JPH04211199A - Wave absorber - Google Patents

Abstract

PURPOSE:To obtain a wave absorber which is less in thickness and weight and excellent in constructing workability and wave absorbing power by forming a composite layer of a thin film formed of a magnetic alloy containing transition metals on the surface of a wave loss layer containing ferrites and a spacer layer formed on the surface of the thin film. CONSTITUTION:This wave absorber is constituted of a ferrite containing layer A having a wave losing power and a composite layer of a magnetic alloy layer B and spacer layer C. The ferrite containing layer A is formed by forming a resin containing a ferrite, such as hematite, magnetite, etc., in a scattered state to a sheet-like shape or drying the resin after the resin is applied to a substrate. The magnetic alloy layer B is formed by depositing a magnetic alloy containing transition metals, such as terbium, iron, cobalt, nickel, etc., on the surface of the layer A by vapor deposition, sputtering, etc. The spacer layer C is formed as required by applying and drying a resin liquid having a low dielectric constant and low permeability.

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 that can be made thinner and lighter. [0002]

BACKGROUND OF THE INVENTION Conventionally, radio wave absorbing materials are known in which ferrite or a mixture of ferrite and metal powder or carbon powder is dispersed in an organic polymer. However, the above-mentioned material has a film thickness of at least 1 mm or more, and at least 4.0 mm in thickness when absorbing radio waves with a wide range of frequencies.
If it is not 5 mm or more, the radio wave absorption ability is poor and it is not practical.
Thick film is required. Therefore, when used, it has the disadvantage of being heavy and having poor construction workability.
There was a demand for the development of a radio wave absorber that is lightweight, easy to work with, and has excellent radio wave absorption ability. [0003]

[Means for Solving the Problems] In order to solve the above problems, the present inventor has conducted extensive research on radio wave absorbers, and has found that a radio wave loss layer containing ferrite is used as a bulk layer, and a transition metal is contained on the surface of this layer. The present inventors have discovered that a multilayer formed of a thin film of a magnetic alloy has a much superior radio wave absorption ability compared to a radio wave loss layer alone containing ferrite at the same film thickness, and has completed the present invention. [0004] That is, the present invention includes a ferrite-containing layer (A) having radio wave loss ability and a film thickness of 1 nm to 1 nm on the core layer (A).
The present invention provides a radio wave absorber characterized in that it has one or more units of a multilayer film including a 200 nm transition metal-containing magnetic alloy layer (B). [0005] Furthermore, the present invention provides the above radio wave absorber, further comprising a spacer layer (C) on the magnetic alloy layer (B).
This invention relates to a radio wave absorber in which a unit film is a multi-layered film. That is, the present invention provides a ferrite-containing layer (
A), a magnetic alloy layer (B) containing a transition metal element with a film thickness of 1 nm to 200 nm on the core layer (A), and the alloy layer (B
) with the spacer layer (C) as a unit film.
The present invention also provides a radio wave absorber characterized by having at least one unit. [00061 In the present invention, the ferrite-containing layer (A)
As the ferrite contained in the ferrite, ferrite conventionally used in radio wave absorbers can be used. Typical examples include hematite (Fe203) and magnetite (Fe304).
, generally an iron oxide containing different metal elements (M is Mn, Co, Ni, Cu,
Zn, Ba, Mg, etc.). [0007] In the present invention, the layer (A) is obtained by, for example, dispersing the above-mentioned ferrite in a resin and molding it into a sheet shape or coating it on a base material and drying it. Examples of resins used here include rosin, shellac, ester rubber, Hypalon (chlorosulfonated polyethylene) rubber, chlorinated rubber, chloroprene rubber, vinyl chloride resin, polyester resin, alkyd resin, phenolic resin, epoxy resin, acrylic resin, Examples include resins such as urethane resin, silicone resin, cellulose resin, and vinyl acetate resin. [0008] When dispersed in a resin, the particle size of ferrite is not particularly limited, but generally the particle size is 100
From the viewpoint of dispersibility, etc., it is preferable that the thickness is in the range of .mu.m or less. In addition, the amount of ferrite blended is not particularly limited, but from the viewpoint of coating film strength, radio wave loss ability, etc.
It is preferably in the range of 10 to 400 parts by weight relative to 0 parts by weight. [0009] In addition to ferrite, which is an essential component, the resin contains iron powder such as electrolytic iron, carbonyl iron or reduced iron, nickel powder such as electrolytic nickel or carbonyl nickel, electrolytic cobalt, reduced cobalt, carbonyl cobalt, etc. One or more types of cobalt powder, carbon, copper powder, brass powder, etc. may be blended and dispersed, and if necessary, additives such as organic solvents and dispersants may be blended. Further, the layer (A) can also be formed in the form of a base material by a method such as vapor deposition or sputtering of the ferrite. [00101 In the present invention, base materials on which the layer (A) can be formed include plastic sheets such as polyethylene terephthalate (PET) and vinyl chloride; metals such as brass, copper, iron, stainless steel, and aluminum; can be mentioned. In the present invention, the layer (A
) may be appropriately selected depending on the frequency of radio waves to be absorbed, but it is usually preferably in the range of 1 μm to 1 mm;
When the thickness is less than 1 μm, the radio wave loss ability tends to be insufficient. On the other hand, as the thickness exceeds 1 mm, the weight increases and the workability becomes worse. [0011] In the present invention, the magnetic alloy layer (B) containing a transition metal element is formed on the radio wave loss layer (A), and the layer (B) functions as a kind of half mirror. In other words, when radio waves enter from outside (in the air),
Most of the radio waves pass through layer (B), and the transmitted radio waves attenuate while passing through layer (A) and reach the lower surface of layer (A), where all or part of the radio waves are reflected. . The radio waves reflected from the surface of the lower layer pass through the layer (A) while being attenuated,
It reaches the interface between layer (A) and layer (B). Layer (B) and Layer (A)
At the interface, layer (B) acts as a kind of half mirror, and most of the radio waves that have passed through layer (A) are reflected at this interface, which is repeated, and the radio waves make multiple round trips within layer (A). Therefore, it is thought that radio waves are efficiently attenuated and absorbed. [0012] The magnetic alloy layer (B) is made of a magnetic alloy thin film containing a transition metal element, and the alloy layer is, for example, a terbium-iron-cobalt alloy (TbF
eCo), iron-nickel alloy (FeNi), manganese-
Copper-bismuth alloy (Mn Cu Bi), gadolinium-terbium-iron alloy (Gd Tb Fe),
Gadolinium-iron-bismuth alloy (Gd Fe B
i), gadolinium-iron-cobalt alloy (Gd Fe
Co), platinum-cobalt alloy (PtCo), dysprosium iron alloy (DyFe), and the like. [0013] This magnetic alloy layer (B) can be formed on the layer (A) by vapor deposition, sputtering, or ion-blating the above-mentioned alloy, or by simultaneously vapor-depositing each elemental metal component forming the alloy. The layer (B) can also be formed by performing , sputtering, ion blating, or the like. Moreover, after forming the layer (A) and the layer (B), it can be peeled off from the base material to form a free film. [0014] The thickness of the magnetic alloy layer (B) is 1 nm to 20 nm.
It is necessary that the film thickness is within the range of 0 nm, preferably within the range of 10 nm to 150 nm, and if the film thickness is less than 1 nm,
On the other hand, if the thickness exceeds 200 nm, it will take a long time to form the layer (B), and a considerable proportion of radio waves will be transmitted from the outside (in the air). Then, it is reflected by layer (B), and the radio wave absorber is no longer effective enough. [0015] In the present invention, the radio wave absorber may have only one unit of a multilayer consisting of a ferrite-containing layer (A) and a magnetic alloy layer (B) as a unit film, or may have the above multilayer as a unit. The membrane may have two or more units. Furthermore, in the present invention, in addition to the layer (A) and the alloy layer (B) constituting the unit film, the alloy layer (
B) It may have only one unit of a multilayer having a spacer layer (C) thereon as a unit film, or it may have two or more units of the above multilayer as a unit film. [0016] The spacer layer (C) is a layer exhibiting low dielectric constant and low magnetic permeability, and is a layer between the layer (A) and the alloy layer (B) when a plurality of unit films are used. It may act as an adhesive for the radio wave absorber, or it may improve the material properties of the radio wave absorber. The spacer layer (C) can be, for example, a clear resin layer, which is obtained by applying a resin liquid onto the layer (B) and drying it. Examples of resins used here include rosin, hexalac, polyethylene, styrene resin, vinyl chloride resin, polyester resin, alkyd resin, phenol resin, epoxy resin, acrylic resin, urethane resin, silicone resin, cellulose resin, and acetic acid resin. Examples include resins such as vinyl resins. [0017] Also, a layer obtained by coating and drying a pigment such as an extender pigment or a coloring pigment dispersed in a liquid of these resins, and the layer exhibits a low dielectric constant and a low magnetic permeability. If it is, it is included in the spacer layer (C). The thickness of the spacer layer (C) is not particularly limited, but it is usually preferably in the range of 1 μm to 100 μm. Also, the spacer layer (C) exists between the layer (B) and the layer (A), and when using multiple unit films, the spacer layer (C) may or may not be present on the top layer. It's okay. [0018] The unit film has a layer (A) and an alloy layer (B)
In any of the cases of layer (A), alloy layer (B), and spacer layer (C), the radio wave absorption ability can be further increased by having a plurality of unit films. In other words, there is a preferable film thickness for a unit film depending on the radio wave frequency and the type of radio wave absorber, but in general, when the overall film thickness and the material of the layer (A) are the same, the unit film thickness is better than the unit film - unit alone. By making it thinner and stacking multiple units, the radio wave absorption ability can be increased. The reason for this is each layer (A)
Since the radio waves entering the layer (A) undergo multiple reflections within each layer (A),
A) Layer (A) because the distance the radio waves travel through becomes longer
This is thought to be due to the fact that the same effect can be obtained as the film thickness increases. [00191 The radio wave absorber of the present invention only needs to have one or more units of the above multilayer unit film, and when multiple units are stacked, those of the same type and the same film thickness may be stacked, or those of different types may be stacked. or those with different film thicknesses may be stacked on top of each other. Furthermore, by increasing the number of laminated layers, the frequency of the radio waves to be absorbed can be shifted to the lower frequency side, so the number of laminated layers can be changed depending on the target frequency. [002O1 The radio wave absorber of the present invention may consist only of a multilayer of one or more units, and this multilayer itself may be formed on a substrate such as a metal structure for the purpose of absorbing radio waves. Furthermore, the radio wave absorber of the present invention may be one in which the above-mentioned multilayer is formed on a plastic film, or the above-mentioned multilayer is formed in a plastics film on a thin metal plate, or without lamination. It may be something. [0021] When using the radio wave absorber of the present invention,
The radio wave absorber can be attached to a base material intended for radio wave absorption using an adhesive such as an adhesive. In addition, by applying an adhesive in advance to the side opposite to the radio wave absorber layer (B) and laminating a release paper on top of it, it can be applied to the base by simply peeling off the release paper and pasting it at the construction site. A radio wave absorber can be formed. [0022]

[Effects of the Invention] Compared to conventional products, the radio wave absorber of the present invention has a much superior radio wave absorption ability with the same film thickness, so it can be made thinner and thinner, which improves construction workability. I can do it. Furthermore, since it is in the form of a film, it is also possible to wind it up into a coil in some cases. [0023]

[Examples] The present invention will be explained in more detail below with reference to Examples. In addition, hereinafter, "part" means "part by weight". Example 1 A nickel-based ferrite-containing coating material prepared by blending and dispersing 340 parts of ferrite containing the nickel element per 100 parts of resin solid content in a urethane resin solution was applied to a brass plate with a thickness of 10 mm so that the dry film thickness was 950 μm. applied and dried. Next, 50 parts m of terbium-iron cobalt alloy (TbFeCo) was vapor-deposited on the ferrite-containing layer to form a radio wave absorber on the brass plate. [0024] Example 2 In Example 1, the thickness of the ferrite-containing layer was 350 μm.
A radio wave absorber was obtained on a brass plate in the same manner except that m was used, and then a ferrite-containing layer of 100 μm was applied on the terbium-iron-cobalt alloy layer of the radio wave absorber, and 50 parts m of By sequentially laminating a total of 6 units, each consisting of a multi-layer consisting of a terbium-iron-cobalt alloy layer, a total film thickness of 9
A desired radio wave absorber having a multilayer structure of 50 μm and 7 units was obtained. Comparative Example 1 A radio wave absorber was obtained on a brass plate in the same manner as in Example 1 except that the terbium-iron-cobalt alloy layer was not formed. [0025] Example 3 A barium-based ferrite coating material prepared by blending and dispersing 250 parts of ferrite containing barium element per 100 parts of resin solid content in a urethane resin solution was coated on a 10 mm thick brass plate with a 50 μm thick polyethylene coating. It was coated on a laminate plate on which terephthalate was laminated so that the dry film thickness was 500 μm and dried. Next, 1100 nm of terbium iron-cobalt alloy was deposited on the ferrite-containing layer to obtain a radio wave absorber on the brass plate. [0026] Example 4 A radio wave absorber was obtained on a brass plate in the same manner as in Example 3 except that the thickness of the ferrite-containing material was 200 μm,
Next, on the terbium-iron-cobalt alloy layer of this radio wave absorber, a total of 3 units are formed, with 1 unit being a multilayer consisting of a ferrite-containing layer of 100 μm and a terbium-iron-cobalt alloy layer of 1100 nm thick on this ferrite-containing layer. By sequentially laminating the above, four units of multilayer with a total film thickness of 500 μm were formed on the brass plate via the polyethylene terephthalate layer, and the intended radio wave absorber was obtained on the brass plate. Comparative Example 2 A radio wave absorber was obtained on a brass plate in the same manner as in Example 3 except that the terbium-iron-cobalt alloy layer was not formed. [0027] Example 5 In the urethane resin solution, for 100 parts of resin solid content,
A barium-based ferrite coating material containing 30 parts of ferrite containing the barium element was applied onto a 10 mm thick brass plate to a dry film thickness of 20 μm and dried. Next, 1100 nm of terbium-iron-cobalt alloy was vapor-deposited on this ferrite layer, and a urethane resin clear was further applied to a thickness of 5 μm on this vapor-deposited film. Next, 23 units of the above ferrite layer, (terbium-iron-cobalt) alloy layer and urethane resin clear layer are laminated on top of this as a unit film to form a multi-layer of 24 units in total, and the desired radio wave absorption is formed on the brass plate. I got a body. [0028] Examples 6 and 7 In Example 5, a total of 28 units were stacked in Example 6. Example 7 was obtained by stacking 32 units. As is clear from FIG. 3 described later in the radio wave absorbers of Examples 5, 6, and 7, as the number of laminated layers increases, the frequency of the absorbed radio waves shifts to the lower frequency side. [0029] Example 8 Example 5 except that the urethane resin clear was not applied on the deposited film of terbium-iron-cobalt alloy and the ferrite layer (terbium-iron-cobalt) alloy layer was used as a unit film. A radio wave absorber was obtained in the same manner as in 5.

Example 9 The barium-based ferrite coating material used in Example 5 was coated with a thickness of 1
It was coated on a 0 mm brass plate to a dry film thickness of 100 μm and dried. Next, 1100 nm of terbium-iron-cobalt alloy was deposited on this ferrite layer. Then, three units of the above 100 μm ferrite layer-(terbium-iron-cobalt) alloy layer multilayer were laminated thereon as a unit film. Furthermore, the above-mentioned barium-based ferrite coating material was applied and dried to a dry film thickness of 50 μm, and a terbium-iron-cobalt alloy was applied on top of this to a thickness of 1100 μm.
n was deposited. Then, seven units of the above-mentioned 50 μm ferrite layer-(terbium-iron-cobalt) alloy layer multilayer were laminated thereon as a unit film to obtain a radio wave absorber.

The radio wave absorption characteristic curves of the radio wave absorbers on brass plates obtained in Examples 1 to 9 and Comparative Example 1.2 were measured in the frequency range of 1 to 18 GHz. The results are shown in FIGS. 1 to 4 below.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing radio wave absorption characteristic curves of radio wave absorbers obtained in Example 1.2 and Comparative Example 1. The solid line shows the radio wave absorption characteristic curve of the radio wave absorber obtained in Example 1, the broken line in Example 2, and the dashed-dotted line in Comparative Example 1.

FIG. 2 is a diagram showing radio wave absorption characteristic curves of radio wave absorbers obtained in Example 3.4 and Comparative Example 2. The solid line shows the radio wave absorption characteristic curve of the radio wave absorber obtained in Example 3, the broken line in Example 4, and the dashed-dotted line in Comparative Example 2.

FIG. 3 is a diagram showing radio wave absorption characteristic curves of the radio wave absorbers obtained in Examples 5 to 7. The solid line shows the radio wave absorption characteristic curve of the radio wave absorber obtained in Example 5, the broken line in Example 6, and the dashed-dotted line in Example 7.

FIG. 4 is a diagram showing radio wave absorption characteristic curves of the radio wave absorbers obtained in Examples 8 and 9. The solid line shows the radio wave absorption characteristic curve of the radio wave absorber obtained in Example 8, and the broken line shows the radio wave absorption characteristic curve of the radio wave absorber obtained in Example 9.

[Figure 1]

[Figure 2]

[Figure 3]

[Figure 4]

Claims (4)

[Claims] [Claim 1] A ferrite-containing layer (
A radio wave absorber characterized by having one or more units of a multilayer consisting of A) and a magnetic alloy layer (B) containing a transition metal element with a film thickness of 1 nm to 200 nm on the core layer (A) as a unit film. . [Claim 2] A ferrite-containing layer (
A), a magnetic alloy layer (B) containing a transition metal element with a film thickness of 1 nm to 200 nm on the core layer (A), and the alloy layer (B
) with the spacer layer (C) as a unit film.
A radio wave absorber characterized by having more than one unit. 3. The radio wave absorber according to claim 1 or 2, having two or more units of multilayer as a unit film. 4. The radio wave absorber according to claim 1, wherein the magnetic alloy layer (B) is a terbium-iron-cobalt alloy layer.