JPH08181483A - Electromagnetic wave absorbing fiber composite - Google Patents

Abstract

PURPOSE: To provide an electromagnetic wave absorbing fiber composite as an electromagnetic wave absorbing material that is lightweight and excellent in handleability, and further has sound absorbing capability. CONSTITUTION: A mat-like sound absorber 9 is formed by holding powder 4 in voids among fibers 1 through binder 2. A conductive layer 5 is formed on one side of the sound absorber 9, and a resistance film layer 6 is formed on the other side.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic wave absorbing fiber composite, and more particularly, to an application requiring prevention of electromagnetic wave interference and sound insulation such as partition walls and partitions such as houses and offices handling OA equipment. , Particularly suitable electromagnetic wave absorbing fiber composites.

[0002]

2. Description of the Related Art In recent years, problems relating to the electromagnetic wave environment have been taken up seriously, and electromagnetic interference has become a major social problem. The following are examples of such electromagnetic interference. (1) Radar radio waves and TV radio interference due to buildings Electromagnetic interference caused by unnecessary reflected electromagnetic waves caused by high-rise buildings and large-scale buildings (large bridges, noise barriers on elevated roads, steel towers).

The electromagnetic waves reflected by the wall surface or the like generate a ghost image on the television screen or radar screen. (2) Communication failure in electronic communication During data communication on a wireless LAN in a living space or office, a communication failure occurs due to multipath due to reflection of electromagnetic waves or unnecessary electromagnetic wave reflection in the living space.

It is expected that in the future, as offices and homes become more OA, they will become an important social problem. (3) Generation of electromagnetic interference waves from electronic circuits Electromagnetic interference waves (noise) generated from OA devices, personal computers, etc. cause reception failures on televisions and radios, and malfunctions on other electronic devices.

For the above (3), various measures have been taken, such as suppressing electromagnetic wave radiation from electric and electronic devices, reducing noise, and enhancing the electromagnetic wave shielding ability of damaged electronic devices.

As one of the effective measures against the electromagnetic wave reception trouble shown in (1) or (2), there is a method of installing an electromagnetic wave absorbing material on the electromagnetic wave reflecting surface to eliminate unnecessary electromagnetic wave reflection.

The electromagnetic wave absorbing material is a material that converts electromagnetic wave energy into heat energy, and as will be described below, the electromagnetic wave loss can be roughly classified into three types: conductive loss, dielectric loss and magnetic loss. (Edited by Yasutaka Shimizu; Electromagnetic Wave Absorption and Shielding, 1989, p107-, published; Nikkei Technical Book) (a) Conductive electromagnetic wave absorbing material A material that absorbs electromagnetic waves by the conductive current flowing through the resistor and the resistance wire. Woven fabric and the like. (B) Dielectric Electromagnetic Wave Absorbing Material There are foamed polystyrene having a small relative permittivity, carbon rubber which is a dielectric loss material, carbon rubber in which graphite is mixed, and carbon foamed polyurethane. (C) Magnetic electromagnetic wave absorbing material A typical magnetic loss material, which is obtained by sintering ferrite, which is a metal fiber having electromagnetic wave absorbing properties, and is a ferrite plate or rubber ferrite obtained by kneading ferrite powder into rubber. There are things.

The thickness and structure of these electromagnetic wave absorbing materials are designed and used as an electromagnetic wave absorber as a measure against the electromagnetic interference of the above (1) or (2), such as an outer wall of a building or a building. Is used in various fields.

However, since most of these electromagnetic wave absorbers are plate-shaped, block-shaped or sheet-shaped, there is a problem in handleability. For example, a ferrite sintered body has a large weight, as can be seen from its structure.
Poor handleability is a problem. In addition, since rubber ferrite, conductive woven fabric and the like are sheet-shaped, it is difficult to maintain the structure independently, and the increase in weight due to the increase in thickness causes a problem that the handleability deteriorates. .

On the other hand, in recent years, noise barriers on elevated roads or O
In fields such as partition walls and partitions that handle equipment A, such as houses and offices, demands for sound absorbing performance as well as electromagnetic wave absorbing performance have become strict. In these fields, the following two methods are generally mentioned as methods for improving the soundproof performance.

One is a method of shielding the propagation of sound waves by installing a material such as a metal plate having a high surface density at a position where the propagation path of sound waves is blocked, that is, at a wall or a partition portion. But,
Although this method improves soundproofing and obtains high electromagnetic wave shielding performance, it may cause ghost interference or communication failure of TV radio waves due to reflection of electromagnetic waves, and the soundproofing performance is not sufficient.

[0012]

As described above, most of the conventional electromagnetic wave absorbing materials have a dense plate-like, block-like or sheet-like structure and have a void structure inside the electromagnetic wave absorber. Since it does not exist, the weight becomes large, and since it has a shape such as a rubber sheet or a woven fabric, the structure cannot be retained and there is a problem in handleability.

Another problem is that most of them are non-porous materials and do not have sound absorbing characteristics. In other words, because general urethane foam and glass wool, which are sound absorbing materials, use the porosity of the material,
For example, when a sound wave enters a continuous bubble or hole, the sound pressure decreases due to viscous friction with the bubble wall surface during propagation of the sound wave due to the continuous bubble having a complicated cross-sectional shape. Acoustic energy is absorbed in the material.
That is, the dense plate-shaped, block-shaped or sheet-shaped electromagnetic wave absorbing material has a limit in improving the sound absorbing property.

As described above, it has been impossible to provide an electromagnetic wave absorbing material which is lightweight and easy to handle, and at the same time has a sound absorbing property, by the conventional technique.

In view of the above circumstances, an object of the present invention is to provide, as an electromagnetic wave absorbing material, an electromagnetic wave absorbing fiber composite which is lightweight, has excellent handleability, and at the same time has sound absorbing performance.

[0016]

In order to solve the above-mentioned problems, the invention according to claim 1 holds a powder 4 in a space between fibers 1 via a binder 2 to form a mat-shaped sound absorber 9. The sound absorbing body 9 is characterized in that the conductive layer 5 is formed on one surface and the resistance coating layer 6 is formed on the other surface.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the resistance coating layer 6 is acoustically transparent.

The invention according to claim 3 is characterized in that, in the invention according to any one of claims 1 and 2, the conductive layer 5 is acoustically transparent.

The invention as claimed in claim 4 is as follows.
The invention according to any one of claims 3 to 3 is characterized in that the sheet resistance value Rs of the resistance coating layer 6 is about 377 ± 38 ohms.

The invention as defined in claim 5 is defined in claims 1 to 1.
The invention according to any one of claims 4 to 4 is characterized in that it is arranged on the incident side of an electromagnetic wave that absorbs the resistance coating layer 6.

The invention according to claim 6 is defined by claim 1
In the invention according to any one of claims 5, the sound absorber 9
It is configured as a quarter of the wavelength of the electromagnetic wave that absorbs the thickness of the.

The present invention will be described in detail below. In order to solve the above problems, the inventors have studied and investigated from various angles. Regarding the sound absorbing performance, the inventors have already invented a sound absorbing material composed of powder, fiber and resin binder. That is, it was found that by providing the structure in which the powder is adhered and held through the binder in the voids between the fibers of the structure composed of the fiber and the binder, excellent sound absorbing performance can be obtained particularly in the low frequency range. ing.

Therefore, the inventors have paid attention to the structure in which fibers, binders and powders are combined, and as a result, as an electromagnetic wave absorbing material, they are excellent in handleability and sound absorbing performance, and at the same time, as shown below. It has been found that an electromagnetic wave absorbing fiber composite having high electromagnetic wave absorbing performance can be provided.

That is, the binder 2 is placed in the voids 3 between the fibers 1.
The powder 4 is held via the vias to form a mat-shaped sound absorber 9. Then, by laminating the conductive layer 5 on one surface of the sound absorbing body 9 and the resistance coating layer 6 on the other surface, the resistance coating layer 6 is formed.
The electromagnetic wave energy can be absorbed by matching the sheet resistance value Rs of the sheet with the impedance of the free space, and it is an electromagnetic wave absorbing fiber composite having abundant voids 3 inside the structure composed of the fiber 1 and the binder 2. Moreover, it is lightweight and easy to handle.

Furthermore, by using an acoustically transparent material as the resistance coating layer 6 and holding the powder 4 in the void 3 inside the sound absorber 9, it is possible to obtain a high sound absorbing performance particularly in the low sound range. It will be.

As a concrete form of the electromagnetic wave absorbing fiber composite of the present invention, as shown in FIG. 1, the powder 4 holds the binder 2 in a large number of voids 3 formed between the structure of the fiber 1 and the binder 2. An example is a mode in which the sound absorbing body 9 is adhered and held via the above to form the sound absorbing body 9, and further, the conductive layer 5 is adhered and laminated on the back surface of the sound absorbing body 9, and the resistance coating layer 6 is adhered and laminated on the front surface.

In general, when a high electromagnetic wave absorption performance is required, not only the reflection coefficient S thereof is reduced, but also
At the same time, it is necessary to reduce the transmission coefficient T as well. Since the electromagnetic wave absorbing fiber composite according to the present invention has a structure in which the conductive layer 5 is laminated on the back surface thereof, it is possible to completely eliminate transmitted waves. That is, by reflecting the electromagnetic wave that has entered the electromagnetic wave absorbing fiber composite between the conductive layer 5 and the resistance coating layer 6, the electromagnetic wave is attenuated and a higher electromagnetic wave absorbing performance can be obtained. In other words, the electromagnetic wave that has entered the electromagnetic wave absorbing fiber composite does not pass through the conductive layer 5,
The electromagnetic wave is reflected between the conductive layer 5 and the resistance coating layer 6, and this electromagnetic wave is attenuated, so that a higher electromagnetic wave absorption performance can be obtained.

At this time, it is necessary to select the material used for the conductive layer 5 in consideration of the deterioration of the sound absorption characteristics due to the conductive layer 5. Examples of the conductive layer 5 in the present invention include a metal plate such as an iron plate, an aluminum plate or a galvanized steel plate, or a conductive plate obtained by conductively plating a non-conductive material. Further, if the conductive layer 5 is acoustically transparent, that is, if the conductive sheet has a thickness of 50 μm or less, the sound absorbing property is not impaired while maintaining the electromagnetic wave absorbing performance. A typical example of the acoustically transparent conductive sheet is aluminum foil.

The electromagnetic wave absorption in the structure of the present invention is λ /
It functions as a type 4 electromagnetic wave absorbing material, and the mechanism of electromagnetic wave absorption will be briefly described below.

When considering a λ / 4 type electromagnetic wave absorbing material, a model as shown in FIG. 2 can be considered. In this figure,
The resistance coating layer 6 is formed of a resistance paste or the like, and the conductive layer 5 is formed of a metal plate or the like. Further, 9 is a sound absorbing body composed of the powder 4 and the fiber 1, and the distance between the resistance coating layer 6 and the conductive layer 5 is λ / 4. here,
λ is the central wavelength of the electromagnetic wave that is desired to be absorbed.

Now, considering the case where the resistance coating layer 6 is not provided, when an electromagnetic wave is incident on the conductive layer 5, a standing wave is generated by the incident wave and the reflected wave. Therefore, from the conductive layer 5 to λ /
The impedance becomes infinite at a position 4 away, that is, at the position of the material surface on the electromagnetic wave incident side.

In order to show the performance of the electromagnetic wave absorbing material, it is required that the surface of this material has a small electromagnetic wave reflection coefficient. Therefore, assuming that the load impedance of the front surface of the material is Z and the load impedance of the vacuum is Z ₀ , the electric field reflection coefficient S of the front surface of the material is expressed in decibels as follows.

S = 20log | (Z−Z ₀ ) / (Z + Z ₀ ) | (1) From this equation (1), the load impedance Z becomes infinite when the resistive coating layer 6 is not provided. It can be seen that it does not absorb electromagnetic waves.

Next, as in the model shown in FIG. 2, by placing the resistive coating layer 6 at a position where the impedance becomes infinite, that is, at a position λ / 4 away from the conductive layer 5, a load at that position is placed. The impedance Z becomes the sheet resistance value Rs of the resistance coating layer 6. Therefore, the reflection coefficient S in this case is expressed by the following equation.

S = 20log | (R _S −Z ₀ ) / (R _S + Z ₀ ) | (2) Therefore, Rs is set to the vacuum radio characteristic impedance Z.
_By setting it to ₀ (= 377Ω), the impedance is perfectly matched as can be seen from the equation (2), and the reflection coefficient S in this case is −∞ in decibel display, and the electromagnetic wave is completely absorbed.

In the model of FIG. 2, the distance between the conductive layer 5 and the resistance coating layer 6 is λ / 4, but in the present invention, the sound absorber 9 is used as a spacer between the conductive layer 5 and the resistance coating layer 6. It is configured to be inserted. At that time, with respect to the center frequency of the electromagnetic wave to be absorbed, the wavelength thereof is λ ₀ , and the real term of the complex relative permittivity of the sound absorbing body 9 is ε r, the distance between the conductive layer 5 and the resistive coating layer 6, that is, The spacer thickness d is expressed by the following equation.

D = λ ₀ / (εr) ^1/2 (3) That is, the resistive coating layer 6 and the conductive layer 5 are laminated on both surfaces of the sound absorbing body 9 having the thickness d in the mathematical expression (3). As a result, the electromagnetic wave absorbing fiber composite of the present invention having extremely excellent electromagnetic wave absorbing performance can be obtained.

Examples of the resistance coating layer 6 used in the present invention include a sheet-shaped paper or cloth coated with carbon, a resistance cloth knitted with conductive fibers, and the like, and the surface resistance value Rs thereof is 377Ω. As long as it can be designed, various things can be used. However, with the method of applying carbon or the like, it is difficult to make the sheet resistance value Rs uniform, and it is more preferable to use a resistance cloth made of conductive fibers because the resistance value variation is reduced.

Here, the design of the sheet resistance value Rs of the resistance coating layer 6 made of conductive fibers is as follows. Resistive coating layer 6
The sheet resistance value Rs of is greatly affected by the resistance value R (Ω / m) of the conductive fiber and the fiber structure, which are determined by the material and type of the sheet. Here, Rs is represented by the following equation, where n is the number of fibers per unit length (1 m).

Rs = R / n (4) From this equation (4), it is possible to set the target surface resistance value Rs by changing the resistance value R and the number of conductive fibers. Become.

Specific examples of the conductive fibers include acrylic fibers having a copper conductive layer formed on the surface thereof, but are not particularly limited thereto. That is, it has an appropriate resistance value,
In addition, if the fiber is flexible, it is possible to make a resistance cloth having a sheet resistance Rs of 377Ω.

The electromagnetic wave absorbing fiber composite of the present invention comprises:
Since the electromagnetic waves are absorbed by matching the impedance at the surface resistance coating layer 6 portion, the thickness d is designed according to the size of the wavelength of the target electromagnetic wave, as shown in Expression (3). There is a need. Also, the surface resistance value R
The sheet resistance value R is greatly affected by s and thickness d.
It is necessary to make the variation between s and the thickness d as small as possible.

From the above, the optimum thickness d of the sound absorbing body 9 used for the electromagnetic wave absorbing fiber composite varies depending on the frequency of the target electromagnetic wave and cannot be generally stated. However, it is desirable that the surface resistance value Rs of the resistance coating layer 6 be within plus or minus 10% around 377Ω regardless of the target frequency range. Outside this range, sufficient electromagnetic wave absorption performance cannot be obtained due to an increase in the amount of electromagnetic wave reflection.

Next, the part of the sound absorber 9 in the electromagnetic wave absorbing fiber composite of the present invention will be described in detail below.

Among the fibers 1 used for the sound absorber 9, synthetic fibers such as polyester fibers, nylon fibers, polyacrylonitrile fibers, polypropylene fibers, polyethylene fibers, polyvinyl chloride fibers, or wood fibers, cotton, hemp are used as the organic fibers. Examples thereof include fibers, bamboo, linter (forehead of cotton flower), natural fibers such as silk and wool, and regenerated cellulose fibers such as rayon.

As the inorganic fiber, rock fiber,
Examples thereof include glass fiber, alumina fiber and SiC fiber. The fibers 1 do not necessarily have to be in a non-sheet form (separated), and may be in a sheet form. Examples thereof include organic fiber structures such as non-woven fabrics, artificial burps, and filter papers, or inorganic fiber structures such as granular cotton.

The powder 4 used in the present invention usually has a particle size of about 0.1 to 1000 μm and a bulk density of about 0.1 g / cm.
^It ranges from about ³ to about 1.5 g / cm ³ .

Specifically, gold mica powder, silica powder,
Acrylic ultrafine powder, talc powder, calcium silicate powder, fluororesin powder, perlite, bentonite, shirasu balloon, Ishimatsuko, pullulan, fused silica powder, graphite, crystalline cellulose powder, silicon carbide powder, Examples include diatomaceous earth, nylon powder, and rock wool shot. Although the mixing ratio of the powder 4 is not particularly limited,
The volume ratio of the fiber 1 is preferably about 20 to 80%.

As the binder 2 used in the present invention, a resin binder such as polyethylene resin, polystyrene resin, methacrylic resin, polyurethane resin, phenol resin, urea resin, or natural starch (rice starch, corn starch, tapioca starch) or modified starch is used. Nari, starch paste and the like. Also, the method of mixing the binder 2 is not particularly limited. For example, a method of mixing them in the form of fine particles, or a method of applying the liquid binder 2 and using it may be mentioned.

By using a foamable resin binder as the binder 2, the adhesiveness between the fiber 1 and the powder 4 is improved. Therefore, it has an advantage that it has high structure retention and is less likely to cause performance deterioration. At that time, the method for foaming the resin binder is not particularly limited, and basically the following method is used.

(1) Method of using reaction product gas (2) Method of using foaming agent The method of (1) is a product released when a liquid raw material is resinified, for example, carbon dioxide gas, formaldehyde, steam. Is used as a foaming agent, and is vaporized by reaction heat or heating to form a foam.

The method (2) is further divided into a method using a volatile foaming agent and a method using a decomposable foaming agent.

The volatile foaming agent is a method in which a gas such as carbon dioxide gas, propane, butane, ether, acetone, benzene or the like or a volatile liquid is absorbed in a resin or a raw material and vaporized to foam. On the other hand, in the method utilizing a decomposable foaming agent, the resin is foamed by heating after the foaming agent is dispersed or dissolved in the resin raw material. As the foaming agent used at this time, in addition to inorganic compounds such as ammonium carbonate and sodium bicarbonate, azo compounds, sulfonylhydrazide compounds, nitrozo compounds, azide compounds are used,
It is appropriately selected depending on the use conditions and the resin raw material.

From the above, the electromagnetic wave absorbing fiber composite of the present invention has a fiber 1, a binder 2 and a powder, whereas the conventional electromagnetic wave absorbing material has a block shape or a sheet shape having no voids 3 therein. Since the sound absorbing body 9 is composed of the body 4, good sound absorbing performance is obtained by having open cells having a complicated cross-sectional shape, and at the same time, the powder 4 is bonded and held in the internal void of the sound absorbing body 9. Due to the vibration of the powder 4, a good sound absorbing characteristic can be obtained especially in a low frequency range.

In the electromagnetic wave absorbing fiber composite of the present invention, it is necessary to appropriately select the binder 2 in consideration of the adhesiveness or wettability of the fiber 1 and the powder 4 to the binder 2.

The amount of the binder 2 is 5 with respect to the fiber 1.
It is preferably about 20% by weight. If it is more than this, the sound absorbing effect due to the vibrating action of the powder 4 becomes small, which causes the sound absorbing performance in the low frequency range to deteriorate.

The electromagnetic wave absorbing fiber composites of these inventions are
It is also particularly suitable for soundproof walls of elevated roads, partitions such as houses and offices that handle OA equipment, and partitions that require soundproofing performance at the same time as electromagnetic wave absorbing performance.

[0058]

In the invention described in claim 1, the incident electromagnetic wave is reflected and absorbed between the conductive layer 5 and the resistance coating layer 6.

Further, the sound absorbing body 9 has a space 3 and is lightweight, and has a conductive structure 5 and a resistance coating layer 6 on both sides of the sound absorbing body 9 to maintain a plate-like structure.

The sound waves transmitted through the conductive layer 5 or the resistive coating layer 6 are well absorbed by the voids 3, and the powder 4 vibrates by the sound waves, and particularly absorbs the sound waves in the low frequency range.

The electromagnetic wave incident from the resistance coating layer 6 side is reflected by the conductive layer 5 and hardly penetrates.

According to the second aspect of the present invention, the resistance coating layer 6 is acoustically transparent, and the sound wave is transmitted without being reflected, and the transmitted sound wave is efficiently absorbed by the sound absorber 9.

In the third aspect of the present invention, the conductive layer 5 is acoustically transparent, and the sound wave is transmitted without being reflected,
The transmitted sound waves are efficiently absorbed by the sound absorber 9.

According to the fourth aspect of the invention, the sheet resistance value Rs of the resistance coating layer 6 is about 377 ± 38 ohms, which perfectly matches the vacuum radio wave characteristic impedance. Is reflected by the conductive layer 5,
In the invention described in claim 5, which is completely absorbed in the resistance coating layer 6, in the resistance coating layer 6, the incident electromagnetic wave is little reflected and is well absorbed.

According to the sixth aspect of the invention, the surface resistance value Rs of the resistance coating layer 6 is matched with the vacuum electromagnetic wave characteristic impedance by setting the thickness of the sound absorbing body 9 to 1/4 of the wavelength of the electromagnetic wave to be absorbed. You can Therefore, the electromagnetic wave incident from the resistance coating layer 6 side is reflected by the conductive layer 5, reaches the resistance coating layer 6, and is completely absorbed.

[0066]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be specifically described below in detail. (Example) Rock fiber (fiber diameter: 10
μm) as powder 4 vermiculite (particle size; 180-
250 μm) is selected as a resin binder for phenol foamed resin fine particles as the binder 2, and after mixing each material, the binder 2 is foamed and cured by heating at 130 ° C. for several minutes to absorb the noise. To get The amount of the binder 2 was about 10% by weight based on the total weight of all the fibers 1 and the powder 4. The mixing weight ratio of each material in the sound absorbing body 9 was 45% by weight of the fiber 1, 45% by weight of the powder 4 and 10% by weight of the phenol foam resin.

Next, a thickness of 40 is formed on one surface of the obtained sound absorbing body 9.
A conductive layer 5 was formed by bonding and laminating a μm aluminum foil. Further, on the other surface of the sound absorbing body 9, a resistance cloth having a sheet resistance value of about 377Ω obtained by knitting conductive fibers is adhered and laminated to form a resistance coating layer 6, which is an electromagnetic wave absorption fiber composite. The body was made. Comparative Example Commercially available glass wool 24K was used as a comparative material as an electromagnetic wave absorbing material.

Table 1 below shows the thickness and density of the electromagnetic wave absorbing materials of Examples or Comparative Examples and the physical properties of the constituent materials.

[0069]

[Table 1]

In Table 2 below, the sound absorption coefficient and the peak frequency of the electromagnetic wave absorbing materials of the above Examples and Comparative Examples and the reflection coefficient (d in the microwave region (frequency near 2.5 GHz))
B) is measured and shown.

[0071]

[Table 2]

The sound absorption coefficient referred to here is determined by JIS-A1.
405 is the vertical incident sound absorption coefficient measured according to the “method of measuring the normal incident sound absorption coefficient of building materials by the in-pipe method”, and the thickness is 3
It is measured when an electromagnetic wave absorbing fiber composite of 0 mm or an electromagnetic wave absorbing material is measured. The sound absorption coefficient is calculated using standing waves.

FIG. 3 shows the frequency dependence of the sound absorption coefficient of the electromagnetic wave absorbing fiber composite of the example, and FIG. 4 shows the frequency dependence of the sound absorption coefficient of the electromagnetic wave absorbing material of the comparative example. Here, the frequency at which the sound absorption coefficient is maximized is the sound absorption peak frequency. As shown in these figures, it is understood that the sound absorbing performance in the low frequency range is excellent in the examples of the present invention.

Further, as shown in Table 2, in the embodiment, at the center frequency of the electromagnetic wave to be absorbed corresponding to the thickness d of this material d = 0.03 m, that is, at 2.5 GHz, -1
It can be seen that the electromagnetic wave absorption performance (reflection coefficient) of about 0 to -20 dB is obtained, while the comparative example does not absorb electromagnetic waves in the same frequency range.

[0075]

EFFECT OF THE INVENTION The electromagnetic wave absorbing fiber composite according to the first aspect of the present invention is light in weight, has a plate-like structure, is easy to install and handle, has good sound absorbing characteristics even in a low sound range, and absorbs sound. It is an electromagnetic wave absorbing material that also has performance.

Further, in particular, the electromagnetic wave from the resistance coating layer side is not reflected and is well absorbed, and the electromagnetic wave absorbing material has a good electromagnetic wave absorbing property.

According to the second aspect of the invention, the sound absorbing characteristic is further improved by the resistance coating layer.

According to the third aspect of the invention, the sound absorbing characteristic is further improved by the conductive layer.

According to the invention described in claim 4, the electromagnetic wave is absorbed more completely in the resistance coating layer.

According to the fifth aspect of the invention, it is possible to more reliably absorb the incident electromagnetic wave without reflecting it.

According to the sixth aspect of the invention, it is possible to more completely absorb the electromagnetic wave having a wavelength corresponding to the thickness of the sound absorbing body.

[Brief description of drawings]

FIG. 1 is an explanatory view schematically showing a cross section of an electromagnetic wave absorbing fiber composite of the present invention.

FIG. 2 is a model diagram for explaining an electromagnetic wave absorption mechanism in the above section.

FIG. 3 is a graph showing the sound absorption coefficient of the electromagnetic wave absorbing fiber composite in the above Example.

FIG. 4 is a graph showing a sound absorption coefficient of an electromagnetic wave absorbing material of a comparative example.

[Explanation of symbols]

 1 Fiber 2 Binder 3 Void 4 Powder 5 Conductive Layer 6 Resistive Coating Layer 9 Sound Absorber

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[Procedure amendment]

[Submission date] February 24, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0069

[Correction method] Change

[Correction content]

[0069]

[Table 1]

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hideyuki Ando, 1048, Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Works Co., Ltd. (72) Inventor, Koji Tsuji, 1048, Kadoma, Kadoma City, Osaka Prefecture 72) Inventor Hajime Sugiyama 1048, Kadoma, Kadoma-shi, Osaka Prefecture Matsushita Electric Works Co., Ltd.

Claims (6)

[Claims] 1. A matte sound absorbing body is formed by holding powder in a space between fibers through a binder, and a conductive layer is formed on one surface of the sound absorbing body while a resistance coating layer is formed on the other surface. An electromagnetic wave absorbing fiber composite characterized by being formed. 2. The electromagnetic wave absorbing fiber composite according to claim 1, wherein the resistance coating layer is acoustically transparent. 3. The electromagnetic wave absorbing fiber composite according to claim 1, wherein the conductive layer is acoustically transparent. 4. The sheet resistance value of the resistance coating layer is about 377 ± 38.
The electromagnetic wave absorbing fiber composite according to any one of claims 1 to 3, wherein the electromagnetic wave absorbing fiber composite is formed as an ohm. 5. The electromagnetic wave absorbing fiber composite according to any one of claims 1 to 4, wherein the resistance coating layer is arranged on the incident side of the electromagnetic wave to be absorbed. 6. The electromagnetic wave absorbing fiber composite according to any one of claims 1 to 5, wherein the thickness of the sound absorbing body is ¼ of the wavelength of the electromagnetic wave to be absorbed.