JP2006083615A - Radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave absorber non-inflammable with thin thickness and excellent in oblique incidence characteristics of radio wave and low in cost. <P>SOLUTION: The radio wave absorber is formed of a hardened body containing cement powder or silica powder as a main raw material, and natural sandy titanic iron ore is used as a radio wave absorbing material for a part of aggregate mixed in the cement and silica. After mixing and forming, the hardened body is formed by a calcium silicate hydrate, and radio wave in a range of frequency band 2-7 GHz is absorbed. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a radio wave absorber, and more specifically, interior and exterior materials for wireless LAN countermeasures in buildings, intelligent transport systems (ITS) such as roads and tunnels in civil engineering, and dedicated short-range communication (DSRC). It is related to non-combustible radio wave absorbers that are used as exterior materials for measures against range communication and reduce each radio interference.

  Conventionally, radio wave absorbers developed for countermeasures against radio wave interference include a synthetic resin material or rubber material mixed with a magnetic material and molded into a plate shape, or a surface of the molded body to impart nonflammability. There are λ / 4-method wave absorbers with a thickness of 30 mm or more made of non-flammable glass foam, or a non-flammable material such as a calcium oxide plate attached thereto (see, for example, Patent Document 1).

However, the radio wave absorber made of a synthetic resin material or a rubber material has a combustibility and has a problem that the cost is high in the production process because it is a multilayer.
In addition, non-combustible materials have a problem that the overall thickness is large and the oblique incidence characteristics of radio waves are poor.

Further, as a non-combustible radio wave absorber, radio wave absorption of a hardened body mainly composed of cementitious powder or siliceous powder containing an aggregate made of Mg—Zn ferrite and / or Ni—Zn ferrite. A body has been proposed (see, for example, Patent Document 2).
The hardened body mainly composed of cementitious powder or siliceous powder described in Patent Document 2 has excellent radio wave absorption performance in the frequency band (470 to 770 MHz) for television UHF broadcasting. In the two frequency bands used (2.5 GHz band and 5.2 GHz band) and the frequency bands of ITS and DSRC (5.8 GHz band), the effect of radio wave absorption cannot be expected.
Therefore, it is not effective as an exterior material for wireless LAN, ITS, or DSRC.

JP-A-6-240777 JP 2002-294900 A

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide an inexpensive radio wave absorber that is nonflammable and thin in thickness and excellent in oblique incidence characteristics of radio waves. Is to provide.

The present inventors have studied on the premise of mass production, and have used conventional molding technology (for example, extrusion method, papermaking method, pressure method, etc.) of plates made mainly of cementitious powder or siliceous powder. A part of the aggregate in the composition is replaced with a naturally-occurring sandy iron ore, such as ilmenite, which can be obtained at a low price, as an electromagnetic wave absorbing material, kneaded and molded into a hardened body by hydraulic properties .
Then, the mixing ratio of the radio wave absorbing material (ilmenite) and the cement is adjusted in consideration of radio wave absorption characteristics, molding strength, required product strength, etc. for wireless LAN, ITS, and DSRC. As a result, it was found that it is nonflammable, thin and has an excellent function of oblique incidence of radio waves.
That is, the radio wave absorber of the present invention is a radio wave absorber composed of a hardened body mainly made of cementitious powder or siliceous powder, and is an aggregate of the cement blended in the cementitious powder or siliceous powder. In part, using sandy iron ore naturally produced as an electromagnetic wave absorbing material, after mixing and molding this, a hardened body with calcium silicate hydrate, in the frequency range of 2-7GHz It absorbs radio waves (claim 1).
Titanium ore as the radio wave absorbing material has a particle size that does not hinder molding, and the particle size is preferably 10 μm to 500 μm. In addition, slate plates, calcium silicate plates, extruded plates, PC (precast concrete) plates, and the like are given as general names of the above-mentioned hardened products mainly containing cementitious powder or siliceous powder. In addition, inorganic materials (other than metals) and organic fibers can be appropriately blended in these cured products.
The main raw material cementitious powder includes those containing siliceous powder.

In addition, the blending ratio of the cement and the radio wave absorbing material is such that the blending amount of the main material of cementitious powder or siliceous powder is 20 wt% to 40 wt%, and the blending amount of titanite is 20 wt% to 60 wt%. (Claim 2).
Further, the thickness of the cured body is in the range of 5 mm to 20 mm, and the reflection attenuation amount is 15 dB or more in the range of the oblique incident angle of radio waves from 0 ° to 60 °.

  The radio wave absorber of the present invention can provide a radio wave absorber that is nonflammable because it does not use an organic substance, is thin, and has excellent radio wave absorption characteristics when the radio wave is obliquely inserted. In addition, conventional cement board or siliceous board molding technology and equipment can be used, thereby enabling mass production and supplying inexpensive radio wave absorbers that can be used in buildings and civil engineering.

Hereinafter, embodiments of the radio wave absorber according to the present invention will be described.
The radio wave absorber of the present invention is a radio wave absorber composed of a hardened body mainly composed of cementitious powder or silicate powder, and is an aggregate to be blended with the main material of cementitious powder or silicate powder. In some of these, sandy iron ore naturally produced as a radio wave absorbing material, for example, ilmenite, is used, mixed and molded, and then hardened with calcium silicate hydrate.
Then, the mixing ratio of the radio wave absorbing material (ilmenite) and the cement is adjusted in consideration of the radio wave absorption characteristics, the molding strength, the required product strength, and the like. In particular, the thickness (wall thickness) of the finished product was thin, and the oblique incidence characteristics of radio waves were adjusted.

As a result, the particle size of the iron ore of the radio wave absorbing material used in the present invention is 10 μm to 500 μm, the blending amount is in the range of 20 wt% to 60 wt%, and the blending amount of the cementitious powder or siliceous powder is The range is 20 wt% to 40 wt%. The thickness of the cured body to be molded is in the range of 5 mm to 20 mm.
Examples will be described below.

(1) The amount of addition of titanite (ilmenite), which is a radio wave absorption material, is changed, the amount of cementitious powder is kept constant at 39 wt%, the transmission line theory is used, and a 7D coaxial tube S is used with a vector network analyzer. -Radio wave absorption and material constants were measured by the parameter method. Among them, the matching thickness of the blending ratio [Ilmenite: 25 wt%, cementitious powder: 39 wt%] was determined, and the radio wave absorption characteristics and the radio wave absorption amount during oblique insertion were calculated.
The calculation formula of the radio wave absorption amount (reflection attenuation amount) and the reflection coefficient is as follows.

Material constant (ε ′, ε ″: complex relative dielectric constant, μ ′, μ ″: complex ratio) when the addition amount of the above ilmenite is varied from 0 to 25 wt% and the addition amount of cementitious powder is 39 wt%. The magnetic permeability and radio wave absorption characteristics (reflection loss dB) are shown in FIG.
FIG. 2 shows the matching thickness characteristics when the addition amount of titanite (ilmenite) is varied from 0 to 25 wt% and the addition amount of cementitious powder is constant 39 wt%.
Further, FIG. 3 shows radio wave absorption characteristics (calculated values) based on material constants (constant thickness). Sample 1 has a blending ratio (ilmenite: 30 wt%, cementitious powder: 30 wt%) thickness t = 11.9 mm, and sample 2 has a blending ratio (ilmenite: 25 wt%, cementitious powder: 39 wt%). t = 14.5 mm. In addition, FIG. 4 shows the radio wave absorption characteristics (circular polarization) of the sample according to the oblique incidence angle change.

(2) The amount of radio wave absorption and material constants were measured by changing the addition amount of cementitious powder while keeping the addition amount of titanite (ilmenite) as a radio wave absorption material constant (30 wt%). Among them, the matching thickness of the blending ratio [ilmenite: 30 wt%, cementitious powder: 30 wt%] was determined, and the radio wave absorption characteristics and the radio wave absorption amount during oblique insertion were calculated. The calculation formula is the same as above.
Furthermore, the TE and TM wave return loss (measured value) due to oblique incidence was measured by the free space method. The radio wave absorption characteristics are shown in FIGS. 9 and 10, respectively.
FIG. 5 shows material constants and radio wave absorption characteristics when the addition amount of the cementitious powder is changed from 10 to 30 wt% and the titania (ilmenite) addition amount is constant 30 wt%.
FIG. 6 shows the matching thickness characteristics when the amount of cementitious powder added is changed from 10 to 30 wt% and the amount of titanite (ilmenite) added is constant 30 wt%.
Further, FIG. 7 shows material constants and radio wave absorption characteristics when the addition amount of titanite (ilmenite) is changed from 30 to 50 wt% and the addition amount of cementitious powder is 11 to 16 wt%.
FIG. 8 shows material constants, specific gravity, and radio wave absorption characteristics when the addition amount of the cementitious powder is changed from 10 to 30 wt% and the titania (ilmenite) addition amount is constant 30 wt%.

  As shown in FIG. 4, the radio wave series configured as described above has a blending ratio (ilmenite: 30 wt%, cementitious powder: 30 wt%) and a thickness t = 11.9 mm, and a blending ratio (ilmenite: 25 wt%, (Cementitious powder: 39 wt%) Thickness t = 14.5 mm can be confirmed to exhibit performance with a return loss of 15 dB or more in the range of the incident angle of radio waves from 0 ° to 60 °.

  The radio wave absorber of the present invention is expected to expand its use as an interior / exterior material for wireless LAN countermeasures in buildings and an exterior material for ITS / DSRC countermeasures for roads, tunnels, etc. in civil engineering.

The graph which shows the material constant and electromagnetic wave absorption characteristic by a titanium iron ore (ilmenite) addition amount change (a cementitious powder addition amount is 39 wt% constant). The graph which shows the matching thickness characteristic by a titanium iron ore (ilmenite) addition amount change (a cementitious powder addition amount is 39 wt% constant). The graph which shows the electromagnetic wave absorption characteristic (calculated value) by a material constant (constant thickness). The graph which shows the electromagnetic wave absorption characteristic (circular polarization) by an oblique incident angle change. The graph which shows the material constant and electromagnetic wave absorption characteristic by cementitious powder addition amount change (titanium iron (ilmenite) addition amount constant 30wt%). The graph which shows the matching thickness characteristic by cementitious powder addition amount change (titanium iron (ilmenite) addition amount constant 30 wt%). The graph which shows the material constant and electromagnetic wave absorption characteristic by a titanium iron ore (ilmenite) addition amount change (the amount of cementitious powder additions 11-16 wt%). The graph which shows the material constant, specific gravity, and electromagnetic wave absorption characteristic by cementitious powder addition amount change (titanium iron (ilmenite) addition amount constant 30 wt%). The graph which shows the electromagnetic wave absorption characteristic of TE wave by oblique incidence. The graph which shows the electric wave absorption characteristic of TM wave by oblique incidence.

Claims (3)

It is a radio wave absorber made of a hardened material mainly composed of cementitious powder or siliceous powder, and is naturally used as a radio wave absorbing material on a part of the aggregate blended with cementitious powder or silicic powder. Radio waves characterized by absorbing radio waves in the frequency band of 2 to 7 GHz, which are formed by mixing and forming sandy ilmenite produced to form a hardened body with calcium silicate hydrate. Absorber. The blending ratio of the cementitious powder or siliceous powder and the radio wave absorbing material is in the range of 20 wt% to 40 wt% of the cementitious powder or siliceous powder and 20 wt% to 60 wt% of the titanite ore. The radio wave absorber according to claim 1. The thickness of the cured body is in the range of 5 mm to 20 mm, and the return loss is 15 dB or more in the range of the oblique incident angle of radio waves from 0 ° to 60 °. Radio wave absorber.

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