JP2002294900A - Radio wave absorber, precast concrete plate - Google Patents

Abstract

(57) [Summary] [Problem] A frequency band (470-470) for television UHF broadcasting
770 MHz) is provided. A hardened cement body (1) is formed on one surface of a mesh member (radio wave reflector) (2) made of stainless steel, and a fluorine-based resin layer (hardened film) is formed on the other surface. The hardened cement body 1 is made of Mg—Zn ferrite and / or Ni
-An aggregate made of Zn-based ferrite is contained at a ratio of 35% or more and 60% or less with respect to the total volume of the hardened cement.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber and a precast concrete plate integrated with the radio wave absorber, and more particularly to a frequency band (470) for UHF broadcasting of television.
(To 770 MHz).

[0002]

2. Description of the Related Art The phenomenon of ghosting on a television screen in a building is caused by the reflection of television waves on the outer wall surface of the building. Particularly in a high-rise building or the like, a large area of reflection of a television wave causes a large ghost, which is an obstacle to reception. Conventionally, measures have been taken to prevent such television ghost failures.

For example, JP-B-55-13600 and JP-B-55-49798 describe that a number of electromagnetic wave absorbing tiles made of a ferrite sintered body are attached to the outer wall of a high-rise building. . However,
In this method, since the ferrite sintered body is heavy, there is a problem in terms of workability and safety when attaching the tile. Further, the plane size of the tile made of the ferrite sintered body is 10
Since it is as small as about 0 mm × 100 mm, the work of attaching tiles is complicated.

Further, when a tile made of a ferrite sintered body is used, relatively good radio wave absorption performance can be obtained in a frequency band (90 to 220 MHz) for television VHF broadcasting. There is also a problem that the radio wave absorption performance in the frequency band for use (470-770 MHz) is not sufficient. Japanese Patent Application Laid-Open No. 2000-40894 discloses a λ combining a radio wave reflector and a resistive film.
(Wavelength of incident radio wave) / 4 type radio wave absorber (Japanese Unexamined Patent Publication No.
It is described that a carbon fiber paper is coated with a resin on both sides or one side as a resistive film. The resistive film is used by being buried in a dielectric layer, and a radio wave reflector (for example, a concrete structure in which electrode bars are buried) is formed on one surface of the dielectric layer.

In this method, good radio wave absorption performance can be obtained only in a part of a frequency band for UHF broadcasting (a specific narrow frequency band), but sufficient radio wave absorption performance can be obtained in other frequency bands. Absent.

[0006]

SUMMARY OF THE INVENTION An object of the present invention is to provide a frequency band (470 to 770 MHz) for television UHF broadcasting.
z) To provide a radio wave absorber having high radio wave absorption performance as a whole.

[0007]

SUMMARY OF THE INVENTION In order to solve the above-mentioned problems, the present invention provides a radio wave reflecting plate made of a metal plate or a net, and a cement formed on one surface of the radio wave reflecting plate. And a cementitious hardened material, wherein the hardened cementitious material is M
Provided is a radio wave absorber characterized by containing an aggregate made of g-Zn based ferrite and / or Ni-Zn based ferrite at a ratio of 35% or more and 60% or less with respect to the total volume of the hardened cement. I do.

According to the electromagnetic wave absorber of the present invention, the aggregate constituting the hardened cementitious material is made of Mg-Zn ferrite and / or Ni-Zn ferrite (that is, Mg-Zn ferrite). Or Ni-Zn ferrite,
470).
Sufficient radio wave absorption performance can be obtained in the entire frequency band of up to 770 MHz.

If the content of the aggregate made of Mg—Zn ferrite and / or Ni—Zn ferrite relative to the total volume of the hardened cement is less than 35%, the dielectric constant and permeability of the hardened cement obtained are reduced. The magnetic susceptibility is too small to obtain sufficient radio wave absorption performance. The content is 6
If it exceeds 0%, the dielectric constant and the magnetic permeability of the obtained cement hardened body become excessive, and sufficient radio wave absorption performance cannot be obtained.

In the radio wave absorber of the present invention, it is preferable that the ferrite aggregate contains 50% by volume or more of the ferrite aggregate having a particle size of 2 mm or more. Thereby, compared with the case where the content of particles having a particle diameter of 2 mm or more is less than 50% by volume, the dielectric constant and the magnetic permeability of the obtained cured cement body are increased, and higher radio wave absorption performance is obtained.

However, if the maximum particle size of the ferrite aggregate exceeds 7 mm, it is not preferable from the viewpoint of workability in forming a hardened cement body. That is, when forming a cementitious hardened body, a cementitious material containing at least cement, water and an aggregate made of the ferrite is kneaded, and the material is poured into a mold. , And it is difficult to adjust the material to a predetermined thickness during the casting operation.

As the cement of the cementitious material, various hydraulic cements such as ordinary Portland cement, early-strength Portland cement, alumina cement, flash eye cement and blast furnace slag cement can be used. Also,
Various additives such as a filler material, an admixture, and a water reducing agent may be added to the cementitious material as needed.

As an embodiment of the radio wave absorber of the present invention,
A configuration in which a decorative material is provided on the surface of the cementitious cured body opposite to the radio wave reflecting plate is exemplified. As this cosmetic material,
For example, a synthetic resin layer (a cured product of a coating film), a decorative tile, a stone material, and the like can be given. The present invention also provides a precast concrete plate in which a concrete hardened body is formed on the surface of the radio wave absorber of the present invention on the side of the radio wave reflecting plate. Various types of concrete such as ordinary concrete for precast concrete and lightweight concrete can be used as the concrete for the hardened concrete.

The present invention also relates to the method for producing a precast concrete plate of the present invention, wherein at least cement, water and the aggregate comprising ferrite, which are materials for the cementitious hardened body, are provided in a formwork. After casting the containing cementitious material and installing the radio wave reflecting plate on the cast cementitious material, before the cast cementitious material hardens, it is placed on the radio wave reflecting plate. A method for manufacturing a precast concrete plate, comprising casting a concrete material for the hardened concrete body.

According to this method, a precast concrete plate in which a hardened concrete body is formed on the surface on the radio wave reflecting side of the radio wave absorber can be obtained in one hardening step. Also,
After laying a decorative material on the bottom of the formwork, the material for the cement hardened body is cast on the decorative material, and after the radio wave reflecting plate is installed thereon, the concrete material for the concrete hardened material is removed. It can also be cast to produce precast concrete slabs.

[0016]

Embodiments of the present invention will be described below. FIG. 1 is a sectional view showing a radio wave absorber corresponding to one embodiment of the present invention. First, a cement mortar having a composition shown in Table 1 below was prepared and kneaded as a material for a cementitious cured product.

[0017]

[Table 1]

This cement mortar was prepared by adding
It was poured into a mold having a size of 0 cm × 90 cm so as to have a thickness of 12 mm. On this cement mortar layer, a stainless steel mesh having dimensions of about 60 cm × 90 cm (hole size: 5 cm × 5 cm, cross-sectional diameter of mesh material: 3.
2 mm), and the mesh body was fixed to cement mortar with an anchor.

In this state, the cement mortar is hardened by being left for a predetermined time, and then the mold is removed. As a result, as shown in FIG. A cured product 1 was obtained. Reference numeral 6 in FIG. 1 indicates an anchor. The cement hardened body 1 was left for another two weeks to develop strength. Thereafter, a paint containing a fluorine-based resin as a film-forming component was applied to the surface of the hardened cement body 1 on the side opposite to the reticulated body 2 and dried sufficiently.

Thus, the radio wave absorber shown in FIG. 1 is obtained. In this radio wave absorber, a reticulated body (radio wave reflector) 2 made of stainless steel is formed on one surface of a hardened cement body 1 and a fluororesin layer (cured product of a coating film) 3 as a decorative material is formed on the other surface. Is formed. The hardened cement 1 has M
50.4% by volume of an aggregate composed of pulverized g-Zn ferrite and having a ratio of particles of 2 mm or more of 55% is contained.

On the fluorine resin layer 3 side of the radio wave absorber,
A radio wave is incident perpendicularly to the plate surface,
The radio wave absorption performance in the range of 800 Hz was measured. The result is shown by a graph in FIG. As can be seen from this graph, the frequency band for TV UHF broadcasting (470 to 77).
At 0 MHz), the radio wave absorber of this embodiment had a radio wave absorption rate of 98% or more and an absorption amount of 17 dB or more. Since the amount of radio wave absorption required for a normal TV radio wave absorber is 13 dB or more, it can be said that the radio wave absorber of this embodiment has extremely good radio wave absorption performance.

FIG. 3 is a sectional view showing a precast concrete plate corresponding to one embodiment of the present invention. This precast concrete plate was produced by the following procedure. First, cast cement mortar in the form by the method described above,
On this cement mortar layer, a stainless steel mesh 2
Was installed. Next, before the cement mortar layer is hardened, a reinforcing bar 51 is arranged in a space above the mesh body 2 in the formwork, and a concrete material is cast on the mesh body 2 to form a cement mortar layer and a concrete layer. Were simultaneously cured.
Next, the mold was removed after a sufficient hardening time had elapsed, thereby obtaining an object in which the reticulated body 2 and the hardened concrete body 5 were integrated on one surface of the hardened cement body 1.

This object was left for another two weeks in order to sufficiently develop the strength of the hardened cement body 1 and the hardened concrete body 5. Thereafter, a paint containing a fluorine-based resin as a film-forming component is applied to the surface of the object opposite to the concrete hardened body 5 of the cement hardened body 1 and dried sufficiently to form a fluorine-based resin layer ( (Cosmetic material) 3 was formed.

As a result, as shown in FIG. 3, a precast concrete plate in which the concrete hardened body 5 is formed on the surface of the radio wave absorber 4 on the side of the net (radio wave reflector) 2 is obtained. The radio wave absorption performance of this precast concrete plate was the same as the radio wave absorption performance of the radio wave absorber of FIG. That is, even if the reinforcing bar 51 was disposed in the hardened concrete body 5, the radio wave absorbing performance was not affected.

Therefore, by using this precast concrete plate as an outer wall plate of a high-rise building and using the fluorine-based resin layer (decorative material) 3 facing outward, the U-shape of the television is improved.
Radio waves in the entire HF broadcast frequency band (470 to 770 MHz) are absorbed by the radio wave absorber 4 at a high absorption rate. As a result, a television ghost failure in a high-rise building is effectively prevented.

[0026]

As described above, according to the radio wave absorber and the precast concrete plate of the present invention, the frequency band (470-770 MHz) for television UHF broadcasting.
The entire radio wave is absorbed at a high absorption rate. As a result, a television ghost failure in a high-rise building is effectively prevented.

Further, according to the method of the present invention, the operation of producing the precast concrete plate of the present invention can be performed efficiently.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing a radio wave absorber corresponding to one embodiment of the present invention.

FIG. 2 is a graph showing the results of measuring the radio wave absorption performance of the radio wave absorber manufactured in the embodiment.

FIG. 3 is a sectional view showing a precast concrete plate corresponding to one embodiment of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Cement hardened body 2 Reticulated body (radio wave reflector) 3 Fluorine-based resin layer (decorative material) 4 Radio wave absorber 5 Concrete hardened body 51 Reinforcing bar

Continued on the front page (72) Inventor Wignaraja Shiva Kumaran 1-25-1, Nishi Shinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. (72) Inventor Kaori Makino 1-25-1, Nishi Shinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. (72) Inventor Hideki Ichihara 1-25-1, Nishishinjuku, Shinjuku-ku, Tokyo Taisei Construction Co., Ltd. (72) Inventor Manabu Teranishi 5-36-11, Shimbashi, Minato-ku, Tokyo FD -K Inc. (72) Inventor Masao Kosaka 30-13 Motoyogi-cho, Shibuya-ku, Tokyo Showa Mining Co., Ltd.F-term (reference) EA09 GA33W GA33X GA34W GB01W GB03W GB23X GB28W GB42W 2E162 CA11 CB17 EA11 EA18 5E321 AA41 AA44 BB22 BB25 BB60 CC16 GG11

Claims (5)

[Claims] 1. A radio wave reflection plate comprising a metal plate or a net-like body, and a cementitious cured body formed on one surface of the radio wave reflection plate.
A radio wave absorber comprising an aggregate made of g-Zn-based ferrite and / or Ni-Zn-based ferrite at a ratio of 35% or more and 60% or less based on the total volume of the hardened cement. 2. The radio wave absorber according to claim 1, wherein the ferrite aggregate contains at least 50% by volume of the ferrite aggregate having a particle size of 2 mm or more. 3. The radio wave absorber according to claim 1, further comprising a decorative material on a surface of the hardened cementitium opposite to the radio wave reflection plate. 4. A precast concrete plate wherein a cured concrete body is formed on the surface of the radio wave absorber according to claim 1 on the side of the radio wave reflection plate. 5. The method for producing a precast concrete plate according to claim 4, wherein the mold includes at least cement, water, and an aggregate made of the ferrite, which is a material for the cementitious hardened body. After placing the cementitious material, and installing the radio wave reflecting plate on the cast cementitious material, before the cast cementitious material hardens, the radio wave reflecting plate is placed on the radio wave reflecting plate. A method for manufacturing a precast concrete plate, comprising casting a concrete material for a concrete hardened body.