JPS6242559Y2 - - Google Patents

Description

[Detailed description of the invention] This invention relates to a radio wave absorber using ferrite powder produced by a wet method.

Conventionally, ferrite materials are well known as radio wave absorbers that absorb high frequency signals such as microwaves. This ferrite is produced using a dry method in which oxides, hydroxides, carbonates, etc. of heavy metals such as barium and strontium are mechanically mixed, heated, and produced through a solid reaction, resulting in high production costs and powder particles. The diameter tends to be nonuniform, resulting in large deviations in quality, making it difficult to obtain products with stable quality. On the other hand, wet methods have recently become popular, as they do not require a solid reaction and therefore do not require a calcination step, can reduce costs, and can make the powder particle size small and uniform. However, in either method, the ferrite powder must be molded to form a radio wave absorber, and the drawback of high cost cannot be overcome.
Moreover, an important characteristic of a radio wave absorber is that it has good radio wave attenuation properties over a wide frequency band, but in reality, products made from one type of ferrite powder have a limit to their ability to widen the range. Therefore, it is necessary to use a composite combination of radio wave absorbers obtained by molding various types of ferrite powders, and therefore, it is difficult to implement a method that aims to widen the radio wave attenuation property due to an increase in cost. There was an inconvenience.

This invention was proposed in light of the above,
The object of the present invention is to provide a new and improved radio wave absorber in which ferrato powder is solidified by a wet method.

According to the present invention, a radio wave absorber made of ferrite powder is wet-impregnated and fixed in a foamable resin. In this impregnation step, a suspension in which ferrite powder is dispersed in an aqueous binder solution is used to impregnate and fix the foamable resin. Here, the impregnation and fixation density of the ferrite powder is changed stepwise to form layers with different relative magnetic permeability μ or relative dielectric constant ε, thereby improving the properties.

First, for convenience of explanation, a schematic manufacturing process of a radio wave absorber as an example will be described. In Figure 1,
1 is a flexible, open-cell foamed resin made of, for example, ether polyurethane, and has a porosity of about 90% or more. 2 is a divalent iron ion Fe ²⁺ and a divalent heavy metal ion other than iron such as Mg ²⁺ , Mn ²⁺ ,
An appropriate amount of a strong alkali, such as NaOH, is added to a mixed aqueous solution of Co ²⁺ , Ni ²⁺ , Cu ^{2+ ,} etc., and while heating it to a temperature of about 100°C, air is blown to cause an oxidation reaction and precipitate. A spinel-type ferrite powder obtained by drying the powder, discarding the remaining liquid, and having a particle size of about 0.05 μm to 1 μm.
3 is an aqueous solution prepared by mixing and stirring a starch-based adhesive or a polyvinyl alcohol-based adhesive as a binder having adhesive properties in water, and 4 is a treatment tank for this.
Therefore, in order to obtain a radio wave absorber, as shown in FIG. 2, the foamed resin 1 is immersed in an aqueous solution 3 mixed with a desired amount of ferrite powder 2 to perform a so-called impregnation treatment. Here, the method of impregnation treatment is as follows.
As shown in FIG. 3, the concentration n of the ferrite powder 2 in the aqueous solution 3 is varied, and the foamed resin 1 is impregnated in a predetermined area at a depth d from the surface according to this change. In other words, the ferrite powder concentration n and the depth d are set to different values n ₁ and d ₁ , n ₂ and d _{2 . .} . Form multiple impregnated fixed layers.

For example, a three-layer fixed layer 6 as shown in FIG.
7 and 8, first, the foamed resin 1 is immersed in a mixed solution 3 in which the concentration of ferrite powder 2 is n ₁ , and the immersion time is controlled to increase the depth from the resin surface.
Impregnate with a mixed solution of concentration n ₁ up to d ₁ . Thereafter, it is dried and fixed to obtain an impregnated fixed layer 8 having a concentration n ₁ and a depth d ₁ .

Next, this foamed resin 1 is immersed in a mixed solution having a concentration of n ₂ to be impregnated from the surface to a depth d ₂ (d ₁ >d ₂ ) and dried to form an impregnated fixed layer 7 . Finally, it is immersed in mixed solution 3 with a concentration of n ₃ to a depth of d ₃ (d ₁ > d ₂ > d ₃ ) from the surface.
The impregnated fixing layer 6 is formed by dipping until drying.

Here, each depth d ₁ , d ₂ ..., d _o is the concentration
_These are values set corresponding _{to n 1 , n .} Therefore, in the impregnated fixed layers 6, 7, and 8 formed by the mixed impregnation method according to the present invention, the concentration of ferrite powder in each layer is not uniform, and the outer layer is denser and the inner layer is lighter. Become.

FIG. 4 shows the ferrite powder-impregnated fixing layers 6, 7,
8, . . . are cross-sectional views of a multilayered radio wave absorber.

The radio wave absorber having the above structure includes impregnated fixing layers 6, 7, 8 having different impregnation fixing degrees of ferrite powder 2,
... is formed in multiple layers, and the relative magnetic permeability .mu. and relative dielectric constant .epsilon. of each impregnated fixed layer vary in various ways, so that it exhibits radio wave absorption and radio wave attenuation effects in all frequency bands. In other words, as is well known, in order to perform radio wave absorption and radio wave attenuation effects, the voltage standing wave ratio VSWR must be 2.0 or less, and the normalized impedance in front of it must be The relative magnetic permeability μ and relative permittivity ε expressed in complex numbers must be set so that VSWR is equal to VSWR, but the thickness d of the radio wave absorber in equation (1) is determined by This is because the normalized impedance Z _L in the entire frequency band can be set to 2.0 or less in absolute value. In equation (1), λ is the wavelength of the radio wave to be absorbed and attenuated. Furthermore, as described above, ferrite powder is mixed with an aqueous binder solution, and this mixed solution is impregnated and fixed in the foamed resin, so it is always flexible and can be used as a sealing material to prevent high frequency leakage. It is suitable as For example, when installing a gasket as a gasket to a high-frequency leak passage in an open minute space in a high-frequency device such as a microwave oven, it is easy to install, only requires the use of a single radio wave absorber, and is inexpensive. be.

In the above example, ether-based polyurethane was used as the foamable resin for impregnating and fixing the spinel-type ferrite powder, but this invention uses a resin that has a low dielectric constant, high frequency permeability, and flexibility. For example, it is clear that ester polyurethane or the like may be used.

According to this invention, it is flexible as a radio wave absorber, is inexpensive, and can be easily extended to a wide band, so it is more practical and effective than conventional rubber ferrite or sintered ferrite. It is possible to provide a radio wave absorber with remarkable

[Brief explanation of the drawing]

Figures 1 and 2 are cross-sectional views of a processing tank for a foamable resin and an adhesive aqueous solution to explain the manufacturing process of a radio wave absorber, which is an embodiment of this invention, and Figure 3 is a cross-sectional view of a treatment tank for an aqueous solution of ferrite powder. FIG. 4 is a stepwise broken line characteristic diagram showing the relationship between the concentration and the impregnation depth of the impregnated fixed layer, and FIG. 4 is a cross-sectional view of the radio wave absorber according to the present invention. 1... Foamed resin, 2... Ferrite powder, 3...
...aqueous solution.

Claims (1)

[Scope of utility model registration request] It is made up of multiple wet-impregnated fixed layers obtained by impregnating a foamable resin into a mixed solution of a binder aqueous solution and ferrite powder. μ
Alternatively, a radio wave absorber characterized by having a dielectric constant ε set in different states.