Communications: directive radio wave systems and devices (e.g. – Radio wave absorber
Patent
1993-01-26
1995-02-28
Hellner, Mark
Communications: directive radio wave systems and devices (e.g.,
Radio wave absorber
H01Q 1700
Patent
active
053941497
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to a method of absorbing electromagnetic waves such as TV and radio waves using a carbon fiber-containing composition as a wave absorber.
BACKGROUND OF THE INVENTION
It is known that a variety of structures such as skyscrapers, power-transmission towers, bridges, rapid transit railroads, speedways, golf practice range facility, etc. as well as aircraft may shield and reflect TV, radio and other waves to cause ghosts in an expansive area.
For the purpose of preventing such ghosts, it was proposed to use wave absorbers molded from a concrete, e.g. orthodox concrete, mortar, lightweight concrete, etc., containing carbon fibers as described inter alia, in Japanese Unexamined Patent Publication Nos. 108603/1983 and 108602/1983.
However, the wave-absorbing efficiency of the conventional wave absorber can be improved only by increasing the proportion of carbon fiber or increasing the thickness of the absorber.
The complex relative dielectric constant .epsilon. of a dielectric material is given by: imaginary part .epsilon." represents a loss factor.
It is also known that when the real part .epsilon.' and imaginary part .epsilon." values are plotted on the abscissa and the ordinate, respectively, a characteristic curve of D(=d/.lambda..sub.0), where d is the thickness of a sample and .lambda..sub.0 is the wavelength of the electromagnetic wave incident on the sample, can be constructed in the absence of reflection as shown in FIG. 3. The figures given in FIG. 3 are values of D.
By way of illustration, assuming that the waves of TV Channel 2 in Japan (allocated frequency: 96-102 MHz, video carrier frequency 97.25 MHz, audio carrier frequency 101.75 MHz) are absorbed without reflection by a 10 cm-thick wall, the wavelength .lambda..sub.0 of the longer wavelength video carrier wave is: satisfy the above value of D is:
When the thickness of the sample is 5 cm, D=0.016.
It is clear that a larger value is necessary for the real part .epsilon.'.
However, in the conventional carbon fiber-containing wave absorber, it was difficult to realize such a large value for the real part .epsilon.'. Thus, the conventional wave absorber was deficient in wave absorbing capacity.
The present invention has been accomplised under the circumstances described above. The object of the present invention is to provide a wave-absorbing method in which electromagnetic waves can be absorbed with high efficiency even using a carbon fiber-containing composition of reduced carbon fiber content and reduced thickness.
DISCLOSURE OF THE INVENTION
To accomplish the above-mentioned object, the present invention provides the wave-absorbing method characterized in that a carbon fiber-containing composition containing carbon fibers oriented in a specific direction is disposed in such a manner that the longitudinal axis of said carbon filaments is aligned with the direction of the electric field of an electromagnetic wave to be absorbed.
The disposition of a wave absorber with the longitudinal axis of carbon fibers aligned with the direction of the electric field of an electromagnetic wave means not only the disposition of the carbon fiber-containing composition with the longitudinal axis of its carbon fibers perfectly lined up with the direction of the electric field but also means the following disposition. That is, the disposition of the wave absorber satisfies the following conditions: real part and imaginary part of the complex relative dielectric constant of said carbon fiber-containing composition on which the wave to be absorbed is incident at a given angle, and .epsilon.'max, .epsilon.'min, .epsilon."max and .epsilon."min represent the maximum and minimum values of .epsilon.' respectively.
The degree of carbon fiber orientation is defined herein as
This matter is now described below in further detail. For, explaining the degree of orientation, FIG. 4 is a side view showing a sample of the carbon fiber-containing composition cut on an optional plane. Two lines passing through the center of t
Fujita Jun-ichi
Kiura Mitsuo
Okazaki Hiroyuki
Yoshida Yoshiaki
Hellner Mark
Osaka Gas Company Limited
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