JPH0152920B2 - - Google Patents

Description

[Detailed description of the invention]

B. Field of Industrial Application The present invention relates to a radio wave absorber element that is spread on indoor surfaces, that is, ceilings, walls, and floors, in order to configure a radio anechoic chamber. The present invention provides a radio wave absorber element that has effective attenuation/absorption characteristics for vertical and oblique incidence of radio waves in a frequency band and is nonflammable. B. Prior Art Conventional radio wave absorbing materials used to construct radio anechoic chambers include foam-molded materials using pre-foamed polystyrene coated with carbon powder;
Commonly used materials include foamed polyurethane impregnated with carbon powder, a fibrous web mixed with carbon powder-mixed foamed polyurethane, and a hair lock material made of a mat of animal hair, chemical fiber, etc., impregnated with carbon powder-containing conductive rubber. It is being Furthermore, these materials can be made into zigzag shapes,
It is also being made into a square pyramid shape to improve broadband frequency characteristics and polarization characteristics. C. Problems to be Solved by the Invention Conventional radio wave absorbers use plastic foam or organic fiber webs as carriers to hold carbon powder in a spatially dispersed manner as described above. It has poor heat resistance, which is required as a heat-resistant 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~
In the high frequency range including 12GHz (X band), the voltage standing wave ratio (VSWR) is 1.2 or less,
Although it exhibits excellent radio wave absorption characteristics, its VSWR is only 1.5 in the relatively low frequency band below 1 GHz.
As described above, radio wave experiments in the low frequency range had the disadvantage of requiring complex correction calculations. D. Means for Solving the Problems The present invention has discovered that an extremely preferable radio wave absorbing material can be obtained by employing glass wool mat as a carrier for carbon powder, and by molding the material into a predetermined shape, We have succeeded in obtaining an element with excellent radio wave absorption characteristics and non-flammability. That is, when we measured the dielectric constant of glass wool mats, we found that glass wool mats with bulk densities of 12 to 96 Kg/ ^m3 have a relative permittivity ε _y of 1.01 to 1.14 and a dielectric loss tangent tan δ of 30 MHz radio waves.
It was confirmed that the value was 2.41×10 ^-4 to 10.7×10 ^-4 and comparable to that of conventionally used styrofoam. That is, it has been found that it has sufficient radio wave transmittance as a carrier for carbon powder and is preferable. Furthermore, fine graphite powder was dispersed and adhered as carbon to glass wool mat, and the dielectric constants (relative dielectric constant ε _y , dielectric loss tangent tan δ) were measured by varying the carbon content, and the following results were obtained. For glass wool mat with bulk density 32Kg/ ^m3 ,
A synthetic resin emulsion with a carbon content of 10% was impregnated, squeezed, dried, and measured at 30MHz.

[Table] In addition, commercially available graphite-coated foamed polystyrene has ε _y of 9.5 and tan δ of 2.0, and graphite-impregnated foamed polyurethane has ε _y of 6.1 and tan δ of 2.0, which are approximately the same performance as the above. It was hot. Further, the dielectric constant of a carbon-containing glass wool mat (bulk density 32 Kg/m ³ ) with a carbon content of 17.5 g/m was measured at different frequencies, and the attenuation constant was calculated. For comparison, a commercially available hair lock radio wave absorber was also measured. The results are shown in the table below.

[Table] Judging from the above results, carbon-containing glass wool mat is an extremely excellent radio wave absorbing material.
To obtain a return loss of 15 to 20 dB at 1000 MHz, the thickness should be 2.3 to 3.1 m, which is 1/50 of the hair lock. As mentioned above, carbon-containing glass wool mat has radio wave absorption properties that are equal to or better than conventional radio wave absorbing materials, and is nonflammable.
If it remains flat, sufficient broadband characteristics, oblique incidence characteristics, and polarization characteristics cannot be obtained. Therefore, as described in the claims, the present invention uses a carbon-containing glass wool mat having a carbon fine powder film coated on all or part of the surface of a constituent glass filament to form a regular square pyramid part and the regular square pyramid part. By forming a base plate part adhered to the bottom surface of the square pyramid part, and laminating the carbon-containing glass wool mats so that the carbon content increases sequentially from the inclined side surface of the square pyramid part toward the bottom surface of the base part. The present invention provides an element that can constitute a radio wave absorber having good broadband characteristics, oblique incidence characteristics, and polarization characteristics. In this case, the apex angle of the square pyramid is usually 15 to 45 degrees, but preferably as acute as possible. E. Function The radio wave absorber element of the present invention is nonflammable because it uses glass wool mat as a carbon carrier, and is formed by a regular square pyramid part and a base plate part. In the past, carbon-containing glass wool mats were layered in such a way that the carbon content increased sequentially, so not only vertically incident radio waves but also obliquely incident incoming radio waves penetrated into the absorber without being reflected from the surface, and had an effect on the carbon resistor. Furthermore, even if the incoming radio waves are vertically or horizontally polarized, the above-mentioned good radio wave absorption characteristics are maintained. F. Examples Example 1 Glass wool mat (bulk density 32Kg/m ³ thickness 15mm)
[Paramount Glass Industries Co., Ltd. Feather Glass FG-
232] and graphite fine particle-containing synthetic resin emulsion (carbon content 10%) [CY manufactured by Lion Corporation.
-311] was impregnated, the degree of squeezing was adjusted, and then dried to prepare a carbon-containing glass wool mat.
Its carbon content is 5, 10, 15, 25, 35, 45
Six types of g/ were prepared, and elements having a regular square pyramid part and a base plate part as shown in FIGS. 1 and 2 were manufactured. FIG. 1 is a perspective view of the element, and FIG. 2 is a sectional view taken along a vertical plane passing through the center line of the inclined side surface of the regular square pyramid. The regular square pyramid 1 has an apex 2, four triangular inclined side surfaces 4, and a square bottom 3, where a is the side length of the bottom and h is the height. The base plate part 5 is a flat plate adhered to the bottom part 3 of the square pyramid part 1, and b is its thickness. In this example, a=10cm, b=4.5cm, h=20cm
A device was manufactured. At this time, the apex angle θ was approximately 28°. The regular quadrangular pyramid part 1 is made of carbon-containing glass wool mat 1 so that the carbon content becomes 5, 10, 15 g/inward from the surface of the inclined side surface 4.
Formed by laminating 0, 11, 12,
The base plate part 5 to be adhered to the bottom surface is made of carbon-containing glass wool mats 13, 14, so that the carbon content is 25, 35, 45g/ from top to bottom.
15 are stacked. Note that 20 is a hollow portion. Therefore, when a radio wave is incident from the direction of the apex 2 of the square pyramid part 1, the attenuation constant α is proportional to the cross-sectional area of the square pyramid and increases exponentially in proportion to the carbon content, which is favorable. This provides excellent radio wave absorption performance. FIG. 3 is a sectional view of a radio wave absorber formed by arranging a large number of the above-mentioned elements so that the base plate portions are adjacent to each other. In this case, it is preferable that the base plate part has a large area such as 5' and the square pyramid parts 1 are arranged. Reference numeral 6 denotes a metal plate for blocking radio waves which is lined on the lower surface of the base plate portion 5', and in this embodiment, an aluminum plate with a thickness of 0.2 mm is used. FIG. 4 is a graph showing the measurement results of the voltage standing wave ratio with respect to the frequency of a vertically incident radio wave on the radio wave absorber shown in FIG.
Standing wave ratio is 1.2 even at frequencies above 400MHz and below 1GHz.
It did not exceed 1.1 at frequencies above 3 GHz, demonstrating extremely good radio wave absorption performance. In addition, there was no difference in absorption performance whether the arriving radio wave was vertically or horizontally polarized, and the oblique incidence characteristics had exactly the same absorption performance up to an angle of incidence of about 60°. Example 2 Using a carbon-containing glass wool mat similar to that used in Example 1, a skirt portion 2 was formed at the lower part of the square pyramid portion 1' as shown in the sectional view in FIG.
A laminate of carbon-containing glass wool mats 10', 11', and 12' was cut and molded to form 1. In this case, a large hollow part 20' exists inside the square pyramid part 1'. The base plate portion 5' was also completely the same as in the previous embodiment. Note that the apex angle θ of the square pyramid part 1'
was set at approximately 45°. The radio wave absorption performance in this case was equivalent to or better than that in Example 1. G. Effects of the Invention As explained above, the radio wave absorber element of the present invention has excellent vertical and oblique incidence absorption characteristics for radio waves from several tens of MHz to several GHz, and does not have polarization characteristics.
Moreover, since it is non-flammable, it is possible to construct an anechoic chamber with excellent performance and safety.Since the element is made of glass wool mat, it has excellent sound wave absorption properties, so it is easy to spread the element. The anechoic chamber can also be used as an anechoic chamber for acoustic measurements.

[Brief explanation of drawings]

FIG. 1 is a perspective view of an embodiment of the device of the present invention, and FIG.
3 is a longitudinal sectional view of the radio wave absorber in which the elements of the present invention are arranged, and FIG. 4 is a graph showing the measurement results of the voltage standing wave ratio with respect to the frequency of the vertically incident radio waves. FIG. 5 is a longitudinal sectional view of a radio wave absorber in which elements of the present invention are arranged according to another embodiment. DESCRIPTION OF SYMBOLS 1... Regular square pyramid part, 2... Vertex, 3... Bottom surface, 4... Inclined side surface, 5... Base plate part, 6... Metal plate, 10, 11,
12, 13, 14, 15... Carbon-containing glass wool mat.

Claims (1)

[Claims] 1 A carbon-containing glass wool mat with a fine carbon powder film coated on all or part of the surface of the constituent glass filament is used to form a regular square pyramid and a base plate adhered to the bottom of the square pyramid. . A radio wave absorber element, characterized in that the carbon-containing glass wool mats are laminated so that the carbon content increases sequentially from the inclined side surface of the square pyramid toward the bottom of the base plate.