JP2000353893A - Wave absorber and its manufacture - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wave absorber with excellent micro wave absorbing characteristics, reduce its size and enhance its heat resistance and durability by sequentially filling a formwork with mixed powders, composed of hollow glass spherical bodies, ferrite powder and binder, different in ferrite concentration, and integrally molding it to provide a gradient in ferrite concentration. SOLUTION: Filling a formwork with mixed powders obtained by mixing hollow glass spherical bodies, ferrite powder, and binder such as water glass is utilized as a method to distribute ferrite in an absorber space. At this time, by sequentially filling mixed powers different in ferrite concentration, the ferrite concentration gradient can be freely controlled, and a wave absorber of laminate structure having a stepwise or continuous ferrite concentration gradient can be easily manufactured. A hollow glass spherical body composed of volcanic glass, such as Sirasu-balloon and perlite, is suitable for the purpose.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a compact, lightweight, low-cost, lightweight radio wave absorber having excellent radio wave absorption characteristics in the microwave band, and having excellent heat resistance and durability, and a method of manufacturing the same.

[0002]

2. Description of the Related Art Existing broadband radio wave absorbers include a dielectric type (a resistor in which carbon is dispersed in an organic foam), a magnetic type (mainly ferrite), and a combination of a dielectric and a magnetic substance. There is a complex type.

[0003] The dielectric type is generally formed by molding urethane containing carbon into a pyramid shape. However, urethane is severely deteriorated by absorbing moisture in the air, and generally needs to be replaced in 5 to 6 years, and has a problem in durability. It is flammable because it uses organic materials such as urethane and carbon. Further, a sufficient thickness (generally, about 1 m to 2 m) is required to provide sufficient radio wave absorption characteristics, so that there is a problem that the effective space in the room becomes narrow.

[0004] Ferrite tiles generally used in the magnetic material type have excellent low-frequency characteristics and can obtain sufficient absorption characteristics with a thickness of 10 mm or less, but the absorption characteristics deteriorate as the frequency increases. In general, it is used as a radio wave absorber for low frequencies of 1 GHz or less.

[0005] Even in the case of a composite type in which a dielectric type and a magnetic type are combined, it is necessary to rely on the dielectric type for the electromagnetic wave absorption characteristics in the microwave band, and the thickness can be made thinner than only the dielectric type. Yes, but problems with durability and flammability remain.

[0006] These radio wave absorbers are mainly used for the inner wall of an anechoic chamber. Anechoic chambers are used for measuring the intensity of electromagnetic waves radiated from electronic devices and, conversely, for noise resistance tests that apply strong electromagnetic waves.However, in the noise resistance test, a radio wave absorber is used to apply a strong electric field. It is desirable to have a high risk of generating heat and to have excellent heat resistance.

[0007] Current laws and regulations on electromagnetic waves of electronic equipment cover the frequency band below the microwave band (1 GHz or less).
Many were considered only up to GHz. However, with the increase in processing speed of electronic devices and the rapid spread of mobile phones and the like, the necessity of an anechoic chamber capable of evaluating electromagnetic waves in the microwave band (1 GHz or more) is increasing.
In order to make the conventional anechoic chamber compatible with the microwave band and secure an effective space, a small-sized radio wave absorber having excellent radio wave absorption characteristics in the microwave band has been desired.

As a radio wave absorber corresponding to a microwave band, it is known that when a ferrite powder is dispersed in a space, it has excellent radio wave absorption characteristics in a microwave band. Although there is a radio wave absorber molded into a pyramid shape or the like, there is a problem that the foaming and solidifying processes are complicated, and it is difficult to form a controlled laminated structure due to the use of the foaming process, which tends to increase the cost.

[0009]

SUMMARY OF THE INVENTION The present invention solves the above-mentioned drawbacks of the conventional radio wave absorber, has excellent radio wave absorption characteristics in the microwave band, is small in size, and has low heat resistance and durability. It is an object of the present invention to provide a radio wave absorber that is excellent, inexpensive, and lightweight.

[0010]

In order to solve these problems, a mixed powder is formed by using a hollow glass sphere such as a shirasu balloon and ferrite powder with a binder such as water glass to form a mixed powder. After successively filling mixed powders with different ferrite concentrations, they are integrally molded and have a stepwise or continuous ferrite concentration gradient to provide excellent electromagnetic wave absorption characteristics in the microwave band, small size and heat resistance It has become possible to manufacture a radio wave absorber that is excellent in performance, durability, low cost and lightweight.

The radio wave absorber of the present invention is excellent in heat resistance because the inorganic material such as the hollow glass sphere and the ferrite powder occupies a large part of the volume, so that it has excellent heat resistance even when heated to 150 ° C. No change was observed, and the radio wave absorption characteristics after heating were confirmed to be equivalent to those before heating. Regarding the heat generation of the radio wave absorber under the strong electric field in the noise resistance test, stable radio wave absorption characteristics were exhibited without being affected by the heat.

When a solid glass powder is used in place of the hollow glass spherical body, the mixed powder of ferrite and the inorganic binder and the compact tend to have a dense structure. And the moldability was inferior, and the weight could not be reduced.

Therefore, as a result of using hollow glass spheres such as glass balloons made of artificial glass, shirasu balloons made of volcanic glass, and pearlite, a mixed powder of ferrite and an inorganic binder and a molded body thereof are formed of hollow glass spheres. Because of the open voids derived from the porous shape, carbon dioxide gas easily penetrated, and the curing time was 30 seconds or less, and the composition was cured in a short time, and was excellent in moldability, resulting in a lightweight cured product. However, when a hollow glass sphere having an average particle diameter of 500 μm or more was used, molding was possible, but the strength was weak and the surface shape was rough, so that it was easy to break,
It was not suitable as a radio wave absorber.

Further, when a fine hollow glass sphere having a diameter of 20 μm or less (fine shirasu balloon or the like) disclosed in Japanese Patent No. 2562788 is used, a hardened body using a shirasu balloon or the like having a diameter of 20 μm or more is used. In addition, there is an advantage that the structure is dense, the surface is smooth, and the strength is high while being lightweight. The fine hollow glass spheres are 20
μm or less, which is very fine, but because of the porous spherical shape, it is easy to generate fine voids communicating with each other, and the curing time is 3 minutes.
It was cured in a short time of 0 seconds or less, and was excellent in moldability.

Carbon dioxide gas injection utilizes a reaction in which water glass is instantaneously hardened by carbon dioxide gas. Since there is an appropriate gap caused by the hollow glass spherical body, carbon dioxide gas penetrates into all corners and hardens. It has an excellent feature that the reaction is easily completed in a short time. The heat treatment was performed at 100 ° C. or higher to increase the strength and stability of the molded body. As the binder, silica sol or alumina sol, ethyl silicate, or the like could be used in addition to water glass.

Although the use of an inorganic binder as a binder is superior in terms of heat resistance, even when an organic binder is used, it can be easily formed integrally by pressurizing and heating, and a hollow glass spherical body can be obtained. And the inorganic material of ferrite powder occupies a large part in volume, so that it was excellent in heat resistance, and the radio wave absorption performance was the same as that in the case of using the inorganic binder.

The radio wave absorber obtained according to the present invention has excellent durability because it is lightweight, has high strength, has excellent heat resistance, and is hardly affected by moisture in the air.

Regarding the radio wave absorption characteristics, the ferrite is dispersed in the space by using a hollow glass spherical body, and for example, a pyramid shape, a prism shape, a hollow shape as shown in FIGS. By molding into a single structure of such a shape, it has excellent radio wave absorption characteristics in the microwave band.

In terms of the internal structure, the layer near the surface of the radio wave absorber has a characteristic close to that of air. Is small and is absorbed as it enters the interior, so that it is known that radio wave absorption characteristics in a wide band are improved. As an arrangement of the layers having different radio wave absorption characteristics, a continuous laminated structure is ideal rather than stepwise.

However, at present, a stepwise laminated structure is realized by using a method of bonding urethane materials having different carbon contents with an adhesive or the like, and continuously changing the content of the radio wave absorbing material. That was impossible.
In order to realize a continuous laminated structure, it is necessary to bond a large number of urethane materials having slightly different contents of radio wave absorbing materials, and the manufacturing process is complicated and difficult to manufacture. In particular, there was no inorganic radio wave absorber having a three-dimensional laminated structure.

In the present invention, as a method of distributing the ferrite in the absorber space, a method is used in which a mixed powder obtained by mixing a hollow glass sphere and a ferrite powder is filled in a mold. The ferrite concentration gradient can be freely controlled by sequentially filling mixed powders with different ferrite concentrations, making it easy to manufacture a radio wave absorber with a laminated structure with a stepwise or continuous ferrite concentration gradient It is possible. Then, after being pressed against the mold at an arbitrary pressure, it is possible to perform integral molding in a short time (30 seconds or less) with one injection of carbon dioxide gas. Here, if carbon dioxide gas is injected while pressurizing, the process can be simplified.

Further, a radio wave absorber having a complicated shape can be formed by using an arbitrary mold, and it is easy to form a planar or three-dimensional laminated structure at the same time. Further, a step of processing and bonding materials is not required, the thickness of the laminate can be freely controlled, and a three-dimensional laminated structure can be simultaneously realized while having a complicated shape.

For example, in the case of a planar laminated structure as shown in FIGS. 1 (c) and 1 (d), it can be easily manufactured simply by sequentially filling mixed powders having different ferrite concentrations.

Also, a three-dimensional laminated structure as shown in FIGS. 1 (e) to 1 (h) can be easily manufactured. In particular, with respect to (g) and (h), the structures come from all directions including oblique directions. An ideal ferrite concentration gradient can be imparted even to radio waves that emit light, and further excellent radio wave absorption characteristics can be obtained.

Glass balloons as hollow glass spheres,
When a shirasu balloon or pearlite was used, a radio wave absorber could be manufactured in either case, but from the viewpoint of radio wave absorption characteristics, a hollow glass sphere made of volcanic glass such as a shirasu balloon or perlite was suitable. The chemical composition of volcanic glass varies slightly depending on the location, but 65 to 73% of silicon dioxide, 12 to 18% of alumina, and 1 to 3 of iron.
%, Calcium oxide 2-4%, sodium oxide 3-4
%, Potassium oxide 2-3%.
Since it contains impurities such as iron in addition to silicon dioxide as the main component, it has been confirmed that it exhibits excellent electromagnetic wave absorption characteristics in the microwave band.

Further, by using a fine hollow glass sphere having an average particle diameter of 20 μm or less, the ferrite powder can be more uniformly dispersed in space, so that the electromagnetic wave absorption characteristics in the microwave band can be improved.

Therefore, the radio wave absorber according to the present invention is
The synergistic effect of the radio wave absorption effect of both the ferrite and the hollow glass sphere and the three-dimensional effect such as a three-dimensional layered structure, it is compact, lightweight and shows excellent radio wave absorption characteristics in the microwave band. Since it is an easy manufacturing method that enables molding in a short time, it can be manufactured in a short time and at low cost without the need for complicated chemical processes or advanced manufacturing equipment. .

From the above, according to the present invention, it has excellent radio wave absorption characteristics in the microwave band, is small in size, has heat resistance,
A radio wave absorber having excellent durability, low cost and light weight can be easily manufactured.

[0029]

EXAMPLE 1 Ferrite, shirasu balloon and water glass were stirred with a stirrer at a composition ratio (weight ratio) shown in Table 1 below, and then a pyramid-shaped outer frame having a base of 100 mm and a height of 110 mm, a base of 60 mm and a height of 60 mm The space between the inner frames of a 60 mm pyramid was filled, and carbon dioxide gas was injected to form the inner frame. The evaluation of the radio wave absorption characteristics was performed by attaching a radio wave absorber to a metal reflector as shown in FIG. FIG. 3 shows the characteristics of the completed radio wave absorber. From this figure, from 1 GHz to 2
It has radio wave absorption characteristics exceeding 20 dB over almost the entire region of 0 GHz, and it has been confirmed that even a single structure has excellent radio wave absorption characteristics in the microwave band.

[0030]

[Table 1]

[0031]

Embodiment 2 A radio wave absorber having a three-layer structure as shown in FIG. 4 was prepared in the same manner as in Embodiment 1 except that the ferrite content per mounting area was the same and the ferrite content was a three-dimensional laminated structure. did. In the first embodiment, 100 mm × 1
160 g of ferrite is used per 00 mm.
In order to realize a three-dimensional laminated structure, the radio wave absorber this time had a base of 60 mm x 60 mm,
About 36% of the ferrite of 57 g was used for one radio wave absorber. Table 2 shows the volume and the amount of ferrite used in each layer. The amounts of shirasu balloon and water glass were adjusted according to the amount of ferrite. The evaluation of the radio wave absorption characteristics was performed by attaching a radio wave absorber to a metal reflector as shown in FIG. FIG. 5 shows the characteristics of the completed radio wave absorber. In most of the frequency range from 1 GHz to 20 GHz, it has a radio wave absorption characteristic that is higher than that of Example 1 by nearly 10 dB, and it was confirmed that a more excellent radio wave absorption characteristic was obtained by forming a laminated structure.

[0032]

[Table 2]

[0033]

The radio wave absorber according to the present invention has excellent radio wave absorption characteristics in the microwave band since ferrite can be dispersed in space by using a hollow glass sphere. As for the shape, it can be molded into any shape with excellent absorption characteristics, and the structure can be freely controlled such as a laminated structure with a ferrite concentration gradient, so that it has better radio wave absorption characteristics Can be. Therefore, by adding to a conventional radio wave absorber up to the 1 GHz band, it can be used as a radio wave anechoic chamber corresponding to the microwave band.

Also, because of the small size, a wider effective space can be secured, and since the hollow glass spheres and the inorganic material of the ferrite powder occupy a large part of the volume, they are excellent in heat resistance and are excellent in air. Because it is not affected by moisture or the like, it has excellent durability and can be used stably for a long period of time.

Furthermore, since the absorber itself is simple to manufacture, it can be produced at a low cost, and is relatively lightweight because a hollow glass sphere having a low specific gravity is used. In addition, effective use of the abundant Shirasu resources in Kagoshima Prefecture will lead to regional revitalization.

With the recent increase in the performance and speed of electronic devices and the spread of microwave-based devices such as mobile phones, the demand for microwave bands has been increasing, and at the same time, the demand for anechoic chambers compatible with microwave bands has been increasing. As the supply of radio wave absorbers corresponding to such demands is desired, mass demand of radio wave absorbers according to the present invention can be expected.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a cross-sectional structure and a cross-sectional shape of a radio wave absorber according to the present invention. The color depth means the ferrite concentration. (A) Single structure type (b) Single structure hollow type (c) Planar laminated structure type (d) Planar laminated structure hollow type (e) Three-dimensional laminated structure type (part 1) (f) Three-dimensional laminated Structural hollow type (Part 1) (g) Three-dimensional laminated structure type (Part 2) (h) Three-dimensional laminated structure hollow type (Part 2)

FIG. 2 is a cross-sectional view of a radio wave absorber used in Example 1 for measuring radio wave absorption characteristics.

FIG. 3 is a graph showing a radio wave absorption characteristic of a radio wave absorber obtained in Example 1.

FIG. 4 is a cross-sectional view of a radio wave absorber used in Example 2 for measuring radio wave absorption characteristics.

FIG. 5 is a graph showing a radio wave absorption characteristic of a radio wave absorber obtained in Example 2.

[Brief description of reference numerals]

 REFERENCE SIGNS LIST 1 single structure type radio wave absorber 2 metal reflector 3 hollow portion 4 laminated structure type radio wave absorber 5 layer 2 in table 2 6 layer 2 in table 2 7 layer 3 in table 2

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Kenichi Sodeyama 1445-1 Oda, Hayato-cho, Aira-gun, Kagoshima Prefecture Inside the Kagoshima Industrial Technology Center (72) Inventor Kazuto Hamaishi 1445-1, Oda, Hayato-cho, Aira-gun, Kagoshima F-term in Kagoshima Prefectural Industrial Technology Center (reference) 4G005 AA01 AB13 AB27 DA17Z EA09 4G018 AC05 AC08 5E321 BB25 BB31 BB53 BB60 GG05 GG07 GG11

Claims (15)

[Claims] 1. A radio wave absorber comprising a mixed powder of a hollow glass sphere having an average particle size of 20 μm to 500 μm and ferrite as a main raw material and an auxiliary raw material serving as a binder. 2. A radio wave absorber comprising a mixed powder of a shirasu balloon having an average particle diameter of 20 μm to 500 μm and ferrite as a main raw material and an auxiliary raw material serving as a binder. 3. A radio wave absorber comprising a mixed powder of a fine hollow glass sphere having an average particle diameter of 20 μm or less and ferrite as a main raw material and an auxiliary raw material serving as a binder. 4. A mixed powder composed of a hollow glass sphere having an average particle diameter of 20 μm to 500 μm and ferrite as a main raw material and an auxiliary raw material serving as a binder, and having a stepwise or continuous ferrite concentration gradient in a planar manner. A radio wave absorber characterized by having a laminated structure. 5. A planar laminated structure comprising a mixed powder of a shirasu balloon having an average particle diameter of 20 μm to 500 μm and ferrite as a main raw material and an auxiliary raw material serving as a binder, and having a stepwise or continuous ferrite concentration gradient. A radio wave absorber characterized by having it. 6. A mixed powder of fine hollow glass spheres having an average particle size of 20 μm or less and ferrite as a main raw material and an auxiliary raw material serving as a binder, and having a stepwise or continuous ferrite concentration gradient in a planar manner. A radio wave absorber characterized by having a laminated structure. 7. A mixed powder of a hollow glass sphere having an average particle diameter of 20 μm to 500 μm and ferrite as a main raw material and an auxiliary raw material serving as a binder, and a stepwise or continuous ferrite concentration gradient is three-dimensionally formed. A radio wave absorber characterized by having a laminated structure. 8. A three-dimensional laminated structure comprising a mixed powder of a shirasu balloon having an average particle diameter of 20 μm to 500 μm and ferrite as a main raw material and an auxiliary raw material serving as a binder, and having a stepwise or continuous ferrite concentration gradient. A radio wave absorber characterized by having it. 9. A mixed powder of a fine hollow glass sphere having an average particle diameter of 20 μm or less and ferrite as a main material and an auxiliary material serving as a binder, and a stepwise or continuous three-dimensional ferrite concentration gradient is obtained. A radio wave absorber characterized by having a laminated structure. 10. A mixed powder obtained by mixing a hollow glass sphere having an average particle diameter of 20 μm to 500 μm and ferrite as main raw materials, and a binder added to a powder which has been uniformly mixed in advance, in a given mold. A method for manufacturing a radio wave absorber, characterized in that the compounding ratio is controlled, the powder is filled so as to form a laminated structure having a stepwise or continuous ferrite concentration gradient, and then molded integrally by pressing and heating. 11. A powder mixture obtained by mixing a shirasu balloon having an average particle diameter of 20 μm to 500 μm and ferrite as main raw materials and a binder to which powder has been uniformly mixed in advance and adding a binder to an arbitrary mold. The method for manufacturing a radio wave absorber characterized in that after the powder is filled so as to form a layered structure having a stepwise or continuous ferrite concentration gradient by controlling the pressure, and then integrally molded by applying pressure and heat. 12. A powder mixture obtained by adding a binder to a powder obtained by uniformly mixing a fine hollow glass sphere having an average particle diameter of 20 μm or less and ferrite as main raw materials in advance,
It is characterized by the fact that after mixing the powder into an arbitrary formwork by controlling the ferrite compounding ratio and forming a laminated structure with a stepwise or continuous ferrite concentration gradient, it is integrally molded by pressing and heating. Manufacturing method of a radio wave absorber. 13. A mixed powder obtained by adding a hollow glass sphere having an average particle diameter of 20 μm to 500 μm and ferrite as main raw materials and water glass as a binder with respect to a powder which has been uniformly mixed in advance in an arbitrary mold. In addition, after controlling the ferrite compounding ratio and filling the powder into a laminated structure with a stepwise or continuous ferrite concentration gradient, it is characterized by being integrally molded by carbon dioxide injection and heat treatment. Manufacturing method of radio wave absorber. 14. A mixed powder obtained by adding a water glass as a binder to a powder which is preliminarily and uniformly mixed with a shirasu balloon having an average particle diameter of 20 μm to 500 μm as a main raw material, in a given mold, Radio wave absorption characterized by controlling the ferrite compounding ratio, filling the powder into a laminated structure with a stepwise or continuous ferrite concentration gradient, then injecting carbon dioxide and heat-treating to form a single unit. How to make the body. 15. A mixed powder in which water glass is added as a binder to a powder obtained by mixing a fine hollow glass sphere having an average particle diameter of 20 μm or less and ferrite as main raw materials in advance and uniformly mixing the powder in an arbitrary mold. In addition, after controlling the ferrite compounding ratio and filling the powder into a laminated structure with a stepwise or continuous ferrite concentration gradient, it is characterized by being integrally molded by carbon dioxide injection and heat treatment. Manufacturing method of radio wave absorber.