JP2000091783A - Laminated wide-band wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make thin an absorber, make it flexible, and absorb an electromagnetic wave in a wide frequency range of a quasi-microwave band and quasi- millimeter wave band by sequentially laminating an electronic wave reflection layer, a wave absorption layer where metal magnetic material powder is flat, and an electronic wave absorption layer where the metal magnetic material powder is granular in one piece. SOLUTION: A carbon fiber with a fiber length of approximately 2 mm is dispersed into chloroprene rubber by 30 wt.% for forming into a sheet with a thickness of 0.5 mm, thus forming a wave reflection layer 1. Then, flat powder made of nano-crystallization alloy being made of Fe-Cu-Nb-Si-B family is dispersed into the chloroprene rubber by 78 wt.% and is formed into a sheet with a thickness of 0.5 mm, thus forming a wave absorption layer 2. Then, carbonyl iron alloy granular powder is dispersed into the chloroprene rubber by 73 wt.% for forming into a sheet with a thickness of 0.5 mm, thus forming a wave absorption layer 3. These three kinds of sheets are successively laminated in one piece, thus forming a lamination-type wide-band wave absorber with an entire thickness of 1.5 mm and hence absorbing electromagnetic waves in a wide frequency range.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laminated broadband radio wave absorber for absorbing quasi-microwave and quasi-millimeter-wave electromagnetic waves.

[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, a radio wave absorber that absorbs these unnecessary electromagnetic waves is required, and as an electromagnetic wave absorber in the quasi-microwave band and quasi-millimeter wave band, powder of sintered ferrite is mixed with a resin such as rubber or plastic. There has been proposed a sheet formed by attaching a metal electromagnetic wave reflection layer such as a metal mesh material or a lattice-shaped metal member to a sheet.

[0003]

However, in the conventional radio wave absorber, the mixing amount of the pulverized powder of the ferrite sintered body and the resin or the thickness of the radio wave absorber is adjusted, so that the spatial impedance and the radio 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.

In order to obtain a large absorption by a resin mixed with a ground powder of a ferrite sintered body, the thickness must be at least 4 mm.
mm or more, and cannot be used at all for electronic devices that require small size and light weight. Further, even when used as a building material, it is heavy and inflexible, so that when it is used for a wall or a ceiling, the mounting workability is extremely poor, and the handleability is poor.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and is a laminated type broadband radio wave 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. It is intended to provide an absorber.

[0006]

Means for Solving the Problems That is, the first invention is:
It has a radio wave reflection layer made of a flexible resin having conductivity, and a plurality of radio wave absorption layers in which a metal magnetic substance powder is dispersed in the flexible resin, wherein the radio wave reflection layer and the metal magnetic substance powder have a flat shape. This is a laminated broadband electromagnetic wave absorber obtained by sequentially laminating and integrating a radio wave absorption layer of powder and a radio wave absorption layer of the metal magnetic powder in the form of particles.

According to a second aspect of the present invention, a radio wave reflecting layer made of a conductive flexible resin and a plurality of radio wave absorbing layers having different impedance matching frequencies in which a metallic magnetic powder is dispersed in the flexible resin are sequentially laminated. The integrated broadband radio wave absorber is a laminated broadband radio wave absorber formed by laminating a plurality of radio wave absorbing layers in ascending order of impedance matching frequency.

In the first and second inventions, the dispersion amount of the metallic magnetic powder in the radio wave absorption layer is 65 to 92% by weight, and the thickness of one layer of the radio wave reflection layer and the radio wave absorption layer is 0.2%. To 1.2 mm, and the total thickness of the laminated
It is desirable to set it to 6 to 2.5 mm.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A laminated broadband radio wave absorber according to the present invention will be described with reference to FIG. FIG. 1 is a sectional view of a laminated broadband radio wave absorber according to one embodiment of the present invention. The laminated broadband radio wave absorber according to the present invention includes a radio wave reflection layer 1 in which a fibrous material having conductivity is dispersed in a flexible resin, and a radio wave absorption layer in which a flat metal powder is dispersed in a flexible resin. Layer 2
And a radio wave absorbing layer 3 in which a metal magnetic material granular powder is dispersed in a flexible resin is sequentially laminated and thermocompression-bonded.

The conductive material dispersed in the radio wave reflection layer 1 is, for example, carbon fiber or metal fiber, which is dispersed in a flexible resin and formed into a sheet. It is desirable that the radio wave reflection layer 1 has a sheet resistance value of 100 kΩ □ or less.

The flat metal powder dispersed in the electromagnetic wave absorbing layer 2 is a metal having a specific gravity of 6.0 or more, for example, Fe--C
A flat powder produced by milling a granular powder with an attritor by a water atomizing method from a nano-crystallized alloy comprising a u-Nb-Si-B system, and dispersing this in a flexible resin. Form into a sheet. Carbonyl iron alloy, amorphous alloy, Fe
A flat-shaped powder such as a Si-based alloy, molybdenum permalloy, or supermalloy may be used. Further, it is preferable that an antioxidant is applied to the surface of the metal magnetic substance flat powder. The electromagnetic characteristics of the electromagnetic wave absorbing layer 2 at 1 GHz are μ ′ (real part of complex magnetic permeability) ≧ 5 and μ ″ (imaginary part of complex magnetic permeability) ≧ 3 and ε ′ (real part of complex dielectric constant).
It is desirable that ≧ 20 and ε ″ (imaginary part of complex permittivity) ≧ 0.5.

The metal magnetic powder in the form of a metal having a specific gravity of 6.0 or more, such as carbonyl iron powder, is dispersed in the flexible resin. Form into a sheet. As magnetic metal powder, F
a nano-crystallized alloy composed of e-Cu-Nb-Si-B,
Granular powders such as amorphous alloys, Fe-Si alloys, molybdenum permalloy, and supermalloy may be used.
Further, it is preferable that an antioxidant is applied to the surface of the metal magnetic substance flat powder. The electromagnetic characteristics of the electromagnetic wave absorbing layer 3 at 5 GHz are μ ′ (real part of complex magnetic permeability) ≧ 1.2 and μ ″ (imaginary part of complex magnetic permeability) ≧ 0.5
It is desirable that ε ′ (real part of complex permittivity) ≧ 5 and ε ″ (imaginary part of complex permittivity) ≧ 0.1.

[0013] The flexible resin is an organic material which is flexible, has a specific gravity of 1.5 or less, and has weather resistance, such as chloroprene rubber, butyl rubber, urethane rubber, silicone resin, vinyl chloride resin, and the like. Phenol resin and the like.

The amount of dispersion of the metallic magnetic powder in the radio wave absorbing layers 2 and 3 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 7
0 to 88% by weight.

The thickness of each of the radio wave reflection layer 1 and the radio wave absorption layers 2 and 3 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.

[0016]

(Example 1) Carbon fiber having a fiber length of about 2 mm was dispersed in chloroprene rubber at 30% by weight, and 0.5 m
The radio wave reflection layer 1 was formed into a sheet having a thickness of m. next,
A flat powder of a nanocrystallized alloy composed of an Fe-Cu-Nb-Si-B system was dispersed in chloroprene rubber at 78% by weight, and a sheet having a thickness of 0.5 mm was formed to form a radio wave absorbing layer 2. Next, the carbonyl iron alloy granular powder was dispersed in chloroprene rubber by 73% by weight and sheeted to a thickness of 0.5 mm to form the radio wave absorbing layer 3. By sequentially laminating and integrating these three types of sheets, the overall thickness becomes 1.
A 5-mm laminated broadband radio wave absorber was formed. FIG. 1 shows a cross-sectional view of the structure of the laminated type broadband radio wave absorber. Also,
FIG. 6 shows the result of evaluating the radio wave absorption performance of this laminated broadband radio wave absorber. A high absorption rate of 70% or more was obtained in a wide frequency range of 1.3 to 20 GHz.

(Example 2) Carbon fiber having a fiber length of about 2 mm was dispersed in chloroprene rubber by 40% by weight,
The radio wave reflection layer 1 was formed into a sheet having a thickness of 1 mm. Next, a flat powder of a nano-crystallized alloy composed of an Fe-Cu-Nb-Si-B system was dispersed in chloroprene rubber by 73% by weight and sheeted to a thickness of 0.5 mm to form a radio wave absorbing layer 2. . Next, 82% by weight of Fe-Cu-Nb-Si-B nanocrystalline alloy powder was dispersed in chloroprene rubber and sheeted to a thickness of 0.5 mm to form a radio wave absorbing layer 3. did. Next, 70% by weight of the carbonyl iron alloy granular powder was dispersed in chloroprene rubber.
The sheet was formed into a sheet having a thickness of 4 mm, and the radio wave absorbing layer 3 was formed. These four types of sheets were sequentially laminated and integrated to form a laminated broadband electromagnetic absorber having a total thickness of 1.8 mm. FIG. 2 shows a cross-sectional view of the structure of the laminated type broadband radio wave absorber. FIG. 7 shows the results of evaluating the radio wave absorption performance of the laminated broadband radio wave absorber. 0.5-10GH
A high absorption rate of 70% or more was obtained in a wide frequency range of z.

(Example 3) A carbon fiber having a fiber length of about 2 mm was dispersed at 40% by weight in
To form a sheet having a thickness of 1 mm. Next, the flat powder of the amorphous alloy was dispersed in silicon rubber at 78% by weight and sheeted to a thickness of 0.4 mm to form the radio wave absorbing layer 2. Next, a flat powder of molybdenum permalloy is dispersed in silicon rubber by 86% by weight,
The electromagnetic wave absorbing layer 2 was formed into a sheet having a thickness of 0.4 mm. Next, the carbonyl iron alloy granular powder was dispersed in silicon rubber at 80% by weight and sheeted to a thickness of 0.6 mm to form the radio wave absorbing layer 3. The total thickness is 1.8 mm by sequentially laminating and integrating these four types of sheets.
Was formed. FIG. 3 shows a cross-sectional view of the structure of the laminated type broadband radio wave absorber. FIG. 8 shows the results of evaluating the radio wave absorption performance of the laminated type broadband radio wave absorber. 7 in a wide frequency range of 0.7 to 30 GHz
A high absorption of 0% or more was obtained.

(Comparative Example 1) The three types of sheets formed in Example 1 were applied to a radio wave reflecting layer 1, a radio wave absorbing layer 3, and a radio wave absorbing layer 2.
In this order to produce a laminated electromagnetic wave absorber. FIG. 4 is a cross-sectional view of the laminated electromagnetic wave absorber. FIG. 9 shows the results of evaluating the radio wave absorption performance of this laminated sheet. The frequency range in which a high absorptance of 70% or more is obtained is described in Example 1.
The band was remarkably narrow compared to the performance of the structure.

Comparative Example 2 Carbon fibers having a fiber length of about 2 mm were dispersed in chloroprene rubber at 30% by weight,
The radio wave reflection layer 1 was formed into a sheet having a thickness of 1 mm. Next, a flat powder of a nano-crystallized alloy composed of an Fe-Cu-Nb-Si-B system was dispersed in chloroprene rubber at 78% by weight, and a sheet having a thickness of 1.0 mm was formed to form the radio wave absorbing layer 2. . By laminating and integrating these two types of sheets, a laminated electromagnetic wave absorber having an overall thickness of 1.5 mm was formed. FIG. 5 shows a sectional view of the structure of the laminated electromagnetic wave absorber. FIG. 10 shows the results of evaluating the radio wave absorption performance of the laminated radio wave absorber. The frequency range in which a high absorptance of 70% or more was obtained even though the thickness was the same as that of Example 1 was considerably narrower than the performance of the structure of Example 1.

[0021]

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

[Brief description of the drawings]

FIG. 1 is a sectional view of a laminated broadband radio wave absorber according to Embodiment 1 of the present invention.

FIG. 2 is a sectional view of a laminated broadband radio wave absorber according to Embodiment 2 of the present invention.

FIG. 3 is a sectional view of another laminated broadband radio wave absorber according to Embodiment 3 of the present invention.

FIG. 4 is a sectional view of Comparative Example 1.

FIG. 5 is a sectional view of Comparative Example 2.

FIG. 6 is a diagram showing a result of evaluating radio wave absorption performance of Example 1 according to the present invention.

FIG. 7 is a diagram showing a result of evaluating radio wave absorption performance of Example 2 according to the present invention.

FIG. 8 is a diagram showing a result of evaluating radio wave absorption performance of Example 3 according to the present invention.

FIG. 9 is a diagram showing the results of evaluation of radio wave absorption performance of Comparative Example 1.

FIG. 10 is a view showing a result of evaluation of radio wave absorption performance of Comparative Example 2.

[Explanation of symbols]

 1 Radio wave reflection layer 2 Radio wave absorption layer 3 Radio wave absorption layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Shunichi Nishiyama 5200 Sankashiri, Kumagaya-shi, Saitama F-term in the Magnetic Materials Research Laboratory, Hitachi Metals Co., Ltd. 5E321 AA41 BB25 BB32 BB34 BB44 GG05 GG12

Claims (4)

[Claims] 1. A radio wave reflection layer comprising a conductive flexible resin, and a plurality of radio wave absorption layers in which a metal magnetic powder is dispersed in the flexible resin, wherein the radio wave reflection layer and the metal magnetic powder are provided. A laminated broadband electromagnetic wave absorber characterized in that a radio wave absorbing layer of flat powder and a radio wave absorbing layer of metal magnetic powder are sequentially laminated and integrated. 2. A radio wave reflecting layer made of a conductive flexible resin and a plurality of radio wave absorbing layers having different impedance matching frequencies in which a metallic magnetic powder is dispersed in the flexible resin are sequentially laminated and integrated. What is claimed is: 1. A multilayered broadband radio wave absorber, wherein a plurality of radio wave absorbing layers are stacked in ascending order of impedance matching frequency. 3. The laminated broadband radio wave absorber according to claim 1, wherein the amount of dispersion of the metal magnetic substance powder in the radio wave absorption layer is 65 to 92% by weight. 4. The thickness of one layer of the radio wave reflection layer and the radio wave absorption layer is 0.2 to 1.2 mm, and the total thickness of the laminated layers is 0.6 to 2.5 mm. The multilayered broadband radio wave absorber according to any one of claims 1 to 3.