JPH0145237B2 - - Google Patents

Description

[Detailed Description of the Invention] A. Field of Industrial Application The present invention relates to a radio wave absorber element that is spread and coated on the indoor surfaces, that is, the ceiling, walls, and floor, in order to construct a radio anechoic chamber. The object of the present invention is to provide a resistive film parallel type radio wave absorber element that has effective attenuation/absorption characteristics against vertical and oblique incidence of radio waves in a wide frequency band from 10 MHz to several GHz, and is nonflammable.

B. Prior Art Conventional radio wave absorbing materials used to construct radio anechoic chambers include materials made by foaming pre-foamed polystyrene coated with carbon powder, materials made by combining carbon-containing foamed polyurethane with a fiber web, and materials made by combining carbon-containing foamed polyurethane with a fiber web. Hairlock materials containing carbon-containing conductive rubber on fiber mats, or materials in which paper with a carbon-containing resistance film and foamed polystyrene are alternately laminated, are used, and these materials are further layered into zigzag or square pyramid shapes. Efforts are also being made to improve broadband frequency characteristics, oblique incidence characteristics, polarization characteristics, etc.

C. Problems to be Solved by the Invention Conventional radio wave absorbers use plastic foam or organic fiber webs as carriers and spacers in order to maintain the resistive film made of carbon powder in a spatially distributed manner as described above. However, it has poor heat resistance as a building material and is not satisfactory in terms of fire and other disaster prevention, and improvements have been desired.

Also, its radio wave absorption characteristics are 8 to 12 GHz.
The voltage standing wave ratio (VSWR) shows excellent performance of 1.2 or less in the high frequency band including
In the low frequency band below 1GHz, the
The VSWR was over 1.5, which could not be said to be sufficient performance.

D. Means for Solving the Problems In order to solve the above problems, the present inventors first filed a patent application in 1983 for an invention relating to a radio wave absorber using glass wool mat itself as a carrier for a resistive film containing carbon powder. No. 29389, but the present invention is a further improvement thereof.

That is, glass wool mat with a bulk density of about 10 to 100 Kg/ ^m3 has good radio wave transmittance and is suitable as a carbon powder-containing resistive film carrier.
In order to form a carbon powder-containing resistance film with good continuity, a relatively large amount of carbon powder-containing treatment agent is required, and treatments such as impregnation and drying are troublesome, and the dimensional stability and maintenance of the molded product are difficult. shape,
It was difficult to say that the strength was sufficient, and it had to be handled carefully when constructing an anechoic chamber.

Therefore, the present invention uses glass fiber cloth as a carrier for a resistance coating containing carbon powder, and uses glass wool mat as a spacer to create a resistance coating parallel type absorbent material in the form of a multilayer laminated sheet, and uses this material to form a square pyramid part and a base plate part. By constructing a radio wave absorber element, the above-mentioned conventional problems as well as the drawbacks of the previous invention are solved.

In the element of the present invention, in the square pyramid part, the carbon powder-containing resistance coating forms an inclined surface parallel to each inclined side surface of the square pyramid part, and in the base plate part, forms a horizontal plane parallel to the bottom surface of the square pyramid part. There is.

The glass fiber cloth needs to be a woven cloth as thin as possible and have a thread density that allows the carbon powder-containing resistance coating formed thereon to be continuous in the surface direction.

Glass wool mat has a bulk density of 10-100Kg/ ^m3
The thickness is preferably 20 to 50 kg/ ^m3 , and the thickness must be sufficiently small relative to the shortest wavelength of radio waves.
For example, when absorbing radio waves up to about 10 GHz, the thickness is preferably 5 mm or less.

It is desirable that the apex angle of the square pyramid be as acute as possible, but a range of 15 to 45 degrees is usually practical.

E Function The radio wave absorber element of the present invention is mainly made of glass fiber cloth and glass wool mat, so it is nonflammable, and the resistive film is laminated in parallel as a whole, and in particular, it has a square pyramid, so it has good radio wave consistency. Excellent in
It can effectively absorb vertically incident and obliquely incident radio waves, and also improve polarization characteristics.

In addition, a product with sufficient shape retention and strength and excellent handling properties can be obtained.

Example: Glass fiber woven fabric with a thickness of 0.18 mm (manufactured by Nitto Boseki Co., Ltd.)
WE18K-104) was impregnated with a synthetic resin emulsion containing graphite particles (CY-311 manufactured by Lion; carbon content 10%, synthetic resin content 10%) and dried to form carbon powder with a sheet electrical resistance value of 627Ω/ ^m2. A containing resistive film was formed.

Approximately 4mm thick bulk specific gravity 32Kg/m ³ as a spacer
Using a glass wool mat (Feather Glass FG-232 manufactured by Paramount Glass Industries), the glass fiber woven fabric on which the above-mentioned resistance film was formed were alternately laminated and bonded using a small amount of adhesive, and the structure shown in Figure 1 was obtained. A multilayer sheet as shown was prepared.

Using the multilayer sheet, an element having a square pyramid part and a base plate part as shown in FIGS. 2 and 3 was manufactured.

Fig. 2 is a perspective view of the element, and Fig. 3 is a cross-sectional view taken on a vertical plane passing through the center line of the inclined side surfaces of a regular square pyramid. 4, a is the side length of the bottom surface, and h is the height. The base plate portion 5 is a flat plate adhered to the bottom surface 4 of the square pyramid portion 1, and b is its thickness.

In this example, a=5cm, b=5.2cm, h=10cm,
The element has a square pyramid with an apex angle θ≒28°.

In addition, 10 is a glass fiber woven fabric on which carbon powder-containing resistance coatings 11 are formed on both sides, and 12 is a glass wool mat. The base plate portion 5 forms a horizontal plane parallel to the bottom surface 4 of the square pyramid portion, and has parallel resistance coatings.

As shown in Fig. 4, this element constitutes a radio wave absorber by arranging a large number of base plate parts adjacent to each other, but in this case, the base plate part has a large area and each square pyramid part is arranged and bonded. It is preferable to do so.

Reference numeral 6 denotes a metal plate for blocking radio waves that is lined on the lower surface of the base plate, and in this example, an aluminum plate with a thickness of 0.2 mm was used.

FIG. 5 is a graph showing the measurement results of the frequency of a vertically incident radio wave and the voltage standing wave ratio for the radio wave absorber shown in FIG. ,
At frequencies above 3 GHz, it was 1.1, indicating good radio wave absorption performance.

Moreover, this performance was maintained even when the wave was vertically or horizontally polarized, and the oblique incidence characteristics showed almost the same absorption performance up to an incident angle of 60°.

G. Effects of the Invention As explained above, the element of the present invention has good dimensional stability and strength, and is easy to handle, and the radio wave absorber constituted by this element has excellent radio wave absorption performance. Since it is nonflammable, it greatly contributes to the performance and safety of the anechoic chamber.

[Brief explanation of drawings]

FIG. 1 is a side view of a multilayer sheet for device construction of the present invention, FIG. 2 is a perspective view of an embodiment of the device of the present invention,
Figure 3 is a longitudinal cross-sectional view of the same, Figure 4 is a side view of a part of the radio wave absorber in which elements are arranged in cross section, and Figure 5 shows the measurement results of the voltage standing wave ratio with respect to the frequency of vertically incident radio waves. It is a graph. DESCRIPTION OF SYMBOLS 1... Regular square pyramid part, 2... Apex, 3... Inclined side surface, 4... Bottom surface, 5... Base plate part, 6... Metal plate,
10... Glass fiber woven fabric, 11... Carbon powder-containing resistance film, 12... Glass wool mat.

Claims (1)

[Claims] 1 A multilayer sheet made by alternately laminating glass fiber cloth and glass wool mat on which a resistance film containing carbon powder is formed is used to form a regular square pyramid part and a base plate part adhered to the bottom surface of the regular square pyramid part. 1. A resistive film parallel type radio wave absorber element, characterized in that: has an inclined laminated surface parallel to each inclined side surface thereof, and a base plate portion has a horizontal laminated surface parallel to the bottom surface of a square pyramid.