JPH1088692A - Radio wave absorption body - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a lightweight radio wave absorption body excellent in radio wave absoption characterixtcs. SOLUTION: An uneven pattern is formed on the surface of a mixture mixing ferrite flying ash 4 with concrete 5 as a unit to constitute a radio wave absorption body. A projection has double thickness 2d of the thickness (d) of a recess section 3, the projection 2 has the same width as that of the recess section 3, and the size is as same as the thickness (d). Then, a radio wave incident to the radio absorption body is absorbed by the ferrite flying ash 4. When the width of the recess section 3 is greatly shorter than the wave length, the same function as that of a plate burying the recess section 3 of the uneven pattern therein is provided, and radio wave ab sorption characteristics as the whole radio wave absorption body is is the same as that of the plate having 1.85 in thickness.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber obtained by integrally kneading a radio wave absorbing material having electromagnetic wave absorbing properties and an inorganic cured material.

[0002]

2. Description of the Related Art In recent years, in urban areas, high-rise buildings have been promoted for the purpose of effectively utilizing land space.
However, when a building is raised in height, a broadcast wave or the like is reflected on an outer wall of the building, and an area where broadcast waves cannot be received appears or a ghost occurs in a television receiver, thereby causing radio interference.

[0003] Therefore, in recent years, the outer wall of a building is provided with a radio wave absorbing function to absorb broadcast radio waves and external electromagnetic waves.
A radio wave absorbing curtain wall that solves the above-described radio wave interference is used. FIG. 7 is a perspective view showing the structure of a radio wave absorbing curtain wall 10 conventionally used.

In this radio wave absorbing curtain wall 10, a ferrite tile (ferrite molding) 12 having a property of absorbing a radio wave is attached to the outside of a concrete 14 having a property of transmitting a radio wave, and further outside the concrete 14. Porcelain tiles 11 for decoration and protection are stuck. A wire mesh 13 having a function as a reinforcing material and a radio wave reflector is disposed inside the concrete 14.

According to the radio wave absorbing curtain wall 10 having the above-described structure, radio waves arriving from the outside of the building are transmitted through the ferrite tile 12 and absorbed, reflected by the wire mesh 13, and again. Is transmitted and absorbed, so that the intensity of the reflected radio wave is weakened. As a result, radio interference can be reduced.

[0006]

However, the above-described radio wave absorbing curtain wall 10 has a wire mesh 13 inside the concrete 14 for the purpose of increasing the radio wave absorbing efficiency and reducing the radio wave transmitted inside the building.
Is arranged, the thickness of the concrete 14 is increased, and accordingly, the weight of the radio wave absorbing curtain wall 10 is also increased.

Further, the wire mesh 13 is provided inside the concrete 14, and the ferrite tile 1 is provided on the outer surface.
2 has to be stuck, which takes time for the construction, and as a result, there is a problem that the construction cost also increases.

[0008] In view of the above problems, it is a first object of the present invention to provide a light-weight radio wave absorber that is excellent in radio wave absorption efficiency.

[0009] In addition to the first object, the present invention provides:
A second object is to provide a radio wave absorber excellent in workability.

[0010]

Means for Solving the Problems In order to solve the above-mentioned problems, the invention of claim 1 has an unevenness pattern formed on the surface of a radio wave absorber obtained by integrally kneading a radio wave absorbing material and an inorganic cured material. .

According to a second aspect of the present invention, in the radio wave absorber according to the first aspect, the radio wave absorbing material is ferrite fly ash.

According to a third aspect of the present invention, in the radio wave absorber according to the first aspect, the radio wave absorbing material is a ferrite strip.

According to a fourth aspect of the present invention, a carbon fiber is added to the radio wave absorber according to any one of the first to third aspects of the present invention.

[0014]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an external perspective view of a radio wave absorber 1 according to the present invention, and FIG. 2 is a view showing a cross section of the radio wave absorber 1 of FIG. 1 taken along line V-V. In both figures, XYZ rectangular coordinate axes are attached to clarify the directional relationship.

As shown in the figure, on the surface of the radio wave absorber 1, a concave / convex pattern formed by repeating a concave portion 3 and a convex portion 2 is formed. The convex portion 2 has a thickness 2d which is twice the thickness (length in the X-axis direction) d of the concave portion 3, and the width (length in the Z-axis direction) of the convex portion 2 and the concave portion 3 is Equal, and the size is the same as the thickness d. That is, the radio wave absorber 1
It can also be considered that a plurality of protrusions 2 having a thickness 2d and a width d and a recess 3 having a thickness d and a width d connected in the width direction are connected to each other.

The radio wave absorber 1 is formed by integrally kneading a concrete 5 which is an inorganic hardened material and a ferrite fly ash 4 which is a radio wave absorbing material, and having the above-mentioned shape. .

Ferrite fly ash 4 is obtained by mixing fly ash and iron oxide generated when incinerating municipal waste, and
It is obtained by firing under a temperature condition of 00 to 800 ° C, and is a ferrite fly ash from which harmful heavy metals do not elute. As is well known, ferrite has good magnetic permeability and electromagnetic wave absorption characteristics, and the ferrite fly ash 4 also has similar characteristics. Therefore, the radio wave absorber 1 in which the ferrite fly ash 4 and the concrete 5 are integrally kneaded is made of concrete having electromagnetic wave absorption characteristics. The ferrite fly ash 4 used here preferably has an average particle diameter of 100 μm or less, because it has good electromagnetic wave absorption characteristics.

The radio wave absorber 1 made of concrete having such electromagnetic wave absorption characteristics has an average thickness (thickness 1....) By forming the above-mentioned uneven pattern.
Electromagnetic wave absorption characteristics equivalent to those of a flat electromagnetic wave absorber thicker than 5d) are obtained. This will be described using the experimental results shown below.

In the experiment, first, a thickness of 26.6 mm (hereinafter, referred to as a thickness)
A flat plate having a thickness of L, a flat plate having a thickness of 53.6 mm (hereinafter referred to as a thickness of 2 L), a concave portion having a thickness of L and a convex portion having a thickness of 2 L are connected in parallel, and the radio wave shown in FIG. Three types of plates (average thickness 1.5 L) having the same concavo-convex pattern as the absorber 1 are prepared as test samples. Next, a metal plate is placed behind these specimens, and the frequency of the specimen is 500 to 250.
A 0 MHz radio wave is incident, and the return loss of the radio wave reflected from the plate is measured. The above three types of plates are all made of concrete having electromagnetic wave absorption characteristics. Here, the return loss is an index indicating the degree to which the reflected radio wave is attenuated as compared to the incident radio wave. A large return loss means that the radio wave absorption characteristics are excellent.

In addition to the actual measurement of the return loss, the magnetic permeability and permittivity of the test specimen were measured, and from the results, the return loss of the radio wave was calculated for the above three types of plates.

FIG. 3 is a diagram showing the results of actual measurement of the radio wave reflection attenuation for the above three types of plates, and FIG. 4 is a diagram showing the calculation results. As is clear from the comparison between the results of FIGS. 3 and 4, the measured and calculated results for the flat plate generally agree with each other, whereas the peak of the return loss of the plate having the concavo-convex pattern is the calculated result. The actual measurement result is shifted to the lower frequency side as compared with. The peak frequency of the return loss of the plate having the concavo-convex pattern (actual measurement result) is the same as the peak frequency of the flat plate having a thickness of 49.2 mm (thickness of 1.85 L). That is, a plate having an uneven pattern (average thickness is 1.5 L) has an effect equivalent to a flat plate having a thickness of 1.85 L with respect to the return loss of radio waves. This is because, based on the wavelength of the radio wave used in the experiment, the interval between the concavo-convex patterns of the test piece (width L of the concave portion) is very small. This is probably because they have similar radio wave absorption characteristics.

Therefore, when it is desired to absorb radio waves of a predetermined frequency, if the required thickness of a flat plate is 1.85 L, the average thickness is 1.85 L using a plate having a concavo-convex pattern.
Since only 5 L is required, the weight of the radio wave absorber is reduced to about 19
% Can be reduced.

As described above, the average thickness of the radio wave absorber 1 according to the present invention is 1.5d, but the return loss is equivalent to that of a 1.85d flat plate. In other words, in other words, the weight of the plate can be reduced by about 19%. In order to effectively reduce the return loss of the VHF television frequency (frequency of 50 to 250 MHz), which is a problem as radio interference, d = 70 mm (see FIG. 2).
The degree is preferred.

Further, since the radio wave absorber 1 is formed by kneading the ferrite fly ash 4 and the concrete 5 integrally, the radio wave absorber 1 can be used as it is as an outer wall for radio wave absorption of a building. Lamination work is not required. As a result, it is not necessary to take time for construction, and it is possible to suppress an increase in construction cost.

In the above description, the ferrite fly ash 4 was used as a radio wave absorbing material. However, the present invention is not limited to this, and any material having electromagnetic wave absorption characteristics may be used. It may be a piece.

FIG. 5 is a diagram showing a cross section of a radio wave absorber 1 using a ferrite strip 6 as a radio wave absorbing material. The ferrite strip 6 is a strip obtained by finely crushing a ferrite tile (see FIG. 7). In order to obtain the radio wave absorber 1 by mixing it with the concrete 5 as a radio wave absorbing material, the average particle size is 5 mm or less. Is more preferable.

As described above, even when the ferrite strip 6 is used as the radio wave absorbing material, the same effect as when the ferrite fly ash 4 is used can be obtained.

Further, by adding the carbon fiber 7 having the property of reflecting radio waves to the radio wave absorber 1, it is possible to further enhance the radio wave absorption characteristics. FIG. 6 is a view showing a cross section of the radio wave absorber 1 in which the ferrite fly ash 4 and the concrete 5 are integrally kneaded, and further the carbon fiber 7 is added.

In the radio wave absorber 1 to which the carbon fiber 7 is added,
A part of the incident radio wave is absorbed by the ferrite fly ash 4, and another part is irregularly reflected by the carbon fiber 7, and the irregularly reflected radio wave is further absorbed by the ferrite fly ash 4. The radio wave absorption characteristics as a whole are higher than when the carbon fiber 7 is not added.

Therefore, in this case, the same effect as that when the carbon fiber 7 is not added can be obtained, and further, higher radio wave absorption characteristics can be obtained. In addition,
In order to obtain good radio wave absorption characteristics, the addition amount of the carbon fiber 7 should be 0.5% to 1.5%, and its elastic modulus should be 100% to 100%.
It is desirable to set it to 300 × 10 ⁶ N / m ² .

Although the embodiment of the present invention has been described above, the present invention is not limited to the above example.
For example, the inorganic cured product may be mortar.

[0033]

As described above, according to the first, second and third aspects of the present invention, the unevenness pattern is formed on the surface of the electromagnetic wave absorber obtained by integrally kneading the electromagnetic wave absorbing material and the inorganic cured material. Is formed, it has electromagnetic wave absorption characteristics equivalent to a flat plate radio wave absorber thicker than its average thickness, and as a result, it is possible to achieve weight reduction while maintaining high radio wave absorption characteristics . Further, since it can be used as it is as a radio wave absorbing outer wall of a building, it does not take much time for construction, and an increase in construction cost can be suppressed.

According to the fourth aspect of the present invention, since carbon fibers are added, in addition to the same effects as described above, radio waves irregularly reflected by the carbon fibers are further absorbed, and higher radio waves are obtained. Absorption characteristics can be obtained.

[Brief description of the drawings]

FIG. 1 is an external perspective view of a radio wave absorber according to the present invention.

FIG. 2 is a view showing a cross section of the radio wave absorber of FIG. 1 as viewed along the line VV.

FIG. 3 is a diagram showing actual measurement results of radio wave reflection attenuation amounts for three types of plates.

FIG. 4 is a diagram showing calculation results of radio wave reflection attenuation amounts for three types of plates.

FIG. 5 is a diagram showing a cross section of a radio wave absorber using a ferrite strip as a radio wave absorbing material.

FIG. 6 is a view showing a cross section of a radio wave absorber obtained by integrally kneading ferritized fly ash and concrete and further adding carbon fibers.

FIG. 7 is a perspective view showing the structure of a conventionally used radio wave absorbing curtain wall.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Radio wave absorber 2 Convex part 3 Concave part 4 Ferrite fly ash 5 Concrete 6 Ferrite strip 7 Carbon fiber

Continuing from the front page (72) Inventor Katsuo Yoshida 4-640 Shimoseito, Kiyose-shi, Tokyo Inside the Obayashi-gumi Technical Research Institute Co., Ltd. Inventor Akihiro Zama 2-3 Kanda Tsukamachi, Chiyoda-ku, Tokyo Obayashi Corporation Tokyo head office (72) Inventor Yoshihiro Hayashi No. 6 107 Takinocho, Nishinomiya-shi, Hyogo Shinmeiwa Industry Co., Ltd. 72) Inventor Masahiko Ikeda 6-107, Takino-cho, Nishinomiya-shi, Hyogo Pref.Shin-Meiwa Industrial Co., Ltd. Within the Technology Division (72) Inventor Akira Kojima 580 Tobacho, Maebashi-shi, Gunma Gunma College of Technology

Claims (4)

[Claims] 1. A radio wave absorber obtained by integrally kneading a radio wave absorbing material and an inorganic cured material, wherein a radio wave absorber is formed on the surface thereof. 2. The radio wave absorber according to claim 1, wherein the radio wave absorption material is ferrite fly ash. 3. The radio wave absorber according to claim 1, wherein the radio wave absorbing material is a ferrite strip. 4. The radio wave absorber according to claim 1, wherein carbon fibers are added.