JP5654249B2 - Laminated wood-based electromagnetic wave absorbing plate and method - Google Patents

Description

The present invention relates to a laminated wood-based radio wave absorbing plate material using a magnetic board or a conductive board formed by mixing a magnetic powder or a conductive powder in a wood-based powder and solidifying with a binder resin as a high dielectric constant layer material, and its production Regarding the method.

The types of radio wave absorbers are (1) single-layer flat plate type with metal plate backing, (2) Salisbury type using a resistive film, (3) taper type using dielectric loss material, and (4) using dielectric loss material. Broadly divided into multilayer flat plate types.

(4) The multilayer flat plate type wave absorber, wherein the peak of return loss is in the 2.2 to 2.8 GHz band and the 4.8 to 5.5 GHz band in which the wave absorbing layers having different wave absorbing characteristics are laminated. An electromagnetic wave absorber exhibiting a bimodal characteristic having a characteristic has been proposed (Patent Documents 1 to 3). In addition, it consists of a sheet layer containing magnetic material from the incident side, a spacer layer, a lightweight body layer containing carbon and ferrite, and a wave absorbing plate composed of a reflective layer, and is effective for multiple GHz bands of 2 GHz and 5 GHz. Building materials have been proposed (Patent Document 4).

In addition, the radio wave matching layer formed by laminating the first dielectric layer, the second dielectric layer, and the third dielectric layer in this order, and the opposite side of the second dielectric layer A radio wave reflection-suppressing building material comprising a reflective layer provided on the surface of the first dielectric layer, wherein the second dielectric layer is made of a low dielectric constant material having a relative dielectric constant of approximately 1. The first and third dielectric layers are made of a material having a relative dielectric constant higher than that of the low dielectric constant material, and the reflection layer is made of a material that reflects radio waves. A characteristic radio wave reflection-suppressing building material has been proposed (Patent Document 5).

Further, the first ferrite plate having a predetermined thickness and a metal plate for electromagnetic wave reflection attached to the back surface, and a thickness that is located on the front side of the first ferrite plate and is thinner than the first ferrite plate A dielectric means having a predetermined width between the second ferrite plate and the first and second ferrite plates (
An electromagnetic wave absorber provided with an air layer, a low dielectric constant foamed resin, and a low dielectric constant fiber assembly has been proposed (Patent Document 6).

Furthermore, the present inventors have developed a wood-based radio wave absorption board excellent in radio wave absorption performance (Patent Documents 7 to 9, Non-Patent Documents 1 and 2).

JP 2004-179479 A JP 2004-186546 A JP 2007-329397 JP 2005-150530 A JP 2003-283180 A JP-A-9-219596 WO2005 / 069712 JP 2007-134466 Gazette Japanese Unexamined Patent Publication No. 2007-245419

Koichi Narita, Hideo Oka, Experimental study on fabrication of electromagnetic wave absorber for GHz band using magnetic wood, IEEJ electromagnetic environment study material, The Institute of Electrical Engineers of Japan, January 18, 2000, EMC-00-1 17, p. 121-127 Mitsuji Sato, Hideo Oka, Yasuji Namasaki, Examination on radio wave absorption characteristics of powder type magnetic wood using logarithmic mixing rule of Lichtenecker, Society of Instrument and Control Engineers Tohoku Branch 288th meeting, document number 228-6 (2006. 5.17) Pages 1-4

With the recent development of communication equipment, there is an increasing demand for electromagnetic environment control such as prevention of radio wave interference, radio wave leakage prevention, and radio wave eavesdropping in buildings. In particular, the spread of wireless LAN is remarkable, and there is an interest in problems such as deterioration of communication quality due to multipath and information leakage due to radio wave diffusion. Currently, in wireless LAN, radio waves are used in two bands, 2.4 to 2.5 GHz band (also referred to as 2.4 GHz band) and 5.15 to 5.25 GHz band (also referred to as 5.2 GHz band). In offices and the like, there are cases where 2.4 GHz and 5.2 GHz are mixed, and a radio wave absorber having high absorption performance in both bands is required as a building material. There is also a need for a 2 to 10 GHz wave absorber including a 5.8 GHz DSRC (ETC) wave absorber.

In order to widen the radio wave absorption band, a technique related to a laminated radio wave absorber in which materials having different dielectric constants and magnetic permeability are laminated and reflection (multiple reflection) is performed at the interface of each layer has been proposed. In multilayered wave absorbers, the dielectric constant, permeability, etc. of each absorber layer are stepped from the incident direction to the inside of the wave absorber in order to prevent large reflections of radio waves on the incident surface of the wave absorber. It is desirable to enlarge it.

However, the radio wave absorption performance of the radio wave absorbing plate material and the thinning are in a contradictory relationship, and in particular, 1 to 3 GH.
Since the electromagnetic wave absorbing plate material for absorbing low frequency electromagnetic waves such as z requires a thickness of the radio wave absorbing layer, it is difficult to reduce the thickness and weight.

In addition, the multilayered wave absorber has a wider frequency band that can be absorbed as the number of layers increases. However, the thickness required for the laminated wave absorber as a whole increases, and the manufacturing process increases and the cost increases.

The present inventor has so far developed a wood-based radio wave absorption board that is a bonded molded body made of a binder resin of wood powder and magnetic powder such as ferrite, but the peak of radio wave absorption has a frequency of 0.8 to
It was a narrow band such as the 1.4 GHz band. Moreover, a wood-based radio wave absorption board having a radio wave absorption capacity of 10 dB or more having a bandwidth of 1.5 GHz or more has been developed (Patent Document 8).
However, as shown in FIG. 9, the second embodiment has a radio wave absorption peak in the 5 GHz band.
In the case of No. 1, the radio wave absorption capability in the 2.0 to 2.8 GHz band was not sufficient.

Although a conventional three-layered wave absorber using general building materials has been proposed with absorption peaks at 2.45 GHz and 5.2 GHz, the amount of radio wave absorption remains at a level of 15 dB. The range of radio wave absorption is also narrow at each peak.

In the present invention, the lowest radio wave absorption performance in the entire frequency band of 2 to 6 GHz is 20 dB level (
19 dB or more), that is, in the entire band of 2 GHz to 6 GHz (bandwidth is 4 GHz), the radio wave absorption performance is as wide as 19 dB or more, and is in a two-wavelength region, particularly 2.4 GHz band and 5.2 GHz
Excellent electromagnetic wave absorption in the vicinity of two wavelengths in the z-band, suitable for interior materials such as indoor interior materials and ceiling materials,
An object of the present invention is to provide a low-priced laminated wave absorbing plate material that is easy to manufacture.

The wood-based radio wave absorption board previously developed by the present inventors is a 0.8 to 1.4 GHz band or 5 GHz.
Although the present invention has a large radio wave absorption capability only in a narrow band such as a band and the radio wave absorption capability is not sufficient in a wide band of 2 to 6 GHz, the present inventors have proposed such a wooden radio wave absorption board. Even so, by laminating in combination with a low dielectric constant layer, 2 GHz to 6 GHz
It has a radio wave absorption performance of 19 dB or more within the entire band of z (that is, the bandwidth is 4 GHz) (
That is, it has been found that a laminated wave absorbing plate material having a bandwidth of 4 GHz) can be obtained.

The present invention comprises at least two high dielectric constant layers on a metal plate that reflects electromagnetic waves, and at least 1
A radio wave absorbing plate material laminated in combination with a low dielectric constant layer, wherein the high dielectric constant layer is 2
(A) a wood-based magnetic board having a dielectric constant of 2 to 31 in a single layer in a band of ˜6 GHz;
(B) It consists of a wooden conductive board, and the low dielectric constant layer has a thickness of 0.6 mm or more and 2 to 2
Dielectric constant at monolayer is also one or less than 2 (C) a non-magnetic board consists (D) Check <br/> air layer in 6GHz band, the first layer of the metal plate side (A) wood magnetic Board or (B) Wood-based conductive bow
The surface layer on the incident side of the radio wave is (A) a wooden magnetic board or (B) a wooden conductive
Or a non-magnetic board, and a laminated wave absorbing plate material characterized by having a wave absorbing performance of 19 dB or more in the entire band of 2 GHz to 6 GHz.

The wood-based magnetic board can be formed by pressing and molding wood powder and ferrite powder with a binder resin. The wood-based conductive board may be formed by press-molding a carbon material selected from graphite powder, carbon fiber, and conductive carbon black with a binder resin.

As the nonmagnetic board, any of a board obtained by bonding wood powder or pearlite powder with a binder resin and press-molding, a foamed urethane resin, or a foamed styrene resin can be used.

It is preferable that the dielectric constant of the high dielectric constant layer be sequentially increased from the incident side to the reflection side of the radio wave. The wooden magnetic board or the wooden conductive board preferably has a radio wave absorption peak in the 2 GHz to 6 GHz band, particularly in the 4 GHz to 6 GHz band. A laminate having a radio wave absorption peak of 30 dB or more can be produced as the laminated radio wave absorber plate.

Since this laminated type electromagnetic wave absorbing plate is made of wood, it is useful as a building material, particularly as a building material for interior materials, and is useful for indoor electromagnetic environment control.

Further, the present invention has a dielectric constant of 2 to 31 in a single layer in a band of 2 GHz to 6 GHz, at least two layers of a wooden magnetic board or a wooden conductive board, and a thickness of 0.6 mm or more,
At least one nonmagnetic board having a dielectric constant of 1 or more and less than 2 in a single layer in the 2 to 6 GHz band
A method for producing a laminated wave absorbing plate material as described above, wherein the layer is laminated on a metal plate that reflects electromagnetic waves using an adhesive.

Furthermore, the present invention provides an air layer having a thickness of 0.6 mm or more between at least two layers of a wood-based magnetic board or a wood-based conductive board having a dielectric constant of 2 to 31 in a single layer in the 2 to 6 GHz band. 2. A method for producing a laminated wave absorbing plate material according to claim 1, wherein the laminate is laminated on a metal plate that reflects electromagnetic waves using an adhesive.

The present invention provides a laminated radio wave absorption plate material having a radio wave absorption performance of 19 dB or more (20 dB level) within the entire band of 2 GHz to 6 GHz (that is, the bandwidth is 4 GHz) by using an inexpensive material by a simple manufacturing method. can do. According to the laminated wave absorbing plate material of the present invention, for example, a plurality of GHz of 2 GHz band and 5 GHz band or 5.8 GHz band for DSRC (ETC).
Because the radio waves of the band can be absorbed simultaneously, the communication environment can be improved efficiently. further,
It can be used as an interior building material in place of conventional inorganic materials by utilizing timber with poor utility value.

It is a graph which shows the complex dielectric constant computed by the Nicolson-Ross method of the wood type magnetic board. It is a graph which shows the complex magnetic permeability computed by the Nicolson-Ross method of the wood type magnetic board. It is a graph which shows the electromagnetic wave absorption characteristic of the wood type magnetic board whose sample thickness computed from the material constant shown by FIG. 1, FIG. 2 is 5 mm and 10 mm. It is sectional drawing which shows the concept of the multilayer structure of the laminated | stacked electromagnetic wave absorption board | plate material of this invention. 6 is a graph showing the radio wave absorption performance of the laminated radio wave absorption plate materials of Examples 1 and 2 and Comparative Example 1. 6 is a graph showing the radio wave absorption performance of the laminated radio wave absorber plate of Example 3. 7 is a graph showing the radio wave absorption performance of the laminated radio wave absorber plate of Example 4. 7 is a graph showing the radio wave absorption performance of the laminated radio wave absorption plate material of Comparative Example 2. 10 is a graph showing the radio wave absorption performance of the laminated radio wave absorber plate of Example 5. 10 is a graph showing the radio wave absorption performance of the laminated radio wave absorption plate material of Example 6. 10 is a graph showing the radio wave absorption performance of the laminated radio wave absorber plate of Example 7. It is a graph which shows the electromagnetic wave absorption characteristic of the wood type magnetic board of a prior art example.

In the present invention, a wood-based magnetic board or a wood-based conductive board having a dielectric constant of 2 to 31 in a single layer in the 2 to 6 GHz band is used as the high dielectric constant layer of the laminated wave absorbing plate material. This board is produced by mixing magnetic powder or conductive powder with wood-based powder, solidifying it with a binder resin, and press-molding it. The magnetic powder is preferably ferrite powder. The conductive powder is preferably a carbon material selected from graphite powder, carbon fiber, and conductive carbon black. Hereinafter, although the case where a ferrite powder is used is explained in full detail, when using electroconductive powder, it can implement similarly by replacing with ferrite powder and using electroconductive powder.

The band for reducing the reflection of the radio wave by the radio wave absorber and the attenuation rate in the band are basically determined by the type and amount of the substance that absorbs the radio wave contained in the radio wave absorber and the thickness of the absorber. When the substance contained in the radio wave absorber is a magnetic powder, the electromagnetic wave is attenuated by magnetic permeability loss.
When the substance contained in the radio wave absorber is a conductive powder, the electromagnetic wave is attenuated by dielectric loss.
The type of conductive (dielectric) material is represented by a complex relative dielectric constant. The thickness d of the radio wave absorber that can efficiently reduce reflection at a certain wavelength λ is determined by the complex relative dielectric constant. The larger the real part of the complex dielectric constant, the thinner the absorber at the frequency where the absorption effect is maximized.
In addition, the larger the imaginary part of the complex dielectric constant, the better the electromagnetic wave is absorbed.

In the present invention, a wood-based board is used, but the dielectric constant is 2 or more by adjusting the kind and composition ratio of the wood-based powder, magnetic powder or conductive powder, and the binder resin as the raw material,
The range can be 31 or less. The total thickness of the high dielectric constant layer is preferably 20 to 50 mm, and if it is too thick, the cost is increased, which is not preferable. More preferably, 2
5 to 45 mm. At least two such high dielectric constant layers are used and laminated with at least one low dielectric constant layer to adjust desired radio wave absorption performance in the 2 GHz to 6 GHz band.

When ferrite powder is used as the magnetic powder and pressure-molded at about 5 to 10 MPa, the specific gravity can be reduced to about 0.7 to 2.2. The bending strength of the board is 10 to 33N.
It is about / mm ² and has sufficient strength as a building material.

At least two layers of this high dielectric constant wood board are laminated on a metal plate such as aluminum that reflects electromagnetic waves in combination with at least one low dielectric constant layer. Lamination is not limited to alternating layers, and a high dielectric constant layer may be laminated without a low dielectric constant layer interposed. In order to improve the radio wave absorption performance as the low dielectric constant layer, the thickness is required to be at least 0.6 mm, and the total thickness is preferably 5 to 35 mm, more preferably 15 to 30 mm. When using a non-magnetic board layer as the low dielectric constant layer,
A nonmagnetic board layer may be laminated. When a nonmagnetic board is used as the low dielectric constant layer, it may be provided on the outermost surface on the radio wave incident side. However, when an air layer is used, the lower dielectric layer is lower than the outermost layer . Even when combined with a low dielectric constant layer, only one wooden board layer is structurally almost the same as a single board wooden radio wave absorption board, and a radio wave absorption performance of 19 dB or more cannot be obtained in the entire band of 2 GHz to 6 GHz. . A total of seven or more layers is not preferable because the number of boards and the manufacturing process increase, resulting in high costs. More preferably, the total is 4 to 6 layers.

The low dielectric constant layer is composed of a nonmagnetic board or air layer having a dielectric constant of 1 or more and less than 2 in a single layer in the 2 to 6 GHz band. The dielectric constant of the air layer is approximately 1. Non-magnetic boards having a dielectric constant of 1 or more and less than 2 include wood-based boards containing only magnetic powder or conductive powder and phenol resin, or wood-based boards made of pearlite powder and phenol resin alone, foamed urethane resin sheet or foamed styrene resin. A sheet etc. are mentioned.

As a method of laminating a low-permittivity nonmagnetic board with a high-dielectric constant layer, for example, heat laminating or using an adhesive is used. Adhesives include vinyl acetate resin-based woodworking bonds, nitrile rubber-based bonds, urethane, SBR, vinyl chloride and chloroprene rubber-based adhesives, epoxy resins and polyamidoamines ( A two-component adhesive comprising a curing agent). When an air layer is used as the low dielectric constant layer, it is bonded to a spacer appropriately provided between the two high dielectric constant layers.

The composition of such a wooden board and the pressure molding method were developed by the present inventors and described in Patent Documents 7 to 9, Non-Patent Documents 1 and 2, and the like. For example, a fixed amount of wood powder is filled into a plate-shaped frame, and the composition is poured into the frame by pouring mixed or dispersed magnetic powder or conductive powder and binder, or by spraying. Prepare this by pressing
Molded by heating and pressing.

Phenol resin, epoxy resin, melamine resin, urea resin, unsaturated polyester resin, etc. are used as binders for making wood boards, but phenol resin is a thermosetting resin and it is heat resistant when used as a building material. It is excellent in properties, and some of the raw materials are in the form of powder. As ferrite powder,
Mn—Zn and Ni—Zn ferrite powders are preferred.

The wood powder may be one or more selected from various types of hardwoods and conifers, and chips (wood pieces) and sawdust are preferable. Generally, the average particle size of wood flour is 200 μm ~
The average particle diameter of the ferrite powder is preferably in the range of about 3 to 200 μm. A ferrite powder or carbon material powder or fiber having a larger particle size is more effective, but it is more difficult to uniformly disperse the plate material by mixing with the wood powder.

It is possible to adjust the peak frequency and attenuation of electromagnetic wave reflection in the GHz frequency band of a single plate by the combination setting of the particle size and content of wood powder and ferrite powder or carbon material powder and fiber, and board thickness. it can.

A single board wood board was prepared by the following method, and this board was laminated to produce a laminated wave absorbing plate material, and its wave absorption characteristics were measured.
<Production of wood-based board>
Magnetic powder and wood powder 10% at 190 ° C and 49 N / cm ² with phenol resin as binder
It was heat-compressed for a minute and formed into a board shape having a shape of 250 mm × 250 mm × 18 mm to produce a wooden board. Magnetic powder is Mn-Zn ferrite (BSF-547, manufactured by Toda Kogyo Co., Ltd., average particle size 3, 3 μm), wood powder is sawdust (particle size 2 mm or less, manufactured by Segawa Kogyo), and binder is A phenol resin (SA-100, manufactured by Asahi Organic Materials) was used. An appropriate amount of water was used when mixing the powder. The magnetic powder has a weight content of 33% (Sample A), 50% (Sample B), and 66% (Sample C).
) And 80% (sample D), changing to four stages, four types of radio wave absorption boards shown in Table 1 were produced and used as samples.

<Measurement method of radio wave absorption characteristics>
For the measurement, an annular sample processed to an outer diameter of 6.95 mm, an inner diameter of 3.05 mm, and a thickness of 3.0 mm was used, and a frequency of 0.5 GHz to 1 was measured with a network analyzer (Agilent E8361A).
Material constants (complex dielectric constant and complex permeability) at 8 GHz were determined by the Nicolson-Ross method. From the obtained material constant, the thickness was set to 5 mm and 10 mm as a single-layer type wave absorber with the back surface of the sample lined with an aluminum reflector, and the frequency characteristics of the radio wave absorption amount were calculated for each sample.

<Measurement results of radio wave absorption characteristics>
1 and 2 show graphs of material constants calculated by the Nicolson-Ross method. The real part of the complex dielectric constant shown in FIG. 1-1 shows a high value for the sample having a high weight content of the magnetic powder, and decreases as the frequency increases. In addition, the imaginary part of the complex dielectric constant shown in FIG. 1-2 similarly shows a high value for the sample having a high weight content of the magnetic powder, and increases as the frequency increases, contrary to the real part. The complex permeability shown in FIG. 2A decreases as the frequency increases in both the real part and the imaginary part, but the sample with a high weight content shows a high value on the low frequency side. 2-6GH
The dielectric constant e ′ at z is as follows: Sample A = 2.71 to 2.54, Sample B = 4.38 to 4.00, Sample C = 6.77 to 6.11, Sample D = 11.47 to 10 .39.

The bending strengths of Samples A, B, C, and D are 10.1 N / mm ² , 14.8 N / mm ² , and 22 respectively.
. 5N / mm ^2, a 33.0N / mm ^2, the flexural modulus, respectively 1640N / mm ^2, 2430N / m
m ² , 3970 N / mm ² , 8830 N / mm ² , and sufficient strength as a building material.

FIG. 3 shows a graph showing the radio wave absorption characteristics of the wooden boards having sample thicknesses calculated from the material constants of 5 mm (FIG. 3-1) and 10 mm (FIG. 3-2). As a tendency, a sample having a higher weight content of magnetic powder has a higher peak at a lower frequency, but a sample having a lower weight content has a highest peak at a frequency exceeding 10 GHz when the sample is thicker. Thickness from 5mm to 10
As it increases to mm, the radio wave absorption peak shifts to the low frequency side.

Also, the amount of absorption exceeding 20 dB is the value of sample C (ferrite content 66w) when the sample thickness is 5 mm.
t%) is 28.5 dB at 6.02 GHz, and the sample thickness is 10 mm.
(Ferrite content 50 wt%), it is 24.2 dB at 12.05 GHz,
Sample C (ferrite content 66 wt%) is 25.2 dB at 2.51 GHz, and sample D (ferrite content 80 wt%) is 25.7 dB at 1.38 GHz.
It showed a good value. However, the amount of radio wave absorption in the 2 to 6 GHz band is small.

[Examples 1 and 2]
<Preparation of laminated electromagnetic wave absorbing plate>
In FIG. 4, the conceptual diagram of the multilayered structure of the laminated | stacked electromagnetic wave absorption board | plate material of this invention is shown. FIG. 4 shows three sample layers,
5 shows a five-layer structure of two air layers. As a sample layer, a laminate having a structure in which Sample A, Sample B, Sample C, and Sample D were combined was produced. Table 2 shows the samples and thicknesses used in the layers of Examples 1 and 2 and Comparative Example 1.

FIG. 5 shows the radio wave absorption performance of the laminated radio wave absorbing plate materials of Examples 1 and 2 and Comparative Example 1. In Example 1, the total thickness of the laminated wave absorbing plate material is 22.6 mm, and the total thickness of the wave absorbing board is 7.6 mm. As shown in FIG. 5, the thickness is 20 in the range of 2.38 GHz to 7.45 GHz.
Absorption performance exceeding dB was obtained. In Example 2, the total thickness of the laminated wave absorbing plate material is 28.
mm, and the total thickness of the radio wave absorption board is 16.3 mm, from 1.98 GHz to 6.35.
Absorption performance of 19 dB or more was obtained in the GHz range.

In Comparative Example 1, the total thickness of the laminated wave absorbing plate material is 33 mm, the total thickness of the wave absorbing board is 26 mm, and absorption performance exceeding 10 dB is obtained in a wide band from 0.77 GHz to 10.47 GHz. In the 2-6 GHz band, absorption performance exceeding 19 dB was not obtained. This is because the thickness of the air layer between the first layer and the third layer is 0.5 mm, and the effect interposed in the first layer and the third layer cannot be obtained. This is presumably because it is not substantially different from the rate layer 1 layer.

[Examples 3 to 7]
<Production of wood-based board>
A wood-based board was produced in the same manner as in Examples 1 and 2. The conductive powder is graphite (1500M84C
Carbon fiber (S-244 Osaka Gas Chemical) or carbon black (Carbon MBPEC-416 Resino Color) was used. Tables 3, 4, and 5 show the compositions of Samples EP. Similarly, nonmagnetic boards having the compositions shown in Tables 6 and 7 were produced.

<Preparation of laminated electromagnetic wave absorbing plate>
A laminated wave absorbing plate was prepared in the same manner as in Examples 1 and 2. Each layer structure is shown in Tables 8-10. The alphabetical characters in each table are the sample type, mm is the thickness of the sample or air layer, and the numerical value at the bottom is 4
The dielectric constant in GHz is shown.

The radio wave absorption characteristics measured in the same manner as in Examples 1 and 2 are shown in FIGS. In Example 3,
The lowest radio wave absorptivity in the 2 GHz to 6 GHz band was 20.8 dB, and the 20 dB level band was 1.90 GHz to 6.34 GHz. In Example 4, the lowest radio wave absorption capability in the 2 GHz to 6 GHz band is 20.5 dB, and the 20 dB level band is 1.81 GHz.
It was ˜6.56 GHz. In Example 5, the lowest radio wave absorption capability in the 2 GHz to 6 GHz band was 22.3 dB, and the 20 dB level band was 1.82 GHz to 6.91 GHz. In Example 6, the lowest radio wave absorptivity in the 2 GHz to 6 GHz band was 20.4 dB, and the 20 dB level band was 1.95 GHz to 6.03 GHz. In Example 7,
The lowest radio wave absorption capability in the 2 GHz to 6 GHz band was 22.3 dB, and the 20 dB level band was 1.89 GHz to 6.41 GHz. In any case, it was found that a product having a radio wave absorption performance of 19 dB or more in the entire band of 2 GHz to 6 GHz (bandwidth: 4 GHz) was obtained.

Comparative Example 2 is an example in which three layers of high dielectric constant layers are laminated without providing a low dielectric constant layer. As shown in FIG. 8, the radio wave absorption capability in the 5 GHz band is improved as compared with the case of a single radio wave absorption board. However, the desired radio wave absorption performance could not be obtained.

Effective use of inexpensive wood powder (wood powder), low price, light weight, high performance 2 GHz to 6 G
It has a radio wave absorption performance of 19 dB or more in the whole band of Hz, especially 2.4 GHz band and 5.2 GHz.
Excellent electromagnetic wave absorption in the vicinity of two wavelengths in the z-band, suitable for interior materials such as indoor interior materials and ceiling materials,
It is highly expected to be used as a low-priced laminated wave absorber that is easy to manufacture.

Claims (10)

An electromagnetic wave absorbing plate material in which at least two high dielectric constant layers and at least one low dielectric constant layer are combined and laminated on a metal plate that reflects electromagnetic waves,
The high dielectric constant layer has a dielectric constant of 2 to 31 in a single layer in the 2 to 6 GHz band (A)
It consists of a wood-based magnetic board or (B) a wood-based conductive board,
The low dielectric constant layer is a thickness of 0.6mm or more, the dielectric constant of a single layer is also less than 2 (C) a non-magnetic board 1 or in 2~6GHz band consists (D) air layer,
The first layer on the metal plate side is (A) a wooden magnetic board or (B) a wooden conductive board,
The surface layer on the incident side of the radio wave is (A) a wooden magnetic board or (B) a wooden conductive board,
Or (C) a non-magnetic board,
A laminated wave absorbing plate material having a wave absorbing performance of 19 dB or more in the entire band of 2 GHz to 6 GHz. 2. The laminated electromagnetic wave absorbing plate material according to claim 1 , wherein the wood-based magnetic board is formed by bonding wood powder and ferrite powder with a binder resin and press-molding. Woody conductive board, graphite powder, carbon fiber, laminated electromagnetic wave absorber of the carbon material selected from conductive carbon black according to claim 1, wherein the bonded by a binder resin is obtained by pressure molding Board material. The non-magnetic board is one of a board obtained by bonding wood powder or pearlite powder with a binder resin and press-molding, a foamed urethane resin, or a foamed styrene resin.
The laminated electromagnetic wave absorbing plate material described. 2. The laminated wave absorbing plate material according to claim 1, wherein the dielectric constant of the high dielectric constant layer is sequentially increased from the incident side to the reflecting side. The laminated electromagnetic wave absorbing plate material according to claim 1, wherein the wooden magnetic board or the wooden conductive board has a peak of radio wave absorption in a 4.0 GHz to 7.5 GHz band. The laminated wave absorbing plate material according to claim 1, which has a wave absorption peak of 30 dB or more. A building material comprising the laminated wave absorbing plate material according to any one of claims 1 to 7. At least two layers of a wood-based magnetic board or a wood-based conductive board having a dielectric constant of 2 to 31 in a single layer in a 2 to 6 GHz band, and a thickness of 0.6 mm or more and a single layer in a 2 to 6 GHz band The method for producing a laminated wave absorbing plate material according to claim 1, wherein at least one layer of a nonmagnetic board having a dielectric constant of 1 or more and less than 2 is laminated on a metal plate that reflects electromagnetic waves using an adhesive. . Metal that reflects electromagnetic waves with an air layer having a thickness of 0.6 mm or more between at least two layers of a wooden magnetic board or a wooden conductive board having a dielectric constant of 2 to 31 in a single layer in the 2 to 6 GHz band 2. The method for producing a laminated wave absorbing plate material according to claim 1, wherein the lamination is performed using an adhesive on the plate.

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