Electromagnetic wave absorber

Abstract

To provide a technology advantageous for improving the reattachment of an electromagnetic wave absorber.SOLUTION: In an electromagnetic wave absorber in which a resistive layer and a dielectric layer are laminated, the electromagnetic wave absorber is detachable from an object, and the dielectric layer has adhesive force for adhering to the object.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an electromagnetic wave absorber.

Background Art

[0002] An electromagnetic wave absorber that absorbs electromagnetic waves of a predetermined frequency is known. Patent Document 1 shows an electromagnetic wave absorber in which an electromagnetic wave absorption layer, a spacer layer, and a reflection layer are laminated.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] When temporarily using an electromagnetic wave absorber in an emmission inspection or the like, the electromagnetic wave absorber may be attached to an object using an adhesive or the like and peeled off after use. When reusing the electromagnetic wave absorber, the reattachability of the electromagnetic wave absorber may be poor due to deterioration of the adhesive associated with the previous use of the electromagnetic wave absorber. An object of the present invention is to provide a technique advantageous for improving the reattachability of an electromagnetic wave absorber.

Means for Solving the Problems

[0005] In view of the above problems, an electromagnetic wave absorber according to an embodiment of the present invention is an electromagnetic wave absorber in which a resistance layer and a dielectric layer are laminated, the electromagnetic wave absorber is detachable from an object, and the dielectric layer has an adhesive force for adhering to the object.

Effects of the Invention

[0006] According to the present invention, it is possible to provide a technique advantageous for improving the reattachability of an electromagnetic wave absorber.

Brief Description of the Drawings

[0007]

Figure 1

Figure 2

Figure 3

Mode for Carrying Out the Invention

[0008] Hereinafter, embodiments will be described in detail with reference to the accompanying drawings. Note that the following embodiments do not limit the invention according to the claims, and not all combinations of the features described in the embodiments are essential for the invention. Two or more of the features described in the embodiments may be arbitrarily combined. Also, the same or similar configurations are assigned the same reference numerals, and duplicate descriptions are omitted.

[0009] With reference to FIGS. 1 to 3, the electromagnetic wave absorber according to the embodiment of the present disclosure will be described. Hereinafter, in this specification, the "conductor pattern" means an aggregate of units that are geometric figures and an object that selectively transmits electromagnetic waves of a certain frequency. It can be said that the "conductor pattern" has a function similar to that of a so-called antenna. In this specification, the "electromagnetic wave in the millimeter wave region" means an electromagnetic wave having a wavelength of 1 mm to 10 mm. The "electromagnetic wave in the millimeter wave region" can also be said to be an electromagnetic wave having a frequency of 30 GHz to 300 GHz. In this specification, "~" indicating a numerical range means including the numerical values described before and after it as the lower limit value and the upper limit value.

[0010] FIG. 1(a) is a cross-sectional view showing a configuration example of the electromagnetic wave absorber 100 of the present embodiment. In the electromagnetic wave absorber 100, a resistance layer 101 and a dielectric layer 102 are laminated. The electromagnetic wave absorber 100 may be composed of only two layers, the resistance layer 101 and the dielectric layer 102. Although details will be described below, the electromagnetic wave absorber 100 is configured to be detachable from the object 200 to which it is attached, as shown in FIG. 2. Specifically, the dielectric layer 102 of the electromagnetic wave absorber 100 has an adhesive force for adhering to the object 200.

[0011] Here, first, the electromagnetic wave absorber 150 of the comparative example will be described, and then the configuration and effects of the electromagnetic wave absorber 100 of the present embodiment will be described. FIG. 1(b) is a cross-sectional view showing a configuration example of the electromagnetic wave absorber 150 of the comparative example. In the electromagnetic wave absorber 150 of the comparative example, a resistance layer 101, a dielectric layer 152, a reflection layer 153, an adhesive layer 154, and a release film 155 are laminated in this order.

[0012] The resistance layer 101 may be, for example, a single layer, or may include, for example, a base material 112 and a conductor pattern 111 formed on the base material 112. The resistance layer 101 may be provided with a frequency selective surface (FSS). The FSS is a surface that can block or transmit only electromagnetic waves of a specific frequency by forming a continuous structure of a shape equal to or less than the wavelength with a conductive member or the like.

[0013] The conductor pattern 111 disposed on the resistance layer 101 is formed on the base material 112 by, for example, thin metal wires, conductive thin films, fixed objects of conductive pastes, etc. Examples of the metal include copper, aluminum, tungsten, iron, molybdenum, nickel, titanium, silver, gold, or alloys containing two or more of these metals (for example, steels such as stainless steel and carbon steel, brass, phosphor bronze, zirconium copper alloy, beryllium copper, iron nickel, nichrome, nickel titanium, kanthal, hastelloy, rhenium tungsten, etc.).

[0014] Examples of the conductive thin film include metal particles, carbon nanoparticles, carbon fibers, etc. Note that the conductor pattern 111 may be formed using a plurality of materials in order to adjust the transmission characteristics of the resistance layer 101.

[0015] The base material 112 is a flat member, and the thickness may be, for example, 5 μm to 500 μm. The material of the base material 112 can be appropriately selected according to the use of the electromagnetic wave absorber 100.

[0016] For example, the base material 112 can be made of resin. The resin may be a thermoplastic resin or a thermosetting resin. When considering the three-dimensional moldability of the electromagnetic wave absorber 100, etc., the base material 112 may contain a thermoplastic resin. Examples of the thermoplastic resin include polyolefin resin, polyester resin, polyester-polyether resin, polyacrylic resin, polystyrene resin, polyimide resin, polyimide amide resin, polyamide resin, polyurethane resin, polycarbonate resin, polyarylate resin, melamine resin, epoxy resin, urethane resin, silicone resin, fluororesin, etc.

[0017] The base material 112 may contain optional components as long as the effects of the present embodiment are not impaired. Examples of the optional components include, for example, inorganic fillers, colorants, curing agents, anti-aging agents, light stabilizers, flame retardants, conductive agents, antistatic agents, plasticizers, etc.

[0018] The dielectric layer 152 is disposed between the resistance layer 101 and the reflection layer 153. The dielectric layer 152 may have a single-layer structure or a laminated structure. The material used for the dielectric layer 152 can be appropriately selected according to the application, and examples include plastic films, paper, cloth, non-woven fabrics, rubber sheets, foamed sheets, etc. Among these, from the viewpoint of easily achieving weight reduction while increasing the thickness, a foamed sheet may be used for the dielectric layer 152. As the foamed sheet, for example, a foamed sheet formed by foaming the resin constituting the above-mentioned plastic film into a sheet shape can be used. Specific examples of the foamed sheet include polyethylene foam, polypropylene foam, polyurethane foam, etc.

[0019] In addition, a plastic film mixed with a metal filler may be used for the dielectric layer 152. As the plastic film, either a thermoplastic resin or a thermosetting resin may be used, but a thermoplastic resin similar to the above-described base material 112 may be used. Further, as the metal filler, barium titanate, strontium titanate, calcium titanate, titanium oxide, etc. having a high dielectric constant may be used.

[0020] When considering the wavelength shortening effect by the dielectric layer 152, the thickness of the dielectric layer 152 is appropriately changed according to the wavelength of the electromagnetic wave to be absorbed and the relative dielectric constant of the dielectric layer 152. When considering the wavelength shortening effect by the dielectric layer 152, the thickness of the dielectric layer 152 may satisfy the following formula (1). (Thickness of dielectric layer 152) = (λ) × (1 / 4) / (ε) 1 / 2 ···(1) Here, λ is the wavelength of the electromagnetic wave incident on the dielectric layer 152, and ε is the relative dielectric constant of the dielectric layer 152. The thickness of the dielectric layer 152 may be appropriately adjusted to adjust the absorption characteristics of the electromagnetic wave absorber 100. For example, the thickness of the dielectric layer 152 can be changed in the range of 0.1 times to 3.0 times the thickness obtained by formula (1).

[0021] When the relationship between the thickness of the dielectric layer 152 and the wavelength λ satisfies the relationship of formula (1), the electromagnetic wave absorber 100 has a so-called λ / 4 structure. In this case, the phase of the electromagnetic wave reflected by the reflection layer 153 after passing through the dielectric layer 152 and the electromagnetic wave reflected by the resistance layer 101 is inverted, that is, the phase difference becomes 180 degrees. Thereby, the intensity of the electromagnetic wave reflected from the electromagnetic wave absorber 100 can be reduced.

[0022] The reflective layer 153 reflects the electromagnetic waves that impinge on the surface of the electromagnetic wave absorber 150 and pass through the dielectric layer 152. Among the electromagnetic waves impinging on the electromagnetic wave absorber 150, some are reflected by the resistance layer 101 or absorbed by the resistance layer 101. On the other hand, the electromagnetic waves that are neither reflected nor absorbed by the resistance layer 101 pass through the resistance layer 101. The electromagnetic waves that have passed through the resistance layer 101 are reflected by the reflective layer 153 toward the resistance layer 101.

[0023] For example, if the reflective layer 153 has conductivity in the plane direction of either of the two surfaces facing the dielectric layer 152 and the adhesive layer 154 respectively, it can reflect the electromagnetic waves that have passed through the resistance layer 101. Specifically, a structure in which a metal foil such as aluminum foil or copper foil, or a metal plate such as a copper plate is laminated on a resin film such as polyethylene terephthalate can be used as the reflective layer 153. Instead of the metal foil or metal plate, a transparent conductive film such as ITO, or a mesh sheet formed of metal wires or the like may be used.

[0024] In the electromagnetic wave absorber 150 of the comparative example, an adhesive layer 154 is disposed on the surface of the reflective layer 153 opposite to the surface in contact with the dielectric layer 152 in order to attach the electromagnetic wave absorber 150 to various objects. Examples of the adhesive layer 154 include acrylic adhesives, urethane adhesives, rubber adhesives, polyester adhesives, silicone adhesives, polyvinyl ether adhesives, and the like. A release film 155 may be disposed on the surface of the adhesive layer 154 opposite to the surface in contact with the reflective layer 153. The release film 155 is removed when the electromagnetic wave absorber 150 is used. By covering the adhesive layer 154 with the release film 155, the handling property during distribution is improved.

[0025] Incidentally, an electromagnetic wave absorber may be temporarily used in aiming inspection or the like. Since the electromagnetic wave absorber 150 of the comparative example is attached to an object via the adhesive layer 154, it is conceivable to attach the electromagnetic wave absorber 150 to a partition or the like in advance and then use it. In that case, a space for storing the partition is required when the electromagnetic wave absorber 150 is not used. Further, for example, it is conceivable to attach the electromagnetic wave absorber 150 to the object when in use and peel off the electromagnetic wave absorber 150 from the object when not in use. In that case, problems such as deterioration of the adhesive layer 154 and a part of the adhesive layer 154 remaining on the object and contaminating the object may occur. That is, the electromagnetic wave absorber 150 of the comparative example may have poor reattachability.

[0026] Furthermore, as described above, resin films such as polyethylene terephthalate are used for the base material 112 of the resistance layer 101 and the reflection layer 153. Although thin film films are used as these resin films, since resin films are attached to both sides of the dielectric layer 152, the electromagnetic wave absorber 150 has poor flexibility, and it is difficult to bend the electromagnetic wave absorber 150 unless a dielectric with a high dielectric constant and a thin film is used as the dielectric layer 152. When bent, there is a possibility of creasing.

[0027] Therefore, as shown in Fig. 1(a), the electromagnetic wave absorber 100 of the present embodiment is composed of two layers, namely, a resistance layer 101 and a dielectric layer 102, and further, the dielectric layer 102 has an adhesive force for attaching to an object. Specifically, the dielectric layer 102 provided in the electromagnetic wave absorber 100 of the present embodiment is composed of a dielectric material and a magnetic material having magnetism. For example, the dielectric layer 102 is a magnetic sheet in which magnetic powder is added to the dielectric material as a magnetic material and magnetized. Thereby, as shown in Fig. 2, although the object 200 that can be attached is mainly limited to members made of iron or the like, since no adhesive layer is required, an electromagnetic wave absorber 100 with excellent reattachability is realized.

[0028] Furthermore, many of the objects 200 to which a magnetic sheet or the like can be adsorbed contain ferromagnetic materials such as iron and may have conductivity. Therefore, the electromagnetic wave absorber 100 of the present embodiment can cause the object 200 to which the dielectric layer 102 is attached to function as a reflection layer. That is, the electromagnetic wave absorber 100 of the present embodiment does not need to include a reflection layer in addition to the adhesive layer. Therefore, by using the radio wave reflector (object 200) itself to be pasted as the reflection layer, unlike the electromagnetic wave absorber 150, one surface of the dielectric layer 102 is not fixed. As a result, the electromagnetic wave absorber 100 has a configuration with excellent flexibility.

[0029] The electromagnetic wave absorber 100 has a simpler configuration than the electromagnetic wave absorber 150. Therefore, for example, it is possible to shorten the manufacturing process when manufacturing the electromagnetic wave absorber 100. Also, as described above, the electromagnetic wave absorber 100 has high flexibility and excellent workability. For example, when winding processing is performed on the electromagnetic wave absorber 150, the sheet may break due to poor flexibility. On the other hand, in the electromagnetic wave absorber 100 of the present embodiment, winding processing such as roll-to-roll is possible, and productivity can be improved.

[0030] Examples of the dielectric material used for the dielectric layer 102 include various rubber materials such as nitrile rubber and acrylic rubber, and thermoplastic elastomers such as styrene-based elastomers, olefin-based elastomers, polyester-based elastomers, and polyurethane-based elastomers. Examples of the magnetic material used for the dielectric layer 102 include various magnetic materials such as anisotropic or isotropic barium ferrite and strontium ferrite.

[0031] The volume ratio of the magnetic material in the dielectric layer 102 may be 20% or more. When the ratio of the magnetic material contained in the dielectric layer 102 decreases, it becomes difficult for the object 200 to adhere (adsorb) thereto, and it may become difficult to use. For example, the volume ratio of the magnetic material in the dielectric layer 102 may be 30% or more. On the other hand, when the ratio of the magnetic material contained in the dielectric layer 102 increases, the workability during the formation of the dielectric layer 102 decreases, and for example, it may break when bent. Therefore, the volume ratio of the magnetic material in the dielectric layer 102 may be 60% or less. Further, in order to ensure more flexibility, the volume ratio of the magnetic material in the dielectric layer 102 may be 50% or less.

[0032] The magnetic powder used as the magnetic material may have a particle diameter of about 1 μm or more. When mixing the magnetic powder into the dielectric material, if the particle diameter becomes small, the magnetic powder may aggregate. On the other hand, the magnetic powder used as the magnetic material may have a particle diameter of 100 μm or less. The thickness of the dielectric layer 102 can be appropriately set according to the wavelength of the electromagnetic wave to be absorbed, using the above formula (1) etc. For example, it may be 200 μm to 5000 μm, it may be 300 μm to 4000 μm, or it may be 1000 μm to 3000 μm. The particle diameter is selected so that the particles of the dielectric material are appropriately added to the dielectric layer 102. Further, when the thickness of the dielectric layer 102 is as thin as 25 μm to 200 μm, for example, the particle diameter of the dielectric powder may be half or less of the thickness of the dielectric layer 102.

[0033] FIG. 3 is a perspective view showing a modified example of the electromagnetic wave absorber 100 shown in FIG. 1(a). In the configuration shown in FIG. 1(a), for example, a conductor pattern 111 is formed on a base material 112, and the electromagnetic wave absorber 100 can be manufactured by attaching the base material 112 on which the conductor pattern 111 is formed and the dielectric layer 102 with an adhesive layer or the like. On the other hand, in the configuration shown in FIG. 3, the conductor pattern 111 of the resistance layer 101 may be directly formed on the dielectric layer 102. A thin protective layer may be disposed on the resistance layer 101 (conductor pattern 111). For the protective layer, for example, various materials described above as the material of the base material 112 can be used. In that case, since the protective layer does not need to support (handle) the conductor pattern 111 like the base material 112 in the manufacturing process of the electromagnetic wave absorber 100, it can be made thin. For example, the protective layer can be formed by spray coating a fluororesin or the like. Different from the case where the base material 112 having a smooth surface as described above is disposed on the resistance layer 101, in the configuration shown in FIG. 3, the surface of the resistance layer 101 may have irregularities corresponding to the shape of the conductor pattern 111.

[0034] Also, in the configuration shown in FIG. 3, it is not necessary to dispose the base material 112 as the resistance layer 101. Therefore, furthermore, an electromagnetic wave absorber 100 with high flexibility and excellent processability can be realized.

[0035] In the above-described embodiments, the electromagnetic wave absorber 100 that can be attached to and detached from the object 200 has been described by the dielectric layer 102 including a dielectric material and a magnetic material having magnetism. However, the configuration of the electromagnetic wave absorber 100 is not limited to the configuration as described above. In the above-described electromagnetic wave absorber 100, using the object 200 as a reflective layer has been described. However, for example, a metal (foil or film) such as aluminum may be disposed on the surface opposite to the surface on which the resistance layer 101 of the dielectric layer 102 is disposed. A metal film is disposed on the surface opposite to the surface on which the resistance layer 101 of the dielectric layer 102 is disposed by using a sputtering method or the like within a range where the magnetic force for attaching (adsorbing) to the object 200 of the magnetic sheet used as the dielectric layer 102 is not inhibited. The influence of the thin-film metal film on the flexibility of the electromagnetic wave absorber 100 is small. Also, by disposing the metal film, the metal film can function as a reflective layer. That is, the functionality of the electromagnetic wave absorber 100 is also improved.

[0036] Also, the configuration of the dielectric layer 102 is not limited to the magnetic sheet as described above. It is only necessary that the dielectric layer 102 has an adhesive force for attaching to the object 200. For example, an acrylic resin, a silicone resin, or the like may be used as the dielectric layer 102, and attachment to and detachment from the object 200 may be repeated. Thereby, the same effects as those of the above-described electromagnetic wave absorber 100 can be obtained. When an acrylic resin, a silicone resin, or the like is used as the dielectric layer 102, a release film may cover the surface of the dielectric layer 102 in order to improve the handling property during distribution at the time of shipment or the like. The release film is removed when the electromagnetic wave absorber 100 is used.

[0037] As described above, the electromagnetic wave absorber 100 of the present embodiment is configured to be detachable from the object 200. Further, when the electromagnetic wave absorber 100 is detached and attached, the possibility that the surface of the object 200 becomes rough and the possibility that the adhesive force decreases due to adhesion of dust or dirt are low. Therefore, the reattachability of the electromagnetic wave absorber 100 can be remarkably improved. Furthermore, as described above, the electromagnetic wave absorber 100 of the present embodiment can have high flexibility. Therefore, after temporarily using the electromagnetic wave absorber 100 in an emmission inspection or the like, for example, the electromagnetic wave absorber 100 can be rolled up small and stored. Compared with the case of attaching to a partition or the like as in the electromagnetic wave absorber 150 of the comparative example and performing the taking in and out of the partition every time it is used, the necessity of considering the storage space and the like is remarkably reduced, and an electromagnetic wave absorber 100 that is easy to use for the user can be realized. Thus, the electromagnetic wave absorber 100 of the present embodiment realizes not only an improvement in the attachability of the electromagnetic wave absorber 100 but also an electromagnetic wave absorber 100 that is easy to use for the user.

[0038] The invention is not limited to the above-described embodiment, and various modifications and changes are possible within the scope of the gist of the invention.

Explanation of Signs

[0039] 100: Electromagnetic wave absorber, 101: Resistance layer, 102: Dielectric layer, 200: Object

Claims

1. An electromagnetic wave absorber in which a resistance layer and a dielectric layer are laminated, wherein the electromagnetic wave absorber is detachable from an object, and the dielectric layer has an adhesive force for adhering to the object. An electromagnetic wave absorber characterized by this.

2. The electromagnetic wave absorber according to claim 1, characterized in that the object to which the dielectric layer is attached functions as a reflection layer.

3. The electromagnetic wave absorber according to claim 1, characterized in that the dielectric layer contains a dielectric material and a magnetic material having magnetism.

4. The electromagnetic wave absorber according to claim 3, characterized in that the dielectric layer is a magnetic sheet in which magnetic powder is added to the dielectric material as the magnetic material.

5. The electromagnetic wave absorber according to any one of claims 1 to 4, characterized in that the resistance layer includes a conductor pattern.

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