JP3469482B2 - Radio wave absorber - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention belongs to the technical field of electromagnetic wave absorbers.

[0002]

2. Description of the Related Art Radio wave absorbers are used to prevent radio wave interference due to 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 passing through the absorption layer is reflected by the reflection layer and reaches the absorption layer again to be absorbed. That is, since the light is absorbed twice before and after the reflection in the reflective layer, the absorption efficiency is good.

[0003]

By the way, 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 should be selected. The radio wave absorber used cannot absorb the high frequency band, and the radio wave absorber using the radio wave absorber suitable for the high frequency band cannot absorb the low frequency band. That is, it was difficult to absorb radio waves in a wide band with one type of radio wave absorber.

[0004]

According to a first aspect of the present invention, there is provided a radio wave absorber having a structure in which an absorption layer that absorbs radio waves and a reflection layer that reflects radio waves are laminated. The layer includes at least two types of radio wave absorbers, one of the 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. It is an inclined structure.

A radio wave absorber according to a second aspect of the present invention is the radio wave absorber according to the first aspect, wherein two types of radio wave absorbers contained in the absorption layer have different specific gravities.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION In the reflection layer of the radio wave absorber according to claim 1 or 2, for example, a metal foil, a metal wire grid, a synthetic resin sheet, or the like is vapor-deposited or sputtered with a metal.
Ion plating or electroless plating may be used, but the essential point is that it reflects radio waves, and is not limited to these examples.

The absorption layer of the radio wave absorber according to claim 1 or 2 is, for example, a metal-based radio wave absorber such as ferrite, iron, nickel, cobalt, titanium oxide, or zinc oxide, or a non-metal wave absorber such as carbon fiber. Contains two or more types. Note that these are examples of the radio wave absorber, and the radio wave absorber is not particularly limited.

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

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 which are incident from the absorption layer side are absorbed in the ferrite region and are transmitted in the high frequency band. Radio waves are absorbed in the area of titanium oxide. Also, the radio waves that have not reached the reflection layer and have reached the reflection layer are reflected here and then return to the absorption layer again. As described above, the radio waves in the low frequency band are in the ferrite region, and the radio waves in the high frequency band are in the titanium oxide region. Absorbed in the area.

To make the absorption layer have such a graded structure,
For example, a laminating method in which a first layer including the first electromagnetic wave absorber is laminated on a reflective layer, and a second layer including the second electromagnetic wave absorber is laminated thereon, and a paint including the first electromagnetic wave absorber is applied to the reflective layer. It is possible to employ a multi-coating method in which a paint containing the second electromagnetic wave absorber is applied on top of this.

Further, as described in claim 2, by making the specific gravities of the two kinds of electromagnetic wave absorbers different from each other, the inclined structure can be formed by the following method. That is, the first electromagnetic wave absorber having a relatively large specific gravity and the second electromagnetic wave absorber having a relatively small specific gravity are dispersed in a binder to be used as paint, and the paint is applied to the reflective layer to form an inclined structure. It can also be formed. In this case, when the reflection layer is placed horizontally and coated on the upper surface thereof, the first radio wave absorber having a relatively large specific gravity settles down and gathers on the reflection layer side, and the second radio wave absorber having a relatively small specific gravity. Is on the upper layer side of the coating 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. Moreover, in the surface layer of the coating film, the second radio wave absorber sinks and the binder becomes high in concentration, so that the strength of the surface layer of the coating film becomes high.

It is known that among the above-mentioned electromagnetic wave absorbers, for example, ferrite is effective in the low frequency band and titanium oxide is effective in the high frequency band. Therefore, for example, if ferrite and titanium oxide are included in the absorption layer, they are effective from the low frequency band to the high frequency band.

[0013]

Embodiments of the present invention will now be described more concretely by describing embodiments of the present invention with reference to the drawings. (Embodiment 1) FIG. 1 is a schematic diagram for explaining the structure of the electromagnetic wave absorber 10 of this embodiment. It should be noted that, for convenience of description, the dimensions, the shape of particles, and the like are different from the actual ones.

As shown in FIG. 1, the radio wave absorber 10 of this embodiment has a structure in which an absorption layer 14 is laminated on a reflection layer 12. The reflective layer 12 is a metal foil in this embodiment, and the upper surface 12a thereof is roughened. The reflective layer 1
2 may have another structure, for example, a structure in which a metal is plated or vapor-deposited on a plastic plate. Roughing is
Although it is provided to diffusely reflect radio waves, it may have another structure capable of diffusely reflecting radio waves, such as knurling. Alternatively, roughening or the like need not be performed.

The absorbing layer 14 includes two types of magnetic particles 16 and 18, a magnetic particle 16 having a relatively large specific gravity (eg titanium oxide powder) and a magnetic particle 18 having a relatively small specific gravity (eg ferrite powder), and a binder. It is composed of 20. In this embodiment, magnetic particles 16 and 1 are used as radio wave absorbers.
8 is adopted, but a radio wave absorber having another property can also be used. Further, the shape thereof 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 addition, 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 absorption layer 14 includes magnetic particles 16, 18,
It is formed by coating a paint containing the binder 20 and a solvent. That is, the reflective layer 12 was placed substantially horizontally, and the upper surface of the reflective layer 12 was coated with the aforementioned paint. The coating is sufficiently stirred before coating, and the distribution of the magnetic particles 16 and 18 inside the coating is almost uniform.

With this paint, the magnetic particles 16,
Even though the distribution of 18 is substantially uniform, the magnetic particles 16 having a relatively large specific gravity settle faster and evaporate from the solvent until the binder 20 solidifies, and the magnetic particles 16 in a portion close to the reflective layer 12 are formed. The concentration becomes 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 near the reflection layer 12 as shown in the drawing, and the magnetic particles 18 having a small specific gravity are in the upper layer. A graded structure with a high concentration on the side is obtained. Further, in the surface layer of the absorption layer 14, the magnetic particles 1
Since 6 and 18 both settle and the binder 20 has a high concentration, the strength of the surface layer of the absorption layer 14 increases.

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

The upper surface 12 of the reflecting layer 12 is not absorbed.
The radio wave reaching a is reflected here and returns to the absorption layer 14 again, and similarly to the above, 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. At this time, since the radio waves are irregularly reflected by the rough surface processing applied to the upper surface 12a (see FIG. 1C), if the angle between the path of the radio waves and the upper surface 12a of the reflecting layer 12 becomes small due to the irregular reflection, the absorbing layer 14 Since the path of the radio wave in the interior becomes long, the collisions with the magnetic particles 16 and 18 increase, and the absorption efficiency is increased. (Embodiment 2) FIG. 2 is a schematic diagram for explaining the structure of the electromagnetic wave absorber 30 of this embodiment. Similar to FIG. 1, the size, the shape of particles, etc. are different from the actual ones.

As shown in FIG. 2, the radio wave absorber 30 of this embodiment has a structure in which an absorption layer 32 is laminated on the reflection 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, the reflective particles 34 of the radio wave reflecting material are further added. Although the reflective particles 34 are metal particles in this embodiment,
Other materials such as mica, ceramics, plastic, and the like, on the surface of which metal is plated or vapor-deposited, may be used.
Further, the shape may be various such as particle, powder, fiber, and flake. In FIG. 2, the magnetic particles 16 are indicated by □ and the magnetic particles 18 are indicated by □ in order to clearly distinguish the respective particles.
Is indicated by ◯, and the reflective particles 34 are indicated by Δ.

This absorbing layer 32 is also the absorbing layer 14 of the first embodiment.
Similarly, the magnetic particles 16 and 18, the reflective particles 34, the binder 20 and the solvent are formed by coating a paint, and the magnetic particles 16 and the magnetic particles are formed between the coating and the solidification of the paint. 18 and the reflective particles 34 settle according to the difference in their respective specific gravities, the concentration of the magnetic particles 16 is relatively high in the portion close to the reflective layer 12, and the concentration of the magnetic particles 18 is higher on the upper layer side than that. It has a structure. Also,
In the same manner as in Example 1, the binder 2 is used on the surface layer of the absorption layer 32.
0 has a high concentration, and the strength of the surface layer is high.

The radio wave absorber 30 is used by being attached to, for example, the wall surface of a building by an attaching means such as an adhesive, a double-sided tape, bolts and screws. 2 in the absorption layer 32
Since the magnetic particles 16 and 18 of different types are included and the effective frequency band is usually different depending on the type of magnetic substance, it is possible to efficiently absorb radio waves in a wide frequency band that cannot be handled by one type of magnetic substance. For example, magnetic particles 16, 1
If one of 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. Therefore, the radio wave in the low frequency band incident on the absorption layer 14 is in the ferrite region. Radio waves in the high frequency band are absorbed and absorbed in the titanium oxide region. Therefore, radio waves can be efficiently absorbed from the low frequency band to the high frequency band.

The upper surface 12 of the reflecting layer 12 is not absorbed.
The radio wave reaching a is reflected here and returns to the absorption layer 32 again, and similarly to the above, 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. At this time, since the radio waves are diffusely reflected by the rough surface processing applied to the upper surface 12a, if the angle between the path of the radio waves and the upper surface 12a of the reflecting layer 12 becomes smaller due to the diffuse reflection, the travel time of the radio waves in the absorbing layer 14 becomes longer. Therefore, the number of collisions with the magnetic particles 16 and 18 is increased, and the absorption efficiency is improved.

Further, in this embodiment, since the absorbing layer 32 includes the reflecting particles 34, the incident electric wave and the electric wave reflected by the reflecting layer 12 are also reflected by the reflecting particles 34. Therefore, for example, as shown in FIG. 2A, when the radio wave incident at the incident angle θ1 is reflected by the reflective particles 34 at the reflection angle θ2 larger than θ1, the path of the radio wave and the upper surface 12a of the reflection layer 12 are formed. Since the angle with and becomes smaller and the path of the radio wave in the absorption layer 14 becomes longer, the collisions with the magnetic particles 16 and 18 increase, and the absorption efficiency increases.

Further, as shown in FIG. 2B, even when the reflection particles 34 and the reflection layer 12 are reflected a plurality of times, the travel time of the radio wave in the absorption layer 14 becomes long, and accordingly, the magnetic particles are increased. The collision with 16 and 18 increases, and the absorption efficiency is improved. Although the embodiments of the present invention have been described above including the examples, 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]

The radio wave absorber according to claim 1 includes at least two types of radio wave absorbers in the absorption layer, and one of the two types of radio wave absorbers has a relatively high concentration on the reflection layer side, and the other one. Since it has an inclined structure in which the concentration is relatively high on the side opposite to the reflection layer side, it is possible to absorb radio waves in a wide band with one type of radio wave absorber.

In order to obtain this tilted structure, as described in claim 2, the two types of electromagnetic wave absorbers contained in the absorption layer may be made to have different specific gravities, and coating may be performed by using a paint containing them. According to the structure of claim 2, the inclined structure can be easily obtained.

[Brief description of drawings]

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

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

[Explanation of symbols]

10 ... Radio wave absorber, 12 ... Reflective layer, 12a ... Top surface, 14
... Absorption layer, 16 ... Magnetic particles (radio wave absorber), 18 ... Magnetic particles (radio wave absorber), 20 ... Binder, 30 ... Radio wave absorber, 32 ... Absorption layer, 34 ... Reflection particles.

─────────────────────────────────────────────────── ─── Continuation of the front page (56) Reference JP-A-10-150291 (JP, A) JP-A-5-101883 (JP, A) JP-A-58-127400 (JP, A) JP-A-1- 223242 (JP, A) JP-A-10-290094 (JP, A) JP-A-4-211199 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) H05K 9/00 B32B 7 / 02

Claims (2)

(57) [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,
Radio wave absorption, characterized in that one of these 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 opposite side to the reflection layer side. Material. 2. The radio wave absorber according to claim 1, wherein the two types of radio wave absorbers contained in the absorption layer have different specific gravities.