JPH03203396A - Wave absorbing body for tv frequency band - Google Patents

Abstract

PURPOSE:To realize a wave absorbing body which can be formed easily and can absorb a wide band range of TV waves by setting the peak value of the imaginary part of the complex permeability of the body formed mainly of cement and a magnetic granular substance mixed with each other at a specific dry weight ratio to a level lower than the frequency band of TV waves. CONSTITUTION:The peak value of the imaginary part of the complex permeability of a formed body composed mainly of cement and a magnetic granular substance mixed with each other at a dry weight ratio of 10-25 : 75-90 is set to a level lower than the frequency band of TV waves. When the mixing ratio of the magnetic powder is increased, the imaginary part becomes higher and the ratio of the real component to the imaginary part becomes smaller. Accordingly, when the thickness and absorbing characteristics of this absorbing body is taken into account, the mixing ratio of the magnetic granular substance is adequate within the above mentioned range. Thus a wave absorbing body which can be formed easily and can absorb a wide band range of TV waves is obtained. In addition, the wave absorbing characteristics of this body can be finely adjusted by adding carbon fibers by 0.01-1.0%.

Description

Detailed Description of the Invention (Industrial Field of Application) The present invention provides a TV that uses cement and magnetic powder or cement, magnetic powder and carbon fiber as main raw materials.
This relates to radio wave absorbers for frequency bands.

(Prior art) TV radio waves have a working frequency of around 100 MHz and a wavelength of about 3 m, from 1 ch to 3 ch, and a 4 ch -1 working frequency of around 200 MHz and a wavelength of about 1.5 m.
Radio waves with different frequencies (wavelengths) of up to 8 times more are used, ranging from 13ch to 82ch, with frequencies in the vicinity of 2ch, 800MHz, and wavelengths of approximately 0.5m.

Therefore, the means to prevent false images (ghosts) by absorbing TV radio waves in a wide band with a wavelength difference of more than 2 meters using a radio wave absorbing material having a specific thickness is to use a radio wave absorbing material having a high frequency, that is, a short wavelength, for example, in the radar band ( 9, 4GHz, ripple 0
．． 3m) There are fewer types of radio wave absorbing materials available as a solution compared to countermeasures against false images.

There are two main solutions known at present: a method using sintered ferrite tiles and a method using pyramid-shaped block materials made of a carbon powder and expanded polystyrene composite.

However, the sintered ferrite tile material is too hot
Since the process of firing at such high temperatures is unavoidable, deformations such as uneven firing and warpage of tiles during firing occur. For the purpose of reducing the non-uniformity of the firing conditions, there is a restriction on the size of the tile shape, and the size is about 10 ca + 10 cm. This value is approximately 1/30 of the wavelength of 100MHz.
However, in order to obtain good absorption properties, there are many technical and especially economical problems in construction, so it is not widely used in general buildings.

In addition, in the case of pyramid-shaped block materials, the thickness of the currently known TV wave absorbing material is 1 to 2 meters, and there are many spatial problems when using it on the outer wall of a building, and when using it in an anechoic chamber etc. However, there is a problem that it occupies a large amount of space in the room.

Furthermore, molded products made by mixing concrete with carbon fiber carbon beads and steel fibers (Yasutaka Shimizu, EMC1983, 13, B (Ko 2, p. 86) are known. However, the reported value of the thickness of the molded product is 23. Since it is thick at .79C1l and the reported value of the absorption frequency band is around 100-200MHz, there is a problem that it is not possible to use all TV liquid wavenumber bands.Furthermore, the volume ratio of cement: ferrite: sand is reduced to 1. :
The value of transmission attenuation (unit: dB) for radio wave absorbing building materials with a ratio of 4:3 (of which ferrite weight is 66% of the total)
/cs) has been reported (Japanese Patent Application No. 47-113980
Publication No.). However, the above-mentioned publication does not mention the value of return loss (unit: dB), and the amount of radio waves directly reflected on the surface of the molded product is completely unknown.

(Issue S to be solved by the invention) The present invention overcomes the economical, geometrical, and spatial disadvantages of existing radio wave absorbers, is easy to install, and can be used for TVs that cover a wide band.
The purpose of the present invention is to provide a molded product that is capable of absorbing radio waves in the V wavenumber band.

(Means for Solving the Problems) The present invention provides that the peak value of the imaginary component of the complex magnetic permeability of a molded product whose main raw materials are cement 10 to 25% and magnetic powder granules 75 to 90% by dry weight is A radio wave absorber for the TV frequency band characterized by being below the TV radio wave frequency band, or a dry weight ratio of cement 10 to 25% and magnetic powder and granules 75 to 75%.
TV
The gist of the present invention is a radio wave absorber for the TV frequency band, which is characterized by being below the radio wave frequency band, and more preferably, in the radio wave absorber for the TV frequency band, the dry weight ratio of cement is 10 to 17%, Magnetic powder 83-90
% as the main raw materials, or the main raw materials are 10 to 17% cement, 83 to 90% magnetic powder, carbon fiber 〇, and 1% Ol to 1% by dry weight. . Incidentally, the magnetic powder is preferably Mn-based ferrite.

(for production) The present invention will be explained in detail below.

The cement referred to in the present invention refers to hydraulic cement (for example,
Portland cement, white Portland cement, alumina cement, pozzolanic cement, truss cement,
Santorin cement, lime slag cement, pozzolana portland cement, silica cement, tras portland cement, blast furnace cement, iron portland cement, fly ash cement, solidite cement, shale ash portland cement), air hard cement (magnesia cement), special cement (Fire-resistant cement, acid-resistant cement, water glass cement, high sulfate slag cement) and other cements that are generally called cements are not particularly limited.

The blending ratio is in the range of 1 ovt% or more to 2 hlt% or less of the total dry weight ratio, and in the range of 10vt% or less, the molded product will not coagulate, and if it exceeds 25vt%, the radio wave Its original function as an absorbent is inferior.

Magnetic particles include oxidized magnetic materials and metal magnetic materials, such as (FeO-Fe203゜7-Fe2O3, Mn
0-Fe2O,, Mn0-ZnO-Fe20s+ Cu
O-ZnO-Fe2 o:l.

CuO-Mn0-Fe2O,, N1O-ZnO-Fe2
0. , N1O-CuO-ZnO-Fe20. .

MgO-Fe20B, MgO-ZnO-Fe303゜M
gO-Mn0-Fe2O, Li0-ZnO-Fe2O
There are oxide magnetic materials such as , etc., and metal magnetic materials such as iron powder, silicon steel powder, permalloy powder, and sendust powder. Of these, if limited to oxide magnetic materials, trace elements (e.g. CaO, 5i02, etc.) are added to them before firing for the purpose of improving magnetic properties, promoting sintering reaction, controlling intracrystalline/grain boundary resistance, etc. It is desirable to add. Furthermore, Mn-based ferrites such as Mn-Zn and Mn-Mg systems are magnetic materials that are relatively easy to obtain, are available in large quantities at low prices, and have excellent absorption properties. Appropriate.

There are no particular regulations regarding the size or particle size distribution of the magnetic powder particles, but because the magnetic powder particles of the present invention have a considerably large amount of crosstalk with cement, ease of molding is used as a guideline for the particle size size. It is considered appropriate to do so.

Regarding the particle system distribution of powder and granules, for example, the sieve distribution curve by Fuller and Thorpson, the Grain distribution curve, etc.
German standard for fine aggregate proposed by f' (D I N104
5) may be referred to, and it is not necessary to completely satisfy the values proposed by the above proponent. The blending range of the magnetic powder will be described later.

Carbon fiber is a general term for rayon-based, acrylonitrile-based, lignin/poval-based, pitch-based, and tar-based materials, and by mixing one or more types into concrete, the radio wave absorption characteristics of molded products can be finely adjusted. . The blending ratio Y is 0 or 010
1≦Y≦1, and kneading a large amount of carbon fiber exceeding 1 wt% is not only technically difficult, but also
In particular, in the present invention, where the blending ratio of magnetic particles is high, this is rather undesirable. Further, if fine adjustment is not required, there is no need to mix it.

Regarding the shape of carbon fiber, curled or straight long fibers or short fibers may be used.
To put it bluntly, a short fiber shape is preferable for ease of cross-crossing and dispersion.

In the present invention, the materials mentioned above, namely cement, magnetic powder, or cement, magnetic powder, and carbon fiber, are referred to as main raw materials in the present invention. materials, setting/hardening accelerators, waterproofing materials, antifreezing materials, foaming materials, coloring materials, mixed materials, fire resistance accelerators, etc.) are added as appropriate.

FIG. 1 shows a schematic diagram of the invention. A conductor called a shorting plate is installed on the back side of the radio wave absorber. This plate can be replaced by a metal plate such as an iron plate or a copper plate, as well as a wire mesh, reinforcing steel, etc., and has the function of reducing the thickness of the radio wave absorbing material described in the present invention.

The mixing ratio of the main raw materials is cement 10vt% by dry weight.
or more and 25vt% or less, magnetic powder or granules from 75vt% or more to 90vt%, or cement 10wt% or more and 25vt% or less, magnetic powder or granules from 75wt% or more to 90wt% or less, carbon fiber〇, 01vt%
The range is from 1 wt % or more to 1 wt % or less.

The reason for increasing the blending ratio of magnetic powder and granules is as follows.
The purpose is to increase the imaginary component μ of magnetic permeability (marked 0 in Figure 2) and to reduce the value of the real component μ' (marked in Figure 2)/μ' (marked O in Figure 2) of magnetic permeability. For details on the radio wave absorption mechanism, see Yoshiyuki Naito: Radio Wave Absorber, Ohmsha (1
987) As it is described on page 8B, I will not omit it here, but if you want to reduce the thickness of a radio wave absorbing material with a conductor called a shorting plate installed on the back side, you should increase μ' and improve the absorption characteristics. If you want to do so, it is better to reduce the value of μ'/μ''. In other words, as shown in Figure 2 (C) and (d)
The frequencies (resonant frequencies) near the mark (the peak value of the imaginary component of complex magnetic permeability) shown in , and the frequencies higher than the vicinity of the mark satisfy the above conditions, and as a result of careful consideration of the blending conditions of the main raw materials, magnetic powder and granules are The blending amount is 75% or more or 90% by dry weight
It has been discovered that a range of % or less is appropriate as a radio wave absorber for the TV frequency band.

Carbon fiber is added as appropriate to compensate for the lack of radio wave loss caused by magnetic powder, and as shown in Figure 5, it is added at 0% or 0.01wt%.
A small amount addition range of ~lvt% is preferable.

Since the radio wave absorbing material of the present invention can be easily produced into a large-sized molded product, it is possible to reduce the reduction in radio wave absorption performance due to gaps between panels. For example, if the area above the 4th floor of a 10-story building (assumed to be 1000R) causes radio wave interference, installing 10A++ square tiles with a porosity of 33% will require work for approximately 67,000 tiles. . Moreover, if there is a gap of 1 mm between panels, radio waves (10
0 MHz) increases by about 33 times, and the absorption characteristics drastically decrease (edited by Japan Broadcasting Corporation; Guidebook for countermeasures against radio wave interference by radio wave absorbers, July 1980, p. 6).

However, if the radio wave absorber described in the present invention is
By making the bottom shape 1 m in size, the installation can be simplified to about 330 pieces and the man-hours to about 1/200, and the problem of gaps can be solved.

(Example) The present invention will be explained below according to examples.

Example 1 A molded product with a thickness of 5 mm and an inner diameter of 18.9 mm and an outer diameter of 38.8 N.
After cutting with an ultrasonic processing machine, the cylindrical cut sample was placed in a 39D pongee tube, and a 100M sample was cut with a network analyzer.
The real (μ') and imaginary (μ'') magnetic permeabilities were measured from Hz to 800 MHz.

The blending ratio in terms of dry weight ratio of the molded product used for measurement is:
Mn-Zn ferrite powder 4 (1wt% (2/3 times the cement weight ratio) to 90vt% (9% of the cement weight ratio)
), and the remainder was white Portland cement.

In Fig. 2 (a) to (d), the frequency indicated by the square mark is
Indicates the resonance frequency of each molded product, for example, magnetic powder 75
The resonant frequency of the vt% molded product is 350MHz and 8
The resonance frequency of the 7.5vt% molded product is 18[)M)Iz.

However, as shown in Figures 2(a) and (b),
The imaginary magnetic permeability μ' (line) of molded products with a magnetic powder blending ratio of 40 wt% or 80 wt% only increases gradually with increasing frequency, and no clear resonance phenomenon is observed.

This applies to the TV frequency band (100MHz to 770M
Hz), it can be said that this shows that there is a minimum effective amount of magnetic powder and granules mixed as a condition for generating resonance loss (absorption) of radio waves.

Figure 3 shows the relationship between the blending ratio of magnetic powder and the resonance frequency. In the observed TV frequency band, the range where the resonance phenomenon was observed was when the concrete:magnetic powder weight ratio was 1. : Range from 3 to 9, especially 1:
In the range from 5 to 1:9, resonance was observed even at low frequencies corresponding to the VHF band. Although the value of the resonance frequency is not a measure that represents all of the radio wave absorption characteristics, at least the blending conditions of the magnetic powder to efficiently absorb TV radio waves are preferably in the range of 75 wt% or more and 90 wt% or less. More preferably, it is 83vt% or more and 90vt% or less.

Example 2 FIG. 4 shows the radio wave absorption characteristic values of the product of the present invention and the comparative product in the TV frequency band. Note that the return loss is '
These are the measurement results of a network analyzer in which a sample was placed in an 89D coaxial tube.

In the figure, the mixing conditions for radio wave absorbers are as follows from the top: Mn-
Zn ferrite 40. Ovt%, 80. Ovt%, 75. Owt%, 87 Jvt%, and other compounds are carbon fiber (straight/single fiber) 0.2
5vt% was constant, and the remainder was white Portland cement.

Focusing on 100MHz, which corresponds to channels 1 to 3 of TV radio waves, if the magnetic powder is dilute, as shown in the previous example, there is no effective absorption of radio waves;
At 0.0 wt%, [1.7 dB (absorption rate 14.8
%) and 1.6 dB (absorption rate 30.8%) at 60.0 wt%. However, the same thickness (25m)
Also, for example, magnetic powder 75. The return loss at Ovt% is 10.2 dB (absorption rate 90.5%), and the same attenuation at 87.5% magnetic powder is 1.
It was 8.4 dB (absorption rate 97.7%). These values are approximately 91.4% and 98.7% of the currently used ferrite sintered tile materials (approximately 7 mem thick).
(However, the radio wave absorption of ferrite sintered tile material is 20 dB (99% absorption)
).

Note that the hatched portions in FIG. 4 indicate frequency bands corresponding to VHF and UHF.

Example 3 Next, an example will be shown in which excessive blending of carbon fiber actually worsens the radio wave absorption characteristics.

In Figure 5, the top shows the Mn-Zn ferrite blending amount of 75
．． 0wt%, and the lower one is the same blending amount of 90. The relationship between the return loss at 100 MHz and the amount of carbon fiber blended in Owt% radio wave absorber is shown. 20.25°3 in the diagram
Each number at 0 represents the thickness of the radio wave absorber.

In the figure, the appropriate carbon fiber content of the radio wave absorber of the present invention exhibiting an absorption rate of 90% (10 dB) or more is Oν
It is in the range of 1.0 wt% from t%. Among these, for example, magnetic powder 75. The optimum amount of carbon fiber for a magnetic powder of 90 vt% and a thickness of 20 mm is 0.4 wt%. However, the addition of excess carbon fiber above the above does not necessarily improve the absorption properties.

Example 4 Table 1 shows the blending ratio of the main raw materials in terms of dry weight ratio, as well as the dependence of thickness and return loss (dB value) on each frequency. The measurement conditions and sample cutting conditions are as in Example 1.
The same conditions as in Example 2 were also applied.

In this example (Table 1), in addition to the products of the present invention (A-N), C0-Z> are shown as comparative products.

Inadequate blending of magnetic powder and excessive addition of carbon fiber do not necessarily result in satisfactory radio wave absorption characteristics.
There is also no specific absorbent thickness.

In the table, samples (I-N) were prepared with the blending ratio of magnetic powder in the range of 83% (approximately 5 times the weight of cement) to 90% (approximately 9 times the weight of cement).
A concrete molded product capable of absorbing radio waves in the TV band even at a thickness of around 20 m+s was obtained.

(Effect of the invention) By molding the radio wave absorber of the present invention into a panel material,
It allows freedom of shape and simplifies the construction process. Furthermore, since it is possible to mass produce the panels as panel materials, the economical benefits of the present invention are great compared to conventional radio wave absorbing tile materials (approximately 10 squares) ε.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of the radio wave absorber for the TV frequency band according to the present invention, and FIGS. 2(a), (b), (e), and (d) show the magnetic properties of complex magnetic permeability from 100 MHz to 600 MHz. FIG. 3 is a diagram showing the dependence on the blended amount of powder and granules (the solid line portion corresponds to the real component of the complex magnetic permeability, and the dashed line portion corresponds to the imaginary component of the complex magnetic permeability). FIG. 4 is a diagram showing the influence of the blending ratio of cement and magnetic powder, and FIG. The figure is a diagram showing the return loss (100 MHz) of the radio wave absorbing material of the present invention in carbon fiber blends j10 to 1 and Ovt%. In the case of cement, there are porcelain particles, five (Ucement, porcelain materials) (; carbon fiber Fig. 2 f (SHE) f (MHz) (a) (b) ( C) (d) /DO2003004120500600j (MHz) 0 (!1 Particulate matter blending ratio (wt%) 50 70 60 δ590 -l l'l f・2 f:3 /:J f:5 j:6 1nia f:lJ
f・9 f:j0 Cement: Soya powder grain scoop (compound weight ratio) CF (wt%)

Claims (5)

[Claims] (1) The peak value of the imaginary component of the complex magnetic permeability of a molded product whose main raw materials are 10 to 25% cement and 75 to 90% magnetic powder by dry weight is below the TV radio wave frequency band. Radio wave absorber for TV frequency band. (2) The peak value of the imaginary component of the complex magnetic permeability of a molded product whose main raw materials are 10 to 25% cement, 75 to 90% magnetic powder, and 0.01 to 1% carbon fiber in dry weight ratio is:
A radio wave absorbing material for a TV frequency band, characterized in that it is below a TV radio wave frequency band. (3) The peak value of the imaginary component of the complex magnetic permeability of the molded product whose main raw materials are 10 to 17% of cement and 83 to 90% of magnetic powder and granules in dry weight ratio is below the TV radio wave frequency band. Radio wave absorber for TV frequency band. (4) The peak value of the imaginary component of the complex magnetic permeability of a molded product whose main raw materials are 10 to 17% cement, 83 to 90% magnetic powder, and 0.01 to 1% carbon fiber in dry weight ratio is:
A radio wave absorbing material for a TV frequency band, characterized in that it is below a TV radio wave frequency band. (5) Claim (
1), (2), (3) or (4) radio wave absorber for TV frequency band.