JPH05183331A - Radio wave absorbing wall for tv frequency band - Google Patents

Abstract

PURPOSE:To facilitate the installation and to absorb a radio wave over a wide TV frequency band by forming the wall with cement and magnetic particles, providing a specific shape and selecting the length of the wall in the magnetic field direction of the TV radio wave to be a required absorbing wavelength or over. CONSTITUTION:A groove 12 whose depth is (d2-d1) is provided to the wall in the electric field direction of a TV radio wave, a thickness d1 of a recessed part of a forming and a thickness d2 of a projection of a forming are selected to be 0<d1<=50mm and d2<d2<=50mm and 0.2<=(d2-d1)/d2<=1.0. Then the wall is made of major components as 5-20% of cement and 80-95% of magnetic particles in the dry weight ratio, and the length of the wall in the magnetic field direction of the TV radio wave is selected to be the required absorbing wave or over. In this case a cement called generally a cement such as hydraulic cement, air setting cement, and special cement is enough for the purpose. Furthermore, the magnetic particles are oxide magnetic particles and metallic magnetic particles. Then a gap being a groove 12 is provided in the direction of the electric field and a substance with a low dielectric constant is used inbetween, then the substantial induction rate is reduced and the absorbing performance is improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorption wall for TV frequency band, which is mainly composed of cement and magnetic powder particles.

[0002]

2. Description of the Related Art TV radio waves have a wavelength of about 3 and a wavelength of about 3 MHz.
1ch to 3ch with m as the operating frequency, around 200MHz, 4ch to 12ch with 600nm as the operating frequency, 600
Around 1 MHz with a frequency of about 0.5 m as a wavelength
From 3ch to 62ch, radio waves with different frequencies (wavelengths) of up to 8 times are actually used.

Therefore, there are few types of radio wave absorbers having a unique thickness and capable of absorbing TV radio waves with a wavelength difference of more than 2 m and preventing false images (ghosts). For this reason, it is not uncommon to see double or triple images on the TV screen in urban areas where high-rise buildings are scattered.

There are mainly two currently known solutions, and there are a method of using a sintered ferrite tile material and a method of using a pyramid type block material composed of carbon powder and a styrofoam composite.

However, since the step of firing the sintered ferrite tile material at a high temperature of 1000 ° C. or more is inevitable, uneven firing or warping of the tile during firing occurs. For the purpose of reducing the unevenness of the firing conditions, the shape of the tile is limited in size, and its size is 10 cm ×
It will be about 10 cm. This value is about 1/30 of 1ch wavelength,
It is 1/15 of 8ch wavelength, and it is necessary to row at least 15 to 30 ferrite tiles continuously in order to obtain good absorption characteristics. Very laborious processes such as polishing reduce the construction efficiency. In the case of pyramid type block material,
Currently known TV absorbers have a thickness of 1-2 m,
There are many spatial problems when it is used for the outer wall of a building, and when it is used in an anechoic chamber, etc., it occupies a large space in the room.

In Japanese Patent Publication No. 55-49798, in order to reduce the weight and the cost, the ferrite plates are continuous in the magnetic field direction and are spaced so as to be discontinuous in the electric field direction.
There is disclosed a radio wave absorption wall characterized by being lined up.
In addition, Japanese Patent Publication No. 55-29599 discloses a method of continuously changing the thickness of a radio wave absorber by using a weight-shaped ferrite member.

However, when both are used, 1
There is a drawback that a large number of ferrite tiles with a size of about 0 × 10 cm must be lined up and used, and like general ferrite tile materials, they are not widely used in general buildings.

Next, as a method for overcoming the shape defect and producing a large-sized electromagnetic wave absorber, the following method is currently disclosed.

A radio wave absorbing wall body has been reported which is characterized by using a ferrite as a coarse aggregate and a fine aggregate and providing an electric wave absorbing layer made of concrete.
No. 66999). In addition, regarding a composite electromagnetic wave absorber using a mixture of magnetic powder particles and a non-magnetic substance such as cement or rubber, Japanese Patent Laid-Open Publication No. 50-155999 discloses that the return loss is reported. , The same 51
No. 121200, No. 51-110951.
No. 52-67945, No. 54-41495, and No. 60-89902.

However, in the radio wave absorber described above, in the low frequency side of TV frequency (90 to 230 MHz,
There is no description of an absorber having an absorption frequency region (corresponding to 1 to 12 channels), and if it is stated strongly for comparison, it is disclosed in Japanese Patent Laid-Open No. 52-6.
The electromagnetic wave absorber (thickness 150 mm) described in 7945 is
It only shows good characteristics in the frequency range of 300 MHz or higher, and most of the radio wave absorbers in which magnetic powder particles and non-magnetic materials are mixed have the radio wave absorption region in the frequency range of 500 MHz to 1 GHz or higher.

[0011]

DISCLOSURE OF THE INVENTION The present invention overcomes the economical, shape and spatial drawbacks of existing electromagnetic wave absorbers, is easy to construct, and is capable of absorbing radio waves in the TV frequency band over a wide band. The purpose is to improve the absorption characteristics of the body.

[0012]

The present invention has a groove having a depth (d ₂ −d ₁ ) in the electric field direction of TV radio waves, and the molded body concave portion thickness d ₁ and the molded body convex portion thickness d ₂ are , 0 <d ₁ ≦ 5
0 mm, d ₁ <d ₂ ≦ 50 mm, and 0.2 ≦ (d ₂ −
d ₁ ) / d ₂ ≦ 1.0, the length of the TV radio wave in the magnetic field direction is the required absorption, composed of the main components of 5 to 20% of cement and 80 to 95% of magnetic powder granules in the dry weight ratio. A radio wave absorption wall for TV frequency band, which is characterized by being equal to or more than the wavelength
Or has a groove depth in the direction of the electric field of the TV radio wave _{(d n + 1 -d n)} , the molded body thickness d _n and moldings thickness d _{n + 1}
(N = 1, 2, 3 ...) is 0 <d _n ≦ 50 mm, and d _n
<D _{n + 1} ≦ 50mm and _{0.2 ≦ (d n -d 1)} , / d n
≤1.0, characterized by dry weight ratio of cement 5-20
%, Magnetic powder granules 80-95%
The electromagnetic wave absorption wall for TV frequency band, characterized in that the magnetic field length of V electric wave is equal to or longer than the required absorption wavelength, or T
There is a gap in the electric field direction of V radio waves, and the thickness d of the molded body is 1
Cement 5 by dry weight ratio, characterized by 0 ≦ d ≦ 50 mm
The electromagnetic wave absorption wall for the TV frequency band is characterized in that the magnetic field length of the TV radio wave in the magnetic field direction, which is composed of the main components of ˜20% and magnetic powder granules 80 to 95%, is not less than the required absorption wavelength.

[0013]

The present invention will be described in detail below. 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, santorin cement, lime slag cement, pozzolan Portland cement, silica cement, trasportland cement, blast furnace Cement, iron Portland cement, fly ash cement, solidit cement, shale ash Portland cement), air-hardening cement (magnesia cement), special cement (fire resistant cement, acid resistant cement, water glass cement, high sulfate slag cement), etc. The cement is not particularly limited as long as it is called cement.

The blending ratio is 5 wt% of the total dry weight ratio.
It is in the range of not less than 25 wt% and not more than 25 wt%, and the molded product is hard to congeal in the range of less than 5 wt%, and the original function as a radio wave absorber is inferior in the range of more than 25 wt%.

[0015] The magnetic powder and granular material is an oxide magnetic material and the metallic magnetic, for example _{(FeO-Fe 2 O 3,} γ-F
_{e 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, M
_{gO-ZnO-Fe 2 O 3} , MgO-MnO-Fe 2 O
₃ , there are oxide magnetic materials such as LiO—ZnO—Fe ₂ O ₃ and metal magnetic materials such as iron powder, silicon steel powder, permalloy powder and Sendust powder.

If the oxide magnetic material is limited, trace elements (for example, CaO, SiO ₂₎ are used for the purpose of improving magnetic properties, accelerating the sintering reaction, controlling the resistance of crystal grains and grain boundaries.
Etc.) is preferably added before firing.

Further, it is relatively easy to obtain at present, and a large amount of
Magnetic materials that are inexpensively available on the market and have excellent absorption characteristics include Mn—Zn-based materials and Mn-based materials.
A Mn-based ferrite such as -Mg-based ferrite or a Ni-Zn-based ferrite is suitable.

The size and particle size distribution of the magnetic powder granules are not particularly specified, but because the amount of the magnetic powder granules of the present invention to be kneaded with the cement is considerably high, the magnetic powder granules are also mixed with the cement bone. By considering it as a substitute for the material, it is considered appropriate to use the ease of molding as a guide for the particle size.

Regarding the grain-based distribution of the powder or granular material, for example, F
Fluler distribution curve by uller and Thompson, and German standard for fine aggregate proposed by Graf (DIN
1045) may be referred to, and it is not always necessary to completely satisfy the values of the above-mentioned proponents.

The compounding ratio of the magnetic powder particles is in the range of 75% to 95% by weight in terms of dry weight ratio, and 95% by weight.
%, The molded body is hard to solidify,
In the range of less than wt%, the original performance as a radio wave absorber is poor.

In the present invention, the materials described above, that is, cement and magnetic powder granules are referred to as the main components, and water and admixtures (eg, AE material, dispersion material, setting / hardening accelerator, waterproofing) are used for molding. Materials, anti-freezing materials, foaming materials, coloring materials, mixing materials, fire resistance promoting materials, etc.) are appropriately added. Further, the absorption permittivity may be improved by finely adjusting the complex dielectric constant of the molded body by freeze-drying one or more kinds of long fiber-shaped or short fiber-shaped carbon fibers in concrete.

The electromagnetic wave absorption characteristics depend on the values of the real number component / imaginary number component of magnetic permeability and the real number component / imaginary number component of permittivity. Of these, the imaginary permeability and the real permittivity are particularly important in the present invention.

Increasing the imaginary magnetic permeability is an essential factor for reducing the thickness of the electromagnetic wave absorber, and decreasing the real number dielectric constant is essential for widening the electromagnetic wave absorption characteristics.

However, in order to increase the imaginary magnetic permeability, as shown in FIG. 3, the ratio of the magnetic powder particles in the main component must be increased. Increase.

In order to solve this contradictory requirement, a gap or groove is provided in the direction of the electric field, and a substance having a low dielectric constant (for example, air, concrete, mortar, etc.) is sandwiched between them, so that the real dielectric constant is apparent. Can be reduced and absorption characteristics can be improved.

FIG. 4 shows the apparent real number permittivity change amount and the apparent imaginary permeability change amount of the absorbing wall of the present invention having a gap and a groove in relation to the gap and the groove depth. Here, the apparent real number dielectric constant and the apparent imaginary number magnetic permeability were calculated using the average thickness values obtained by averaging the irregularities of the test piece.

The gaps and groove depths on the horizontal axis were also organized by the value (%) divided by the average thickness.

In the figure, the value of Δμ ″ shows almost zero variation regardless of the presence or absence of a gap and a groove in the electric field direction. This is a feature of the present invention in which there is no gap or groove in the magnetic field direction, Due to the change in shape, the magnetic characteristics (μ ″) are not affected.

Regarding Δε ′, it decreases as the gap in the electric field direction and the groove depth increase, and the apparent real number dielectric constant is
It can be reduced to about 10% to 60%. As described above, this makes it possible to obtain a high μ ″ and a low ε ′ even at a high mixing ratio of the magnetic powder particles, and it becomes easy to obtain a good absorption condition in a wide frequency range.

That is, the geometrical features described in the present invention are as follows.
By combining with the features of the constituent components according to the present invention that can easily form gaps and grooves by casting or the like, TV waves are most effectively and economically absorbed.

1 and 2 show a schematic diagram of the present invention. In the figure, d ₁ , d ₂ and d are the thickness of the electromagnetic wave absorber.

On the back surface of the electromagnetic wave absorbing wall described in the present invention, a conductor called a short circuit plate is installed. This plate is an iron plate,
In addition to metal plates such as copper plates, wire mesh and reinforcing bars can be used instead. In the figure, 10: rebar, 11: radio wave absorption concrete panel, 12: groove, 13: surface layer (tile, mortar, rock, board) are shown.

Further, in FIG. 5 (a), the two-step thickness (d ₁ ,
For d _2), in FIG. 5 (b), 3 Dan'atsumi (d _1,
FIG. 5C shows the case of d ₂ , d ₃ ), and the case of 4 steps thickness (d ₁ , d ₂ , d ₃ , d ₄ ).

By forming the absorption wall with a plurality of thicknesses, the frequency band that can be absorbed can be broadened. Even if the depth of the groove is about 20% of the average thickness of the absorber, it is effective,
More preferably, it is 50% or more of the average thickness.

The ratio of grooves or gaps is 1/3 of the entire width.
It is desirable to be 3 times or more, and more desirably 1/2
It is desirable to be 2 times or less. The grooves and gaps in the direction of the electric field apparently reduce the real number dielectric constant and improve the absorption characteristics. 6 and 7 are explanatory views of another example of the present invention.

The required absorption wavelength in the present invention means 3.2 m for 1 channel (90 to 96 MHz) of TV channel and 4 channels (17 channels).
1.7m at 0 to 176MHz, 12ch (216 to 222MH)
z) 1.4m, 13ch (470-476MHz) 0.6m
With respect to the size of the absorption wall, by molding the length in the magnetic field direction to a size that is equal to or larger than the required absorption wavelength, it is possible to reduce the deterioration of the electromagnetic wave absorption performance due to the gap between the electromagnetic wave absorber and the electromagnetic wave absorber.

For example, if the area of the fourth floor or above of a 10-story building (assuming 1000 m ² ) causes radio interference, 10
If you attach cm square tiles to the entire surface, you will need to work for about 100,000 sheets. Moreover, if there is a gap of 1 mm between the electromagnetic wave absorber and the electromagnetic wave absorber in the magnetic field direction, the reflectance of radio waves (100 MHz) will increase about 33 times, and the absorption characteristics will drastically decrease. Countermeasure guidebook, July 6, 1981).

However, the electromagnetic wave absorption wall described in the present invention is
The length in the magnetic field direction is greater than or equal to the required absorption wavelength (for example, 3m x 1
By molding into m), the total number of attachments can be reduced to about 330 and the man-hours can be simplified to about 1/300, and the problem of gaps can be solved.

[0039]

EXAMPLE 1 An example of the characteristics of the radio wave absorption wall for the TV frequency band of the present invention will be shown. The compounding ratio of the molded product was 87.5% of Mn-Zn ferrite powder granules (about 7 times the weight of concrete) and the balance white Portland cement in dry weight ratio, and the measurement frequency was TV.
The frequency was changed from 90MHz to 770MHz, which corresponds to the entire radio wave.

As shown in FIG. 8, the radio wave absorption measurement value of the material of the present invention was 19.4 dB (100 MHz) at a thickness d ₁ = 27 mm and a thickness d ₂ = 43 mm, for example. This value is about 99.8% of the electromagnetic wave absorption amount (compared to 20 dB) of the currently used ferrite sintered tile material (thickness about 7 mm).
Absorb TV radio waves equivalent to.

Similarly, at 200 MHz and 600 MHz, it is possible to absorb radio waves of 17.4 dB and 14.5 dB, which correspond to 99.2% and 97.4% of the 20 dB converted value, respectively.

This value is sufficient even when compared with a sintered ferrite tile material in consideration of the mounting state (often a material that easily reflects radio waves such as windows, sash frames, balconies, etc. is exposed on the surface). It is considered to be the absorption characteristics that make it usable.

Here, 10 dB corresponds to absorbing 90% of the electric wave, and 20 dB corresponds to absorbing 99% of the electric wave.

However, the radio wave of the comparative material shown in FIG. 8 (1 step of the radio wave absorption wall having a thickness of 30 mm, which is composed mainly of Mn-Zn ferrite powder particles 87.5% by dry weight and the balance white Portland cement). Absorption measurement value is 100MH
15.1dB at z, 13.2dB at 200MHz, 600MHz
Is 7.3 dB, and the reflection amount of the comparative example with respect to the present invention example is 1
2.7 times at 00MHz, 2.6 times at 200MHz, 600MH
It is as large as 5.2 times z, and it appears as a clear difference especially on the high frequency side.

Example 2 Table 1 shows the blending ratio of the main raw materials in the dry weight ratio, the thicknesses d ₁ , d ₂ , d and the gap and groove width ratio (%), and the return loss (dB value). .

[0046]

[Table 1]

[0047]

[Table 2]

[0048]

EFFECTS OF THE INVENTION By using the radio wave absorbing wall of the present invention in place of the radio wave absorbing tile material (10 cm × 10 cm) which has been used conventionally, the shape is given freely and the construction process is simplified and mass produced. Is possible.

Conventionally, ε'is determined by the content of the magnetic powder particles, and μ'and μ "are determined depending on the compounding amount of the magnetic powder particles.
There is a drawback that both the value of and the electromagnetic wave absorption characteristics are almost determined. By changing the shape described in the present invention, ε'and the ferrite compounding ratio can be determined separately, and by setting a low apparent dielectric constant, good absorption characteristics can be obtained even in a wide frequency range.

[Brief description of drawings]

FIG. 1 is a perspective view of a TV frequency band electromagnetic wave absorber according to the present invention.

FIG. 2 is a perspective view showing another embodiment of the present invention.

FIG. 3 is a chart of μ ″ and ε ′ according to a change in the mixing ratio of magnetic powder particles.

FIG. 4 is a table showing changes in apparent imaginary permeability and changes in apparent real permittivity with changes in the gap or groove depth of the absorber of the present invention.

5 (a), (b), (c) are partial cross-sectional views of an example of the present invention.

6 (a), (b), (c) and (d) are partial cross-sectional views of another example of the present invention.

7 (e), (f), and (g) are partial cross-sectional views of another example of the present invention, similar to FIG.

FIG. 8 is a chart of a measurement example of a radio wave absorber.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (71) Applicant 000002886 Dainippon Ink and Chemicals, Inc. 3-35-58 Sakashita, Itabashi-ku, Tokyo (72) Inventor Takeshi Yamamoto 1618 Ida, Nakahara-ku, Kawasaki-shi, Kanagawa Shin-Nihon Steel Engineering Co., Ltd.

Claims (3)

[Claims] 1. A depth (d ₂ −) in the electric field direction of TV radio waves.
d ₁ ), and the thickness d ₁ of the concave portion of the molded body and the thickness d ₂ of the convex portion of the molded body are 0 <d ₁ ≦ 50 mm and d ₁ <d ₂ ≦
50 mm and 0.2 ≦ (d ₂ −d ₁ ) / d ₂ ≦ 1.0 were satisfied, and it was composed of the main components of cement 5 to 20% and magnetic powder granules 80 to 95% in dry weight ratio. The length of the TV radio wave in the magnetic field direction is equal to or longer than the required absorption wavelength.
Electromagnetic wave absorption wall for V frequency band. 2. A depth (dn _{+ 1-} d) in the electric field direction of TV radio waves.
_n ), the molded body thickness d _n and the molded body thickness d _{n + 1} (n = 1, 2, 3 ...) Are 0 <d _n ≦ 50 mm and d _n <d _{n + 1.} ≦ 50 mm, and 0.2 ≦ (d _n -d ₁₎
The electromagnetic wave absorption wall for TV frequency band according to claim 1, wherein / d _n ≦ 1.0 is satisfied. 3. The radio wave absorption wall for a TV frequency band according to claim 1, wherein there is a gap in the electric field direction of TV radio waves, and the thickness d of the molded body satisfies 10 ≦ d ≦ 50 mm.