JP7473054B2 - Electromagnetic Wave Attenuation Film - Google Patents

Description

The present invention relates to an electromagnetic wave attenuation film that can capture incident waves and attenuate reflected waves.

Radio waves with a frequency band of several gigahertz (GHz) are used in mobile communications such as mobile phones, wireless LANs, and electronic toll collection systems (ETC).

As an example of an electromagnetic wave absorbing sheet that absorbs such electromagnetic waves, Non-Patent Document 1 proposes an electromagnetic wave absorber in which multiple metal patterns are periodically arranged in two layers, with circular metal patterns with slightly different diameters arranged on different layers, providing absorption characteristics in two bands.

Institute of Electronics, Information and Communication Engineers Transactions B Vol. J103-B No. 12 pp. 684-686

However, when a radio wave absorber is created by providing a conductive element on one surface of a base material and stacking multiple layers of these to form an absorbing layer, a deviation in the positional accuracy between the layers may occur due to elongation or deflection of the laminated film on which the conductive elements are provided, resulting in a deviation in the absorption frequency. The absorber proposed in Non-Patent Document 1 had the problem that dielectric substrates such as FR4 on which a predetermined conductive pattern is formed must be precisely bonded and stacked.
In addition, there are concerns that the frequency and angular characteristics may change due to misalignment between the elements caused by deterioration of the overlapping parts over time. In addition, from the standpoint of process and cost, it is not desirable to increase the number of substrates on which elements are provided.
An object of the present invention is to solve such conventional problems and to easily and inexpensively obtain an electromagnetic wave attenuation film which has little shift in absorption peak frequency and little change in frequency characteristics and angular characteristics over time.

In order to solve the above problems, one representative electromagnetic wave attenuation film of the present invention is an electromagnetic wave attenuation film that includes an electromagnetic wave attenuation base having a dielectric substrate having a front and a back surface, a thin-film conductive layer disposed on both the front and back surfaces of the dielectric substrate, a support layer disposed on the back surface of the electromagnetic wave attenuation base, and a flat inductor disposed on the back surface of the support layer, the thin-film conductive layer including a plurality of conductive elements.

The present invention can provide a thin electromagnetic wave attenuation film that can attenuate radio waves in the millimeter wave band. In addition, by simultaneously forming a thin-film conductive layer on the front and back of a single-layer substrate, the positional accuracy of the thin-film conductive layer can be ensured, making it possible to easily manufacture an electromagnetic wave attenuation film that has absorption performance at the desired frequency.

1 is a schematic plan view showing an electromagnetic wave attenuation film according to a first embodiment of the present invention. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. 1. 1 is a cross-sectional view of a thin-film conductive layer disposed on a dielectric via an adhesive layer and patterned. 1 is a cross-sectional view of a flat inductor formed in a mesh shape. 3A to 3C are schematic diagrams showing examples of the shape of a thin-film conductive layer in plan view. 3A to 3C are schematic diagrams showing examples of combinations of shapes of thin-film conductive layers in plan view. 1 is a graph showing the relationship between the size of a conductive element and the wavelength of an electromagnetic wave that is attenuated. 11 is an image showing simulation results of electric field strength for an example distance between a front conductive element and a rear conductive element. 11 is an image showing simulated electric field strength results for different example distances between the front conductive element and the back conductive element. FIG. 2 is a schematic plan view showing an electromagnetic wave attenuation film according to an application of the first embodiment of the present invention. 13 is a graph showing a simulation result of the attenuation of electromagnetic waves depending on a change in the thickness of a conductive element. FIG. 4 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention. 13 is a schematic diagram showing a part of a cross section taken along line II-II in FIG. 12. FIG. 2 is a schematic diagram showing an example of a part of a cross section taken along line II in FIG. 1 when a blackening layer is provided. 2 is a schematic diagram showing another example of a part of the cross section taken along line II in FIG. 1 in the case where a blackening layer is provided. FIG. 2 is a schematic diagram showing another example of a part of the cross section taken along line II in FIG. 1 in the case where a blackening layer is provided. FIG. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. 1 when a top coat layer is provided. FIG. FIG. 2 is a schematic diagram showing a part of a cross section of the electromagnetic wave attenuation film shown in Examples 1 to 6. FIG. 13 is a schematic diagram showing a part of a cross section of the electromagnetic wave attenuation film shown in Example 7. FIG. 21 is a schematic plan view showing a portion of the electromagnetic wave attenuation film of Example 18. FIG. 13 is a schematic diagram showing a portion of a cross section of the electromagnetic wave attenuation film of Example 18 taken along line II. FIG. 3 is a schematic diagram showing a portion of a cross section of the electromagnetic wave attenuation film of Example 18 taken along line III-III. 1 is a graph showing the electromagnetic wave attenuation characteristics of Example 1. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 2. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 3. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 4. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 5. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 6. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 7. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 8. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 9. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 10. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 11. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 12. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 13. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 14. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 15. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 16. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 17. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 18. 13 is a graph showing the electromagnetic wave attenuation characteristics of Examples 12 and 13. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 19. 1 is a graph showing the electromagnetic wave attenuation characteristics of Reference Example 1. 1 is a graph showing electromagnetic wave attenuation characteristics of Reference Examples 2 and 3. 1 is a schematic diagram showing a part of a cross section of an electromagnetic wave attenuation film of Comparative Example 1. FIG. 1 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 1. 13 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 2. 13 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 3.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings. Note that the present invention is not limited to this embodiment. In addition, in the description of the drawings, the same parts are indicated by the same reference numerals. Furthermore, the reference numerals may be omitted for the same parts.

When disclosing embodiments, directions may be indicated using the x-, y-, and z-axes shown on the drawings. Unless otherwise specified, "plane" refers to the xy plane, "planar view" refers to the view from the z-axis direction, "plan view" refers to the surface seen from the z-axis direction, and "planar shape" and "planar shape" refer to the shape of the drawing seen from the z-axis direction.

In addition, in the disclosure of the embodiments, the "front surface" of an object means the surface when the object is viewed from the positive side of the z axis, the "back surface" means the surface when the object is viewed from the negative side of the z axis, and the "side surface" means the outer peripheral surface sandwiched between the front surface and the back surface. The "thickness direction" means the z axis direction.

In addition, in the disclosure of the embodiments, "center of gravity" means the center of gravity in the planar shape.

[First embodiment]
Fig. 1 is a schematic plan view showing an electromagnetic wave attenuation film 1 according to a first embodiment of the present invention. Fig. 2 is a schematic view showing a part of a cross section taken along line II in Fig. 1. For example, the cross section is taken between α and β on line II.

The electromagnetic wave attenuation film 1 includes a dielectric substrate (dielectric layer) 10, an electromagnetic wave attenuation base 20 composed of a thin-film conductive layer 30 formed on the front surface 10a of the dielectric substrate 10, a thin-film conductive layer 31 formed on the rear surface 10b of the dielectric substrate 10, a support layer 11 formed on the rear surface of the rear thin-film conductive layer 31, and a flat inductor 50 formed on the rear surface of the support layer 11. The thin-film conductive layers 30 and 31 are thin conductive layers. The thin-film conductive layers 30 and 31 may include a plurality of conductive elements (hereinafter, the thin-film conductive layers may be referred to as conductive elements when considering specific shapes, arrangements, etc.). The flat inductor 50 is conductive, and generates a current near the surface inside the flat inductor 50 due to an external magnetic flux. In addition, the flat inductor 50 has a function of generating a magnetic field near the surface outside the flat inductor 50 in accordance with the current. The shape of the flat inductor 50 can be a flat plate (Slab). The front surface can be the surface on which the electromagnetic wave is incident. The back surface is the surface of the dielectric substrate opposite the front surface.
In addition, when the electromagnetic wave attenuated by the electromagnetic wave attenuation film has a frequency f at which it has a single minimum value, this frequency f is defined as the attenuation central frequency f. In addition, when the electromagnetic wave attenuated by the electromagnetic wave attenuation film has multiple minimum values, the frequency that is the average of multiple frequencies that are −3 dB from the minimum value with the greatest attenuation is defined as the attenuation central frequency f. The attenuation central wavelength can be determined by dividing the speed of light in the dielectric substrate and the support layer by the attenuation central frequency f described below.
The electromagnetic wave attenuation film 1 may also be provided with a topcoat layer 200 (described later) for achieving impedance matching with air and for improving the weather resistance of the sheet.

(Electromagnetic Wave Attenuating Substrate)
As shown in FIG. 2, the electromagnetic wave attenuating substrate 20 has a configuration in which thin-film conductive layers 30, 31 are disposed on the front surface 10a and rear surface 10b of a dielectric substrate 10.
A representative example of the material constituting the dielectric substrate 10 is a synthetic resin. The type of synthetic resin is not particularly limited as long as it has sufficient strength, flexibility and processability as well as insulation. This synthetic resin can be a thermoplastic resin. Examples of synthetic resins include polyesters such as polyethylene terephthalate (PET); polyarylene sulfides such as polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamide, polyimide, polyamideimide, polyethersulfone, polyetheretherketone, polycarbonate, acrylic resin, polystyrene, etc., but are not limited thereto. These materials may be used alone, or two or more types may be mixed, or a laminate may be formed. In addition, the dielectric substrate 10 may contain conductive particles, insulating particles, magnetic particles, or a mixture thereof.
To form the electromagnetic wave attenuating substrate 20, a laminate in which thin-film conductive layers 30, 31 are formed on both sides of a dielectric substrate 10 via an anchor layer and an adhesive layer may be used.
The dielectric substrate 10 also has a bending rigidity of 7000 MPa·mm ⁴ or less.

In an embodiment of the present invention, the thickness of the dielectric substrate and the support layer can be made sufficiently thin relative to the wavelength of the electromagnetic wave. It is known that when the dielectric substrate and the support layer are sufficiently thin relative to the wavelength of the electromagnetic wave, no traveling waves are generated in the dielectric substrate and the support layer. "Sufficiently thin" can be less than 1/2 of the wavelength. When it is less than 1/2 of the wavelength, the traveling wave is not guided. This is a phenomenon called cutoff of the electromagnetic wave. Furthermore, it can be less than 1/10 of the wavelength. In general, when the difference in the propagation distance of the electromagnetic wave is less than 1/10 of the wavelength, no substantial phase difference occurs. In other words, when the distance between the conductive element and the planar inductor is less than 1/10 of the wavelength at the dielectric substrate and the support layer, the electromagnetic wave re-emitted by the conductive element and the reflected wave of the planar inductor do not generate a substantial phase difference due to the distance. It is believed that electromagnetic waves are not guided in a sufficiently thin dielectric substrate and support layer sandwiched between conductors, and usually, when the electromagnetic wave becomes so thin, it is cut off (cut off), and no electric field or magnetic field is localized in such a dielectric substrate and support layer. In addition, this wavelength in the embodiment of the present invention can be the attenuation central wavelength. Furthermore, unexpectedly, attenuation is obtained even when the dielectric substrate and support layer are 1/100th of the wavelength or less. Such a thickness is the same level as the unevenness of the highest precision mirror surface, and attenuation is obtained with a structure that is substantially thin compared to the scale of the electromagnetic wave.

As a result of various experiments and simulations, the inventors found that even in a sufficiently thin dielectric substrate and support layer, stationary localization of the electric field and magnetic field due to electromagnetic waves occurs. In addition, the resonant frequency band and the amount of absorption change depending on the thickness of the support layer, so the design needs to be changed accordingly. The thickness of the dielectric substrate 10 can be 5 μm or more and 300 μm or less. Furthermore, the thickness of the dielectric substrate 10 can be 5 μm or more and 100 μm or less. This is thinner than 1/2 the wavelength of the millimeter wave band, and even thinner than 1/10 the wavelength of the millimeter wave band. Therefore, the electromagnetic wave attenuation film is capable of attenuating electromagnetic waves in the millimeter wave band, even though it is a thin film. The thickness of the dielectric substrate 10 is constant or variable. Similarly, the thickness of the support layer 11 can be 5 μm or more and 250 μm or less. Furthermore, it can be 10 μm or more and 200 μm or less. Furthermore, it can be 15 μm or more and 150 μm or less.

In an embodiment of the present invention, the electromagnetic wave attenuating substrate 20 may have a support layer 11 and an adhesive layer 12 therebetween. The support layer 11 may be a single layer or a multilayer. The material of the support layer 11 may be the same as that of the dielectric substrate 10. For example, the support layer 11 may be a single material, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, or silicone resin. The support layer 11 may be an extruded film. The extruded film may be a non-stretched film or a stretched film. The support layer may also be formed by coating on the back surface of the electromagnetic wave attenuating substrate 20. The adhesive layer 12 may be composed of two layers, a molding layer and an anchor layer. Furthermore, an adhesive layer may be provided to improve adhesion between the adhesive layer 12 and the conductive element. The adhesive layer 12, the molding layer, the anchor layer, and the adhesive layer may be made of the same material as that constituting the dielectric substrate.

The thin-film conductive layer 30 formed on the front surface 10a of the dielectric substrate 10 and the thin-film conductive layer 31 formed on the back surface 10b cover the entirety or part of the front surface 10a and the back surface 10b in a plan view of the electromagnetic wave attenuation film 1. The thin-film conductive layers 30 and 31 can be formed by forming layers of a conductive material directly on both sides of the dielectric substrate 10 by vapor deposition or sputtering, as shown in FIG. 2, and then patterning the layers by etching or the like. FIG. 3 is a cross-sectional view of a thin-film conductive layer disposed on a dielectric via an adhesive layer and patterned. The thin-film conductive layers 30 and 31 can be formed by forming a thin-film conductive layer by a method of laminating a conductive material foil to the dielectric substrate 10 via an adhesive layer 13, as shown in FIG. 3, and then patterning and arranging the conductive material by etching or the like. As shown in FIG. 3, even when a conductive pattern is formed on the dielectric substrate 10 via an adhesive layer 13, the adhesive layer 13 is patterned to the same dimensions as the conductive pattern. Therefore, even if stress is applied by bending the electromagnetic wave attenuation film on which the conductive pattern is formed on the dielectric substrate 10, the stress is separated for each conductive pattern, so there is no misalignment between the conductive patterns formed on the front and back of the dielectric.

The flat inductor 50 covers all or part of the back surface of the support layer 11. As long as the performance of the electromagnetic wave attenuation film 1 is not significantly impaired, there may be areas that are not covered by the thin film conductive layers 30, 31 or the flat inductor 50, for example, on part of the periphery of the electromagnetic wave attenuation film 1.

The materials of the thin-film conductive layers 30, 31 and the flat inductor 50 are not particularly limited as long as they are conductive. From the viewpoint of corrosion resistance and cost, aluminum, copper, silver, gold, platinum, tin, nickel, cobalt, chromium, molybdenum, iron and alloys thereof are preferred. The thin-film conductive layers 30, 31 and the flat inductor 50 can be formed by vacuum deposition on the dielectric substrate 10, or by bonding a conductive material foil to the dielectric substrate 10 via an adhesive layer 13. The thickness of the adhesive layer 13 for bonding the conductive material foil to the dielectric can be 10 nm or more and 2000 nm or less. If it is less than 10 nm, the adhesion of the conductive material foil to the dielectric may decrease, and if it exceeds 2000 nm, productivity may decrease. The adhesive layer 13 also has a bending rigidity of 7000 MPa·mm4 or ^less . Furthermore, the ratio of the thickness of the thin-film conductive layers 30, 31 to the thickness of the adhesive layer 13 is preferably 1:2.
The planar inductor 50 may be a conductive compound. Furthermore, the planar inductor 50 may be a continuous surface or may have a pattern such as a mesh or patch.
The thickness of the thin film conductive layers 30, 31 can be 10 nm or more and 1000 nm or less. If the thickness is less than 10 nm, the function of attenuating electromagnetic waves may be reduced. If the thickness exceeds 1000 nm, the productivity may decrease.
The flat inductor 50 can be a casting, a rolled metal plate, a metal foil, a vapor deposition film, a sputtered film, or a plating. The thickness of the rolled metal plate can be 0.1 mm or more and 5 mm or less. The thickness of the metal foil can be 5 μm or more and less than 100 μm. When the flat inductor 50 is a vapor deposition film, a sputtered film, or a plating film, the thickness can be 0.5 μm or more and less than 5 mm. The thickness of the flat inductor 50 can be 0.5 μm to 5 mm. When the flat inductor 50 is a casting, the thickness is not specified, but the maximum dimension can be 10 mm or more. The thickness of the flat inductor 50 can be equal to or more than the skin depth determined by the attenuation central wavelength. The thickness of the flat inductor 50 can be greater than the thickness of the thin film conductive layers 30 and 31.
The thin-film conductive layers 30, 31 and the planar inductor 50 may be made of the same metal type. This same metal type may be the same pure metal or an alloy of the same metal (e.g., both are aluminum alloys), or the thin-film conductive layers 30, 31 may be a pure metal and the planar inductor 50 may be an alloy of the metal of the thin-film conductive layer 30. Also, the thin-film conductive layers 30, 31 and the planar inductor 50 may be made of different metal types.
4 is a cross-sectional view of a flat inductor formed in a mesh shape. When the flat inductor 50 is formed in a mesh shape, it is considered that light transmission and moisture permeability can be obtained. By having moisture permeability, it is considered that there is an advantage that it is easy to handle because of high moisture permeability even when an environmentally friendly water-based adhesive is used as the adhesive used for pasting it to wallpaper, etc.

The shapes and combinations of the conductive elements 30 and 31 will be described. Fig. 5 is a schematic diagram showing an example of the shape of the conductive element in plan view. Examples include a linear shape as shown in Fig. 5(a) and a planar shape as shown in Fig. 5(b). The linear shape includes an open-ended shape consisting of a straight line, a Y-shape, a cross, or a combination of these shapes, and a loop shape such as a circle, an ellipse, or a polygon. The planar shape includes a polygonal square, a hexagon, a cross, other polygons, a circle, and an ellipse. The corners of the square, hexagon, cross, and other polygons can be rounded, but are not limited to these.
6 is a schematic diagram showing an example of a combination of shapes of conductive elements in a plan view. A combination of conductive elements of different sizes is also possible, and a combination of a single shape or a combination of multiple shapes is also possible.

The electromagnetic wave attenuation film 1 is believed to exhibit a unique mechanism at specific wavelengths due to the above-mentioned configuration.

Electromagnetic waves incident on the electromagnetic wave attenuation film of the present invention behave as follows. Specifically, the electromagnetic field and current generated by the incident wave are considered to be as follows.

First, the fluctuation of the magnetic flux of the incident wave that has passed through the conductive element induces an alternating current in the planar inductor 50 that is parallel to the plane of incidence of the planar inductor 50 according to Faraday's law. This alternating current generates a fluctuating magnetic field in the dielectric substrate adjacent to the planar inductor 50 according to Ampere's law. In addition, the fluctuating magnetic field becomes a fluctuating magnetic flux with the magnetic permeability as a coefficient.

The electric field generated by the fluctuating magnetic flux normally induces a current in a direction that suppresses the magnetic flux according to Henry's law. However, in the case of the configuration of the present application, contrary to expectations, it acts in the opposite direction, strengthening the current. As a result, a current greater than that induced by the incident wave flows in the conductive element. In other words, although the area of the conductive element is smaller than the area of the planar inductor 50, it can generate a current of the same magnitude as that of the planar inductor 50.

The direction of the current generated in this conductive element is opposite to that of the flat inductor 50. A closed circuit can be formed by the opposite currents flowing in the conductive element and the flat inductor 50, and the displacement current flowing between them. If the closed circuit is only between the conductive element and the flat inductor 50, and no electric flux is generated horizontally to the electromagnetic wave attenuation film in the space outside the electromagnetic wave attenuation film, no reflected wave can be generated. In addition, the reflected wave by the flat inductor 50 and the electromagnetic wave re-emitted by the current in the conductive element are out of phase with each other by π, so they cancel each other out.

Due to the above principle, reflected waves are attenuated by the electromagnetic wave attenuation film. From the viewpoint of energy, it is believed that multiple mechanisms act synergistically as follows:

The first mechanism is the generation of a non-propagating periodically oscillating electromagnetic field by the incident wave. First, the plate inductor 50 induces a magnetic flux in the tangential direction of the plate inductor 50 to the incident wave. The induced magnetic flux generates an electric field in a direction extending from a pair of opposing sides of the thin-film conductive layers 30, 31 (i.e., the conductive element) and perpendicular to the plate inductor 50. Next, when the electromagnetic wave is incident on the plate inductor, the fluctuating magnetic flux induces a current so as to approach the surface of the plate inductor. The current induced in the plate inductor generates a magnetic field in the dielectric substrate 10 and the support layer 11, which are close to the surface of the plate inductor. This electric field and the current in the conductive element and the plate inductor 50 generate a magnetic field between the conductive element and the plate inductor 50 in the same direction as the magnetic flux induced by the plate inductor 50. Here, the conductive element is shaped like a plate and is made of metal. The electric field generated in the dielectric substrate fluctuates with the same period as the period of the incident wave. The periodic variation of the magnetic field periodically varies the electric field between the thin-film conductive layers 30, 31 and the planar inductor 50. As a result, a periodically varying electromagnetic field that does not travel is generated between the thin-film conductive layers 30, 31 and the planar inductor 50. As will be shown later by a current density simulation, an AC current is induced in the conductive element by the magnetic field in the periodically varying electromagnetic field. In addition, the periodically varying electric field generates a periodically varying potential in the conductive element. The electromagnetic field does not travel but remains in place, and the induced AC current loses power, resulting in the energy of the electromagnetic field being converted into heat and absorbing the electromagnetic waves. In addition, it is considered that the AC current induced in the conductive element re-emits the electromagnetic waves from the surface of the conductive element opposite to the surface in contact with the dielectric substrate 10 and the support layer 11.
In other words, it is considered that part of the energy of the electromagnetic wave captured by the electromagnetic wave attenuation film is converted into heat energy, and the rest is re-emitted. According to the classical theory of electromagnetic fields represented by Maxwell's equations, the frequency of the induced alternating current is the same as that of the incident wave, so the frequency of the re-emitted electromagnetic wave is the same as that of the incident wave. As a result, an electromagnetic wave with the same frequency as the incident wave is re-emitted. If an oscillating electromagnetic field is considered as a quantum, it is also possible that the quantum loses energy and an electromagnetic wave with a longer wavelength and lower energy is re-emitted. It is also considered that the re-emission includes stimulated emission and spontaneous emission due to the incident electromagnetic wave. It is considered that stimulated emission is the emission of an electromagnetic wave that is coherent with the reflected wave in which the incident wave is reflected in the reflection direction of the incident wave, i.e., the specular reflection direction. It is considered that spontaneous emission attenuates with time. It is also considered that the spatial distribution of spontaneous emission is close to Lambertian reflection when the electromagnetic wave attenuation film does not have a diffraction structure, an interference structure, or a refraction structure.
The attenuation central wavelength correlates with the dimension W1 (see FIG. 7; hereinafter, sometimes referred to as "width W1") in the planar direction of the conductive elements 30, 31. FIG. 7 is a graph showing the relationship between the dimension of the conductive element and the wavelength of the electromagnetic wave to be attenuated. In FIG. 7, W1 represents the length of one side of a square. That is, the wavelength of the electromagnetic wave that is suitably attenuated by the first mechanism can be changed by changing the dimension W1, and in the electromagnetic wave attenuation film 1, the attenuation of the electromagnetic wave can be set easily and with a high degree of freedom. Therefore, a configuration can be made that can easily capture linearly polarized electromagnetic waves in the band of 15 GHz or more and 150 GHz or less.

It is considered that the periodic fluctuation of the electromagnetic field that does not travel occurs between the opposing sides in the planar shape of the conductive element. Therefore, in order for the first mechanism to occur, it is preferable that the sides of a certain length face each other. Based on this and the results of the study by the inventors, a section in the thin-film conductive layer with a width W1 of 0.25 mm or more can be used as a conductive element. When a conductive element can have multiple W1s, the maximum value among them can be defined as W1 for that conductive element. By setting W1 within the range of about 0.25 mm to 4 mm, it becomes possible to attenuate electromagnetic waves in the band of 15 GHz or more and 150 GHz or less. The relationship between the frequency of the attenuated electromagnetic wave and the width of the conductive element can be expressed as a straight line on a graph in which each is logarithmic, as shown in FIG. 7. In other words, the frequency of the attenuated electromagnetic wave is a power function of the width of the conductive element. The power of the function is approximately -1, and is almost inversely proportional.
The thin-film conductive layer may include a plurality of conductive elements of different types each having a different dimension W1. In this case, the attenuation peaks of the respective electromagnetic waves are overlapped, and the band of the electromagnetic waves that can be attenuated can be broadened.

The second mechanism is the confinement of the electromagnetic field by the thin-film conductive layers 30, 31 and the planar inductor 50. In the electromagnetic wave attenuation film 1, the dielectric substrate 10 and the support layer 11 are sandwiched between the thin-film conductive layers 30, 31 and the planar inductor 50. Therefore, the electric field generated in the dielectric substrate 10 and the support layer 11 of the electromagnetic wave attenuation film 1 by the electromagnetic wave is confined in the dielectric substrate 10 and the support layer 11 between the thin-film conductive layers 30, 31 including the conductive elements and the planar inductor 50 by the charge and current of the conductive elements. That is, the conductive elements suppress the electromagnetic field and confine the electromagnetic field in the dielectric substrate 10 and the support layer 11. That is, the conductive elements can function as a choke. In other words, the conductive elements can be a choke plate that functions as a choke.
It is also believed that the magnetic flux is induced by the periodic fluctuation of the trapped electric field. This causes the oscillating electromagnetic field to accumulate, increasing the energy density of the electromagnetic field. In general, the higher the energy density, the easier it is to attenuate, so this mechanism efficiently attenuates the electromagnetic wave. In addition, in the second mechanism, the higher the dielectric tangent of the dielectric substrate 10 and the support layer 11, the greater the energy loss of the electromagnetic field accumulated in the dielectric substrate. In addition, the magnetic field accumulated in the dielectric substrate is accompanied by a large current in the conductive element, and the electric field accumulated in the dielectric substrate generates a large potential difference. The large current and the large potential difference can increase the power loss, which is the product of the two. The energy of the electromagnetic wave is consumed as power loss, and as a result, the electromagnetic wave is attenuated.

The third mechanism is power loss in an electric circuit including a capacitor formed by the opposing thin-film conductive layers 30, 31 and the planar inductor 50, and the dielectric substrate 10 and support layer 11 therebetween. In the electromagnetic wave attenuation film 1, the dielectric substrate 10 and support layer 11 are sandwiched between the thin-film conductive layers 30, 31 and the planar inductor 50. Therefore, the dielectric substrate 10 and support layer 11 function as a capacitor. Therefore, electromagnetic waves incident on the dielectric substrate 10 and support layer 11 of the electromagnetic wave attenuation film 1 are attenuated by the electric circuit including the capacitor. The larger the capacitance of the capacitor, the more charge it can store, and thus the more energy it can handle.
Since the capacitance is inversely proportional to the thickness of the dielectric substrate 10 and the support layer 11, from this viewpoint, it is more preferable that the thickness of the dielectric substrate 10 and the support layer 11 is thin. Furthermore, since the distance between the thin-film conductive layers 30, 31 and the planar inductor 50 is determined by the thickness of the dielectric substrate 10 and the support layer 11, the electrical resistance between the thin-film conductive layers 30, 31 and the planar inductor 50 is proportional to the thickness of the dielectric substrate 10 and the support layer 11. If the resistance of the dielectric substrate 10 and the support layer 11 is small, the leakage current in the dielectric substrate 10 and the support layer 11 increases, and the current flowing in the electric circuit including the capacitor of the thin-film conductive layer 30 and the planar inductor 50 increases. Therefore, the power loss due to the leakage current is likely to increase, and the energy of the electromagnetic wave is likely to be absorbed due to the power loss. Furthermore, in the electromagnetic wave attenuation film 1 according to the embodiment of the present invention, even if the thickness of the dielectric substrate 10 and the support layer 11 at the location where the conductive element is arranged is changed, the wavelength of the attenuated electromagnetic field does not shift, so that the thickness of the dielectric substrate 10 and the support layer 11 can be designed according to the characteristics of the electric circuit including the capacitor.

As described above, electromagnetic waves incident on the electromagnetic wave attenuation film 1 are captured by generating an electromagnetic field in the dielectric substrate 10 and support layer 11 close to the surface of the planar inductor by the first mechanism, and then confining the electromagnetic field generated by the electromagnetic wave by the second mechanism. In this way, the electromagnetic wave attenuation film 1 is capable of capturing electromagnetic waves. The captured electromagnetic waves are attenuated by the electric field loss and power loss by the second mechanism, and the power loss by the electrical circuit by the third mechanism.

In the electromagnetic wave attenuation film 1 of the first embodiment, as shown in FIG. 2, the thin-film conductive layer 30 formed on the front surface 10a of the dielectric substrate 10 and the thin-film conductive layer 31 formed on the rear surface 10b include conductive elements. When the distance on the same plane between the center of gravity of the conductive element arranged on the front surface 10a of the dielectric substrate 10 and the center of gravity of the conductive element arranged on the rear surface 10b is l, and the shortest distance from the center of gravity of the conductive element to the plate end is a, it is possible to create an absorber that can obtain attenuation at a target frequency by arranging the conductive element at a position that satisfies the following formula (1). FIG. 8 is an image showing the simulation result of the electric field intensity for an example of the distance between the conductive element on the front surface and the conductive element on the rear surface. When the distance l is arranged at a position 2a that satisfies the following formula (1) and an electromagnetic wave is incident from the front surface side, as shown in FIG. 8, it can be seen that a strong electric field is generated as a resonant coupling is observed between the conductive element 30 on the front surface and the conductive element 31 on the rear surface. This makes it possible to efficiently attenuate electromagnetic waves.
l≦5.2a... (1)
Fig. 9 is an image showing the simulation result of the electric field intensity for another example of the distance between the front conductive element and the back conductive element. When the conductive element is arranged with l set to 5a, which is larger than 4a, it is possible to attenuate the electromagnetic wave, but as shown in Fig. 9, the front conductive element and the back conductive element resonate independently, and the resonance of the front and back conductive elements is not combined, so the effect of arranging the conductive elements on the front and back is reduced. Furthermore, when l is 5.2a or more and the distance between the front and back conductive elements is large, it becomes difficult to attenuate the electromagnetic wave at the target frequency.

In the electromagnetic wave attenuation film 1, the role played by the third mechanism is also important. When electromagnetic waves are incident on the front surface 10a of the dielectric substrate 10, an electric field is generated in the dielectric substrate 10, and an electric field is also generated in the support layer 11 disposed between the rear surface 10b and the planar inductor 50, resulting in the electromagnetic field being confined below the conductive element. In other words, an electromagnetic field with high energy density is generated below the conductive element. It is believed that the confined electromagnetic field is attenuated by power loss due to the second mechanism and dielectric loss due to the third mechanism.

[First embodiment (application)]
FIG. 10 is a schematic plan view showing an electromagnetic wave attenuation film according to an application of the first embodiment of the present invention. FIG. 10(a) is an overall plan view, and FIG. 10(b) is a partial plan view. In this application, a plurality of front conductive elements 30 and rear conductive elements 31 are arranged in a checkerboard pattern, and the front and rear conductive elements are designed to have different sizes. FIG. 10(a) shows the distance l in the planar direction of the center of gravity of the front and rear conductive elements, and the shortest distances a and a' from the center of gravity of the rear or front conductive element to the plate end. In FIG. 10(a), when referring to the size of the rear conductive element (or the front conductive element), a (or a') can be a representative parameter, but is not limited to this, and may be, for example, an area. In this application, the conductive elements may be arranged so that the shortest distance from the center of gravity to the plate end of the front or rear conductive element satisfies formula (1). FIG. 10(b) shows the space (s) in the front and rear conductive elements. The other configurations are the same as those in the first embodiment, so a description will be omitted.

In this application, it is possible to obtain a dual-band electromagnetic wave attenuation film using different absorption peak frequencies based on the phenomenon that the front conductive element and the back conductive element resonate at their respective frequencies. Furthermore, as described below, in this application, it has been found that when the dual-band absorption peak frequencies are spaced apart by a certain distance, good attenuation characteristics tend to be obtained by designing the size (a') of the front conductive element to be smaller than the size (a) of the back conductive element. As a suitable example, in a dual-band with absorption peak frequencies spaced apart by a frequency interval of 28 GHz band and 39 GHz band or more, good attenuation characteristics are obtained when the size of the front conductive element is smaller than the size of the back conductive element. Specifically, it is expected that the above tendency will be observed if the dual-band has absorption peak frequencies spaced apart by a frequency interval of 29.5 GHz, which is the upper limit of the 28 GHz band, and 34 GHz, which is the lower limit of the 39 GHz band, or more.
This is thought to be because forming a larger conductive element on the front side where the electromagnetic waves are incident contributes to attenuation of low-frequency electromagnetic waves through resonance, but impedance matching cannot be achieved for high-frequency electromagnetic waves, and it increases reflection as a reflector, resulting in a deterioration of attenuation characteristics. On the other hand, when the dual-band absorption peak frequencies are close to each other, there was no significant difference in attenuation characteristics due to the difference in the size relationship of the conductive elements on the front and back. Note that arranging the conductive elements on the front and back in a checkerboard pattern is desirable in terms of improving dual-band characteristics, as it suppresses coupling between frequencies and makes it easier to control the resonating frequency of each conductive element, but this arrangement is not limited to this.

In conventional technology, it was believed that making the resonating conductor thicker than the skin depth would generate sufficient AC current in the resonant layer, and that the power loss of that AC current would attenuate electromagnetic waves. However, the inventors discovered that when the thickness of the conductive element is less than the skin depth, the attenuation of electromagnetic waves actually increases.

Figure 11 is a graph showing the results of a simulation of the attenuation of electromagnetic waves depending on the thickness of the conductive element. The conductive element is made of aluminum. The incident wave is a linearly polarized sine wave that is incident perpendicularly to the electromagnetic attenuation film. In the simulation, the flat inductor is a perfect conductor. The attenuation of electromagnetic waves as an electromagnetic attenuation film is indexed by monostatic RCS, which is based on the case of only a flat inductor. The vertical axis showing the attenuation of electromagnetic waves is expressed in decibels. Monostatic RCS (Radar Cross-Section) is an index that indicates the ease of detection of an object by a monostatic radar, and can be calculated by the following relational expression. Note that a monostatic radar transmits and receives at the same point.

As a result of the simulation, large attenuation of electromagnetic waves was observed when the thickness was 40 nm or more and 400 nm or less, as shown in Fig. 11. Conversely, when the thickness was less than 40 nm, a decrease in attenuation of electromagnetic waves was observed.
In addition, when the conductive element is provided with a blackening layer, stable film formation is possible if the combined thickness of the conductive element and the blackening layer is 1000 nm or less.

The phenomenon shown in FIG. 11 shows an interesting relationship with the skin depth. The skin depth of aluminum at a frequency of 41 GHz is about 400 nm. That is, when the thickness of the conductive element is equal to or less than the skin depth of the material, the attenuation of the electromagnetic wave increases. Also, when it is less than 1/e2 of the skin depth, the attenuation of the electromagnetic wave decreases. This is because, when the conductive layer is thicker than the skin depth, sufficient resistance is not obtained, and the voltage drop required for power loss is not obtained, and the current is concentrated only near the center of the conductive element, and the current in the area where the potential difference occurs is reduced. On the other hand, even if the thickness of the conductive layer is equal to or less than the skin depth, it is considered that a sufficient current for power loss is not obtained when it is less than 1/e2 of the skin depth. Needless to say, the power loss is given as the product of the current and the voltage. That is, it can be said that sufficient attenuation of the electromagnetic wave is obtained within a range in which the following LN function formula (2), which is expressed using the natural logarithm of the value of the thickness T of the conductive element normalized by the skin depth d, is satisfied.
−2≦ln(T/d)≦0 … (2)
Furthermore, when a metal with low admittance is used for the conductive element, electromagnetic wave attenuation can be obtained even within the range of the following formula (3). Furthermore, when the ratio of the area of the conductive element to the front surface of the dielectric substrate is large, electromagnetic wave attenuation can be obtained even within the range of the following formula (3). When this area ratio is large, the ratio of the area of the conductive element to the front surface of the dielectric substrate can be 50% or more and 90% or less.
0 < ln (T / d) ≦ 1 ... (3)
Considering the formulas (2) and (3), the attenuation of the electromagnetic wave can be obtained within the range of the following formula (4).
−2≦ln(T/d)≦1 … (4)
In the embodiment of the present invention, the skin depth can be calculated using the attenuation central frequency f. That is, when the attenuation central frequency f is used, the skin depth d is calculated as shown in the following formula (5), as is well known.

In addition, the simulation results showed that attenuation increased when the thickness of the conductive element was thinner than the skin depth. This is believed to be because the current generated by the magnetic flux of the dielectric substrate of the conductive element reaches the opposite surface of the dielectric substrate, and this current emits electromagnetic waves that are π out of phase with the reflected waves from the flat inductor, which offset the reflected waves from the flat inductor. In addition, as the thickness of the conductive element becomes thinner than the skin depth, the current in the conductive element is restricted, and as a result, the magnetic field is generated not only near the center of the conductive element but throughout the entire conductive element, and the current induced by the generated magnetic field is also generated throughout the entire conductive element, which increases the emission of electromagnetic waves that offset the reflected waves from the flat inductor, which is believed to result in greater attenuation of the reflected waves.
In addition, the electric field of the dielectric substrate between the conductive element and the flat inductor attracts the conductive element and the flat inductor. If the electric field fluctuates periodically, the force of attraction to the conductive element also fluctuates periodically. Therefore, the electric field of the dielectric substrate between the conductive element and the flat inductor causes the conductive element to vibrate. The energy of this vibration is converted into heat and lost. For this reason, it is thought that the mechanics of the electromagnetic field acting on the conductive element also contributes to the attenuation of electromagnetic waves.
In addition, if the periodic fluctuation of the electromagnetic field that does not progress is regarded as a quantum, it can be considered that the quantum is trapped by the electromagnetic field with a momentum of zero. In addition, since the thickness of the conductive element is on the order of several hundred nm, it is possible that the energy level in the conductive element may be affected.
Thus, the phenomena in the embodiments of the present invention can be interpreted not only as classical electromagnetic phenomena, but also as classical mechanics or quantum mechanics.
Therefore, when interpreting formula (4), the range is reasonably defined, but it is not a range that is strictly calculated by taking into account all physical phenomena. Therefore, when determining whether a target product falls within the range of the above formula, it is appropriate to interpret it taking into account the physical phenomena that are manifested.
In the prior art, there are usually no examples of using a conductor that is approximately at or thinner than the skin depth. Therefore, it is considered that the embodiment of the present invention has a different mechanism of interaction with electromagnetic waves in the millimeter wave band from the prior art.

[Second embodiment]
A second embodiment of the present invention will be described with reference to Figures 12 and 13. The second embodiment differs from the first embodiment in the arrangement of the conductive elements. In the following description, the same reference numerals may be used to designate configurations that are common to those already described, and duplicated descriptions may be omitted. It is believed that the first, second, and third mechanisms described above are also realized in the second embodiment.

Fig. 12 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention. Fig. 13 is a schematic view showing a part of a cross section taken along line II-II in Fig. 12. For example, the cross section is taken between α and β on line II-II.
The electromagnetic wave attenuation film 61 includes a dielectric substrate 62, a plurality of conductive elements 30A, 31A, and a planar inductor 50. The conductive elements 30A, 31A may have a thickness of 1000 nm or less.

The dielectric substrate 62 of the second embodiment can be made of the same material and have the same structure as the dielectric substrate 10 of the first embodiment. As shown in FIG. 13, the electromagnetic wave attenuating substrate 60 has thin-film conductive layers 30A, 31A disposed on the front surface 62a and back surface 62b of the dielectric substrate 62. To form the electromagnetic wave attenuating substrate 60, a laminate in which thin-film conductive layers are formed on both sides of the dielectric substrate 62 via anchor layers and adhesive layers may be used.

The support layer 11 can be an extruded film. The extruded film can be a non-stretched film or a stretched film. The support layer can also be formed by coating on the back surface of the electromagnetic wave attenuation substrate 60. The support layer has a bending stiffness of 7000 MPa·mm4 or ^less .

The thin-film conductive layer 30A formed on the front surface 62a of the dielectric substrate 62 and the thin-film conductive layer 31A formed on the rear surface 62b cover all or part of the front surface 62a and rear surface 62b in a plan view of the electromagnetic wave attenuation film 61. The planar inductor 50 covers all or part of the rear surface 62b. As long as the performance of the electromagnetic wave attenuation film 61 is not significantly impaired, the planar inductor 50 may have a portion that is not covered by the thin-film conductive layers 30A, 31A or the planar inductor 50, for example, at a part of the periphery of the electromagnetic wave attenuation film 61.
A planar inductor 50 is provided on the back surface of the support layer 11, and an adhesive layer may be provided between the back surface of the support layer 11 and the planar inductor 50. The adhesive layer and the planar inductor 50 can be formed using the same material and the same manufacturing method as in the first embodiment.

The attenuation setting in the electromagnetic wave attenuation film 61 of the second embodiment can be controlled by the arrangement positions of the conductive elements 30A, 31A arranged on the front surface 62a and the back surface 62b of the dielectric substrate 62. When the distance in the planar direction of the centers of gravity of the front and back conductive elements is l and the shortest distance from the center of gravity of the conductive element to the plate end is a, it is possible to create an electromagnetic wave attenuation film 61 having electromagnetic wave attenuation performance in multiple frequencies by mixing a combination of front and back conductive elements that satisfies the following formula (6) and a combination of front and back conductive elements that satisfies the following formula (7). The range of combinations is not particularly limited, but may be, for example, between a predetermined front (back) conductive element and an adjacent back (front) conductive element when the electromagnetic wave attenuation film is viewed in plan.
When the relationship between the distance l in the planar direction of the center of gravity of the front and rear conductive elements and the shortest distance a from the center of gravity of the conductive element to the plate end satisfies the following formula (6), the front and rear conductive elements overlap in the planar direction, the capacitance C shown in the following formula (8) increases, and the resonance frequency shifts to a lower frequency range. As a result, by mixing areas on a single plane where the front and rear conductive elements are overlapped in the planar direction and areas where they are not overlapped, it is possible to create an electromagnetic wave attenuation film that has attenuation at multiple frequencies without changing the dimensions of the conductive elements.
l < 2a ... (6)
l ≧ 2a … (7)

ω0=1/sqrt(LC)...(8)
ω0: Resonant frequency L: Reactance C: Capacitance

Furthermore, by adjusting the ratio of the combination of the front and back conductive elements overlapping in the planar direction and the combination of the non-overlapping combination on one plane, or the area ratio of the front and back conductive elements overlapping in the planar direction, it is possible to control the frequency at which the electromagnetic waves attenuate, and to create an electromagnetic wave attenuation film having an attenuation peak that attenuates a wide band or attenuates only a specific frequency among multiple frequencies. The method of calculating the mixing ratio is not particularly limited, but it is also possible to calculate it from the ratio of the number of combinations that satisfy formula (6) to the number of combinations that satisfy formula (7). As shown in FIG. 12, adjacent front conductive elements or rear conductive elements may overlap each other, but they may be treated as independent conductive elements in the calculation of the combination.

<Blackened layer>
In the embodiment of the present invention, a blackening layer may be provided by performing a blackening treatment around the thin-film conductive layer.
Fig. 14 is a schematic diagram showing an example of a part of a cross section taken along line II in Fig. 1 when a blackening layer is provided. As shown in Fig. 14, a blackening layer 32 may be provided on the front surface of the thin-film conductive layer 30, a blackening layer 33 on the side surface, a blackening layer 34 on the rear surface of the thin-film conductive layer 31, and a blackening layer 35 on the side surface.
15 is a schematic diagram of another example showing a part of the cross section taken along line II in FIG. 1 when a blackening layer is provided. As shown in FIG. 15, a blackening layer may be formed before forming the thin-film conductive layers 30 and 31 on the dielectric substrate 10, and then a thin-film conductive layer may be formed and patterned to the same dimensions as the blackening layer by etching or the like, and blackening layers 36 and 37 may be provided between the thin-film conductive layers 30 and 31 and the dielectric substrate 10, with a blackening layer 32 provided on the front surface of the thin-film conductive layer 30, a blackening layer 33 provided on the side surface, and a blackening layer 34 provided on the rear surface of the thin-film conductive layer 31 and a blackening layer 35 provided on the side surface.
16 is a schematic diagram of another example showing a part of the cross section taken along line II in FIG. 1 when a blackening layer is provided. As shown in FIG. 16, before forming the thin-film conductive layers 30 and 31 on the dielectric substrate 10, a blackening layer may be formed via an adhesive layer 13, and then a thin-film conductive layer may be formed, and the adhesive layer, blackening layer and thin-film conductive layer may be patterned to the same dimensions by etching or the like, so that the adhesive layer 13 and blackening layers 36 and 37 are provided between the thin-film conductive layers 30 and 31 and the dielectric substrate 10, and a blackening layer 32 may be provided on the front surface of the thin-film conductive layer 30, a blackening layer 33 may be provided on the side surface, and a blackening layer 34 may be provided on the back surface of the thin-film conductive layer 31, and a blackening layer 35 may be provided on the side surface.
The blackening treatment may be performed by either sulfur blackening or substitution blackening to form a blackening layer. By forming such a blackening layer on the surface of the conductive element, it is possible to obtain effects such as suppressing an increase in the resistance value of the conductive element and suppressing metallic luster to improve visibility. In addition, a conductive element can be formed by providing a blackening layer on the surface of the dielectric substrate 10 or providing a blackening layer via an adhesive layer 13 and then etching a multilayer conductor layer in which a thin film layer is laminated. By forming such a blackening layer between the dielectric substrate and the conductive element, it is possible to improve the adhesion of the conductive element to the dielectric substrate. The thickness of the blackening layer is preferably 200 nm or less. If it is 200 nm or more, there is a possibility that productivity will decrease. In addition, the surface roughness of the blackening layer is Ra 0.5 μm or more.

The thin-film conductive layer 31 may have a support layer 11 on the surface (back surface) opposite to the dielectric substrate 10. The thickness of the support layer 11 may be 5 μm or more and 250 μm or less. It may further be 10 μm or more and 200 μm or less. The support layer 11 may be a single layer or a multilayer. The material of the support layer 11 may be the same as that of the dielectric substrate 10. For example, the support layer 11 may be a simple substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, or silicone resin. The support layer 11 may be an extruded film. The extruded film may be a non-stretched film or a stretched film. The support layer 11 may also be formed by coating on the back surface of the electromagnetic wave attenuation substrate 20.

The thin-film conductive layer 30 may have a topcoat layer 200 on the surface (front surface) opposite the dielectric substrate 10. FIG. 17 is a schematic diagram showing a part of the cross section taken along line II in FIG. 1 when the topcoat layer 200 is provided. The flat inductor 50 may also have a topcoat layer 200 on the surface (back surface) opposite the dielectric substrate 10. The thickness of the topcoat layer 200 may be 0.1 μm or more and 50 μm or less. It may also be 1 μm or more and 5 μm or less. The topcoat layer 200 is a single layer or a multilayer. The material of the topcoat layer 200 may be a simple substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, or silicone resin. It may also contain insulating particles, magnetic particles, conductive particles, or a mixture thereof. The particles may be inorganic particles. By providing the topcoat layer 200, the impedance is matched with the air through which the radio waves propagate, and the radio waves can be effectively attenuated by the thin-film conductive layer. In addition, the thin-film conductive layers 30, 31 and the flat inductor 50 can be provided with corrosion resistance, chemical resistance, heat resistance, abrasion resistance, impact resistance, and the like. For example, by using cross-linked acrylic resin, cross-linked epoxy resin, polyamide, polyimide, polyamideimide, silicone resin, and the like, it is possible to improve solvent resistance and also improve heat resistance. In addition, by using urethane resin, and the like, it is possible to improve impact resistance, and by using silicone resin, it is possible to improve abrasion resistance.

Furthermore, in order to impart design properties, the topcoat layer 200 may contain pigments, etc. Examples of pigments used include organic pigments and inorganic pigments. Examples of organic pigments that can be used include organic pigments such as azo pigments, lake pigments, anthraquinone pigments, phthalocyanine pigments, isoindolinone pigments, and dioxazine pigments. Examples of inorganic pigments that can be used include yellow lead, yellow iron oxide, cadmium yellow, titanium yellow, barium yellow, aureolin, molybdate orange, cadmium red, red iron oxide, red lead, cinnabar, mars violet, manganese violet, cobalt violet, cobalt blue, cerulean blue, ultramarine, Prussian blue, emerald green, chrome vermilion, chromium oxide, viridian, iron black, and carbon black. Examples of inorganic white pigments that can be used include titanium oxide (titanium white, titanium white), zinc oxide (zinc white), basic lead carbonate (lead white), basic lead sulfate, zinc sulfide, lithopone, and titanox. In particular, inorganic pigments not only have a very high level of hiding power, but also have excellent light resistance (fade resistance) and chemical resistance, so they are extremely suitable in terms of durability and robustness when it is desired to impart design to the topcoat layer.

When the top coat layer 200 is multi-layered, it may be divided into a durability-imparting layer and a design-imparting layer. If necessary, a protective layer for protecting the design-imparting layer may be provided on the design-imparting layer. In addition, the top coat layer 200 may be formed by providing an adhesive layer or a pressure-sensitive adhesive layer on the surface in contact with the thin-film conductive layer 30 and bonding a durability-imparting layer and a design-imparting layer that are separately prepared together.
When the topcoat layer 200 is laminated to the electromagnetic wave attenuation film of the present invention, the desired electromagnetic wave attenuation characteristics can be maintained by laminating the topcoat layer 200 in a manner that prevents air bubbles or the like from being trapped between the thin-film conductive layer 30 and the topcoat layer 200 .

When the electromagnetic wave attenuation film of the present invention is applied to a building material such as wallpaper, a pattern may be provided on the top coat layer 200 or the design-imparting layer in order to impart design. The type of pattern is not particularly limited, and any pattern according to the application of the building material such as wallpaper can be used. For example, wood grain patterns, cork patterns, stone patterns, marble patterns, abstract patterns, etc., which are widely used in the field of conventional building materials, can be adopted. In addition, for example, when the purpose is simple coloring or color adjustment, a solid color can be adopted. In addition, an uneven pattern may be provided as necessary. The type of the uneven pattern is not particularly limited, and any pattern according to the application of the building material such as wallpaper can be used. For example, various patterns such as wood grain patterns, stone patterns, Japanese paper patterns, marble patterns, cloth patterns, and geometric patterns, which are widely used in the field of conventional building materials such as wallpaper, can be adopted. In addition, a simple matte pattern, sand grain pattern, hairline pattern, suede pattern, etc. can also be used. The method of forming the uneven pattern is not particularly limited, and any method of forming an uneven pattern can be used. For example, a mechanical embossing method using a metal embossing plate can be used.
By providing design in this way, when the electromagnetic wave attenuation film of the present invention is used as a building material, it becomes possible to harmonize the color tone and texture with the atmosphere of the space.

The inventors' study revealed that the attenuation by the first mechanism changes depending on the admittance (the reciprocal of electrical resistance) of the metal constituting the conductive element. Good electromagnetic wave attenuation was obtained when the admittance (siemens/m) was 10 million or more. Silver is known to be the material with the highest admittance among normal conductors, and its admittance is 61 to 66 x ¹⁰⁶ , so the upper limit of the admittance is approximately 70 million. Metals with admittances of 5 million or more and 70 million or less can be used. The metals constituting the conductive element can be ferromagnetic, paramagnetic, diamagnetic, or antiferromagnetic. Examples of ferromagnetic metals are nickel, cobalt, iron, or alloys thereof. Examples of paramagnetic metals are aluminum, tin (β-tin), or alloys thereof. Examples of diamagnetic metals are gold, silver, copper, tin (α-tin), zinc, or alloys thereof. An example of a diamagnetic alloy is brass, an alloy of copper and zinc. An example of an antiferromagnetic metal is chromium. Conductive elements of these metals have shown good electromagnetic wave attenuation.

<Production Method>
An example of a method for manufacturing the electromagnetic wave attenuation film 1 will be described.

There are various possible means for obtaining the electromagnetic wave attenuation film of the present invention, but the manufacturing method described below is simple and provides high accuracy in the placement of the thin-film conductive layer.

First, a method for manufacturing the electromagnetic wave attenuating substrate 20 will be described. To this end, thin-film conductive layers 30, 31 consisting of a predetermined repeating pattern of conductive elements are formed simultaneously on the front surface 10a and back surface 10b of the dielectric substrate 10. The conductive elements may be formed in any manner that can obtain the required pattern, and for example, a photolithography method can be used. Note that the front surface 10a and back surface 10b of the dielectric substrate 10 may be subjected to either a sulfur blackening treatment or a substitution blackening treatment in advance to form a blackening layer, if necessary.

Materials for the dielectric substrate 10 include, but are not limited to, polyesters such as polyethylene terephthalate (PET); polyarylene sulfides such as polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamide, polyimide, polyamideimide, polyethersulfone, polyetheretherketone, polycarbonate, acrylic resin, polystyrene, etc.

When using photolithography, first, a metal film is formed on both the front surface 10a and the back surface 10b of the dielectric substrate 10 so as to encompass all of the areas of the pattern that is ultimately desired. The metal film may be formed by physical deposition such as vapor deposition or sputtering, or by attaching a metal foil or the like. Alternatively, it may be formed by plating. The plating may be electrolytic plating or electroless plating. The plating may be copper plating, electroless nickel plating, electrolytic nickel plating, zinc plating, electrolytic chrome plating, or a laminate of these. The metal film may be formed on the front surface 10a and the back surface 10b simultaneously, or may be formed separately. If formed separately, the order of formation may not matter.

Next, a resist layer is formed on the metal film formed on the front surface 10a and back surface 10b of the dielectric substrate 10. The resist layer may be formed by applying a normal resist solution and drying it, but a method using a dry film resist is preferable because there is no risk of liquid dripping due to insufficient drying. The resist layer may be formed simultaneously on the front surface 10a and back surface 10b, or may be formed separately. If the resist layers are formed separately, the order of formation does not matter, just like the formation of the metal film.

Next, the front 10a and rear 10b sides of the dielectric substrate 10 are exposed simultaneously through a material that blocks light in a pattern, such as a photomask. In the embodiment of the present invention, when a photolithography method is adopted, "simultaneous formation" refers to carrying out the exposure process simultaneously. The two photomasks on the front 10a and rear 10b sides typically have different pattern shapes and/or positions. If the positions of the two photomasks can be appropriately controlled during exposure, the positional relationship of the thin film conductive layers 30, 31 obtained in the end will be as designed, and the risk of misalignment after formation or when using the electromagnetic wave attenuation film will be minimized.

Then, the resist layer is developed using a developer to remove unnecessary portions. Development can be performed simultaneously on the front 10a and back 10b sides of the dielectric substrate 10, or separately. However, simultaneous development is preferable because it eliminates the risk of problems caused by the developer flowing around to the opposite side.

Then, the metal layer is removed from the portion exposed by removing the resist layer. The metal layer is generally removed by wet etching, but dry etching or any other method may be used as long as it is possible to selectively remove only the exposed portion. The metal layer may be removed simultaneously on the front 10a side and the back 10b side of the dielectric substrate 10, or may be removed separately. However, if wet etching is used, it is simplest to remove them simultaneously.

Finally, the resist layer remaining on the metal layer with the unnecessary portions removed and the pattern formed, i.e., the thin-film conductive layers 30 and 31, is removed. The resist layer may be removed simultaneously on the front 10a side and the back 10b side of the dielectric substrate 10, or may be removed separately, but it is simplest to remove them simultaneously. Note that if there are design reasons that make it convenient to leave the resist layer on the thin-film conductive layers 30 and 31, this step can be omitted.

As already mentioned, the thin-film conductive layers 30, 31 do not have to be formed on the dielectric substrate 10 by photolithography. Printing, inkjet, and any other forming method can be used. In the present invention, "simultaneous formation" means that transfer is performed simultaneously when a printing method is used, and that deposition is performed simultaneously when an inkjet method is used.

In addition, in the embodiments of the present invention, the "metal film" does not have to be made of metal. For example, it may be a conductive organic material such as PEDOT/PSS, or a conductive oxide such as InGaZnO.

After these steps are completed, the thin-film conductive layers 30 and 31 may be subjected to either a sulfide blackening treatment or a substitution blackening treatment to form a blackening layer, as necessary.

Next, the support layer 11 on which the planar inductor 50 is formed is prepared. Note that this step is performed after the formation of the thin-film conductive layers 30, 31 on the dielectric substrate 10 for the sake of convenience of explanation only, and it goes without saying that the order may be reversed, or both steps may be performed in parallel.

The support layer 11 on which the planar inductor 50 is formed can typically be obtained by laminating the planar inductor 50 on the support layer 11. The material of the support layer 11 can be the same as the material of the dielectric substrate 10. Then, the planar inductor 50 as a metal film can be formed on the support layer 11 in the same way as forming a metal film on the dielectric substrate 10. Alternatively, the planar inductor 50 can be obtained by laminating a cast or rolled metal plate to the support layer 11.

The material of the support layer 11 may be the same as that of the dielectric substrate 10. The support layer 11 may be made of the same material as that of the dielectric substrate 10, or a different material may be used.

The material of the flat inductor 50 may be the same as that of the thin-film conductive layers 30 and 31. The flat inductor 50 may be made of the same material as that of the thin-film conductive layers 30 and 31, or a different material may be used.

Then, the electromagnetic wave attenuation film 1 of the present invention can be obtained by bonding the support layer 11 on which the flat inductor 50 is formed to the back surface 10b side of the dielectric substrate 10 (electromagnetic wave attenuation substrate 20) on which the thin-film conductive layers 30, 31 are formed, on the side opposite the flat inductor 50.

As another method for obtaining the electromagnetic wave attenuation film of the present invention, thin-film conductive layers 30, 31 may be formed simultaneously on both sides of the front surface 10a and back surface 10b of the dielectric substrate 10, and then a support layer 11 may be laminated on the back surface 10b side of the dielectric substrate 10, and a flat inductor 50 may be formed on the side of the support layer 11 opposite the dielectric substrate 10.

When providing the topcoat layer 200, an electromagnetic wave attenuation film may be attached via an adhesive layer, but the method of forming the topcoat layer 200 is not limited to this and may be a coating method or the like. The coating method may be appropriately selected from methods used in film manufacturing. Examples of coating methods include gravure coating, reverse coating, gravure reverse coating, die coating, and flow coating.

[Example]
Each embodiment of the present invention will be further described using examples. Figure 18 is a schematic diagram showing a part of the cross section of the electromagnetic wave attenuation film shown in Examples 1 to 6. l and l1 are the distance between the center of gravity of the conductive element on the front and back of the dielectric substrate, a, a1, and a2 are the distance from the center of gravity of the conductive element to the plate end, t is the dielectric substrate film thickness, ts is the support layer film thickness, tm is the thin-film conductive layer film thickness, tmb is the flat inductor film thickness, and h is the topcoat layer film thickness. Note that in Examples 1 to 7, the conductive elements have the same shape and dimensions, so a, a1, and a2 are equal.
When conductive elements of the same shape are uniformly arranged as in the first embodiment shown in Fig. 1, l is equal to l1. On the other hand, when conductive elements with different distances between them are mixed as in the second embodiment shown in Fig. 12, l and l1 have different values. The structures of the electromagnetic wave attenuation films of Examples 1 to 6 are shown in Table 1. Examples 1 to 5 correspond to the examples of the first embodiment, and Example 6 corresponds to the example of the second embodiment.

<Production Method>
A common manufacturing method for producing the electromagnetic wave attenuation films according to Examples 1 to 4 will be described. A copper layer was formed to a thickness of 500 nm on both sides of a PET sheet having a thickness of 50 μm by sputtering. Next, after cleaning the copper layer, a dry resist film was laminated onto the copper layer on both sides of the PET sheet. After that, both sides were exposed to light simultaneously through a photomask having a plate-shaped pattern, and then the acrylic negative resist layer was developed simultaneously on both sides using a mixed alkaline aqueous solution of sodium carbonate and sodium bicarbonate, and unnecessary resist was removed to expose a part of the underlying thin film conductive layer.

Next, both sides of the copper layer, partially covered with the resist layer, were simultaneously immersed in a ferric chloride solution, and the exposed parts of the copper layer were removed by etching. The remaining resist layer was then simultaneously removed from both sides using an alkaline solution, yielding a plate-shaped copper pattern. Next, the surface and sides of the copper pattern were subjected to a blackening treatment.

Next, a 100 μm thick PET film was laminated via an adhesive layer to the back side of the film having plate-shaped copper patterns on both sides to form a support layer, and a 50 nm thick aluminum foil was further laminated via an adhesive layer to the back side of the support layer to form a flat inductor. The above is the manufacturing procedure for Examples 1 to 4 according to the first embodiment.

A manufacturing method for producing the electromagnetic wave attenuation film according to Example 5 will be described. Using the same manufacturing procedures as in Examples 1 to 4, thin-film conductive layers were formed on the front and back surfaces of a dielectric substrate, a support layer was formed on the back surface of the thin-film conductive layer via an adhesive layer, a flat inductor was then formed on the back surface of the support layer, and a topcoat layer was then formed on the front surface of the dielectric substrate. The topcoat layer was formed using the procedure shown below.
The main component is an acrylic resin composition consisting of a mixture of 80 parts by mass of methyl methacrylate monomer and 20 parts by mass of cyclohexyl methacrylate, and the solid content of the acrylic resin composition is 100 parts by mass. In this, 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber ("ADEKA STAB LA-46" manufactured by ADEKA CORPORATION), 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber of a different composition ("TINUVIN 479" manufactured by Chiba Specialty Chemicals Co., Ltd.), 3 parts by mass of a benzotriazole-based ultraviolet absorber ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.), 10 parts by mass of a hindered amine-based radical absorbing agent ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.), and 10 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.) are added. A base solution with a solid content of 33 parts by mass, to which ethyl acetate solvent was added to adjust the solid content, and a hexamethylene diisocyanate type hardener solution with a solid content of 75 parts by mass, to which ethyl acetate solvent was added to adjust the solid content, were mixed so that the ratio of the base solution to the hardener solution was 10:1 (the ratio of the number of hydroxyl groups in the base solution to the number of isocyanate groups in the hardener solution was 1:2 at this time), and ethyl acetate was added as a solvent component to adjust the solid content to 20 parts by mass. The coating liquid was applied to a thickness of 6 μm after the solvent volatilized, to obtain a topcoat layer. The above is the manufacturing procedure of Example 5 according to the first embodiment.

A manufacturing method for producing the electromagnetic wave attenuation film of Example 6 will be described. Using the same manufacturing procedures as Examples 1 to 4, the positions of the thin-film conductive layers formed on the front and back surfaces of the dielectric substrate were mixed in a single plane with 50% of the thin-film conductive layers overlapping in the planar direction (l<2a) and 50% of the thin-film conductive layers not overlapping (l≧2a). Next, a support layer was formed on the thin-film conductive layer side of the back surface via an adhesive layer, and then a flat inductor was formed on the back surface of the support. This completes the manufacturing procedures for Example 6 according to the second embodiment.

Example 7 differs from Examples 1 to 5 in that the planar inductor has a mesh shape. Fig. 19 is a schematic diagram showing a part of a cross section of the electromagnetic wave attenuation film shown in Example 7. wp is the pitch of the mesh-shaped planar inductor, and w is the line width of the mesh-shaped planar inductor. The structure of the electromagnetic wave attenuation film of Example 7 is shown in Table 2.
A manufacturing method for producing an electromagnetic wave attenuation film according to Example 7 will be described. Using the same manufacturing procedure as in Examples 1 to 4, thin-film conductive layers were formed on the front and back surfaces of a dielectric substrate, and a support layer was formed on the back surface of the thin-film conductive layer via an adhesive layer. Then, a mesh-like flat inductor having a copper pattern with a thickness of 500 nm formed by etching on one side was placed on the back surface of the support layer via an adhesive layer, and laminated to form the mesh-like flat inductor. The mesh-like copper pattern had a pitch of 0.44 mm and a line width of 0.085 mm.

In Examples 8 to 10, the dimensions of the thin-film conductive layer are changed between the one placed in front of the dielectric and the one placed on the back of the dielectric, resulting in electromagnetic wave attenuation films with absorption at two frequencies. The structures of the electromagnetic wave attenuation films in Examples 8 to 10 are shown in Table 3. a and a1 are equal.
The manufacturing method for producing the electromagnetic wave attenuation films according to Examples 8 to 10 was the same as that of Examples 1 to 4, in which thin-film conductive layers were formed on the front and back surfaces of the dielectric substrate, and a support layer was formed on the thin-film conductive layer side of the back surface via an adhesive layer. A 50 nm thick aluminum foil was laminated on the back surface of the support layer via the adhesive layer to form a flat inductor.

Examples 11 to 15 are electromagnetic wave attenuation films in which the dimensions of the support layer are changed. As with Examples 1 to 4, the first embodiment shown in Fig. 1 is adopted. The structures of the electromagnetic wave attenuation films of Examples 11 to 15 are shown in Table 4. a, a1, and a2 are equal.
The manufacturing method for producing the electromagnetic wave attenuation films according to Examples 11 to 15 was the same as that of Examples 1 to 4, in which thin-film conductive layers were formed on the front and back surfaces of the dielectric substrate, and a support layer was formed on the back surface of the thin-film conductive layer side via an adhesive layer. A 50 nm thick aluminum foil was laminated on the back surface of the support layer via the adhesive layer to form a flat inductor.

Examples 16 and 17 are electromagnetic wave attenuation films in which the dimensions of the support layer are changed. As in Examples 1 to 4, the first embodiment shown in Figure 1 is adopted. The structures of the electromagnetic wave attenuation films of Examples 16 and 17 are shown in Table 5. a, a1, and a2 are equal.
In Examples 16 and 17, a planar inductor was formed on the back surface of a support layer using a manufacturing method similar to that of Examples 11 to 15, and then a topcoat layer was formed on the front surface of the dielectric substrate using a manufacturing method similar to that of Example 5.

Example 18 is an electromagnetic wave attenuation film in which adjacent thin film conductive layers on the front surface of the dielectric are different in size. FIG. 20 is a schematic plan view showing a part of the electromagnetic wave attenuation film of Example 18. FIG. 21 is a schematic view showing a part of the cross section of the electromagnetic wave attenuation film of Example 18 taken along line II. FIG. 22 is a schematic view showing a part of the cross section of the electromagnetic wave attenuation film of Example 18 taken along line III-III. l1 to l4 indicate the distance between the centers of gravity of the conductive elements on the front and back surfaces of the adjacent dielectric substrates, and a, a1 to a4 indicate the distance from the center of gravity of each conductive element to the plate end. The structure of the electromagnetic wave attenuation film of Example 18 is shown in Table 6.
The manufacturing method for producing the electromagnetic wave attenuation film of Example 18 was the same as that of Examples 11 to 15, and after forming a flat inductor on the back surface of the support layer, a topcoat layer was formed on the front surface side of the dielectric substrate by the same manufacturing method as that of Example 5.

Example 19 and Reference Example 1 are electromagnetic-wave-absorbing films according to the application form of the first embodiment described above. In Example 19, the size (a') of the conductive element on the front side is set smaller than the size (a) of the conductive element on the rear side, and in Reference Example 1, it is set larger. The structures of the electromagnetic-wave-absorbing films of Example 19 and Reference Example 1 are shown in Table 7. l, a, and a' represent the dimensions shown in FIG. 10. _{a max} means the maximum size of the conductive elements. The value of s (see FIG. 10(b)) is determined so that the amount of attenuation is optimized based on the size of the conductive element, and is 1034.157 μm in Example 19 and 246.573 μm in Reference Example 1.
The electromagnetic wave attenuation films according to Example 19 and Reference Example 1 were produced in the same manner as in Examples 1-4.

Similarly, Reference Examples 2 and 3 are electromagnetic-wave-absorbing films according to applied forms of the first embodiment. In Reference Example 2, the size of the conductive element on the front side is set smaller than the size of the conductive element on the rear side, and in Reference Example 3, it is set larger. The structures of the electromagnetic-wave-absorbing films of Reference Examples 2 and 3 are shown in Table 8. l, a, and a' represent the dimensions shown in FIG. 10. _{a max} means the maximum size of the conductive elements. The value of s (see FIG. 10(b)) is determined so that the amount of attenuation is optimized based on the size of the conductive elements, and is 102.091 μm in Reference Example 2 and 350.492 μm in Reference Example 3.
The electromagnetic wave attenuation films according to Reference Examples 2 and 3 were produced in the same manner as in Examples 1 to 4.

<Common evaluation items>
The electromagnetic wave attenuation films according to Examples 1 to 19 produced by the above-mentioned production method were subjected to a bending test, and the electromagnetic wave attenuation characteristics and weather resistance were evaluated.
(Bending test)
A bending test was carried out on the electromagnetic wave attenuation films of Examples 1 to 19. Using the electromagnetic wave attenuation film produced in each Example, a bending test was carried out by sandwiching a sample between a set of two bending R jigs (mandrels), and the position of the conductive element of the test piece after the test was observed under a microscope to confirm the presence or absence of positional deviation of the thin film conductive layer. The evaluation results are shown in Tables 1 to 7.

(Electromagnetic wave attenuation characteristics)
Using the configuration after the bending test, a simulation of the electromagnetic wave absorption characteristics was performed. The evaluation results are shown in Tables 1 to 6. Graphs of the monostatic RCS attenuation for each frequency are shown in Figures 23 to 41.
23 is a graph showing the electromagnetic wave attenuation characteristics of Example 1. A good absorption characteristic of −13 dB was shown at 74 GHz.
24 is a graph showing the electromagnetic wave attenuation characteristics of Example 2. A good absorption characteristic of −14 dB was shown at 74 GHz.
25 is a graph showing the electromagnetic wave attenuation characteristics of Example 3. A good absorption characteristic of −17 dB was shown at 79 GHz.
26 is a graph showing the electromagnetic wave attenuation characteristics of Example 4. A good absorption characteristic of −15 dB was shown at 78 GHz.
27 is a graph showing the electromagnetic wave attenuation characteristics of Example 5. A good absorption characteristic of −10 dB was shown at 75 GHz.
28 is a graph showing the electromagnetic wave attenuation characteristics of Example 6. Good absorption characteristics of −13 dB and −14 dB were observed at 58 GHz and 67 GHz, respectively.
29 is a graph showing the electromagnetic wave attenuation characteristics of Example 7. A good absorption characteristic of −11 dB was shown at 75 GHz.
30 is a graph showing the electromagnetic wave attenuation characteristics of Example 8. Good absorption characteristics of −11 dB at 28 GHz and −21 dB at 60 GHz were shown.
31 is a graph showing the electromagnetic wave attenuation characteristics of Example 9. Good absorption characteristics of −11 dB at 39 GHz and −14 dB at 60 GHz were shown.
32 is a graph showing the electromagnetic wave attenuation characteristics of Example 10. Good absorption characteristics of −10 dB at 28 GHz and −13 dB at 39 GHz were shown.
35 is a graph showing the electromagnetic wave attenuation characteristics of Example 13. A good absorption characteristic of −15 dB was shown at 29 GHz.
36 is a graph showing the electromagnetic wave attenuation characteristics of Example 14. A good absorption characteristic of −28 dB was shown at 40 GHz.
37 is a graph showing the electromagnetic wave attenuation characteristics of Example 15. A good absorption characteristic of −26 dB at 100 GHz was shown.
38 is a graph showing the electromagnetic wave attenuation characteristics of Example 16. A good absorption characteristic of −15 dB was shown at 30 GHz.
39 is a graph showing the electromagnetic wave attenuation characteristics of Example 17. A good absorption characteristic of −21 dB was shown at 28 GHz.
40 is a graph showing the electromagnetic wave attenuation characteristics of Example 18. A good absorption characteristic of −26 dB at 60 GHz was shown.

(Weatherability)
Furthermore, the electromagnetic wave attenuation film thus produced was pressed onto a stainless steel plate via an adhesive layer, and exposed to a temperature equivalent to 10 years of outdoor exposure using a sunshine weather meter. The surface of the electromagnetic wave attenuation film was then wiped with a cotton cloth to check the remaining condition of the topcoat layer, or the electromagnetic wave attenuation layer including the electromagnetic wave attenuation substrate, support layer, and flat inductor. The evaluation results are shown in Tables 1 to 6. If there was no effect on any of the layers after wiping, the result was rated as ◯, and if peeling occurred to an extent that did not interfere with practical use, the result was rated as △.

(Actual measurement)
In order to examine the validity of the attenuation mechanism based on the experimental results, the amount of electromagnetic wave attenuation was measured for the electromagnetic wave attenuation film of Example 4. The procedure for the measurement was as follows.
Two metal plates of the same dimensions were prepared, and the electromagnetic wave attenuation film of Example 4 was attached to one of them so as to cover the entire surface. In an anechoic chamber, radio waves were irradiated to the metal plate with the electromagnetic wave attenuation film attached and the metal plate without the film attached, and the amount of reflected radio waves was measured using a network analyzer (Model E5071C manufactured by KEYSIGHT). The monostatic RCS attenuation was evaluated by setting the reflection amount of the metal plate without the electromagnetic wave attenuation film attached as 100 (reference). As a result, good absorption characteristics of -15 dB at 78 GHz were shown, as in FIG. 26.
For the electromagnetic wave attenuation films of Examples 11 and 12, the electromagnetic wave attenuation was measured in the same manner as in Example 4. The evaluation results are shown in Table 4. Figures 33 and 34 show graphs of the measured monostatic RCS attenuation for each frequency.
33 is a graph showing the electromagnetic wave attenuation characteristics of Example 11. A good absorption characteristic of −15 dB was shown at 31 GHz.
34 is a graph showing the electromagnetic wave attenuation characteristics of Example 12. A good absorption characteristic of −15 dB was shown at 29 GHz.
As a result, the electromagnetic wave absorption amount of the electromagnetic wave attenuation film of Example 12 showed good absorption characteristics of -15 dB at 29 GHz, similar to Fig. 35. Therefore, the actual measured values of the electromagnetic wave absorption characteristics of Example 12 and the simulated values of the electromagnetic wave absorption characteristics of Example 13 were consistent. Fig. 41 is a graph showing the electromagnetic wave attenuation characteristics of Examples 12 and 13.

For the electromagnetic wave attenuation films of Example 19 and Reference Example 1, the electromagnetic wave attenuation was measured in the same manner as in Example 4. The evaluation results are shown in Table 7. Figures 42 and 43 show graphs of the measured monostatic RCS attenuation for each frequency.
42 is a graph showing the electromagnetic wave attenuation characteristics of Example 19. It has absorption peaks at 27.5 GHz and 39 GHz (dual band), and the attenuation of each absorption peak frequency was −17 dB and −20 dB before the bending test, respectively, and −16 dB and −29 dB after the bending test, both of which showed good absorption characteristics.
43 is a graph showing the electromagnetic wave attenuation characteristics of Reference Example 1. It had absorption peaks at 28.3 GHz and 38.4 GHz (dual band), and the attenuation of each absorption peak frequency was −21 dB and −9 dB before the bending test, respectively, and became −24 dB and −9 dB after the bending test.
From the above, it has been shown that by adopting a configuration of an electromagnetic wave attenuating base in which conductive elements are arranged on the front and back surfaces of a dielectric substrate, not only is positional deviation due to bending reduced, but changes in electromagnetic wave attenuation characteristics are also reduced.
In addition, it was shown that, in the above absorption peak frequency interval, when the size of the conductive element on the front side is smaller than the size of the conductive element on the rear side, good absorption characteristics tend to be obtained. When the ratio of the absorption peak frequency on the high frequency side divided by the absorption peak frequency on the low frequency side (hereinafter referred to as "absorption peak frequency ratio") is used as an index of the absorption peak frequency interval, it is 1.418 for Example 19 and 1.357 for Reference Example 1.

Next, a simulation of the electromagnetic wave absorption characteristics was carried out for the electromagnetic wave attenuation films according to Reference Examples 2 and 3. The evaluation results are shown in Table 8. Fig. 44 shows a graph of the monostatic RCS attenuation for each frequency.
FIG. 44 is a graph showing the electromagnetic wave attenuation characteristics of Reference Examples 2 and 3.
Reference Example 2 had absorption peaks at 29.4 GHz and 34.25 GHz (dual band), and the attenuations at the respective absorption peak frequencies were −22 dB and −20 dB, both of which showed good absorption characteristics. The absorption peak frequency ratio was 1.165.
Reference Example 3 had absorption peaks at 29.25 GHz and 34.25 GHz (dual band), and the attenuations at each absorption peak frequency were −37 dB and −10 dB, respectively, both of which showed good absorption characteristics. The absorption peak frequency ratio was 1.171.
Reference Examples 2 and 3 also show that there is a tendency for good absorption characteristics to be obtained when the size of the conductive element on the front side is smaller than the size of the conductive element on the rear side at a predetermined absorption peak frequency interval. The predetermined absorption peak frequency interval is not particularly limited, but in the case of a dual band of 28 GHz and 39 GHz, the above tendency is considered to be maintained when the frequency intervals are 29.5 GHz and 34 GHz or more apart (absorption peak frequency ratio of 1.153 or more).

(comprehensive evaluation)
The electromagnetic wave attenuation films of Examples 1 to 19 were produced and evaluated. As a result, in the electromagnetic wave attenuation films having thin-film conductive layers simultaneously formed on the front and back surfaces of the dielectric substrate, no displacement of the thin-film conductive layer occurred even after the bending test, and the structure before the test was maintained.
The frequency absorption was as designed, and an absorption level of -10 dB was ensured. As a result of the weather resistance test, it was confirmed that there was no deterioration in either the top coat layer or the electromagnetic wave attenuation layer, and that the formation of the top coat layer in particular improved weather resistance, resulting in particularly good practical properties.

(Example 20)
A laminated sheet was separately prepared by laminating a design-imparting layer having a wood grain pattern on a durability-imparting layer on the electromagnetic wave-attenuating film of Example 3, and the laminated sheet was attached to the thin-film conductor layer 30 with an adhesive while taking care not to trap air bubbles between the thin-film conductor layer 30 and the durability-imparting layer to form the top coat layer 200 of the present invention, and the electromagnetic wave-attenuating film of Example 20 was produced.
As a result, electromagnetic wave attenuation characteristics were obtained that were comparable to those of Example 3. Furthermore, when the electromagnetic wave attenuation film of Example 20 was attached next to a decorative sheet with a wood grain pattern indoors, the electromagnetic wave attenuation film of Example 20 did not look out of place with the decorative sheet with a wood grain pattern, and the entire room was harmoniously decorated with a wood grain pattern.

(Example 21)
A laminate sheet was separately prepared by laminating a design-imparting layer having a wood grain pattern on a durability-imparting layer on the electromagnetic wave-attenuating film of Example 10, and the laminate sheet was attached to the thin-film conductor layer 30 with an adhesive while taking care not to trap air bubbles between the thin-film conductor layer 30 and the durability-imparting layer to form a top coat layer 200 related to the present invention, and the electromagnetic wave-attenuating film of Example 21 was produced.
As a result, electromagnetic wave attenuation characteristics were obtained that were comparable to those of Example 10. Furthermore, when the electromagnetic wave attenuation film of Example 21 was attached next to a decorative sheet with a wood grain pattern indoors, the electromagnetic wave attenuation film of Example 21 did not look out of place with the decorative sheet with a wood grain pattern, and the entire room was harmoniously decorated with a wood grain pattern.

(Example 22)
A laminate sheet was separately prepared by laminating a design-imparting layer having a marble pattern on a durability-imparting layer on the electromagnetic wave-attenuating film of Example 3, and the laminate sheet was attached to the thin-film conductor layer 30 with an adhesive while taking care not to trap air bubbles between the thin-film conductor layer 30 and the design-imparting layer 200 to form the top coat layer 200 of the present invention, and the electromagnetic wave-attenuating film of Example 22 was produced.
As a result, electromagnetic wave attenuation characteristics were obtained that were comparable to those of Example 3. Furthermore, when the electromagnetic wave attenuation film of Example 22 was installed next to a marble-patterned flooring material in a room, the electromagnetic wave attenuation film of Example 22 did not look out of place with the marble-patterned flooring material and did not impair the luxurious feel of the marble-patterned flooring material in the room.

(Example 23)
A laminate sheet was separately prepared by laminating a design-imparting layer having a marble pattern on a durability-imparting layer on the electromagnetic wave-attenuating film of Example 10, and the laminate sheet was attached to the thin-film conductor layer 30 with an adhesive while taking care not to trap air bubbles between the thin-film conductor layer 30 and the design-imparting layer 200 to form the top coat layer 200 of the present invention, and the electromagnetic wave-attenuating film of Example 23 was produced.
As a result, electromagnetic wave attenuation characteristics were obtained that were comparable to those of Example 10. Furthermore, when the electromagnetic wave attenuation film of Example 23 was installed next to a marble-patterned flooring material in a room, the electromagnetic wave attenuation film of Example 23 did not look out of place with the marble-patterned flooring material and did not impair the luxurious feel of the marble-patterned flooring material in the room.

[Comparative Example]
The structure and evaluation results of the electromagnetic wave attenuation film according to the comparative example are shown in Table 9. Also, graphs of the monostatic RCS attenuation for each frequency are shown in Figures 46 to 48.

(Comparative Example 1)
The electromagnetic wave attenuation film according to Comparative Example 1 differs from the configuration of the Examples having a configuration in which a thin-film conductive layer is formed on both the front and back surfaces of a dielectric substrate (electromagnetic wave attenuation substrate) in that it has a laminated laminate configuration. Fig. 45 is a schematic diagram showing a part of a cross section of the electromagnetic wave attenuation film of Comparative Example 1. Explanation of the same configuration as Fig. 2 or Fig. 18 is omitted. It has a configuration in which an upper lamination layer 40 and a lower lamination layer 41, each having a thin-film conductive layer 30 formed only on the front surface of a dielectric substrate 10, are laminated. The structure of the electromagnetic wave attenuation film of Comparative Example 1 is shown in Table 9.

<Production Method>
Similar to Example 1, two layers were prepared, an upper lamination layer 40 and a lower lamination layer 41, in which a thin-film conductive layer 30 was disposed only on the front side of a dielectric substrate 10. The lower lamination layer 41 was attached to the rear side of the upper lamination layer 40 via an acrylic adhesive layer 12. Next, a PET film having a thickness of 100 μm was laminated via the adhesive layer 12 to form a support layer 11, and an aluminum flat inductor 50 was attached to the rear side of the support layer 11 using an adhesive layer, to produce an electromagnetic wave attenuation film by multilayer lamination.

<Evaluation method and results>
The bending test, electromagnetic wave attenuation characteristics, and weather resistance of the electromagnetic wave attenuation film were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 9.
After conducting a bending test of the electromagnetic wave attenuation film formed by the multi-layer bonding of Comparative Example 1, the position of the conductive element of the test piece was observed. As a result, a shift occurred in the film of the upper bonding layer 40 and the film of the lower bonding layer 41, and the positioning positions of the conductive elements 30 in the upper and lower layers were shifted by approximately 5 mm from before the test.
46 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 1. The target absorption frequency was around 75 GHz in the design value, whereas the absorption peak frequency of the electromagnetic wave absorbing sheet produced by laminating was 57 GHz, which was significantly different from the design value.
Regarding weather resistance, when wiped with a cotton cloth, the thin metal layer peeled off, and the results were not very good.

(Comparative Examples 2 and 3)
Comparative Examples 2 and 3 have the same configuration as the electromagnetic-wave-absorbing film according to Example 1, etc., except for some differences in the dimensions of the components of the electromagnetic-wave-absorbing film, and therefore the differences will be mainly described.
Comparative Example 2 has a structure in which the conductive elements are formed in a positional relationship that does not satisfy the following formula (1), where the planar distance between the centers of gravity of the conductive elements on the front and back surfaces of the dielectric substrate is l and the shortest distance from the center of gravity of the conductive elements to the end of the plate is a.
l≦5.2a... (1)
The electromagnetic wave attenuation films of Comparative Example 3 have a structure in which the film thickness of the support layer is less than 5 μm.

<Production Method>
In accordance with Example 1, thin-film conductive layers were formed on the front and back surfaces of a dielectric substrate, a support layer was formed on the back surface on the side of the thin-film conductive layer via an adhesive layer, and then a flat inductor was formed on the back surface of the support layer.

<Evaluation method and results>
The electromagnetic wave attenuation film was subjected to a bending test, and the electromagnetic wave attenuation characteristics and weather resistance test were evaluated in the same manner as in Example 1. The evaluation results are shown in Table 4.
Regarding the bending test, in both Comparative Examples 2 and 3, no displacement of the thin-film conductive layer occurred even after the bending test.
47 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 2. Since 1/a is 6.0 and does not satisfy the relationship of formula (1), no resonant coupling occurs between the conductive elements on the front and back, and the amount of absorption does not reach the target of -10 dB.
Fig. 48 is a graph showing the electromagnetic wave attenuation characteristics of Comparative Example 3. When the thickness of the support layer formed on the back surface of the conductive element on the back surface of the dielectric substrate was 4 µm, which is thinner than 5 µm, as in Comparative Example 3, the absorption amount did not reach the target of -10 dB. For this reason, the thickness of the support layer is preferably 5 µm (0.005 mm) or more.
Regarding weather resistance, when wiped with a cotton cloth, the thin metal layer peeled off, and the results were not very good.

Although each embodiment of the present invention has been described above in detail with reference to the drawings, the specific configuration is not limited to this embodiment, and configuration changes and combinations within the scope of the gist of the present invention are also included. Some examples of changes are given below, but these are not all inclusive, and other changes are also possible. Two or more of these changes may be combined as appropriate.

In the first embodiment, the aspects used in the second embodiment, such as the frequency band and the metal type of the conductive element, can be used as appropriate.

In the present invention, the form of the planar inductor is not limited to being formed on the entire back surface. For example, multiple conductive elements may be arranged in the same manner as on the front surface, or may be arranged in a lattice pattern.

In the present invention, the shape of the conductive elements is not limited to a square, and may be variously set to a circle (including an ellipse), a polygon other than a square, various polygons with rounded corners, an irregular shape, etc. The total area of the conductive elements in the projected area of the front surface is preferably 20% or more.
In this way, electromagnetic waves can be efficiently attenuated.

The electromagnetic wave attenuation film according to the present invention may have a configuration in which the back surface does not have a flat inductor. For example, if the object to which the back surface is bonded is metal, the second and third mechanisms can be exerted without problems by the metal surface of the object to be bonded, even without a flat inductor. In such a case, it is sufficient to provide an attachment layer, such as an adhesive layer, on the back surface that can be bonded to the object.

In the electromagnetic wave attenuation film according to the present invention, parameters such as the structural period and the dimensions of the conductive elements do not necessarily have to be completely consistent at all locations. For example, even if the above parameters vary within the tolerance range in the manufacturing process (roughly 5% above or below), this is also included in the "same shape and size" in the present invention. Furthermore, the "predetermined range of values" can be a range of values with regularity. This regularity can be a Gaussian distribution, a binomial distribution, a random distribution or pseudo-random distribution with equal frequency within a certain section, or the range of the tolerance in the manufacturing process.

In the electromagnetic wave attenuation film of the present invention, a release layer may be provided on a supporting substrate, and then the electromagnetic wave attenuation film of the first and second embodiments may be provided, and an adhesive, pressure sensitive adhesive, etc. may be further provided to form a transfer foil.
By using it as a transfer foil, it is possible to make the film even thinner, further improve its conformability, and transfer it to complex shapes, thereby widening the range of application of the electromagnetic wave attenuation film of the present invention.

In the above examples, the attenuation of electromagnetic waves is considered, but it is known that conductors that attenuate certain electromagnetic waves can be used as antennas to receive radio waves. Therefore, the above-mentioned embodiment can also be used as a receiving antenna. In addition, since the above-mentioned embodiment captures a quantum with zero momentum in a two-dimensional system, it is thought that it can also be used as an element that calculates and records data in the quantum state of a conductive element.

As described above, the mechanism of interaction with electromagnetic waves in the embodiments of the present invention is different from that of the prior art, and therefore products that exhibit an equivalent mechanism should be considered to substantially use the embodiments of the present invention.

The following are examples of items that may be included in the present invention, but the present invention is not limited to these.
(Item 1)
an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
Electromagnetic wave attenuation film.
(Item 2)
an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged,
When the distance in a planar direction between the centers of gravity of the conductive elements on the front and back surfaces of the dielectric substrate is l and the shortest distance from the center of gravity of the conductive element to the end of the plate is a, the following formula (1) is satisfied:
Electromagnetic wave attenuation film.
l≦5.2a... (1)
(Item 3)
an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged,
The thickness of the support layer is 0.005 mm or more.
Electromagnetic wave attenuation film.
(Item 4)
an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged, and when the thickness of the conductive elements is T and the skin depth is d, the following formula (4) is satisfied:
Electromagnetic wave attenuation film.
−2≦ln(T/d)≦1 … (4)
(Item 5)
an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged,
When the distance in the planar direction of the centers of gravity of the conductive elements on the front and rear surfaces of the dielectric substrate is l and the shortest distance from the center of gravity of the conductive element to the plate end is a, a combination of the conductive elements on the front and rear surfaces of the dielectric substrate that satisfies the following formula (6) and a combination of the conductive elements on the front and rear surfaces of the dielectric substrate that satisfies the following formula (7) are mixed, thereby providing electromagnetic wave attenuation performance at multiple frequencies.
Electromagnetic wave attenuation film.
l < 2a ... (6)
l ≧ 2a … (7)
(Item 6)
6. The electromagnetic wave attenuation film according to any one of items 1 to 5, wherein the thin film conductive layer and the planar inductor are spaced apart in a thickness direction of the dielectric substrate or support layer.
(Item 7)
7. The electromagnetic wave attenuation film according to any one of items 1 to 6, further comprising a blackening layer on the front and rear surfaces of the thin film conductive layer on the front surface of the dielectric substrate.
(Item 8)
8. The electromagnetic wave attenuation film according to any one of items 1 to 7, further comprising a blackening layer on the front and rear surfaces of the thin film conductive layer on the rear surface of the dielectric substrate.
(Item 9)
9. The electromagnetic wave attenuating film according to any one of items 1 to 8, further comprising a topcoat layer on the front side of the electromagnetic wave attenuating substrate.
(Item 10)
10. The electromagnetic wave attenuation film according to item 9, wherein the topcoat layer is impedance-matched to an air layer through which electromagnetic waves propagate.
(Item 11)
11. The electromagnetic wave attenuation film according to item 9 or 10, wherein the top coat layer is mainly composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component.
(Item 12)
12. The electromagnetic wave attenuation film according to any one of items 9 to 11, wherein the top coat layer contains an ultraviolet absorbing agent and an ultraviolet scattering agent in an acrylic resin composition.
(Item 13)
13. The electromagnetic wave attenuation film according to any one of items 1 to 12, wherein the thin film conductive layer is made of any one of silver, copper, and aluminum.
(Item 14)
Item 14. The electromagnetic wave attenuation film according to any one of items 1 to 13, wherein the thin-film conductive layer is configured to be capable of capturing electromagnetic waves incident from the front side of the dielectric substrate.
(Item 15)
Item 15. The electromagnetic wave attenuation film according to any one of items 1 to 14, wherein the conductive element is a planar element having a pair of opposing sides.
(Item 16)
The length of a pair of opposing sides of the planar element is 0.25 mm or more and 4 mm or less.
Item 16. An electromagnetic wave attenuation film according to item 15.
(Item 17)
Item 17. The electromagnetic wave attenuation film according to any one of items 1 to 16, wherein the thickness of the dielectric substrate is sufficiently thin relative to the attenuation center wavelength.
(Item 18)
Item 18. The electromagnetic wave attenuation film according to item 17, wherein the thickness of the dielectric substrate is less than 1/10 of the attenuation center wavelength.
(Item 19)
3. The electromagnetic wave attenuation film according to item 2, wherein the size of the conductive elements on the front surface of the dielectric substrate is smaller than the size of the conductive elements on the rear surface of the dielectric substrate and have different absorption peak frequencies.
(Item 20)
20. The electromagnetic wave attenuation film according to item 19, wherein an absorption peak frequency ratio of the mutually different absorption peak frequencies is 1.153 or more.

Reference Signs List 1, 61 Electromagnetic wave attenuation film 10, 62 Dielectric substrate 10a, 62a Front surface 10b, 62b Rear surface 20, 60 Electromagnetic wave attenuation substrate 30, 30A, 31, 31A Thin film conductive layer, conductive element 32, 33, 34, 35, 36, 37 Blackening layer 11 Support layer 12, 13 Adhesive layer 40 Upper lamination layer 41 Lower lamination layer 50 Flat inductor 200 Topcoat layer

Claims (20)

an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
Electromagnetic wave attenuation film. an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged,
When the distance in a planar direction between the centers of gravity of adjacent conductive elements on the front and back surfaces of the dielectric substrate is l and the shortest distance from the center of gravity of the conductive element to an end of the plate is a, the following formula (1) is satisfied:
Electromagnetic wave attenuation film.
l≦5.2a... (1) an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged,
The thickness of the support layer is 0.005 mm or more.
Electromagnetic wave attenuation film. an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged, and when the thickness of the conductive elements is T and the skin depth is d, the following formula (4) is satisfied:
Electromagnetic wave attenuation film.
−2≦ln(T/d)≦1 … (4) an electromagnetic wave attenuating substrate having a dielectric substrate having a front surface and a rear surface, and a thin-film conductive layer disposed on both the front surface and the rear surface of the dielectric substrate;
a support layer disposed on a rear surface of the electromagnetic wave attenuating substrate; and a planar inductor disposed on a rear surface of the support layer.
Equipped with
the thin film conductive layer includes a plurality of conductive elements;
The conductive elements are periodically arranged,
When the distance in the planar direction between the centers of gravity of adjacent conductive elements on the front and rear surfaces of the dielectric substrate is l and the shortest distance from the center of gravity of the conductive element to the plate end is a, a combination of conductive elements on the front and rear surfaces of the dielectric substrate that satisfies the following formula (6) and a combination of conductive elements on the front and rear surfaces of the dielectric substrate that satisfies the following formula (7) are mixed, thereby providing electromagnetic wave attenuation performance at multiple frequencies.
Electromagnetic wave attenuation film.
l < 2a ... (6)
l ≧ 2a … (7) The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the thin-film conductive layer and the planar inductor are spaced apart in the thickness direction of the dielectric substrate or support layer. The electromagnetic wave attenuation film according to any one of claims 1 to 5, characterized in that a blackening layer is provided on the front and back of the thin film conductive layer on the front surface of the dielectric substrate. The electromagnetic wave attenuation film according to any one of claims 1 to 5, characterized in that a blackening layer is provided on the front and back surfaces of the thin film conductive layer on the back surface of the dielectric substrate. The electromagnetic wave attenuation film according to any one of claims 1 to 5, characterized in that it has a topcoat layer on the front side of the electromagnetic wave attenuation substrate. The electromagnetic wave attenuation film according to claim 9, characterized in that the topcoat layer is impedance-matched to the air layer through which the electromagnetic waves propagate. The electromagnetic wave attenuation film according to claim 9, characterized in that the topcoat layer is mainly composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component. The electromagnetic wave attenuation film according to claim 9, characterized in that the topcoat layer contains an ultraviolet absorbing agent and an ultraviolet scattering agent in an acrylic resin composition. The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the thin-film conductive layer is made of silver, copper, or aluminum. The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the thin-film conductive layer is configured to capture electromagnetic waves incident from the front side of the dielectric substrate. The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the conductive element is a planar element having a pair of opposing sides. The electromagnetic wave attenuation film according to claim 15, wherein the length of a pair of opposing sides of the planar element is 0.25 mm or more and 4 mm or less. The electromagnetic wave attenuation film according to any one of claims 1 to 5, wherein the thickness of the dielectric substrate is sufficiently thin relative to the attenuation central wavelength. The electromagnetic wave attenuation film according to claim 17, wherein the thickness of the dielectric substrate is less than 1/10 of the attenuation center wavelength. The electromagnetic wave attenuation film according to claim 2, in which the size of the conductive elements on the front surface of the dielectric substrate is smaller than the size of the conductive elements on the back surface of the dielectric substrate, and the conductive elements have different absorption peak frequencies. The electromagnetic wave attenuation film according to claim 19, wherein the absorption peak frequency ratio of the mutually different absorption peak frequencies is 1.153 or more.

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