JP2735913B2 - Radio wave absorber for TV frequency band - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a TV having a cement and a magnetic powder or a cement, a magnetic powder and carbon fiber as main raw materials.
The present invention relates to a frequency band radio wave absorber.

(Conventional technology) TV radio waves are near 100MHz (1ch to 3ch), near 200MHz (4c
h to 12 ch) and around 600 MHz (13 to 62 ch). When this TV radio wave collides with a building such as a high-rise building, most of it is reflected without being absorbed, and a false image (ghost) is generated on a TV screen. For this reason, the problem of radio interference caused by the construction of high-rise buildings has recently been growing up especially in the suburbs of metropolitan areas, and the compensation for local residents is becoming enormous, especially in densely populated areas.

As a currently known countermeasure against false images, there is a method using a ferrite sintered tile material. However, since a step of firing at a high temperature of 1000 ° C. or more is inevitable for the ferrite sintered tile, deformation such as uneven baking and warpage of the tile during firing occurs. For the purpose of reducing the non-uniformity of the firing conditions, the shape of the tile is limited in size, and the size is about 10 cm × 10 cm. For example, if 10-story 4 floors or more areas of the building (1000 m ² and assumed) is interference, when mounting the 10cm square tiles with 33% porosity, approximately 6
Work for 17,000 sheets is required. In addition, if there is a gap of 1 mm between the panels, the reflectivity of radio waves (100 MHz) increases about 33 times and the absorption characteristics decrease drastically (edited by the Japan Broadcasting Corporation;
July 6).

As described above, the conventional method using ferrite sintered tiles has many problems in terms of technology and process quantity in construction, and is currently not widely used in general buildings for economic reasons.

In addition, pyramid type radio wave absorbers composed of carbon powder and styrofoam composites are known as those that eliminate radio interference, but the thickness of the TV absorber is 1-2 m, and it is necessary to use it on the outer wall of a building. There are many problems in terms of space and durability.

In addition, a radio wave absorber (Yasutaka Shimizu: EMC 1988.6.6 <No. 2>, page 86) in which carbon fiber, carbon beads and steel fiber are mixed with concrete is also known. Since it is as thick as 23.79 cm and the reported value of the absorption frequency band is also around 100 to 200 MHz, there is a problem that it cannot be used for all TV frequency bands.

In addition, the cement: ferrite: sand volume ratio of 1: 4: 3
A transmission attenuation value (unit: dB / cm) has been reported for electromagnetic wave absorbing building materials in which the weight of ferrite is about 66% of the whole (Japanese Patent Application No. 47-113980). However, the publication does not describe the value of the return loss (unit: dB), and the amount of radio waves directly reflected on the surface of the molded body is completely unknown.

(Problems to be Solved by the Invention) The present invention overcomes the economical and shape disadvantages of existing radio wave absorbers, is easy to construct, and enables absorption of TV frequency band radio waves over a wide band. It is intended to be provided.

(Means for Solving the Problems) The gist of the present invention is that a dry weight ratio of cement
For a TV frequency band, a wire mesh whose mesh diameter is equal to or larger than the average diameter of the magnetic particles is embedded as a conductor in a molded body mainly composed of 10 to 25% and magnetic particles of 75 to 90%. Radio wave absorber or cement 10 to 25 by dry weight ratio
%, Magnetic powder 75 ~ 90%, carbon fiber 0.01 ~ 1
% Is a radio wave absorber for TV frequency band, characterized by embedding a wire mesh having a mesh diameter equal to or larger than the average diameter of magnetic powders as a conductor in a molded body whose main raw material is%.

Further, in the above-mentioned radio wave absorber for the TV frequency band, the position X of the conductor satisfies the range of 0.75 ≦ x / d <1.0 (d is the thickness of the absorber) from the incident wave side. Further, the magnetic powder is preferably Mn-based ferrite.

(Operation) Hereinafter, the present invention will be described in detail.

The cement referred to in the present invention is a hydraulic cement (for example, Portland cement, white Portland cement, alumina cement, pozzolan cement, truss cement, santrin cement, lime slag cement, pozzolan portland cement, silica cement, trasportland cement, blast furnace Cement, iron Portland cement, fly ash cement, solid cement, shale ash Portland cement), air-hardened cement (magnesia cement), special cement (fire resistant cement, acid resistant cement, water glass cement, high sulfate slag cement), etc. There is no particular limitation as long as the cement is called cement.

The compounding ratio is in the range of 10 wt% or more to 25 wt% or less in terms of the dry weight ratio. If it is less than 10 wt%, the compact is less likely to coagulate, and if it exceeds 25 wt%, it is used as a radio wave absorber. The original function of is poor.

The magnetic powder and granular material is an oxide magnetic material and the metallic magnetic, for example _{(FeO-Fe 2 O 3,} γ-Fe 2 O 3, MnO-Fe 2 O 3, MnO
−ZnO−Fe ₂ O ₃ , CuO−ZnO−Fe ₂ O ₃ , CuO−MnO−Fe ₂ O ₃ , NiO−
ZnO-Fe ₂ O ₃ , NiO-CuO-ZnO-Fe ₂ O ₃ , MgO-Fe ₂ O ₃ , MgO-Zn
_{O-Fe 2 O 3, MgO} -MnO-Fe 2 O 3, LiO-ZnO-Fe 2 O 3, an oxide magnetic material such as iron powder, silicon steel powder, permalloy powder, metallic magnetic material such as sendust powder There is.

Of these, if limited to oxide magnetic materials, trace elements (for example, CaO, SiO _2, etc.) are fired before firing for the purpose of improving magnetic properties, accelerating the sintering reaction, and controlling intracrystalline and intergranular resistance. It is desirable to add

Furthermore, magnetic materials that are relatively easily available at present, are available in large quantities and inexpensively on the market, and have excellent absorption characteristics include Mn-based ferrites such as Mn-Zn-based and Mn-Mg-based ferrites. Appropriate.

The size and particle size distribution of the magnetic particles are not particularly specified, but the kneading amount of the magnetic particles of the present invention with respect to cement is considerably large, so that the simplicity at the time of molding is regarded as the standard of the particle size. It seems appropriate to do so. Regarding the particle size distribution of the granular material, for example, Fuller and Thomps
It may be possible to refer to the sieve distribution curve by on or the German standard (DIN1045) for fine aggregate proposed by Gref, and it is not necessary to completely satisfy the values of the above proposers.

The compounding ratio of the magnetic material is in the range of 75% to 90% by dry weight ratio of the whole, and if it exceeds 90%, the compact is hard to coagulate, and if it is less than 75%, the electromagnetic wave absorbing material is used. The original function as is inferior.

Carbon fiber is a general term for rayon-based, acrylonitrile-based, lignin-poval-based, pitch-based, and tar-based materials, and finely adjusts the electromagnetic wave absorption characteristics of molded products by kneading one or more types in concrete. . The compounding ratio Y is 0 or 0.01
≦ Y ≦ 1 and kneading a large amount of carbon fiber exceeding 1 wt% is not only technically difficult but also not preferable in the present invention, especially in the case of a high mixing ratio of magnetic particles. Also, if you do not need fine tuning,
There is no need to mix.

Regarding the shape of the carbon fiber, curled or straight long fibers or short fibers may be used, and in short, the shape of short fibers is more desirable than the ease of kneading and dispersion.

As described above, the materials described in the text, namely, cement, magnetic particles, or cement, magnetic particles, and carbon fibers are referred to as main raw materials in the present invention. Materials, setting / hardening promoting materials, waterproofing materials, antifreezing materials, foaming materials, coloring materials, mixed materials, fire resistance promoting materials, etc.) are appropriately added.

FIG. 1 shows a schematic diagram of the present invention. In the figure, d
Represents the thickness of the radio wave absorber, and X represents the embedded position of the conductor, that is, the distance from the radio wave incident side surface of the radio wave absorber to the conductor. As this conductor, a wire mesh is preferably used, and it has a function of increasing the absorption efficiency of the radio wave absorber described in the present invention.

FIG. 2 shows a schematic example of the construction on a building wall surface using the material (a) of the present invention and the ferrite sintered tile materials (b) and (c). It is necessary to devise a way to fix each sheet, such as bonding it or fitting it into a metal jacket.
Guidebook for radio interference caused by radio wave absorbers July 10, 1981
page). Moreover, since the number of constructions is extremely large, there is a risk of loss of life due to falling of the tiles unless the countermeasures against falling are sufficiently considered.

However, in the material of the present invention shown in FIG. 1 and FIG. 2 (a), in the process of forming the radio wave absorber, firing conditions and atmosphere control at a high temperature (for example, Takei Takei: Theory and Application of Ferrite, Maruzen (1960)), there are very few restrictions on molding, such as the capacity of the firing furnace, and large panels can be easily produced. For this reason, construction is completed only by fixing a few places of the molded body, and in the present invention in which a conductor is built in, there is no need to take an electrical short circuit (short circuit) separately from the building.

As for the position and type of conductors, iron plates, copper plates, concrete reinforcing bars (φ10mm, lattice spacing of about 100mm) or wire mesh have been installed in the state of being closely or slightly separated from the back of ferrite sintered tiles. Is known to absorb radio waves (Japan Broadcasting Corporation, Ed .: Guidebook for radio interference by radio wave absorbers July 8, 1981)
page).

However, the experimental example described above is a case where the conductor is present on the back surface of the radio wave absorber, which is different from the case of the radio wave absorber in which the conductor is embedded, which is a feature of the present invention. The biggest difference is that the material of the present invention is a radio wave absorber mainly composed of cement and magnetic powder or cement, magnetic powder and carbon fiber. It is easy to fill in before molding,
In addition, embedding the conductive plate can be a significant reduction in man-hours during construction.

If ferrite sintered tiles are manufactured, even if the conductors are embedded and baked,
The absorption function is reduced, and there is little merit in the conventional material (sintered ferrite tile). This is because the ferrite sintering conditions are very delicate, and even a small amount of impurities before sintering deteriorates the magnetic properties.

In the present invention, when the conductor is a metal net and the mesh diameter is equal to or larger than the average diameter of the magnetic powder, the molding is easy and the exfoliation of the molding is eliminated.

Regarding the position X of the conductor, it may be buried in any position. However, considering the radio wave absorption characteristics of each frequency, the frequency (100 MHz) corresponding to 1 to 3 ch of the TV radio wave with respect to the molded body thickness d It is desirable that the value of X / d is 0.75 or more or less than 1.0 from the radio wave incident side.
For TV radio frequency, X / d of 0.45 to 0.8 is optimal.

The mixing ratio of the main raw materials is 10wt% to 25wt% of cement in dry weight ratio, 75wt% to 90wt% of magnetic powders
10% to 25% by weight of cement or less, 75% to 90% by weight of magnetic powder, carbon fiber
In the range of 0.01 wt% or more to 1 wt% or less, a wideband radio wave can be efficiently absorbed.

Also, by forming the radio wave absorber described in the present invention into, for example, a 3m x 1m panel, the total man-hour for mounting is about 1/20
This can be simplified to 0, and in the example of the 10-story building described above, the total number of installations is about 300 sheets.

Further, as a feature of the present invention, by forming the above-mentioned thick panel material having a length of at least one side of the absorber of the required absorption wavelength, it is possible to reduce a decrease in radio wave absorption performance generated in a gap between the panels. Become.

(Examples) Hereinafter, the present invention will be described with reference to examples.

EXAMPLES The return loss (dB value) of the electromagnetic wave absorber of the present invention in which the thickness d was d = 25 mm and 40 mm was measured in an anechoic chamber. The measurement frequency is 100MHz, which almost corresponds to the center frequency of 1ch to 3ch of TV radio wave, 200MHz which almost corresponds to the center frequency of 4ch to 12ch, 600 which almost corresponds to the center frequency of UHF band
MHz. At the time of measurement, the reflectance of the iron plate was converted to 100%, and the measured values were corrected.

The blending ratio of the molded body used for the measurement in terms of dry weight ratio is shown in FIG. 3 where the mark ● represents 75.0% of Mn-Zn ferrite powder (3 times the weight of cement) passed through a 2.0 mm diameter sieve, and an acrylonitrile-based material. The carbon fiber is 0.125% (about 0.5% of concrete weight), the balance is white Portland cement. The ○ mark in the figure is 90.0% of Mn-Zn ferrite powder and granules passed through a 2.0 mm diameter sieve (about 9 times the weight of concrete). ),
The balance was white Portland cement (all in the scope of the present invention).

In the figure, X indicates a conductor position in the radio wave absorber,
For example, the conductor position when X / d = 0.75 and the thickness is 40 mm corresponds to a position 30 mm away from the incident radio wave side. The conductor used in the examples was a stainless steel wire net having a mesh diameter of 8 mm and a wire diameter of 1 mm.

In FIG. 3, when a radio wave absorber having a thickness of 40 mm is used as indicated by the mark ●, the absorption characteristic at 100 MHz is greatly improved when the position ratio X / d of the conductor ranges from 0.4 to 1.0. For example, when the value of X / d is 0.6, the radio wave absorption characteristic was 6.3 dB (absorption amount 76.6%), but with the change to X / d = 0.9, 16.6 dB (absorption amount 97.8%).
%), The reflection amount is improved by 1/10, and the increase of the return loss is improved by 10.3 dB.

Similarly, for a 25 mm thick radio wave absorber, X / d = 0.6
From 0.8 to 0.8, the position of the conductive plate moves about 5 mm,
The return loss is 4dB, and the absorption is improved from 80.5% to 92.2%.

In other words, these characteristic values obtained at X / d = 0.8 to 0.9 are about 93% of the radio wave absorption (compared with 20dB, absorption = 99%) of the currently used ferrite sintered tile material.
Absorbs radio waves equivalent to ~ 99%.

Similarly, at 200 MHz and 600 MHz,
It absorbs radio waves corresponding to 10.6 dB to 13.1 dB and 8.0 to 8.3 dB, corresponding to 92 to 96% and 85 to 86% of the ferrite sintered tile comparison value, respectively.

That is, in FIG. 3, the VHF band (100 MHz and 2 MHz)
UHF band (600MHz), which is said to be less than 10dB at around 00MHz (above 90% in absorption) and relatively low in ghosting
The position of the conductor which satisfies 8 dB or more (nearby) (absorbed amount is 84% or more) is in the range of about 0.75 or more in X / d value.

A state where a radio wave absorber is mounted on a building (windows, sash frames,
Considering that materials that easily reflect radio waves, such as balconies, are often exposed on the surface), the absorption characteristic value of the material of the present invention is inferior to that of the ferrite sintered tile material in terms of characteristics because reflection occurs even with a perfect absorber. According to the above, it can be said that the construction is a radio wave absorber that is extremely easy (embedded conductor).

(Effect of the Invention) By forming the radio wave absorber having the conductor of the present invention embedded in it into a panel material, the conventional radio wave absorption tile material (about
(10 cm square) can be simplified in the construction process compared to the case of pasting. Furthermore, if several standard sizes are determined at the time of paneling, mass production becomes possible and the price can be reduced.

[Brief description of the drawings]

FIG. 1 is a schematic view of a TV frequency band radio wave absorber according to the present invention, and FIG. 2 (a) is an example of the present invention, (b) and (c).
Fig. 3 is a diagram showing a working example of a ferrite sintered tile radio wave absorber, and Fig. 3 is a graph showing the dependence of the return loss (db value) on the conductor position (X / d) at 100MHz, 200MHz and 600MHz. .

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Takeshi Yamamoto 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Prefecture Nippon Steel Corp. (72) Inventor Hideo Tanaka 1-25-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. (72) Kenji Sugimoto 1-25-Nishi-Shinjuku, Shinjuku-ku, Tokyo 1. Inside Taisei Corporation (72) Inventor Tetsuo Yamada 1-25-1 Nishishinjuku, Shinjuku-ku, Tokyo Inside Taisei Corporation (72) Inventor Tetsuzo Morita 1-25-1 Nishishinjuku, Shinjuku-ku, Tokyo Taisei (72) Inventor Masao Kosaka 2-14-2 Nagatacho, Chiyoda-ku, Tokyo Showa Mining Co., Ltd. (72) Inventor Tadashi Ito 2-2-2 Matsumoto, Urawa-shi, Saitama (56) See References JP-A-64-67997 (JP, A) JP-B-52-27355 (JP, B2)

Claims (3)

(57) [Claims] 1. A wire net having a mesh diameter not less than the average diameter of a magnetic powder is embedded as a conductor in a molded body mainly composed of 10 to 25% of cement and 75 to 90% of a magnetic powder in a dry weight ratio. A radio wave absorber for a TV frequency band. 2. An average of a magnetic powder having a mesh diameter as a conductor in a molded body mainly composed of 10 to 25% of cement, 75 to 90% of magnetic powder and 0.01 to 1% of carbon fiber in a dry weight ratio. TV characterized by embedding a wire mesh with a diameter greater than or equal to
Radio wave absorber for frequency band. 3. The position X of the conductor is 0.75 ≦ x /
3. The radio wave absorber for a TV frequency band according to claim 1, wherein d <1.0 (d is the thickness of the absorber) is satisfied.