JP7823535B2 - Electromagnetic Wave Attenuation Film - Google Patents

Description

Embodiments of the present invention relate to electromagnetic wave attenuation films that can capture incident waves and attenuate reflected waves.

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

As an electromagnetic wave absorbing sheet for absorbing such electromagnetic waves, Patent Document 1 proposes a laminated sheet in which a rubber-like electromagnetic wave absorbing sheet and a paper-like sheet material such as cardboard are laminated together.
Furthermore, with the aim of being able to absorb radio waves in higher frequency bands, Patent Document 2 proposes an electromagnetic wave absorbing sheet that can absorb radio waves in frequency bands of 20 GHz or higher by aligning the longitudinal direction of flat soft magnetic particles with the surface direction of the sheet.

It is also known that radio wave absorbers with a packed structure of particles that have epsilon-iron oxide (ε-Fe2O3) crystals in the magnetic phase exhibit radio wave absorption performance in the range of 25 to 100 GHz (see Patent Document 3).

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

Electromagnetic wave absorbing sheets such as those described above are used in electronic devices as well as for the interior decoration of buildings. Furthermore, as described in Patent Document 6, acrylate copolymer-modified resins such as epoxy resin, polyurethane resin, chlorinated rubber resin, vinyl chloride resin, alkyd resin, unsaturated polyester resin, and epoxy acrylate resin are used as electromagnetic wave absorbing materials. Furthermore, rubber-based materials such as polyamideimide and synthetic rubber, as described in Patent Document 7, are also used.

JP 2011-233834 A Japanese Patent Application Laid-Open No. 2015-198163 JP 2008-060484 A International Publication No. 2010/093027 Japanese Patent Application Laid-Open No. 2020-009829 Patent No. 2612592 Japanese Patent Application Laid-Open No. 2006-86422

In recent years, wireless communications using millimeter wave bands above 30 GHz have become more practical in order to enable larger volumes of data to be sent and received, faster communications, and simultaneous multi-point connections, and the development of millimeter wave-compatible devices that make this possible is progressing. Furthermore, the use of automotive radar equipment that takes advantage of extremely narrow directivity is also progressing.

Interference caused by diffuse reflection of electromagnetic waves within a device's housing can cause the device to malfunction. Therefore, suppressing electromagnetic noise is an important aspect of electromagnetic wave utilization technology.
One method of suppressing electromagnetic noise is to use an electromagnetic wave absorbing sheet as described above, but at present, most of them are compatible with frequencies from 20 GHz to several tens of GHz, and are not compatible with the millimeter wave band.
Although electromagnetic wave absorbing sheets that absorb electromagnetic waves in the millimeter wave band exist, those currently in practical use are thick in order to maintain absorption performance, making it difficult to incorporate them into the housings of devices that are becoming increasingly highly integrated and therefore difficult to suppress electromagnetic noise.

In view of the above, an object of the present invention is to provide a thin electromagnetic wave attenuation film capable of attenuating electromagnetic waves in the millimeter-wave band. Furthermore, because electromagnetic wave absorbers installed in electronic devices, building interiors, and the like are used continuously for long periods of time, another object of the present invention is to provide an electromagnetic wave attenuation film with excellent environmental resistance, such as weather resistance and heat resistance. 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 refers to the ability to achieve a state in which an electric field and a magnetic field are steadily localized. Furthermore, the captured electromagnetic field is partially absorbed by being converted into heat, and partially re-emitted. In other words, the energy of the captured electromagnetic field is converted into heat energy and the energy of the re-emitted electromagnetic wave. Since this re-emission is generally considered to have low directionality, it is considered that electromagnetic waves in the direction of specular reflection are reduced, and the reflected wave is attenuated. Therefore, reflected electromagnetic waves can be attenuated by absorption due to conversion of incident electromagnetic waves to heat and scattering due to re-emission. Because electromagnetic waves are attenuated by this unconventional mechanism, it is possible to achieve attenuation with a thin structure that is one-quarter or less of the wavelength, which was previously thought to be impossible. Furthermore, according to the embodiments of the present application, it is incredibly possible to obtain a film that can attenuate electromagnetic waves with a thickness on the order of ^10-2 of the wavelength.

The present invention provides 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 flat inductor or a laminating layer disposed on the back surface, and a top coat layer made of a resin material may be provided on the thin-film conductive layer.
The thin-film conductive layer is an electromagnetic wave attenuation film that includes a plurality of metal plates and satisfies the following formula in the frequency band of 35 GHz to 50 GHz, where T is the thickness of the metal plates and d is the skin depth:
-2.0 ≦ ln(T/d) ≦ -0.5

Another electromagnetic wave attenuation film according to the present invention is used in the 35 GHz to 50 GHz frequency band and comprises a dielectric substrate having a front and back surface, a thin-film conductive layer disposed on the front surface, and a flat inductor or laminating layer disposed on the back surface. The dielectric substrate has an uneven surface on the front surface, consisting of a first region of relatively low concave portions and a second region of relatively high portions. The thin-film conductive layer includes multiple metal plates disposed in the first region. The first regions are disposed discretely, and the second regions are disposed between the multiple first regions. A topcoat layer made of a resin material may be formed on the thin-film conductive layer.

Embodiments of the present invention provide a thin electromagnetic wave attenuation film that can attenuate 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 present invention. FIG. 2 is a schematic diagram showing a part of a cross section taken along line II in FIG. 1. FIG. 2 is a schematic diagram showing a part of the cross section taken along line II of FIG. 1 when a top coat layer is provided. 10A and 10B are images showing the simulation results of the electric field strength when there is no support cage, and FIG. 10B is a partially enlarged view of FIG. 10A and 10B are images showing the simulation results of the electric field strength when a support cage is provided, and FIG. 10B is a partially enlarged view of FIG. FIG. 3 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 in 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 top coat layer is provided. 10 is a graph showing a simulation result of the attenuation of electromagnetic waves depending on the thickness of the metal plate. 10 is a graph showing the electromagnetic wave attenuation characteristics at 35 GHz of Example 1A. 10 is a graph showing the electromagnetic wave attenuation characteristics at 39 GHz of Example 1A. 10 is a graph showing the electromagnetic wave attenuation characteristics at 41 GHz of Example 1A. 10 is a graph showing the electromagnetic wave attenuation characteristics at 45 GHz of Example 1A. 10 is a graph showing the electromagnetic wave attenuation characteristics at 50 GHz of Example 1A. 10 is a graph showing electromagnetic wave attenuation characteristics according to the proportion of metal area at 39 GHz in Example 1B. 10 is a graph showing electromagnetic wave attenuation characteristics when the metal plate is circular in Example 1C. 10 is a graph showing electromagnetic wave attenuation characteristics when the metal plate is rectangular in Example 1C. 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate has a hexagonal shape in Example 1C. 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate has a convex shape in Example 1C. 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate is triangular in Example 1C. 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate is cross-shaped in Example 1C. 10 is a graph showing the electromagnetic wave attenuation characteristics when the metal plate has a loop shape in Example 1C. 10 is a graph showing the electromagnetic wave attenuation characteristics of a modified example in Example 1C in which two layers of loop-shaped electromagnetic wave attenuation films are stacked on top of each other. 10 is a graph showing electromagnetic wave attenuation characteristics in Example 2. 10 is a graph showing the electromagnetic wave attenuation characteristics when a top coat layer is provided in Example 1A. 10 is a graph showing the relationship between the dimensions of a metal plate and the wavelength of an electromagnetic wave that is 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 planar inductor 50 formed on the back surface 10b of the dielectric substrate. The thin-film conductive layer is a thin layer of conductor. The thin-film conductive layer includes multiple metal plates. The thin-film conductive layer may also include a support cage (described below). The planar inductor is conductive and generates a current near the surface inside the planar inductor due to an external magnetic flux. The current also generates a magnetic field near the surface outside the planar inductor. The planar inductor can have a flat plate shape. The dielectric substrate is an insulating substrate sandwiched between the thin-film conductive layer and the planar inductor. In other words, the thin-film conductive layer and the planar inductor are spaced apart in the thickness direction of the dielectric substrate, sandwiching the dielectric substrate between them. The front surface can be the surface on which electromagnetic waves are incident. The back surface is the surface of the dielectric substrate opposite the front surface. 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. The thin-film conductive layer located on the second region 122 is referred to as a support cage. In other words, the thin-film conductive layer includes a support cage on the second region 122.
Furthermore, when the electromagnetic waves attenuated by the electromagnetic-wave-attenuation film have a frequency f at which they reach a single minimum value, this frequency f is defined as the central attenuation frequency f. When the electromagnetic waves attenuated by the electromagnetic-wave-attenuation film have multiple minimum values, the central attenuation frequency is defined as the average frequency of multiple frequencies that are −3 dB below the minimum value with the greatest attenuation. The central attenuation wavelength can be calculated by dividing the speed of light in the dielectric substrate by the central attenuation frequency f, which will be described later.
The electromagnetic wave attenuation film 1 may also be provided with a top coat layer 200 for achieving impedance matching with air and for improving the weather resistance of the sheet.

Figure 1 is a schematic plan view showing an electromagnetic wave attenuation film 1 according to a first embodiment of the present invention. Figure 2 is a schematic view showing a portion of a cross section taken along line II in Figure 1.

The dielectric substrate 10 is made of a dielectric material and can be sandwiched between conductive materials to form a capacitor. The dielectric substrate 10 can be made of an insulating material.
A typical example of a material constituting the dielectric substrate 10 is a synthetic resin. The type of synthetic resin is not particularly limited as long as it has sufficient strength, flexibility, and processability in addition to insulating properties. This synthetic resin can be a thermoplastic resin. Examples of synthetic resins include polyesters such as polyethylene terephthalate (PET); polyarylene sulfides such as polyphenylene sulfide; polyolefins such as polyethylene and polypropylene; polyamide, polyimide, polyamideimide, polyethersulfone, polyetheretherketone, polycarbonate, acrylic resin, and polystyrene. These materials may be used alone, or two or more types may be mixed or laminated. The dielectric substrate 10 may also contain conductive particles, insulating particles, magnetic particles, or a mixture thereof.

In an embodiment of the present invention, the thickness of the dielectric substrate can be sufficiently thin compared to the wavelength of the electromagnetic wave. It is known that when a dielectric substrate is sufficiently thin compared to the wavelength of the electromagnetic wave, no traveling waves are generated within the dielectric substrate. "Sufficiently thin" can be less than 1/2 of the wavelength. If the thickness is less than 1/2 of the wavelength, traveling waves are not guided. This is a phenomenon known as electromagnetic wave cutoff. Furthermore, the thickness can be less than 1/10 of the wavelength. Generally, when the difference in the propagation distance of an electromagnetic wave is less than 1/10 of the wavelength, no substantial phase difference occurs. In other words, when the distance between the metal plate and the planar inductor is less than 1/10 of the wavelength at the dielectric substrate, there is no substantial phase difference between the electromagnetic wave re-emitted from the metal plate and the reflected wave from the planar inductor due to that distance. It is believed that electromagnetic waves do not guide within a sufficiently thin dielectric substrate sandwiched between conductors. Typically, electromagnetic waves are cut off (cut off) at such a thin thickness, and electric or magnetic fields do not localize in such a dielectric substrate. Note that this wavelength in an embodiment of the present invention can be the attenuation center wavelength. Furthermore, unexpectedly, attenuation was achieved even when the dielectric substrate was less than 1/100 of the wavelength. This thickness is on the same level as the unevenness of the most precise mirror surface, meaning that attenuation is achieved with a structure that is essentially thin compared to the scale of electromagnetic waves.

Through various experiments and simulations, the inventors discovered that standing 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 half the wavelength of the millimeter wave band, and even thinner than 1/10 of the wavelength of the millimeter wave band. Therefore, despite being a thin film, the electromagnetic wave attenuation film is capable of attenuating electromagnetic waves in the millimeter wave band. The thickness of the dielectric substrate 10 can be constant or variable.

The dielectric substrate 10 can be single-layer or multi-layer. The front surface of the dielectric substrate 10 may have an uneven surface. The dielectric substrate 10 may have a carrier 11 and an underlayer 12 on the carrier 11. The front surface of the underlayer 12 may have an uneven surface. The carrier 11 may be an extruded film. The extruded film may be a non-stretched film or a stretched film. The underlayer 12 may be composed of two layers: a molding layer and an anchor layer. Furthermore, an adhesive layer may be provided to improve adhesion between the underlayer 12 and the metal plate and flat inductor. The underlayer 12, molding layer, anchor layer, and adhesive layer can be made of the same materials as those that make up the dielectric substrate.

The carrier 11 forms the back surface 10b of the dielectric substrate 10, and the underlayer 12 forms the front surface 10a of the dielectric substrate 10. If the front surface 10a has irregularities, it is preferable to provide an irregular structure on the underlayer 12. That is, the front surface 10a of the dielectric substrate 10 has irregularities corresponding to the irregularities of the underlayer 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 state of the unevenness of the front surface 10a, as will be described later.

When viewed from above, the thin-film conductive layer 30 covers all or part of the front surface 10a of the electromagnetic wave attenuation film 1. The flat 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, there may be portions of the flat inductor 50 that are not covered by the thin-film conductive layer 30 or the flat inductor 50, such as part of the periphery of the electromagnetic wave attenuation film 1.

The materials for the thin-film conductive layer 30 and the planar inductor 50 are not particularly limited as long as they are conductive. From the viewpoints 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, for example, by vacuum deposition on the dielectric substrate 10. The planar inductor 50 may be made of 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 be reduced. If it exceeds 1000 nm, productivity may be reduced.
The planar inductor 50 can be a casting, a rolled metal plate, a metal foil, a vapor-deposited film, a sputtered film, or a plated film. 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 planar inductor 50 is a vapor-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 planar inductor 50 can be 0.5 μm to 5 mm. When the planar inductor 50 is a casting, the thickness is not specified, but the maximum dimension can be 10 mm or more. The thickness of the planar inductor 50 can be equal to or greater than the skin depth determined by the attenuation center wavelength. The thickness of the planar inductor 50 can be greater than the thickness of the thin-film conductive layer 30.
The thin-film conductive layer 30 and the planar inductor 50 may be made of the same metal. This same metal may be the same pure metal or an alloy of the same metal (e.g., both are aluminum alloys), or the thin-film conductive layer 30 may be made of a pure metal and the planar inductor 50 may be made of an alloy of the metal of the thin-film conductive layer 30. Alternatively, the thin-film conductive layer 30 and the planar inductor 50 may be made of different metals.
The thin-film conductive layer 30 may have a topcoat layer 200 on the surface opposite the dielectric substrate. FIG. 3 is a schematic diagram showing a portion 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 surface opposite the dielectric substrate. The thickness of the topcoat layer 200 may be 0.1 μm or more and 50 μm or less. It may also be 1 μm or more and 5 μm or less. The topcoat layer 200 may be a single layer or multiple layers. The material of the topcoat layer 200 may be a simple substance, a mixture, or a composite of urethane resin, acrylic resin, polyamide, polyimide, polyamideimide, epoxy resin, or silicone resin. It may also contain insulating particles, magnetic particles, conductive particles, or a mixture thereof. The particles may be inorganic particles. The provision of the topcoat layer 200 matches the impedance with the air through which radio waves propagate, enabling radio waves to be effectively attenuated by the thin-film conductive layer. Furthermore, the thin-film conductive layer 30 and the planar inductor 50 can be endowed with corrosion resistance, chemical resistance, heat resistance, abrasion resistance, impact resistance, etc. For example, by using a cross-linked acrylic resin, a cross-linked epoxy resin, polyamide, polyimide, polyamideimide, silicone resin, etc., it is possible to improve solvent resistance and also heat resistance. Furthermore, by using a urethane resin, etc., it is possible to improve impact resistance, and by using a silicone resin, it is possible to improve abrasion resistance.

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 shape of the first region 121 in a plan view may be a square, hexagon, cross, other polygon, circle, or ellipse. The corners of the square, hexagon, cross, or other polygon may be rounded.
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 a planar view of the electromagnetic wave attenuation film 1. The thin-film conductive layer 30 on the first region 121 includes a metal plate. That is, the metal plate is provided on the first region 121. In other words, the metal plate is located on the first region 121. The shape of the metal plate in a planar view can be a square, hexagon, cross, other polygon, circle, or ellipse. The corners of this square, hexagon, cross, or other polygon can be rounded. The second region 122 is formed in a mesh or lattice shape in a planar view according to the above-described aspect of the first region 121.
The surfaces of the first region 121 and the second region 122 that contact the thin-film conductive layer 30 are generally parallel to the back surface. Furthermore, they may have roughened surfaces partially or entirely. As will be described later, by roughening the surfaces of the first region 121 and the second region 122 that contact the thin-film conductive layer 30 partially or entirely, the electrical resistance of the thin-film conductive layer 30 can be adjusted.

2, the thin-film conductive layer 30 is formed on the upper surfaces of the first region 121 and the second region 122. On the other hand, the thin-film conductive layer 30 is not present on the side surface 122a of the second region 122 that extends above the first region 121, and the dielectric substrate 10 is exposed. This allows the thin-film conductive layer 30 in the first region 121 and the thin-film conductive layer 30 in the second region 122 to be electrically insulated from each other. As long as the electrically insulated state can be achieved, part of the side surface 122a may be covered with the thin-film conductive layer 30.
The metal plate in each first region can have a shape that conforms to the shape of the first region 121 in a plan view. That is, the metal plate can have a shape that is the same as or similar to the shape of the first region 121 in a plan view. The dielectric substrate 10 may also include a plurality of metal plates that have the same shape and size in a plan view. Furthermore, the first regions 121 can be spaced apart while remaining parallel to each other, and the arrangement density on the front surface can be generally uniform.

It is believed that the electromagnetic wave attenuation film 1, due to its above-described structure, exhibits a unique mechanism at specific wavelengths.

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 waves are thought to be as follows:

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

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

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

According to the above principle, reflected waves are attenuated by electromagnetic wave attenuation films. From an energy perspective, it is believed that multiple mechanisms act synergistically, as shown below.

The first mechanism is the generation of a non-propagating, periodically oscillating electromagnetic field by the incident wave, as will be shown later by magnetic field density simulations. First, the planar inductor 50 on the back surface of the dielectric substrate 10 induces magnetic flux in the tangential direction of the planar inductor 50 to the incident wave. The induced magnetic flux generates an electric field perpendicular to the planar inductor 50, extending from a pair of opposing edges of the thin-film conductive layer 30 (i.e., the metal plate) on the first region 121. Next, when an electromagnetic wave is incident on the planar inductor, the fluctuating magnetic flux induces a current near the surface of the planar inductor. The current induced in the planar inductor generates a magnetic field in the dielectric substrate 10 near the surface of the planar inductor. This electric field, along with the current in the metal plate and the planar inductor 50, generates 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 metal plate is plate-shaped and made of metal. The electric field generated in the dielectric substrate fluctuates with the same period as the period of the incident wave. The periodic fluctuation of the magnetic field periodically fluctuates the electric field between the thin-film conductive layer 30 and the planar inductor 50. As a result, a non-propagating, periodically fluctuating electromagnetic field is generated between the thin-film conductive layer 30 and the planar inductor 50. As will be shown later by current density simulation, an AC current is induced in the metal plate by the magnetic field in the periodically fluctuating electromagnetic field. Furthermore, the periodically fluctuating electric field generates a periodically fluctuating potential in the metal plate. The electromagnetic field does not propagate but remains in place, and the induced AC current loses power. As a result, the energy of the electromagnetic field is converted into heat, resulting in the absorption of electromagnetic waves. Furthermore, the AC current induced in the metal plate is thought to re-emit electromagnetic waves from the surface of the metal plate opposite the surface in contact with the dielectric substrate 10.
In other words, it is thought that part of the energy of the electromagnetic wave captured by the electromagnetic wave attenuation film is converted into heat energy, and the rest is re-emitted. Furthermore, according to classical electromagnetic theory, expressed in Maxwell's equations, the frequency of the induced alternating current is the same as that of the incident wave, so the frequency of the re-emitted electromagnetic wave is the same as that of the incident wave. As a result, an electromagnetic wave with the same frequency as the incident wave is re-emitted. Furthermore, if we consider an oscillating electromagnetic field as a quantum, it is possible that the quantum loses energy and re-emits a lower-energy, longer-wavelength electromagnetic wave. Re-emission can be thought of as either stimulated emission or spontaneous emission due to the incident electromagnetic wave. Stimulated emission is thought to occur when an electromagnetic wave is reflected in the direction of the incident wave, i.e., the direction of specular reflection, and a coherent electromagnetic wave is emitted. Spontaneous emission is thought to decay over time. Furthermore, the spatial distribution of spontaneous emission is thought to be close to Lambertian reflection if the electromagnetic wave attenuation film does not have a diffractive, interference, or refractive structure.
The attenuation central wavelength correlates with the dimension W1 (see FIG. 7; hereinafter, sometimes referred to as "width W1") in the plane direction of the thin-film conductive layer 30 formed on the first region 121 shown in FIG. 2. That is, the wavelength of the electromagnetic wave that is suitably attenuated by the first mechanism can be changed by changing the dimension W1, and the attenuation of the electromagnetic wave in the electromagnetic wave attenuation film 1 can be set easily and with a high degree of freedom. Therefore, it is possible to easily configure the film to capture linearly polarized electromagnetic waves in the band of 15 GHz or more and 150 GHz or less.

It is believed that periodic fluctuations in the non-propagating electromagnetic field occur between opposing sides of the metal plate in a planar view. Therefore, for the first mechanism to occur, it is preferable that sides of a certain length face each other. Based on this and the inventors' research results, a section of the thin-film conductive layer with a width W1 of 0.25 mm or more can be defined as a metal plate. If a metal plate can have multiple W1 values, the largest of these can be defined as the W1 of that metal plate. By setting W1 within the range of approximately 0.25 mm to 4 mm, it is possible to attenuate electromagnetic waves in the frequency band above 15 GHz and below 150 GHz. 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 logarithmic graph, as shown in Figure 25. In other words, the frequency of the attenuated electromagnetic wave is a power function of the width of the metal plate. The power of this function is approximately -1, meaning that it is almost inversely proportional.
The thin-film conductive layer may include a plurality of metal plates having different dimensions W1. In this case, the attenuation peaks of the respective electromagnetic waves are overlapped, thereby broadening the band of the electromagnetic waves that can be attenuated.

The second mechanism is the confinement of the electromagnetic field by the thin-film conductive layer 30 and the planar inductor 50. In the electromagnetic wave-attenuating film 1, the dielectric substrate 10 is sandwiched between the thin-film conductive layer 30 and the planar inductor 50 in the first region 121. Therefore, the electric field generated in the dielectric substrate 10 of the electromagnetic wave-attenuating film 1 by electromagnetic waves is confined within the dielectric substrate 10 between the thin-film conductive layer 30 including the metal plate and the planar inductor 50 by the charge and current in the metal plate. In other words, the metal plate suppresses the electromagnetic field and confines it within the dielectric substrate 10. In other words, the metal plate can function as a choke. In other words, the metal plate can be a choke plate that functions as a choke.
It is also believed that magnetic flux is induced within the first region by the periodic fluctuations of this trapped electric field. This causes the oscillating electromagnetic field to accumulate within the first region, increasing the energy density of the electromagnetic field. Generally, the higher the energy density, the easier it is to attenuate, so electromagnetic waves are efficiently attenuated by this mechanism. Furthermore, 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 within the dielectric substrate. Furthermore, the magnetic field accumulated in the dielectric substrate is accompanied by a large current in the metal plate, and the electric field accumulated in the dielectric substrate generates a large potential difference. The large current and the large potential difference can increase the power loss, which is the product of these two. The energy of the electromagnetic wave is consumed as power loss, resulting in the attenuation of the electromagnetic wave.

The third mechanism is power loss in an electric circuit including a capacitor formed by the opposing thin-film conductive layer 30 and planar inductor 50 and the dielectric substrate 10 therebetween. In the electromagnetic wave-damping film 1, the dielectric substrate 10 is sandwiched between the thin-film conductive layer 30 and the planar inductor 50 in both the first region 121 and the second region 122. Therefore, the first region 121, the second region 122, and the dielectric substrate 10 function as a capacitor. Therefore, electromagnetic waves incident on the dielectric substrate 10 of the electromagnetic wave-damping film 1 are attenuated by the electric circuit including the capacitor.
The larger the capacitance of a capacitor, the more charge it can store, thereby increasing the amount of energy it can store. Therefore, the larger the capacitance, the greater the capacity it can handle.
Because capacitance is inversely proportional to the thickness of the dielectric substrate 10, a thinner dielectric substrate 10 is preferable from this perspective. Furthermore, because the distance between the thin-film conductive layer 30 and the planar inductor 50 is determined by the thickness of the dielectric substrate 10, the electrical resistance between the thin-film conductive layer 30 and the planar inductor 50 is proportional to the thickness of the dielectric substrate 10. A low resistance of the dielectric substrate 10 increases leakage current in the dielectric substrate 10, increasing the current flowing in the electrical circuit including the capacitor between the thin-film conductive layer 30 and the planar inductor 50. This increases power loss due to leakage current, which in turn increases the absorption of electromagnetic wave energy. Furthermore, in the electromagnetic wave attenuation film 1 according to an embodiment of the present invention, changing the thickness of the dielectric substrate 10 at the location where the metal plate is disposed does not shift the wavelength of the attenuated electromagnetic field, so the thickness of the dielectric substrate 10 can be designed to suit the characteristics of the electrical circuit including the capacitor.

As described above, electromagnetic waves incident on the electromagnetic-wave-attenuating film 1 are trapped by generating an electromagnetic field in the dielectric substrate 10 near the surface of the planar inductor through the first mechanism, and then confining the electromagnetic field generated by the electromagnetic waves through the second mechanism. In this way, the electromagnetic-wave-attenuating film 1 can trap electromagnetic waves. The trapped electromagnetic waves are attenuated by electric field loss and power loss through the second mechanism and power loss through the electrical circuit through the third mechanism. Furthermore, providing the topcoat layer 200 matches the impedance with the air through which the radio waves propagate, enabling the radio waves to be effectively attenuated relative to the thin-film conductive layer. The wavelength of the attenuated electromagnetic waves can be changed by changing the dimension W1 of the metal plate, as shown in Figure 25. More specifically, the frequency at which the reflected wave is minimized, i.e., the frequency at which attenuation is maximized, closely approximates the power of the size of the metal plate, as shown in Figure 25. Therefore, the electromagnetic-wave attenuation characteristics of the electromagnetic-wave-attenuating film 1 can be easily and flexibly set. Therefore, it is easy to set the antenna so as to capture linearly polarized, circularly polarized, or elliptically polarized radio waves in the band of 15 GHz or more and 150 GHz or less.
In the simulation of FIG. 25, the metal plate is square, and W1 is the length of one side.

The dielectric substrate of the electromagnetic wave attenuation film 1 of the first embodiment has a first region 121 and a second region 122, and at least a portion of the side surface 122a of the second region 122 is exposed and not covered by the thin-film conductive layer 30. As a result, the area onto which electromagnetic waves can enter can be easily increased without increasing the planar area of the electromagnetic wave attenuation film, allowing electromagnetic waves to be efficiently captured and attenuated.

In the electromagnetic wave attenuation film 1 of the first embodiment, the thin film conductive layer 30 on the second region 122 that serves as the support cage improves the attenuation of electromagnetic waves mainly by enhancing the second and third mechanisms.
Furthermore, the inventors' investigations have revealed that the electric field is stronger at the periphery of the metal plate, and that a potential is also generated in the support cage close to the periphery.

Figure 4 shows the results of a simulation of the electric field strength when there is no support cage, and Figure 5 shows the results of a simulation of the electric field strength when there is a support cage. In Figures 4 and 5, (a) shows the peripheral portion of the metal plate, and (b) shows an enlarged view. The metal plate is labeled A and the support cage is labeled B.
Comparing Figure 4(b) with Figure 5(b), it can be seen that the electric field intensity is stronger at the periphery of the metal plate in Figure 5(b). In other words, the above-mentioned potential generated in the support cage is thought to contribute to the larger power loss in the first mechanism.

The third mechanism also plays an important role in the electromagnetic wave attenuation film 1. When an electric field is generated in the dielectric substrate 10, the electromagnetic field is confined below the metal plate. In other words, an electromagnetic field with high energy density is generated below the metal plate. It is thought that the confined electromagnetic field is attenuated by power loss due to the second mechanism and dielectric loss due to the third mechanism.

The inventors' research revealed that the attenuation due to the first mechanism varies depending on the admittance (the reciprocal of electrical resistance) of the metal constituting the metal plate. Good electromagnetic wave attenuation was obtained when the admittance (siemens/m) was 10 million or higher. Silver is known to have the highest admittance among normal conductors, with an admittance of 61-66 x 10 ⁶ , equating to an upper limit of approximately 70 million. Metals with admittances between 5 million and 70 million can be used. Metals constituting the metal plate can be ferromagnetic, paramagnetic, diamagnetic, or antiferromagnetic. Examples of ferromagnetic metals include nickel, cobalt, iron, and their alloys. Examples of paramagnetic metals include aluminum, tin (β-tin), and their alloys. Examples of diamagnetic metals include gold, silver, copper, tin (α-tin), zinc, and their alloys. 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. The metal oxide or metal nitride on the surface of the metal plate can be formed by surface treatment. The surface treatment can be a chemical treatment using chemicals, a heat treatment, or both. Furthermore, the metal plate may have a metal oxide film or a layer of a mixture of metal and metal oxide. In such a configuration, the resistance value of the metal plate increases, and the voltage drop increases, resulting in increased power loss and improved electromagnetic wave attenuation.
The metal plate 30A may be a multi-layer film made of layers of different materials, and the layers may be made of conductive or insulating materials.

An example of a manufacturing procedure for the electromagnetic wave attenuation film 1 will now be described.
First, the dielectric substrate 10 is formed. A resin that forms the uneven portion is arranged in layers on the carrier 11, and a first region and a second region are formed on the surface, completing the dielectric substrate 10 having the underlayer 12. The resin that forms 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 underlayer 12 can also be formed from a photocurable resin. The underlayer 12 can also be formed from a thermoplastic resin. In this case, thermal transfer can be used. The underlayer 12 can also be formed from a thermosetting resin. The resin may be a soluble resin that is soluble in a solvent (oil-based ink). The resin may also be a water-soluble resin (water-based ink).

Next, the thin-film conductive layer 30 and the planar inductor 50 are formed on the front surface 10a and back surface 10b of the dielectric substrate 10, respectively. The thin-film conductive layer 30 and the planar inductor 50 can be formed by physical deposition. Physical deposition can be vapor deposition or sputtering. Either the thin-film conductive layer 30 or the planar inductor 50 can be formed first, and they can be made of different materials. The planar inductor 50 can be made of any of a casting, a rolled metal plate, a metal foil, a vapor-deposited film, a sputtered film, and plating. The casting can be made of cast iron or an aluminum alloy. The rolled metal plate can be made of steel, stainless steel, aluminum, or an aluminum alloy. The plating can be electrolytic plating or electroless plating. The plating can be copper plating, electroless nickel plating, electrolytic nickel plating, zinc plating, electrolytic chromium plating, or a laminate of these.
It is important that the thin-film conductive layer 30 is not connected to the metal plate and other parts. If the metal plate and other parts are connected, the width W1 described above will change, which may result in electromagnetic wave attenuation different from what is expected. For this reason, 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 may be used for this step.

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

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

As another example of a manufacturing procedure, after forming the thin-film conductive layer 30 and the planar inductor 50 on the dielectric substrate, a concave-convex shape may be formed on the thin-film conductive layer 30. In this case, transfer using a plate is preferable. When performing thermal transfer, the plate is pressed against the thin-film conductive layer 30 and heated.
In this manufacturing procedure, the thin-film conductive layer 30 pressed against the plate tends to stretch, resulting in a state in which the metal plate is connected to the other parts. Methods to resolve this include the laser etching described above, as well as devising the shape of the plate. For example, if the edges of the convex portions that form the first region on the plate are sharpened, the edges of the metal plate will be cut when the plate is pressed against the thin-film conductive layer 30. This ensures that the metal plate is not connected to the other parts during transfer.

A second embodiment of the present invention will be described with reference to Figures 6 to 9. In the following description, components that are common to those already described will be assigned the same reference numerals, and duplicate explanations will be omitted. It is believed that the first, second, and third mechanisms described above are also realized in the second embodiment.

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

The dielectric substrate 62 of the second embodiment can be made of the same material and structure as the dielectric substrate of the first embodiment. The dielectric substrate 62 may be configured with a base layer provided on the carrier 11, or it can be configured with only the carrier 11. Both the front surface 62a and the back surface 62b are flat or rough. A planar inductor 50 is provided on the back surface 62b, and an adhesive layer may be provided between the back surface 62b and the planar inductor 50. The adhesive layer and the planar inductor 50 can be formed using the same material and manufacturing method as in the first embodiment. Multiple metal plates 30A are arranged on the front surface 62a. The metal plates 30A can be formed by deposition followed by etching. The deposition method can be physical deposition or chemical deposition. Physical deposition is suitable for forming the metal plates. Physical deposition can be vacuum deposition or sputtering. Vacuum deposition is preferred due to its high productivity. A metal plate can be obtained by printing a mask layer in a pattern in the shape of the metal plate, and then removing excess thin-film conductive layer by etching. The etching solution 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. Multiple metal plates 30A may be of the same shape and size and arranged at regular intervals. In other words, two or more multiple metal plates 30A of the same shape and size may be arranged at regular intervals. In other words, the front surface 62a is not entirely covered with a metal layer, and the dielectric substrate 62 is exposed in areas where no metal plate 30A is arranged.

Furthermore, multiple metal plates 30A of the same shape and size as each of the multiple metal plates 30A may be arranged, but they may differ in shape, size, or both. In other words, multiple metal plates of different shapes, sizes, or both may be arranged, or multiple metal plates of the same shape and size may be arranged. The metal plates may be arranged at a constant interval and in a constant direction. Alternatively, they may be arranged at different intervals and in different directions. They may also be arranged at different intervals and in the same direction. Some of the intervals may be constant and some may be arranged in the same direction. Furthermore, multiple metal plates of different shapes, sizes, or both may be grouped into a metal plate set. The spacing between the metal plates constituting the metal plate set may be constant for all or some of them, or may be different for all of them. The orientations of the metal plates constituting the metal plate set may be constant for all or some of them, or may be different for all of them. A metal plate set having multiple metal plates of different shapes, sizes, or both may have different attenuation frequency spectra for each metal plate, allowing for attenuation of multiple frequency bands or a broadband of attenuated frequencies. Furthermore, different spacing between the metal plates can result in different attenuation frequency spectra. Different orientations of the metal plate sets can result in different polarization dependence of attenuation. The multiple metal plates that make up a metal plate set can each attenuate different frequencies, and the frequency differences can be regular.
Multiple metal plate sets may be arranged. Multiple metal plate sets may be arranged, each consisting of metal plates with the same shape, size, and arrangement as the metal plates constituting a given metal plate set. By including multiple different metal plates in the thin-film conductive layer, it is possible to broaden the bandwidth, attenuate electromagnetic waves of multiple frequencies, or both.

The metal plate may be divided into multiple metal segments. In other words, the metal plate may be composed of multiple metal segments. The multiple metal segments within the metal plate may be electrically connected. The multiple metal segments may be electrically connected by wiring. The wiring may have an impedance. This impedance may match the metal segments. The wiring and the multiple metal segments within the metal plate may function as a single entity. The multiple metal segments may have different properties than when they exist alone. Specifically, the resonant frequency and attenuation may be different when they exist alone than when they form part of the metal plate. The cross-sectional shape of the metal plate may be flat, polyhedral, or curved. In the case of a polyhedron or curved shape, the distance between the base and top, i.e., the height, can be 50 μm or less. The ratio of the height to the distance between opposing sides of the metal plate can be 1:100 or more and 1:10 or less.

The attenuation of the electromagnetic wave attenuation film of the second embodiment can be set by changing the width W1 of the metal plate, as in the first embodiment, and it is also easy to set it to capture linearly polarized electromagnetic waves in the band between 15 GHz and 150 GHz.
Furthermore, since the plastic film carrier 11 can be used as the dielectric substrate 62 as is, the electromagnetic wave attenuation film of the second embodiment can be produced more easily than the electromagnetic wave attenuation film of the first embodiment.
A carrier having a roughened surface on part or the whole of the front surface 62a and the back surface 62b can also be used as the dielectric substrate 62. By roughening part or the whole of the front surface 62a, the admittance of the metal plate 30A can be adjusted.

In prior art, including Patent Document 5, it was thought that making the resonating conductor thicker than the skin depth would generate sufficient AC current in the resonant layer, and that the power loss of that AC current would attenuate electromagnetic waves. However, the inventors discovered that when the thickness of the metal plate 30A is less than the skin depth, the attenuation of electromagnetic waves actually increases.

Figure 9 shows the results of a simulation of electromagnetic wave attenuation due to changes in the thickness of the metal plate 30A. The metal plate is made of aluminum. The incident wave is a linearly polarized sine wave, incident perpendicularly to the electromagnetic wave attenuation film. In the simulation, the planar inductor is considered a perfect conductor. The electromagnetic wave attenuation of the electromagnetic wave attenuation film is measured using monostatic RCS, which is based on the case where only the planar inductor is used. The vertical axis showing electromagnetic wave attenuation is expressed in decibels. Monostatic RCS (Radar Cross-Section) is an index that indicates the ease of target detection with monostatic radar, and can be calculated using the following equation 1. Monostatic radar transmits and receives signals at the same location.

As a result of the simulation, large attenuation of electromagnetic waves was observed when the thickness was 40 nm or more and 400 nm or less, as shown in Figure 9. Conversely, when the thickness was less than 40 nm, a decrease in attenuation of electromagnetic waves was observed.
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 Figure 9 shows an interesting relationship with 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 below the skin depth of the material, the attenuation of electromagnetic waves increases. Furthermore, when the thickness is less than 1/ ^e2 of the skin depth, the attenuation of electromagnetic waves decreases. This is thought to be because when the conductive layer is thicker than the skin depth, sufficient resistance is not obtained, resulting in an insufficient voltage drop for power loss. Furthermore, current is concentrated only near the center of the metal plate, reducing the current in the area where the potential difference occurs. On the other hand, even if the thickness of the conductive layer is below the skin depth, when the thickness is less than 1/ ^e2 of the skin depth, sufficient current for power loss may not be obtained. Needless to say, power loss is given as the product of current and voltage. That is, sufficient electromagnetic wave attenuation can be achieved within the range satisfying the following LN function Equation 2, which is expressed using the natural logarithm of the metal plate thickness T normalized by the skin depth d:
-2 ≦ ln(T/d) ≦ 0...(2)
Furthermore, when a metal with low admittance is used for the metal plate, electromagnetic wave attenuation can be obtained even within the range of the following formula 3. Furthermore, when the ratio of the area of the metal plate to the front surface of the dielectric substrate is large, electromagnetic wave attenuation can be obtained even within the range of the following formula 3. When this area ratio is large, the ratio of the area of the 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)
Considering the formulas 1 and 2, the attenuation of the electromagnetic wave can be obtained within the range of the following formula 4.
-2 ≦ ln(T/d) ≦ 1...(4)
In the embodiment of the present invention, the skin depth can be calculated using the attenuation center frequency f. That is, when the attenuation center frequency f is used, the skin depth d is calculated as shown in the following equation 5, as is well known.

Furthermore, the simulation results showed that attenuation increased when the thickness of the metal plate was thinner than the skin depth. This is thought to be because the current generated by the magnetic flux in the dielectric substrate of the metal plate reaches the opposite surface of the dielectric substrate, and this current emits electromagnetic waves that are π-phase-shifted from the reflected waves by the dielectric inductor, canceling out the reflected waves. Furthermore, as the thickness of the metal plate becomes thinner than the skin depth, the current in the metal plate is restricted, causing the magnetic field to be generated not only near the center of the metal plate but throughout the entire metal plate. This in turn causes the current induced by the generated magnetic field to be generated throughout the entire metal plate, increasing the emission of electromagnetic waves that cancel out the reflected waves by the dielectric inductor, resulting in greater attenuation of the reflected waves.
In addition, 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 fluctuates periodically, the force of attraction to the metal plate also fluctuates periodically. 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. For this reason, it is thought that the mechanics of the electromagnetic field acting on the metal plate also contributes to the attenuation of electromagnetic waves.
Furthermore, if we consider the periodic fluctuations of the electromagnetic field as quantum states, we can think of the quantum state as being trapped by the electromagnetic field with zero momentum. In addition, since the thickness of the metal plate is on the order of several hundred nanometers, it is possible that this may affect the energy levels within the metal plate.
Thus, the phenomena in the embodiments of the present invention can be interpreted not only as classical electromagnetic phenomena, but also as classical mechanics and quantum mechanics.
Therefore, when interpreting Equation 4, the range is reasonably defined, but it is not a range that is strictly calculated taking into account all physical phenomena. Therefore, when determining whether a target product falls within the range of the above formula, it is appropriate to interpret it taking into account the physical phenomena that are manifesting.
In the prior art, it is not common to see examples of using a conductor that is approximately skin depth or thinner than the skin depth. Therefore, it is believed that the mechanism of interaction between the embodiment of the present invention and electromagnetic waves in the millimeter wave band is different from the prior art.

The relationship between the thickness of the metal plate and the skin depth that provides desirable electromagnetic wave attenuation for a specific frequency band will be explained in detail in the examples of the second embodiment described below.

Each embodiment of the present invention will be further described using examples.
(Example of 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 a positive type, and the thickness of the photoresist was 10 μm. The formed resist pattern was a pattern in which square openings were arranged at coordinates in a square region with sides of 14 cm in an XY coordinate system, with the X and Y coordinates being a regular square lattice arrangement, and the region exposed to i-line light was the region inside the square.
Furthermore, nickel electroforming was carried out using this master plate to obtain a nickel mold having a pattern in which square convex portions in plan view were regularly arranged on the surface.

Next, UV-curable resin was dropped onto the patterned surface of the nickel mold, and the adhesive surface of a PET film, one side of which had been treated for easy adhesion, was placed on the UV-curable resin. The UV-curable resin was uniformly spread over the patterned surface using a roller, and the UV-curable resin was cured by irradiating it with UV light through the transparent PET film.
The PET film was released from the nickel mold to obtain a dielectric portion consisting of the PET film and the irregular layer made of the ultraviolet curable resin.

A 500 nm thick Al film was formed on both sides of the dielectric substrate by vacuum deposition to form a thin film conductive layer and a planar inductor.
The above is the manufacturing procedure for the examples according to the first embodiment. In this procedure, a plurality of nickel molds were manufactured with different parameters for the concave-convex layer surface, and the electromagnetic wave attenuation films of Examples 1 and 2 were manufactured.
The electromagnetic wave attenuation films according to the respective examples were thin and lightweight, with a thickness of about 60 μm and a weight of about 0.02 g.

(Modification in which a top coat layer is provided in the example according to the first embodiment)
In the example according to the first embodiment, an electromagnetic wave attenuation film was prepared by providing a top coat layer 200 manufactured in the following manner.
The main component is an acrylic resin composition consisting of a mixture of 80 parts by mass of methyl methacrylate monomer and 20 parts by mass of cyclohexyl methacrylate, and the following components are added, relative to 100 parts by mass of the solid content of the acrylic resin composition: 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having the structure shown in Chemical Formula A above ("ADEKA STAB LA-46" manufactured by ADEKA CORPORATION); 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having a different composition from the structure shown in Chemical Formula A above ("TINUVIN 479" manufactured by Chiba Specialty Chemicals Co., Ltd.); 3 parts by mass of a benzotriazole-based ultraviolet absorber ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.); A base solution with a solids content of 33 parts by mass, to which 5 parts by mass of a hindered amine radical scavenger ("Tinuvin 292" manufactured by Chiba Specialty Chemicals Co., Ltd.) had been added, and ethyl acetate solvent had been added to adjust the solids content, was mixed with a hexamethylene diisocyanate-type curing agent solution with a solids content of 75 parts by mass, to which ethyl acetate solvent had been added to adjust the solids content, so that the ratio of the base solution to the curing agent solution was 10:1 (the ratio of the number of hydroxyl groups in the base solution to the number of isocyanate groups in the curing agent solution was 1:2). Ethyl acetate was further added as a solvent component to adjust the solids content to 20 parts by mass, and the resulting coating solution was applied to a thickness of 6 μm after solvent evaporation, yielding a top coat layer 200. The resulting electromagnetic wave-attenuating film was thin and lightweight, with a thickness of approximately 70 μm and a weight of approximately 0.02 g.

(Example of the second embodiment)
[35GHz~50GHz]
Example 1A
In contrast to the general theory described in Equation 4, we have found a range of the relational expression ln(T/d) between the thickness T of the metal plate and the skin depth d that shows preferable electromagnetic wave attenuation in a specific frequency band within the millimeter wave band, and this is explained below.
A simulation conducted in the 35 GHz to 50 GHz band will be described. The dielectric substrate was a PET film with a thickness (H1) of 50 μm, and on one side of the film, metal plates with thin-film conductive layers were set at regular intervals in both the X and Y coordinates. Furthermore, an aluminum plate inductor with a thickness (T2) of approximately 2 mm was set on the other side of the dielectric substrate, and the simulation was conducted.
Simulations were performed on the relationship between electromagnetic wave attenuation and ln(T1/d) for each metal type at frequencies of 35 GHz, 39 GHz, 41 GHz, 45 GHz, and 50 GHz.

The simulation results are explained in Tables 1 and 2 and FIGS. 10 to 14. FIG. 10 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 35 GHz. FIG. 11 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 39 GHz. FIG. 12 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 41 GHz. FIG. 13 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 45 GHz. FIG. 14 is a graph showing the electromagnetic wave attenuation characteristics of Example 1A at 50 GHz. In FIGS. 10 to 14, (a) shows the admittance and skin depth values, (b) shows the configuration of the electromagnetic wave attenuation film, and (c) to (e) show graphs of the attenuation characteristics of silver, copper, and aluminum, respectively. The graph shows the correlation between the thickness T1 of the metal plate normalized by the skin depth d on the horizontal axis and the attenuation of the patterned metal plate when the reflection amount of a metal plate with the same area as the dielectric substrate is set to 100 (reference) on the vertical axis.

If an electromagnetic wave attenuation film has an absorption of 10 dB or more as a guideline for a good attenuation amount, then as is clear from Table 1 and Figs. 10 to 14, it was shown that in the frequency band of 35 GHz to 50 GHz, those that satisfy the relationship -2.0 ≦ ln(T1/d) ≦ -0.5 can obtain a good attenuation amount.
It should be noted that favorable attenuation characteristics of about 10 dB are not limited to the numerical values of the parameters used in Example 1A, and it is naturally expected that they can be realized in a configuration with a certain range. For example, favorable attenuation characteristics of about 10 dB can also be expected in a configuration in which the width W1 of the metal plates is 1.7 mm to 2.3 mm, the distance W3 between adjacent metal plates is 0.9 mm to 1.2 mm, the thickness H1 of the dielectric substrate is 5 μm to 300 μm, and the thickness T2 of the planar inductor is 0.5 μm to 5 mm.

Example 1B
As in Example 1A, the dielectric substrate was a PET film with a thickness (H1) of 50 μm, and the ratio of the total area of the metal plate, a thin-film conductive layer, to the total area of the dielectric substrate in the XY plane was varied. Furthermore, an aluminum plate inductor with a thickness (T2) of approximately 2 mm was set on the other side of the dielectric substrate, and simulations were performed. The metal plate was made of aluminum, with a width W1 of 2.0 mm and a thickness T1 of 149.2 nm. The ratio of the metal area was changed by adjusting the distance W3 between the metal plates.
The simulation results are explained in Table 3 and Fig. 15. Fig. 15 is a graph showing the electromagnetic wave attenuation characteristics as a function of the metal area ratio at 39 GHz for Example 1B. (a) shows the configuration of the electromagnetic wave attenuation film, and (b) shows the attenuation characteristics.
If an absorption amount of 10 dB or more of the electromagnetic wave attenuation film is considered to be a good attenuation amount, Table 3 and FIG. 15 show that in Example 1B, a good attenuation amount can be obtained when the metal area ratio is 20% or more.

Example 1C
As in Example 1A, a PET film with a thickness (H1) of 50 μm was used as the dielectric substrate, and a metal plate as a thin-film conductive layer was arranged on one side of the film in the same pattern as in Figure 6, but the shape was changed to a shape other than square, and an aluminum plate inductor with a thickness (T2) of approximately 2 mm was set on the other side of the dielectric substrate, and a simulation of the electromagnetic wave attenuation characteristics was performed. Aluminum was used as the metal type for the metal plate, and the thickness T1 was set to 149 nm.

Circular
Figure 16 is a graph showing the electromagnetic wave attenuation characteristics of a circular metal plate in Example 1C. (a) shows the shape of the metal plate, where R1 represents the radius of the circle. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in which W4 represents the distance between the centers of the circles. (c) shows the dimensions of R1 and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis.
The simulation results showed good attenuation characteristics with an absorption of 10 dB or more near 43 GHz.

[Rectangular shape]
Figure 17 is a graph showing the electromagnetic wave attenuation characteristics of a rectangular metal plate in Example 1C. (a) shows the shape of the metal plate, with W7 representing the length of the long side of the rectangle and W8 representing the length of the short side. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in the vicinity of the pattern, with W4 representing the distance between the centers of the rectangles. (c) shows the dimensions of W7, W8, and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis.
The simulation results showed good attenuation characteristics with an absorption of 10 dB or more near 39.4 GHz.

[Hexagonal shape]
Figure 18 is a graph showing the electromagnetic wave attenuation characteristics of the hexagonal metal plate in Example 1C. (a) shows the shape of the metal plate, with W9 representing the length of one side of the hexagon. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in which W4 represents the distance between the centers of the hexagons. (c) shows the dimensions of W9 and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis.
The simulation results showed good attenuation characteristics with an absorption of 10 dB or more near 36 GHz.

[Convex shape]
FIG. 19 is a graph showing the electromagnetic wave attenuation characteristics of the convex metal plate in Example 1C. (a) represents the shape of the metal plate. W10 represents the length of the upper edge of the convex upper portion, W11 represents the length of the lower edge of the convex lower portion, W15 represents the length of the side edge of the upper portion, and W16 represents the length of the side edge of the lower portion. The convex shape is symmetrical with respect to the line connecting the midpoint of the upper edge of the upper portion and the lower edge of the lower portion. The center of the convex shape is the center of a rectangle that is tangent to the lower edge of the lower portion, the left and right sides of the lower portion, and the upper edge of the upper portion and surrounds the convex shape. (b) is an enlarged partial view of the vicinity of the arrangement pattern passing through line II-II in FIG. 6 in this example, where W4 represents the distance between the centers of the convex shapes. (c) represents the dimensions W10, W11, W15, W16, and W4. (d) shows the attenuation characteristics with frequency as the horizontal axis.
The simulation results showed good attenuation characteristics with an absorption of 10 dB or more near 35 GHz.

[Triangular shape]
Figure 20 is a graph showing the electromagnetic wave attenuation characteristics of a triangular metal plate in Example 1C. (a) shows the shape of the metal plate, where W12 represents the length of one side of the equilateral triangle. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in Figure 6, in which W4 represents the distance between the centers of the triangles. (c) shows the dimensions W12 and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis.
The simulation results showed good attenuation characteristics with an absorption of 10 dB or more near 44.8 GHz.

[Cross shape]
FIG. 21 is a graph showing the electromagnetic wave attenuation characteristics of a cross-shaped metal plate in Example 1C. (a) shows the shape of the metal plate. The cross shape is symmetrical vertically and horizontally, and is also symmetrical with respect to a 90-degree rotation. W13 represents the length of the opposing outer edges of the cross, and W14 represents the length of one side of a square that contacts the opposing outer edges and surrounds the cross. The center of the square is also the center of the cross. (b) is an enlarged partial view of the arrangement pattern in this example, passing through line II-II in FIG. 6, and W4 represents the distance between the centers of the cross shapes. (c) shows the dimensions W13, W14, and W4. (d) shows the attenuation characteristics with frequency as the horizontal axis.
The simulation results showed good attenuation characteristics with an absorption of 10 dB or more near 35.8 GHz.

[Variations of loop shape]
22A is a graph showing the electromagnetic wave attenuation characteristics of the loop-shaped metal plate in Example 1C. (a) shows the shape of the metal plate. W5 represents the length of one side of the outer square, and W6 represents the length of one side of the inner square. The centers of the outer and inner squares coincide and are the center of the loop shape. (b) is an enlarged view of a portion of the arrangement pattern in this example, passing through line II-II in FIG. 6, in the vicinity of which W4 represents the distance between the centers of the loop shapes. (c) shows the dimensions of W5, W6, and W4. (d) shows the attenuation characteristics with frequency on the horizontal axis.
From the simulation results, a peak in absorption was observed around 42.8 GHz, but an attenuation of 10 dB was not obtained.
Therefore, the electromagnetic wave attenuation characteristics were simulated using a film in which two electromagnetic wave attenuation films with similar shapes and arrangements were stacked. Figure 22B is a graph showing the electromagnetic wave attenuation characteristics of a modification of Example 1C in which two electromagnetic wave attenuation films with loop-shaped metal plates are stacked. (a) shows the configuration of the electromagnetic wave attenuation film of this modification. The dielectric substrate and metal plate used in Figure 22A were stacked in two layers, and a flat inductor was provided on the lower dielectric substrate. H1 represents the thickness of the upper dielectric substrate, and H2 represents the thickness of the lower dielectric substrate. (b) represents the dimensions of H1 and H2. (c) shows the attenuation characteristics with frequency as the horizontal axis.
The simulation results showed good attenuation characteristics around 44.4 GHz.

Example 2
A square PET film with a thickness of 50 μm and sides of 14 cm was prepared as the dielectric substrate. A 100 nm thick thin-film conductive layer of aluminum was formed on one entire surface of the dielectric substrate using vacuum deposition. The thin-film conductive layer was then etched using a mask to form a metal plate at a fixed interval in both the X and Y coordinates. An aluminum flat inductor was attached to the other surface using an adhesive layer. A simulation was also performed using this configuration.
The above is the manufacturing procedure of Example 2 according to the second embodiment. The parameters of Example 2 are as follows.
Metal plate width W1: Sixteen types of metal plates with widths obtained by dividing the range of 1.519 mm to 2.764 mm into 16 equal parts at 0.083 mm intervals were arranged in a 4 x 4 matrix with the same spacing of 0.1 mm and the same orientation to form a metal plate set. Multiple such metal plate sets were arranged with spacing of 0.1 mm and the same orientation. Each metal plate set was also identical. In other words, the metal plates constituting each metal plate set were identical to each other.
Distance W3 between adjacent metal plates: 0.1 mm
Metal plate thickness T1: 149 nm
Thickness T2 of the flat inductor: approx. 2 mm
Dielectric substrate thickness H1: 50 μm
In addition, a simulation was performed using this configuration to examine the validity of the damping mechanism based on the experimental results.

The electromagnetic wave attenuation films according to the examples, which did not include a planar inductor, were thin and lightweight, measuring approximately 60 μm in thickness and weighing approximately 0.02 g. Therefore, they can be easily attached to components, such as those inside the housings of mobile phones and automotive radars, where the effects of electromagnetic radiation noise must be suppressed.
In the simulation, all of Examples 1A to 1C and 2 exhibited good attenuation of millimeter-wave electromagnetic waves. The simulation results for Example 2 are shown in FIG.

(Modification in which a top coat layer is provided in Example 1A according to the second embodiment)
In Example 1A according to the second embodiment, aluminum was used, and the metal plate had a thickness T1 of 153 nm, and a top coat layer 200 manufactured by the following procedure was provided on the metal plate to create an electromagnetic wave attenuation film.
The main component is an acrylic resin composition consisting of a mixture of 80 parts by mass of methyl methacrylate monomer and 20 parts by mass of cyclohexyl methacrylate, and the following components are added, relative to 100 parts by mass of the solid content of the acrylic resin composition: 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having the structure shown in Chemical Formula A above ("ADEKA STAB LA-46" manufactured by ADEKA CORPORATION); 6 parts by mass of a hydroxyphenyltriazine-based ultraviolet absorber having a different composition from the structure shown in Chemical Formula A above ("TINUVIN 479" manufactured by Chiba Specialty Chemicals Co., Ltd.); 3 parts by mass of a benzotriazole-based ultraviolet absorber ("TINUVIN 329" manufactured by Chiba Specialty Chemicals Co., Ltd.); A base solution with a solid content of 33 parts by mass, to which 5 parts by mass of a hindered amine radical scavenger ("Tinuvin 292" manufactured by Chiba Specialty Chemicals Co., Ltd.) had been added, and ethyl acetate solvent had been added to adjust the solid content, was mixed with a hexamethylene diisocyanate-type curing agent solution with a solid content of 75 parts by mass, to which ethyl acetate solvent had been added to adjust the solid content, so that the ratio of the base solution to the curing agent solution was 10:1 (the ratio of the number of hydroxyl groups in the base solution to the number of isocyanate groups in the curing agent solution was 1:2). Ethyl acetate was further added as a solvent component to adjust the solid content to 20 parts by mass, and the resulting coating solution was applied to a thickness of 6 μm after solvent evaporation, yielding a top coat layer 200. The top coat layer thickness was 6 μm.

(Comparative Example 1)
An electromagnetic wave attenuation film was prepared in accordance with Example 1A, without providing a topcoat layer.
Furthermore, the electromagnetic wave attenuation films obtained in the above-mentioned modified examples and Comparative Example 1 were attached to a stainless steel plate with an adhesive, and exposed to a temperature equivalent to 10 years of outdoor exposure using a sunshine weather meter. After that, the surface of the electromagnetic wave attenuation film was wiped with a cotton cloth to check the remaining state of the top coat layer and the electromagnetic wave attenuation layer, and the changes in the monostatic RCS attenuation characteristics.
As a result, it was confirmed that in the modified configuration, there was no deterioration in either the top coat layer or the electromagnetic wave attenuation layer, and that the formation of the top coat layer resulted in impedance matching and improved monostatic RCS attenuation characteristics, as shown in Figure 24.

Each embodiment of the present invention has been described in detail above with reference to the drawings, but the specific configuration is not limited to this embodiment, and configuration changes and combinations may be made without departing from the spirit of the present invention. Some examples of changes are given below, but these are not all inclusive and other changes are also possible. Two or more of these changes may be combined as appropriate.

In the first embodiment, the aspects used in the second embodiment, such as the frequency band and the type of metal used in 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 form of the planar inductor is not limited to being formed on the entire back surface. For example, multiple metal plates may be arranged as on the front surface, or may be 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 oval), a polygon other than a square, various polygons with rounded corners, and an irregular shape.
The total area of the metal plates in the projected area of the front surface is preferably 20% or more.
In this way, electromagnetic waves can be efficiently attenuated.

The electromagnetic wave attenuation film of the present invention can be used by stacking multiple sheets. By varying the structural parameters of the multiple sheets to be stacked, it is possible to adjust the attenuation properties more precisely.

In the first embodiment, the heights of the first and second regions 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 be configured without a planar inductor on the back surface. For example, if the object to which the back surface is bonded is metal, the second and third mechanisms can be successfully implemented by the metal surface of the object to be bonded, even without a planar inductor. In such cases, it is sufficient to provide an attachment layer, such as an adhesive layer, on the back surface that can be bonded to the object.

In the electromagnetic wave attenuation film of the present invention, parameters such as the structural period and dimensions of the metal plates do not necessarily need to be perfectly consistent in all locations. For example, even if the above parameters vary within the tolerance range in the manufacturing process (generally within a 5% range), this is considered "same shape and same size" in the present invention. Furthermore, the "predetermined range of values" can 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 certain area, or the range of tolerance in the manufacturing process.

The support cage may be made up of multiple conductive segments arranged with a gap between them. In this case, the gap can be 1/10 or less of the wavelength of the electromagnetic waves to be captured. The support cage can be made up of multiple conductive segments. In other words, the support cage may be made up of multiple conductive segments.

In the electromagnetic wave attenuation film according to the present invention, a release layer may be provided on the supporting substrate, followed by the electromagnetic wave attenuation film of the first or second embodiment, and then an adhesive, pressure sensitive adhesive, etc. may be provided to form a transfer foil.
Specifically, a release layer is applied and dried on a support substrate, and then a base layer is provided on top of it. In the configuration of the first embodiment, an unevenness is imparted to the base layer, and a thin-film conductive layer is provided by vapor deposition. Then, the thin-film conductive layer formed on the side of the second region is removed, and a layer that will become the dielectric substrate is provided. A transfer foil can be obtained by laminating a flat inductor and an adhesive in this order on the dielectric substrate. In the configuration of the second embodiment, a thin-film conductive layer is provided on the base layer, and a mask layer is printed with a pattern in the shape of the metal plate. Then, excess thin-film conductive layer is removed by etching, resulting in a metal plate. 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 flat inductor layer may be omitted.
By using it as a transfer foil, it is possible to make the film even thinner, improve its conformability, and transfer it to complex shapes, thereby broadening the range of application of the electromagnetic wave attenuation film of the present invention.

According to the above-described embodiments and modifications, the following notes 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 lamination layer disposed on the back surface;
Equipped with
the thin film conductive layer includes 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 lamination layer disposed on the back surface;
Equipped with
the thin film conductive layer includes 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 lamination layer disposed on the back surface;
Equipped with
the thin film conductive layer includes a plurality of metal plates;
the dielectric layer has an unevenness on the front surface, the unevenness being composed of a first region of a relatively low concave portion and a second region of a relatively high concave portion;
The first regions are arranged discretely,
the second region is disposed between a plurality of the 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 lamination layer disposed on the back surface;
Equipped with
the dielectric layer has an unevenness on the front surface, the unevenness being composed of a first region of a relatively low concave portion and a second region of a relatively high concave portion;
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 disposed between a plurality of the first regions.
Electromagnetic wave attenuation film.

In the above examples, we have examined the attenuation of electromagnetic waves, but it is known that conductors that attenuate specific electromagnetic waves can be used as antennas for receiving radio waves. Therefore, the above-mentioned embodiments can also be used as receiving antennas. Furthermore, because the above-mentioned embodiments capture quanta with zero momentum in a two-dimensional system, it is thought that they could also be used as elements that calculate and record data in the quantum state of metal plates.

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

1, 61 Electromagnetic wave attenuation film 10, 62 Dielectric substrate 10a, 62a Front surface 10b, 62b Back surface 30 Thin film conductive layer 30A Metal plate 50 Planar inductor 200 Top coat layer 121 First region 122 Second region

Claims (17)

a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a planar inductor disposed on the back surface;
Equipped with
the thin film conductive layer includes a plurality of metal plates;
The metal plates are arranged discretely,
The metal plate has a polygonal, circular, or elliptical shape,
When the thickness of the metal plate is T and the skin depth is d, the following formula (1) is satisfied:
Electromagnetic wave attenuation film for use in the frequency range of 35 GHz to 50 GHz.
-2.0 ≦ ln(T/d) ≦ -0.5...(1) a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
a planar inductor disposed on the back surface;
Equipped with
the dielectric substrate has, on the front surface, an unevenness consisting of a first region of a relatively low concave portion and a second region of a relatively high concave portion;
the thin-film conductive layer includes a plurality of metal plates disposed in the first region and formed on the upper surface of the second region;
The first regions are arranged discretely,
The metal plate has a polygonal, circular, or elliptical shape,
The second region is disposed between a plurality of the first regions.
Electromagnetic wave attenuation film for use in the frequency range of 35 GHz to 50 GHz. a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
an adhesive layer disposed on the rear surface;
Equipped with
the thin film conductive layer includes a plurality of metal plates;
The metal plates are arranged discretely,
The metal plate has a polygonal, circular, or elliptical shape,
When the thickness of the metal plate is T and the skin depth is d, the following formula (1) is satisfied:
Electromagnetic wave attenuation film for use in the frequency range of 35 GHz to 50 GHz.
-2.0 ≦ ln(T/d) ≦ -0.5...(1) a dielectric substrate having a front surface and a back surface;
a thin film conductive layer disposed on the front surface;
an adhesive layer disposed on the rear surface;
Equipped with
the dielectric substrate has, on the front surface, an unevenness consisting of a first region of a relatively low concave portion and a second region of a relatively high concave portion;
the thin-film conductive layer includes a plurality of metal plates disposed in the first region and formed on the upper surface of the second region;
The first regions are arranged discretely,
The metal plate has a polygonal, circular, or elliptical shape,
The second region is disposed between a plurality of the first regions.
Electromagnetic wave attenuation film for use in the frequency range of 35 GHz to 50 GHz. An electromagnetic wave attenuation film as described in claim 1 or 2, wherein the thin-film conductive layer and the planar inductor are spaced apart in the thickness direction of the dielectric substrate. An electromagnetic wave attenuation film according to any one of claims 1 to 5, characterized in that it comprises a topcoat layer on the thin-film conductive layer. The electromagnetic wave attenuation film described in claim 6, characterized in that the top coat layer is impedance-matched to the air layer through which electromagnetic waves propagate. The electromagnetic wave attenuation film described in claim 7, characterized in that the top coat layer is primarily composed of an acrylic resin composition containing cyclohexyl (meth)acrylate as a monomer component. The electromagnetic wave attenuation film described in claim 8, characterized in that the top coat layer contains an ultraviolet absorber and an ultraviolet scattering agent in an acrylic resin composition. An electromagnetic wave attenuation film according to any one of claims 1 to 9, wherein the metal plate is made of silver, copper, or aluminum. An electromagnetic wave attenuation film according to any one of claims 1 to 10, wherein multiple metal plates of the same shape and size are arranged at distances within a predetermined range. An electromagnetic wave attenuation film according to any one of claims 1 to 11, wherein the thin-film conductive layer is configured to capture electromagnetic waves incident from the front side. An electromagnetic wave attenuation film according to any one of claims 1 to 12, wherein the metal plate has a pair of opposing sides. The electromagnetic wave attenuation film of claim 13, wherein the length of a pair of opposing sides of the metal plate is 0.25 mm or more and 4 mm or less. An electromagnetic wave attenuation film described in any one of claims 1 to 14, wherein the thickness of the dielectric substrate is sufficiently thin relative to the attenuation center wavelength. An electromagnetic wave attenuation film according to any one of claims 1 to 15, wherein the thickness of the dielectric substrate is less than 1/10 of the attenuation center wavelength. 17. The electromagnetic wave attenuation film of claim 1, wherein the metal plate is polygonal with rounded corners.