JP2000232293A - Electromagnetic wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber, which absorbs electromagnetic waves in a specified wide-frequency range, by a method wherein the absorber is formed into a constitution, wherein electromagnetic wave reflective layers consisting of a flexible high-molecular material having a conductivity and electromagnetic wave absorbing layers, which consist of a flexible high-molecular material dispersed with metal magnetic metal powder and respectively have a plurality of pores, are laminated in order and the reflective layers and the absorbing layers are integrally formed. SOLUTION: 30 wt.% of a carbon fiber is dispersed in a flexible high-molecular material, such as chloroprene rubber, butyl rubber, urethane rubber, a silicone resin, a vinyl chloride resin and a phenol resin, the high-molecular material is formed into a sheet and an electromagnetic wave reflective layer 1 is formed. Then 78 wt.% of flatness-shaped powder consisting of an Fe-Cu-Nb-Si-B nano-crystalline alloy is dispersed in a flexible high-molecular material, the high-molecular material is formed into a sheet, an electromagnetic wave absorbing layer 2 is formed and a plurality of 2-mm diameter pores are irregularly provided in this layer 2. Moreover, a flexible high-molecular material is sheeted and a flexible high-molecular material layer 3 of a dielectric constant lower than 10 is formed.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorber for absorbing electromagnetic waves in the quasi-microwave band and the quasi-millimeter wave band.

[0002]

2. Description of the Related Art In recent years, with the advancement of digital devices, the advancement of information and communication technology seen in the rapid spread of mobile phones, the use of higher frequency CPUs in computers, and the spread of high-speed wireless LANs, these devices have been developed. The problem of electromagnetic interference such as mutual interference and malfunction of equipment has arisen due to the electromagnetic waves generated from. As a countermeasure, an electromagnetic wave absorber that absorbs these unnecessary electromagnetic waves is required, and as an electromagnetic wave absorber for the quasi-microwave band and the quasi-millimeter wave band, a powder of sintered ferrite is mixed with a resin such as rubber or plastic. An electromagnetic wave absorber in which a sheet made of a metal and an electromagnetic wave reflection layer made of a metal such as a metal mesh material or a lattice-shaped metal member are bonded has been proposed.

[0003]

However, in the conventional electromagnetic wave absorber, the mixing amount of the pulverized powder of the ferrite sintered body and the resin or the thickness of the electromagnetic wave absorber is adjusted, so that the space impedance and the electromagnetic wave absorber are adjusted. By matching the impedances of the quasi-microwave band and the quasi-microwave band, it is possible to obtain a large absorption in the specific frequency band of interest. It is not possible.

Further, in order to obtain a large absorption by a resin mixed with a ground powder of a ferrite sintered body, the thickness of at least one layer must be at least 4 mm, and electronic equipment which is required to be small and lightweight. Can not be used at all.
Also, even when used as a building material, the weight is heavy,
Due to the lack of flexibility, when used on walls and ceilings, the mounting workability is extremely poor and the handling is inferior.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide an electromagnetic wave absorber which is thin and flexible and absorbs electromagnetic waves in a wide frequency range of a quasi-microwave band and a quasi-millimeter wave band. The purpose is to provide.

[0006]

That is, according to the present invention, an electromagnetic wave reflection layer made of a conductive flexible polymer material and an electromagnetic wave absorption layer in which a metal magnetic powder is dispersed in the flexible polymer material are sequentially formed. An electromagnetic wave absorber laminated and integrated, wherein the electromagnetic wave absorbing layer is an electromagnetic wave absorber having a plurality of holes.

[0007] In the present invention, the volume ratio of the pores is 50%
To 80%. Further, the electromagnetic wave absorbing layer may be composed of a plurality of layers having different volume ratios of the holes, and in this case, it is preferable to sequentially stack the layers having the smaller volume ratio of the holes. Further, it is preferable that the outer surface on the side of the electromagnetic wave absorbing layer be substantially covered with a flexible polymer material having a dielectric constant of 10 or less, and the oxide magnetic powder may be dispersed in the flexible polymer material.

[0008]

FIG. 1 shows an electromagnetic wave absorber according to the present invention.
This will be described with reference to FIG. FIG. 1 is a sectional view of an electromagnetic wave absorber according to one embodiment of the present invention. The electromagnetic wave absorber according to the present invention comprises an electromagnetic wave reflecting layer 1 in which a conductive polymer fibrous material is dispersed in a flexible polymer material, and pores in which a metallic magnetic powder is dispersed in the flexible polymer material. The electromagnetic wave absorbing layer 2 and the flexible polymer material layer 3 having a dielectric constant of 10 or less are sequentially laminated and thermocompression-bonded.

The above-mentioned flexible polymer material is an organic material which is flexible, has a specific gravity of 1.5 or less and has weather resistance, and includes, for example, chloroprene rubber, butyl rubber, urethane rubber, silicone resin, vinyl chloride resin, phenol resin and the like. In particular, when a flexible polymer material is used as the sheath of the electromagnetic wave absorber,
Preferably, the dielectric constant is 10 or less. Dielectric constant is 10
Exceeding this range is not preferable in practice because the broadband property of electromagnetic wave absorption performance is lost. A more preferable dielectric constant is 8 or less.
In addition, Fe—Ni—Zn is used as the flexible polymer material used for the exterior.
-Cu-based, Fe-Mg-Zn-Cu-based and Fe-Mn-
It is preferable to disperse the pulverized Zn-based soft ferrite powder because the reflection of electromagnetic waves can be reduced. The flexible polymer material is
The metal magnetic powder of the electromagnetic wave absorbing layer 2 is prevented from being oxidized.

The conductive material dispersed in the electromagnetic wave reflecting layer 1 is, for example, carbon fiber or metal fiber, which is dispersed in a flexible polymer material and formed into a sheet. The electromagnetic wave reflecting layer 1 preferably has a sheet resistance of 1 kΩ □ or less.

The electromagnetic wave absorbing layer 2 is formed by dispersing a metallic magnetic powder dispersed in Fe—Cu—metal with a specific gravity of, for example, 6.0 or more.
A flat powder having an average particle size of 0.1 to 50 μm and an average thickness of 3 μm or less produced by grinding a powder having a particle shape from an Nb—Si—B-based nanocrystallized alloy by a water atomization method using an attritor, Using flat shaped powder such as carbonyl iron alloy, amorphous alloy, Fe-Si alloy, molybdenum permalloy, supermalloy, etc., this is dispersed in a flexible polymer material and formed into a sheet, and at a frequency of 1 GHz, μ '(Real part of complex permeability) ≧ 5 and μ ″ (imaginary part of complex permittivity) ≧ 3 and ε ′ (real part of complex permittivity) ≧ 20 and ε ″ (imaginary part of complex permittivity) ≧ 0 .5 is desirable. The flat powder tends to have a large magnetic anisotropy, and has a sufficiently large μ ″ (the imaginary part of the complex magnetic permeability) even at 300 MHz or higher, so that a large magnetic loss can be obtained at a wide frequency. Fe—Cu—Nb having an average particle diameter of 50 μm or less as another metal magnetic powder.
-Si-B nanocrystalline alloy, amorphous alloy, Fe
Granular powder such as a Si-based alloy, molybdenum permalloy, and supermalloy may be used. In this case, the frequency is 5 GHz.
In z, μ ′ (real part of complex permeability) ≧ 1.2 and μ ″ (imaginary part of complex permeability) ≧ 0.5 and ε ′ (real part of complex permittivity) ≧ 5 and ε ″ (complex Imaginary part of permittivity) ≧
Preferably, it is 0.1. Further, since these metal magnetic powders are easily oxidized, it is desirable to perform a surface treatment with an antioxidant in advance.

The amount of dispersion of the metallic magnetic powder in the electromagnetic wave absorbing layer 2 is preferably 65 to 92% by weight. If it is less than 65% by weight, the absorption performance is reduced, and if it exceeds 92% by weight, not only is the material cost high, but also the weight is heavy, and the flexibility and durability are reduced, which is not practically preferable. A more preferred dispersion amount is 70
~ 88% by weight.

The electromagnetic wave absorbing layer 2 may be formed of only a layer formed by using any one of the above-mentioned metal magnetic powders. However, when the electromagnetic wave absorbing layer 2 is constituted by combining with another metal magnetic powder. Electromagnetic wave absorption performance can be broadened. Further, if the electromagnetic wave absorbing layer 2 composed of the electromagnetic wave reflecting layer 1 and the electromagnetic wave absorbing layer of the flat metal powder and the electromagnetic wave absorbing layer of the metal magnetic powder in the form of granules are sequentially laminated to form the electromagnetic wave absorbing layer 2, unnecessary electromagnetic waves are generated. It is more preferable that the reflection can be reduced. If the electromagnetic wave absorbing layer 2 is composed of a plurality of layers having different impedance matching frequencies, and the electromagnetic wave absorbing layers are formed in ascending order of the impedance matching frequency from the electromagnetic wave reflecting layer 1, the electromagnetic wave absorbing performance can be broadened and the electromagnetic wave absorbing layer can be formed. This is preferable because unnecessary reflection of electromagnetic waves at the surface can be prevented.

The electromagnetic wave absorbing layer 2 has holes, and the holes reduce the effective dielectric constant of the electromagnetic wave absorbing layer 2 and expand the electromagnetic wave absorption band. It is preferable that the volume ratio of the holes in the electromagnetic wave absorbing layer 2 is 50% to 80%. 50%
If it is less than, it will not show broadband electromagnetic wave absorption performance,
If it exceeds 80%, the electromagnetic wave absorption performance itself deteriorates.
A more preferable volume ratio of the holes in the electromagnetic wave absorbing layer 2 is 55% to 75%. The holes are formed by punching out the electromagnetic wave absorbing layer with a mold having a plurality of punching pins, for example. The shape of the hole is not particularly limited, such as a circle, a rectangle, and an ellipse, but it is preferable that the size of the hole be 0.5 mm ² to 50 mm ² . Also, depending on the installation environment of the electromagnetic wave absorber, if the environmental temperature change is large, swelling or the like may occur due to the difference in thermal expansion between the air in the pores and the flexible polymer material. It is desirable to fill the holes with a dielectric having a dielectric constant of 5 or less. If the dielectric constant exceeds 5, the effect of providing the holes is reduced, which is not preferable.

The dispersion amount of the metallic magnetic powder in the electromagnetic wave absorbing layer 2 is preferably 65 to 92% by weight. If it is less than 65% by weight, the absorption performance is reduced, and if it exceeds 92% by weight, not only is the material cost high, but also the weight is heavy, and the flexibility and durability are reduced, which is not practically preferable. A more preferred dispersion amount is 70
~ 88% by weight.

The thickness of each of the electromagnetic wave reflecting layer 1 and the electromagnetic wave absorbing layer 2 is preferably 0.2 to 1.2 mm. 0.2m
If it is less than m, the absorption performance decreases, and if it exceeds 1.2 mm, not only is the material cost in the case of lamination increased, but also
The weight is heavy, and the flexibility is lowered, which is not preferable for practical use. A more preferred thickness is 0.3 to 1.0 mm. The total thickness of the laminated layers is preferably 0.6 to 2.5 mm. If it is less than 0.6 mm, the absorption performance is reduced, and
When the thickness exceeds 5 mm, not only is the material cost when laminated is high, but also the weight is heavy and the flexibility is reduced, which is not preferable in practical use. A more preferable total thickness is 0.8 to 2.2 mm.
It is.

The thickness of the flexible polymer material 3 is 0.1 mm
~ 0.5 mm is preferred. When the thickness is less than 0.1 mm, the effect of preventing the oxidation of the metal magnetic material powder is reduced. A more preferred thickness is 0.15
mm to 0.4 mm.

[0018]

EXAMPLES Example 1 A carbon fiber having a fiber length of about 2 mm was dispersed in chloroprene rubber at 30% by weight, and 0.3 m
The electromagnetic wave reflection layer 1 was formed into a sheet having a thickness of m. Next, a flat powder (average particle diameter: 20 μm, average thickness: 1 μm) of the Fe—Cu—Nb—Si—B-based nanocrystallized alloy is dispersed in chloroprene rubber by 78% by weight to a thickness of 0.5 mm. The sheet was formed into an electromagnetic wave absorbing layer 2. Through holes having a diameter of 2 mm were irregularly formed in the electromagnetic wave absorbing layer 2. The total volume of the through holes corresponds to 60% of the volume of the entire sheet. Further, a sheet of chloroprene rubber was formed to a thickness of 0.3 mm to form a flexible polymer material layer 3 having a dielectric constant of 10 or less. The dielectric constant of the flexible polymer material layer 3 is 3.4.
Met. An electromagnetic wave absorber having an overall thickness of 1.1 mm was formed by sequentially laminating and integrating these three types of sheets. FIG. 1 is a structural cross-sectional view of this electromagnetic wave absorber, and FIG. 2 is a plan view of the electromagnetic wave absorbing layer portion. FIG. 4 shows the results of evaluating the electromagnetic wave absorbing performance of this electromagnetic wave absorber. High absorption of 50% or more was obtained in a wide frequency range of 2 to 15 GHz. As a comparative example of Example 1, the result of evaluating the electromagnetic wave absorption performance of an electromagnetic wave absorber having no through hole is shown in FIG. The frequency range in which an absorptance of 50% or more can be obtained is 1.5 to 6 GHz, which indicates that the band is narrower than the performance of the first embodiment.

(Example 2) Carbon fiber having a fiber length of about 2 mm was dispersed in chloroprene rubber by 40% by weight,
The reflective layer 1 was formed into a sheet having a thickness of 2 mm. Next, F
A flat powder of an e-Cu-Nb-Si-B-based nano-crystallized alloy (average particle size: 20 μm, average thickness: 1 μm) is dispersed in chloroprene rubber by 73% by weight to form a sheet having a thickness of 0.5 mm. The absorption layer 2a was formed. Through holes having a diameter of 3.2 mm were irregularly formed in the electromagnetic wave absorbing layer 2. The total area of this through hole corresponds to 58% of the area of the entire sheet. Next, 82% by weight of the Fe-Cu-Nb-Si-B nanocrystallized nanocrystalline alloy powder (average particle diameter: 20 µm) was dispersed in chloroprene rubber, and the sheet was formed into a sheet having a thickness of 0.5 mm to absorb electromagnetic waves. The layer 2b was formed. This electromagnetic wave absorbing layer 2
Then, a through-hole having a diameter of 6 mm was irregularly formed. The total volume of the through holes corresponds to 65% of the volume of the entire sheet. Next, carbonyl iron alloy granular powder (average particle diameter 20 μm)
Was dispersed in chloroprene rubber by 70% by weight,
The electromagnetic wave absorbing layer 4 was formed into a sheet having a thickness of 2 mm. Through holes having a diameter of 4 mm were irregularly formed in the electromagnetic wave absorbing layer 2. The total volume of this through hole is 72% of the total sheet volume
Is equivalent to Further, chloroprene rubber was sheeted to a thickness of 0.2 mm to form a flexible polymer material layer 3 having a dielectric constant of 10 or less. The dielectric constant of the flexible polymer material layer 3 was 3.4. These five types of sheets were sequentially laminated and integrated to form an electromagnetic wave absorber having a total thickness of 1.8 mm. FIG. 3 is a structural sectional view of the electromagnetic wave absorber.
Shown in FIG. 5 shows the results of evaluating the electromagnetic wave absorbing performance of this electromagnetic wave absorber. A high absorption rate of 70% or more was obtained in a wide frequency range of 0.7 to 30 GHz. As a comparative example of Example 2, the result of evaluating the electromagnetic wave absorption performance of an electromagnetic wave absorber having no through hole is shown in FIG. 0.5-10G
Although a high absorptance of 50% or more is obtained in the frequency range of Hz, it can be seen that the band is narrower than the performance of the second embodiment.

[0020]

The electromagnetic wave absorber of the present invention is thinner and more flexible than conventional ones, and can absorb electromagnetic waves in a wide frequency range of the quasi-microwave band and the quasi-millimeter wave band.

[Brief description of the drawings]

FIG. 1 is a sectional view of an electromagnetic wave absorber according to a first embodiment of the present invention.

FIG. 2 is a plan view of an electromagnetic wave absorbing layer according to Embodiment 1 of the present invention.

FIG. 3 is a sectional view of an electromagnetic wave absorber according to a second embodiment of the present invention.

FIG. 4 is a diagram showing an evaluation result of electromagnetic wave absorption performance according to Example 1 of the present invention.

FIG. 5 is a diagram showing an evaluation result of electromagnetic wave absorption performance according to Example 2 of the present invention.

FIG. 6 is a diagram showing results of evaluation of electromagnetic wave absorption performance of a comparative example.

FIG. 7 is a diagram showing results of evaluation of electromagnetic wave absorption performance of another comparative example.

[Explanation of symbols]

 REFERENCE SIGNS LIST 1 electromagnetic wave reflecting layer 2, 2 a, 2 b electromagnetic wave absorbing layer 3 flexible polymer material having a dielectric constant of 10 or less 4 vacancy

 ────────────────────────────────────────────────── ─── Continuing from the front page (72) Inventor Shunichi Nishiyama 5200 Sankajiri, Kumagaya-shi, Saitama F-term in the Magnetic Materials Research Laboratory, Hitachi Metals Co., Ltd. 5E321 AA41 BB25 BB32 BB44 BB51 GG11

Claims (5)

[Claims] An electromagnetic wave absorber in which an electromagnetic wave reflecting layer made of a conductive flexible polymer material and an electromagnetic wave absorbing layer in which a metal magnetic powder is dispersed in the flexible polymer material are sequentially laminated and integrated. The electromagnetic wave absorber, wherein the electromagnetic wave absorbing layer has a plurality of holes. 2. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorbing layer includes a plurality of layers having different volume ratios of holes, and is sequentially stacked from a layer having a smaller volume ratio of holes. 3. The electromagnetic wave absorber according to claim 1, wherein the volume ratio of the holes is 50% to 80%. 4. The electromagnetic wave absorber according to claim 1, wherein at least an outer surface of the electromagnetic wave absorber on the side of the electromagnetic wave absorbing layer is substantially covered with a flexible polymer material having a dielectric constant of 10 or less. Electromagnetic wave absorber. 5. The electromagnetic wave absorber according to claim 4, wherein the oxide magnetic powder is dispersed in a flexible polymer material having a dielectric constant of 10 or less.