JP2010153833A - Radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To inexpensively provide a radio wave absorber which is compact and has radio wave absorbing performance to enable the absorber to be used even in a radio-wave dark room, the radio wave absorber being usable over a wide band without spoiling the performance. <P>SOLUTION: The radio wave absorber is made thorough steps of: impregnating a woody material with a thermosetting resin and curing it; carrying out carbonization treatment of the cured one; pulverizing the carbonized one and regulating particle sizes into a carbonized powder 3; dispersing the carbonized powder 3 in an organic binder 2 to form a carbon powder absorber and kneading and dispersing the carbon powder absorber, or coating the organic binder 2 on surfaces of grains of the carbonized powder 3 and ramming down it to make it harden; and molding the previous step one in a predetermined shape. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a radio wave absorber suitable for use in an anechoic chamber or a wall surface of a living room where electromagnetic waves are to be absorbed or blocked.

  Electromagnetic wave absorbers used in anechoic chambers are generally carbon pyramids made of soft resin foam impregnated with carbon, and are combined with ferrite tiles made of sintered ferrite to reduce size and bandwidth. I came.

  The carbon pyramid shows high performance particularly in a high frequency region, but the height of the pyramid is determined in accordance with the length of the wavelength, so that the carbon pyramid becomes very large in the low frequency region. Although ferrite tiles have a narrow frequency range that can be used, especially in the low-frequency region with a long wavelength, they exhibit excellent absorption performance even with thin ones. It constitutes an electromagnetic wave absorber to be demonstrated.

  In Patent Document 1, as a soft resin foam that has been used in the past, a pyramidal electromagnetic wave absorber made of a combination of carbon and urethane using an open cell structure has excellent return loss in the frequency range of 1 to 2 GHz. However, it is shown that the weather resistance is low. Further, it has been shown that a wedge-shaped wave absorber using foamed polystyrene having a closed cell structure, which is a hard resin foam, has excellent weather resistance but poor wave absorption characteristics.

JP-A-63-192299

  Ferrite tiles are excellent in weather resistance and strength, and are excellent in both thin and radio wave absorption characteristics, but have the disadvantage that cracks and chips are likely to occur because they are sintered, without using ferrite tiles. Although it is desired that a broad band is possible, it is very difficult to achieve a wide band without increasing the size of the radio wave absorber.

  In Patent Document 1, in order to improve the weather resistance, which is a defect of a radio wave absorber using a soft resin foam, a conductive cross-linked polyethylene having a closed cell structure that is a hard resin foam and excellent in radio wave absorption characteristics is used. Although a foamable electromagnetic wave absorbing material in which carbon is kneaded uniformly is shown, according to FIG. 5, the normalized thickness for obtaining a return loss of 30 dB is 1.0, and the target frequency is It can be seen that the thickness of the radio wave absorber is about 30 cm when the frequency is set to 1 to 2 GHz, which is specifically taken up in FIG. In other words, a thickness of 1 m is necessary at a lower frequency, for example, 300 MHz, and it can be seen that even if a material having good weather resistance and radio wave absorption characteristics can be obtained, it cannot be reduced in size.

In addition, the resin foam as the main material is easily deformed in the case of a soft resin foam, and even in the case of a hard resin foam, the resin foam is large in size and is likely to be damaged. Since carbon, which is another material, is made by burning petroleum and coal-based raw materials, it includes problems such as resource depletion and CO ₂ emissions, and is also expensive.

  In view of these circumstances, the present invention provides a radio wave absorber having excellent wave resistance and strength, having a radio wave absorption performance that is small and can be used even in an anechoic chamber, and the like, and without impairing those characteristics. It is an object to provide a radio wave absorber that can be used in a wide band.

  An electromagnetic wave absorber used in an anechoic chamber or the like is required to have a reflection of −20 dB or less as an absorption characteristic to be described later in a frequency region of several hundred MHz to several tens of GHz. Mainly composed of carbonized powder impregnated with a curable resin, cured, carbonized, and pulverized carbonized material and an organic binder for binding the carbonized powder to form a desired shape A radio wave absorber characterized by the above can be obtained, and it can sufficiently withstand use in an anechoic chamber or the like.

  The radio wave absorber according to the present invention is obtained by kneading / dispersing the carbonized powder in the organic binder, molding / curing, or applying the organic binder on the surface of the carbonized powder, pressing and solidifying, molding / curing. It is obtained by doing.

  According to the present invention, by gradually inclining the concentration of the carbonized powder, broadband reflection can be suppressed and higher radio wave absorption performance can be obtained.

  According to the present invention, it is possible to obtain a radio wave absorber further including at least one of carbon black, graphite, ferrite powder, and beads made of an insulating material, and these can be used as a layer separate from the carbonized powder, or The electromagnetic wave absorber is configured by mixing with carbonized powder. By further including other materials in this way, for example, carbon black and graphite can compensate for the shortage of characteristics with carbonized powder, especially by utilizing the characteristics of ferrite that is exhibited in the low frequency range, absorption and absorption When the body includes beads made of an insulating material, the reflection of electromagnetic waves is reduced, and it is possible to obtain a radio wave absorber excellent in radio wave absorption performance.

  The radio wave absorber of the present invention is superior in weather resistance and strength compared to a radio wave absorber using a conventional resin foam, and greatly reduces the size when trying to obtain the same radio wave absorption performance at the same frequency. Became possible. In addition, it has become possible to provide a radio wave absorber capable of supporting a wide band without increasing the size and maintaining the strength by combining the materials. Furthermore, by using carbonized powder made from waste material as a material, it has been possible to contribute to resource saving and to reduce the cost to 1/10 or less.

1 is a schematic perspective view of a quadrangular pyramidal wave absorber block 1 of the present invention. It is a schematic sectional drawing of the electromagnetic wave absorber 8a of Example 4 of this invention. It is a schematic perspective view of the wedge-shaped wave absorber block 1a of the present invention. It is a schematic sectional drawing of the electromagnetic wave absorber 8b of Example 5 of this invention. It is the schematic of the electromagnetic wave absorber which shows the other laminated example of this invention, Comprising: (a) is sectional drawing which shows the laminated example parallel to a radio wave flight direction, (b) is a cross section which shows the laminated example similar to an external shape. FIG. It is the schematic perspective view which looked at the electromagnetic wave absorber 8e of Example 6 of this invention from the bottom face direction. It is a schematic perspective view of the conical wave absorber block 1e of the present invention. It is a schematic diagram of the surface state of the radio wave absorber of Example 6 of the present invention. It is the schematic diagram which showed the inside of the electromagnetic wave absorber which disperse | distributed the bead which consists of an insulating material of this invention. It is the schematic which shows the evaluation system of the electromagnetic wave absorption characteristic used by this invention. It is a figure which shows the electromagnetic wave absorption characteristic of the electromagnetic wave absorber by the Example of this invention.

  The radio wave absorber according to the present invention is obtained by carbonizing a wood material impregnated with a thermosetting resin and then carbonizing the resulting carbonized material, and kneading and dispersing the carbonized powder in an organic binder or applying it to the surface. Then, it is a radio wave absorber formed by pressing and hardening the absorber into a predetermined shape and curing.

  In the present invention, waste materials are used among wooden materials. The present invention is aimed at the reuse of waste materials and the utilization of waste, and proposes one means, but of course, if it is a woody material, a radio wave absorber having excellent radio wave absorption characteristics can be obtained. It is manufacturable and does not limit the use of woody materials other than recycled or waste. It is mainly used for building waste and thinned wood waste, large sawdust, sawdust, etc., but this is not particularly limited, for example, wood that was originally intended for use other than this application It is also possible to use a woody material that can be used for other purposes than this application. The wood material is finely pulverized so that the thermosetting resin to be impregnated soaks well.

  Since the carbonization process of the present invention is carried out at a high temperature, the generation of harmful gases such as dioxins is low, but it is preferable to use a halogen-free thermosetting resin to prevent this. Among thermosetting resins, phenol resins, urea resins, melamine resins and the like that do not have a glass transition point are preferable, and among them, phenol resins are particularly preferable.

  The carbonized powder is made by carbonizing a wood material which has been impregnated with a thermosetting resin and then cured at a high temperature to form a carbide, and then pulverizing the carbide. When the carbonized powder is constituted by kneading and dispersing in an organic binder, the size of the carbonized powder is preferably about 10 μm to 1 mm, and more preferably several tens to several hundred μm. Further, it is preferable that the powders have the same size. On the other hand, when the organic binder is applied and pressed on the surface of the carbonized powder, the size of the carbonized powder is allowed to be about 10 μm to 20 mm, and preferably about 50 μm to 5 mm. Since gaps are easily formed, it is also preferable to mix powders of different sizes in order to increase the filling rate.

  The material used for the organic binder is not particularly limited, and various resins can be applied. What is necessary is just to select suitably according to each request | requirement, such as a dielectric constant regarding a radio wave absorption characteristic, a flame retardance / nonflammability, halogen free, biodegradability, intensity | strength, and cost. Specifically, resins and rubbers such as phenol, urea, melamine, urethane, polyethylene, polypropylene, acrylic, polycarbonate, polysulfate, polyvinyl alcohol, epoxy, polyamide, and vinyl acetate. The one prepared by kneading and dispersing the powder and the one prepared by applying to the powder surface have different conditions such as viscosity. For example, the one prepared by adjusting the viscosity by adding a solvent is used. In addition to the organic binder, it does not interfere with the inclusion of known additives such as flame retardants, flame retardant aids, surface treatment agents, fillers, and colorants.

  A conventionally known method is applied to the step of producing carbonized powder by carbonization. First, the waste material that is the raw wood material is pulverized to a certain size. This is a pretreatment for uniformly impregnating, and it is preferable to make it small for materials that are difficult to impregnate. The thermosetting resin is impregnated under reduced pressure or under pressure, and is injected into the tract of the wood material tissue using ultrasonic waves or the like. The wood material impregnated with the thermosetting resin is once heat-cured and then carbonized at a temperature of 700 ° C. or higher, preferably 900 ° C. or higher. When the temperature is lower than 700 ° C., the resistivity of the carbonized powder formed after carbonization is large and not practical. From the viewpoint of the resistance of the carbonized powder, it is preferable to perform carbonization at a higher temperature. However, if the temperature exceeds 1500 ° C., the degree of improvement in resistivity is small, but a special furnace is required and the energy required for carbonization. Is also not preferable.

  As a process for producing carbonized powder by carbonization treatment, a method of preliminarily carbonizing the wood material, impregnating and curing the thermosetting resin, and then performing carbonization treatment at a high temperature may be employed. It is advantageous in terms of energy to perform preliminary carbonization at a low temperature of about 300 to 700 ° C.

  The carbonization treatment is preferably performed in a non-oxidizing atmosphere, and may be performed in a closed furnace other than in a formalin atmosphere or a nitrogen atmosphere.

  After the carbonization treatment, the carbide of the woody material is finely pulverized to obtain a predetermined particle size, and a carbonized powder is produced.

  The carbonized powder is kneaded and dispersed so as to be uniform with the organic binder, or the surface of the carbonized powder is uniformly and extremely thinly coated with an organic binder by a spray method or the like, and then pressed, square pyramid, cone, wedge Molding into a desired shape such as a mold or a flat plate mold. The shape to be molded varies depending on the location because the requirements differ between the anechoic chamber and the wall surface of the living room where electromagnetic waves are to be absorbed or blocked, but the shape can be selected depending on the location, but there are few space restrictions and high reflection attenuation characteristics are required. In this case, a quadrangular pyramid shape, a conical shape, and a wedge shape are preferable. In the case of a flat plate type, it is preferable that the concentration of carbonized powder is gradually inclined so as to suppress reflection in a wide band.

  For the radio wave absorber having the slope of the carbonized powder in order, several types of absorbers having different carbonized powder concentrations (hereinafter referred to as carbonized powder absorber) are prepared, and according to the order of the carbonized powder concentration, It can be manufactured by forming into layers. In this way, by reflecting the carbonized powder absorber having different carbonized powder contents in the order of the concentration of the carbon powder, it is possible to reduce broadband reflection. When used in an anechoic chamber, it is desirable that the electromagnetic wave absorber is multi-layered with a concentration gradient in one direction so that the concentration of the carbonized powder on the electromagnetic wave arrival direction side is lowered. In addition, the order of molding when manufacturing a radio wave absorber having a concentration gradient is not limited to the level of carbonized powder concentration, and may be appropriately selected depending on the shape of the radio wave absorber. Carbonized powder absorbers having different carbonized powder contents may be laminated after being molded and cured, or in the middle of a process, for example, in the state of a slurry in which carbonized powder and an organic binder are kneaded and dispersed. Then, you may take the method of making a multilayer thing.

  In the present invention, the characteristics of the carbonized powder can be supplemented by adding any one or a combination of carbon black, graphite, ferrite powder, and beads made of an insulating material.

  Both carbon black and graphite, like the carbonized powder, cooperate with the organic binder to form a dielectric loss body and function to absorb electromagnetic waves. These powders are easier to atomize than carbonized powder, and it is advantageous to add them when it is desired to increase the concentration. In particular, an absorber with a high carbonized powder concentration is desired in the high frequency range of the GHz band, but when it is not possible to increase the filling rate of the carbonized powder, an excellent radio wave absorption ability can be exhibited. . In addition to mixing powders, for example, an absorber formed of carbon black and an organic binder and a carbonized powder absorber may be laminated.

  Ferrite powder can be expected to have excellent radio wave absorption ability especially in a low frequency region. An electromagnetic wave absorber is formed by laminating an absorber composed of ferrite powder and an organic binder (hereinafter referred to as a ferrite absorber) and a carbonized powder absorber. Can be widened. In this case, the ferrite powder may be appropriately selected according to the magnetic permeability, the dielectric constant, and the frequency band to be used, and typically Ni-Zn-based or Ni-Zn-Cu-based ferrite is used. By using the same kind of material as the carbon powder dispersed in the organic binder, reflection at the bonding interface between the carbonized powder absorber and the ferrite absorber can be prevented, and it can be firmly done without going through a process such as bonding. Can be joined. As a result, a radio wave absorber capable of exhibiting performance in a wide band can be obtained without using a ferrite sintered body that easily generates cracks and chips. Further, the ferrite powder may be mixed with the carbonized powder instead of being laminated.

  Moreover, the radio wave absorber of the present invention may further include beads made of an insulating material. Beads made of an insulating material have the same effect as that of a closed cell structure. The material used is preferably a material having a dielectric constant equal to or lower than that of the organic binder, and the material is not particularly limited. For example, the same kind of resin as the organic binder may be used, or glass may be used. Further, the added beads can be foamed using beads of an expandable resin. This is useful for adjusting the dielectric constant of the entire material, and can reduce reflection.

  The method of kneading and dispersing the carbonized powder, carbon black, graphite, ferrite powder, beads made of an insulating material and the organic binder may be based on a kneader, a mixing roll or other known means. For the above, the optimum means among known means is applied depending on the type of the organic binder selected. A method of forming a cured product by cutting or the like may be employed.

  Further, the method of applying the organic binder to the surface of the beads made of carbonized powder and carbon black, graphite, ferrite powder, and insulating material is preferably a spray method, but does not preclude the use of other means. What applied the organic binder to the powder surface pressurizes and arranges in a desired shape. You may pressurize, heating.

  Embodiments of the present invention will be described below with reference to the drawings.

  Radio wave absorbers (radio wave absorber blocks) according to the following Examples 1 to 7 were manufactured, and radio wave absorption characteristics were evaluated.

  First, the structure and manufacturing method of each radio wave absorber will be described.

Example 1
FIG. 1 is a schematic perspective view of a radio wave absorber block 1 of the present invention. As is clear from FIG. 1, the radio wave absorber block 1 is composed of a collection of quadrangular pyramid type radio wave absorbers 8.

  In Example 1, the radio wave absorber block 1 was manufactured by the following procedure.

  First, building waste that was sufficiently dried as a wood material was crushed into chips of about 10 to 20 mm, mixed at a ratio of wood material 80 mass% and phenol resin 20 mass%, and impregnated with ultrasonic waves under reduced pressure for 2 hours. . This was heat-cured at 180 ° C. and carbonized at 1100 ° C. in a nitrogen atmosphere. The carbonized material after carbonization was pulverized to an average particle size of 500 μm to obtain carbonized powder.

  The carbonized powder thus obtained was kneaded and dispersed in an epoxy resin at a ratio of 35 vol%, and this was molded and cured into a block shape as shown in FIG.

  The radio wave absorber block 1 made of the aggregate of the radio wave absorbers 8 was manufactured by the above procedure. In FIG. 1, the block is represented by a block in which four quadrangular pyramids are gathered. In the present embodiment, the block is a 300 × 300 mm block in which 25 square pyramids are gathered. At this time, the thickness t of the radio wave absorber 8 was 65 mm.

(Example 2)
A radio wave absorber block 1 similar to that in Example 1 was manufactured by changing the manufacturing conditions.

  Specifically, first, building waste material that has been sufficiently dried as a wood material is crushed into chips of about 10 to 20 mm, mixed at a ratio of 80 mass% of wood material and 20 mass% of furan resin, and ultrasonically applied under reduced pressure. Impregnation for 2 hours. This was heat-cured at 120 ° C. and carbonized at 1100 ° C. in a nitrogen atmosphere. The carbonized material after carbonization was pulverized to an average particle size of 500 μm to obtain carbonized powder.

  The carbonized powder thus obtained was kneaded and dispersed in an epoxy resin at a rate of 35 vol% to produce a radio wave absorber block 1.

(Example 3)
The same carbonized powder as used in Example 1 was kneaded and dispersed in 35% by volume of carbon black powder having an average particle size of 0.5 μm in a proportion of 10% by volume in a polyvinyl alcohol resin to obtain the same shape as in Example 1. The radio wave absorber block 1 made of the radio wave absorber 8 was manufactured by molding and reaction curing.

Example 4
As shown in FIGS. 2 to 3, a radio wave absorber block 1 a made of a laminated radio wave absorber 8 a having a carbonized powder absorber 30 as an upper portion and a ferrite absorber 41 as a base portion was manufactured. The specific configuration and manufacturing method are as follows.

  First, the configuration will be described. As shown in FIG. 2, the radio wave absorber 8 a of Example 4 is a laminated radio wave absorber in which the upper part is a carbonized powder absorber 30 and the base is a ferrite absorber 41. As shown in FIG. 3, the radio wave absorber block 1a is formed by alternately arranging blocks having two wedge-shaped radio wave absorbers 8a.

  Next, a manufacturing method will be described.

  A mixture obtained by kneading and dispersing the same carbonized powder as in Example 1 in an epoxy resin at a ratio of 35 vol% and a mixture obtained by kneading and dispersing an Ni-Zn ferrite powder in an epoxy resin at a ratio of 55 vol% were prepared. The mixture is sequentially filled in a mold so as to become a carbonized powder absorber 30 at the top of 8a and a ferrite absorber 41 at the base, and cured to form a laminated wave absorber 8a, which is an aggregate of the wave absorber. Block 1a was produced. The shape of the radio wave absorber block 1a is as shown in FIG. 3, and is 300 × 300 mm in size and 65 mm in thickness t.

(Example 5)
A radio wave absorber 8b having a slope of the carbon powder concentration was manufactured. The specific configuration and manufacturing method are as follows.

  First, the configuration will be described with reference to FIG. 4 and FIG.

  As shown in FIG. 4, the radio wave absorber 8b of the fifth embodiment of the present invention is different in the concentration of the carbonized powder from the low concentration carbonized powder absorber 31, the medium concentration carbonized powder absorber 32, and the high concentration carbonized powder absorber 33. It is a flat-plate type wave absorber in which carbonized powder absorbers are sequentially laminated according to the concentration.

  Next, a manufacturing method will be described.

  First, a mixture obtained by kneading and dispersing the same carbonized powder as in Example 1 in a proportion of 5 vol%, 25 vol%, and 45 vol% in a polycarbonate resin is filled in a mold in order from the one with the highest carbonized powder concentration, and cured. As shown in FIG. 4, the low-concentration carbonized powder absorber 31, the medium-concentrated carbonized powder absorber 32, and the high-concentrated carbonized powder absorber 33 are each one-third in the thickness direction of the radio wave absorber. The absorbent body 8b was molded. The thickness t of the radio wave absorber 8b at this time was 30 mm, and the size was 300 × 300 mm.

  In addition, although it filled and shape | molded in order of the density | concentration in Example 5, the order may be reverse. It is also possible to make absorbent bodies with different concentrations separately and join them by laminating them according to the concentration. Further, the ratio of the thickness of each layer and the number of layers are not limited to the present embodiment. In addition, when using the electromagnetic wave absorber of a present Example, it uses so that the layer of the carbonized powder absorber with a low carbon content may become the electromagnetic wave flight direction. In the present embodiment, a flat plate type is shown, but it is of course possible to adopt a configuration having a concentration gradient such as a quadrangular pyramid type, a conical type, or a wedge type. For reference, FIG. 5 shows a cross-sectional view of a configuration example of the laminated wave absorbers 8c and 8d having a shape other than the flat plate type.

(Example 6)
A radio wave absorber block 1e having a conical outer shape and comprising a hollow radio wave absorber 8e was manufactured. The specific configuration and manufacturing method are as follows.

  First, the configuration will be described with reference to FIG.

  As shown in FIG. 6, the radio wave absorber 8e is hollow and has a hollow shape, and as shown in FIG. 7, the radio wave absorber block 1e is composed of an assembly of the radio wave absorbers 8e.

  The surface of the radio wave absorber 8e of Example 6 has an appearance as shown in FIG.

  Next, a manufacturing method will be described.

  The building waste material sufficiently dried as a wood material was crushed into chips of about 10 to 20 mm, mixed in a ratio of 80 mass% of the wood material and 20 mass% of the phenol resin, and impregnated with ultrasonic waves under reduced pressure for 2 hours. This was heat-cured at 180 ° C. and carbonized at 1100 ° C. in a nitrogen atmosphere. The carbonized material after carbonization was pulverized to an average particle size of 2 mm to obtain carbonized powder. A carbonized powder having a large average particle size as in this embodiment is very advantageous because it can be produced at low cost.

  A polyvinyl alcohol resin was diluted with a solvent and sprayed onto the carbonized powder. This was pressed and molded, and the solvent was evaporated and cured to form a radio wave absorber block 1e made of an aggregate of hollow radio wave absorbers 8e. As shown in FIG. 7, the radio wave absorber block 1g is composed of an aggregate of conical radio wave absorbers 8e. In FIG. 7, the block is represented by a block in which four cones are gathered. However, in this embodiment, the block is a 300 × 300 mm block in which 25 cones are gathered. At this time, the thickness t of the radio wave absorber 8e was 65 mm.

  Since carbonized powder having a large particle size is used in this example, the surface remains uneven as schematically shown in FIG. 8, but a smoother surface can be obtained depending on the size of the powder used. You can also. In the method of constructing a radio wave absorber by pressing and compacting as in this embodiment, the proportion of the organic binder is very small, and a considerable part of the whole is occupied by carbonized powder, so that the radio wave absorber has a very high concentration. I can do it.

(Example 7)
A radio wave absorber having beads dispersed therein was manufactured. The specific configuration and manufacturing method are as follows.

  In addition to the carbonized powder absorber obtained by kneading and dispersing the same carbonized powder as in Example 1 in a phenolic resin at a ratio of 45 vol%, polypropylene beads are added as beads 4 made of an insulating material to obtain the same block shape as in Example 6. A radio wave absorber block made of an aggregate of radio wave absorbers was produced by molding and curing. However, in this embodiment, the radio wave absorber does not have a cavity. As shown schematically in FIG. 9, the inside of the radio wave absorber had a structure in which beads 4 made of carbonized powder 3 and an insulating material were dispersed in a phenol resin matrix (organic binder 2).

  Next, the radio wave absorption characteristics of the radio wave absorbers according to Examples 1 to 7 were evaluated. The specific procedure is as follows.

  As shown in FIG. 10, the wave absorber block of 300 mm × 300 mm shown in each example is installed as a sample 7 on the floor of the anechoic chamber, and around the sample 7 for background absorption, A quadrangular pyramid wave absorber 8 made of urethane foam impregnated with carbon was laid down, and the transmitting antenna 5 and the receiving antenna 6 were arranged on the ceiling side to measure the radio wave absorption characteristics. The distance between the sample and the transmitting / receiving antenna was 3 m. The radio wave absorption characteristics were determined by the ratio of the reflected wave from the metal plate (copper plate in this embodiment) of the same size arranged at the same position as the sample 7 and the reflected wave from the sample 7. The measurement frequency range was 100 MHz to 20 GHz, and measurement was performed from 100 MHz to 1 GHz with a helical antenna and from 1 GHz to 20 GHz with a horn antenna.

  This result is shown in FIG. In any of the examples, it can be seen that a return loss of −20 dB or less can be achieved in a frequency region of 500 MHz or higher.

  It was also found that the difference in the type of thermosetting resin when producing the carbonized powder hardly affects the radio wave absorption characteristics.

  Looking at individual examples, carbon black is added in addition to carbonized powder in Example 3, and the amount of carbon contained is larger than that in Example 1, and the characteristics are improved particularly in the high frequency region. confirmed.

  Further, in the radio wave absorber in which the ferrite powder absorber of Example 4 was provided on the base portion and laminated, the radio wave absorption characteristics on the low frequency side were significantly improved.

  On the other hand, in Example 7, reflection was suppressed and the radio wave absorption characteristics were slightly good in the low frequency region.

(Comparative example)
Next, radio wave absorbers according to Comparative Examples 1 and 2 were manufactured, and strength characteristics were evaluated.

(Comparative Example 1) As Comparative Example 1, a radio wave absorber block having the same shape as that of Example 7 of the present invention was manufactured using conductive cross-linked polyethylene mixed with carbon in the same manner as the foamable radio wave absorber described in Patent Document 1. . A strength comparison test was performed between the comparative example 1 and the example 7 including the beads 4 made of an insulating material. The test was performed using a compressive strength measuring device of a type in which a load was applied vertically from the upper part so that a 30 mm plate-shaped jig hits the tip of one cone instead of the entire block. As a result, in Comparative Example 1, deformation was started with a load of 3 kgf (3 × 9.8 N). In the sample of Example 7, neither deformation nor breakage occurred even at the upper limit of 50 kgf (50 × 9.8 N) of this test. The comparative example 1 is a radio wave absorber having a closed cell structure, whereas the example 7 is a structure in which beads 4 made of an insulating material are dispersed. Dispersion of beads 4 made of a closed cell and an insulating material as a radio wave absorber has a similar effect in terms of radio wave absorption characteristics, but in terms of strength, it was better to disperse beads 4 made of an insulating material. .

(Comparative Example 2) As Comparative Example 2, instead of the carbonized powder of the present invention, a commercially available charcoal powder obtained by pulverizing Bincho charcoal and having an average particle size of 500 μm was kneaded and dispersed in an epoxy resin at a ratio of 35 vol%. A 20 mm square block was produced. Moreover, the 20 mm square block was manufactured similarly using the carbonized powder of Example 1. This was attached to a friction tester, and 100 mm was reciprocated 20 times at 10 mm / s, and it was confirmed whether or not the powder had fallen off. As a result of the friction test, in Comparative Example 2 using the charcoal powder, the charcoal powder on the surface dropped off and a black powder was observed, but no change was observed in the carbonized powder of the present invention. This is presumably because the carbonized powder is in the form of glass because it is impregnated with a thermosetting resin in the present invention, and it is not softly broken like charcoal.

  Although the embodiments of the present invention have been described above, the configuration of the present invention is not limited to these embodiments, and various configurations that can be made by those skilled in the art without departing from the gist of the present invention. It goes without saying that modifications are also included in the present invention.

1 Radio wave absorber block 2 Organic binder 3 Carbonized powder 4 Beads made of insulating material 5 Transmitting antenna 6 Receiving antenna 7 Sample 8 Radio wave absorber 30 Carbonized powder absorber
31 Low concentration carbonized powder absorber
32 Medium concentration carbonized powder absorber
33 High concentration carbonized powder absorber
41 Ferrite powder absorber

Claims (5)

  Carbonized powder obtained by impregnating and curing a woody material with a thermosetting resin and then carbonized, and pulverizing the carbonized material, and an organic binder for binding the carbonized powder to form a desired shape A radio wave absorber characterized by comprising as a main material.   2. The radio wave absorber according to claim 1, wherein the carbonized powder is formed by kneading and dispersing, molding and curing in the organic binder.   2. The radio wave absorber according to claim 1, wherein the organic binder is applied to the surface of the carbonized powder, pressed, molded and cured.   The radio wave absorber according to any one of claims 1 to 3, wherein the concentration of the carbonized powder is sequentially inclined.   Carbon black, graphite, ferrite powder, further comprising any one of beads made of an insulating material, and any one or more of the carbon black, graphite, ferrite powder, beads made of an insulating material, the carbonized powder is The radio wave absorber according to any one of claims 1 to 3, wherein the radio wave absorber is formed as a separate layer or mixed with the carbonized powder.