WO2021049284A1 - インピーダンス整合膜及び電波吸収体 - Google Patents

インピーダンス整合膜及び電波吸収体 Download PDF

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Publication number
WO2021049284A1
WO2021049284A1 PCT/JP2020/031879 JP2020031879W WO2021049284A1 WO 2021049284 A1 WO2021049284 A1 WO 2021049284A1 JP 2020031879 W JP2020031879 W JP 2020031879W WO 2021049284 A1 WO2021049284 A1 WO 2021049284A1
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Prior art keywords
impedance matching
film
radio wave
matching film
wave absorber
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PCT/JP2020/031879
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English (en)
French (fr)
Inventor
陽介 中西
直樹 永岡
広宣 待永
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日東電工株式会社
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Application filed by 日東電工株式会社 filed Critical 日東電工株式会社
Priority to US17/639,964 priority Critical patent/US20220330464A1/en
Priority to CN202080062220.0A priority patent/CN114342183A/zh
Priority to EP20862795.0A priority patent/EP4030880A1/en
Publication of WO2021049284A1 publication Critical patent/WO2021049284A1/ja

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Definitions

  • the present invention relates to an impedance matching film and a radio wave absorber.
  • Patent Document 1 describes a radio wave absorber in which all layers of components are transparent or translucent.
  • this radio wave absorber the entire surface conductor layer, the first dielectric layer, the linear pattern resistance layer, the second dielectric layer, and the pattern layer are laminated in this order.
  • electromagnetic waves can be satisfactorily received in the outermost pattern layer. Since the pattern layer and the second dielectric layer are in contact with each other, the electromagnetic wave received by the pattern layer leaks greatly to the second dielectric layer. Since the second dielectric layer and the linear pattern layer are in contact with each other, the electromagnetic wave leaked to the second dielectric layer can be efficiently converted into heat by the linear pattern layer.
  • a high resistance conductor having a volume resistivity of 1.0 ⁇ 10 -4 ⁇ cm or more and 1.0 ⁇ 10 -1 ⁇ cm or less forms a linear pattern resistance layer.
  • the linear pattern layer efficiently converts the electromagnetic wave leaked to the second dielectric layer into heat, and in Patent Document 1, the linear pattern layer is used for impedance. There is no mention of matching.
  • the present invention provides a novel impedance matching film having transparency.
  • the present invention Impedance matching film It has a plurality of regularly formed openings along the main surface of the impedance matching film.
  • the value obtained by dividing the specific resistance of the material forming the impedance matching film by the thickness of the impedance matching film is 1 to 300 ⁇ / ⁇ .
  • An impedance matching film is provided.
  • a reflector that reflects radio waves and A dielectric layer arranged between the impedance matching film and the reflector in the thickness direction of the impedance matching film is provided.
  • the above impedance matching film is a novel impedance matching film having transparency.
  • FIG. 1A is a plan view showing an example of an impedance matching film according to the present invention.
  • FIG. 1B is a cross-sectional view of an impedance matching film having the IB-IB line of FIG. 1A as a cutting line.
  • FIG. 2A is a plan view showing another example of the impedance matching film according to the present invention.
  • FIG. 2B is a plan view showing still another example of the impedance matching film according to the present invention.
  • FIG. 2C is a plan view showing still another example of the impedance matching film according to the present invention.
  • FIG. 3A is a cross-sectional view showing an example of a radio wave absorber according to the present invention.
  • FIG. 3B is a cross-sectional view showing a modified example of the radio wave absorber according to the present invention.
  • FIG. 3C is a cross-sectional view showing another modified example of the radio wave absorber according to the present invention.
  • FIG. 4 is a cross-sectional view showing another example of the radio wave absorber according to the present invention.
  • the impedance matching film has a plurality of openings from the viewpoint of providing transparency to the impedance matching film.
  • a plurality of openings are regularly formed along the main surface of the impedance matching film.
  • the term "transparency” means transparency to visible light, unless otherwise specified.
  • the impedance matching film 10a has a plurality of openings 11. As a result, the impedance matching film 10a has transparency.
  • the plurality of openings 11 are regularly formed along the main surface 10f of the impedance matching film 10a.
  • the main surface 10f means a front surface and a back surface located apart from each other in the thickness direction of the impedance matching film 10a.
  • Each of the plurality of openings 11 is typically formed as a through hole in the impedance matching film 10a.
  • the value ⁇ / t obtained by dividing the specific resistance ⁇ [ ⁇ ⁇ m] of the material forming the impedance matching film 10a by the thickness t [m] of the impedance matching film 10a is 1 to 300 ⁇ / ⁇ .
  • the dimension of the value ⁇ / t is ⁇ , but the unit of the value ⁇ / t is expressed as ⁇ / ⁇ to avoid confusion with the electric resistance.
  • the value ⁇ / t of the impedance matching film 10a is 1 to 300 ⁇ / ⁇ in order to achieve the desired impedance matching while forming a plurality of openings 11 so that the impedance matching film 10a has the desired transparency. It is advantageous.
  • the specific resistance ⁇ of the material forming the impedance matching film 10a can be determined, for example, by collecting a fragment having a predetermined size from the impedance matching film 10a and measuring the electrical resistance and the dimension of the fragment. Further, the thickness t of the impedance matching film 10a can be determined by observing the cross section of the impedance matching film 10a using, for example, a transmission electron microscope (TEM).
  • TEM transmission electron microscope
  • ⁇ / t may be 250 ⁇ / ⁇ or less, 200 ⁇ / ⁇ or less, or less than 200 ⁇ / ⁇ .
  • ⁇ / t may be 2 ⁇ / ⁇ or more, 3 ⁇ / ⁇ or more, or 4 ⁇ / ⁇ or more. This makes it easy to achieve desired impedance matching with the impedance matching film 10a.
  • the maximum dimension D1 of the opening 11 on the main surface 10f is not limited to a specific value.
  • Maximum dimension D1 is, for example, 7.5 ⁇ 10 4 ⁇ m or less.
  • desired impedance matching can be achieved by the impedance matching film 10a.
  • a radio wave absorber manufactured by using the impedance matching film 10a tends to exhibit good radio wave absorption performance for radio waves of a desired frequency. ..
  • the maximum dimension D1 may correspond to the diagonal length of the quadrangle.
  • the maximum dimension D1 may be 5.0 ⁇ 10 4 ⁇ m or less, 0.5 ⁇ 10 4 ⁇ m or less, 0.1 ⁇ 10 4 ⁇ m or less, and 0.03. It may be ⁇ 10 4 ⁇ m or less.
  • the lower limit of the maximum dimension D1 is not limited to a specific value.
  • the maximum dimension D1 is, for example, 1 ⁇ m or more, 5 ⁇ m or more, or 10 ⁇ m or more. This makes it easy to manufacture the impedance matching film 10.
  • the minimum value D2 of the distance between the openings 11 is not limited to a specific value.
  • the minimum value D2 is, for example, 0.1 to 650 ⁇ m.
  • the impedance matching film 10a can be more reliably transparent, and the impedance matching film 10a can achieve desired impedance matching.
  • a radio wave absorber manufactured by using the impedance matching film 10a tends to exhibit good radio wave absorption performance for radio waves of a desired frequency.
  • the minimum value D2 may be 0.3 ⁇ m or more, or 0.5 ⁇ m or more.
  • the minimum value D2 may be 640 ⁇ m or less, 600 ⁇ m or less, 500 ⁇ m or less, 400 ⁇ m or less, or 300 ⁇ m or less.
  • the value of the thickness t of the impedance matching film 10a is not limited to a specific value as long as ⁇ / t is 1 to 300 ⁇ / ⁇ .
  • the thickness t of the impedance matching film 10a is, for example, 5 to 500 nm. In this case, the warp of the impedance matching film 10a is easily suppressed, and cracks are less likely to occur in the impedance matching film 10a. In addition, it is easy to prevent the characteristics of the impedance matching film 10a from changing when the impedance matching film 10a is placed in a predetermined environment.
  • the thickness t of the impedance matching film 10a may be 10 nm or more, or 15 nm or more. As a result, it is easier to suppress changes in the characteristics of the impedance matching film 10a when the impedance matching film 10a is placed in a predetermined environment.
  • the thickness t of the impedance matching film 10a may be 450 nm or less, or 400 nm or less. As a result, the warp of the impedance matching film 10a can be suppressed more reliably.
  • the specific resistance ⁇ of the material forming the impedance matching film 10a is not limited to a specific value as long as ⁇ / t is 1 to 300 ⁇ / ⁇ . ⁇ is, for example, 5 ⁇ 10 -6 to 2 ⁇ 10 -3 ⁇ ⁇ cm. In this case, when adjusting ⁇ / t to a desired range, the thickness t of the impedance matching film 10 tends to be a desired thickness. As a result, it is easy to prevent the characteristics of the impedance matching film 10a from changing when the impedance matching film 10a is placed in a predetermined environment. In addition, the warpage of the impedance matching film 10a is easily suppressed, and cracks are less likely to occur in the impedance matching film 10a.
  • the resistivity ⁇ of the material forming the impedance matching film 10a may be, for example, 1 ⁇ 10 -5 ⁇ ⁇ cm or more, or 5 ⁇ 10 -5 ⁇ ⁇ cm or more. As a result, the thickness t of the impedance matching film 10 can be easily reduced, and the warpage of the impedance matching film 10a can be easily suppressed. Therefore, cracks are less likely to occur in the impedance matching film 10a.
  • the resistivity ⁇ of the material forming the impedance matching film 10a may be, for example, 1.8 ⁇ 10 -3 ⁇ ⁇ cm or less, or 1.6 ⁇ 10 -3 ⁇ ⁇ cm or less. As a result, the thickness t of the impedance matching film 10 can be easily increased, and it is easy to prevent the characteristics of the impedance matching film 10a from changing when the impedance matching film 10a is placed in a predetermined environment.
  • the arrangement is not limited to a specific arrangement.
  • the plurality of openings 11 are arranged so that their centers form a square lattice on the main surface 10f.
  • the shape is not limited to a specific shape.
  • the plurality of openings 11 are square in a plan view.
  • the aperture ratio of the plurality of openings 11 in the impedance matching film 10a is not limited to a specific value.
  • the aperture ratio of the plurality of openings 11 in the impedance matching film 10a is, for example, 50% or more, 60% or more, or 70% or more.
  • the aperture ratio of the plurality of openings 11 in the impedance matching film 10a is, for example, 99% or less, 97% or less, or 95% or less.
  • the aperture ratio of the plurality of openings 11 is the sum of the sum of the opening area Sa of the plurality of openings 11 and the area Sb of the non-opening portion of the impedance matching film 10a when the impedance matching film 10a is viewed in a plan view.
  • the ratio Sa / (Sa + Sb) of the opening area Sa is the sum of the sum of the opening area Sa of the plurality of openings 11 and the area Sb of the non-opening portion of the impedance matching film 10a when the impedance matching film 10a is viewed
  • the material forming the impedance matching film 10a is not limited to a specific material as long as ⁇ / t can be adjusted to 1 to 300 ⁇ / ⁇ .
  • the material forming the impedance matching film 10a may be an inorganic material such as a metal, an alloy, and a metal oxide, or an organic material such as a conductive polymer and carbon nanotubes.
  • the impedance matching film 10a may be a film having a uniform thickness in which a plurality of through holes are formed, or may be a woven fabric.
  • the fibers forming the woven fabric may be organic materials such as conductive polymers and carbon nanotubes, or inorganic materials such as metals and alloys.
  • the impedance matching film 10a may be formed on, for example, one main surface of the base material 22.
  • the impedance matching film 10a can be provided by the impedance matching film 15a.
  • the impedance matching film 10a may be provided alone without using the base material 22.
  • the base material 22 serves, for example, as a support for supporting the impedance matching film 10a.
  • the impedance matching film 10a in the film 15 with an impedance matching film has a plurality of openings 11 by laser processing or etching on a non-porous film formed on one main surface of the base material 22 by a film forming method such as sputtering. Can be produced by forming.
  • a non-porous film for the impedance matching film 10a may be formed by a film forming method such as ion plating or coating (for example, bar coating).
  • the base material 22 has a thickness of, for example, 10 to 150 ⁇ m, preferably 15 to 100 ⁇ m. As a result, the flexural rigidity of the base material 22 is low, and when the impedance matching film 10a is formed, the base material 22 can suppress the occurrence or deformation of wrinkles.
  • the impedance matching film 10a may be changed to the impedance matching film 10b shown in FIG. 2A, the impedance matching film 10c shown in FIG. 2B, or the impedance matching film 10d shown in FIG. 2C. Good.
  • Each of the impedance matching film 10b, the impedance matching film 10c, and the impedance matching film 10d is configured in the same manner as the impedance matching film 10a except for a portion to be particularly described.
  • the components of the impedance matching film 10b, the impedance matching film 10c, and the impedance matching film 10d, which are the same as or correspond to the components of the impedance matching film 10a, are designated by the same reference numerals, and detailed description thereof will be omitted.
  • the description of the impedance matching film 10a also applies to the impedance matching film 10b, the impedance matching film 10c, and the impedance matching film 10d, unless technically inconsistent.
  • the plurality of openings 11 are circular in a plan view.
  • the plurality of openings 11 are arranged so that their centers form a square quadrilateral grid on the main surface 10f.
  • the plurality of openings 11 have a regular hexagonal shape in a plan view.
  • the plurality of openings 11 are arranged so that their centers form a square quadrilateral grid on the main surface 10f.
  • the plurality of openings 11 have a regular triangular shape in a plan view.
  • the plurality of regular triangular openings 11 having the same orientation are arranged so that their centers form a parallelogram lattice on the main surface 10f.
  • the center of gravity of the plane figure is regarded as the center of the opening in the plan view shape.
  • the plurality of openings 11 may have other polygonal shapes such as a rectangle or an ellipse in a plan view.
  • the plurality of openings 11 may be arranged so that their centers form another planar grid such as a rectangular grid on the main surface 10f.
  • a plane lattice means an array of points on a plane which is invariant by translation in two independent directions by a certain distance.
  • the radio wave absorber 1a can be provided by using the impedance matching film 10a.
  • the radio wave absorber 1a includes an impedance matching film 10a, a reflector 30 that reflects radio waves, and a dielectric layer 20.
  • the dielectric layer 20 is arranged between the impedance matching film 10a and the reflector 30 in the thickness direction of the impedance matching film 10a.
  • the radio wave absorber 1a is, for example, a ⁇ / 4 type radio wave absorber.
  • a radio wave having a wavelength ⁇ O to be absorbed is incident on the radio wave absorber 1a, the radio wave due to reflection (front surface reflection) on the surface of the impedance matching film 10a and the radio wave due to reflection (back surface reflection) on the reflector 30 interfere with each other.
  • the radio wave absorber 1a is designed.
  • the wavelength ⁇ O of the radio wave to be absorbed is determined by the thickness t of the dielectric layer and the relative permittivity ⁇ r of the dielectric layer as shown in the following equation (1). ..
  • the radio wave of the wavelength to be absorbed can be set by appropriately adjusting the relative permittivity and the thickness of the dielectric layer.
  • sqrt ( ⁇ r ) means the square root of the relative permittivity ⁇ r.
  • ⁇ O 4t ⁇ square ( ⁇ r ) Equation (1)
  • the maximum dimension D1 of the opening 11 is, for example, 1/4 or less of the absorption peak wavelength ⁇ p.
  • the absorption peak wavelength ⁇ p is the wavelength of the radio wave having the maximum absolute value of the reflection amount measured based on the Japanese Industrial Standard (JIS) R 1679: 2007 with respect to the radio wave absorber 1a.
  • the absorption peak wavelength ⁇ p is the wavelength of the radio wave having the maximum amount of radio wave absorption in the radio wave absorber 1a.
  • the radio wave absorption amount is an absolute value of the reflection amount measured based on JIS R 1679: 2007. According to such a configuration, the surface reflection of the radio wave having the absorption peak wavelength ⁇ p is appropriately generated in the radio wave absorber 1a, and the radio wave absorber 1a can satisfactorily absorb the radio wave having the absorption peak wavelength ⁇ p.
  • the radio wave absorber 1a performs impedance matching with respect to a radio wave having a frequency of 1 GHz or higher, for example. As a result, the radio wave absorber 1a can effectively absorb radio waves having a frequency of 1 GHz or higher.
  • the frequency of the radio wave whose impedance matching is performed by the radio wave absorber 1a may be 1 GHz or higher, 4 GHz or higher, or 20 GHz or higher.
  • the frequency of the radio wave whose impedance matching is performed by the radio wave absorber 1a is, for example, 3000 GHz or less, 300 GHz or less, or 100 GHz or less.
  • the reflector 30 is not limited to a specific form as long as it can reflect the radio wave to be absorbed.
  • the reflector 30 is, for example, a transparent conductive film. In this case, the reflector 30 has transparency, and the entire radio wave absorber 1a can be easily made transparent.
  • the material forming the transparent conductive film may be an inorganic material such as a metal, an alloy, and a metal oxide, or an organic material such as a conductive polymer and carbon nanotubes.
  • the transparent conductive film has, for example, a plurality of openings 31 regularly formed along the main surface of the transparent conductive film. According to such a configuration, the reflector 30 can appropriately reflect the radio wave to be absorbed and tends to have desired transparency.
  • the transparent conductive film may be a non-porous film.
  • the impedance matching film 10a may be a film having a uniform thickness in which a plurality of through holes are formed, or may be a woven fabric.
  • the fibers forming the woven fabric may be organic materials such as conductive polymers and carbon nanotubes, or inorganic materials such as metals and alloys.
  • the shape of the plurality of openings 31 in the reflector 30 is not limited to a specific shape.
  • the shape of the plurality of openings 31 may be, for example, a quadrangular shape such as a triangle, a square or a rectangle, a hexagonal shape, another polygonal shape, a circular shape, or an elliptical shape in a plan view.
  • the arrangement of the plurality of openings 31 in the reflector 30 is not limited to a specific arrangement.
  • the plurality of openings 31 may be arranged so that, for example, the centers of the plurality of openings 31 form a plane lattice such as a square lattice and a parallelogram lattice.
  • the dielectric layer 20 has a relative permittivity of, for example, 2.0 to 20.0. In this case, the thickness of the dielectric layer 20 can be easily adjusted, and the radio wave absorption performance of the radio wave absorber 1a can be easily adjusted.
  • the relative permittivity of the dielectric layer 20 is, for example, the relative permittivity at 10 GHz measured according to the cavity resonance method.
  • the dielectric layer 20 is formed of, for example, a predetermined polymer.
  • the dielectric layer 20 is, for example, an ethylene vinyl acetate copolymer, a vinyl chloride resin, a urethane resin, an acrylic resin, an acrylic urethane resin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, and a cycloolefin polymer. Contains at least one polymer selected from the group consisting of. In this case, the thickness of the dielectric layer 20 can be easily adjusted, and the manufacturing cost of the radio wave absorber 1a can be kept low.
  • the dielectric layer 20 can be produced, for example, by hot-pressing a predetermined resin composition.
  • the dielectric layer 20 may be formed as a single layer, or may be formed of a plurality of layers made of the same or different materials.
  • the relative permittivity of the dielectric layer 20 is determined, for example, as follows.
  • the relative permittivity ⁇ i of each layer is measured (i is an integer from 1 to n).
  • ⁇ i / T the ratio of thickness to dielectric constant epsilon i of the measured respective layers
  • ⁇ i ⁇ (t i / T ) By adding the ⁇ i ⁇ (t i / T ) for all layers, it can be determined the relative dielectric constant of the dielectric layer 20.
  • the dielectric layer 20 includes, for example, a first layer 21, a second layer 22, and a third layer 23.
  • the first layer 21 is arranged between the second layer 22 and the third layer 23.
  • the first layer 21 is, for example, an ethylene vinyl acetate copolymer, a vinyl chloride resin, a urethane resin, an acrylic resin, an acrylic urethane resin, polyethylene, polypropylene, silicone, polyethylene terephthalate, polyethylene naphthalate, polycarbonate, polyimide, and a cycloolefin polymer. Contains at least one polymer selected from the group consisting of.
  • the second layer 22 also serves as a base material for the impedance matching film 10a.
  • the second layer 22 is arranged at a position closer to the reflector 30 than, for example, the impedance matching film 10a.
  • the second layer 22 may be arranged at a position farther from the reflector 30 than the impedance matching film 10a.
  • the dielectric layer 20 is composed of the first layer 21 and the third layer 23.
  • the impedance matching film 10a and the dielectric layer 20 are protected by the second layer 22, and the radio wave absorber 1a has high durability.
  • the impedance matching film 10a may be in contact with the first layer 21.
  • the material of the second layer 22 is, for example, polyethylene terephthalate (PET), polyethylene naphthalate (PEN), acrylic resin (PMMA), polycarbonate (PC), polyimide (PI), or cycloolefin polymer (COP).
  • PET polyethylene terephthalate
  • PEN polyethylene naphthalate
  • PMMA acrylic resin
  • PC polycarbonate
  • PI polyimide
  • COP cycloolefin polymer
  • the material of the second layer 22 is preferably PET from the viewpoint of the balance between good heat resistance, dimensional stability, and manufacturing cost.
  • the third layer 23 supports, for example, the reflector 30.
  • the reflector 30 may be produced by forming a film on the third layer 23 by using a method such as sputtering, ion plating, or coating (for example, bar coating). Further, a plurality of openings 11 may be formed by laser processing, etching or the like.
  • the third layer 23 is arranged at a position closer to the impedance matching film 10a than the reflector 30 in the radio wave absorber 1a, and constitutes a part of the dielectric layer 20. ..
  • the third layer 23 may be arranged at a position farther from the impedance matching film 10a than the reflector 30. In this case, for example, the reflector 30 is in contact with the first layer 21.
  • the material of the third layer 23 for example, the material exemplified as the material of the second layer 22 can be used.
  • the material of the third layer 23 may be the same as or different from the material of the second layer 22. From the viewpoint of good heat resistance, dimensional stability, and a balance between manufacturing cost, the material of the third layer 23 is preferably PET.
  • the third layer 23 has a thickness of, for example, 10 to 150 ⁇ m, preferably 15 to 100 ⁇ m. As a result, the bending rigidity of the third layer 23 is low, and when the reflector 30 is formed, the occurrence or deformation of wrinkles in the third layer 23 can be suppressed.
  • the third layer 23 may be omitted in some cases.
  • the first layer 21 may be composed of a plurality of layers.
  • the first layer 21 when the first layer 21 is in contact with at least one of the impedance matching film 10a and the reflector 30, the first layer 21 may be composed of a plurality of layers.
  • the first layer 21 may or may not have adhesiveness.
  • the adhesive layer may be arranged in contact with at least one of both main surfaces of the first layer 21, or the adhesive layer is arranged so as to be in contact with both main surfaces. It does not have to be.
  • the adhesive layer is preferably arranged in contact with both main surfaces of the first layer 21.
  • the adhesive layer may not be arranged so as to be in contact with both main surfaces of the second layer 22, even if the second layer 22 does not have adhesiveness. .. In this case, the adhesive layer may be arranged in contact with one main surface of the second layer 22.
  • the third layer 23 may not have adhesiveness, or the adhesive layer may not be arranged in contact with both main surfaces of the third layer 23. In this case, the adhesive layer may be arranged in contact with at least one main surface of the third layer 23.
  • the pressure-sensitive adhesive layer contains, for example, a rubber-based pressure-sensitive adhesive, an acrylic-based pressure-sensitive adhesive, a silicone-based pressure-sensitive adhesive, or a urethane-based pressure-sensitive adhesive.
  • the radio wave absorber 1a may contain at least one of a dielectric loss material and a magnetic loss material.
  • the radio wave absorber 1a may be a dielectric loss type radio wave absorber or a magnetic loss type radio wave absorber.
  • the ⁇ / t required for the impedance matching film 10a tends to be high.
  • the dielectric layer 20 may contain at least one of a dielectric loss material and a magnetic loss material.
  • the material forming the impedance matching film 10a may be a magnetic material.
  • the radio wave absorber 1a can be changed from various viewpoints.
  • the radio wave absorber 1a may be changed as in the radio wave absorber 1b shown in FIG.
  • the radio wave absorber 1b is configured in the same manner as the radio wave absorber 1a except for a portion to be described in particular.
  • the components of the radio wave absorber 1b that are the same as or corresponding to the components of the radio wave absorber 1a are designated by the same reference numerals, and detailed description thereof will be omitted.
  • the description of the radio wave absorber 1a also applies to the radio wave absorber 1b unless there is a technical contradiction.
  • the radio wave absorber 1b further includes an adhesive layer 40a.
  • the reflector 30 is arranged between the dielectric layer 20 and the adhesive layer 40a.
  • the radio wave absorber 1b can be attached to the article by bringing the adhesive layer 40a into contact with the predetermined article and pressing the radio wave absorber 1b against the article. As a result, an article with a radio wave absorber can be obtained.
  • the adhesive layer 40a contains, for example, a rubber-based adhesive, an acrylic-based adhesive, a silicone-based adhesive, or a urethane-based adhesive.
  • the radio wave absorber 1b may further include a separator (not shown). In this case, the separator covers the adhesive layer 40a.
  • the separator is typically a film that can maintain the adhesive strength of the adhesive layer 40a when covering the adhesive layer 40a and can be easily peeled off from the adhesive layer 40a.
  • the separator is, for example, a film made of a polyester resin such as PET. By peeling off the separator, the adhesive layer 40a is exposed, and the radio wave absorber 1b can be attached to the article.
  • the sheet resistance of the non-porous film according to each Example and Comparative Example is determined by the eddy current measuring method in accordance with JIS Z 2316. It was measured.
  • the product of the thickness of the non-porous film measured as described above and the sheet resistance of the non-porous film measured as described above was obtained, and the specific resistance of the material forming the non-porous film was determined. Decided.
  • the specific resistance of the material forming the non-porous film was regarded as the specific resistance of the material forming the alloy film in the film with the alloy film according to each Example and each Comparative Example. The results are shown in Table 1.
  • Radio wave absorption performance Radio waves with frequencies of 1 to 90 GHz were incident on the samples according to each example and comparative example at an incident angle of 0 °, and the absolute value of the amount of reflection at each frequency was specified in accordance with JIS R 1679: 2007. .. For each sample, the maximum value of the absolute value of the reflection amount, the frequency indicating the maximum value (absorption peak frequency), and the frequency range in which the absolute value of the reflection amount indicates 20 dB or more were determined.
  • Example 1 DC magnetron sputtering was performed using an Al (aluminum) target material and a Si (silicon) target material and an argon gas as a process gas to form an Al—Si alloy film on the PET film.
  • DC magnetron sputtering a discharge involving an Al (aluminum) target material and a discharge involving a Si (silicon) target material were simultaneously performed. In this way, the non-porous film according to Example 1 was formed on the PET film.
  • the specific resistance of the material forming the non-porous film according to Example 1 was 1.0 ⁇ 10 -4 ⁇ ⁇ cm.
  • a plurality of square openings were formed in the non-porous film according to Example 1 to obtain a film with an alloy film according to Example 1.
  • the maximum size of the openings was 127 ⁇ m, and the minimum distance between adjacent openings was 10 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • an ITO target material containing 10% by weight of SnO 2 DC magnetron sputtering was performed using argon and oxygen as process gases to form an ITO film on a PET film. Then, the ITO film was annealed at a temperature of 150 ° C. for 1 hour to polycrystallize ITO to obtain a film with a reflector. The sheet resistance of the reflector of the film with the reflector was 20 ⁇ / ⁇ . Next, an acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 615 ⁇ m to obtain an acrylic resin layer A.
  • the film with an alloy film according to Example 1 was laminated on the acrylic resin layer A so that the alloy film of the film with an alloy film according to Example 1 was in contact with the acrylic resin layer A.
  • the reflector film was laminated on the acrylic resin layer A so that the Cu film in the reflector film was in contact with the acrylic resin layer A. In this way, a sample according to Example 1 was obtained.
  • Example 2 A non-porous film according to Example 2 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Example 2 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Example 2 is 1.4 ⁇ 10 -3 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Example 2 was 350 nm.
  • a metal laser pattern processing machine Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Example 2, and a film with an alloy film according to Example 2 was obtained.
  • the maximum size of the openings was 127 ⁇ m, and the minimum distance between adjacent openings was 10 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • Example 2 A sample according to Example 2 was obtained in the same manner as in Example 1 except that the film with an alloy film according to Example 2 was used instead of the film with an alloy film according to Example 1.
  • Example 3 A non-porous film according to Example 3 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Example 3 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Example 3 is 1.0 ⁇ 10 -5 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Example 3 was 5 nm.
  • a metal laser pattern processing machine Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Example 3, and a film with an alloy film according to Example 3 was obtained.
  • the maximum size of the openings was 269 ⁇ m, and the minimum distance between adjacent openings was 10 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • Example 3 instead of the film with an alloy film according to Example 1, the film with an alloy film according to Example 3 was used, and instead of the acrylic resin layer A, an acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 630 ⁇ m.
  • a sample according to Example 3 was obtained in the same manner as in Example 1 except that the acrylic resin layer B thus obtained was used.
  • Example 4 A non-porous film according to Example 4 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Example 4 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Example 4 is 5.0 ⁇ 10 -4 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Example 4 was 25 nm.
  • a metal laser pattern processing machine Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Example 4, and a film with an alloy film according to Example 4 was obtained.
  • the maximum size of the openings was 35 ⁇ m, and the minimum distance between adjacent openings was 10 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • Example 4 instead of the film with an alloy film according to Example 1, the film with an alloy film according to Example 4 was used, and instead of the acrylic resin layer A, an acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 605 ⁇ m.
  • a sample according to Example 4 was obtained in the same manner as in Example 1 except that the acrylic resin layer C thus obtained was used.
  • Example 5 In the same manner as in Example 1, a non-porous film according to Example 5 was formed on the PET film. Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Example 5, and a film with an alloy film according to Example 5 was obtained. In plan view, the maximum size of the openings was 14 ⁇ m, and the minimum distance between adjacent openings was 1 ⁇ m. In plan view, the plurality of openings were formed so that their centers formed a square grid.
  • Example 5 The same as in Example 1 except that the alloy film-attached film according to Example 5 was used instead of the alloy film-attached film according to Example 1 and the acrylic resin layer C was used instead of the acrylic resin layer A. , A sample according to Example 5 was obtained.
  • Example 6 A non-porous film according to Example 6 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Example 6 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Example 6 is 7.8 ⁇ 10 -5 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Example 4 was 25 nm.
  • a metal laser pattern processing machine Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Example 6, and a film with an alloy film according to Example 6 was obtained.
  • the maximum size of the openings was 707 ⁇ m, and the minimum distance between adjacent openings was 50 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • Example 6 instead of the film with an alloy film according to Example 1, the film with an alloy film according to Example 6 was used, and instead of the acrylic resin layer A, an acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 650 ⁇ m. A sample according to Example 6 was obtained in the same manner as in Example 1 except that the acrylic resin layer D thus obtained was used.
  • Example 7 In the same manner as in Example 1, a non-porous film according to Example 7 was formed on the PET film. Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Example 7, and a film with an alloy film according to Example 7 was obtained. In plan view, the maximum size of the openings was 3536 ⁇ m, and the minimum distance between adjacent openings was 250 ⁇ m. In plan view, the plurality of openings were formed so that their centers formed a square grid.
  • An acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 18500 ⁇ m to obtain an acrylic resin layer E.
  • a sample according to Example 7 was obtained.
  • Example 8> A non-porous film according to Example 10 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Example 10 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Example 10 is 1.0 ⁇ 10 -5 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Example 10 was 25 nm.
  • a plurality of square openings were formed in the non-porous film according to Example 10 to obtain a film with an alloy film according to Example 10.
  • the maximum size of the openings was 47192 ⁇ m, and the minimum distance between adjacent openings was 640 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • An acrylic resin having a relative permittivity of 2.6 was molded to a thickness of 51300 ⁇ m to obtain an acrylic resin layer F.
  • a sample according to Example 8 was obtained.
  • ⁇ Comparative example 1> A non-porous film according to Comparative Example 1 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Comparative Example 1 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Comparative Example 1 is 1.0 ⁇ 10 -3 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Comparative Example 1 was 25 nm.
  • a metal laser pattern processing machine Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Comparative Example 1 to obtain a film with an alloy film according to Comparative Example 1.
  • the maximum size of the openings was 1.4 ⁇ m, and the minimum distance between adjacent openings was 10 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • a sample according to Comparative Example 1 was obtained in the same manner as in Example 1 except that the film with an alloy film according to Comparative Example 1 was used instead of the film with an alloy film according to Example 1.
  • ⁇ Comparative example 2> A non-porous film according to Comparative Example 1 was formed on the PET film in the same manner as in Example 1 except for the following points, and a film with an alloy film according to Comparative Example 1 was obtained.
  • DC magnetron sputtering with respect to the discharge power of the discharge involving the Al (aluminum) target material so that the specific resistance of the material forming the non-porous film according to Comparative Example 1 is 1.0 ⁇ 10 -6 ⁇ ⁇ cm. , The ratio of the discharge power of the discharge involving the Si (silicon) target material was adjusted.
  • the conditions of DC magnetron sputtering were adjusted so that the thickness of the alloy film in the film with the alloy film according to Comparative Example 1 was 25 nm.
  • a metal laser pattern processing machine Using a metal laser pattern processing machine, a plurality of square openings were formed in the non-porous film according to Comparative Example 1 to obtain a film with an alloy film according to Comparative Example 1.
  • the maximum size of the openings was 707 ⁇ m, and the minimum distance between adjacent openings was 10 ⁇ m.
  • the plurality of openings were formed so that their centers formed a square grid.
  • a sample according to Comparative Example 2 was obtained in the same manner as in Example 1 except that the film with an alloy film according to Comparative Example 2 was used instead of the film with an alloy film according to Example 1.
  • the samples according to Examples 1 to 8 show good absorption performance for radio waves of a predetermined frequency, and desired impedance matching is achieved by the alloy film of the alloy film-attached film according to each example. It turned out that. On the other hand, it is difficult to say that the samples according to Comparative Examples 1 and 2 show good absorption performance for radio waves of a predetermined frequency, and it is difficult to perform impedance matching with the alloy film of the alloy film-attached film according to each Comparative Example. It has been suggested. Therefore, it was suggested that it is advantageous from the viewpoint of impedance matching that the value of ⁇ / t in the alloy film is at a predetermined value.
  • the alloy film of the film with an alloy film according to each example had a high aperture ratio and had transparency.

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Abstract

インピーダンス整合膜１０ａは、インピーダンス整合膜１０ａの主面１０ｆに沿って規則的に形成された複数の開口１１を有する。インピーダンス整合膜１０ａにおいて、インピーダンス整合膜１０ａをなす材料の比抵抗ρをインピーダンス整合膜１０ａの厚みｔで割った値ρ／ｔが１～３００Ω／□である。

Description

インピーダンス整合膜及び電波吸収体
　本発明は、インピーダンス整合膜及び電波吸収体に関する。
　従来、所定の膜を用いて、電波吸収体の表面のインピーダンスを空気の特性インピーダンスに合わせるインピーダンス整合を図る技術が知られている。一方、従来、透明な電波吸収体を提供することが試みられている。
　例えば、特許文献１には、構成要素の全ての層が透明又は半透明である電波吸収体が記載されている。この電波吸収体では、全面導体層と、第１誘電体層と、線状パターン抵抗層と、第２誘電体層と、パターン層とがこの順序で積層されている。この電波吸収体によれば、最表層のパターン層で良好に電磁波を受信できる。パターン層と第２誘電体層とが接しているので、パターン層が受信した電磁波の第２誘電体層への漏れが大きい。第２誘電体層と線状パターン層とが接しているので、第２誘電体層に漏れた電磁波を線状パターン層が効率良く熱に変換できる。なお、１．０×１０-4Ωｃｍ以上１．０×１０-1Ωｃｍ以下の体積抵抗率を有する高抵抗導体が線状パターン抵抗層をなしている。
特開２００６－１７９６７１号公報
　特許文献１に記載の電波吸収体において線状パターン層は、第２誘電体層に漏れた電磁波を効率良く熱に変換するものであり、特許文献１には、線状パターン層を用いてインピーダンス整合を図ることは記載されていない。
　一方、ヘッドライト及びフロントガラスの周辺に配置されるセンサを用いたセンシングにおいて透明性を有するインピーダンス整合膜が必要になることが想定される。加えて、第５世代移動通信システム（５Ｇ）及びInternet of Things(IoT)等の多岐にわたる技術分野において、透明性を有し、かつ、ノイズ低減に有利なインピーダンス整合膜が必要になることが想定される。このような事情に鑑み、本発明は、透明性を有する新規なインピーダンス整合膜を提供する。
　本発明は、
　インピーダンス整合膜であって、
　当該インピーダンス整合膜の主面に沿って規則的に形成された複数の開口を有し、
　当該インピーダンス整合膜をなす材料の比抵抗を当該インピーダンス整合膜の厚みで割った値が１～３００Ω／□である、
　インピーダンス整合膜を提供する。
　また、本発明は、
　上記のインピーダンス整合膜と、
　電波を反射する反射体と、
　前記インピーダンス整合膜の厚み方向において前記インピーダンス整合膜と前記反射体との間に配置された誘電体層と、を備えた、
　電波吸収体を提供する。
　上記のインピーダンス整合膜は、透明性を有する新規なインピーダンス整合膜である。
図１Ａは、本発明に係るインピーダンス整合膜の一例を示す平面図である。 図１Ｂは、図１ＡのIB-IB線を切断線とするインピーダンス整合膜の断面図である。 図２Ａは、本発明に係るインピーダンス整合膜の別の一例を示す平面図である。 図２Ｂは、本発明に係るインピーダンス整合膜のさらに別の一例を示す平面図である。 図２Ｃは、本発明に係るインピーダンス整合膜のさらに別の一例を示す平面図である。 図３Ａは、本発明に係る電波吸収体の一例を示す断面図である。 図３Ｂは、本発明に係る電波吸収体の変形例を示す断面図である。 図３Ｃは、本発明に係る電波吸収体の別の変形例を示す断面図である。 図４は、本発明に係る電波吸収体の別の一例を示す断面図である。
　インピーダンス整合膜が複数の開口を有することは、インピーダンス整合膜に透明性をもたらす観点から有利である。加えて、インピーダンス整合膜の透明性の空間的なばらつきを抑制するために、インピーダンス整合膜の主面に沿って複数の開口が規則的に形成されていることが有利である。一方、本発明者らの検討によれば、特許文献１の記載は、このようなインピーダンス整合膜を作製するうえで十分ではないことが分かった。そこで、本発明者らは、鋭意検討を重ねた結果、インピーダンス整合膜をなす材料の比抵抗をインピーダンス整合膜の厚みで割った値を所定の範囲に調整することが所望のインピーダンス整合及び高い透明性を両立するうえで有利であることを新たに見出した。本発明者らは、この新たな知見に基づき、本発明に係るインピーダンス整合膜を案出した。本明細書において「透明性」とは、特に説明する場合を除き、可視光に対する透明性を意味する。
　本発明の実施形態について、図面を参照しつつ説明する。なお、本発明は、以下の実施形態には限定されない。
　図１Ａ及び図１Ｂに示す通り、インピーダンス整合膜１０ａは、複数の開口１１を有する。これにより、インピーダンス整合膜１０ａが透明性を有する。複数の開口１１は、インピーダンス整合膜１０ａの主面１０ｆに沿って規則的に形成されている。本明細書において、主面１０ｆは、インピーダンス整合膜１０ａの厚み方向に互いに離れて位置する表面及び裏面を意味する。複数の開口１１のそれぞれは、典型的には、インピーダンス整合膜１０ａにおいて貫通孔として形成されている。インピーダンス整合膜１０ａにおいて、インピーダンス整合膜１０ａをなす材料の比抵抗ρ［Ω・ｍ］をインピーダンス整合膜１０ａの厚みｔ［ｍ］で割った値ρ／ｔが１～３００Ω／□である。なお、値ρ／ｔの次元はΩであるが、電気抵抗との混同を避けるために値ρ／ｔの単位をΩ／□と表記する。インピーダンス整合膜１０ａにおいて、値ρ／ｔが１～３００Ω／□であることは、インピーダンス整合膜１０ａが所望の透明性を有するように複数の開口１１を形成しつつ所望のインピーダンス整合を図るうえで有利である。
　インピーダンス整合膜１０ａをなす材料の比抵抗ρは、例えば、インピーダンス整合膜１０ａから所定の寸法の断片を採取し、その断片の電気抵抗及び寸法を測定することによって決定できる。また、インピーダンス整合膜１０ａの厚みｔは、例えば、透過型電子顕微鏡（TEM）を用いて、インピーダンス整合膜１０ａの断面を観察することによって決定できる。
　インピーダンス整合膜１０ａにおいて、ρ／ｔは、２５０Ω／□以下であってもよく、２００Ω／□以下であってもよく、２００Ω／□未満であってもよい。これにより、インピーダンス整合膜１０ａの透明性が高くなるように複数の開口１１を形成しつつ所望のインピーダンス整合を図りやすい。
　インピーダンス整合膜１０ａにおいて、ρ／ｔは、２Ω／□以上であってもよく、３Ω／□以上であってもよく、４Ω／□以上であってもよい。これにより、インピーダンス整合膜１０ａによって所望のインピーダンス整合を図りやすい。
　主面１０ｆにおける開口１１の最大寸法Ｄ１は、特定の値に限定されない。最大寸法Ｄ１は、例えば、７．５×１０4μｍ以下である。これにより、インピーダンス整合膜１０ａによって所望のインピーダンス整合を図ることができ、例えば、インピーダンス整合膜１０ａを用いて作製される電波吸収体が所望の周波数の電波に対し良好な電波吸収性能を発揮しやすい。図１Ａに示す通り、例えば、開口１１が平面視で四角形状である場合、最大寸法Ｄ１は四角形の対角線の長さに相当しうる。
　最大寸法Ｄ１は、５．０×１０4μｍ以下であってもよく、０．５×１０4μｍ以下であってもよく、０．１×１０4μｍ以下であってもよく、０．０３×１０4μｍ以下であってもよい。
　最大寸法Ｄ１の下限値は、特定の値に限定されない。最大寸法Ｄ１は、例えば、１μｍ以上であり、５μｍ以上であってもよく、１０μｍ以上であってもよい。これにより、インピーダンス整合膜１０の作製が容易になりやすい。
　インピーダンス整合膜１０ａにおいて、開口１１同士の距離の最小値Ｄ２は、特定の値に限定されない。最小値Ｄ２は、例えば、０．１～６５０μｍである。これにより、インピーダンス整合膜１０ａがより確実に透明性を有するとともに、インピーダンス整合膜１０ａによって所望のインピーダンス整合を図ることができる。例えば、インピーダンス整合膜１０ａを用いて作製される電波吸収体が所望の周波数の電波に対し良好な電波吸収性能を発揮しやすい。
　最小値Ｄ２は、０．３μｍ以上であってもよく、０．５μｍ以上であってもよい。最小値Ｄ２は、６４０μｍ以下であってもよく、６００μｍ以下であってもよく、５００μｍ以下であってもよく、４００μｍ以下であってもよく、３００μｍ以下であってもよい。
　インピーダンス整合膜１０ａの厚みｔの値は、ρ／ｔが１～３００Ω／□である限り、特定の値に限定されない。インピーダンス整合膜１０ａの厚みｔは、例えば、５～５００ｎｍである。この場合、インピーダンス整合膜１０ａの反りを抑制しやすく、インピーダンス整合膜１０ａにおいてクラックが発生しにくい。加えて、インピーダンス整合膜１０ａが所定の環境に置かれたときにインピーダンス整合膜１０ａの特性が変化することを抑制しやすい。
　インピーダンス整合膜１０ａの厚みｔは、１０ｎｍ以上であってもよく、１５ｎｍ以上であってもよい。これにより、インピーダンス整合膜１０ａが所定の環境に置かれたときにインピーダンス整合膜１０ａの特性が変化することをより抑制しやすい。インピーダンス整合膜１０ａの厚みｔは、４５０ｎｍ以下であってもよく、４００ｎｍ以下であってもよい。これにより、インピーダンス整合膜１０ａの反りをより確実に抑制できる。
　インピーダンス整合膜１０ａをなす材料の比抵抗ρは、ρ／ｔが１～３００Ω／□である限り、特定の値に限定されない。ρは、例えば、５×１０-6～２×１０-3Ω・ｃｍである。この場合、ρ／ｔを所望の範囲に調整するときに、インピーダンス整合膜１０の厚みｔが所望の厚みになりやすい。その結果、インピーダンス整合膜１０ａが所定の環境に置かれたときにインピーダンス整合膜１０ａの特性が変化することを抑制しやすい。加えて、インピーダンス整合膜１０ａの反りを抑制しやすく、インピーダンス整合膜１０ａにおいてクラックが発生しにくい。
　インピーダンス整合膜１０ａをなす材料の比抵抗ρは、例えば、１×１０-5Ω・ｃｍ以上であってもよく、５×１０-5Ω・ｃｍ以上であってもよい。これにより、インピーダンス整合膜１０の厚みｔを小さくしやすく、インピーダンス整合膜１０ａの反りを抑制しやすい。このため、インピーダンス整合膜１０ａにおいてクラックが発生しにくい。インピーダンス整合膜１０ａをなす材料の比抵抗ρは、例えば、１．８×１０-3Ω・ｃｍ以下であってもよく、１．６×１０-3Ω・ｃｍ以下であってもよい。これにより、インピーダンス整合膜１０の厚みｔを大きくしやすく、インピーダンス整合膜１０ａが所定の環境に置かれたときにインピーダンス整合膜１０ａの特性が変化することを抑制しやすい。
　複数の開口１１は規則的に形成されている限り、その配置は特定の配置に限定されない。例えば、インピーダンス整合膜１０ａにおいて、複数の開口１１は、その中心が主面１０ｆにおいて正方格子をなすように配置されている。
　複数の開口１１は規則的に形成されている限り、その形状は特定の形状に限定されない。例えば、インピーダンス整合膜１０ａによれば、複数の開口１１は平面視で正方形状である。
　インピーダンス整合膜１０ａにおける複数の開口１１の開口率は、特定の値に限定されない。インピーダンス整合膜１０ａにおける複数の開口１１の開口率は、例えば、５０％以上であり、６０％以上であってもよく、７０％以上であってもよい。インピーダンス整合膜１０ａにおける複数の開口１１の開口率は、例えば９９％以下であり、９７％以下であってもよく、９５％以下であってもよい。複数の開口１１の開口率は、インピーダンス整合膜１０ａを平面視したときの複数の開口１１の開口面積Ｓａとインピーダンス整合膜１０ａの非開口部の面積Ｓｂとの和Ｓａ＋Ｓｂに対する、複数の開口１１の開口面積Ｓａの比Ｓａ／（Ｓａ＋Ｓｂ）である。
　インピーダンス整合膜１０ａをなす材料は、ρ／ｔを１～３００Ω／□に調整できる限り、特定の材料に限定されない。インピーダンス整合膜１０ａをなす材料は、金属、合金、及び金属酸化物等の無機材料であってもよいし、導電性高分子及びカーボンナノチューブ等の有機材料であってもよい。
　インピーダンス整合膜１０ａは、複数の貫通孔が形成された均一な厚みを有する膜であってもよいし、織物であってもよい。織物をなす繊維は、導電性高分子及びカーボンナノチューブ等の有機材料であってもよいし、金属及び合金等の無機材料であってもよい。
　図１に示す通り、インピーダンス整合膜１０ａは、例えば、基材２２の一方の主面上に形成されていてもよい。この場合、インピーダンス整合膜付フィルム１５によってインピーダンス整合膜１０ａが提供されうる。なお、基材２２が使用されることなく、インピーダンス整合膜１０ａが単独で提供されてもよい。
　基材２２は、例えば、インピーダンス整合膜１０ａを支持する支持体としての役割を果たす。インピーダンス整合膜付フィルム１５におけるインピーダンス整合膜１０ａは、例えば、スパッタリング等の成膜法によって基材２２の一方の主面上に形成された無孔の膜にレーザー加工又はエッチング等によって複数の開口１１を形成することによって作製できる。場合によっては、イオンプレーティング又はコーティング（例えば、バーコーティング）等の成膜法によってインピーダンス整合膜１０ａのための無孔の膜が形成されてもよい。
　基材２２は、例えば１０～１５０μｍの厚みを有し、望ましくは１５～１００μｍの厚みを有する。これにより、基材２２の曲げ剛性が低く、かつ、インピーダンス整合膜１０ａを形成する場合に基材２２において皺の発生又は変形を抑制できる。
　複数の開口１１の配置及び形状に関し、インピーダンス整合膜１０ａは、図２Ａに示すインピーダンス整合膜１０ｂ、図２Ｂに示すインピーダンス整合膜１０ｃ、又は図２Ｃに示すインピーダンス整合膜１０ｄのように変更されてもよい。インピーダンス整合膜１０ｂ、インピーダンス整合膜１０ｃ、及びインピーダンス整合膜１０ｄのそれぞれは特に説明をする部分を除きインピーダンス整合膜１０ａと同様に構成されている。インピーダンス整合膜１０ａの構成要素と同一又は対応する、インピーダンス整合膜１０ｂ、インピーダンス整合膜１０ｃ、及びインピーダンス整合膜１０ｄのそれぞれの構成要素には同一の符号を付し、詳細な説明を省略する。インピーダンス整合膜１０ａに関する説明は、技術的に矛盾しない限り、インピーダンス整合膜１０ｂ、インピーダンス整合膜１０ｃ、及びインピーダンス整合膜１０ｄにも当てはまる。
　図２Ａに示す通り、インピーダンス整合膜１０ｂにおいて、複数の開口１１は平面視で円状である。加えて、複数の開口１１は、その中心が主面１０ｆにおいて平方四辺形格子をなすように配置されている。
　図２Ｂに示す通り、インピーダンス整合膜１０ｃにおいて、複数の開口１１は平面視で正六角形状である。加えて、複数の開口１１は、その中心が主面１０ｆにおいて平方四辺形格子をなすように配置されている。
　図２Ｃに示す通り、インピーダンス整合膜１０ｃにおいて、複数の開口１１は平面視で正三角形状である。加えて、同じ向きの正三角形状の複数の開口１１は、その中心が主面１０ｆにおいて平行四辺形格子をなすように配置されている。なお、本明細書では、平面図形の重心を平面図形状の開口の中心とみなす。
　複数の開口１１は、平面視で、長方形等の他の多角形状又は楕円状であってもよい。複数の開口１１は、その中心が主面１０ｆにおいて長方形格子等の他の平面格子をなすように配置されてもよい。なお、本明細書において平面格子とは、２つの独立な方向へのそれぞれ一定距離の平行移動で不変な平面上の点の配列を意味する。
　図３Ａに示す通り、例えば、インピーダンス整合膜１０ａを用いて電波吸収体１ａを提供できる。電波吸収体１ａは、インピーダンス整合膜１０ａと、電波を反射する反射体３０と、誘電体層２０とを備えている。誘電体層２０は、インピーダンス整合膜１０ａの厚み方向においてインピーダンス整合膜１０ａと反射体３０との間に配置されている。
　電波吸収体１ａは、例えば、λ／４型の電波吸収体である。電波吸収体１ａに吸収対象とする波長λOの電波が入射すると、インピーダンス整合膜１０ａの表面での反射（表面反射）による電波と、反射体３０における反射（裏面反射）による電波とが干渉するように、電波吸収体１ａが設計されている。λ／４型の電波吸収体においては、下記の式（１）に示す通り、誘電体層の厚みｔ及び誘電体層の比誘電率εrによって吸収対象の電波の波長λOが決定される。すなわち、誘電体層の比誘電率及び厚みを適宜調節することにより、吸収対象の波長の電波を設定できる。式（１）においてｓｑｒｔ（εr）は、比誘電率εrの平方根を意味する。
　λO＝４ｔ×ｓｑｒｔ（εr）　　　式（１）
　電波吸収体１ａにおいて、開口１１の最大寸法Ｄ１は、例えば、吸収ピーク波長λｐの１／４以下である。吸収ピーク波長λｐは、電波吸収体１ａに対し、日本工業規格（JIS）R 1679：2007に基づいて測定される反射量の絶対値が最大となる電波の波長である。換言すると、吸収ピーク波長λｐは、電波吸収体１ａにおいて電波吸収量が最大となる電波の波長である。電波吸収量は、JIS R 1679：2007に基づいて測定される反射量の絶対値である。このような構成によれば、電波吸収体１ａにおいて吸収ピーク波長λｐの電波の表面反射が適切に生じ、電波吸収体１ａが吸収ピーク波長λｐの電波を良好に吸収できる。
　電波吸収体１ａは、例えば、１ＧＨｚ以上の周波数を有する電波に対してインピーダンス整合をなす。これにより、電波吸収体１ａは、１ＧＨｚ以上の周波数を有する電波を効果的に吸収できる。
　電波吸収体１ａがインピーダンス整合をなす電波の周波数は、１ＧＨｚ以上であってもよく、４ＧＨｚ以上であってもよく、２０ＧＨｚ以上であってもよい。電波吸収体１ａがインピーダンス整合をなす電波の周波数は、例えば３０００ＧＨｚ以下であり、３００ＧＨｚ以下であってもよく、１００ＧＨｚ以下であってもよい。
　反射体３０は、吸収対象の電波を反射できる限り特定の形態に限定されない。反射体３０は、例えば透明導電膜である。この場合、反射体３０が透明性を有し、電波吸収体１ａの全体を透明にしやすい。透明導電膜をなす材料は、金属、合金、及び金属酸化物等の無機材料であってもよいし、導電性高分子及びカーボンナノチューブ等の有機材料であってもよい。
　透明導電膜は、例えば、透明導電膜の主面に沿って規則的に形成された複数の開口３１を有する。このような構成によれば、反射体３０は、吸収対象の電波を適切に反射でき、かつ、所望の透明性を有しやすい。透明導電膜は無孔の膜であってもよい。
　反射体３０が複数の開口３１を有する場合、インピーダンス整合膜１０ａは、複数の貫通孔が形成された均一な厚みを有する膜であってもよいし、織物であってもよい。織物をなす繊維は、導電性高分子及びカーボンナノチューブ等の有機材料であってもよいし、金属及び合金等の無機材料であってもよい。
　反射体３０における複数の開口３１の形状は、特定の形状に限定されない。複数の開口３１の形状は、例えば、平面視で、三角形状、正方形及び長方形等の四角形状、六角形状、その他の多角形状、円状、又は楕円状であってもよい。
　反射体３０における複数の開口３１の配置は、特定の配置に限定されない。複数の開口３１は、例えば、複数の開口３１の中心が正方形格子及び平行四辺形格子等の平面格子をなすように配置されていてもよい。
　誘電体層２０は、例えば、２．０～２０．０の比誘電率を有する。この場合、誘電体層２０の厚みを調整しやすく、電波吸収体１ａの電波吸収性能の調整が容易である。誘電体層２０の比誘電率は、例えば、空洞共振法に従って測定される１０ＧＨｚにおける比誘電率である。
　誘電体層２０は、例えば、所定の高分子によって形成されている。誘電体層２０は、例えば、エチレン酢酸ビニル共重合体、塩化ビニル樹脂、ウレタン樹脂、アクリル樹脂、アクリルウレタン樹脂、ポリエチレン、ポリプロピレン、シリコーン、ポリエチレンテレフタレート、ポリエチレンナフタレート、ポリカーボネート、ポリイミド、及びシクロオレフィンポリマーからなる群より選ばれる少なくとも１つの高分子を含む。この場合、誘電体層２０の厚みを調整しやすく、かつ、電波吸収体１ａの製造コストを低く保つことができる。誘電体層２０は、例えば、所定の樹脂組成物を熱プレスすることによって作製できる。
　誘電体層２０は、単一の層として形成されていてもよいし、同一又は異なる材料でできた複数の層によって形成されていてもよい。誘電体層２０がｎ個の層（ｎは２以上の整数）を有する場合、誘電体層２０の比誘電率は、例えば、以下の様にして決定される。各層の比誘電率εiを測定する（ｉは、１～ｎの整数）。次に、測定された各層の比誘電率εiにその層の厚みｔiの誘電体層２０の全体Ｔに対する厚みの割合を乗じて、εi×(ｔi／Ｔ)を求める。すべての層に対するεi×(ｔi／Ｔ)を加算することによって、誘電体層２０の比誘電率を決定できる。
　図３Ａに示す通り、誘電体層２０は、例えば、第一層２１、第二層２２、及び第三層２３を備えている。第一層２１は、第二層２２と第三層２３との間に配置されている。第一層２１は、例えば、エチレン酢酸ビニル共重合体、塩化ビニル樹脂、ウレタン樹脂、アクリル樹脂、アクリルウレタン樹脂、ポリエチレン、ポリプロピレン、シリコーン、ポリエチレンテレフタレート、ポリエチレンナフタレート、ポリカーボネート、ポリイミド、及びシクロオレフィンポリマーからなる群より選ばれる少なくとも１つの高分子を含む。
　電波吸収体１ａにおいて、第二層２２は、インピーダンス整合膜１０ａにとっての基材を兼ねている。第二層２２は、例えば、インピーダンス整合膜１０ａよりも反射体３０に近い位置に配置されている。図３Ｂに示す通り、第二層２２は、インピーダンス整合膜１０ａよりも反射体３０から遠い位置に配置されていてもよい。この場合、第一層２１及び第三層２３によって誘電体層２０が構成される。この場合、第二層２２によって、インピーダンス整合膜１０ａ及び誘電体層２０が保護され、電波吸収体１ａが高い耐久性を有する。この場合、例えば、インピーダンス整合膜１０ａが第一層２１に接触していてもよい。第二層２２の材料は、例えば、ポリエチレンテレフタレート（ＰＥＴ）、ポリエチレンナフタレート（ＰＥＮ）、アクリル樹脂（ＰＭＭＡ）、ポリカーボネート（ＰＣ）、ポリイミド（ＰＩ）、又はシクロオレフィンポリマー（ＣＯＰ）である。なかでも、良好な耐熱性と、寸法安定性と、製造コストとのバランスの観点から、第二層２２の材料は、望ましくはＰＥＴである。
　電波吸収体１ａにおいて、第三層２３は、例えば、反射体３０を支持している。この場合、反射体３０は、例えば、スパッタリング、イオンプレーティング、又はコーティング（例えば、バーコーティング）等の方法を用いて第三層２３上に成膜することによって作製されてもよい。さらに、レーザー加工及びエッチング等によって複数の開口１１が形成されてもよい。図３Ａに示す通り、第三層２３は、例えば、電波吸収体１ａにおいて、反射体３０よりもインピーダンス整合膜１０ａに近い位置に配置されており、誘電体層２０の一部を構成している。なお、図３Ｃに示す通り、第三層２３は、反射体３０よりもインピーダンス整合膜１０ａから遠い位置に配置されていてもよい。この場合、例えば、反射体３０が第一層２１に接触している。
　第三層２３の材料として、例えば、第二層２２の材料として例示された材料を使用できる。第三層２３の材料は、第二層２２の材料と同一であってもよいし、異なっていてもよい。良好な耐熱性と、寸法安定性と、製造コストとのバランスの観点から、第三層２３の材料は、望ましくはＰＥＴである。
　第三層２３は、例えば１０～１５０μｍの厚みを有し、望ましくは１５～１００μｍの厚みを有する。これにより、第三層２３の曲げ剛性が低く、かつ、反射体３０を形成する場合に第三層２３において皺の発生又は変形を抑制できる。なお、第三層２３は、場合によっては省略可能である。
　第一層２１は、複数の層によって構成されていてもよい。特に、図３Ｂ又は図３Ｃに示す通り、インピーダンス整合膜１０ａ及び反射体３０の少なくとも１つに第一層２１が接触している場合に、第一層２１は複数の層によって構成されうる。
　第一層２１は、粘着性を有していてもよいし、粘着性を有していなくてもよい。第一層２１が粘着性を有する場合、第一層２１の両主面の少なくとも一方に粘着層が接して配置されていてもよいし、その両主面に接するように粘着層が配置されていなくてもよい。第一層２１が粘着性を有しない場合、望ましくは、第一層２１の両主面に接して粘着層が配置される。なお、誘電体層２０が第二層２２を含む場合、第二層２２が粘着性を有しなくても、第二層２２の両主面に接するように粘着層が配置されなくてもよい。この場合、第二層２２の一方の主面に接して粘着層が配置されうる。誘電体層２０が第三層２３を含む場合、第三層２３が粘着性を有しなくても、第三層２３の両主面に接して粘着層が配置されなくてもよい。この場合、第三層２３の少なくとも一方の主面に接して粘着層が配置されうる。粘着層は、例えば、ゴム系粘着剤、アクリル系粘着剤、シリコーン系粘着剤、又はウレタン系粘着剤を含んでいる。
　電波吸収体１ａは、誘電損失材料及び磁性損失材料の少なくとも１つを含んでいてもよい。換言すると、電波吸収体１ａは、誘電損失型の電波吸収体であってもよいし、磁性損失型の電波吸収体であってもよい。この場合、インピーダンス整合膜１０ａに求められるρ／ｔは高くなりやすい。誘電体層２０が、誘電損失材料及び磁性損失材料の少なくとも１つを含んでいてもよい。インピーダンス整合膜１０ａをなす材料は磁性体であってもよい。
　電波吸収体１ａは、様々な観点から変更可能である。例えば、電波吸収体１ａは、図４に示す電波吸収体１ｂのように変更されてもよい。電波吸収体１ｂは、特に説明する部分を除き、電波吸収体１ａと同様に構成されている。電波吸収体１ａの構成要素と同一又は対応する電波吸収体１ｂの構成要素には同一の符号を付し、詳細な説明を省略する。電波吸収体１ａに関する説明は、技術的に矛盾しない限り電波吸収体１ｂにも当てはまる。
　図４に示す通り、電波吸収体１ｂは、粘着層４０ａをさらに備えている。電波吸収体１ｂにおいて、反射体３０は、誘電体層２０と粘着層４０ａとの間に配置されている。
　例えば、所定の物品に粘着層４０ａを接触させて電波吸収体１ｂを押し当てることによって、電波吸収体１ｂを物品に貼り付けることができる。これにより、電波吸収体付物品を得ることができる。
　粘着層４０ａは、例えば、ゴム系粘着剤、アクリル系粘着剤、シリコーン系粘着剤、又はウレタン系粘着剤を含んでいる。電波吸収体１ｂは、セパレータ（図示省略）をさらに備えていてもよい。この場合、セパレータは、粘着層４０ａを覆っている。セパレータは、典型的には、粘着層４０ａを覆っているときに粘着層４０ａの粘着力を保つことができ、かつ、粘着層４０ａから容易に剥離できるフィルムである。セパレータは、例えば、ＰＥＴ等のポリエステル樹脂製のフィルムである。セパレータを剥離することによって粘着層４０ａが露出し、電波吸収体１ｂを物品に貼り付けることができる。
　以下、実施例により本発明をより詳細に説明する。ただし、本発明は、以下の実施例に限定されない。まず、実施例及び比較例に関する評価方法について説明する。
　［ＴＥＭ観察］
　集束イオンビーム加工観察装置（日立ハイテクノロジーズ社製、製品名：ＦＢ－２０００Ａ）を用いて、各実施例及び各比較例に係る無孔膜及び各実施例及び各比較例に係る合金膜付フィルムにおける合金膜の断面観察用サンプルを作製した。その後、電界放射型透過電子顕微鏡（日立ハイテクノロジーズ社製、製品名：ＨＦ－２０００）を用いて、断面観察用サンプルを観察し、各実施例及び各比較例に係る無孔膜の厚みを測定した。また、各実施例及び各比較例に係る合金膜付フィルムにおける合金膜の厚みを同様にして測定した。結果を表１に示す。
　［比抵抗］
　非接触式抵抗測定装置（ナプソン社製、製品名：ＮＣ－８０ＭＡＰ）を用いて、JIS Z 2316に準拠して、渦電流測定法によって各実施例及び比較例に係る無孔膜のシート抵抗を測定した。各実施例及び各比較例において、上記のように測定した無孔膜の厚みと、上記のように測定した無孔膜のシート抵抗との積を求め、無孔膜をなす材料の比抵抗を決定した。無孔膜をなす材料の比抵抗を各実施例及び各比較例に係る合金膜付フィルムにおける合金膜をなす材料の比抵抗とみなした。結果を表１に示す。
　［電波吸収性能］
　各実施例及び比較例に係るサンプルに対し、１～９０ＧＨｚの周波数の電波を０°の入射角度で入射させ、JIS R 1679:2007に準拠して、各周波数における反射量の絶対値を特定した。各サンプルに対し、反射量の絶対値の最大値、その最大値を示す周波数（吸収ピーク周波数）、及び反射量の絶対値が２０ｄＢ以上を示す周波数のレンジを決定した。
　＜実施例１＞
　Ａｌ（アルミニウム）のターゲット材及びＳｉ（ケイ素）のターゲット材を用い、かつ、プロセスガスとしてアルゴンガスを用いて、ＤＣマグネトロンスパッタリングを行い、ＰＥＴフィルムの上にＡｌ－Ｓｉ合金膜を形成した。ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電と、Ｓｉ（ケイ素）のターゲット材が関与する放電とを同時に行った。このようにして、ＰＥＴフィルムの上に実施例１に係る無孔膜を形成した。実施例１に係る無孔膜をなす材料の比抵抗は、１．０×１０-4Ω・ｃｍであった。次に、メタルレーザーパターン加工機を用いて、実施例１に係る無孔膜に正方形状の複数の開口を形成し、実施例１に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、１２７μｍであり、隣り合う開口同士の距離の最小値は１０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　１０重量％のＳｎＯ2を含有するＩＴＯのターゲット材を用い、プロセスガスとしてアルゴン及び酸素を用いて、ＤＣマグネトロンスパッタリングを行い、ＰＥＴフィルムの上にＩＴＯ膜を形成した。その後、温度１５０℃の条件でＩＴＯ膜のアニール処理を１時間行って、ＩＴＯを多結晶化させ、反射体付フィルムを得た。反射体付フィルムの反射体のシート抵抗は２０Ω／□であった。次に、２．６の比誘電率を有するアクリル樹脂を６１５μｍの厚みに成形して、アクリル樹脂層Ａを得た。実施例１に係る合金膜付フィルムの合金膜がアクリル樹脂層Ａに接触するように実施例１に係る合金膜付フィルムをアクリル樹脂層Ａに重ねた。次に、反射体付フィルムにおけるＣｕ膜がアクリル樹脂層Ａに接触するように反射体付フィルムをアクリル樹脂層Ａに重ねた。このようにして、実施例１に係るサンプルを得た。
　＜実施例２＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に実施例２に係る無孔膜を形成するとともに、実施例２に係る合金膜付フィルムを得た。実施例２に係る無孔膜をなす材料の比抵抗が１．４×１０-3Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、実施例２に係る合金膜付フィルムにおける合金膜の厚みが３５０ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、実施例２に係る無孔膜に正方形状の複数の開口を形成し、実施例２に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、１２７μｍであり、隣り合う開口同士の距離の最小値は１０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、実施例２に係る合金膜付フィルムを用いた以外は、実施例１と同様にして、実施例２に係るサンプルを得た。
　＜実施例３＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に実施例３に係る無孔膜を形成するとともに、実施例３に係る合金膜付フィルムを得た。実施例３に係る無孔膜をなす材料の比抵抗が１．０×１０-5Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、実施例３に係る合金膜付フィルムにおける合金膜の厚みが５ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、実施例３に係る無孔膜に正方形状の複数の開口を形成し、実施例３に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、２６９μｍであり、隣り合う開口同士の距離の最小値は１０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、実施例３に係る合金膜付フィルムを用い、アクリル樹脂層Ａの代わりに、２．６の比誘電率を有するアクリル樹脂を６３０μｍの厚みに成形して得られたアクリル樹脂層Ｂを用いた以外は、実施例１と同様にして、実施例３に係るサンプルを得た。
　＜実施例４＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に実施例４に係る無孔膜を形成するとともに、実施例４に係る合金膜付フィルムを得た。実施例４に係る無孔膜をなす材料の比抵抗が５．０×１０-4Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、実施例４に係る合金膜付フィルムにおける合金膜の厚みが２５ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、実施例４に係る無孔膜に正方形状の複数の開口を形成し、実施例４に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、３５μｍであり、隣り合う開口同士の距離の最小値は１０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、実施例４に係る合金膜付フィルムを用い、アクリル樹脂層Ａの代わりに、２．６の比誘電率を有するアクリル樹脂を６０５μｍの厚みに成形して得られたアクリル樹脂層Ｃを用いた以外は、実施例１と同様にして、実施例４に係るサンプルを得た。
　＜実施例５＞
　実施例１と同様にして、ＰＥＴフィルムの上に実施例５に係る無孔膜を形成した。メタルレーザーパターン加工機を用いて、実施例５に係る無孔膜に正方形状の複数の開口を形成し、実施例５に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、１４μｍであり、隣り合う開口同士の距離の最小値は１μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、実施例５に係る合金膜付フィルムを用い、アクリル樹脂層Ａの代わりに、アクリル樹脂層Ｃを用いた以外は、実施例１と同様にして、実施例５に係るサンプルを得た。
　＜実施例６＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に実施例６に係る無孔膜を形成するとともに、実施例６に係る合金膜付フィルムを得た。実施例６に係る無孔膜をなす材料の比抵抗が７．８×１０-5Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、実施例４に係る合金膜付フィルムにおける合金膜の厚みが２５ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、実施例６に係る無孔膜に正方形状の複数の開口を形成し、実施例６に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、７０７μｍであり、隣り合う開口同士の距離の最小値は５０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、実施例６に係る合金膜付フィルムを用い、アクリル樹脂層Ａの代わりに、２．６の比誘電率を有するアクリル樹脂を６５０μｍの厚みに成形して得られたアクリル樹脂層Ｄを用いた以外は、実施例１と同様にして、実施例６に係るサンプルを得た。
　＜実施例７＞
　実施例１と同様にして、ＰＥＴフィルムの上に実施例７に係る無孔膜を形成した。メタルレーザーパターン加工機を用いて、実施例７に係る無孔膜に正方形状の複数の開口を形成し、実施例７に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、３５３６μｍであり、隣り合う開口同士の距離の最小値は２５０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　２．６の比誘電率を有するアクリル樹脂を１８５００μｍの厚みに成形して、アクリル樹脂層Ｅを得た。実施例１に係る合金膜付フィルムの代わりに、実施例７に係る合金膜付フィルムを用い、アクリル樹脂層Ａの代わりにアクリル樹脂層Ｅを用いた以外は、実施例１と同様にして、実施例７に係るサンプルを得た。
　＜実施例８＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に実施例１０に係る無孔膜を形成するとともに、実施例１０に係る合金膜付フィルムを得た。実施例１０に係る無孔膜をなす材料の比抵抗が１．０×１０-5Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、実施例１０に係る合金膜付フィルムにおける合金膜の厚みが２５ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、実施例１０に係る無孔膜に正方形状の複数の開口を形成し、実施例１０に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、４７１９２μｍであり、隣り合う開口同士の距離の最小値は６４０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　２．６の比誘電率を有するアクリル樹脂を５１３００μｍの厚みに成形して、アクリル樹脂層Ｆを得た。実施例１に係る合金膜付フィルムの代わりに、実施例８に係る合金膜付フィルムを用い、アクリル樹脂層Ａの代わりにアクリル樹脂層Ｆを用いた以外は、実施例１と同様にして、実施例８に係るサンプルを得た。
　＜比較例１＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に比較例１に係る無孔膜を形成するとともに、比較例１に係る合金膜付フィルムを得た。比較例１に係る無孔膜をなす材料の比抵抗が１．０×１０-3Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、比較例１に係る合金膜付フィルムにおける合金膜の厚みが２５ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、比較例１に係る無孔膜に正方形状の複数の開口を形成し、比較例１に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、１．４μｍであり、隣り合う開口同士の距離の最小値は１０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、比較例１に係る合金膜付フィルムを用いた以外は、実施例１と同様にして、比較例１に係るサンプルを得た。
　＜比較例２＞
　下記の点以外は、実施例１と同様にして、ＰＥＴフィルムの上に比較例１に係る無孔膜を形成するとともに、比較例１に係る合金膜付フィルムを得た。比較例１に係る無孔膜をなす材料の比抵抗が１．０×１０-6Ω・ｃｍとなるように、ＤＣマグネトロンスパッタリングにおいて、Ａｌ（アルミニウム）のターゲット材が関与する放電の放電電力に対する、Ｓｉ（ケイ素）のターゲット材が関与する放電の放電電力の比を調整した。加えて、比較例１に係る合金膜付フィルムにおける合金膜の厚みが２５ｎｍになるようにＤＣマグネトロンスパッタリングの条件を調整した。メタルレーザーパターン加工機を用いて、比較例１に係る無孔膜に正方形状の複数の開口を形成し、比較例１に係る合金膜付フィルムを得た。平面視において、開口の最大寸法は、７０７μｍであり、隣り合う開口同士の距離の最小値は１０μｍであった。平面視において、複数の開口は、それらの中心が正方形格子をなすように形成されていた。
　実施例１に係る合金膜付フィルムの代わりに、比較例２に係る合金膜付フィルムを用いた以外は、実施例１と同様にして、比較例２に係るサンプルを得た。
　表１に示す通り、実施例１～８に係るサンプルは所定の周波数の電波に対し良好な吸収性能を示しており、各実施例に係る合金膜付フィルムの合金膜により所望のインピーダンス整合がなされることが分かった。一方、比較例１及び２に係るサンプルは、所定の周波数の電波に対し良好な吸収性能を示すとは言い難く、各比較例に係る合金膜付フィルムの合金膜によりインピーダンス整合をなすことが難しいことが示唆された。このため、合金膜におけるρ／ｔの値が所定の値にあることがインピーダンス整合の観点から有利であることが示唆された。各実施例に係る合金膜付フィルムの合金膜は、高い開口率を有し、透明性を有していた。
Figure JPOXMLDOC01-appb-T000001
  

Claims (10)

  1. 　インピーダンス整合膜であって、
    　当該インピーダンス整合膜の主面に沿って規則的に形成された複数の開口を有し、
    　当該インピーダンス整合膜をなす材料の比抵抗を当該インピーダンス整合膜の厚みで割った値が１～３００Ω／□である、
    　インピーダンス整合膜。
  2. 　前記主面における前記開口の最大寸法は、７．５×１０4μｍ以下である、請求項１に記載のインピーダンス整合膜。
  3. 　隣り合う前記開口同士の距離の最小値は、０．１～６５０μｍである、請求項１又は２に記載のインピーダンス整合膜。
  4. 　前記厚みは、５～５００ｎｍである、請求項１～３のいずれか１項に記載のインピーダンス整合膜。
  5. 　前記比抵抗は、５×１０-6～２×１０-3Ω・ｃｍである、請求項１～４のいずれか１項に記載のインピーダンス整合膜。
  6. 　請求項１～５のいずれか１項に記載のインピーダンス整合膜と、
    　電波を反射する反射体と、
    　前記インピーダンス整合膜の厚み方向において前記インピーダンス整合膜と前記反射体との間に配置された誘電体層と、を備えた、
    　電波吸収体。
  7. 　前記開口の前記最大寸法は、吸収ピーク波長の１／４以下であり、
    　前記吸収ピーク波長は、当該電波吸収体に対し日本工業規格（JIS）R 1679：2007に基づいて測定される反射量の絶対値が最大となる電波の波長である、
    　請求項６に記載の電波吸収体。
  8. 　１ＧＨｚ以上の周波数を有する電波に対してインピーダンス整合をなす、請求項６又は７に記載の電波吸収体。
  9. 　前記反射体は、透明導電膜である、請求項７又は８に記載の電波吸収体。
  10. 　前記透明導電膜は、前記透明導電膜の主面に沿って規則的に形成された複数の開口を有する、請求項９に記載の電波吸収体。
PCT/JP2020/031879 2019-09-13 2020-08-24 インピーダンス整合膜及び電波吸収体 WO2021049284A1 (ja)

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JP2006179671A (ja) 2004-12-22 2006-07-06 Mitsubishi Gas Chem Co Inc 電波吸収体および電波吸収体の製造方法
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JP2006179671A (ja) 2004-12-22 2006-07-06 Mitsubishi Gas Chem Co Inc 電波吸収体および電波吸収体の製造方法
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