JPH11284383A - Radio wave absorbing material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wave absorbing material which is arranged so that it can keep the wave absorbing performance as designed, without being influenced by the fluctuation of external conditions by fixing the moisture content of, especially, a ceramic radio wave absorbing layer, regardless of the fluctuation of external conditions such as moisture, temperature, etc. SOLUTION: This radio wave absorbing material is provided with waterproof layers 3 or water-repellent layers 3A on both sides of a ceramic wave absorbing layer 1. The face 1B, opposite to the face 1A where radio the waves that this ceramic radio wave absorbing layer 1 is to absorb enter the ceramic radio wave absorbing layer 1, is provided with a radio wave reflecting layer 2. Or, the ceramic radio wave absorbing layer is provided with the waterproof layer 3 or the water-repellent layer 3A, and besides it is provided with a radio wave reflecting layer 2 inside the ceramic radio wave absorbing layer 1, and the moisture content of the ceramic radio wave absorbing layer 1 is put at a desired value. Hereby, it is made into such constitution that it keeps desired radio wave absorbing property.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorbing material, and more particularly, to a ceramic radio wave absorbing layer in which the water content is made substantially constant irrespective of external conditions such as humidity and temperature.
The present invention relates to a novel improvement for maintaining radio wave absorption performance without being affected by external conditions.

[0002]

2. Description of the Related Art Conventionally, various compositions and shapes of electromagnetic wave absorbing building materials have been proposed, and some of them have been put to practical use. For example, according to the specification of Japanese Patent Application No. 9-015350, a conductive face material is provided on a molded body in which ferrite powder and carbon powder are mixed in an inorganic matrix, and a dry weight ratio of ferrite is 30% or more. 70% or less, the dry weight ratio of the carbon powder is 0.5% or more and 10% or less, and the configuration is such that both the radio wave absorption characteristics and the strength as a building material are compatible. Also, Japanese Patent Application Laid-Open
As disclosed in JP-A-321491, in a radio wave absorbing panel in which a plate-shaped radio wave absorber is buried in the vicinity of the surface of a plate-shaped base material, a finishing material having no change in water content over the entire surface is used. The frequency characteristics at which the radio wave absorber exerts the radio wave absorbing effect by being attached are configured to guarantee the frequency characteristics at the time of design.

[0003]

A conventional radio wave absorbing material is:
Because of the above configuration, the following problems exist. That is, in the case of the former conventional configuration, the absorption characteristics of the radio wave absorbing material are greatly affected not only by its composition and shape, but also by its water content, and the target radio wave absorbing material is affected by changes in external conditions such as humidity and temperature. There was a risk that the frequency band would shift.

In the case of the latter conventional structure, attention was paid to the influence of the above-mentioned moisture (humidity). However, in this case, a finished material having no change in water content is used as the front plate of the radio wave absorber. Since the dielectric constant does not change, frequency characteristics at the time of design are guaranteed. However, this method is for the front plate of the radio wave absorber, and is not a countermeasure for changes in the water content of the radio wave absorber, but should avoid changes in the frequency characteristics of the radio wave absorber due to changes in external conditions such as humidity and temperature. Could not.

The present invention has been made in order to solve the above-mentioned problems, and in particular, by making the water content of the electromagnetic wave absorbing layer of a ceramic industry constant irrespective of fluctuations in external conditions such as humidity and temperature. Another object of the present invention is to provide a radio wave absorbing material capable of maintaining radio wave absorbing performance as designed without being affected by fluctuations in external conditions.

[0006]

The radio wave absorbing material according to the present invention comprises a ceramic radio wave absorbing layer on both sides of which a waterproof layer or a water repellent layer is provided, and a radio wave absorbing layer which the ceramic radio wave absorbing layer intends to absorb. The surface opposite to the surface on which the ceramic-based radio wave absorption layer is incident is provided with a radio wave reflection layer, and the waterproof layer or the water repellent layer also serves as a radio wave reflection layer. In addition, the ceramic radio wave absorbing layer is provided with a waterproof layer or a water repellent layer, and the radio wave reflection layer is provided inside the ceramic radio wave absorption layer, and the radio wave reflection layer,
Metal foil, a metal plate, a perforated metal plate and a configuration made of any of a metal mesh, and the ceramic radio wave absorption layer, ferrite powder in an inorganic matrix, metal powder,
The waterproof layer or the water-repellent layer includes at least one selected from carbon powder and carbon fiber, and the waterproof layer or the water-repellent layer is a glass plate, a stone material, a resin sheet, a waterproof paper, a waterproof agent or a water-repellent material. And the waterproof layer or the water-repellent layer is made of a resin.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a radio wave absorbing material according to the present invention will be described below with reference to the drawings. 1 and 2 show the configuration of a radio wave absorber according to the present invention that absorbs radio waves incident from one side, and FIG. 3 shows a radio wave absorber according to the present invention that absorbs radio waves incident from both sides. ing. In FIGS. 1, 2 and 3, a reference numeral 1 denotes a ceramic radio wave absorbing layer.
For example, in a well-known inorganic matrix, a configuration including at least one selected from ferrite powder, metal powder, carbon powder, and carbon fiber is preferable. Can also. When a radio wave to be absorbed enters from one side of the radio wave absorber, a radio wave reflection layer 2 is provided on a surface 1B opposite to the surface 1A on the side where the radio wave is incident on the ceramic radio wave absorption layer 1. And a waterproof layer 3 on both sides 1A and 1B of the ceramic radio wave absorbing material 1.
The waterproof layer 3 may be formed of a water-repellent layer 3A. The waterproof layer 3 or the water-repellent layer 3A provided on the surface 1B opposite to the side where the radio wave is incident can be provided between the radio wave absorption layer 1 and the radio wave reflection layer 2 or the upper surface of the radio wave reflection layer 2 The radio wave reflection layer 2 is further provided with a waterproof layer 3
Alternatively, it may also serve as the water-repellent layer 3A. When the radio wave to be absorbed is incident from both sides, a radio wave reflecting layer 2 is provided inside the ceramic radio wave absorbing layer 1 and a waterproof layer 3 is provided on both sides of the ceramic radio wave absorber, The waterproof layer 3 may be composed of the water-repellent layer 3A. Radio wave reflection layer 2
Is composed of, for example, any one of a metal foil, a metal plate, a perforated metal plate, a metal mesh, and the like. However, when the radio wave reflection layer 2 also serves as the waterproof layer 3 or the water repellent layer 3A,
A metal foil or metal plate is suitable as the radio wave reflection layer. The waterproof layer 3 or the water-repellent layer 3A includes a glass plate, a stone plate, a resin sheet,
Made of waterproof paper, waterproof agent or water repellent, FIG.
As shown in FIG. 2 and FIG. 3, it is not limited to the surface of the ceramic-based radio wave absorption layer 1 on the side where radio waves are incident, and it can be provided inside. The sides may be covered. Therefore, the radio wave absorbing layer 1 set to a predetermined moisture content by the waterproof layer 3 or the water repellent layer 3A can be held.

Further, for example, when the ceramic-based radio wave absorbing layer 1 is intended for a frequency band of 1 GHz to 3 GHz, which is a quasi-microwave, the composition for obtaining effective radio wave absorption characteristics is, for example, ferrite. Powder is mixed in a dry weight ratio of 30% or more and 70% or less, carbon powder is mixed in a dry weight ratio of 0.5% or more and 10% or less, and minerals such as cement, calcium silicate, and gypsum are used as a binder. Reinforced shaped bodies are preferred. A well-known optional decorative layer 4 is provided on the surface of the waterproof layer 3 or the water-repellent layer 3A.
Can also be formed. Further, the above-mentioned waterproof layer 3 or water-repellent layer 3A can also serve as the decorative layer 4. Furthermore, when a transparent material such as glass is used as the waterproof layer 3, a decorative layer 4 can be provided between the waterproof layer 3 and the ceramic radio wave absorbing layer 1.

Next, before describing the relationship between the water content and the reflection loss and frequency of radio waves when the radio wave absorbing material 10 of the present invention having the above-described structure is used, the outside of the general ceramic radio wave absorbing layer 1 will be described. Considering the relationship between the humidity and the equilibrium water content, as shown in FIG. 4, as the external humidity increases from 20% to 95% at a temperature of 20 ° C., the water content of the ceramic radio wave absorbing layer 1 becomes 0.9%. It is clear that the percentage increases from about 5% to about 5%.

Therefore, in the present invention, since the above-mentioned waterproof layer 3 or water-repellent layer 3A is formed on the above-mentioned ceramic radio wave absorbing layer 1, there is a case where the waterproof layer 3 or the water-repellent layer 3A is used. The water content when not used was measured comparatively. Using JIS-A-9510 as a measuring method, water was sprayed on each of the sample of the conventional configuration and the sample of the present invention, and the water content after water spraying was measured. The results, as shown in Table 1 below, show that the water content is 0.0% when glass is installed and 0.2% when a water repellent is applied. .

[0011]

[Table 1]

Further, a moisture permeation experiment was performed on the samples having the conventional configuration and the configuration according to the present invention. That is, the dried sample was allowed to stand in a thermo-hygrostat at a temperature of 35 ° C. and a relative humidity of 95% for 24 hours, and the permeability coefficient of moisture and the water content of the sample after the experiment were compared and measured by increasing the sample weight. The results are as shown in Table 2 of Table 2 below.

[0013]

[Table 2]

According to the above-mentioned measurement results, the moisture permeability coefficient is best at 0.000 in the case of glass, while the water repellent is effective for water, but the moisture permeability is low. Therefore, it has been found that it is not sufficient for moisture, so that a waterproof layer needs to be selected depending on the use environment.

FIG. 5 shows the relationship between the radio wave reflection loss of the radio wave absorbing material 10, that is, the radio wave absorption characteristic and the frequency.
For example, when the radio wave absorbing material 10 has a water content of 0% in the ceramic radio wave absorbing layer 1, the quasi-microwave 2.4 GHz to 2.5 G
Hz is set so as to absorb radio waves in the frequency band of Hz, and when the water content of the ceramic radio wave absorption layer 1 is 2%, the peak of the absorbed radio waves has a frequency of 2.2 GHz.
It has been found that the frequency shifts from z to the frequency band of 2.3 GHz, and by setting and maintaining the water content of the ceramic radio wave absorbing layer 1 to a desired value as in the radio wave absorber 10 according to the present invention, It has been clarified that radio wave absorption characteristics in a desired frequency band can be obtained.

[0016]

The radio wave absorber according to the present invention is configured as described above, so that the following effects can be obtained. In other words, a water-proof layer or a water-repellent layer is provided on both sides of the ceramic radio wave absorption layer to maintain the water content previously adjusted in the manufacturing process so that radio wave absorption characteristics in a desired frequency band can be obtained. It is possible to stably obtain various radio wave absorption characteristics.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a radio wave absorbing material for absorbing a radio wave incident from one side according to the present invention.

FIG. 2 is a cross-sectional view showing a radio wave absorbing material for absorbing a radio wave incident from one side according to the present invention when the radio wave reflection layer also functions as a waterproof layer or a water repellent layer.

FIG. 3 is a cross-sectional view showing a radio wave absorbing material for absorbing radio waves incident from both sides according to the present invention.

FIG. 4 is a characteristic diagram showing a relationship between humidity and an equilibrium water content of a radio wave absorber.

FIG. 5 is a characteristic diagram showing a relationship between a frequency of a radio wave and a radio wave reflection loss due to a radio wave absorbing material.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 Electric wave absorption layer of ceramics 1A Surface on which the electric wave to be absorbed by the electric wave absorption layer of ceramics enters 1B Surface opposite to the surface on which the electric wave to be absorbed by the electric wave absorption layer of ceramics enters 2 Radio wave reflection Layer 3 Waterproof layer 3A Water-repellent layer 4 Makeup layer

Continuing on the front page (72) Inventor Li Choken 6-1 Kashiwara, Ishioka-shi, Ibaraki Pref. Inside the Building Materials Technology Laboratory (72) Inventor Takayuki Maejima 6-1 Kashiwara, Ishioka-shi Ibaraki Pref. 72) Inventor Nobuto Akiyama 2-5-5 Tsurumi-chuo, Tsurumi-ku, Yokohama-shi, Kanagawa Prefecture Ask Inc. (72) Inventor Masanobu Kitamura 1-16-7 Arai, Nakano-ku, Tokyo (72) Inventor Keiji Nakayama Tokyo 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Inventor Makoto Ishikura 5-36-11 Shimbashi, Minato-ku, Tokyo Fuji Electric Chemical Co., Ltd. (72) Inventor Makoto Isomura Shimbashi, Minato-ku, Tokyo 5-36-11 Inside Fuji Electric Chemical Co., Ltd.

Claims (6)

[Claims] 1. Waterproof layers on both sides of the ceramic radio wave absorbing layer (1)
(3) or a water repellent layer (3A) is provided, and the surface (1B) opposite to the surface (1A) on the side on which the radio wave to be absorbed by the ceramic radio wave absorbing layer is incident on the ceramic radio wave absorbing layer (1A) ) Is provided with a radio wave reflection layer (2). 2. The radio wave absorber according to claim 1, wherein the waterproof layer (3) or the water repellent layer (3A) also functions as the radio wave reflection layer (2). The ceramic radio wave absorbing layer (1) is provided with a waterproof layer (3) or a water repellent layer (3A), and the radio wave reflection layer (2) is provided inside the ceramic radio wave absorbing layer. A radio wave absorbing material characterized by being. 4. The radio wave reflection layer (2) according to claim 1, wherein the radio wave reflection layer (2) is made of any one of a metal foil, a metal plate, a perforated metal plate, and a metal mesh. Radio wave absorber. 5. The ceramic radio wave absorbing layer (1), wherein the inorganic matrix contains at least one selected from ferrite powder, metal powder, carbon powder and carbon fiber. Item 5. The radio wave absorber according to any one of Items 1 to 4. 6. The waterproof layer (3) or the water-repellent layer (3A) is made of at least one of a glass plate, a stone, a resin sheet, a waterproof paper, a waterproofing agent and a water-repellent material. The radio wave absorber according to any one of 1 to 5.