Electromagnetic wave reflecting sheet and reflectarray for deployable antenna

Abstract

[Problem] The present invention addresses the problem of providing a lightweight and flexible electromagnetic wave reflecting sheet that has folding parts that are highly resistant to deterioration even when repeatedly folded and unfolded, that can be stowed compactly, and that is suitable for use in a deployable reflectarray antenna to be mounted on an artificial satellite. [Solution] In this electromagnetic wave reflecting sheet, a first layer consisting of a fiber base material having a metal pattern formed directly on at least one surface thereof and a second layer consisting of a fiber base material having a metal film formed directly over at least one entire surface thereof are arranged such that the first layer and the second layer face one another, and, furthermore, a reflecting element row is formed from elements comprising the metal pattern in the first layer, and the second layer is used as a ground layer, thereby forming a reflectarray for a deployable antenna.

Description

Electromagnetic wave reflective sheets and reflect arrays for deployable antennas

[0001] This invention relates to an electromagnetic wave reflective sheet that can be used in applications such as deployable reflect array antennas for artificial satellites. More specifically, this invention relates to an electromagnetic wave reflective sheet that is lightweight, does not deteriorate at the folded portion, and leaves minimal creases when deployed.

[0002] Due to the miniaturization and weight reduction of equipment used in artificial satellites, and the decrease in satellite launch costs, the practical application of small artificial satellites has become relatively easy. As a result, it is becoming possible to construct "satellite constellations" in which a large number of small non-geostationary satellites launched into medium and low Earth orbits are coordinated and operated as an integrated system.

[0003] Small satellite constellations are a promising platform for providing new applications such as wireless communication and Earth observation, but high-gain antennas are necessary to improve the data rate and resolution of wireless communication. Furthermore, due to the volume and mass limitations at launch, antennas for satellites must be lightweight and have efficient storage capabilities, as they are deployable planar antennas that can be folded and stored on the ground and deployed in orbit. In addition, it is necessary that the folded parts do not deteriorate physically and that the antenna performance does not deteriorate as a result of repeated folding and unfolding.

[0004] In recent years, reflect array antennas, which can emit (reflect) electromagnetic waves of a specific frequency at a specific angle, have been developed for use on artificial satellites. A reflect array is constructed by arranging multiple patch-type resonant elements on the surface of an electromagnetic wave reflector.

[0005] Reflective arrays typically require rigid substrates and support structures to maintain their planar shape. Therefore, it is difficult to increase the size of the openings within a limited volume and mass, resulting in a lack of ease in simultaneously improving lightness and storage efficiency.

[0006] As electromagnetic wave reflecting components for reflect arrays, various electromagnetic wave reflectors have been proposed to solve the problem of radio wave dead zones that have arisen with the practical application of various wireless devices compatible with millimeter waves.

[0007] For example, Patent Document 1 discloses a metasurface reflector comprising a dielectric substrate, a metal ground layer provided on the bottom surface of the dielectric substrate, and a plurality of supercells having cross-shaped metal resonators formed on the dielectric substrate.

[0008] Furthermore, Patent Document 2 discloses an electromagnetic wave reflector that includes a dielectric layer and a reflection control region consisting of a plurality of element patterns, characterized in that the cross-sectional shape of the element patterns includes rounded corners and rounded edges.

[0009] All of these designs utilize a metal ground layer, resulting in insufficient lightness. Furthermore, they fail to consider crucial storage efficiency, flexibility, and resistance to deterioration of the folded portion, which are essential for deployable antennas that repeatedly fold and unfold.

[0010] As a compact and sizable reflect array antenna, a deployable reflect array antenna using a two-layer woven fabric membrane has been proposed (Non-Patent Documents 1 and 2).

[0011] Japanese Patent Publication No. 2021-048465, Japanese Patent Publication No. 7492072

[0012] T. Tomura, et al., “Two-layer pop-up origami deployable membrane reflectarray antenna stowed in 1U CubeSat,” in Proc. 36th Annual AIAA / USU Conference on Small Satellites, 2022T. Tomura, et al., “Space demonstration of two-layer pop-up origami deployable membrane reflectarray antenna by 3U CubeSat Origami Sat-2,” in Proc. 37th Annual AIAA / USU Conference on Small Satellites, 2023

[0013] The present invention aims to provide an electromagnetic wave reflective sheet for a reflect array antenna that can be used in a deployable antenna mounted on a satellite, which suppresses deterioration of the folded portion, is lightweight and flexible, and can be compactly stored.

[0014] As a result of diligent research, the inventors have found that an electromagnetic wave reflective sheet made of a flexible woven fabric, which is useful for reflect arrays having at least a reflective element pattern layer and a ground layer, can solve the above problems, and have completed the present invention.

[0015] In other words, the present invention relates to the following electromagnetic wave reflective sheets and reflect arrays: (1) An electromagnetic wave reflective sheet comprising at least a first layer made of a fibrous substrate on which a metal pattern is directly formed on at least one side, and a second layer made of a fibrous substrate disposed opposite to the first layer and on which a metal film is directly formed on which at least one entire side.

[0016] (2) The electromagnetic wave reflective sheet according to (1), wherein a gap layer having a predetermined distance is provided between the first layer and the second layer. (3) The electromagnetic wave reflective sheet according to (2), wherein spacers are partially provided inside the gap layer. (4) The electromagnetic wave reflective sheet according to (1), wherein the metal pattern forms a reflector element for a reflect array composed of rectangular patches with cross slots.

[0017] (5) A reflect array for a deployable antenna, comprising at least a reflect element layer made of a fiber substrate on which a plurality of reflect elements for a reflect array, each having a metal pattern, is directly formed on at least one side, and a ground layer made of a fiber substrate disposed opposite the reflect element layer and on which a metal film is directly formed on at least one entire side.

[0018] (6) The reflect array for a deployable antenna according to (5), wherein the reflecting elements are composed of rectangular patches having cross slots. (7) The reflect array for a deployable antenna according to (5), wherein a gap layer having a predetermined distance is provided between the reflecting element layer and the ground layer. (8) The reflect array for a deployable antenna according to (7), wherein spacers are partially provided inside the gap layer.

[0019] The electromagnetic wave reflective sheet of the present invention exhibits excellent resistance to deterioration of the folded portion even after repeated folding and unfolding, and is also lightweight and highly flexible. Therefore, it can be suitably used in reflect array antennas that combine lightweight design and high storage efficiency, as they can be stored in a folded state and unfolded to expand the transmitting and receiving surface when in use. It is particularly useful for deployable reflect array antennas mounted on artificial satellites, but is not limited to this and can be used as a reflector for various reflect array antennas, such as for improving the radio wave environment in coverage holes.

[0020] This is a schematic diagram showing a cross-section of an example of the electromagnetic wave reflective sheet of the present invention. This is a schematic diagram showing an example of a unit cell in which reflective elements used in the reflect array of the present invention are arranged. This is a photograph showing an example of the first layer of the electromagnetic wave reflective sheet of the present invention. This is a photograph showing an example of the second layer of the electromagnetic wave reflective sheet of the present invention.

[0021] I. Electromagnetic Wave Reflecting Sheet The electromagnetic wave reflecting sheet of the present invention comprises at least a first layer made of a fiber substrate on which a metal pattern is directly formed on at least one side, and a second layer made of a fiber substrate arranged opposite to the first layer and on which a metal film is directly formed on at least one entire side. Preferably, a gap layer having a predetermined distance is provided between the first layer and the second layer. More preferably, a spacer is partially arranged inside the gap layer.

[0022] Figure 1 schematically shows a cross-section of an example of the electromagnetic wave reflective sheet of the present invention. Figure 1(a) shows the folded state, and Figure 1(b) shows the unfolded state. In Figure 1, 1 is the electromagnetic wave reflective sheet, A is the first layer, B is the second layer, C is the void layer, 2 is the metal pattern, 3 is the fibrous substrate of the first layer, 4 is the metal coating of the second layer, 5 is the fibrous substrate of the second layer, 6 is the spacer, 7 is the folding direction, and 8 is the unfolding direction. However, this is one embodiment of the present invention, and the present invention is not limited thereto.

[0023] 1. The first layer of the electromagnetic wave reflecting sheet of the present invention includes a first layer in its laminated structure, which is made of a fibrous substrate on which a metal pattern is directly formed on at least one side.

[0024] (1) Fiber base material The fiber base material is not particularly limited, but fabrics made of fiber materials are preferably used. Specific fiber materials include, but are not limited to, natural fibers such as cotton, linen, wool, and silk; regenerated fibers such as rayon and cupro; semi-synthetic fibers such as acetate and triacetate; polyamide (nylon 6, nylon 66, etc.) fibers; polyester (polyethylene terephthalate, polytrimethylene terephthalate, etc.) fibers; synthetic fibers such as polyurethane, polyacrylic, aramid, and poly(p-phenylenebenzobisoxazole); and inorganic fibers such as glass fibers, liquid crystal polyester (LCP) fibers, basalt fibers, and carbon fibers. From the viewpoint of versatility, flexibility, and strength, synthetic fibers are preferred as the fiber material. Among these, polyimide fibers are particularly preferred for aerospace applications, and polyester fibers are particularly preferred for other general applications.

[0025] The thickness of the fibrous base material in the first layer is not particularly limited, but is preferably 1 to 5000 μm, more preferably 10 to 1000 μm, and even more preferably 20 to 500 μm. When the thickness of the fibrous base material of the first layer is within this range, the storage efficiency when folded tends to be higher.

[0026] The aforementioned fibrous base material may be any of the following: woven fabric, knitted fabric, nonwoven fabric, etc., but woven fabric is preferred. The shape of the yarn constituting the base material is not particularly limited.

[0027] (2) Metal pattern A metal pattern is directly formed on the surface of the fiber substrate and constitutes the first layer. The metal pattern is formed on at least one side of the fiber substrate, and may be formed on only one side or on both sides.

[0028] The metal pattern is formed directly on the surface of the first layer of fiber substrate without an adhesive layer or the like between it and the first layer of fiber substrate. A method for forming the metal pattern on the surface of the fiber substrate without using an adhesive will be described later. By not using an adhesive, the electromagnetic wave reflective sheet can be made even lighter.

[0029] When using a relatively thick or low-permeability fabric as the fibrous base material, the metal pattern may be formed on only one side of the fibrous base material. On the other hand, when the metal pattern is formed on both sides of the fibrous base material, degradation of the fibrous base material due to radiation or atomic oxygen can be suppressed, resulting in a highly durable electromagnetic wave reflective sheet.

[0030] Furthermore, the metal pattern may be formed not only on the surface of the fibrous substrate but also to penetrate in the thickness direction of the fibrous substrate. The metal pattern may also penetrate from the front surface to the back surface of the fibrous substrate.

[0031] The aforementioned metal pattern is composed of a material containing a metal. The metal contained in the material constituting the metal pattern is not particularly limited, but it can be one or more metals selected from gold, silver, copper, nickel, tin, iron, aluminum, platinum, palladium, rhodium, ruthenium, iridium, osmium, indium, rubidium, and cobalt, or a mixture or alloy of such metals. Of these, gold, silver, copper, nickel, and tin are preferred. Among these, copper is particularly preferred due to its high conductivity and cost-effectiveness.

[0032] The metal pattern can have good conductivity, with a surface resistance of preferably 500 mΩ / □ or less, and more preferably 200 mΩ / □ or less.

[0033] The amount of metal impregnated per unit area of ​​the aforementioned metal pattern (μg / mm²) ２ The concentration is not particularly limited, but is preferably 3.0 μg / mm³. ２ The above is a more preferable 5.0 μg / mm ２ That concludes the explanation. There is no particular lower limit to the amount of metal added, but it is preferably 500 μg / mm². ２ More preferably, 100 μg / mm ２ The following applies: If the amount of metal added to the metal pattern is within this range, it tends to suppress cracking of the metal pattern when folded.

[0034] The form of the metal contained in the metal pattern is not particularly limited. In order to form a higher-definition pattern, it is preferable that the metal contains metal particles, and more preferably, it contains metal particles with an average particle diameter of 1 to 200 nm.

[0035] A plating treatment may be performed using these metal particles as nuclei to deposit the same kind or different kinds of metals. According to this, the amount of metal can be further increased to enhance conductivity.

[0036] The average particle diameter of the metal particles refers to the primary particle diameter without considering aggregation, and can be represented by the arithmetic mean value of the sphere-equivalent particle diameters (the diameters when each particle is converted into a sphere with the same volume) of 100 or more particles actually measured using any method known in the art, for example, a transmission electron microscope (TEM). Specifically, the "average particle diameter of the metal particles" in the present invention means the arithmetic mean value of the sphere-equivalent particle diameters of 100 metal particles actually measured by a transmission electron microscope.

[0037] (3) Method for forming the metal pattern The metal pattern can be made into a desired shape as needed. The method for directly forming a metal pattern with a desired shape on a fiber substrate is not particularly limited, and examples include a method of forming by printing using an ink composition containing a metal, a method of forming by a plating treatment such as electroplating or electroless plating, and the like.

[0038] <Printing method> The metal pattern can be formed using a printing method. Examples of the printing method include screen printing, gravure printing, inkjet printing, xerography, stamping, flexographic printing, offset printing, painting, airbrushing, etc. In any of these methods, an ink composition containing a metal is used. Among these methods, a printing method by an inkjet method is particularly preferably employed.

[0039] The ink composition containing the metal is preferably an ink composition containing the above-described metal particles. In particular, it is preferable to contain metal particles having an average particle diameter of 1 to 200 nm. When an ink composition containing metal particles having such an average particle diameter is applied to the surface of a fiber substrate (fabric), not only the gaps between the tissues of the fiber substrate but also the gaps between the yarns constituting the fiber substrate, that is, the gaps between single fibers, the metal particles penetrate. As a result, the uniformity of the formed metal pattern is improved, and the occurrence of metal dropout is less likely to occur.

[0040] Examples of the ink composition include a dispersion of metal particles. A dispersion of metal particles means a solution in which metal particles are appropriately dispersed in a solvent. Since metal particles in a solvent tend to aggregate, aggregation can be suppressed and the dispersion of metal particles can be stabilized by adding a dispersant to coat the surface of the metal particles.

[0041] The solvent is not particularly limited, and examples thereof include water, alcohol solvents (monoalcohol solvents, diol solvents, polyhydric alcohol solvents, etc.), hydrocarbon solvents, ketone solvents, ester solvents, ether solvents, glyme solvents, halogen solvents, and the like. These solvents may be used alone or in combination of two or more.

[0042] As the dispersant, any known one can be appropriately selected and used. Examples thereof include, but are not limited to, amine compounds and thiol compounds. The amine compound is preferably an aliphatic amine compound, and more preferably an aliphatic amine compound having 4 to 10 carbon atoms in the alkyl moiety. Examples of the aliphatic amine compound include alkylamines such as octylamine, dodecylamine, and hexadecylamine, and alkenylamines such as oleylamine. The thiol compound is preferably an aliphatic thiol compound. Examples of the aliphatic thiol compound include alkylthiols such as hexanethiol, pentanedithiol, decanethiol, and dodecanethiol. The dispersant may be used alone or in combination of two or more. By using a dispersant having a small number of carbon atoms, it can be desorbed or decomposed under easy conditions.

[0043] The proportion of metal particles in the ink composition is preferably 0.1 to 70% by mass, more preferably 1 to 60% by mass, and even more preferably 10 to 50% by mass, based on the total mass of the ink composition.

[0044] In addition to metal particles, solvents, and dispersants, the ink composition may also contain known additives for the purpose of adjusting its printability. Examples of additives include thickeners and stabilizers.

[0045] <Plating Method> The metal pattern can be formed by a plating method (metal plating treatment). Examples of metal plating treatments include electroplating and electroless plating, and either is acceptable. Preferably, electroless plating is used. The metal used in the plating treatment can be selected from the same group of metals as those contained in the ink composition. Among these, gold, silver, copper, nickel, and tin are preferred. Copper is more preferably used.

[0046] The metal plating process can employ conventionally known methods, and there are no particular limitations on the chemicals, equipment, or conditions used. Optimal conditions can be selected and implemented depending on the type and amount of metal to be deposited. The materials used for pattern formation by the plating process, such as resists, dry films, resist stripping solutions, and etching solutions, as well as the processing conditions, are not particularly limited; any known materials used in normal pattern formation can be used under any processing conditions.

[0047] <Printing Method and Plating Method> In this invention, a plated metal film may be formed on a metal pattern formed by the printing method using the ink composition described above, by further applying the above-described plating method. This makes it possible to further increase the amount of metal imparted to the metal pattern, thereby improving conductivity and antenna performance. In addition, the adhesion strength of the metal pattern to the fiber substrate is increased, making it less likely for the metal pattern to detach from the fiber substrate. In this invention, when a plated metal film is formed on a metal pattern formed by the printing method in this way, the metal pattern formed by the printing method and the plated metal film together may be referred to as the "metal pattern".

[0048] The metal constituting the plated metal film formed on the metal pattern by the printing method may be the same type as the metal particles contained in the ink composition or a different type. Preferably, the metal particles contained in the ink composition and the metal used in the plating process are of the same type. More preferably, copper is used for both the metal particles contained in the ink composition and the metal used in the plating process.

[0049] Particularly preferable is forming a metal pattern using an inkjet method with an ink composition containing copper particles, and then performing a copper plating treatment to form a metal pattern directly fixed to the fiber substrate. This results in a first layer having a metal pattern with increased metal content and improved adhesion to the fiber substrate.

[0050] When performing metal plating on a metal pattern created by printing, conventionally known methods can be used, and there are no particular limitations on the chemicals, equipment, or conditions used. Optimal conditions can be selected and implemented depending on the type and amount of metal to be deposited.

[0051] For example, when performing electroless plating, a metal pattern can be printed on a fibrous substrate using an ink composition, the solvent of the ink composition can be removed by heating or drying, and then the fibrous substrate can be immersed in an electroless plating solution to perform electroless plating.

[0052] In the present invention, when a plating metal film is formed on a metal pattern by a printing method as needed, the amount of metal in the obtained metal pattern is the sum (hereinafter, "total metal amount") of the metal imparted amount derived from an ink composition or the like containing metal imparted by a printing method such as inkjet printing and the metal imparted amount derived from the plating metal film deposited by the plating treatment.

[0053] The total metal amount of the metal pattern in the first layer is preferably 3.0 μg / mm ２ or more, more preferably 5.0 μg / mm ２ or more. The upper limit is not particularly limited, but is preferably 500 μg / mm ２ or less, more preferably 100 μg / mm ２ or less.

[0054] 2. Second layer The electromagnetic wave reflection sheet of the present invention includes a second layer having a metal film directly formed on at least one entire surface in its laminated structure. The metal film may be formed on only one side of the fiber base material of the second layer or on both sides. When formed on both sides, deterioration of the fiber base material due to radiation, atomic oxygen, etc. is suppressed, and a more durable electromagnetic wave reflection sheet can be obtained.

[0055] (1) Fiber base material The fiber base material is not particularly limited, and any material that can be used for the fiber base material of the first layer can be used, and a fabric made of such a fiber material is preferably used. From the viewpoints of versatility, flexibility, and strength, the fiber material is preferably a synthetic fiber. Among them, polyimide fiber is particularly preferable for aerospace applications, and polyester fiber is particularly preferable for other general applications.

[0056] The thickness of the fiber base material in the second layer is not particularly limited, but is preferably 10 to 5000 μm, more preferably 10 to 1000 μm. When the thickness of the fiber base material of the second layer is within this range, the storage property when folded tends to be high.

[0057] The fiber base material may be any of a woven fabric, a knitted fabric, a non-woven fabric, etc., but is preferably a woven fabric. The shape of the yarns constituting the base material is not particularly limited either.

[0058] (2) The metal coating of the second layer is formed directly on the entire surface of the fiber substrate without providing an adhesive layer or the like between it and the second layer of the fiber substrate. It may be formed on one side of the fiber substrate or on both sides. Furthermore, the metal coating is formed uniformly on the entire surface of the second layer. By forming the metal coating directly on the fiber substrate without using an adhesive in the second layer, the electromagnetic wave reflective sheet can be made even lighter.

[0059] For a method of directly forming a metal coating on the surface of a fiber substrate without using an adhesive, the same method as described above for directly forming a metal pattern on the fiber substrate in the first layer can be used.

[0060] When using a relatively thick or poorly permeable fabric as the fibrous base material, the metal coating may be formed on only one side of the fibrous base material. On the other hand, when the metal coating is formed on both sides of the fibrous base material, degradation of the fibrous base material due to radiation and atomic oxygen can be suppressed, resulting in a highly durable electromagnetic wave reflective sheet.

[0061] Furthermore, the metal coating may be formed not only on the surface of the fibrous substrate but also to penetrate in the thickness direction of the fibrous substrate. The metal coating may also penetrate from the front surface to the back surface of the fibrous substrate.

[0062] (3) Method for forming a metal film Any known method can be used to form the metal film. Examples include a method of forming the film by printing using an ink composition, dry film formation methods such as vacuum deposition and sputtering, and wet film formation methods such as electroless plating and electroplating. In addition, a combination of these methods may be used to form the metal film.

[0063] Preferably, the method may involve printing a metal film onto a fibrous substrate of the second layer using an ink composition, similar to the method for forming a metal pattern in the first layer; forming a metal film by a plating method (metal plating treatment); or a combination of these methods.

[0064] When printing using the ink composition, the ink composition is applied to the entire surface of the fibrous substrate in a solid form. The composition and other conditions of the ink composition are the same as those used in the method for forming the metal pattern in the first layer.

[0065] Furthermore, when using a plating method, examples of metal plating treatments include electroplating and electroless plating, and either is acceptable. Preferably, electroless plating is used. Examples of metals used in the plating treatment include gold, silver, copper, nickel, and tin. Preferably, copper is used.

[0066] Metal plating can be performed using conventionally known methods, and there are no particular limitations on the chemicals, equipment, or conditions used. Optimal conditions can be selected and implemented depending on the type and amount of metal to be deposited.

[0067] In this invention, a plated metal film may be formed on a metal film formed by the printing method using the ink composition described above, by further applying a metal plating treatment using the plating method described above. This makes it possible to further increase the amount of metal imparted to the metal film, thereby improving conductivity and antenna performance, as well as suppressing deterioration of the fiber substrate and increasing durability. In addition, the metal film can be made less likely to detach from the fiber substrate. In this invention, when a plated metal film is formed on a metal film formed by the printing method in this way, the metal film formed by the printing method and the plated metal film may be collectively referred to as the "metal film".

[0068] Particularly preferable is to form a metal film on the entire surface of the fiber substrate using an inkjet method with an ink composition containing copper particles, and then perform a copper plating treatment to form a metal film that is directly fixed to the fiber substrate. This results in a second layer having a metal film with increased metal content and improved adhesion to the fiber substrate.

[0069] The metal film can have good conductivity, with a surface resistance of preferably 500 mΩ / □ or less, and more preferably 200 mΩ / □ or less.

[0070] The amount of metal imparted per unit area of ​​the aforementioned metal film (total amount of metal; μg / mm²) ２The concentration is not particularly limited, but is preferably 3.0 μg / mm³. ２ The above is a more preferable 5.0 μg / mm ２ That concludes the explanation. There is no particular lower limit to the amount of metal added, but it is preferably 100 μg / mm². ２ More preferably, 50 μg / mm² ２ The following applies: If the amount of metal impregnated by the metal coating is within this range, it tends to suppress cracking of the metal pattern when folded.

[0071] 3. Structure of the electromagnetic wave reflective sheet The electromagnetic wave reflective sheet of the present invention is a laminated structure comprising at least the first layer and the second layer described above, wherein the surface of the first layer opposite to the surface on which the metal pattern is formed and the surface of the second layer on which the metal film is formed are arranged to face each other (see Figure 1).

[0072] (1) Void layer In the present invention, a void layer (air layer) having a predetermined gap is preferably provided between the first layer and the second layer. The specific dimensions of the gap can be appropriately determined by the frequency to be reflected, etc., and are not particularly limited, but it is most preferable to make it 1 / 10 of the wavelength to be reflected. For example, if the frequency to be reflected is 6 GHz, the wavelength is about 50 mm, so the preferred thickness of the void layer is 5.0 mm.

[0073] The lower limit of the spacing dimension is not particularly limited, but is preferably 0.5 mm or more, more preferably 1.0 mm or more. The upper limit of the spacing dimension is not particularly limited, but is preferably 50 mm or less, more preferably 30 mm or less. If the spacing is too wide, the flatness during unfolding may decrease, and if the spacing is too narrow, the first and second layers may come into contact with even slight external force.

[0074] Note that the above spacing dimensions are for when the antenna is in use (deployed). By employing the spacers described later, it is possible to achieve virtually no gaps when the antenna is folded. This allows for flexible adjustment of the spacing between the reflective elements and the ground layer when used in a deployable reflect array antenna that repeatedly folds and unfolds, while also achieving a lightweight design and high storage efficiency.

[0075] (2) Spacers Spacers may be partially provided inside the above-mentioned void layer. By providing spacers in the void layer, the void layer is held stably. That is, the first layer and the second layer can be stacked with a predetermined gap between them via spacers.

[0076] Specifically, it is desirable to partially place a material with a certain degree of hardness (rigidity) as a spacer between the first and second layers. This ensures that the spacing between the layers is reliably maintained. Such a spacer may have a bonding region with the first layer, a space-holding region, and a bonding region with the second layer, and the boundaries between the bonding region and the space-holding region of the first and second layers may bend. Having a bendable boundary allows the spacer to bend when the first and second layers are pulled from side to side, reducing the thickness of the void layer and allowing the layers to be laminated in close contact. Materials that can be used for such a spacer include paper and synthetic resin films (e.g., polyimide resin, polyester resin such as PET, polyurethane resin).

[0077] By using such spacers, a gap is maintained between the first and second layers when the antenna is deployed, and when it is retracted, the first and second layers come into close contact, reducing the thickness. This improves both lightness and storage efficiency.

[0078] The shape of the spacer is not particularly limited, but a spacer with a bendable cross-section, such as a U-shape or square shape, can be used. In the example in Figure 1, a U-shaped spacer 6 is placed between the fibrous base material 3 of the first layer A and the metal film 4 of the second layer B. When the antenna is folded (when the member is pulled in the direction of arrow 7 in Figure 1(a)), the spacer bends, bringing the first and second layers into close contact and reducing the overall thickness of the member. When the antenna is unfolded (when the member is pulled in the direction of arrow 8 in Figure 1(a)), the spacer rises, creating a gap between the first and second layers (Figure 1(b). Note that the present invention is not limited to these examples, including the direction of pulling.

[0079] The thickness of the spacer is not particularly limited, but is preferably around 10 to 200 μm. If it is too thick, the gap between the first and second layers may not be tightly sealed when the spacer is bent, which may reduce storage efficiency. If it is too thin, the strength may decrease, and stability during deployment may be reduced. In the example in Figure 1, it is U-shaped, but the cross-sectional shape of the spacer is not particularly limited as long as it can achieve the above objectives.

[0080] (3) Other Optional Layers The electromagnetic wave reflective sheet of the present invention may have optional layers provided on the surface of the metal pattern of the first layer as needed for purposes such as improving strength, surface protection, preventing deterioration, and maintaining weather resistance. Examples of such optional layers include a surface resin layer. The resin constituting the surface resin layer is not particularly limited, but examples include polyurethane resin, polyester resin, silicone resin, epoxy resin, acrylic resin, and polyimide resin. Of these, polyurethane resin or epoxy resin is preferred from the viewpoint of rigidity characteristics and durability characteristics, and polyurethane resin is particularly preferred. The resin may be compounded with curing agents, flame retardants, corrosion inhibitors, etc., as needed.

[0081] The thickness of the electromagnetic wave reflective sheet of the present invention is not particularly limited, but is preferably 0.5 to 50 mm, more preferably 0.5 to 10 mm. The size of the electromagnetic wave reflective sheet of the present invention can be appropriately set depending on the application. For example, in the case of a deployable reflect array antenna mounted on an artificial satellite, 10 m ２ A size of approximately 500 x 500 mm is expected. On the other hand, for general applications such as coverage hole countermeasures, the size varies depending on the application, but for example, for coverage hole countermeasures, a size of approximately 500 x 500 mm is expected.

[0082] II. Reflective Array for Deployable Antenna The reflective array of the present invention includes at least a reflective element layer having a plurality of reflective elements made of a fiber substrate and a metal pattern formed on the surface of the fiber substrate, and a ground layer having a metal film formed on at least one entire surface of the fiber substrate, wherein the surface of the reflective element layer opposite to the surface on which the reflective elements are formed and the surface of the ground layer on which the metal film is formed are arranged to face each other.

[0083] The deployable reflect array for antennas of the present invention exhibits excellent resistance to deterioration of the folded portion even after repeated folding and unfolding, and is lightweight and highly flexible, making it compact for storage and useful for deployable reflect array antennas mounted on artificial satellites.

[0084] The first layer of the electromagnetic wave reflective sheet of the present invention described above corresponds to the reflective element layer in the reflect array described above, and the second layer corresponds to the ground layer. Figure 2 schematically shows a unit cell in which one reflective element is arranged. The reflect array of the present invention is constructed by arranging a plurality of such unit cells at regular intervals. Figure 3 shows a photograph of a fabric in which a plurality of reflective elements are arranged as an example of the first layer of the present invention. Figure 4 shows a photograph of a fabric in which a metal film is formed as an example of the second layer of the present invention.

[0085] <Reflective Element Layer> The metal pattern formed in the first layer of the electromagnetic wave reflecting sheet can be an arrangement of reflective elements (element pattern) that can constitute a desired reflect array. Multiple reflective elements are arranged on the surface of a reflect array that reflects electromagnetic waves of a specific frequency incident from a predetermined direction in a desired direction. By changing the dimensions, shape, and arrangement of the reflective elements, the resonant frequency of each reflective element can be changed, thereby controlling the reflection phase of the electromagnetic wave, and thereby controlling the incident direction and reflection direction of the electromagnetic wave.

[0086] In the present invention, a desired reflect array can be formed by patterning such multiple reflective element arrays on a fibrous substrate using a conductive material containing metal according to a predetermined program.

[0087] Figure 2 schematically shows an example of a unit cell in which one reflective element is placed. The reflective element can be made up of a rectangular patch 9 with cross slots 10 as shown in Figure 2, but the shape of the reflective element is not limited to this. In this example, the reflective element is formed on a fibrous substrate 11.

[0088] The reflect array of the present invention is constructed by arranging multiple such unit cells at regular intervals. The preferred element spacing is basically to be less than one wavelength of the wavelength to be reflected, preferably about 0.4 to 0.9 wavelengths. Multiple reflecting elements of different sizes can be repeatedly arranged according to the desired antenna performance. The reflection phase can be controlled by the length of the patch and the length of the cross slot. In the present invention, by forming the reflecting elements on a flexible fiber substrate by a metal pattern forming method, a reflect array that is bendable and has excellent lightness and flexibility can be made.

[0089] <Ground Layer> The ground layer (12 in Figure 2) is provided to reflect electromagnetic waves that reach the reflect array. In this invention, by using a metal film formed on a fiber substrate as the ground layer, a reflect array that is bendable and has excellent lightness and flexibility can be made. The metal film is formed on at least the side of the fiber substrate to which the electromagnetic waves are incident. In Figure 2, a void layer 13 is provided between the fiber substrate 11 and the ground layer 12.

[0090] <Reflect Array> Figures 3 and 4 show photographs of an example of the reflect array of the present invention. Figure 3 shows the first layer, i.e., a fabric, with multiple reflective elements patterned on it. Figure 4 shows the second layer, i.e., a fabric with a metal coating formed on the surface facing the first layer, and is used as the ground layer. In the present invention, a spacer having a certain degree of hardness and rigidity can be provided so that a gap is created between the first and second layers. Furthermore, by using a foldable structure as the spacer, the thickness of the reflect array itself can be reduced when folded, and a sufficient gap can be secured when unfolded.

[0091] The present invention will be described below with reference to examples, but the present invention is not limited in any way by these examples. The evaluation methods for various physical properties in these examples are as follows.

[0092] <Method for Measuring Metal Addition Amount> The amount of metal added to a metal pattern on a fiber substrate was measured as follows. First, the area to be measured for metal addition was cut out together with the fiber substrate to form a sample (approximately 30 mm x 30 mm), and its area was measured. Next, the cut-out sample was immersed in nitric acid diluted to a concentration of 50% by mass to completely dissolve the metal layer and obtain an aqueous solution in which the metal was dissolved. The obtained aqueous solution was diluted to a predetermined concentration, and the metal concentration in the aqueous solution was measured by atomic absorption spectrometry. From the area of ​​the cut-out sample and the metal concentration obtained by atomic absorption spectrometry, the amount of metal per unit area (metal addition amount; μg / mm²) was calculated. ２ ) was calculated.

[0093] [Example 1] (1) A polyester plain weave fabric was used as the fibrous base material for forming the first layer (warp: processed polyester yarn 33dtex / 36f, weft: processed polyester yarn 69dtex / 150f, weave density: warp 189 threads / 25.4 mm, weft 120 threads / 25.4 mm, thickness 90 μm). "IJ-02" (manufactured by Ishihara Chemical Co., Ltd.) was used as the ink composition containing copper particles. This ink composition contains 35-45% by mass of copper particles with an average particle diameter of 70 nm, 50-60% by mass of diethylene glycol monobutyl ether, and an activator (less than 5% by mass).

[0094] The ink composition was applied to the aforementioned fabric using an inkjet printing device (manufactured by Seiren Co., Ltd., product name "SIT-M10", number of nozzles: 3 or more) to form a metal pattern of a specified shape (Figures 2 and 3) on the fibrous substrate.

[0095] A fabric printed with a metallic pattern was immersed for 20 minutes in an electroless copper plating solution at 40°C containing 8.75 g / L of copper chloride dihydrate, 20 g / L of a complexing agent (product name "EDP-300"; manufactured by ADEKA Corporation), 40 mL / L of a 32% by mass sodium hydroxide aqueous solution, and 8.75 mL / L of a 37% by mass formaldehyde aqueous solution to perform electroless plating. Afterwards, it was rinsed with water and dried in a 65°C oven for 10 minutes.

[0096] The amount of metal imparted per unit area of ​​the metal pattern (total metal content) is 38.6 μg / mm². ２This total amount of metal is the sum of the amount of metal derived from the ink composition produced by inkjet printing and the amount of metal derived from the plated metal film formed in the plating process.

[0097] (2) Formation of the second layer Using an inkjet printing apparatus (manufactured by Seiren Co., Ltd., product name "SIT-M10", number of nozzles: 3 or more), the same ink composition used for the first layer was applied to form a solid metal coating on the fibrous substrate. The second layer was prepared under the same conditions as the materials and methods used for forming the first layer.

[0098] The amount of metal imparted per unit area of ​​the metal coating is 38.6 μg / mm². ２ This total amount of metal is the sum of the amount of metal derived from the ink composition produced by inkjet printing and the amount of metal derived from the plated metal film formed in the plating process.

[0099] (3) Formation of spacers Cardboard (pulp paper) with lengths of 162.5 mm and 135 mm, width of 19 mm, and thickness of 90 μm was prepared to be used as spacer material. Folds were made in the width direction so that each side was 7 mm, 5 mm, and 7 mm (total 19 mm) to form a U-shape (16 spacers of length 162.5 mm and 40 spacers of length 135 mm were made).

[0100] The fabricated spacers were placed parallel to each other between the first and second layers, and the two 7mm sides of the U-shape were attached to the first and second layers respectively using double-sided adhesive (manufactured by NICHIBAN Co., Ltd.), so that the first and second layers were joined via the spacers. The spacing between the parallel spacers was set so that the ends of the 7mm sides attached to the first and second layers were 5mm apart on each side.

[0101] The electromagnetic wave reflective sheet of the present invention exhibits excellent resistance to deterioration of the folded portion even after repeated folding and unfolding, and is also lightweight and highly flexible. Therefore, it can be suitably used in deployable reflector array antennas that combine lightness and high storage efficiency. It is particularly useful for deployable reflector array antennas mounted on artificial satellites, but is not limited to this and can be used as a reflector for various reflector array antennas, such as for improving the radio wave environment in coverage holes.

[0102] 1. Electromagnetic wave reflective sheet 2. Metal pattern (reflective element) 3. First layer fiber substrate 4. Second layer metal coating 5. Second layer fiber substrate 6. Spacer 7. Folding direction 8. Unfolding direction 9. Rectangular patch 10. Cross slot 11. Fiber substrate 12. Ground layer 13. Void (air layer) A. First layer B. Second layer C. Void layer

Claims

1. An electromagnetic wave reflective sheet comprising at least a first layer made of a fibrous substrate on which a metal pattern is directly formed on at least one side, and a second layer made of a fibrous substrate disposed opposite to the first layer and on which a metal film is directly formed on at least one entire side.

2. The electromagnetic wave reflecting sheet according to claim 1, wherein a gap layer having a predetermined distance is provided between the first layer and the second layer.

3. The electromagnetic wave reflecting sheet according to claim 2, wherein spacers are partially provided inside the void layer.

4. The electromagnetic wave reflective sheet according to claim 1, wherein the metal pattern forms a reflective element for a reflect array, which is composed of rectangular patches having cross slots.

5. A reflector array for a deployable antenna, comprising at least a reflector element layer made of a fiber substrate on which a plurality of reflector elements for a reflector array, each having a metal pattern, are directly formed on at least one side, and a ground layer made of a fiber substrate disposed opposite the reflector element layer and on which a metal film is directly formed on at least one entire side.

6. The reflect array for a deployable antenna according to claim 5, wherein the reflecting element is composed of a rectangular patch having cross slots.

7. The reflect array for a deployable antenna according to claim 5, wherein a gap layer having a predetermined distance is provided between the reflecting element layer and the ground layer.

8. The reflect array for a deployable antenna according to claim 7, wherein a spacer is partially provided inside the void layer.

Images