JP2000151179A - Radio wave absorption material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a radio wave absorption material that can absorb a wide range of radio wave. SOLUTION: In a radio wave absorption material 30, an absorption layer 32 is laminated on a reflection layer 12. In inclination structure of the radio wave absorption material 30, the absorption layer 32 is formed by applying paint where magnetic particles 16 and 18, a reflection particle 34, a binder 20, and a solvent are blended. Until the paint is hardened, the magnetic particles 16 and 18 and the reflection particle 34 are allowed to settle according to the difference of each specific gravity, the concentration of the magnetic particle 16 is relatively high near the reflection layer 12, and that of the magnetic particle 18 is high at an upper-layer side as compared with the reflection layer 12. The magnetic particles 16 and 18 absorb an effective frequency band, thus efficiently absorbing a radio wave in a wide frequency range. The radio wave being allowed to enter is reflected by the reflection particle 34 at a reflection angle θ2 being large than α1, and is subjected to reflection for a plurality of times, thus lengthening the traveling distance of the radio wave in the absorption layer, and hence increasing absorption efficiency.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention belongs to the technical field of radio wave absorbing materials.

[0002]

2. Description of the Related Art Radio wave absorbing materials have been used to prevent radio interference caused by reflection of radio waves. Some of such radio wave absorbers include an absorption layer that absorbs radio waves and a reflection layer that reflects radio waves. With this laminated structure, the radio wave incident from the absorption layer side is first absorbed by the absorption layer, and the radio wave that has passed through the absorption layer is reflected by the reflection layer and is again absorbed by the absorption layer. That is, since the light is absorbed twice before and after the reflection in the reflection layer, the absorption efficiency is good.

[0003]

Since the frequency band of the radio wave absorbed by the absorption layer is substantially determined by the type of the radio wave absorber contained in the absorption layer, for example, a radio wave absorber suitable for a low frequency band is used. The radio wave absorber used could not absorb the high frequency band, and the radio wave absorber using the radio wave absorber suitable for the high frequency band could not absorb the low frequency band. That is, it was difficult to absorb a wide range of radio waves with one type of radio wave absorbing material.

[0004]

According to a first aspect of the present invention, there is provided a radio wave absorbing material having a structure in which an absorbing layer for absorbing a radio wave and a reflecting layer for reflecting a radio wave are laminated. The layer includes at least two types of radio wave absorbers, one of the two types of radio wave absorbers having a relatively high density on the reflection layer side and the other having a relatively high density on the side opposite to the reflection layer side. This is the inclined structure.

According to a second aspect of the present invention, there is provided the radio wave absorbing material according to the first aspect, wherein the two types of radio wave absorbers included in the absorbing layer have different specific gravities.

[0006]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The reflecting layer of the radio wave absorbing material according to claim 1 or 2 is formed by depositing a metal on a metal foil, a metal wire grid or a sheet of a synthetic resin, sputtering, or the like.
Ion plating or electroless plating can be used, but the point is that it is only necessary to reflect radio waves, and the invention is not limited to these examples.

[0007] The absorbing layer of the radio wave absorbing material according to the first or second aspect is made of a metal-based radio wave absorber such as ferrite, iron, nickel, cobalt, titanium oxide, zinc oxide or the like, or a non-metallic radio wave absorber such as carbon fiber. Is contained in two or more types. These are examples of the radio wave absorber, and the radio wave absorber is not particularly limited.

[0008] In the present invention, the absorbing layer has a gradient structure in which one of at least two types of radio wave absorbers has a relatively high concentration on the reflection layer side and the other has a relatively high concentration on the side opposite to the reflection layer side. I have to. For example, using ferrite and titanium oxide, the titanium oxide has a relatively high concentration on the reflection layer side, and the ferrite has a relatively high concentration on the opposite side.

[0009] Since ferrite is effective in the low frequency band and titanium oxide is effective in the high frequency band, radio waves in the low frequency band incident from the absorption layer are absorbed in the ferrite region, and transmitted through the high frequency band. Radio waves are absorbed in the region of titanium oxide. In addition, radio waves that have reached the reflection layer without being absorbed are reflected here and return to the absorption layer again, and as described above, low-frequency radio waves are in the ferrite region, and high-frequency radio waves are titanium oxide. Absorbed in the area.

In order to make the absorption layer have such a tilted structure,
For example, a lamination method in which a first layer including a first radio wave absorber is laminated on a reflective layer, and a second layer including a second radio wave absorber is laminated thereon, , And a paint containing a second radio wave absorber is applied thereon.

Further, by making the specific gravity of the two kinds of radio wave absorbers different from each other, the inclined structure can be formed by the following method. In other words, a first radio wave absorber having a relatively large specific gravity and a second radio wave absorber having a relatively lower specific gravity are dispersed in a binder to form a paint, and this paint is applied to a reflective layer to form an inclined structure. It can also be formed. In this case, when the reflective layer is placed horizontally and painted on its upper surface, the first radio wave absorber having a relatively large specific gravity sinks and collects on the reflective layer side, and the second radio wave absorber having a relatively small specific gravity is provided. Is the upper layer side of the paint film,
The first radio wave absorber has a relatively high concentration on the reflection layer side, and the second radio wave absorber has a relatively high concentration on the side opposite to the reflection layer side. In addition, in the surface layer of the coating film, the second radio wave absorber sinks and the concentration of the binder becomes high, so that the strength of the surface layer of the coating film increases.

Among the above-mentioned radio wave absorbers, for example, it is known that ferrite is effective in a low frequency band and titanium oxide is effective in a high frequency band. Therefore, if, for example, ferrite and titanium oxide are included in the absorption layer, it is effective from a low frequency band to a high frequency band.

[0013]

Next, embodiments of the present invention will be described more specifically with reference to the accompanying drawings. (Embodiment 1) FIG. 1 is a schematic diagram illustrating the structure of a radio wave absorber 10 of the present embodiment. Note that, for convenience of explanation, dimensions, shapes of particles, and the like are different from actual ones.

As shown in FIG. 1, the radio wave absorbing material 10 of the present embodiment has a structure in which an absorbing layer 14 is laminated on a reflecting layer 12. The reflective layer 12 is a metal foil in this embodiment, and its upper surface 12a is roughened. In addition, the reflection layer 1
2 may have another structure, for example, a structure in which metal is plated or deposited on a plastic plate. Rough surface processing
Although provided for irregularly reflecting radio waves, other structures capable of irregularly reflecting radio waves, such as knurls, may be used. Alternatively, rough surface processing or the like need not be performed.

The absorbing layer 14 is composed of two types of magnetic particles 16, 18 of magnetic particles 16 having a relatively large specific gravity (eg, titanium oxide powder) and magnetic particles 18 having a relatively small specific gravity (eg, ferrite powder) and a binder. 20. In this embodiment, the magnetic particles 16 and 1 are used as radio wave absorbers.
8, but a radio wave absorber of other properties can also be used. Further, the shape is not limited to the particle shape, and may be various shapes such as a powder shape, a fiber shape, and a flake shape. In FIG. 1, in order to clearly show the distinction between the magnetic particles 16 and the magnetic particles 18, the magnetic particles 16 are indicated by □ and the magnetic particles 18 are indicated by ○.

The absorbing layer 14 comprises magnetic particles 16, 18,
It is formed by applying a paint containing a binder 20 and a solvent. That is, the reflective layer 12 was placed substantially horizontally, and the above-described paint was applied to the upper surface of the reflective layer 12. Before painting, the paint is sufficiently agitated, and the distribution of magnetic particles 16 and 18 therein is substantially uniform.

In this paint, the magnetic particles 16,
Even though the distribution of the magnetic particles 16 is substantially uniform, the magnetic particles 16 having a relatively large specific gravity settle down faster until the solvent evaporates and the binder 20 solidifies, and the magnetic particles 16 in a portion close to the reflective layer 12 Is relatively high.

When the solvent is volatilized and the binder 20 is solidified, the concentration of the magnetic particles 16 is relatively high in the portion close to the reflective layer 12 and the magnetic particles 18 having a low specific gravity are in the upper layer as shown in FIG. A graded structure with a high concentration on the side is obtained. In the surface layer of the absorption layer 14, the magnetic particles 1
Since both the binders 6 and 18 settle and the binder 20 has a high concentration, the strength of the surface layer of the absorption layer 14 increases.

The radio wave absorbing material 10 is used by being attached to, for example, a wall surface of a building by attaching means such as an adhesive, a double-sided tape, a bolt or a screw. 2 in the absorption layer 14
Since magnetic particles 16 and 18 of different types are included and the effective frequency band usually differs depending on the type of magnetic material, radio waves in a wide frequency band that cannot be handled by one type of magnetic material can be efficiently absorbed. For example, the magnetic particles 16, 1
If one of ferrites 8 is ferrite and the other is titanium oxide, the ferrite is effective in the low frequency band and the titanium oxide is effective in the high frequency band. Absorbed (Fig. 1 (a)
Radio waves in the high frequency band are absorbed in the titanium oxide region (see FIG. 1 (b)). Therefore, radio waves can be efficiently absorbed from the low frequency band to the high frequency band.

The upper surface 12 of the reflection layer 12 is not absorbed.
The radio wave that has reached a is reflected here and returns to the absorption layer 14 again, and the radio wave in the low frequency band is absorbed in the ferrite region and the radio wave in the high frequency band is absorbed in the titanium oxide region, as described above. At this time, since the radio waves are irregularly reflected by the roughening process performed on the upper surface 12a (see FIG. 1C), if the angle between the path of the radio waves and the upper surface 12a of the reflective layer 12 becomes smaller due to the irregular reflection, the absorption layer 14 is formed. Since the distance of the radio wave in the inside becomes long, the collision with the magnetic particles 16 and 18 increases and the absorption efficiency is improved. (Embodiment 2) FIG. 2 is a schematic diagram illustrating the structure of a radio wave absorber 30 of the present embodiment. Note that the dimensions, the shape of the particles, and the like are different from the actual ones as in FIG.

As shown in FIG. 2, the radio wave absorbing material 30 of the present embodiment has a structure in which an absorbing layer 32 is laminated on the reflecting layer 12. The reflection layer 12 is the same as that of the first embodiment, and is made of metal foil, and the upper surface 12a is roughened. In the absorbing layer 32, the same magnetic particles 16 and 18 as in Example 1 are dispersed in the same binder 20 as in Example 1, but in this example, reflective particles 34 of a radio wave reflecting material are further added. The reflecting particles 34 are metal particles in the present embodiment,
Other materials such as mica, ceramics, plastics, and the like, which are plated or vapor-deposited on the surface thereof, may be used.
In addition, the shape may be various such as particle, powder, fiber, and flake. In FIG. 2, the magnetic particles 16 are indicated by squares and the magnetic particles
Is indicated by ○, and the reflective particles 34 are indicated by △.

This absorbing layer 32 is also the absorbing layer 14 of the first embodiment.
In the same manner as described above, the magnetic particles 16, 18, the reflective particles 34, the binder 20, and the solvent are mixed to form a coating material. 18 and the reflective particles 34 settle according to the difference in their specific gravities, and the concentration of the magnetic particles 16 is relatively high in a portion close to the reflective layer 12 and the concentration of the magnetic particles 18 is higher in the upper layer side. It has a structure. Also,
As in the case of the first embodiment, the binder 2
0 is a high concentration and the strength of the surface layer is high.

The radio wave absorbing member 30 is used by being attached to, for example, a wall surface of a building or the like by attaching means such as an adhesive, a double-sided tape, a bolt or a screw. 2 in the absorption layer 32
Since magnetic particles 16 and 18 of different types are included and the effective frequency band usually differs depending on the type of magnetic material, radio waves in a wide frequency band that cannot be handled by one type of magnetic material can be efficiently absorbed. For example, the magnetic particles 16, 1
If one of ferrites 8 is ferrite and the other is titanium oxide, the ferrite is effective in the low frequency band and the titanium oxide is effective in the high frequency band. Absorbed radio waves in the high frequency band are absorbed in the region of titanium oxide. Therefore, radio waves can be efficiently absorbed from the low frequency band to the high frequency band.

The upper surface 12 of the reflection layer 12 is not absorbed.
The radio wave that has reached a is reflected here and returns to the absorption layer 32 again, and the radio wave in the low frequency band is absorbed in the ferrite region and the radio wave in the high frequency band is absorbed in the titanium oxide region, as described above. At this time, since the radio waves are irregularly reflected by the rough surface processing performed on the upper surface 12a, if the angle between the path of the radio waves and the upper surface 12a of the reflective layer 12 becomes smaller due to the irregular reflection, the travel of the electric waves in the absorption layer 14 becomes longer. Therefore, the collision with the magnetic particles 16 and 18 increases, and the absorption efficiency is improved.

Further, in the case of the present embodiment, since the reflecting particles 34 are included in the absorbing layer 32, the incident radio waves and the radio waves reflected by the reflecting layer 12 are also reflected by the reflecting particles 34. Therefore, for example, as shown in FIG. 2A, when a radio wave incident at an incident angle θ1 is reflected by the reflective particles 34 at a reflection angle θ2 larger than θ1, the path of the radio wave and the upper surface 12a of the reflective layer 12 Is smaller, and the path of the radio wave in the absorption layer 14 is longer. Therefore, the collision with the magnetic particles 16 and 18 is increased and the absorption efficiency is increased.

Also, as shown in FIG. 2B, when a plurality of reflections are made by the reflective particles 34 and the reflective layer 12, the travel of the radio wave in the absorption layer 14 becomes longer. The number of collisions with 16, 16 increases, and the absorption efficiency is improved. As described above, the embodiments of the present invention including the examples have been described. However, it is needless to say that the present invention is not limited to these examples, and can be variously implemented without departing from the gist of the present invention.

[0027]

According to the radio wave absorbing material of the present invention, the absorbing layer contains at least two types of radio wave absorbers, and one of the two types of radio wave absorbers has a relatively high concentration on the reflection layer side and the other has a high density. Is an inclined structure having a relatively high concentration on the side opposite to the reflection layer side, so that a single type of radio wave absorbing material can absorb a wide range of radio waves.

In order to obtain this inclined structure, the specific gravity of the two types of radio wave absorbers contained in the absorption layer may be made different from each other and the coating may be applied using a paint containing them. According to the structure of claim 2, the inclined structure can be easily obtained.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating the structure of a radio wave absorber according to a first embodiment.

FIG. 2 is a schematic diagram illustrating the structure of a radio wave absorber according to a second embodiment.

[Explanation of symbols]

10: radio wave absorber, 12: reflective layer, 12a: upper surface, 14
... Absorbing layer, 16: Magnetic particles (radio wave absorber), 18: Magnetic particles (radio wave absorber), 20: Binder, 30: Radio wave absorber, 32: Absorbing layer, 34: Reflecting particles.

Claims (2)

[Claims] 1. A structure in which an absorption layer that absorbs radio waves and a reflection layer that reflects radio waves are laminated, wherein the absorption layer includes at least two types of radio wave absorbers,
The two types of radio wave absorbers have an inclined structure in which one of the two types of radio wave absorber has a relatively high concentration on the reflection layer side and the other has a relatively high concentration on the side opposite to the reflection layer side. Wood. 2. The radio wave absorber according to claim 1, wherein the two types of radio wave absorbers included in the absorption layer have different specific gravities.