, and even more preferably 0.01×λ or less. If the line spacing of the mesh is 0.5×λ or less, performance can be ensured. Furthermore, the line spacing of the mesh may be 0.001×λ or more.

[0048] When a metal material is used, the method of forming the ground layer can be selected from dry coating such as sputtering or vapor deposition, wet coating such as gravure coating or die coating by turning the metal material into ink, surface treatment such as plating, etc. Alternatively, a rolled metal plate can be used as the ground layer. When an inorganic oxide material is used, dry coating can be selected as the method of forming the ground layer. When an organic material is used, wet coating can be selected as the method of forming the ground layer. Also, the ground layer can be formed by painting or spraying.

[0049] If the ground layer is in the form of a thin film formed by plating or vapor deposition, the flexibility of the reflect array can be improved, making it possible to use it on curved surfaces or implement a roll-to-roll production process.

[0050] When the ground layer is in the form of a thin film, its thickness is preferably larger than the skin depth calculated from equation (10) in the same manner as for the element pattern. In addition, in order to increase the reflection efficiency of electromagnetic waves, it is also necessary to reduce loss due to the ground layer, so it is preferable that the surface roughness of the ground layer is small.

[0051] When the ground layer has a periodic structure, it can selectively reflect or transmit a specific frequency. For example, when a structure in which patch-shaped conductive patterns are periodically arranged is used as the ground layer, it is possible to reflect only a specific frequency, and therefore it is possible to impart a function of transmitting frequencies other than the operating frequency. In addition, when a structure in which holes are periodically arranged where no conductive material exists is used, it is possible to design a reflect array that asymmetrically reflects the operating frequency while transmitting only a specific frequency.

[0052] In the present disclosure, the surface resistance is measured in accordance with JIS-K-7194. The surface resistance can be measured by any suitable method, including a four-terminal method, a two-terminal method, a four-probe method, a dielectric method, and an eddy current method. The surface resistance of the ground layer can be measured, for example, using Loresta GP MCP-T610 (product name, manufactured by Mitsubishi Chemical Analytech Co., Ltd.).

[0053] (Additional Functionality Layer) The function of the additional functional layer can be selected according to need. Examples of the functions that can be added include anti-deterioration properties, design properties, protection and scratch resistance, waterproof properties, gas and water vapor barrier properties, flame retardancy, non-combustibility, self-extinguishing properties, weather resistance, antifouling properties, antibacterial and antiviral properties, chemical resistance, deodorizing properties, and adhesive and bonding properties. One of these functions may be added, or a combination of multiple functions may be added. The thickness of the additional functional layer is, for example, 5 μm or more and 6 mm or less.

[0054] Methods for laminating a sheet-like additional functional layer include lamination using lamination, extrusion lamination, etc., and methods for applying a liquid additional functional layer include, but are not limited to, printing, coating, dry lamination, wet lamination, etc. In addition, if the additional functional layer does not have tackiness or adhesiveness, there is a method of adhering it to the reflect array using an adhesion improving layer (adhesive).

[0055] weather resistance Possible causes of deterioration of reflectarrays include oxidation due to exposure to the atmosphere, absorption of water vapor, and alteration due to light (ultraviolet rays) such as sunlight. In order to prevent deterioration due to oxygen and water vapor, it is possible to provide a layer with excellent gas barrier properties, such as a barrier film, on the surface of the reflectarray. In addition, to prevent deterioration due to oxygen in particular, it is necessary to have an oxygen permeability of the functional layer of 500cc / m 2 ·atm·day or less is preferable. If this condition can be met, the films may be laminated, or an overcoat layer may be applied by dry coating or wet coating. These layers may be single layers, or multiple layers may be combined or laminated. Examples of barrier films include single films such as ethylene-vinyl alcohol copolymer resins, coextruded multilayer nylon (Ny) films, and wet-coated films such as polyvinylidene chloride (PVDC)-coated or polyvinyl alcohol (PVA)-coated films.

[0056] In addition, to prevent deterioration of the dielectric layer, an antioxidant, deterioration inhibitor, or antioxidant material may be added when forming the dielectric layer. Similarly, to prevent deterioration due to water vapor, a material with a water vapor permeability of 300 g / m 2 It is preferable to provide a layer having a luminance of 0.1 Å or less per day. To prevent light from sunlight, etc., it is possible to provide a film having UV-cutting properties or a layer having light-shielding properties. In addition, an ultraviolet scattering agent, an ultraviolet absorbing agent, or a light stabilizer may be added. Examples of UV-cutting films include vinyl chloride resins and polyolefin resins.

[0057] Design When a reflectarray is installed on the exterior or interior of a building, for example, it is possible to add a design to it so that it blends in with the space. Specifically, the design can be added by attaching a sheet-shaped material with a design to the reflectarray using an adhesive, or by fusing and attaching a sheet-shaped material to the reflectarray by applying heat and pressure. For example, a decorative sheet in which a printed pattern and a surface embossed pattern are in harmony by laminating a base sheet, a base pattern layer, and a transparent thermoplastic resin layer in this order, and a decorative sheet with a color close to that of real wood or stone by laminating a pattern layer, a transparent resin layer, and a surface protection layer in this order can be given.

[0058] Protection and scratch resistance Protection and scratch resistance refers to the function of preventing scratches on the reflectarray and deterioration of the reflectarray itself. Methods for imparting such functions include coating the reflectarray to increase its surface hardness or laminating a synthetic resin film. Protection and scratch resistance are evaluated using a pencil hardness test based on JIS K5600-5-4, and it is preferable that the hardness is H or higher. In addition, a load of 1,000gf / cm is used using steel wool (#0000). 2 It is preferable that when rubbed with a material, no scratches occur up to 1000 reciprocating strokes. Examples of synthetic resins include polyethylene terephthalate, cycloolefin polymer, polyethylene, polypropylene, polyvinyl chloride, polystyrene, polymethyl methacrylate, polyester, polyformaldehyde, polyamide, polyphenylene ether, vinylidene chloride, polyvinyl acetate, polyvinyl acetal, AS resin, ABS resin, acrylic resin, fluororesin, nylon resin, polyacetal resin, polycarbonate resin, polyamide resin, and polyurethane resin.

[0059] Flame retardant, non-flammable, self-extinguishing A method of imparting flame retardancy and non-combustibility to a reflectarray is to laminate non-combustible materials, semi-non-combustible materials, or flame retardant materials that have been certified as fireproof under the Building Standards Act. Examples include flame retardant fibers, flame retardant plastics, non-combustible paints, and flame retardant paints. Flame retardant fibers include halogen-based compounds, phosphorus-based compounds, vinylon fibers, polyetherimide fibers, aramid fibers, polyester fibers, and vinylon fibers. Flame retardant plastics include plastic materials to which halogen-based, phosphorus-based, or inorganic flame retardants such as aluminum hydroxide and magnesium hydroxide have been added. Examples of materials that have self-extinguishing properties include nylon, polycarbonate, and polyvinyl chloride.

[0060] Antifouling, antibacterial, antiviral As a method for imparting antifouling properties to the reflect array, it is considered to laminate or coat a substrate having hydrophilicity or water repellency. As a material having hydrophilicity, a photocatalytic material, a silica-based material, etc. can be used. As a material having water repellency, a fluororesin-based material, a silicone-based material, etc. can be used. As an antibacterial or antiviral material, a photocatalytic material, a chlorine-based material, an organic material containing a cationic polymer as a component, a material containing a metal carrier such as silver or zinc, etc. can be used. As a formation method, a method of laminating these material films or using them in a coating process, mixing them when forming a dielectric layer, etc. can be adopted.

[0061] (Adhesion improving layer) The adhesion improving layer is a layer having an adhesive force for bonding layers together. The adhesion improving layer may be composed of two or more layers, or may be composed of a combination of multiple materials. In this embodiment, the adhesion improving layer bonds the ground layer and the dielectric layer, or the dielectric layer and the element pattern, or the dielectric layer, the element pattern, and the additional function layer, and is composed of an adhesive. The adhesive may be a water-dispersion adhesive, a solution-based adhesive, a solvent-free adhesive, or a solid-based adhesive. Examples of adhesives include epoxy resin adhesives, polyvinyl acetate adhesives, nitrile rubber adhesives, phenol resin adhesives, vinyl acetate adhesives, chloroprene rubber adhesives, acrylic resin adhesives, polyvinyl alcohol resin adhesives, silicone rubber adhesives, styrene butadiene rubber adhesives, and urethane adhesives. In addition to the adhesive, the adhesion improving layer may contain any synthetic resin or other substance or any member. The thickness of the adhesion improving layer is, for example, 5 μm or more and 500 μm or less.

[0062] If the additional functional layer does not have tackiness or adhesiveness, it can be attached to the reflect array using an adhesion improving layer. The functional layer is a general term including a single or multiple additional functional layer, a single or multiple adhesion improving layer, or a layer in which an additional functional layer and an adhesion improving layer are stacked one or more times.

[0063] (installation layer) The installation layer is a layer for fixing the reflectarray to the support. For example, an adhesive layer, a sticky layer, or a magnet can be used if the support is made of metal. When a magnet is used, the position and angle of the reflectarray can be easily changed.

[0064] (Support) The reflectarray is installed on a support. The support may be a newly installed panel or pole, or an existing signboard, wall, ceiling, etc. may be used. The support preferably has a mechanism that can adjust the angle of the reflectarray up and down or left and right, and more preferably has a mechanism that moves the position of the reflectarray up, down, left and right. The reflectarray is installed on the support and used as a reflectarray device.

[0065] (Layer structure variations) Figures 3A and 3B (hereinafter collectively referred to as Figure 3 for convenience) are schematic diagrams showing examples of variations in the layer structure of a reflect array. However, the layer structure is not limited to this example. Figure 3(a) shows an embodiment in which an additional function layer 4 is laminated on the top surface of a structure (hereinafter referred to as the "basic structure") in which a ground layer 3, a dielectric layer 2, and an element pattern 1 are laminated, and adjacent element patterns 1 are connected by the additional function layer 4 in which a groove is formed. FIG. 3(b) shows an embodiment similar to FIG. 3(a) except that a gap is formed between adjacent element patterns 1 where no additional functional layer 4 is present. FIG. 3(c) shows a state in which additional functional layers 4 are uniformly laminated on both the upper and lower surfaces of the basic structure. FIG. 3(d) shows a mode in which the additional function layer 4 is laminated uniformly so as to cover not only the upper and lower surfaces of the basic structure but also the side surfaces.

[0066] FIG. 3(e) shows a state in which an adhesion improving layer 6 and an additional functional layer 4 are uniformly laminated on the upper surface of the basic structure. FIG. 3( f ) shows an embodiment similar to FIG. 3( e ), except that a gap is formed between adjacent element patterns 1 where neither the additional functional layer 4 nor the adhesion improving layer 6 is present. FIG. 3(g) shows a mode in which an adhesion improving layer 6 and an additional functional layer 4 are uniformly laminated on the upper and lower surfaces of the basic structure, respectively. Figure 3(h) shows an embodiment in which an additional functional layer 4 is uniformly laminated on the top surface of the basic structure, and an adhesion improving layer 6 is further laminated between the dielectric layer 2 and the element pattern 1, and between the dielectric layer 2 and the ground layer 3.

[0067] (Air bubbles mixed in) When a functional layer is laminated on a reflectarray of a basic configuration, the functional layer may contain multiple bubbles, but it is preferable to have fewer bubbles because they have a negative effect on the appearance of the reflectarray and the reflector performance. In particular, bubbles on the side of the element pattern change the reflection phase in the unit cell, and have adverse effects such as an increase in unnecessary reflection and a decrease in reflection intensity in the desired direction, so it is strongly required to suppress their occurrence. In addition, the larger the bubble diameter is relative to the wavelength of the radio wave, the greater the adverse effects described above. From the above perspective, for example, when using radio waves in the 1 GHz to 300 GHz band, it is preferable that the bubble diameter of the bubbles on the side of the element is less than 100 μm.

[0068] For example, for 100 randomly selected element patterns on a reflect array, it is preferable that there are fewer than 5 element patterns having bubbles on their sides with a bubble diameter of 100 μm or more, more preferably fewer than 3, and even more preferably 0.

[0069] Figure 4 is a photograph of a portion of the element pattern observed from the top of the functional layer using an optical microscope. When a transparent or semi-transparent adhesion improving layer and an opaque additional functional layer are present on the top of the element pattern, the additional functional layer is removed by peeling, scraping, dissolving, or the like while leaving the adhesion improving layer, and the entire periphery of the element pattern is observed from the top of the adhesion improving layer using an optical microscope. When the element pattern cannot be observed using the above-mentioned method, the reflect array is cut in the thickness direction, and the cross section of the element pattern is observed using an optical microscope. In Figure 4, the presence of bubbles is observed above the side 5 of the element pattern.

[0070] In measuring the bubble diameter in a reflectarray with a functional layer, the entire circumference or cross section of the element pattern is observed with an optical microscope at a magnification of 50 to 400 times to obtain the bubble diameter. The magnification during the entire circumference observation is set arbitrarily, and the magnification during the cross section observation is set so that the upper and lower surfaces of the element pattern are simultaneously displayed on one screen. Here, when measuring the bubble diameter, only bubbles that can be clearly observed in their entirety from the observation image are measured, and the longest line segment among the lengths of the line segments connecting two points on the bubble's contour line is measured as the bubble diameter. When making an actual measurement, the above-mentioned bubble detection and bubble diameter measurement may be performed on element patterns (for example, 100 pieces) selected at random on the reflect array.

[0071] (Bubble suppression) Next, a configuration for efficiently suppressing the generation of microfine-sized bubbles will be described. Fig. 5 is a schematic cross-sectional view showing a part of the basic layer configuration of a reflectarray including the side surface of the element pattern 1. However, the following description is not limited to the layer configuration shown in Fig. 5, and it goes without saying that it can be applied to the layer configuration shown in Fig. 3 and other layer configurations within the scope of the present invention.

[0072] The layer structure of Figure 5 includes a ground layer 3 including a first surface and a second surface located opposite the first surface, a dielectric layer 2 including a third surface opposite the second surface and a fourth surface located opposite the third surface, an element pattern 1 including a fifth surface opposite the fourth surface, a sixth surface located opposite the fifth surface, and an element pattern side surface 5 (first side surface) located between the fifth and sixth surfaces, and an additional function layer 4 covering the sixth surface and the first side surface, and the first side surface includes a first end connected to the fifth surface, a second end connected to the sixth surface, and an intermediate point therebetween.

[0073] 6 is an enlarged schematic diagram of the vicinity of the first side surface of the element pattern 1. The thickness L (μm) of the element pattern 1 satisfies the following formula (1). 1.0≦L (1) Since it is believed that the occurrence of microfibers with diameters of approximately 1 μm or more becomes a problem when the thickness L satisfies formula (1), the provision of formula (1) makes it possible to provide a configuration that is more specialized for suppressing microfibers.

[0074] In addition, the angle (general tilt angle) α (°) between the straight line connecting the first end and the second end and the perpendicular line from the second end to the fifth surface is specified to satisfy the following formula (2). α≧10 (2) As a result, the side surface of element pattern 1 assumes an overall configuration in which it expands so as to be displaced outward from the upper surface (sixth surface) to the lower surface (fifth surface).

[0075] Next, the side of element pattern 1 is divided at N points at equal intervals in the thickness direction using N calculated from the following equation (3), and the division point closest to the second end is designated as the first point, and the division point closest to the first end is designated as the Nth point. N=[L] (3) (N=1, 2) Here, N is the maximum integer value not exceeding L (μm).

[0076] Then, the angle (point inclination angle) βi (°) between a straight line connecting the (i-1) point and the i point and a perpendicular line from the second end to the lower surface is specified to satisfy the following formula (4) for any i (i = 1 to N + 1). βi≧0 (4) (i is an integer satisfying 1≦i≦N+1. However, the 0th point corresponds to the 2nd end, and the N+1th point corresponds to the 1st end.)

[0077] 7A and 7B (hereinafter collectively referred to as FIG. 7 for convenience) are schematic diagrams showing examples of the division of the side shape of the element pattern and the inclination angles α and βi. FIG. 7(a) shows α when formula (1) is not satisfied and N=0 (La<1.0). For thicknesses where La is less than 1.0 μm, if α≧10, it is considered that there is almost no risk of microfiber-sized bubbles being generated by entrapment of an air layer even if the first side has any shape.

[0078] Figure 7(b) shows β1 when N = 1 (1.0 ≦ Lb < 2.0). If the conditions of the general inclination angle α ≧ 10 and the point inclination angles β1, β2 ≧ 0 are satisfied, it is considered that there is almost no possibility of microfubble-sized bubbles being generated by entrapment of air layers even if each of the two divided sections of the first side surface has an arbitrary shape.

[0079] Figure 7(c) shows β2 when N = 2 (2.0 ≦ Lc < 3.0). If the conditions of the general inclination angle α ≧ 10 and the point inclination angles β1 to β3 ≧ 0 are satisfied, it is considered that there is almost no possibility of microfubble-sized bubbles being generated by entrapment of air layers, even if each of the three divided sections of the first side surface has an arbitrary shape.

[0080] Figure 7(d) shows β3 when N = 3 (3.0 ≦ Ld < 4.0). If the conditions of the general inclination angle α ≧ 10 and the local inclination angles β1 to β4 ≧ 0 are satisfied, it is considered that there is almost no possibility of microfubble-sized bubbles being generated by entrapment of air layers, even if each of the four divided sections of the first side surface has an arbitrary shape.

[0081] In this way, when the thickness of element pattern 1 satisfies formula (1), if the conditions of formulas (2) and (4) are satisfied in the divided sections N+1 scaled to a size of approximately 1 μm according to formula (3) according to the thickness, even if each of the divided sections N+1 of the first side surface has an arbitrary shape, there will be no depressions into which bubbles larger than microfables can enter, making it possible to suppress the generation of bubbles. Therefore, the growth of a large number of bubbles with diameters of 100 μm or more can also be efficiently suppressed.

[0082] Examples and comparative examples will be described. The specifications of the configuration of the reflect array used are shown in Table 1. Also, Fig. 8 is a graph showing the reflection angle and reflection intensity (bistatic RCS) in the examples and comparative examples. [Table 1]

[0083] Example 1 The reflect array was constructed by laminating an additional functional layer with a thickness of 0.098 mm on the element pattern side of the basic configuration, which used 0.018 mm (L = 18 μm) copper for the element pattern and ground layer, and a 0.764 mm thick glass / fluororesin composite material for the dielectric. However, the conductivity of copper was set to 5.8 x 10^7 siemens / m, the real part of the relative dielectric constant of the dielectric was set to 2.6, tan δ was set to 0.0025, and the real part of the relative dielectric constant of the additional functional layer was set to 2.70, tan δ was set to 0.0060.

[0084] The operating frequency was set to 27.2 GHz, the target reflection characteristics were set to θi = 33°, θr = 0°, and the size Sx of the reflection control area in the x-axis direction was determined to be 20.238 mm using equation (5). The reflection control area was divided into three parts, and the size of the unit cell in the x-axis and y-axis directions was 6.746 mm. The shape of the element was a cross patch in which two square patches were perpendicular to each other in the xy plane. Here, the element lengths of each element pattern in the reflection control area were the same, and only the element widths were different. The reflect array has a total of 81 unit cells arranged in a 9 x 9 array in the x-axis and y-axis directions, and its size in the xy plane is 60.714 mm square.

[0085] The general inclination angle α of all element patterns is 10°, and the side shape is a uniform plane (point inclination angles β1 to β19 = 10°) (β1 to β19 are sometimes collectively referred to as simply β), and an air layer of 0.1 mm is inserted on the side of the element pattern in four unit cells. The reflection characteristics when polarized waves parallel to the y-axis are irradiated onto the reflect array at θix = 33° and θiy = 0° were analyzed using HFSS.

[0086] The reflection characteristics of the reflectarray in the xz plane are shown in Table 1. The radio wave incident at θi=33° was reflected in the desired direction of θr=0°, and the RCS was 0.22 dBsm. The relationship between the reflection angle and the reflection intensity is shown in Figure 5.

[0087] Example 2 In a reflectarray similar to that in Example 1, the general inclination angle α of all element patterns was 15°, and the side shape was a uniform plane (point inclination angles β1 to β19 = 15°), and an air layer of 0.1 mm was inserted on the side of the element pattern in two unit cells. The reflection characteristics when the reflectarray was irradiated with polarized waves parallel to the y-axis at θix = 33° and θiy = 0° were analyzed using HFSS.

[0088] The reflection characteristics of the reflectarray in the xz plane are shown in Table 1. The radio wave incident at θi=33° was reflected in the desired direction of θr=0°, and the RCS was 0.23dBsm. The relationship between the reflection angle and the reflection intensity is shown in Figure 5.

[0089] Example 3 In a reflectarray similar to that in Example 1, the general inclination angle α of all element patterns was 30°, and the side shape was a uniform plane (point inclination angles β1 to β19 = 30°), and an air layer of 0.1 mm was inserted on the side of the element pattern in 0 unit cells (no air bubbles). The reflection characteristics when the reflectarray was irradiated with polarized waves parallel to the y-axis at θix = 33° and θiy = 0° were analyzed using HFSS.

[0090] The reflection characteristics of the reflectarray in the xz plane are shown in Table 1. The radio wave incident at θi=33° was reflected in the desired direction of θr=0°, and the RCS was 0.25 dBsm. The relationship between the reflection angle and the reflection intensity is shown in Figure 5.

[0091] Comparative Example 1 In a reflectarray similar to that in Example 1, the general inclination angle α of all element patterns was 0°, the side shape was a uniform plane, and an air layer of 0.1 mm was inserted on the side of the element pattern in 27 unit cells. The reflection characteristics when the reflectarray was irradiated with polarized waves parallel to the y-axis at θix=33° and θiy=0° were analyzed using HFSS.

[0092] The reflection characteristics of the reflectarray in the xz plane are shown in Table 1. The radio wave incident at θi=33° was reflected in the desired direction of θr=0°, and the RCS was -1.2dBsm. The relationship between the reflection angle and the reflection intensity is shown in Figure 5.

[0093] Comparative Example 2 In a reflectarray similar to that in Example 1, the general inclination angle α of all element patterns was 0°, the side shape was a uniform plane, and an air layer of 0.1 mm was inserted on the side of the element pattern in 27 unit cells. The reflection characteristics when the reflectarray was irradiated with polarized waves parallel to the y-axis at θix=33° and θiy=0° were analyzed using HFSS.

[0094] The reflection characteristics of the reflectarray in the xz plane are shown in Table 1. The radio wave incident at θi=33° was reflected in the desired direction of θr=0°, and the RCS was -1.18dBsm. The relationship between the reflection angle and the reflection intensity is shown in Figure 5.

[0095] Comparative Example 3 In a reflectarray similar to that in Example 1, the general inclination angle α of all element patterns was 0°, the side shape was a uniform plane, and an air layer of 0.1 mm was inserted on the side of the element pattern in eight unit cells. The reflection characteristics when the reflectarray was irradiated with polarized waves parallel to the y-axis at θix=33° and θiy=0° were analyzed using HFSS.

[0096] The reflection characteristics of the reflectarray in the xz plane are shown in Table 1. The radio wave incident at θi=33° was reflected in the desired direction of θr=0°, and the RCS was -1.06dBsm. The relationship between the reflection angle and the reflection intensity is shown in Figure 5.

[0097] In Example 1, four bubbles were caught in the element pattern at an inclination angle of α / β=10°, in Example 2, two bubbles were caught in the element pattern at an inclination angle of α / β=15°, and in Example 3, zero bubbles were caught in the element pattern at an inclination angle of α / β=30°, demonstrating that good reflection intensity and suppression of unwanted reflection are possible. On the other hand, in Comparative Examples 1 to 3, the inclination angle α / β=0° was all set, and unwanted reflection to the back side of the reflector was observed with 27 bubbles caught in the element pattern in Comparative Example 1, 27 bubbles caught in the element pattern in Comparative Example 2, and eight bubbles caught in the element pattern in Comparative Example 3. When the number of bubbles caught in the element pattern exceeds a certain number (four bubbles), the unwanted reflection to the back side of the reflector increases, and the RCS in the desired reflection angle θr=0° direction decreases. It is believed that by providing an inclination angle on the side of the element pattern such that the general inclination angle α or the point inclination angle βi is displaced outward, it is possible to reduce the intrusion of air bubbles between the additional functional layer and the side of the element pattern, thereby realizing the suppression of unwanted reflections.

[0098] Although the embodiment of the present invention has been described above, the present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the gist of the present invention. [Explanation of symbols]

[0099] 1...element pattern, 2...dielectric layer, 3...ground layer, 4...additional function layer, 5...side surface of element pattern

Claims

1. The device includes a ground layer, a dielectric layer, and an element pattern. Further, an additional functional layer is provided which covers at least the upper surface and the side surface of the element pattern, The thickness L (μm) of the element pattern satisfies the following formula (1), 1.0≦L (1) the side surface has a first end connected to a lower surface of the element pattern and a second end connected to the upper surface; An angle α (°) between a straight line connecting the first end and the second end in a cross section and a perpendicular line from the second end to the lower surface satisfies the following formula (2), α≧１０ （２） When the side surface is divided at N points at equal intervals in the thickness direction, using N calculated from the following formula (3), and the division point closest to the second end is defined as a first point, and the division point closest to the first end is defined as an Nth point, an angle βi between a line connecting the (i-1)th point and the i-th point in a cross section and a perpendicular line from the second end to the lower surface satisfies the following formula (4) for any i (i = 1 to N + 1), N = [L] (3) (N is an even number) β ≧ 0 (4) (i is an integer satisfying 1≦i≦N+1, where the 0th point corresponds to the second end, and the N+1th point corresponds to the first end.) Furthermore, each of the divided sections has an arbitrary shape (excluding a shape in which a straight line connecting the first end and a midpoint between the first end and the second end, and a straight line connecting the second end and the midpoint each have an angle of 0° or more with respect to a perpendicular line from the second end to the lower surface). The reflect array is characterized by:

2. The reflect array according to claim 1 , further comprising an adhesion improving layer.

3. The reflect array according to claim 1 , wherein the element pattern has a cross patch shape.

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