JPH088429B2 - Radio wave absorption method - Google Patents

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION The present invention uses a radio wave absorber which is a carbon fiber-containing composition formed by containing carbon fibers.
The present invention relates to a method of efficiently absorbing TV radio waves and radio waves.

[0002]

2. Description of the Related Art Various structures such as high-rise buildings, transmission line towers, bridges, Shinkansen, highways, golf driving ranges, aircraft, etc. shield and reflect high-quality TV and radio waves, and spread over large areas. Are known to cause ghost disorders.

Conventionally, in order to prevent such ghost damage, for example, as disclosed in Japanese Patent Laid-Open Nos. 58-108603 and 58-108602, ordinary concrete, mortar and lightweight concrete are disclosed. It is known to use a radio wave absorber formed by containing carbon fiber in such concrete.

[0004]

However, in the conventional electromagnetic wave absorber, in order to improve the electromagnetic wave absorption efficiency, it is necessary to increase the carbon fiber content or to thicken the electromagnetic wave absorber. It was

The complex permittivity ε of the dielectric is expressed by the following equation. [epsilon] = [epsilon] '-j [epsilon] "In the above equation, the real number part [epsilon]' indicates the normal permittivity, and the imaginary part [epsilon]" indicates the loss rate.

The real part ε'is plotted on the abscissa and the imaginary part ε "is plotted on the ordinate, and the relational value D (= D) between the thickness d of the sample and the wavelength λ _{0 of} the radio wave incident on the sample. d / λ
It is known that the result shown in the graph of FIG. 3 can be obtained when the characteristic curve under the non-reflection condition in ( ₀ ) is obtained.
Numerical values in FIG. 3 are values of D.

[0007] For example, 2 ch television radio waves (assigned frequency: 96 to 102 MHz, video carrier frequency 97.25 M
Hz, audio carrier frequency 101.75 MHz) with a thickness of 1
Considering the case of non-reflective absorption on a 0 cm wall surface, the wavelength λ ₀ of the radio wave for video transmission, which is a long wavelength, is λ ₀ = (3 × 10 ¹⁰ ) ÷ (97.25 × 10 ⁶ ) ≈308 .48 cm, the relation value D becomes D = 10 / 308.48 ≈0.032, and the values of the real part ε ′ and the imaginary part ε ″ when this relation value D is satisfied are ε′≈61 ε ″. ≈10.

Further, when the thickness of the sample is set to 5 cm, D≈0.016, which means that the real part ε'needs to be larger.

However, the conventional radio wave absorber containing carbon fibers has a drawback that it is difficult to obtain such a large real part ε ', and therefore the radio wave absorber does not have a sufficient radio wave absorption capability.

Therefore, Japanese Patent Laid-Open No. 58-188193
As disclosed in
The absorber is composed of aver and each absorber is
In which the fibers are aligned in a certain direction, and
Absorber so that the fiber orientation direction of each layer is different from each other
Is laminated, and one absorber is effective in the direction of the radio wave
Even if it does not work, the other absorber works effectively
Regardless of the attachment direction of the body, as a whole,
A radio wave absorber designed to have uniform radio wave absorption characteristics
However, since the absorber is laminated, the thickness is large.
There was a drawback that became.

The radio wave absorption method of the present invention has been made in view of such circumstances, and the radio wave is absorbed even when a carbon fiber-containing composition having a small thickness and a low carbon fiber content is used. The purpose is to be able to absorb enough.

[0012]

In order to achieve the above-mentioned object, the electromagnetic wave absorption method of the present invention attempts to absorb the electromagnetic waves.
Irradiating radio waves in any direction of the carbon fiber-containing composition
When the real part of the complex dielectric constant of the carbon fiber-containing composition is
Let ε ', the imaginary part be ε ″, and their maximum and minimum values
Where ε _max ′, ε _min ′, ε _max ″, ε _min ″
And the degree of orientation A of the carbon fiber is ε _max '− ε _min ',
When the orientation degree B is defined by ε _max ″ −ε _min ″,
Orientation A of carbon fiber is 25 or more and / or orientation
Orient the carbon fiber in a specific direction so that the degree B is 5 or more.
Using the carbon fiber-containing composition contained as
Align the orientation direction with the electric field direction of the radio wave to be absorbed.
The carbon fiber-containing composition is arranged so that the carbon fiber
It is characterized by absorbing radio waves by a fiber-containing composition .

Attempts to absorb the orientation direction of the contained carbon fibers
That radio waves Rutowa to match the electric field direction, be arranged to match the full electric field direction orientation direction <br/> direction of the carbon fibers is of course a, the radio wave to be absorbed in the carbon fiber-containing composition Let ε ′ be the real part and ε ″ be the real part and the imaginary part of the complex permittivity of the carbon fiber-containing composition when irradiated in an arbitrary direction, and the maximum and minimum values thereof are ε _max ′, ε _min ′, ε
_max ″, ε _min ″, ε ′ ≧ ε _min ′ + (ε _max ′ −ε _min ′) × 0.5 and / or ε ″ ≧ ε _min ″ + (ε _max ″ −ε _min ″ ) × 0.5. Degree of orientation is A = ε _max '−ε _min ', B = ε _max ″
−ε _min ”.

More specifically, as shown in the side view for explaining the degree of orientation of FIG. 4, a test body of the carbon fiber-containing composition is cut along an arbitrary plane, and the cut surface passes through the center O. When two axes orthogonal to each other are XX ′ and YY ′,
Cut line P-P 'passing through the center O with XX' as a reference line
And the angle of intersection is θ, and the real part ε ′ of the complex permittivity that becomes maximum when the angle of intersection θ is changed in the range of 0 ° to 180 °.
And imaginary part ε ″ are respectively defined as ε _max ', ε _max ″,
The real part of the smallest complex dielectric constant epsilon 'and imaginary part epsilon "respectively ε _min', ε _min" as, (ε _max '
−ε _min ') is the orientation degree A, (ε _max ″ −
ε _min ″) is the orientation degree B (measurement of ε ′ and ε ″ is performed by applying an electric field parallel to the cut line PP ′).

When the carbon fibers are oriented at random, ε _max '= ε _min ', ε _max ″ =
Since ε _min ″, A = 0 and B = 0. The larger A and B are, the more oriented the carbon fiber-containing composition is.
When <25 and B <5, the degree of orientation is small, and it is necessary to increase the carbon fiber content and mix a large amount of carbon fibers, or to increase the thickness of the absorber.

As the carbon fiber, various carbon fibers such as rayon type, polyacrylonitrile (PAN) type, phenol resin type, coal pitch type and petroleum pitch type can be used, and the fiber diameter is usually about 2 to 30 μm. The average fiber length is about 0.1-10 mm, preferably 0.2-when the matrix is mortar or concrete.
It is preferable to use 0.8 mm, and in the case of resin, about 0.2 to 5 mm.

The length of the carbon fiber as referred to herein is not the length of the carbon fiber to be added when producing the carbon fiber-containing composition, but the value in the state of being present in the carbon fiber-containing composition. The longer the length of the carbon fiber is, the more preferable it is, but when producing the carbon fiber-containing composition, in particular, the mortar- or concrete-made carbon fiber-containing composition, because the carbon fiber is cut by the mixing during the production, and, From the viewpoint of workability, it is difficult to obtain a product having a length exceeding 10 mm.
On the other hand, if the carbon fiber content is less than 0.1 mm, the absolute values of both the real part ε ′ and the imaginary part ε ″ of the complex permittivity ε do not increase (ε′≈10, ε ″ ≈ even if the carbon fiber content is increased.
It is only about 1-2).

The base material constituting the electromagnetic wave absorber is mortar composed of cement, fine aggregate, admixture and water, or a hydraulic composition such as concrete in which coarse aggregate is mixed with mortar, gypsum, epoxy. Resins such as resins, ceramics, and rubber can be applied.

The carbon fiber content is preferably 0.5 to 10% by weight based on the hydraulic component (eg cement) in the hydraulic composition (eg mortar). If it is less than 0.5% by weight, matching conditions for radio waves are difficult,
On the other hand, if it exceeds 10% by weight, it becomes difficult to uniformly disperse the carbon fibers in the matrix.

When the carbon fiber is contained in the resin, the carbon fiber content of the resin is preferably 5 to 25% by weight. If it is less than 5% by weight, the matching condition for radio waves is difficult, while if it exceeds 25% by weight, it is difficult to uniformly disperse the carbon fibers in the matrix.

[0021]

According to the configuration of the radio wave absorption method of the present invention, the radio wave to be absorbed can be applied to either horizontal polarization or vertical polarization. For example, in the case of horizontally polarized radio waves, the direction of the electric field generated by it is horizontal, so that the aligned carbon fibers should be oriented in the horizontal direction that intersects the traveling direction of the radio waves. Is composed of the electromagnetic wave absorber itself, or the electromagnetic wave absorber is attached to various structures. By doing this, with respect to the electric field direction of the radio wave,
The permittivity increases, and matching is achieved where the value of D in FIG. 3 is small, and as a result, it is possible to absorb radio waves with a thin radio wave absorber that has never existed before.

[0022]

EXAMPLES Examples of the present invention will be described in detail below.

<First Example> Ordinary Portland cement, silica sand No. 6 as fine aggregate, methyl cellulose as an admixture, water, and a fiber diameter of 13 μm and an average fiber length of 3 mm, 6 mm and 8 mm. Carbon fibers (S-231, S-232, S-233: all manufactured by Donac Co., Ltd.) were mixed in the proportions shown in Table 1 to prepare a radio wave absorber test body using mortar as a base material.

[Table 1]

As a procedure for producing, first, ordinary Portland cement, methyl cellulose and carbon fiber were mixed in a volume of 5
Preliminary kneading was performed for 60 seconds with a liter omni mixer, water was then added and kneading for 120 seconds, after which silica sand No. 6 was added and kneading for 60 seconds to prepare a carbon fiber-containing mortar.

The mortar thus obtained was mixed with 40 × 40
In the mold of size × 160, the carbon fibers are placed by hand while aligning them so that the longitudinal direction of the carbon fibers faces the longitudinal direction of the mold.
After curing at 80 ° C in a constant temperature and humidity atmosphere of 80% for 1 day and then removing from the mold, the cured product is then cured in a constant temperature water tank at 20 ° C, and then removed from the constant temperature water tank, and then at 20 ° C.
It was cured for 1 day under a constant temperature and humidity atmosphere of 60%.

As shown in the perspective view of FIG. 1, the cured product 1 thus obtained is cut along the transverse cutting lines X1, X2, X3, X4, X.
5 and the vertical cutting lines Y1 and Y2, the size of which is located on the central side of the mold is about 40 × 40 × 10
As shown in the perspective view of FIG. 2 (a), the vertical type test specimens A1 and A2 for measurement in which the longitudinal direction of the carbon fibers are aligned so as to face the thickness direction, and FIG. As shown in the perspective view of 2 (b), horizontal type test specimens B1 and B2 for measurement were obtained in which the longitudinal direction of the carbon fibers was aligned in the direction orthogonal to the thickness direction.

Specimens A1, A2, B for each of these measurements
After roughly scraping each of 1 and B2 with a paper file of A60 so as to have a thickness of 10 mm, finishing is performed with a paper file of A200 so that the facing surfaces are parallel to each other.

Prior to the measurement of the capacitance Cp and the electric conductivity value G, on the day before the measurement, the product was forcedly dried at 100 ° C. for 7 hours by a dryer, and after the forced drying, it was vacuum-cooled by a desiccator and completely cooled to room temperature. Then, each lot was placed in a polyethylene bag with a zipper containing a desiccant (silica gel) so as not to absorb moisture.

Then, each test body A1, A2, B1, B2
As shown in the schematic configuration diagram of the measuring device of FIG. 5, each of them is sandwiched between the copper plates 3 and 3 for electrodes of an impedance analyzer (4191A: Yokogawa Hewlett-Packard Co.) 2 and an electrostatic field is applied in the thickness direction. The capacitance Cp and the conductivity value G are measured, and based on the measured capacitance Cp and the conductivity value G, the value ε ′ of the real part and the value ε ″ of the imaginary part of the complex permittivity (relative permittivity). I asked each one.

That is, the capacitance Cp and the value ε'of the real part
The following relational expression Cp = ε ₀ · ε ′ · S / d ε ′ = Cp · d / (ε ₀ · S) holds between and. Here, ε ₀ is a dielectric constant in a vacuum of 8.8.
54 × 10 ⁻¹² , and S is the area of the specimen,
d is the thickness of the test body, and the value ε'of the real part can be obtained by obtaining the capacitance Cp.

Between the conductivity value G and the value ε ″ of the imaginary part, the following relational expression G = σ · S / d σ = G · d / S ε ″ = σ / (ε ₀ · ω) = Σ / (ε ₀ · 2πf) = G · d / (S · ε ₀ · 2πf) holds. Here, σ is the conductivity, ε ₀ is the dielectric constant in a vacuum of 8.854 × 10 ⁻¹² , S is the area of the test body, d is the thickness of the test body, and f is It is the frequency of the known radio wave to be absorbed, and the value ε ″ of the imaginary part can be obtained by obtaining the conductivity value G.

Thus, the chopped carbon fibers having an average fiber length of 3 mm have a content of 1% by weight, 2% by weight, 3% by weight, 4% by weight with respect to the mortar as shown in the above table. %, 5% by weight, and
Longitudinal type test bodies A1 and A2 prepared by the same manner as those containing carbon fibers and those not containing carbon fibers
When the frequency of the radio wave is fixed to 100 MHz and the value ε ′ of the real part and the value ε ″ of the imaginary part of the complex permittivity (relative permittivity) are obtained for each of the horizontal type test bodies B1 and B2, The results shown in each of Table 2 and the graph of Fig. 6 were obtained.Because the fibers were cut during mixing, the average fiber length of the carbon fibers in the sample was about 0.2 to 0.8 mm. The higher the content (% by weight) of carbon fiber is, the shorter the carbon fiber is cut, which is considered to be because the higher the content of carbon fiber is, the higher the viscosity is and the more easily it is sheared.

[Table 2]

Also, for a chopped carbon fiber having an average fiber length of 6 mm, the real part ε ′ and the imaginary part ε ″ of the complex permittivity (relative permittivity) were obtained in the same manner. The results shown in Table 3 and the graph of Fig. 7 were obtained, and the average fiber length of the carbon fibers in the sample was about 0.
It is 6 to 1.0 mm.

[Table 3]

The relationship between the average fiber length (mm) of residual fibers and the carbon fiber content (% by weight) when the mortar was prepared by containing chopped carbon fibers having an average fiber length of 6 mm was measured. Then, the results shown in the graph of FIG. 8 were obtained.

The carbon fiber content here is indicated by the weight ratio with respect to the cement, and when the aggregate and the like are included, the content rate becomes about half.

In the above results, the higher the carbon fiber content, the shorter the average fiber length of the residual fibers. The higher the carbon fiber content, the higher the viscosity and shear force. This is because the carbon fibers are cut.

Further, carbon fibers having an average fiber length of 3 mm (about 0.9 mm in the sample) were contained at a content of 2% by weight with respect to the mortar, and they were extruded by a single screw type vacuum extruder. However, a vertical type test body in which the longitudinal direction of the carbon fibers is aligned in the thickness direction and a horizontal type test body in which the longitudinal direction of the carbon fibers are aligned in a direction orthogonal to the thickness direction 9 and FIG. 10 are obtained by calculating the relations between the radio frequency and the real part value ε ′ of the complex permittivity (relative permittivity) and the imaginary part value ε ″ of The results shown in the graph are obtained.

From the above results, the following is clear. The vertical type test bodies A1 and A2 in which the longitudinal directions of the carbon fibers are aligned in the thickness direction are horizontal types in which the longitudinal directions of the carbon fibers are aligned in the direction orthogonal to the thickness direction. The value ε'of the real part of the complex permittivity (relative permittivity) can be made larger than those of the test bodies B1 and B2.

As can be seen from FIGS. 6 and 7, when the carbon fiber length is 3 mm, the content ε ′ of the real part of the complex permittivity (relative permittivity) becomes large when the content is 4% by weight. When the carbon fiber length is 6 mm, the value ε'in the real part of the complex permittivity (relative permittivity) becomes large even when the content rate is 2% by weight, and when the long carbon fiber content is included, the content rate is At least, it can absorb radio waves well.

By using a vacuum extrusion molding machine, the orientation of the carbon fibers can be naturally aligned in a specific direction (extrusion direction) better than when aligned by hand, and workability can be improved.

With the above configuration, for example, in the case of horizontal polarization, as shown in the perspective view of FIG.
The outer wall T of the building on the side located in the incident direction of the radio wave W is made of the mortar obtained as described above or the concrete in which coarse aggregate is added to the carbon fiber
(Shown by) are aligned so that they are oriented in the horizontal direction along the wall surface direction, and ghost obstacles can be prevented.

More specifically, as shown in the operation explanatory view of FIG. 12, a voltage is induced in the carbon fiber by the electric field E generated by the incidence of the radio wave W to absorb the radio wave W. At this time, if the incident direction of the radio wave W is inclined at a predetermined angle θ with respect to the outer wall T of the building, the electric field component becomes Ecos θ, but by absorbing only the radio wave W by that amount, there is a ghost obstacle prevention effect. .

In the case of targeting vertically polarized waves, the building outer wall T may be constructed in a state where the carbon fibers are oriented in the vertical direction along the wall surface direction.

<Second Embodiment> A carbon fiber having a fiber diameter of 13 μm and an average fiber length of 0.70 mm (S-244: manufactured by Donac Co., Ltd.) was dried, and the dried carbon fiber was roughly as shown in FIG. As shown in the configuration diagram, a liquid epoxy resin (Epicoat 827: manufactured by Yuka Shell Co., Ltd.) as a main component, which is stored in the mixing tank 4, is mixed and stirred.

Next, after degassing by evacuation, the epoxy resin liquid mixed with carbon fibers is cooled, and a curing agent (HARDNER H4510: manufactured by ACR Co., Ltd.) as an auxiliary agent is added to 50 weight% of the main agent. %, Mixed and stirred, and suctioned by a vacuum pump 6 using a cylindrical mold 5 having a diameter of 40 mm and a height of 300 mm, and after completion of the suction, the cylindrical mold 5
The lower opening of the is closed with a rubber stopper 7, then taken out, put in a water tank for 24 hours, cooled to room temperature, and then released from the mold.

After that, it is heated and dried at 80 ° C. by a drier, cut so that the longitudinal direction of the carbon fibers is 10 mm in thickness and 40 mm in diameter, and the longitudinal direction of the carbon fibers is aligned in a specific direction. A vertical type test body A3 aligned so as to face each other and a horizontal type test body B3 aligned so that the longitudinal direction of the carbon fibers were oriented in a direction orthogonal to the thickness direction were obtained. It was confirmed by dissolving the sample in a solvent and measuring that the length of the carbon fiber in the sample was almost the same as the value before mixing because the sample was not mixed.

Then, the carbon fiber contents were set to 5% by weight, 10% by weight and 15% by weight with respect to the total weight of the main agent, the auxiliary agent and the carbon fiber, respectively, and both the test bodies A3 and B3 were subjected to the above-mentioned first embodiment. Similar to the example, an impedance analyzer (4191A: manufactured by Yokogawa Hewlett-Packard Co.) 2 was used (see FIG. 5) and sandwiched between the electrode copper plates 3 and 3 to measure the capacitance Cp and the conductivity value G, and The value ε ′ of the real part of the complex permittivity (relative permittivity) was calculated based on the measured capacitance Cp and the conductivity value G, and FIG.
The results shown in the graph are obtained.

As a result, in the vertical type test body A3, the value ε'of the real part can be made extremely large as compared with the horizontal type test body B3, and the value increases in proportion to the carbon fiber content. It was clear that it could be done.

<Third Embodiment> A carbon fiber having a fiber diameter of 13 μm and an average fiber length of 0.60 mm was dried, and the dried carbon fiber was treated with an epoxy resin (Epicoat) in the same manner as in the second embodiment. 827: manufactured by Yuka Shell Co., Ltd.) is used as a matrix to obtain a carbon fiber-containing composition, which is cut so that the longitudinal directions of the carbon fibers are aligned in a specific direction, and as shown in FIG. Specimens C of the type in which the
1 and a test body C2 of a type in which the longitudinal direction of the carbon fibers is aligned in a direction inclined by 30 ° with respect to the thickness direction,
A test body C3 of a type in which the longitudinal direction of the carbon fibers is oriented in a direction inclined by 60 ° with respect to the thickness direction, and a test of a type in which the longitudinal direction of the carbon fibers is oriented in a direction orthogonal to the thickness direction. Got body C4. It was confirmed by dissolving the sample in a solvent and measuring that the length of the carbon fiber in the sample was almost the same as the value before mixing because the sample was not mixed.

Then, the carbon fiber content was set to 10% by weight based on the total weight of the main agent, the auxiliary agent, and the carbon fiber, and each of the test bodies C1, C2, C3 and C4 was used, and the measurement frequency was set to 9
At 2.75 MHz, the angle of the electric field direction (in FIG. 15, E is attached with a vector display symbol) with respect to the longitudinal direction of the carbon fiber is 0 °, ± 30 °, ± 60 °, ±
As in the first embodiment, an impedance analyzer (4191A: Yokogawa Hewlett-Packard Co., Ltd.) 2 was used so as to be 90 ° (see FIG. 5), and was sandwiched between the electrode copper plates 3 and 3, and electrostatic The capacitance Cp and the conductivity value G are measured,
Based on the measured capacitance Cp and the conductivity value G,
When the value ε ′ of the real part and the value ε ″ of the imaginary part of the complex permittivity were obtained, the results shown in Table 4 and the graph of FIG. 15 were obtained.

[Table 4]

From these results, it can be seen that both the real part ε ′ and the imaginary part ε ″ of the complex permittivity become higher as the carbon fibers are arranged in the electric field direction of the radio wave to be absorbed. It was clear that it could be done.

The electromagnetic wave absorber made of resin as a base material obtained as described above is applied to various structures such as power line towers, bridges, bullet trains, highways, golf driving ranges, and outer surfaces of aircraft. The carbon fibers may be attached and used in the same direction as the direction of the electric field generated by the electric wave to be absorbed.

In both the first and second embodiments described above, in the measurement of the complex permittivity (relative permittivity), the real part of the high complex permittivity (relative permittivity) was measured while the frequency was fixed at 100 MHz. The value ε'can be obtained.

The radio wave absorber is usually designed to absorb radio waves of a specific frequency. In this case, it is possible to absorb not only the radio wave having the frequency to be absorbed used in the design but also the radio wave having a frequency close to that frequency. When the value ε ′ of the real part and the value ε ″ of the imaginary part of the complex permittivity (relative permittivity) are well matched, radio waves in a wider range of frequencies can be absorbed.

Considering, for example, a case of designing to absorb a radio wave of 2 cH, there is a relationship between the frequency and the reflection coefficient as shown in FIG. 16, and there are 1 cH and 3 cH close to the frequency of 2 cH. Even with respect to radio waves, the reflection coefficient is about -14 dB, and it is clear that these radio waves can be absorbed well. Also, 4cH to 12c
The frequency of the H radio wave is concentrated in the vicinity of 200 MHz, and by designing to absorb the 200 MHz radio wave, the 4 cH to 12 cH radio wave can be favorably absorbed.

In both the first and second embodiments described above, the value ε'of the real part of the complex permittivity (relative permittivity) required for the radio waves to be absorbed is used as the carbon used. In terms of the relationship with the average fiber length of the fibers, it is preferable to design so that the carbon fiber content is obtained as small as possible. <Fourth Example> 2000 g of ordinary Portland cement, 1000 g of silica sand No. 6 as fine aggregate, 15 g of admixture, and 100 of water.
0 g, carbon fiber having a fiber diameter of 18 μm and a fiber length of 0.5 mm (DONACARBO S-344: manufactured by DONAC CORPORATION)
160 g was mixed to obtain a mortar containing carbon fibers. A molding plate was prepared from this mortar using an extruder, and was cured in the same manner as in the first embodiment to obtain a cured product. And
The cured body is cut to a thickness of 20 cm to prepare a sample, and the direction (orientation) of the carbon fiber in the sample is parallel to the electric field vector of the radio wave (plane wave), and the magnetic field vector and the poin The fourth embodiment is arranged so as to be perpendicular to any of the teaching vectors. On the other hand, the first comparative example was arranged such that the direction (orientation) of the carbon fiber was parallel to the magnetic field vector of the radio wave (plane wave) and perpendicular to both the electric field vector and the pointing vector. Then, the test piece is arranged so that the direction (orientation) of the carbon fiber is parallel to the pointing vector of the radio wave (plane wave) and is perpendicular to both the electric field vector and the magnetic field vector. As a comparative example, a radio wave attenuation amount was measured as a physical quantity of the radio wave absorbing ability of each of the fourth embodiment, the first and second comparative examples. The radio wave attenuation amount was calculated as 10 · log (reflected radio wave energy / incident radio wave energy). As a result of this measurement, in the case of the fourth embodiment, as shown in the graph of FIG. 17 showing the relationship between the frequency and the amount of radio wave attenuation, -18 dB at 432 MHz.
There was attenuation of radio waves. On the other hand, in the case of the first comparative example, as shown in the graph showing the relationship between the frequency and the radio wave attenuation amount in FIG. 18, a maximum of −5 dB near 650 MHz.
In the case of the second comparative example, there is only a certain degree of radio wave attenuation,
As shown in the graph of FIG. 19 showing the relationship between the frequency and the amount of radio wave attenuation, there is almost no attenuation of radio waves in the range of 45 MHz to 1 GHz, and the longitudinal direction of the carbon fiber is in the longitudinal direction for frequencies in the television band. It was clear that the radio waves can be favorably absorbed by arranging them in the electric field direction of the radio waves.

[0057]

As is apparent from the above description, according to the radio wave absorption method of the present invention, regardless of whether the radio wave to be absorbed is horizontally polarized wave or vertically polarized wave, the mounting posture of the electromagnetic wave absorber can be changed. Since the direction of the aligned carbon fibers is made to correspond to the direction of the electric field by making it correspond to the direction of the electric field generated by the radio wave, even if the carbon fiber content is low or the amount of carbon fiber itself is low. The radio waves can be efficiently absorbed by the carbon fiber and attenuated. Moreover,
For example, stacking absorbers with different orientations
Without a single layer, the carbon fiber is oriented in one direction
Since only the collector is used, it was possible to absorb radio waves with high absorption efficiency while using a radio wave absorber having a low carbon fiber content, a thin thickness, and a light weight. For this reason, the outer walls of high-rise buildings and the soundproof walls of bullet trains and highways are constructed with electromagnetic wave absorbers, or high-rise buildings, power lines, steel towers,
By attaching a radio wave absorber to various structures such as bridges, bullet trains, highways, driving ranges, and the outer surface of aircraft,
It has become possible to prevent ghost failures with good handleability and at low cost.

[Brief description of drawings]

FIG. 1 is a perspective view of a cured body for obtaining a test body of a radio wave absorber used in the radio wave absorption method of the present invention.

FIG. 2 shows a perspective view of a test body, FIG. 2 (a) is a perspective view of a vertical type test body, and FIG. 2 (b) is a perspective view of a horizontal type test body.

FIG. 3 is a graph showing a characteristic curve under a non-reflection condition.

FIG. 4 is a side view for explaining the degree of orientation.

FIG. 5 is a schematic configuration diagram of a measuring device.

FIG. 6 is a graph showing the relationship between the carbon fiber content and the relative dielectric constant.

FIG. 7 is a graph showing the relationship between carbon fiber content and relative dielectric constant.

FIG. 8 is a graph showing the relationship between the average fiber length of residual fibers and the carbon fiber content when the chopped carbon fiber having an average fiber length of 6 mm is prepared and adjusted.

FIG. 9 is a graph showing a relationship between frequency and a real part of relative permittivity.

FIG. 10 is a graph showing the relationship between frequency and the imaginary part of the relative permittivity.

FIG. 11 is a schematic perspective view showing a state of use in a building.

FIG. 12 is an explanatory diagram of an electric field generation state.

FIG. 13 is a schematic configuration diagram of an apparatus for producing a radio wave absorber using resin as a base material.

FIG. 14 is a graph showing the relationship between the carbon fiber content and the relative dielectric constant.

FIG. 15 is a graph showing the relationship between the direction of carbon fibers and the relative dielectric constant with respect to the angle of the electric field direction.

FIG. 16 is a graph showing the relationship between frequency and reflection coefficient.

FIG. 17 is a graph showing the relationship between frequency and radio wave attenuation amount in the fourth embodiment.

FIG. 18 is a graph showing the relationship between the frequency and the amount of radio wave attenuation in the first comparative example.

FIG. 19 is a graph showing the relationship between the frequency and the amount of radio wave attenuation in the second comparative example.

[Explanation of symbols]

 CF ... Carbon fiber W ... Radio wave

Front Page Continuation (72) Inventor Yoshiaki Yoshida 17 Nakadoji Minami-cho, Shimogyo-ku, Kyoto Prefecture Kyoto Research Search Park KRI International (56) References JP-A-58-188193 (JP, A) JP-A-58-184799 (JP, A) JP 58-108603 (JP, A)

Claims (3)

[Claims] 1. A set containing carbon fibers for absorbing radio waves to be absorbed.
The composition containing carbon fibers when the composition is irradiated in any direction
Let ε ′ be the real part and ε ″ of the imaginary part of the complex permittivity of the product,
The maximum and minimum values of them are given by ε _max ',
ε _min ', ε _max ″, ε _min ″,
Orientation degree A is ε _max '− ε _min ' and orientation degree B is ε
_When it is defined by _max “−ε _min ”, the carbon fiber distribution
The orientation A is 25 or more, and / or the orientation B is 5 or more.
Containing carbon fibers oriented in a specific direction so that
Using a composition containing elemental fibers, the orientation direction of the included carbon fibers is absorbed.
The above mentioned so that it matches the electric field direction of the radio wave to be collected.
Disposing a carbon fiber-containing composition, the carbon fiber-containing composition
Wave absorber wherein the absorbing radio waves by. 2. The radio wave absorbing method according to claim 1, wherein the matrix of the carbon fiber-containing composition is an outer wall made of mortar or concrete, and the carbon fiber content is 0.5 to 10% by weight. 3. The radio wave absorption method according to claim 1, wherein the matrix of the carbon fiber-containing composition is a resin, and the carbon fiber content is 5 to 25% by weight.