JP2021170614A - Power-resistant radio wave absorber - Google Patents

Abstract

To provide a radio wave absorber that has both power resistance that does not change the strength and appearance of a structure even when repeatedly irradiated with electromagnetic waves having a high power density, and absorption performance as a radio wave absorber.SOLUTION: A pyramid type radio wave absorber with excellent heat resistance which can handle high power irradiation includes: a base material made of non-combustible paper with many hollow cells; a conductive material layer made of an inorganic conductive material fixed to the surface of the base material; and an overcoat layer in which the conductive material is coated with a coating agent of an inorganic compound, in which the conductive material and a binder that fixes the conductive material are inorganic substances.SELECTED DRAWING: Figure 1

Description

The present invention relates to a radio wave absorber, and more particularly to a technical field of a power resistant radio wave absorber in which the strength, absorption performance, appearance, etc. of a structure do not change even when repeatedly irradiated with electromagnetic waves having a high power density. be.

Conventionally, there has been a demand for a radio wave absorber having good heat resistance, and an absorber such as a type in which carbon fine particles are attached to a ceramic mold has been commercialized. The absorber is only required to have self-extinguishing property so as not to cause great damage due to combustion of the absorber in the event of a fire in an anechoic chamber. However, in recent years, there has been an increase in demand for an anechoic chamber for performing a test of irradiating a large amount of electric power, and the radio wave absorber installed therein is also required to have stricter heat resistance than before. Specifically, even if electromagnetic waves having a high power density (eg, 1.5 W / square centimeter) are repeatedly irradiated, the strength, absorption performance, appearance, etc. of the structure do not change.

When a large amount of power is applied to an absorber of the type in which carbon particles are attached to a conventional ceramic mold, the organic components (binder, etc.) and carbon particles contained in the ceramic mold due to the heat generated when the electromagnetic waves are absorbed. Furthermore, it is known that the binder for fixing the carbon particles to the ceramic mold burns, resulting in a significant change in the strength and absorption performance of the structure.

In addition, there are absorbers on the market in which a conductive material or the like is attached to a core material having a honeycomb structure in order to improve heat dissipation, but if the opening of the honeycomb is enlarged in order to improve heat dissipation, the absorption performance deteriorates. Therefore, the general idea is that there is a limit to the maximum size of the opening. Further, as for the material of the core material, paper mixed with aramid fibers is fixed in a honeycomb shape with phenol resin, or non-combustible paper mixed with inorganic fibers is fixed in a corrugated shape with an adhesive. However, it is presumed that phenolic resin, organic binder components contained in non-combustible paper, etc. cannot withstand the heat generated when they absorb electromagnetic waves.

Therefore, various technical proposals have been made conventionally. For example, a technique in which the title of the invention is "radio wave absorber and method for producing the same" is disclosed (see Patent Document 1).
Specifically, "it has excellent radio wave absorption characteristics in a wide frequency band, can suppress temperature rise even when irradiated with high power radio waves, and realizes a low-cost radio wave absorber." As a means, the radio wave absorber includes a structure composed of an aggregate of a plurality of tubular portions. The plurality of tubular portions are each formed of a material containing a heat-resistant base material and a conductive material. , It has an opening at least on one end side and is arranged so as to face the thickness direction, that is, the direction of arrival of radio waves. A radio wave reflector such as a metal plate is arranged on the back surface of the radio wave absorber. The structure includes a tapered portion having a tapered shape that tapers toward the surface side, and a base portion of the tapered portion that is arranged on the side opposite to the radio wave arrival side. The opening of each tubular portion is a tapered portion. The invention "is arranged on the surface of the radio wave." Has become a publicly known technique. However, the techniques described in Patent Document 1 are common in that the shape is a pyramid type and that a honeycomb structure is used as the core material, but the difference is that the structure of directly coating the surface of the conductive material is different. There is no description. That is, the configuration in which the conductive material is directly coated as in the present invention to block the supply of oxygen and prevent the conductive material from burning is not adopted.

Further, a technique in which the title of the invention is "a nonflammable honeycomb radio wave absorber and a radio wave absorber using the same" is disclosed (see Patent Document 2). Specifically, "Providing a nonflammable honeycomb radio wave absorber that is mainly used in an anechoic chamber and has excellent fire resistance and radio wave absorption effect, and is lightweight and has high strength, and a radio wave absorber using the same." As a solution, "it is composed of a honeycomb structure which is an aggregate of a large number of cells, and (1) the honeycomb structure contains a water-containing inorganic compound and a conductive material, or (2) the honeycomb structure. A nonflammable honeycomb radio wave absorber is obtained by containing a water-containing inorganic compound in the body and providing a conductive layer made of a conductive material on the surface of the structure. Further, a plurality of these nonflammable honeycomb radio wave absorbers are provided on a shield panel. Alternatively, it is arranged on a ferrite tile on a shield panel to form a radio wave absorber. ”Has been published and is a known technique. However, the techniques described in Patent Document 2 are common in that a non-combustible material is used as the core material and an inorganic compound is used as the binder, but there is no description of a configuration in which the surface of the conductive material is directly coated. , It is different. That is, the configuration in which the conductive material is directly coated as in the present invention to block the supply of oxygen and prevent the conductive material from burning is not adopted.

Further, a technique in which the title of the invention is "radio wave absorber" is disclosed (see Patent Document 3).
Specifically, the problem is "providing a radio wave absorber having a radio wave absorber that is lightweight, inexpensive, and has a wide measurement space", and as a solution, "in a radio wave absorber formed of a conductive coating material". The resistance coating body is formed of a lattice type radio wave absorbing part or a honeycomb type radio wave absorbing part formed in the direction perpendicular to the metal plate, and the lattice type radio wave absorbing parts are laminated to form a multilayer core type. Alternatively, it is a radio wave absorber characterized in that it is formed by laminating honeycomb type radio wave absorbers. " However, the technique described in Patent Document 3 is for forming a honeycomb type radio wave absorber by laminating a large number of core materials. On the other hand, the present invention differs in that a pyramid shape having a honeycomb structure is formed from a single layer of core material. Further, there is no description or suggestion about coating a conductive material with a coating agent using an inorganic compound.

Therefore, the present inventors conducted the following experiments in order to establish a radio wave absorber having excellent power resistance.
(1) When a conventional flame-retardant absorber was irradiated with an electric power of 1.5 W / square centimeter, it burned and the electric power resistance could hardly be confirmed. (2) By adhering a conductive material to the aramid honeycomb core When it was used as an absorber, absorption performance was obtained, but the base material melted and the power resistance could hardly be confirmed. It also includes the problem that the aramid honeycomb core is very expensive.
(3) When the conductive material was attached to the conventional ceramic mold with an inorganic binder, the organic binder of the ceramic mold burned.
(4) When the organic binder of the ceramic mold was eliminated as much as possible to improve the heat resistance, there was a problem that the ceramic mold was loosened when the conductive material was dispersed in water and impregnated into the mold.
(5) When a conductive material was attached to the ceramic sintered body to form an absorber, good heat resistance and absorption performance could be obtained, but the ceramic sintered body used as the base material was expensive and heavy. There was a problem that it was very large and it was difficult to process it into a pyramid shape.
(6) When a conductive material was attached to the non-combustible paper corrugated base material, absorption performance could be obtained, but power resistance was insufficient (better than aramid honeycomb).
(7) When a conductive material was attached to a base material having a large opening (18 mm), which was neither a honeycomb structure nor a corrugated structure, improvement in heat dissipation was confirmed, but carbonization occurred at the end of the base material. However, with regard to the radio wave absorption characteristics, almost the same absorption performance could be obtained.
(8) When the surface of (7) was coated with an inorganic material, the present invention was completed by succeeding in balancing the power resistance and the absorption performance.

As a result of trying to solve these problems, the present inventor uses a core material of non-combustible paper having an opening of 18 mm as a base material, which has conventionally been considered difficult to obtain sufficient absorption performance in order to secure heat dissipation. By selecting a material that eliminates organic substances (less than 5%) as much as possible from the conductive material and the binder for fixing it while ensuring heat dissipation, and overcoating the surface with an inorganic coating agent, it becomes a conductive material. It was possible to obtain a radio wave absorber that has both power resistance and absorption performance that can withstand irradiation of 1.5 W / square centimeter by preventing oxygen from being supplied and burning.

Japanese Patent Application Laid-Open No. 2003-115693 Japanese Patent Application Laid-Open No. 2000-777883 Registration No. 2660647

An object of the present invention is to provide a radio wave absorber that has both power resistance that does not change the strength and appearance of the structure even when repeatedly irradiated with electromagnetic waves having a high power density and absorption performance as a radio wave absorber. Is to be.

The present invention is a pyramid-shaped radio wave absorber having excellent heat resistance that can cope with high-power irradiation.
A base material made of non-combustible paper having a large number of hollow cells, a conductive material layer made of an inorganic conductive material fixed to the surface of the base material, and an overcoat in which the conductive material layer is further coated with a coating agent of an inorganic compound. The conductive material and the binder for fixing the conductive material, which are composed of layers, adopt a structure in which they are inorganic substances.

Further, in the present invention, it is also possible to adopt a structure in which the conductive material is scaly graphite.

Further, the present invention can also adopt a configuration in which the shape of the cell is a regular hexagon.

Further, the present invention can also adopt a structure having a corrugated honeycomb shape in which a corrugated plate is sandwiched between flat plates in which the honeycomb-shaped hollow cells are continuously parallel to each other.

Further, the present invention adopts a configuration in which the cross-sectional shape of the honeycomb-shaped hollow cell is a Namida-shaped shape and a large number of inverted Namida-shaped shapes facing the Namida-shaped shape are continuously arranged. You can also.

According to the power-resistant radio wave absorber according to the present invention, even if it is irradiated with a large amount of power (1.5 W / square centimeter), state changes such as carbonization and combustion do not occur, it can be used repeatedly, it has excellent power resistance, and it has radio wave absorption performance. Demonstrates the same excellent effect.

Further, according to the power-resistant radio wave absorber according to the present invention, the conductive material fixed to the surface of the core material of the non-combustible paper is overcoated with an inorganic coating agent on the surface, so that the conductive material is oxygenated. It exerts an excellent effect that it can be prevented from being supplied and burned.

Further, according to the power-resistant radio wave absorber according to the present invention, since non-combustible paper is used as the core material as the base material, the workability and cost are improved as compared with the ceramic sintered material, the aramid honeycomb, and the like. It exerts an excellent effect such as having the superiority of.

Further, when the power-resistant radio wave absorber according to the present invention adopts a configuration in which scaly graphite is used as the conductive material, the characteristics of graphite having excellent heat resistance and the small coefficient of thermal expansion make it dimensionally stable at high temperatures. It has excellent properties, and in particular, it exhibits an excellent effect of being excellent in radio wave absorption characteristics in the 1 to 18 GHz band.

Further, in the power-resistant radio wave absorber according to the present invention, when a configuration in which the hollow cells have a regular hexagonal shape in cross-sectional view is adopted, cells having the same shape can be arranged without gaps. This can be an equilateral triangle or a square. A regular hexagon is the best in this respect because the direction of force distribution is evenly and isotropically equal. That is, for example, when it is installed on the wall of an anechoic chamber or the like, when an external load is applied due to contact with a person, the effect of being excellent in strength that it is not easily damaged is exhibited.

Further, when the power-resistant radio wave absorber according to the present invention adopts a corrugated honeycomb-shaped structure in which a corrugated honeycomb plate is sandwiched between flat plates in which honeycomb-shaped hollow cells are continuously parallel to each other, the regular hexagonal shape is used. It has the effect of being excellent in cost performance while having the same strength as the honeycomb structure.

Further, in the power-resistant radio wave absorber according to the present invention, a honeycomb structure is adopted in which a honeycomb-shaped hollow cell has a Namida-shaped cross-sectional shape and a large number of inverted Namida-shaped shapes facing the Namida-shaped shape are continuously arranged. In this case, since there are no corners in the shape of the cell, heat generation in heat dissipation and radio wave absorption does not occur locally and becomes even, so the effect of superior durability is exhibited without concentration of deterioration. It is something to do.

It is a basic structure explanatory drawing explaining the basic structure of the power-resistant radio wave absorber which concerns on this invention. It is an Example explanatory drawing which shows the shape example in the cross-sectional view of the core material used for the electric power withstanding radio wave absorber which concerns on this invention. It is a state explanatory drawing which shows the laminated state of the base material of the withstand power radio wave absorber which concerns on this invention. It is a comparison explanatory drawing of the radio wave attenuation amount of the withstand power radio wave absorber which concerns on this invention, and the conventional product.

The present invention is a pyramid-shaped radio wave absorber having excellent heat resistance that can cope with high-power irradiation, and has a base material made of non-combustible paper having a large number of hollow cells and an inorganic conductivity fixed to the surface of the base material. The most characteristic feature is that the conductive material layer made of a material and an overcoat layer obtained by coating the conductive material with a coating agent of an inorganic compound, and the conductive material and the binder for fixing the conductive material are inorganic compounds. It is a thing.
Hereinafter, description will be given based on the drawings. However, the shape and structure are not limited to those described in the drawings, and the changes can be made within the range in which the effect exerted as the creation of the technical idea of the present invention can be obtained.

FIG. 1 is a basic configuration explanatory diagram illustrating a basic configuration of a power-resistant radio wave absorber according to the present invention. 1 (a) is a plan view, FIG. 1 (b) is a front view, FIG. 1 (c) is a side view, and FIG. 1 (d) is a bottom view. A plurality of quadrangular pyramid-shaped pyramid shapes are arranged side by side, and FIG. 1 shows one of them. The matching body is a radio wave absorber in the 1 GHz to 18 GHz band. Each configuration will be described below.

The hollow cell 10 is said to have a structure in which regular hexagons or regular hexagonal columns are arranged without gaps in a narrow sense, but in a broad sense, it includes not only regular hexagonal columns but also a solid forming a three-dimensional filling space, and is viewed in cross section. In, other regular polygons, circular shapes, etc. are also included, and further, the same shape that is repeatedly and continuously arranged is included.

The non-combustible paper 20 is a paper produced by impregnating a paper containing aluminum hydroxide with a resin. In an experimental example, Shin Nihon Feather Core Co., Ltd. (Kokaba, Iwatsuki-ku, Saitama City, Saitama Prefecture) The roll core SF (trade name) provided from 1-3-9) was used. Aluminum hydroxide, which is the base material of the roll core-SF, has autolysis property of generating water by heat, so that it is hard to burn and is also used as a building material.

The base material 30 is a core material in which the non-combustible paper 20 is continuously molded into a substantially cylindrical cylinder, and is characterized in that the difference in strength in the thickness direction is small. However, in the present invention, since it is molded into a pyramid shape, the advantage of such a feature is not utilized, but the strength as a base material is high.

When the base material 30 is a corrugated honeycomb structure, the flat plate 31 becomes a part of the base material 30 that constitutes the base material 30 by sandwiching the corrugated plate 32 from both sides so as to form the shape of the hollow cell 10. It is a member.

When the base material 30 is a corrugated honeycomb structure, the corrugated plate 32 is sandwiched between the flat plates 31 arranged in parallel so as to form the shape of the hollow cell 10, and the same shape is continuously arranged. It is a part of the material. Although FIG. 2B shows a wavy shape, the shape is not limited to this, and any shape such as a trapezoid or a triangle that repeats and continues the same shape may be used.

The conductive material 40 is a powder or fiber added to impart conductivity to the non-combustible paper serving as the base material 30, and is roughly classified into carbon-based, metal-based, metal oxide-based, metal film-based, and metal oxide. There are types such as a film system, and claim 2 specifies that scaly graphite is used. The scaly graphite is strong against thermal shock, and the strength increases as the temperature rises, and the coefficient of thermal expansion is small. It is possible to prevent damage due to deterioration of thermal influence while maintaining good radio wave absorption characteristics without giving to the material 30 or the like. However, unlike ceramics with strong ionic bonds and materials such as crystalline diamond with all carbons covalently bonded, scaly graphite bonded by van der Waals force is fragile. , Binder 80 is required, and it is preferable to use the coating agent 60 from the viewpoint of blocking the supply of oxygen to the conductive material 40 and improving the strength. Since scaly graphite is cheaper than lump graphite, it has a feature of being excellent in cost performance.

The coating agent 60 is coated so as to cover the surface of the conductive material layer 50 fixed to the base material 30 made of noncombustible paper 20, and the overcoat layer 70 made of an inorganic compound for blocking the supply of oxygen to the conductive material 40. It is a coating agent for forming.

The binder 80 is an adhesive for fixing the conductive material 40, and uses a material in which 95% or more is an inorganic compound, the organic substance is less than 5%, and the organic substance is eliminated as much as possible to improve the flame retardancy.

FIG. 2 is an explanatory view of an example showing a shape embodiment in a cross-sectional view of the core material used for the power-resistant radio wave absorber according to the present invention, and FIG. FIG. 2 (b) shows a case of a square shape, and FIG. 2 (b) shows a case where the shape of the hollow cell in a cross-sectional view is a corrugated shape continuous between two parallel straight lines, and is shown in FIG. 2 (c). ) Indicates a case where the shape of the hollow cell in the cross-sectional view is a corrugated tear-shaped honeycomb in which a tear-shaped shape and a reverse tear-shaped shape are continuous between two parallel straight lines.

In the regular hexagonal shape shown in FIG. 2 (a), the direction in which the force is distributed acts evenly at equal angles without leaving a gap. The square shape is the best in terms of strength and ease of manufacture. That is, for example, when it is installed on the wall of an anechoic chamber or the like, it exhibits the effect of being excellent in strength due to human contact.

FIG. 3 is a state explanatory view showing a laminated state of the power-resistant radio wave absorber according to the present invention. In FIG. 3, a conductive material layer 50 made of a conductive material 40 is fixed to the surface of a base material 30 made of non-combustible paper 20, and an overcoat layer 70 made of a coating agent 60 made of an inorganic compound is further formed on the surface thereof. It shows that it is.

The conductive material layer 50 is formed into a pyramid shape by mixing the conductive material 40 with a binder 80 in which organic substances are excluded as much as possible (the conductive material 40 and the binder 80 for fixing the conductive material 40 are 95% or more of inorganic compounds). It is a layer fixed to the formed non-combustible paper 20. As shown in FIG. 3, the conductive material layer 50 is formed not only inside the hollow cell 10 but also in the gap between the cells. It is a layer that converts radio waves into heat and dissipates heat due to the presence of the conductive material layer 50. In the present invention, it withstands power irradiation of 1.5 W / square centimeter and absorbs radio waves in the 1 GHz to 18 GHz band satisfactorily.

The overcoat layer 70 is a film layer obtained by applying a coating agent 60 so as to cover the surface of the conductive material layer 50 fixed to the noncombustible paper 20. The laminated state of the overcoat layer and the conductive material layer 50 is shown in FIG. Similar to the conductive material layer 50, the overcoat layer 70 is formed not only inside the hollow cell 10 but also in the gaps between the cells.

FIG. 4 is a comparative explanatory view of the amount of radio wave attenuation between the power-resistant radio wave absorber according to the present invention and the conventional product, and FIG. 4 (a) is a conventional radio wave absorber (hollow ceramic molding product having a height of 45 cm). 4 (b) shows the radio wave attenuation amount of the power-resistant radio wave absorber 1 (similar outer shape solid) according to the present invention, and shows the radio wave attenuation amount of the power-resistant radio wave absorber according to the present invention. 1 has a wide range of radio wave absorption from 0.5 GHz to 18 GHz, and as shown in FIG. 4, exhibits particularly high radio wave absorption performance in the gigahertz band of 0.5 GHz to 4.5 GHz as compared with the conventional product.

According to the power-resistant radio wave absorber according to the present invention, the power resistance that does not change the strength and appearance of the structure even when repeatedly irradiated with electromagnetic waves having a high power density and the absorption performance as a radio wave absorber are obtained. Since it is possible to provide a compatible radio wave absorber, it is considered that it has high industrial utility in an anechoic chamber or the like.

1 Power-resistant radio wave absorber 10 Cavity cell 20 Non-combustible paper 30 Base material 31 Flat plate 32 Wavy plate 40 Conductive material 50 Conductive material layer 60 Coating agent 70 Overcoat layer 80 Binder

Claims (5)

It is a pyramid-shaped radio wave absorber with excellent heat resistance that can handle high-power irradiation.
A base material (30) made of non-combustible paper (20) having a large number of hollow cells (10),
A conductive material layer (50) made of an inorganic conductive material (40) fixed to the surface of the base material (30),
Further, the surface of the conductive material layer (50) is composed of an overcoat layer (70) coated with an inorganic compound coating agent (60).
The power-resistant radio wave absorber (1), wherein the conductive material (40) and the binder (80) for fixing the conductive material (40) are 95% or more of an inorganic compound. The power-resistant radio wave absorber (1) according to claim 1, wherein the conductive material (40) is scaly graphite. The power-resistant radio wave absorber (1) according to claim 1 or 2, wherein the shape of the hollow cell (10) is a regular hexagon in a cross-sectional view. The first or second aspect of the present invention, wherein the honeycomb-shaped hollow cells (10) have a corrugated honeycomb shape in which a corrugated plate (32) is sandwiched between flat plates (31) that are continuously parallel to each other. Power-resistant radio wave absorber (1). Claim 1 is characterized in that the cross-sectional shape of the honeycomb-shaped hollow cell (10) is a Namida-shaped shape, and a large number of inverted Namida-shaped shapes facing the Namida-shaped shape are continuously arranged. Alternatively, the withstand power radio wave absorber (1) according to claim 2.

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