JP7231089B2 - electromagnetic wave attenuation film - Google Patents

Description

Embodiments of the present invention relate to electromagnetic wave attenuation films capable of capturing incident waves and attenuating reflected waves.

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

As a radio wave absorbing sheet for absorbing such radio waves, Patent Document 1 proposes a laminate sheet obtained by laminating a rubber radio wave absorbing sheet and a paper-like sheet material such as corrugated cardboard.
Furthermore, for the purpose of absorbing radio waves in a higher frequency band, Patent Document 2 discloses that by aligning the longitudinal direction of flat soft magnetic particles with the surface direction of the sheet, a frequency band of 20 GHz or more is obtained. A radio wave absorbing sheet capable of absorbing radio waves has been proposed.

Further, it is known that a radio wave absorber having a packed structure of particles having epsilon iron oxide (ε-Fe2O3) crystals in the magnetic phase exhibits radio wave absorption performance in the range of 25 to 100 GHz (see Patent Document 3). ).

Patent document 4 has a plastic film and a single-layer or multi-layer metal thin film provided on at least one surface thereof, and the metal thin film has a large number of substantially parallel and intermittent linear scratches having an irregular width and A metal thin film-plastic composite film with linear scratches suitable for an electromagnetic wave absorber formed at intervals in a plurality of directions has been proposed.
Patent Document 5 discloses a resonance layer in which a plurality of patch conductors having individual resonance frequencies are arranged in a predetermined periodic pattern, a dielectric layer that multiple-reflects radio waves resonating in the resonance layer, and radio waves incident from the dielectric layer. A radio wave absorbing structure is disclosed that includes a reflective conductor layer that reflects the wave toward the dielectric layer.

The electromagnetic wave absorbing sheet as described above is used not only in electronic devices but also in the interior of buildings. In addition, as the electromagnetic wave absorbing material, as described in Patent Document 6, epoxy resin, polyurethane resin, chlorinated rubber resin, vinyl chloride resin, alkyd resin, unsaturated polyester resin, epoxy acrylate resin, etc. acrylate copolymer-modified resin is used. Rubber-based materials such as polyamide-imide and synthetic rubber as described in Patent Document 7 are also used.

JP 2011-233834 A JP 2015-198163 A JP 2008-060484 A WO2010/093027 JP 2020-009829 A Patent No. 2612592 JP-A-2006-86422

In recent years, wireless communication using the millimeter-wave band of 30 GHz or higher has been put to practical use in order to enable large-capacity data transmission, high-speed communication, and simultaneous connection of multiple points. Development of compatible devices is progressing. In addition, the use of in-vehicle radar equipment that utilizes extremely narrow directivity is being promoted.

Interference due to irregular reflection of electromagnetic waves inside the housing of the device causes malfunction of the device. Therefore, suppression of electromagnetic wave noise is important as one of electromagnetic wave utilization techniques.
As one method of suppressing electromagnetic wave noise, the use of the electromagnetic wave absorbing sheet as described above can be considered, but at present, most of them are compatible with frequencies from 20 GHz to several tens of GHz, and are compatible with the millimeter wave band. do not have.
Although there are electromagnetic wave absorbing sheets that absorb electromagnetic waves in the millimeter wave band, those currently in practical use are thick in order to maintain absorption performance. Therefore, it is difficult to suppress the electromagnetic noise by incorporating it into the housing of the device, which is becoming more and more highly integrated.

In view of the above circumstances, it is an object of the present invention to provide a thin electromagnetic wave attenuation film capable of attenuating electromagnetic waves with frequencies in the millimeter wave band. Furthermore, electromagnetic wave absorbers installed in electronic devices, interiors of buildings, etc. are used continuously for a long period of time. It also aims to provide The electromagnetic wave attenuation film of the present invention is considered to be a film capable of steadily localizing an electromagnetic field. In other words, the electromagnetic wave attenuation film of the present invention is considered to be a film capable of capturing an electromagnetic field. "Capturing" an electromagnetic field can be a state in which the electric and magnetic fields are constantly localized. Also, the trapped electromagnetic field is partly absorbed by being converted into heat, and partly reemitted. That is, the captured electromagnetic field energy is converted into thermal energy and reemitted electromagnetic energy. Since this re-emission is generally considered to have low directivity, it is considered that the electromagnetic wave in the specular reflection direction is reduced and the reflected wave is attenuated. Therefore, the reflected wave of the electromagnetic wave can be attenuated by absorption due to conversion of the incident electromagnetic wave into heat and scattering due to re-emission. Since the electromagnetic wave is attenuated by such a mechanism different from the conventional one, it is possible to attenuate the wavelength with a thin structure of 1/4 or less of the wavelength, which was conventionally considered impossible. Further, embodiments of the present application provide films that are capable of attenuating electromagnetic waves with thicknesses on the order of 10 ⁻² wavelengths, which is incredible.

SUMMARY OF THE INVENTION The present invention is an electromagnetic wave attenuation film comprising a dielectric substrate having a front surface and a back surface, a thin film conductive layer disposed on the front surface, and a planar inductor or laminate layer disposed on the back surface. A top coat layer made of a resin material may be provided on the thin film conductive layer.
The thin film conductive layer includes a plurality of metal plates, and is an electromagnetic wave attenuation film characterized by satisfying the following formula in a frequency band of 57 GHz to 90 GHz, where T is the thickness of the metal plate and d is the skin depth. .
-2.5 ≤ ln(T/d) ≤ -1.0

Another electromagnetic wave attenuation film according to the present invention is used in the 57 GHz to 90 GHz frequency band and includes a dielectric substrate having a front surface and a back surface, a thin film conductive layer disposed on the front surface, and a planar inductor or laminate disposed on the back surface. a layer; The dielectric substrate has, on its front surface, irregularities consisting of a relatively low recessed first region and a relatively high second region. A thin film conductive layer includes a plurality of metal plates disposed in the first region. The first regions are arranged discretely and the second regions are arranged between the plurality of first regions. A top coat layer made of a resin material may be formed on the thin film conductive layer.

According to the embodiments of the present invention, it is possible to provide a thin electromagnetic wave attenuation film capable of attenuating radio waves in the millimeter wave band. It is also possible to provide an electromagnetic wave attenuation film with excellent weather resistance.

1 is a schematic plan view showing an electromagnetic wave attenuation film according to a first embodiment of the invention; FIG. FIG. 2 is a schematic diagram showing a part of a cross section taken along line II of FIG. 1; FIG. 2 is a schematic diagram showing a part of a cross section taken along line II of FIG. 1 when a topcoat layer is provided; It is an image which shows the simulation result of the electric field strength when there is no support cage, (b) is the elements on larger scale of (a). It is an image which shows the simulation result of the electric field strength when there exists a support cage, (b) is the elements on larger scale of (a). FIG. 4 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention; FIG. 7 is a schematic diagram showing a part of a cross section taken along line II-II of FIG. 6; FIG. 7 is a schematic diagram showing a part of the cross section taken along line II-II in FIG. 6 when a topcoat layer is provided; 4 is a graph showing simulation results of electromagnetic wave attenuation due to changes in the thickness of a metal plate. It is a graph which shows the electromagnetic wave attenuation characteristic in 57 GHz of Example 1A. 4 is a graph showing electromagnetic wave attenuation characteristics at 66 GHz of Example 1A. It is a graph which shows the electromagnetic wave attenuation characteristic in 71 GHz of Example 1A. It is a graph which shows the electromagnetic wave attenuation characteristic in 81 GHz of Example 1A. It is a graph which shows the electromagnetic wave attenuation characteristic in 86 GHz of Example 1A. It is a graph which shows the electromagnetic wave attenuation characteristic in 90 GHz of Example 1A. 10 is a graph showing electromagnetic wave attenuation characteristics according to metal area ratios at 81 GHz in Example 1B. 10 is a graph showing electromagnetic wave attenuation characteristics of a rectangular metal plate in Example 1C. 10 is a graph showing electromagnetic wave attenuation characteristics of a hexagonal metal plate in Example 1C. 10 is a graph showing electromagnetic wave attenuation characteristics when the metal plate has a convex shape in Example 1C. 10 is a graph showing electromagnetic wave attenuation characteristics of a triangular metal plate in Example 1C. 10 is a graph showing electromagnetic wave attenuation characteristics of a cross-shaped metal plate in Example 1C. It is a graph which shows the electromagnetic wave attenuation characteristic in Example 1A. 7 is a graph showing electromagnetic wave attenuation characteristics in Example 2. FIG. 4 is a graph showing electromagnetic wave attenuation characteristics when a topcoat layer is provided in Example 1A. 4 is a graph showing the relationship between the dimensions of a metal plate and the wavelength of electromagnetic waves to be attenuated;

The electromagnetic wave attenuation film 1 includes a dielectric substrate (dielectric layer) 10, a thin film conductive layer 30 formed on the front surface 10a of the dielectric substrate 10, and a flat inductor 50 formed on the back surface 10b of the dielectric substrate. and A thin film conductive layer is a layer of thin conductor. A thin film conductive layer includes a plurality of metal plates. The thin film conductive layer may also include a support cage (described below). A planar inductor is electrically conductive, and an external magnetic flux induces a current near the surface inside the planar inductor. It also has the function of generating a magnetic field in the vicinity of the surface of the outside of the planar inductor along with the current. The shape of the flat inductor can be a flat plate (Slab). The dielectric substrate is an insulating substrate sandwiched between the thin film conductive layer and the flat inductor. In other words, the thin film conductive layer and the flat inductor are spaced apart in the thickness direction of the dielectric substrate with the dielectric substrate therebetween. The front surface can be the surface on which electromagnetic waves are incident. The back surface is the surface opposite the front surface of the dielectric substrate. The dielectric substrate 10 may have a first region 121 with a relatively low front surface and a second region 122 with a relatively high front surface surrounding the first region. A thin conductive layer located over the second region 122 is referred to as a support cage. In other words, the thin film conductive layer includes a support cage over the second region 122 .
When the electromagnetic wave attenuated by the electromagnetic wave attenuation film has a single minimum frequency f, this frequency f is defined as the attenuation center frequency f. When the electromagnetic wave attenuated by the electromagnetic wave attenuation film has a plurality of minimum values, the attenuation center frequency is the average frequency of the plurality of frequencies that is −3 dB from the maximum attenuation of the minimum value. The attenuation center wavelength can be obtained by dividing the speed of light in the dielectric substrate by the attenuation center frequency f, which will be described later.
The electromagnetic wave attenuation film 1 may also include a top coat layer 200 for matching impedance with air and enhancing the weather resistance of the sheet.

FIG. 1 is a schematic plan view showing an electromagnetic wave attenuation film 1 according to the first embodiment of the invention. FIG. 2 is a schematic diagram showing a part of the cross section taken along line II of FIG.

The dielectric substrate 10 is made of a dielectric material and sandwiched between conductive materials to form a capacitor. Dielectric substrate 10 can be an insulating material.
A representative example of the material forming the dielectric substrate 10 is a synthetic resin. The type of synthetic resin is not particularly limited as long as it has insulating properties as well as sufficient strength, flexibility and workability. The synthetic resin can be a thermoplastic resin. Synthetic resins include polyesters such as polyethylene terephthalate (PET); polyarylene sulfides such as polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamides, polyimides, polyamideimides, polyethersulfones, polyetheretherketones, polycarbonates, and acrylics. resin, polystyrene, and the like. These materials may be used singly, two or more of them may be mixed, or a laminate may be formed. Dielectric substrate 10 may also contain conductive particles, insulating particles, magnetic particles, or a mixture thereof.

In embodiments of the present invention, the thickness of the dielectric substrate can be made sufficiently thin with respect to the wavelength of the electromagnetic wave. It is known that traveling waves do not occur in the dielectric substrate if the dielectric substrate is sufficiently thin with respect to the wavelength of the electromagnetic wave. "Sufficiently thin" can be less than 1/2 wavelength. Below 1/2 wavelength, traveling waves are not guided. This is a phenomenon called electromagnetic wave cutoff. Furthermore, it can be 1/10 or less of the wavelength. In general, when the difference in propagation distance of electromagnetic waves is 1/10 or less of the wavelength, no substantial phase difference occurs. In other words, when the distance between the metal plate and the flat inductor is 1/10 or less of the wavelength at the dielectric base material, the electromagnetic wave reemitted from the metal plate and the reflected wave from the flat inductor have a substantial position due to the distance. no difference. It is believed that electromagnetic waves will not be guided within a sufficiently thin dielectric substrate sandwiched between conductors, and electromagnetic waves are normally cut off at such thinness, and such Electric and magnetic fields are not localized on the dielectric substrate. Note that this wavelength in the embodiment of the present invention can be the attenuation center wavelength. Moreover, unexpectedly attenuation is obtained even when the dielectric substrate is less than 1/100th of the wavelength. Such a thickness is at the same level as the unevenness of the mirror surface with the highest precision, and attenuation is obtained with a structure that is substantially thin with respect to the scale of the electromagnetic wave.

As a result of various experiments and simulations, the inventors have found that stationary localization of electric and magnetic fields due to electromagnetic waves occurs even within a sufficiently thin dielectric substrate. 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 of the wavelength in the millimeter waveband, and even thinner than 1/10 of the wavelength in the millimeter waveband. Therefore, the electromagnetic wave attenuation film can attenuate electromagnetic waves in the millimeter wave band even though it is a thin film. The thickness of dielectric substrate 10 may be constant or variable.

Dielectric substrate 10 can be a single layer or multiple layers. The front surface of the dielectric substrate 10 may have unevenness. The dielectric substrate 10 may have a carrier 11 and an underlying layer 12 on the carrier 11 . The front surface of the underlayer 12 may have unevenness. Carrier 11 can be an extruded film. Extruded films can be unstretched films or stretched films. The base layer 12 may be composed of two layers, a molding layer and an anchor layer. Further, an adhesive layer may be provided to improve adhesion between the underlying layer 12 and the metal plate and flat inductor. The underlying layer 12, the molding layer, the anchor layer, and the adhesive layer can use the same materials as those constituting the dielectric substrate.

The carrier 11 constitutes the back surface 10 b of the dielectric substrate 10 , and the base layer 12 constitutes the front surface 10 a of the dielectric substrate 10 . When the front surface 10a has unevenness, it is preferable to provide the base layer 12 with an uneven structure. That is, the front surface 10a of the dielectric substrate 10 has unevenness corresponding to the unevenness of the base layer 12, and the back surface 10b of the dielectric substrate 10 is generally flat.
The characteristics of the electromagnetic wave attenuation film 1 change depending on the unevenness of the front surface 10a. This point will be described later.

The thin-film conductive layer 30 covers the whole or part of the front surface 10 a of the electromagnetic wave attenuation film 1 in plan view. A flat plate inductor 50 covers all or part of the back surface 10b. As long as the performance of the electromagnetic wave attenuation film 1 is not significantly impaired, the flat inductor 50 may have a portion not covered by the thin film conductive layer 30 or the flat inductor 50, for example, in a portion of the peripheral edge of the electromagnetic wave attenuation film 1. good too.

Materials for the thin-film conductive layer 30 and the planar inductor 50 are not particularly limited as long as they have conductivity. 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 layer 30 and the planar inductor 50 can be formed by vacuum deposition on the dielectric substrate 10, for example. 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 layer 30 can be 10 nm or more and 1000 nm or less. If it is less than 10 nm, the function of attenuating electromagnetic waves may deteriorate. If it exceeds 1000 nm, productivity may drop.
The planar inductor 50 can be cast metal, rolled metal plate, metal foil, evaporated films, sputtered films and plated. 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 plate inductor 50 is a deposited film, a sputtered film, or a plated film, the thickness can be 0.5 μm or more and less than 5 mm. The thickness of the plate inductor 50 can be 0.5 μm to 5 mm. Also, when the flat plate inductor 50 is cast, the thickness is not specified, but the maximum dimension can be 10 mm or more. Also, the thickness of the flat plate inductor 50 can be made equal to or greater than the skin depth determined by the attenuation center wavelength. Also, the thickness of the planar inductor 50 can be greater than the thickness of the thin film conductive layer 30 .
The materials of the thin film conductive layer 30 and the planar inductor 50 can be the same metal species. The same metal species may be the same pure metal or an alloy of the same metal (eg, both aluminum alloys), or the thin film conductive layer 30 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 layer 30 and the plate inductor 50 may be made of different metals.
The thin film conductive layer 30 may have a topcoat layer 200 on the opposite side of the dielectric substrate. FIG. 3 is a schematic diagram showing a part of the cross section taken along line II of FIG. 1 when a topcoat layer is provided. The planar inductor 50 may also have a topcoat layer 200 on the opposite side of the dielectric substrate. The thickness of the topcoat layer 200 can be 0.1 μm or more and 50 μm or less. Furthermore, it can be 1 μm or more and 5 μm or less. The topcoat layer 200 may be a single layer or multiple layers. The material of the topcoat layer 200 can be a single substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamide-imide, epoxy resin, and silicone resin. It may also contain insulating particles, magnetic particles, conductive particles, or a mixture thereof. The particles can be inorganic particles. By providing the topcoat layer 200, the impedance matches the air through which radio waves propagate, and the radio waves can be effectively attenuated by the thin-film conductive layer. Further, the thin film conductive layer 30 and the flat inductor 50 can be provided with corrosion resistance, chemical resistance, heat resistance, friction resistance, impact resistance, and the like. For example, by using crosslinked acrylic resins, crosslinked epoxy resins, polyamides, polyimides, polyamideimides, silicone resins, etc., it is possible to improve heat resistance while improving solvent resistance. Further, by using a urethane resin or the like, the impact resistance can be improved, and by using a silicone resin, the friction resistance can be improved.

The dielectric substrate 10 may have a first region 121 with a relatively low front surface and a second region 122 with a relatively high front surface. The planar view shape of the first region 121 can be a square, hexagon, cross, other polygons, circle, or ellipse. The squares, hexagons, crosses and other polygons can have rounded corners.
The first regions 121 are arranged discretely. The first regions 121 are arranged in a two-dimensional matrix at a predetermined pitch. The second region 122 surrounds the first region 121 in plan view of the electromagnetic wave attenuation film 1 . The thin conductive layer 30 on the first region 121 includes a metal plate. That is, a metal plate is provided on the first region 121 . In other words, the metal plate is located on the first area 121 . The planar shape of the metal plate can be square, hexagon, cross, other polygons, circle, or ellipse. The squares, hexagons, crosses and other polygons can have rounded corners. The second region 122 is formed in a mesh shape or a lattice shape in plan view according to the above-described aspect of the first region 121 .
The surfaces of the first region 121 and the second region 122 in contact with the thin-film conductive layer 30 are generally parallel to the rear surface. Furthermore, a part or the entire surface may have a rough surface. As will be described later, the electrical resistance of the thin-film conductive layer 30 can be adjusted by roughening the surfaces of the first region 121 and the second region 122 that are in contact with the thin-film conductive layer 30 partially or entirely.

As shown in FIG. 2, the thin film conductive layer 30 is formed on the top surfaces of the first region 121 and the second region 122 . On the other hand, the thin film conductive layer 30 does not exist on the side surface 122a of the second region 122 extending above the first region 121, and the dielectric substrate 10 is exposed. Thereby, the thin film conductive layer 30 in the first region 121 and the thin film conductive layer 30 in the second region 122 can be electrically insulated. A portion of the side surface 122a may be covered with the thin film conductive layer 30 as long as it can be electrically insulated.
The metal plate of each first region can have a shape that follows the shape of the first region 121 in plan view. That is, it can be the same as or similar to the planar view shape of the first region 121 . Moreover, the dielectric base material 10 may include a plurality of metal plates having the same shape and size when viewed from above. Further, the first regions 121 can be discrete while remaining parallel to each other, and the density of placement on the front surface can be generally uniform.

The electromagnetic wave attenuation film 1 is considered to exhibit a unique mechanism at a specific wavelength due to the above-described 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 transmitted through the metal plate induces an alternating current in the plane inductor 50 parallel to the plane of incidence of the plane inductor 50 according to Faraday's law. This alternating current produces a varying magnetic field in the dielectric substrate adjacent to the planar inductor 50 according to Ampere's law. Also, the varying magnetic field becomes a magnetic flux that varies with the magnetic permeability as a coefficient.

An electric field generated by a fluctuating flux normally induces a current directed to constrain the flux according to Henry's law. However, in the case of the configuration of the present application, contrary to expectations, it works in the opposite direction to increase the current. This causes the metal plate to carry more current than was induced by the incident wave. That is, although the area of the metal plate is smaller than the area of the planar inductor 50 , it can generate a current comparable to that of the planar inductor 50 .

The direction of current generated in this metal plate is opposite to that of the flat inductor 50 . A closed circuit can be formed by the opposing currents flowing through the metal plates and the planar inductor 50 and the displacement current flowing between them. If a closed circuit is formed only between the metal plate and the flat inductor 50 and no horizontal electric flux is generated in the electromagnetic wave attenuation film in the space outside the electromagnetic wave attenuation film, reflected waves cannot be generated. Further, the reflected wave from the flat plate inductor 50 and the electromagnetic wave re-emitted by the current of the metal plate are out of phase by π, so they cancel each other out.

Reflected waves by the electromagnetic wave attenuation film are attenuated by the above principle. From the energy point of view, it is believed that multiple mechanisms act synergistically, as described below.

The first mechanism is the generation of a non-traveling, periodically oscillating electromagnetic field by the incident wave, as shown later by magnetic field density simulations. First, magnetic flux is induced in the incident wave in the tangential direction of the flat inductor 50 by the flat inductor 50 on the back surface of the dielectric substrate 10 . The induced magnetic flux generates an electric field perpendicular to the planar inductor 50 in a direction extending from a pair of opposing sides of the thin film conductive layer 30 (ie, metal plate) on the first region 121 . Then, when an electromagnetic wave is incident on the planar inductor, the fluctuating magnetic flux induces a current close to the surface of the planar inductor. Current induced in the planar inductor produces a magnetic field in the dielectric substrate 10 in close proximity to the surface of the planar inductor. This electric field and the current in the metal plate and the planar inductor 50 generate a magnetic field between the metal plate and the planar inductor 50 in the same direction as the magnetic flux induced by the planar inductor 50 . Here, the shape of the metal plate is plate-like, and the material thereof is metal. The electric field generated in the dielectric substrate fluctuates with the same period as the incident wave. The periodic variation of the magnetic field causes the electric field between thin film conductive layer 30 and planar inductor 50 to vary periodically. As a result, a non-progressing, periodically fluctuating electromagnetic field is generated between the thin film conductive layer 30 and the planar inductor 50 . Alternating currents are induced in metal plates by magnetic fields in a periodically varying electromagnetic field, as shown later by current density simulations. Also, the periodically varying electric field produces a periodically varying potential in the metal plate. The electromagnetic field does not progress and stays in place, the induced alternating current is a power loss, and as a result the energy of the electromagnetic field is converted into heat, which absorbs the electromagnetic waves. Also, it is considered that the alternating current induced in the metal plate re-radiates electromagnetic waves from the surface of the metal plate opposite to the surface in contact with the dielectric substrate 10 .
In other words, part of the electromagnetic wave energy captured by the electromagnetic wave attenuation film is converted into heat energy, and the rest is reemitted. In addition, according to the classical theory of electromagnetism represented by Maxwell's equations, etc., the frequency of the induced alternating current is the same as the frequency of the incident wave, so the frequency of the reemitted electromagnetic wave is the same as the frequency of the incident wave. be the same. As a result, an electromagnetic wave of the same frequency as the incident wave is re-emitted. In addition, when an oscillating electromagnetic field is considered as a quantum, it is conceivable that the quantum loses energy and reemerges electromagnetic waves with lower energy and longer wavelength. Re-emission is considered to include stimulated emission and spontaneous emission by incident electromagnetic waves. Stimulated emission is considered to emit an electromagnetic wave that is coherent with a reflected wave in which the incident wave is reflected in the reflection direction of the incident wave, that is, in the specular reflection direction. Spontaneous emission is thought to decay with time. Also, the spatial distribution of spontaneous emission is considered to be close to Lambertian reflection when the electromagnetic wave attenuation film does not have a diffractive structure, an interference structure, or a refractive structure.
The attenuation center wavelength correlates with the dimension W1 in the planar direction of the thin film conductive layer 30 formed on the first region 121 shown in FIG. That is, the wavelength of the electromagnetic wave that is preferably 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 easily set with a high degree of freedom. Therefore, it is possible to easily obtain a configuration capable of capturing linearly polarized electromagnetic waves in the band of 15 GHz or more and 150 GHz or less.

Periodic fluctuations in the non-progressing electromagnetic field are thought to occur between opposite sides of the planar shape of the metal plate. Therefore, for the first mechanism to occur, it is preferable that the sides of a certain length face each other. Based on this fact and the results of studies by the inventors, it is possible to use a section of the thin film conductive layer with a width W1 of 0.25 mm or more as a metal plate. If a plurality of W1 values are possible for a certain metal plate, the maximum value among them can be defined as W1 for that metal plate. 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. As shown in FIG. 25, the relationship between the frequency of the attenuated electromagnetic wave and the width of the metal plate can be expressed as a straight line on a graph with each logarithm. That is, the frequency of the attenuated electromagnetic wave is a power function of the width of the metal plate. The power of the function is approximately -1 and is almost inversely proportional.
The plurality of metal plates included in the thin film conductive layer may be arranged in a plurality of types with different dimensions W1. In this case, the attenuation peaks of the respective electromagnetic waves are superimposed, and the bands of electromagnetic waves that can be attenuated can be broadened.

The second mechanism is electromagnetic field confinement by thin film conductive layer 30 and planar inductor 50 . In the electromagnetic wave attenuation film 1 , the dielectric substrate 10 is sandwiched between the thin film conductive layer 30 and the flat inductor 50 in the first region 121 . For this reason, the electric field generated in the dielectric substrate 10 of the electromagnetic wave attenuation film 1 by the electromagnetic wave is generated in the dielectric substrate 10 between the thin film conductive layer 30 including the metal plate and the flat inductor 50 by the charge and current of the metal plate. trapped in That is, the metal plate suppresses the electromagnetic field and confines the electromagnetic field to the dielectric substrate 10 . That is, the metal plate can act as a choke. In other words, the metal plate can be a choke plate that functions as a choke.
Magnetic flux is also believed to be induced in the first region by periodic variations in this confined electric field. This concentrates the oscillating electromagnetic field in the first region and increases the energy density of the electromagnetic field. Generally, the higher the energy density, the easier it is to attenuate, so this mechanism efficiently attenuates electromagnetic waves. In the second mechanism, the higher the dielectric loss tangent of the dielectric substrate 10, the greater the energy loss of the electromagnetic field accumulated in the dielectric substrate. Also, a magnetic field integrated in a dielectric substrate accompanies a large current in the metal plate, and an electric field integrated in the dielectric substrate produces a large potential difference. Power loss, which is the product of large current and large potential difference, can be increased. As a power loss, the energy of the electromagnetic waves is consumed and the electromagnetic waves are attenuated as a result.

A third mechanism is due to power loss in the electrical circuit including the capacitors due to the opposing thin film conductive layers 30 and planar inductors 50 and the dielectric substrate 10 therebetween. In the electromagnetic wave attenuation film 1 , the dielectric substrate 10 is sandwiched between the thin film conductive layer 30 and the flat inductor 50 both in the first region 121 and the second region 122 . Therefore, first region 121, second region 122, and dielectric substrate 10 function as a capacitor. Therefore, the electromagnetic wave incident on the dielectric substrate 10 of the electromagnetic wave attenuation film 1 is attenuated by the electric circuit including the capacitor.
The larger the capacitance of the capacitor, the greater the amount of energy that can be stored by accumulating a large amount of electric charge.
Since the capacitance is inversely proportional to the thickness of the dielectric substrate 10, from this point of view, it is more preferable that the thickness of the dielectric substrate 10 is thin. In addition, since the distance between the thin film conductive layer 30 and the flat inductor 50 is determined by the thickness of the dielectric substrate 10, the electrical resistance between the thin film conductive layer 30 and the flat inductor 50 is determined by the thickness of the dielectric substrate 10. proportional to If the resistance of the dielectric substrate 10 is small, the leak current in the dielectric substrate 10 increases, and the current flowing through the electric circuit including the capacitor of the thin film conductive layer 30 and the flat inductor 50 increases. Therefore, the power loss due to leakage current is likely to increase, and the power loss is likely to absorb the energy of electromagnetic waves. In addition, in the electromagnetic wave attenuation film 1 of the embodiment of the present invention, even if the thickness of the dielectric substrate 10 at the location where the metal plate is arranged is changed, the wavelength of the attenuated electromagnetic field does not shift, so the electric circuit including the capacitor does not shift. The thickness of the dielectric substrate 10 can be designed in accordance with the characteristics of .

As described above, the electromagnetic wave incident on the electromagnetic wave attenuation film 1 generates an electromagnetic field in the dielectric substrate 10 near the surface of the flat inductor by the first mechanism, and the electromagnetic field generated by the electromagnetic wave by the second mechanism. is captured by being trapped. Thus, the electromagnetic wave attenuation film 1 can capture electromagnetic waves. The trapped electromagnetic waves are attenuated by electric field losses and power losses due to the second mechanism and power losses due to the electrical circuit of the third mechanism. Also, by providing the topcoat layer 200, the impedance matches the air through which radio waves propagate, and the radio waves can be effectively attenuated by the thin-film conductive layer. The wavelength of the electromagnetic wave to be attenuated can be changed by changing the dimension W1 of the metal plate, as shown in FIG. More specifically, the frequency at which the reflected wave is minimized, that is, the frequency at which attenuation is maximized, exhibits a very high degree of approximation to the power of the size of the metal plate, as shown in FIG. Therefore, in the electromagnetic wave attenuation film 1, the electromagnetic wave attenuation characteristics can be easily set with a high degree of freedom. Therefore, it is easy to set to capture linearly polarized, circularly polarized, or elliptically polarized radio waves in the band from 15 GHz to 150 GHz.
In the simulation of FIG. 25, the metal plate is square and W1 is the length of one side.

The dielectric base material of the electromagnetic wave attenuation film 1 of the first embodiment has a first region 121 and a second region 122, and at least part of the side surface 122a of the second region 122 is not covered with the thin film conductive layer 30. , exposed. As a result, it is possible to easily increase the area to which electromagnetic waves can enter without increasing the planar view area of the electromagnetic wave attenuation film, and to efficiently capture and attenuate electromagnetic waves.

In the electromagnetic wave attenuation film 1 of the first embodiment, the thin film conductive layer 30 on the second region 122, which serves as a support cage, mainly enhances the second mechanism and the third mechanism, thereby improving the attenuation of electromagnetic waves. do.
Furthermore, according to the inventors' study, it is considered that the electric field is strong at the peripheral edge of the metal plate, and that the support cage near the peripheral edge also generates an electric potential.

FIG. 4 shows the simulation result of the electric field strength without the support cage, and FIG. 5 shows the simulation result of the electric field strength with the support cage. 4 and 5, the peripheral edge of the metal plate in (a) is enlarged in (b), and the metal plate is denoted by A and the support cage by B, respectively.
Comparing FIG. 4(b) and FIG. 5(b), it can be seen that the electric field intensity at the peripheral edge of the metal plate is stronger in FIG. 5(b). That is, it is believed that the above-mentioned electric potential generated in the support cage contributes to greater power loss in the first mechanism.

In the electromagnetic wave attenuation film 1, the role played by the third mechanism is also important. When an electric field is induced in the dielectric substrate 10, the electromagnetic field is confined below the metal plate. That is, an electromagnetic field with high energy density is generated below the metal plate. The confined electromagnetic field is believed to be attenuated by power loss by the second mechanism and dielectric loss by the third mechanism.

The inventors' studies have shown that the attenuation due to the first mechanism changes depending on the admittance (reciprocal of electrical resistance) of the metal forming the metal plate. An admittance (siemens/m) of 10,000,000 or more was obtained, and good attenuation of electromagnetic waves was obtained. Silver is known as a substance having the highest admittance among normal conductors, and since its admittance is 61 to 66×10 ⁶ , the upper limit of the admittance is about 70 million. A metal having an admittance of 5 million or more and 70 million or less can be used. The metal that makes up the metal plate 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. Metal plates of these metals have shown good electromagnetic wave attenuation.
On the other hand, in the present invention, the surface of the metal plate may be oxidized, nitrided or oxynitrided. Metal oxide and metal nitride on the surface of the metal plate can be formed by surface treatment. The surface treatment can be chemical treatment using chemicals, heat treatment, or both. Also, a metal oxide film may exist in the metal plate, or a layer in which metal and metal oxide are mixed may exist. In such a configuration, the resistance value of the metal plate increases, the voltage drop increases, the power loss increases, and the attenuation of electromagnetic waves can be improved.
Also, the metal plate 30A can be a multilayer film in which films of different materials are laminated. The material of the laminated film can be a conductor or an insulator.

An example of the manufacturing procedure of the electromagnetic wave attenuation film 1 will be described.
First, the dielectric substrate 10 is formed. The dielectric substrate 10 having the base layer 12 is completed by disposing the resin for forming the irregularities in layers on the carrier 11 and forming the first region and the second region on the surface. The resin forming the underlayer 12 can be a photosensitive resin. In this case, photolithography can be used. The photosensitive resin can be a negative resist or a positive resist. The base layer 12 can also be formed from a photocurable resin. The base layer 12 can also be formed of a thermoplastic resin. Thermal transfer can be used in this case. The base layer 12 can also be formed of a thermosetting resin. The resin may be a solvent-soluble soluble resin (oily ink). Also, the resin may be a water-soluble resin (aqueous ink).

Next, a thin film conductive layer 30 and a flat inductor 50 are formed on the front surface 10a and the rear surface 10b of the dielectric substrate 10, respectively. Thin film conductive layer 30 and planar inductor 50 may be formed by physical deposition. Physical deposition can be evaporation or sputtering. Either the thin film conductive layer 30 or the flat inductor 50 may be formed first, and the materials of both may be different. Also, the flat plate inductor 50 can be any one of casting, rolled metal plate, metal foil, evaporated film, sputtered film and plating. The casting material can be cast iron or aluminum alloy. The material of the rolled metal plate can be steel, stainless steel, aluminum, or aluminum alloy. Plating can be electrolytic or electroless. The plating can be copper plating, electroless nickel plating, electrolytic nickel plating, zinc plating, electrolytic chrome plating, or a laminate thereof.
In the thin film conductive layer 30, it is important that the metal plate and other portions are not connected. Since the width W1 described above changes if they are connected, there is a possibility that the attenuation property of the electromagnetic waves will differ from the assumption. Therefore, a step of removing the thin film conductive layer 30 formed on the side surface of the second region may be added. Laser etching or the like can be used for this step.

When the topcoat layer 200 is provided, the coating method is not particularly limited, and may be appropriately selected from methods used in film production. Examples of coating methods include gravure coating, reverse coating, gravure reverse coating, die coating, and flow coating.

In the manufacturing procedure described above, the carrier 11 may be peeled off after the underlying layer 12 is formed. In this way, a single-layer dielectric substrate consisting of only the underlying layer 12 is formed.

As another example of the manufacturing procedure, after the thin film conductive layer 30 and the flat inductor 50 are formed on the dielectric substrate, the uneven shape may be formed on the thin film conductive layer 30 side. In this case, transfer using a plate is suitable. When thermal transfer is performed, a plate is pressed against the thin film conductive layer 30 to heat it.
In this manufacturing procedure, the thin-film conductive layer 30 pressed by the plate tends to be stretched to connect the metal plate and other portions. As a method for solving this problem, in addition to the above-described laser etching, there is an improvement in plate shape. For example, if the periphery of the convex portion forming the first region is sharpened on the plate, the peripheral edge of the metal plate is cut when the plate is pressed against the thin film conductive layer 30 . As a result, it is possible to ensure that the metal plate is not connected to other portions during transfer.

A second embodiment of the present invention will be described with reference to FIGS. 6 to 9. FIG. In the following description, the same reference numerals are given to the same configurations as those already described, and redundant descriptions will be omitted. Also in the second embodiment, each of the above-described first, second, and third mechanisms is considered to occur.

6 and 7 show an electromagnetic wave attenuation film 61 of the second embodiment. FIG. 6 is a schematic plan view showing an electromagnetic wave attenuation film according to a second embodiment of the present invention, and FIG. 7 is a schematic view showing a part of the cross section taken along line II-II of FIG. FIG. 8 is a schematic diagram showing a part of the cross section along line II-II in FIG. 6 when a topcoat layer is provided.
The electromagnetic wave attenuation film 61 includes a dielectric substrate 62, a plurality of metal plates 30A, and a flat inductor 50. As shown in FIG. The thickness of the metal plate 30A can be 1000 nm or less.

The dielectric substrate 62 of the second embodiment can be made of the same material and configuration as the dielectric substrate of the first embodiment. The dielectric base material 62 may have a configuration in which an underlying layer is provided on the carrier 11, or may be configured from the carrier 11 alone. Both the front surface 62a and the rear surface 62b are flat or rough. Although the flat inductor 50 is provided on the back surface 62b, an adhesive layer may be provided between the back surface 62b and the flat inductor 50. FIG. The adhesive layer and the flat inductor 50 can be formed using the same material and manufacturing method as in the first embodiment. A plurality of metal plates 30A are arranged on the front surface 62a side. The metal plate 30A can be formed by etching after formation by a deposition method. This deposition method can be a physical deposition method or a chemical deposition method. Physical deposition methods are suitable for forming metal plates. Physical deposition can be vacuum evaporation or sputtering. A vacuum deposition method is preferable because of its high productivity. A metal plate can be obtained by printing a mask layer in a pattern in the shape of a metal plate, and then removing excess thin film conductive layer by etching. The etchant used for etching can be a sodium hydroxide solution. The concentration of the sodium hydroxide solution can be 0.001 mol/L or more and 1 mol/L or less. The metal of the metal plate 30A can be the same metal as in the first embodiment. The metal plates are arranged discretely. The attenuation center frequency can be expressed as a power function of the width of the metal plate. The plurality of metal plates 30A may have the same shape and size and may be arranged at regular intervals. In other words, two or more metal plates 30A having the same shape and size may be arranged at regular intervals. That is, the entire front surface 62a is not covered with a metal layer, and the dielectric base material 62 is exposed at a portion where the metal plate 30A is not arranged.

Alternatively, a plurality of metal plates 30A having the same shape and size as the metal plates 30A of the plurality of metal plates 30A having different shapes, sizes, or both may be arranged. In other words, a plurality of metal plates having different shapes, sizes, or both may be arranged, or a plurality of metal plates having the same shape and size may be arranged. The metal plates can be arranged at regular intervals and in regular orientations. Also, the spacing may be different and the orientation may also be different. Furthermore, the spacing may be different and the orientation may be the same. Also, the intervals may be constant and the directions of some may be the same. Furthermore, a metal plate set may include a plurality of metal plates that differ in shape, size, or both. All or part of the arrangement intervals of the metal plates constituting the metal plate set can be constant, or all can be different. The orientations of the metal plates that make up the metal plate set can be all or partly the same, or all can be different. A metal plate set having a plurality of metal plates that differ in shape, size, or both has a different spectrum of frequencies attenuated by each metal plate, and attenuates multiple frequency bands or broadens the attenuated frequency band. can do. Also, if the arrangement intervals of the metal plates are different, the attenuated frequency spectrum can also be different. Different orientations of the metal plate sets can result in different polarization dependence of the attenuation. The plurality of metal plates that constitute the metal plate set may have different frequencies attenuated, and the difference between the frequencies may be regular.
A plurality of metal plate sets may be arranged. A plurality of metal plate sets composed of metal plates having the same shape, size, arrangement, and the same shape, size, and arrangement as metal plates constituting a certain metal plate set may be arranged. Including multiple different metal plates in the thin film conductive layer allows for broadening the bandwidth, attenuating electromagnetic waves at multiple frequencies, or both.

The metal plate may be divided into multiple metal segments. In other words, the metal plate may consist of a plurality of metal segments. A plurality of metal segments within the metal plate may be conducting. The multiple metal segments may be interconnected with wires. The wiring may have impedance. This impedance may be matched to the metal segment. Multiple metal segments within the wiring and metal plate may function as a unit. Multiple metal segments may have different properties than when present alone. Specifically, the resonance frequency and the damping property may be different depending on whether the damping property exists alone or in the metal plate. Also, the cross-sectional shape of the metal plate can be planar, polyhedral, or curved. In the case of a polyhedron or curved surface, the distance between the base and the top, ie, the height, can be 50 μm or less. Also, the ratio of the height to the distance between the opposing sides of the metal plate can be 1:100 or more and 1:10 or less.

The attenuation property of the electromagnetic wave attenuation film of the second embodiment can be set by changing the width W1 of the metal plate in the same manner as in the first embodiment. It is also easy to set up to capture
Further, since the plastic film carrier 11 can be used as the dielectric substrate 62 as it is, the electromagnetic wave attenuation film of the second embodiment can be manufactured more easily than the electromagnetic wave attenuation film of the first embodiment.
The dielectric substrate 62 can also be a carrier having a rough surface on part or all of the front surface 62a and the rear surface 62b. The admittance of the metal plate 30A can be adjusted by roughening part or all of the front surface 62a.

In the prior art including Patent Document 5, it was thought that by making the resonant conductor thicker than the skin depth, sufficient alternating current is generated in the resonant layer, and the power loss of the alternating current attenuates the electromagnetic wave. However, the inventors have found that the attenuation of electromagnetic waves rather increases when the thickness of the metal plate 30A is equal to or less than the skin depth.

FIG. 9 shows simulation results of electromagnetic wave attenuation due to changes in the thickness of the metal plate 30A. The material of the metal plate is aluminum. The incident wave was a linearly polarized sinusoidal wave, which was incident perpendicularly to the electromagnetic wave attenuation film. In the simulation, the flat plate inductor was assumed to be a perfect conductor. The electromagnetic wave attenuation property of the electromagnetic wave attenuation film is measured by monostatic RCS based on the case of only a flat inductor. The vertical axis representing the attenuation of electromagnetic waves is expressed in decibels. Monostatic RCS (Rader Cross-Section) is an index representing the ease of detecting an object with a monostatic radar, and can be calculated by the following formula 1. Monostatic radar performs transmission and reception at the same point.

As a result of the simulation, as shown in FIG. 9, a large attenuation of electromagnetic waves was recognized when the thickness was 40 nm or more and 400 nm or less. When the thickness is less than 40 nm, the attenuation of electromagnetic waves is reduced.
In addition, when the metal plate 30A includes a conductive layer and a clad, stable film formation is possible if the thickness of the metal plate 30A including the conductive layer and the clad is 1000 nm or less.

The phenomenon shown in FIG. 9 has an interesting relationship with the skin depth. The skin depth of aluminum at a frequency of 41 GHz is approximately 400 nm. That is, when the thickness of the metal plate is less than the skin depth of the material, the attenuation of electromagnetic waves increases. In addition, the attenuation of electromagnetic waves is reduced below 1/e ² of the skin depth. This is because if the conductive layer is thicker than the skin depth, sufficient resistance cannot be obtained and the voltage drop necessary for power loss cannot be obtained, and the current is concentrated only near the center of the metal plate, causing a potential difference. It is conceivable that the current in the region is reduced. On the other hand, even if the thickness of the conductive layer is equal to or less than the skin depth, if the thickness is less than 1/ ^e2 of the skin depth, sufficient current for power loss may not be obtained. It goes without saying that power loss is given as the product of current and voltage. That is, if the following LN function formula 2 expressed using the natural logarithm of the value obtained by normalizing the thickness T of the metal plate with the skin depth d is satisfied, sufficient attenuation of electromagnetic waves can be obtained. I can say
-2 ≤ ln(T/d) ≤ 0 (2)
Further, when a metal having a low admittance is used for the metal plate, attenuation of electromagnetic waves can be obtained even within the range of the following formula (3). Further, when the area of the metal plate occupies a large proportion of the front surface of the dielectric base material, attenuation of electromagnetic waves can be obtained even within the range of formula 3 below. When this area ratio is large, the ratio of the area of the metal plate to the front surface of the dielectric substrate can be 50% or more and 90% or less.
0 < ln(T/d) ≤ 1 (3)
Based on Equations 1 and 2, the attenuation of electromagnetic waves can be obtained within the range of Equation 4 below.
-2 ≤ ln(T/d) ≤ 1 (4)
In addition, in the embodiment of the present invention, this skin depth can be calculated using the attenuation center frequency f. In other words, using the attenuation center frequency f, the skin depth d is calculated by the following equation 5 as well known.

The simulation results also showed that the attenuation increased when the thickness of the metal plate was less than the skin depth. This is because the current generated by the magnetic flux of the dielectric base material of the metal plate reaches the opposite side of the dielectric base material, and the reflected wave due to the dielectric inductor is canceled by the current. It is considered that this is because an electromagnetic wave with a phase difference of π is emitted. In addition, as the thickness of the metal plate becomes thinner than the skin depth, the current in the metal plate is regulated. A current is also generated across the metal plate, and it is believed that the reflected wave is more attenuated due to the increased emission of electromagnetic waves that cancel the reflected wave by the dielectric inductor.
Also, the electric field of the dielectric substrate between the metal plate and the dielectric inductor attracts the metal plate and the dielectric inductor. If the electric field is periodically fluctuating, the attractive force on the metal plate will also be periodically fluctuating. Therefore, the electric field of the dielectric substrate between the metal plate and the dielectric inductor causes the metal plate to vibrate. The energy of this vibration is converted into heat and lost. Therefore, the dynamics of the electromagnetic field acting on the metal plate may also contribute to the attenuation of the electromagnetic wave.
In addition, when 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 as a state of zero momentum. In addition, since the thickness of the metal plate is on the order of hundreds of nanometers, the energy level in the metal plate may be affected.
Thus, the interpretation of the phenomena in the embodiments of the present invention can be interpreted not only as classical electromagnetics, but also as classical mechanics or quantum mechanics.
Therefore, in interpreting Equation 4, the range is rationally determined, but it is not a range that is strictly calculated considering all physical phenomena. Therefore, when judging whether the target product falls within the range of the above formula, it is appropriate to consider and interpret the manifesting physical phenomenon.
It should be noted that, in the prior art, an example of using a conductor that is about the skin depth or thinner than the skin depth is not usually seen. Therefore, it is considered that the embodiment of the present invention differs from the conventional one in the interaction mechanism itself with electromagnetic waves in the millimeter wave band.

The relationship between the thickness of the metal plate and the skin depth, which exhibits desirable attenuation of electromagnetic waves, for a specific frequency band will be described in detail in examples according to the second embodiment, which will be described later.

Each embodiment of the present invention will be further described using examples.
(Example according to the first embodiment)
First, a master plate for nickel electroforming was prepared. A resist pattern was formed on the surface of a silicon wafer by photolithography. The photoresist used was of positive type, and the thickness of the photoresist was 10 μm. The formed resist pattern is a pattern in which square openings are arranged in a square region of 14 cm on a side in the XY coordinate system at coordinates that form a square lattice array with a constant period for both the X coordinate and the Y coordinate, and the i-line is exposed. The area is the inner area of said square.
Further, nickel electroforming was performed using this master plate to obtain a nickel mold having a pattern in which square projections in plan view were regularly arranged on the surface.

Next, an ultraviolet curable resin was dripped onto the patterned surface of the nickel mold, and the easily adhesive surface of a PET film having one surface treated for easy adhesion was placed on the ultraviolet curable resin. A roller was used to spread the UV-curable resin uniformly over the pattern surface, and the UV-curable resin was cured by irradiating UV rays through the transparent PET film.
The PET film was released from the nickel mold to obtain a dielectric portion composed of the PET film and the uneven layer made of the ultraviolet curable resin.

An Al film having a thickness of 500 nm was formed on both surfaces of the dielectric substrate using a vacuum deposition method to form a thin film conductive layer and a flat inductor.
The above is the manufacturing procedure of the example according to the first embodiment. In this procedure, a plurality of nickel molds with different parameters of the uneven layer surface were produced, and the electromagnetic wave attenuation films of Examples 1 and 2 were produced.
Each electromagnetic wave attenuation film according to each example had a thickness of about 60 μm and a weight of about 0.02 g, and was thin and lightweight.

(Modified example in which a top coat layer is provided in the example according to the first embodiment)
In the example according to the first embodiment, the electromagnetic wave attenuation film was produced by providing the topcoat layer 200 manufactured by the following procedure.
The structure represented by the above chemical formula A is mainly composed of an acrylic resin composition composed 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. 6 parts by mass of a hydroxyphenyltriazine-based UV absorber ("ADEKA STAB LA-46" manufactured by ADEKA Corporation) having a Specialty Chemicals Co., Ltd. "Tinuvin 479") 6 parts by mass, benzotriazole-based UV absorber (Ciba Specialty Chemicals Co., Ltd. "Tinuvin 329") 3 parts by mass, hindered amine radical scavenger (Ciba Specialty 5 parts by mass of "TINUVIN 292" manufactured by Chemicals Co., Ltd.) was added, and an ethyl acetate solvent was added to adjust the solid content. A hexamethylene diisocyanate type curing agent solution with a solid content of 75 parts by mass was used, and the ratio of the main solution and the curing agent solution was 10: 1 (at this time, the ratio of the number of hydroxyl groups in the main solution and the number of isocyanate groups in the curing agent solution was 1: 2), and ethyl acetate was added as a solvent component to adjust the solid content to 20 parts by mass. A coat layer 200 was obtained. The produced electromagnetic wave attenuation film had a thickness of about 70 μm and a weight of about 0.02 g, and was thin and lightweight.

(Example according to the second embodiment)
[57GHz to 90GHz]
(Example 1A)
With respect to the general theory described in Equation 4, the range of the relational expression ln(T/d) between the thickness T of the metal plate and the skin depth d, which shows preferable attenuation of electromagnetic waves in a specific frequency band in the millimeter wave band, is Since I was able to find it, I will explain it below.
Simulations performed in the band from 57 GHz to 90 GHz will be described. A PET film having a thickness (H1) of 50 μm was used as a dielectric substrate, and a metal plate, which was a thin film conductive layer, was set on one side of the film at regular intervals in both the X and Y coordinates. Furthermore, on the other surface of the dielectric base material, a flat aluminum inductor having a thickness (T2) of about 2 mm was set and a simulation was performed.
A simulation was performed on the relationship between the attenuation of electromagnetic waves and ln(T1/d) for each metal type with respect to frequencies of 57 GHz, 66 GHz, 71 GHz, 81 GHz, 86 GHz and 90 GHz.

The simulation results are described in Tables 1, 2 and FIGS. 10-15. FIG. 10 is a graph showing electromagnetic wave attenuation characteristics at 57 GHz of Example 1A. FIG. 11 is a graph showing electromagnetic wave attenuation characteristics at 66 GHz of Example 1A. FIG. 12 is a graph showing electromagnetic wave attenuation characteristics at 71 GHz of Example 1A. FIG. 13 is a graph showing electromagnetic wave attenuation characteristics at 81 GHz of Example 1A. FIG. 14 is a graph showing electromagnetic wave attenuation characteristics at 86 GHz of Example 1A. FIG. 15 is a graph showing electromagnetic wave attenuation characteristics at 90 GHz of Example 1A. 10 to 15, (a) shows the admittance and skin depth values, (b) shows the structure of the electromagnetic wave attenuation film, and (c) to (e) show the attenuation characteristics of silver, copper, and aluminum, respectively. Show the graph. In the graph, the natural logarithm of the value obtained by normalizing the thickness T1 of the metal plate by the skin depth d is taken on the horizontal axis, and the reflection amount of the metal plate having the same area as the dielectric base is set to 100 (reference). The vertical axis represents the amount of attenuation in the patterned metal plate, and the correlation between the two is shown in the figure.

Assuming that the absorption amount of the electromagnetic wave attenuation film is 10 dB or more as a guideline indicating a good attenuation amount, as is clear from Table 1 and FIGS. /d) ≤ -1.0 was shown to provide good attenuation.
It should be noted that the good attenuation characteristic of about 10 dB is not limited to the parameter values used in Example 1A, and can naturally be expected to be realized in a configuration with a certain range. For example, the width W1 of the metal plate is 0.9 mm to 1.4 mm, the distance W3 between the adjacent metal plates is 0.5 mm to 0.7 mm, the thickness H1 of the dielectric substrate is 5 μm to 300 μm, and the thickness of the flat plate inductor is If the thickness is T2, a good attenuation characteristic of about 10 dB can be expected even with a configuration of 0.5 μm to 5 mm.

電磁波減衰フィルムの吸収量が１０ｄＢ以上を良好な減衰量を示す目安とすると、表３及び図１６から、実施例１Ｂにおいて、金属面積の割合が１０～４０％付近で良好な減衰量を得られることが示された。 (Example 1B)
In the same manner as in Example 1A, a PET film having a thickness (H1) of 50 μm was used as the dielectric substrate, and the total area of the metal plate, which is a thin conductive layer on one side thereof, was equal to the total area of the XY plane of the dielectric substrate. It was set by changing the ratio of the occupancy. Furthermore, on the other surface of the dielectric base material, a flat aluminum inductor having a thickness (T2) of about 2 mm was set and a simulation was performed. The metal plate was made of aluminum as a metal species, had a width W1 of 1.0 mm and a thickness T1 of 80 nm, and the metal area ratio was changed by adjusting the distance W3 between the metal plates.
The simulation results are illustrated in Table 3 and FIG. FIG. 16 is a graph showing electromagnetic wave attenuation characteristics according to metal area ratios at 81 GHz in Example 1B. (a) shows the configuration of the electromagnetic wave attenuation film, and (b) shows the attenuation characteristics.

If the absorption amount of the electromagnetic wave attenuation film is 10 dB or more as a guideline to indicate a good attenuation amount, it can be seen from Table 3 and FIG. was shown.

(Example 1C)
As in Example 1A, a PET film having a thickness (H1) of 50 μm was used as a dielectric substrate, and a metal plate as a thin film conductive layer was arranged on one side thereof in a pattern arrangement similar to that in FIG. The shape was changed to a shape other than a square, and an aluminum plate inductor with a thickness (T2) of about 2 mm was set on the other side of the dielectric base material to simulate electromagnetic wave attenuation characteristics. The metal plate used aluminum as a metal species, and the thickness T1 was set to 80 nm.

[Rectangular]
FIG. 17 is a graph showing electromagnetic wave attenuation characteristics of a rectangular metal plate in Example 1C. (a) shows the shape of the metal plate, where W7 is the length of the longer side of the rectangle, and W8 is the length of the shorter side. (b) is a partially enlarged view of the vicinity of the arrangement pattern passing through line II-II in FIG. 6 in this embodiment, and W4 represents the distance between the centers of the rectangles. (c) represents dimensions of W7, W8 and W4. (d) shows attenuation characteristics with the horizontal axis representing frequency.
From the simulation results, a good attenuation characteristic with an absorption amount of 10 dB or more appeared near 82.8 GHz.

[Hexagonal shape]
FIG. 18 is a graph showing electromagnetic wave attenuation characteristics of a hexagonal metal plate in Example 1C. (a) is the shape of the metal plate, and W9 represents the length of one side of the hexagon. (b) is a partially enlarged view of the vicinity of the arrangement pattern passing through line II-II in FIG. 6 in this embodiment, and W4 represents the distance between the centers of the hexagons. (c) represents the dimensions of W9 and W4. (d) shows attenuation characteristics with the horizontal axis representing frequency.
From the simulation results, a good attenuation characteristic with an absorption amount of 10 dB or more appeared near 71.2 GHz.

[Convex shape]
FIG. 19 is a graph showing electromagnetic wave attenuation characteristics when the metal plate has a convex shape in Example 1C. (a) represents the shape of the metal plate. W10 is the length of the upper side of the upper part protruding inside the convex shape, W11 is the length of the lower side of the lower part of the convex shape, W15 is the length of the side of the upper part, and W16 is the length of the side of the lower part. represents The convex shape is bilaterally symmetrical with respect to a straight line connecting the midpoint of the upper side of the upper portion and the lower side of the lower portion. Also, the center of a rectangular shape that is in contact with the lower side of the lower portion, the left and right side sides of the lower portion, and the upper side of the upper portion and that surrounds the convex shape is defined as the center of the present convex shape. (b) is a partially enlarged view of the vicinity of the arrangement pattern passing through line II-II in FIG. 6 in this embodiment, and W4 represents the distance between the centers of the convex shapes. (c) represents dimensions of W10, W11, W15, W16 and W4. (d) shows attenuation characteristics with the horizontal axis representing frequency.
From the simulation results, a good attenuation characteristic with an absorption amount of 10 dB or more appeared around 87 GHz.

[Triangular]
FIG. 20 is a graph showing the electromagnetic wave attenuation characteristics of the triangular metal plate in Example 1C. (a) shows the shape of the metal plate, and W12 represents the length of one side of the equilateral triangle. (b) is a partially enlarged view of the vicinity of the arrangement pattern passing through line II-II in FIG. 6 in this embodiment, and W4 represents the distance between the centers of the triangles. (c) represents the dimensions of W12 and W4. (d) shows attenuation characteristics with the horizontal axis representing frequency.
From the simulation results, a good attenuation characteristic with an absorption amount of 10 dB or more appeared near 80.8 GHz.

[Cross shape]
FIG. 21 is a graph showing electromagnetic wave attenuation characteristics of a cross-shaped metal plate in Example 1C. (a) represents the shape of the metal plate. The cross shape is symmetrical vertically and horizontally and is also symmetrical with respect to rotation of 90 degrees. W13 represents the length of the outer sides of the cross facing each other on the top, bottom, left, and right, and W14 represents the length of one side of the square surrounding the cross shape by contacting the sides facing each other on the top, bottom, left, and right of the outer side. Moreover, let the center of the said square be the center of this cross shape. (b) is a partially enlarged view of the vicinity of the arrangement pattern passing through line II-II in FIG. 6 in this embodiment, and W4 represents the distance between the centers of the crosses. (c) represents dimensions of W13, W14 and W4. (d) shows attenuation characteristics with the horizontal axis representing frequency.
From the simulation results, a good attenuation characteristic with an absorption amount of 10 dB or more appeared around 90 GHz.

(Example 2)
A square PET film having a thickness of 50 μm and a side of 14 cm was prepared as a dielectric substrate. A thin film conductive layer of aluminum with a thickness of 100 nm was formed on the entire one surface of the dielectric substrate using a vacuum deposition method. After that, using a mask, the thin film conductive layer was etched so that a metal plate was formed with constant intervals of both X and Y coordinates. On the other side, an aluminum plate inductor was attached using an adhesive layer. Also, a simulation was performed with this configuration.
The above is the manufacturing procedure of Example 2 according to the second embodiment. The parameters for Example 2 are as follows.
Width W1 of the metal plate: 16 types of metal plates with a width of 1.025 mm to 0.9 mm divided into 16 equal parts every 0.083 mm, 4 × 4 in the same direction at the same intervals of 0.1 mm They were arranged in a matrix to form a metal plate set. A plurality of these metal plate sets were arranged in the same direction at intervals of 0.1 mm. All metal plate sets were identical. That is, the metal plates that make up each metal plate set are not different between each metal plate set.
Distance W3 between adjacent metal plates: 0.1 mm
Metal plate thickness T1: 80 nm
Thickness T2 of flat plate inductor: about 2mm
Thickness of dielectric substrate H1: 50 μm
In addition, in order to examine the validity of the damping mechanism based on the experimental results, a simulation was performed using this configuration.

The electromagnetic wave attenuation films according to the respective examples, which did not contain a flat inductor, were all about 60 μm thick and about 0.02 g in weight, and were thin and lightweight. Therefore, it can be easily attached to parts where it is desired to suppress the influence of radiation noise caused by electromagnetic waves in the housings of mobile phones, in-vehicle radars, and the like.
In the simulation, all of Examples 1A to 1C and 2 showed good attenuation for electromagnetic waves in the millimeter wave band. Moreover, the attenuation factor was obtained by actual measurement, and the effectiveness of this configuration was confirmed. Although there are differences from the experimental results, which are considered to be effects other than attenuation based on various parameters and Maxwell's equations in the simulation, similar attenuation trends can be seen, so the mechanism in the embodiment of the present invention is considered appropriate. . In addition, the simulation and the actual measurement showed a similar tendency although there was a difference in the attenuation rate, and it was shown that the attenuation center frequency can be appropriately set.
22 and 23 show monostatic RCS damping characteristics in simulation results and actual measurement results of Examples 1A and 2, respectively. In Example 1A, aluminum having a metal plate width W1 of 1.0 mm, a distance W3 between adjacent metal plates of 0.5 mm, and a metal plate thickness T1 of 100 nm was used. In addition, the procedure of actual measurement is as follows.
Two metal plates of the same size were prepared, and the electromagnetic wave attenuation film of each example was attached to one of them so as to cover the whole. In an anechoic chamber, radio waves were irradiated to the metal plate with the electromagnetic wave attenuation film and the metal plate without the film, and the amount of reflected radio waves was measured using a network analyzer (Model E5071C manufactured by KEYSIGHT). The amount of monostatic RCS attenuation was evaluated with the amount of reflection of a metal plate to which no electromagnetic wave attenuation film was adhered as 100 (reference).

(Modification in which a topcoat layer is provided in Example 1A according to the second embodiment)
In Example 1A according to the second embodiment, an electromagnetic wave attenuation film was produced by using aluminum and setting the thickness T1 of the metal plate to 80 nm and providing the top coat layer 200 manufactured by the following procedure.
The structure represented by the above chemical formula A is mainly composed of an acrylic resin composition composed 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. 6 parts by mass of a hydroxyphenyltriazine-based UV absorber ("ADEKA STAB LA-46" manufactured by ADEKA Corporation) having a Specialty Chemicals Co., Ltd. "Tinuvin 479") 6 parts by mass, benzotriazole-based UV absorber (Ciba Specialty Chemicals Co., Ltd. "Tinuvin 329") 3 parts by mass, hindered amine radical scavenger (Ciba Specialty 5 parts by mass of "TINUVIN 292" manufactured by Chemicals Co., Ltd.) was added, and an ethyl acetate solvent was added to adjust the solid content. A hexamethylene diisocyanate type curing agent solution with a solid content of 75 parts by mass was used, and the ratio of the main solution and the curing agent solution was 10: 1 (at this time, the ratio of the number of hydroxyl groups in the main solution and the number of isocyanate groups in the curing agent solution was 1: 2), and ethyl acetate was added as a solvent component to adjust the solid content to 20 parts by mass. A coat layer 200 was obtained. The thickness of the topcoat layer was 6 μm.

(Comparative example 1)
An electromagnetic wave attenuation film was produced according to Example 1A without providing a topcoat layer.
Further, the electromagnetic wave attenuation film obtained in the modified example and comparative example 1 was crimped to a stainless steel plate via an adhesive, exposed to outdoor exposure for 10 years with a sunshine weather meter, and then the surface of the electromagnetic wave attenuation film was covered with a cotton cloth. After wiping with , the remaining state of the top coat layer and the electromagnetic wave attenuation layer, and changes in monostatic RCS attenuation characteristics were examined.
As a result, in the structure of the modified example, there was no deterioration in both the top coat layer and the electromagnetic wave attenuation layer, and it was confirmed that the formation of the top coat layer improved the monostatic RCS attenuation characteristics by matching the impedance, as shown in FIG. rice field.

As described above, each embodiment of the present invention has been described in detail with reference to the drawings, but the specific configuration is not limited to this embodiment. included. Some examples of modifications are given below, but not all of them, and other modifications are possible. Two or more of these changes may be appropriately combined.

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

In the first embodiment, the metal layer in the second region may be omitted and only a metal plate may be formed.

In the present invention, the aspect of the flat plate inductor is not limited to that formed on the entire back surface. For example, a plurality of metal plates may be arranged in the same manner as the front surface, or they may be arranged in a grid pattern.

In the present invention, the shape of the metal plate is not limited to a square, but can be set to various shapes such as a circle (including an ellipse), a polygon other than a square, various polygons with rounded corners, and irregular shapes.
It is preferable that the total area of the metal plate occupying the projected area of the front surface is 20% or more.
In this way, electromagnetic waves can be efficiently attenuated.

The electromagnetic wave attenuation film according to the present invention can be used by laminating a plurality of sheets. By differentiating the structural parameters of a plurality of laminated sheets, it becomes possible to adjust the damping properties in more detail.

In the first embodiment, the height of the first area and the second area may be reversed. In this case, the metal plate is in a relatively high position and the support cage is in a relatively low position.

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

In the electromagnetic wave attenuation film according to the present invention, it is not essential that the parameters such as the structural period and the dimensions of the metal plate are completely the same in all parts. For example, in the present invention, even when the above parameters vary within the tolerance range (approximately about 5% above and below) in the manufacturing process, it is included in "same shape and same size". Also, the “predetermined range of values” may be a regular range of values. This regularity can be a Gaussian distribution, a binomial distribution, a random or pseudo-random distribution with equal frequency within a given section, or a range of tolerances in the manufacturing process.

The support cage may consist of a plurality of spaced apart conductive segments. The gap in this case can be 1/10 or less of the wavelength of the electromagnetic wave to be captured. A support cage can be constructed from a plurality of conductive segments. In other words, the support cage may consist of multiple conductive segments.

In the electromagnetic wave attenuation film related to the present invention, after providing the release layer on the support base material, the electromagnetic wave attenuation film of the first embodiment and the second embodiment is provided, and an adhesive, adhesive, etc. is provided, and the transfer foil may be
Specifically, a base layer is provided after a release layer is coated and dried on a supporting substrate. In the case of adopting the configuration of the first embodiment, unevenness is imparted to the underlying layer, and the thin film conductive layer is provided by vapor deposition. After that, the thin film conductive layer formed on the side surface of the second region is removed, and a layer serving as a dielectric substrate is provided. A transfer foil can be obtained by laminating a flat inductor and an adhesive in this order on a dielectric substrate. In the case of the configuration of the second embodiment, a thin-film conductive layer is provided as a base layer, and a mask layer is printed in a pattern in the shape of a metal plate. After that, a metal plate can be obtained by removing the excess thin film conductive layer by etching. Furthermore, a transfer foil can be obtained by laminating a dielectric substrate, a flat inductor, and an adhesive in this order. When transferring to a metal housing or the like, the layer of the flat inductor may be omitted.
By using a transfer foil, it is possible to further reduce the thickness, further improve the followability, and it is possible to transfer to a complicated shape. can be widened.

According to the embodiments and modifications described above, the following remarks can be derived.
[Appendix 1]
a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a flat inductor or a bonding layer disposed on the back surface;
with
the thin film conductive layer comprises a plurality of metal plates;
The thickness T of the metal plate is 1000 nm or less,
Electromagnetic wave attenuation film.
[Appendix 2]
a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a flat inductor or a bonding layer disposed on the back surface;
with
the thin film conductive layer comprises a plurality of metal plates;
When the thickness of the metal plate is T and the skin depth is d, the following formula (2) is satisfied,
Electromagnetic wave attenuation film.
-2 ≤ ln(T/d) ≤ 0 (2)
[Appendix 3]
a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a flat inductor or a bonding layer disposed on the back surface;
with
the thin film conductive layer comprises a plurality of metal plates;
the dielectric layer has an uneven surface on the front surface, comprising a relatively low concave first region and a relatively high second region;
The first regions are arranged discretely,
The second region is arranged between the plurality of first regions,
the metal plate is disposed in the first region;
When the thickness of the metal plate is T and the skin depth is d, the following formula (2) is satisfied,
Electromagnetic wave attenuation film.
-2 ≤ ln(T/d) ≤ 0 (2)
[Appendix 4]
a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a flat inductor or a bonding layer disposed on the back surface;
with
the dielectric layer has an uneven surface on the front surface, comprising a relatively low concave first region and a relatively high second region;
the thin film conductive layer includes a plurality of metal plates disposed in the first region and a support cage disposed in the first region;
The first regions are arranged discretely,
The second region is arranged between the plurality of first regions,
Electromagnetic wave attenuation film.

In the above embodiments, the attenuation of electromagnetic waves is considered, and it is known that a conductor that attenuates a specific electromagnetic wave serves as an antenna for receiving radio waves. Therefore, the embodiments described above can also be used as receiving antennas. In addition, in the above-described embodiment, since quanta with zero momentum are captured in a two-dimensional system, it is conceivable that it can be used as an element for performing data calculation and recording in the quantum state of a metal plate.

As described above, the embodiment of the present invention differs from the conventional technology in the mechanism of interaction with electromagnetic waves, so products that exhibit an equivalent mechanism are considered to substantially use the embodiment of the present invention. should be caught.

1, 61 electromagnetic wave attenuation films 10, 62 dielectric substrates 10a, 62a front surfaces 10b, 62b rear surface 30 thin-film conductive layer 30A metal plate 50 flat inductor 200 topcoat layer 121 first region 122 second region

Claims (14)

a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a flat plate inductor disposed on the back surface;
with
the thin film conductive layer comprises a plurality of metal plates;
The metal plates are discretely arranged and
The ratio of the area of the plurality of metal plates to the area of the dielectric substrate is 10 to 40%,
When the thickness of the metal plate is T and the skin depth is d, the following formula (1) is satisfied,
An electromagnetic wave attenuation film used in the frequency band of 57 GHz to 90 GHz.
-2.5 ≤ ln(T/d) ≤ -1.0 (1) a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a bonding layer arranged on the back surface;
with
the thin film conductive layer comprises a plurality of metal plates;
The metal plates are discretely arranged and
The ratio of the area of the plurality of metal plates to the area of the dielectric substrate is 10 to 40%,
When the thickness of the metal plate is T and the skin depth is d, the following formula (1) is satisfied,
An electromagnetic wave attenuation film used in the frequency band of 57 GHz to 90 GHz.
-2.5 ≤ ln(T/d) ≤ -1.0 (1) 2. The electromagnetic wave attenuation film of claim 1 , wherein the thin film conductive layer and the planar inductor are spaced apart in the thickness direction of the dielectric substrate. The electromagnetic wave attenuation film according to any one of claims 1 to 3 , further comprising a topcoat layer on the thin film conductive layer. 5. The electromagnetic wave attenuation film according to claim 4 , wherein the top coat layer is impedance-matched with an air layer through which electromagnetic waves propagate. 6. The electromagnetic wave attenuation film according to claim 5 , wherein the top coat layer is mainly composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component. 7. The electromagnetic wave attenuation film according to claim 6 , wherein the top coat layer contains an ultraviolet absorber and an ultraviolet scattering agent in the acrylic resin composition. 8. The electromagnetic wave attenuation film according to any one of claims 1 to 7 , wherein said metal plate is made of silver, copper or aluminum. 9. The electromagnetic wave attenuation film according to any one of claims 1 to 8 , wherein a plurality of said metal plates having the same shape and size are arranged with a distance within a predetermined range. 10. The electromagnetic wave attenuation film according to any one of claims 1 to 9 , wherein said thin film conductive layer is configured to be capable of capturing electromagnetic waves incident from said front side. 11. The electromagnetic wave attenuation film according to any one of claims 1 to 10 , wherein said metal plate has a pair of opposing sides. 12. The electromagnetic wave attenuation film according to claim 11 , wherein the pair of opposing sides of the metal plate has a length of 0.25 mm or more and 4 mm or less. 13. The electromagnetic wave attenuation film according to any one of claims 1 to 12 , wherein the thickness of the dielectric substrate is sufficiently thin with respect to the attenuation center wavelength. 14. The electromagnetic wave attenuation film according to any one of claims 1 to 13 , wherein the thickness of the dielectric substrate is less than 1/10 of the attenuation center wavelength.

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