JP6726796B1 - Radio wave absorber containing carbon fiber and method of manufacturing the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a radio wave absorber which suppresses deterioration of radio wave absorption characteristics on the low frequency side and also suppresses dimensional shrinkage due to foaming by a mold while obtaining good radio wave absorption performance on the high frequency side of carbon fiber. Is an issue. The present invention relates to a radio wave absorber in the megahertz band to the gigahertz band, which is configured by combining a ferrite tile type absorber and a solid three-dimensional foamed rigid urethane absorber. The urethane absorbent has a configuration in which the carbon fibers are three-dimensionally and uniformly dispersed by mixing the carbon fibers with the polyol and the polyisocyanate and foaming them. [Selection diagram] Figure 1

Description

The present invention relates to a radio wave absorber technology, and more particularly, to a technology for imparting radio wave absorption performance in a wide frequency band by combining a ferrite sintered body with a hard urethane in which carbon fibers are dispersed.

In recent years, as the spread of mobile phones has shown, the radio wave environment is deteriorating, and a radio wave environment that should be called "radio wave flood" is occurring around us. It can be said that the need for various electromagnetic wave absorbers is ever increasing in order to improve the environment. In particular, recently, an anechoic chamber for measuring noise of electronic devices is required to have electromagnetic wave absorption performance in a wide frequency band from the megahertz band to the gigahertz band.

As a method of imparting radio wave absorption performance in a wide frequency band, conventionally, a method of combining a ferrite sintered body and a matching radio wave absorber in which urethane or silicon contains carbon particles is used. In such a method, there is a method of absorbing radio waves in the megahertz band by the effect of the ferrite sintered body and absorbing radio waves in the gigahertz band by the effect of the radio wave absorber containing carbon particles. However, when the content of the carbon fine particles is increased, the absorption performance in the gigahertz band is improved, while the absorption performance in the megahertz band is deteriorated. This is because the absorption performance of the ferrite sintered body is canceled by the influence of the surface reflection of the carbon fine particles. Therefore, the radio wave absorption performance in the megahertz band and the gigahertz band has a trade-off relationship with the carbon particle concentration, and it has been difficult to provide excellent radio wave absorption performance in a wide frequency band.

Therefore, the present inventors have focused on using carbon fibers instead of carbon fine particles in order to solve this problem. It was found from the results of various experiments that carbon fibers have a characteristic of being able to absorb radio waves in the megahertz band in a smaller amount than carbon fine particles. However, until now, it has not been possible to find an effective method for obtaining a radio wave absorber in which carbon fibers are uniformly dispersed, and it has been impossible to solve the problem that the absorption performance varies. Further, when the foaming base material and the carbon particles are foamed together, there is a problem that shrinkage is likely to occur at the time of die-cutting and dimensional stability is lacking.

In view of such a problem, the present inventors have earnestly studied, and as a result, by mixing and foaming carbon fiber into a polyol and a polyisocyanate, which are raw materials of hard urethane, a radio wave absorber in which carbon fibers are uniformly dispersed is obtained. The inventors of the present invention have found that they can be obtained, and have completed the present invention that makes it possible to maintain the radio wave absorption performance of a megahertz absorber at a constant level even when sufficient absorption performance is given to the gigahertz band.

Note that various technical proposals have been made in the past regarding radio wave absorbers in a wider frequency range. For example, a technique in which the name of the invention is "radio wave absorber" is disclosed (see Patent Document 1). Specifically, the problem is "to provide a radio wave absorber having a suitable complex permittivity that can be appropriately used even outdoors." As a solution, "expansion ratio is 1.5 to 6.0". Carbon fibers having a length of 0.5 to 10.0 mm and a length of 0.5 to 10.0 mm are dispersed at 0.0001 to 0.02 g/cm 3 per unit volume after foaming so as to obtain consistency with space. In addition, the invention comprises a foam made of foamed silicon having a portion whose cross-sectional area gradually increases in the radio wave traveling direction.” However, since the technique described in Patent Document 1 uses silicon as the foaming material, it is not possible to increase the foaming ratio as described in paragraph “0016” of the specification (at 6 times or more, Not suitable as a wave absorber due to reduced mechanical strength). Therefore, the effect is greatly different from that of the present invention that enables the provision of a lightweight electromagnetic wave absorber. Further, as described in paragraph “0017”, it is considered that the reason why it is difficult to uniformly disperse the carbon fibers is that the carbon fibers are insufficiently dispersed due to the low expansion ratio.

In addition, a technology in which the name of the invention is “radio wave absorber” is disclosed (see Patent Document 2). Specifically, the object is to “provide a lightweight and quasi-incombustible radio wave absorber capable of absorbing a radio wave having a thin thickness and a frequency of about 100 to 900 MHz.” , "A phenolic resin foam is composed of a dielectric material in which carbon fibers are dispersed and a conductor adhered to one surface of the dielectric material. The fiber content is 0.5 to 10% by weight, and the conductor is a metal plate." Therefore, it is common with the present invention in that carbon fibers are dispersed in the phenol foam resin. However, the technique described in Patent Document 2 is a radio wave absorber in the megahertz band of 100 to 900 MHz, and is intended to obtain a thin plate shape, light weight, and quasi-incombustibility, and like the present invention. The problem of providing a radio wave absorber in a wide frequency range from the megahertz band to the gigahertz band has not been solved.

Further, a technology in which the title of the invention is “a radio wave absorber and a method for manufacturing the same” is disclosed (see Patent Document 3). Specifically, with the aim of "providing a lightweight electromagnetic wave absorber that does not generate toxic gas even when burned", as a solution means A porous structure is formed by a rubber composition in which conductive carbon black as an absorbing material is mixed, and the rubber composition is mixed with carbon fibers, a flame retardant-imparting filler, a cross-linking agent, a foaming agent and the like. The porous structure is heat-treated to reconstruct the structure of the conductive carbon black.” Therefore, it is common with the present invention in that carbon fibers are dispersed in the matrix. However, the technique described in Patent Document 3 is a radio wave absorber specialized for an ETC communication frequency of 5.8 GHz, and is intended to obtain a thin plate-like lightweight and quasi-noncombustible material. It does not solve the problem of providing a radio wave absorber in a wide frequency range from the megahertz band to the gigahertz band as in the present invention. In addition, since carbon fibers are mixed into an uncrosslinked rubber composition and molding is carried out by crosslinking, it is considered that uniformity in dispersion cannot be obtained.

Japanese Unexamined Patent Publication No. 7-86783 JP-A-9-92996 JP-A-2006-73760

INDUSTRIAL APPLICABILITY The present invention suppresses the deterioration of the radio frequency absorption characteristic on the low frequency side in the ferrite tile type absorber while obtaining the good radio frequency absorption performance of the solid foamed hard urethane and the carbon fiber on the high frequency side. It is an object to provide an electromagnetic wave absorber with uniform dispersion and suppressed dimensional shrinkage.

The present invention is a radio wave absorber from the megahertz band to the gigahertz band, which is configured by combining a ferrite tile type absorber and a solid three-dimensional foamed hard urethane absorber, and the solid three-dimensional foamed hard urethane absorber. The body employs a constitution in which the carbon fibers are three-dimensionally and uniformly dispersed by mixing the polyol and the polyisocyanate with the carbon fibers and foaming them.

Further, according to the present invention, the solid three-dimensional foamed rigid urethane absorbent is formed by mixing polyol and polyisocyanate with a carbon fiber and a powder magnetic material and foaming the resulting mixture to obtain the magnetic properties of the carbon fiber and the powder. It is also possible to adopt a configuration in which the materials are three-dimensionally and uniformly dispersed.

Further, the present invention can adopt a configuration in which the solid three-dimensional foamed rigid urethane absorber has a plurality of matching bodies each having a shape in which a cross-sectional area in a vertical direction gradually increases in a traveling direction of radio waves. ..

Further, the present invention may employ a configuration in which the solid three-dimensional foamed rigid urethane absorbent is arranged in a part or the whole of the gap area of the carbon fiber coating-shaped absorbent having a double cross shape.

Further, the present invention may be a carbon fiber-containing radio wave absorber in which the carbon fiber has a length of 5 mm to 7 mm.

Further, the present invention relates to a radio wave absorber of a megahertz band to a gigahertz band having a plane perpendicular to a traveling direction of a radio wave in parallel, which is a solid three-dimensional foamed solid urethane foamed solid urethane foam absorber. The solid three-dimensional foamed hard urethane absorbent is composed of a layer of a rigid urethane absorber and a layer of a styrofoam material composed of a styrofoam material having no dielectric loss, and has a shape that engages with the shape of the layer of the styrofoam material. It is also possible to adopt a constitution in which the body is foam-cured and is integrated with the styrofoam layer in the process of foam-curing.

Further, the present invention, the layer of the polystyrene foam material has a plurality of shapes in which the area of the cross section in the vertical direction gradually decreases toward the traveling direction of the radio wave, and the layer of the solid three-dimensional foamed rigid urethane absorber is It is also possible to adopt a configuration having a plurality of matching bodies in which the area of the cross section in the vertical direction gradually increases in the traveling direction of the radio wave.

Further, the present invention is a method of manufacturing a radio wave absorber from the megahertz band to the gigahertz band, a ferrite tile type absorber, and a solid three-dimensional foamed rigid urethane absorber, in combination,
It is also possible to adopt a configuration in which the solid three-dimensional foamed hard urethane absorbent is foamed by mixing carbon fiber with polyol and polyisocyanate to thereby three-dimensionally disperse the carbon fiber.

Further, the present invention may employ a configuration in which the solid three-dimensional foamed rigid urethane absorbent is foamed by mixing polyol and polyisocyanate with carbon fiber and further powdery magnetic material.

Further, the present invention is a method of manufacturing a radio wave absorber of a megahertz band to a gigahertz band having a plane perpendicular to a traveling direction of radio waves in parallel, wherein the solid three-dimensional foamed rigid urethane absorber is used. In the process of molding a layer of a styrofoam material composed of a layer of a three-dimensional styrofoam rigid urethane absorber and a styrofoam material without dielectric loss, the solid three-dimensional shape is formed so as to engage with the shape of the styrofoam material layer. It is also possible to adopt a configuration in which the mold-foam hard urethane absorber is foam-cured and is integrated with the styrofoam layer in the foam-curing step.

Further, the present invention can also be applied to a method for producing a carbon fiber-containing radio wave absorber having a configuration in which the length of the carbon fiber is 5 mm to 7 mm.

Further, the present invention can adopt a configuration in which the frequency band to be absorbed is changed by adjusting the content rate of the carbon fiber.

Further, the present invention is characterized in that the layer of the styrofoam material is molded so as to have a plurality of shapes in which the area of the cross section in the vertical direction gradually decreases in the traveling direction of the radio wave, and the solid three-dimensional foamed hard urethane absorber is formed. The layer of the solid three-dimensional foamed rigid urethane absorber composed of is molded so as to have a plurality of matching bodies whose cross-sectional area in the vertical direction gradually increases in the traveling direction of radio waves. Means can also be employed.

Further, the present invention is a method for manufacturing a radio wave absorber in the megahertz band to the gigahertz band, which is configured by combining a ferrite tile type absorber and a solid three-dimensional foamed rigid urethane absorber, wherein the solid three-dimensional It is also possible to adopt a configuration in which the type foamed hard urethane absorbent is foamed by mixing the carbon fiber with the polyol and the polyisocyanate to thereby three-dimensionally and uniformly disperse the carbon fiber.

Further, the present invention may be a method for producing a structure in which the carbon fiber has a length of 5 mm to 7 mm.

It is also possible to adopt a manufacturing method of a structure in which the frequency band to be absorbed is changed by adjusting the content rate of the carbon fiber.

The layer of the styrofoam material is molded so as to have a plurality of shapes in which the area of the cross section in the direction perpendicular to the traveling direction of the radio wave is gradually reduced, and the layer of the solid three-dimensional foamed rigid urethane absorber is It is also possible to use a manufacturing method of a structure in which a plurality of matching bodies whose cross-sectional areas in the vertical direction gradually increase in the traveling direction are formed to be molded.

According to the carbon fiber-containing radio wave absorber and the method for producing the same according to the present invention, it is possible to obtain good radio wave absorption performance on the high frequency side of the carbon fiber, suppress deterioration of the radio wave absorption characteristic on the low frequency side, and foam by the mold. It exhibits an excellent effect that it is possible to provide an electromagnetic wave absorber with suppressed dimensional shrinkage.

Further, according to the carbon fiber-containing radio wave absorber according to the present invention, since the internal structure in the matching shape is a solid structure made of hard urethane, it is possible to obtain a more excellent radio wave due to the internal radio wave absorption effect as compared with the hollow structure. It exhibits an excellent effect that it can have absorption characteristics.

Further, according to the carbon fiber-containing radio wave absorber according to the present invention, carbon fibers that cause high dielectric loss are three-dimensionally and uniformly dispersed, and bulkiness does not occur, which is a problem in the conventional technology. It is possible to solve the problem that the absorption performance varies. Regarding the problem, when the powder magnetic material is used together with the carbon fiber and the polyol or polyisocyanate as the base material is soaked together to foam, the carbon fiber plays a matrix role. As a result, it is possible to suppress the precipitation of the powder magnetic material and to further reduce the variation of the electromagnetic wave absorption characteristics.

According to the radio wave absorber containing carbon fiber of the present invention, since the matching body is a hard urethane foam, it exhibits an excellent effect that it can be manufactured at a light weight, a high rigidity, and a low cost.

Further, in the case of the carbon fiber-containing radio wave absorber according to the present invention, when adopting a structure in which the length of the carbon fiber is 5 mm to 7 mm, generally commercially available carbon fiber can be used, so that it is easily available. It has an excellent effect that there are few problems of property and cost.

Further, the carbon fiber-containing radio wave absorber according to the present invention has a plane having a plane perpendicular to the traveling direction of radio waves in parallel, and is composed of a layer of a solid three-dimensional urethane absorber and a layer of styrofoam material without dielectric loss. In the case of using, it has an excellent effect that when it is used for a floor or a wall, there is no unevenness due to the matching body as in the prior art, and the part that a person contacts can be made flat.

Further, since the carbon fiber-containing radio wave absorber according to the present invention has the excellent feature of self-adhesiveness that other foam materials do not have, since it uses hard urethane foam as a material, it has a solid polystyrene foam layer and a solid foam material. It exhibits an excellent effect that a strong adhesive effect can be obtained even when it is bonded to the layer of the three-dimensional urethane absorbent.

It is a basic-structure explanatory drawing explaining the basic structure of the carbon fiber containing radio wave absorber which concerns on this invention. It is a figure which shows the return loss of a conventional ferrite tile type absorber and a conventional urethane type absorber. It is a figure which shows the return loss of the conventional carbon fiber coating type absorber. It is a figure which shows the return loss of the conventional urethane type absorber and the carbon fiber containing radio wave absorber which concerns on this invention. FIG. 5 is a comparative diagram showing a difference in return loss due to a difference in shape of a matching body in the carbon fiber-containing radio wave absorber according to the present invention. It is a figure which shows the return loss when the magnetic material of a powder is included in the electromagnetic wave absorber containing carbon fiber which concerns on this invention. It is an example explanatory view showing the example of the composition which has the plane perpendicular to the advancing direction of an electric wave in parallel in the electromagnetic wave absorber containing carbon fiber concerning the present invention.

The present invention mixes a carbon fiber with a polyol and a polyisocyanate, which are raw materials of hard urethane, and foams them to form a matching shaped electromagnetic wave absorber in which carbon fibers are uniformly dispersed, and a ferrite sintered body. The greatest feature is that it is an effective electromagnetic wave absorber in a wide range. Hereinafter, description will be given with reference to the drawings. However, it is not limited to the shapes and configurations described in the drawings, and can be changed within a 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 view for explaining the basic configuration of a carbon fiber-containing radio wave absorber according to the present invention. The carbon fiber-containing radio wave absorber 1 according to the present invention is a radio wave absorber in the megahertz band to the gigahertz band, and is configured by combining a ferrite tile type absorber 10 and a solid three-dimensional foamed rigid urethane absorber 20. The solid three-dimensional urethane absorber 20 has a basic configuration in which the carbon fibers 30 are three-dimensionally and uniformly dispersed by mixing and foaming the carbon fibers 30 in the polyol 21 and the polyisocyanate 22. It is a thing. Characteristic carbon fiber-containing radio wave absorber (1).

The ferrite tile type absorber 10 is an absorber having a good radio wave absorption particularly in the megahertz band, and is a mixture of iron oxide (Fe2O3) with a divalent metal oxide (NiO, ZnO, etc.) and sintering at a temperature of a few thousand degrees. It is a solid consisting of the above-mentioned ferrite sintered body and is used after being processed into a tile shape. Since the ferrite tile type electromagnetic wave absorber was researched and developed in the 1960s, it has been put to practical use and developed in the fields of communication such as TV broadcasting, various radios and various radars, and the EMC field of noise suppression and noise evaluation of electric and electronic devices. However, today, it is indispensable in an anechoic chamber used for noise evaluation of electric and electronic devices, and the present invention is mainly used for the purpose of absorbing radio waves in the megahertz band.

The solid three-dimensional foamed rigid urethane absorber 20 includes a polyisocyanate having two or more NCO (isocyanate) groups and a polyol having two or more OH (hydroxyl) groups, a catalyst (amine compound, etc.), a foaming agent (water, (A hydrocarbon, etc.), a foam stabilizer (silicone oil), etc., and a uniform urethane resin foam obtained by simultaneously performing a foaming reaction and a resinification reaction. It should be noted that soft urethane is disadvantageous in shape retention and dimensional stability since it retains flexibility after foaming, and has the drawback of increasing the cost of raw materials. Further, in the case of expanded polystyrene, if a material such as carbon is present in the gap between beads, there is a problem that contraction easily occurs when the material is removed from the mold.

Polyol 21 includes polyether polyol and polyester polyol, and is used in an arbitrary combination according to the target performance of polyurethane. In the present invention, polyester polyol is used in order to obtain a rigid urethane foam. Such a polyester polyol also has an effect of improving heat insulation performance and combustion characteristics.

The polyisocyanate 22 forms the solid three-dimensional foamed rigid urethane absorbent body 20 from a urethane bond formed by reacting with the polyol 21. In addition, by increasing the ratio of isocyanurate bond in the foam and using a specific catalyst, an isocyanurate ring is generated from the trimerization reaction of isocyanate, and this isocyanurate ring is more stable than urethane bond in thermal stability. Since the hard urethane foam containing the isocyanurate ring is highly flame-retardant, the polyisocyanurate foam containing the isocyanurate ring in a certain proportion or more, as compared with the normal hard urethane foam, has high flame retardancy. It is also effective to use the matching body of “” for the wall or floor material of the anechoic chamber.

The expansion ratio is preferably in the range of 25 to 35 times, more preferably 30 times. The reason is that there are problems of strength and cost. This is because if it is about 10 to 20 times, it becomes heavy, and if it is 100 times, it is better not to use it in consideration of safety. There is also a problem that the atmospheric pressure is lost when the magnification is increased. As a result of the experiment, the limit was 35 times.

Next, regarding the flame retardant, the flame retardant test results are shown in Table 1 below. As shown in Table 1, when the amount of the flame retardant added was 0%, there was no self-extinguishing property, and the result was that burning continued for about 10 seconds. On the other hand, when the amount of the flame retardant added was increased to 2.5%, 5% and 7.5%, 2.5% extinguished the fire in about 3 seconds and 5% and 7.5% extinguished the fire immediately. Therefore, it can be said that it is desirable to add at least 5% or more of the flame retardant. In such an experiment, flame contact was performed using a gas burner using 10 cm×10 cm×10 cm hard urethane.

The carbon fibers 30 are three-dimensionally uniformly dispersed in the solid three-dimensional foamed hard urethane absorber 20 which is a hard foamed urethane, and are electromagnetic wave absorbers that utilize ohmic loss, which plays a role in absorbing electromagnetic waves particularly in the GHz band. The fiber length is effective in the range of 5 mm to 7 mm, and more preferably 6 mm. Regarding the fiber length, if the length is 4 mm or less, the radio wave absorption property is not good, and if it exceeds 7 mm, uniform dispersion becomes difficult. By increasing or decreasing the content of the carbon fiber 30, the absorption characteristics particularly in the high frequency gigahertz band are changed. Therefore, it is possible to change the absorption frequency band by adjusting the content rate of the carbon fiber 30.

Various methods were attempted for uniform mixing, but it was effective to disperse the carbon fiber 30 by impregnating the base polyol or polyisocyanate with the carbon fiber 30 to foam the carbon fiber 30. It should be noted that in the case where the carbon fiber 30 was mixed paper and processed into chips with a shredder, good electromagnetic wave absorption characteristics could be obtained by packing in a box with an optimum addition amount according to the volume. However, it has been confirmed that over time, the electromagnetic wave absorption characteristics, in which the bulkiness is reduced due to its own weight, cannot be maintained. Therefore, in order to prevent the bulkiness after filling the box, spray glue was applied to the chips and the box was filled. Although good electromagnetic wave absorption characteristics could be confirmed even with such a configuration, bulkiness still occurred due to its own weight.

The powdery magnetic material 31 is dispersed together with the carbon fiber 30 by impregnating it with a polyol or polyisocyanate as a base material and foaming it. In particular, in order to improve the electric wave absorption characteristics of the megahertz band only with the dielectric material, it is necessary to increase the height of the absorber. By using the magnetic material together, the height of the absorber can be kept at the same level of several dB. It is possible to improve (see FIG. 6). By dispersing the magnetic material 31 of the powder together with the carbon fiber 30, the carbon fiber 30 plays a matrix function, contributes to the improvement of the dispersibility of the magnetic material 31 of the powder, and suppresses precipitation. This makes it possible to reduce variations in electromagnetic wave absorption characteristics.

2 to 4 compare the electromagnetic wave absorption characteristics between the conventional electromagnetic wave absorber and the electromagnetic wave absorber obtained by the carbon fiber-containing electromagnetic wave absorber 1 or the manufacturing method 2 of the carbon fiber-containing electromagnetic wave absorber according to the present invention. In this evaluation method, the value on the vertical axis is on the lower side of the graph, that is, the larger the electromagnetic wave absorption, the better the characteristic. In general, it is desirable to have electromagnetic wave absorption characteristics with little change in all measured frequency bands.

FIG. 2 is a diagram showing return loss of a conventional ferrite tile type and a conventional urethane type. FIG. 2A shows the return loss characteristic of the conventional ferrite tile type in the megahertz band, FIG. 2B shows the return loss characteristic of the conventional urethane type gigahertz band, and FIG. 2C shows the return loss characteristic of the conventional ferrite tile type. FIG. 2(d) shows the reflection attenuation characteristics in the conventional urethane type megahertz band, FIG. 2(e) shows the reflection attenuation characteristics in the conventional urethane type gigahertz band, and FIG. 2(f) shows the conventional configuration. The urethane type configuration is shown.

As shown in FIGS. 2(a) and 2(b), the conventional ferrite tile type has good absorption characteristics in the megahertz band, but poor absorption characteristics in the gigahertz band, so that a wide range of radio wave absorption characteristics cannot be obtained.

Further, as shown in FIGS. 2D and 2E, the conventional urethane type has a slightly lower absorption characteristic in the megahertz band than the ferrite tile type, but has excellent radio wave absorption characteristics in the gigahertz band. .. However, in order to further improve the absorption characteristics in the gigahertz band, as the carbon concentration is increased, the carbon content changes in the direction indicated by the arrow, and the absorption characteristics particularly in the megahertz band deteriorates remarkably.

FIG. 3 is a diagram showing the return loss of the conventional carbon fiber coating type, FIG. 3(a) shows the return loss in the megahertz band of the carbon fiber coated type, and FIG. 3(b) is the carbon fiber coated type. 3C shows the return loss in the gigahertz band of the mold, FIG. 3C shows the configuration of the carbon fiber clothing mold, and FIG. 3D shows the return loss in the megahertz band in which the carbon fiber clothing mold is combined with the conventional urethane type. 3(e) shows the return loss in the gigahertz band in which the conventional urethane type is combined with the carbon fiber clothing type, and FIG. 3(f) shows the conventional urethane type matching body for the carbon fiber clothing type. The combined configuration is shown.

As shown in FIGS. 3(a) and 3(b), the carbon fiber coating type is as good as −20 dB or less in the megahertz band, but in the gigahertz band, the return loss decreases toward the high frequency, and in the high frequency band. Radio wave absorption performance drops sharply. On the other hand, in the configuration in which the conventional urethane type absorber is combined with the carbon fiber coating type shown in FIGS. 3(d) and 3(e), the average frequency shifts around -20 dB in the megahertz band, and the gigahertz frequency is also increased. Even in the band, it is stable at -20 dB to -40 dB. However, as an ideal value, it is desired to set the megahertz band to −20 dB or less.

FIG. 4 is a graph for comparing the return loss of the conventional urethane type and the carbon fiber-containing radio wave absorber according to the present invention, and FIG. 4( a) is a graph showing matching between the carbon fiber coating type and the conventional urethane type. FIG. 4B shows the return loss in the megahertz band in which the body is combined, and FIG. 4B shows the return loss in the gigahertz band in which the conventional urethane type matching body is combined with the carbon fiber film type, and FIG. FIG. 4(d) shows a three-dimensional structure in which a matching body of a conventional urethane type is combined with the carbon fiber coating type, and FIG. 4(d) shows a rectangular type of hard urethane foam containing the carbon fiber of the present invention in the carbon fiber coating type. FIG. 4(e) shows return loss in the megahertz band in which matching bodies are combined, and FIG. 4(e) is a gigahertz band in which a rectangular type matching body made of hard urethane foam containing carbon fibers according to the present invention is combined with the carbon fiber coating type. 4(f) shows a three-dimensional structure in which a carbon fiber coating type is combined with a rectangular type matching body made of hard urethane foam containing carbon fibers according to the present invention. Note that FIG. 4(a) has the same contents as FIG. 3(d), FIG. 4(b) has the same contents as FIG. 3(e), and FIG. 4(c) has the same contents as FIG. 3(f). These are shown for comparison.

As shown in FIG. 4, the radio wave absorber in which the carbon fiber coating type absorber 40 is combined with the conventional urethane type is as good as −20 dB or less in the GHz band as shown in FIG. 4B, As shown in FIG. 4A, in the megahertz band, a region that does not fall below -20 dB occurs. On the other hand, in the present invention, since it is −20 or less in any frequency band of the megahertz band and the gigahertz band, it has been revealed that a wide range of electromagnetic wave absorption is realized.

FIG. 5 is a comparative diagram showing the performance difference depending on the shape of the matching body in the carbon fiber-containing radio wave absorber according to the present invention. The data connected by the triangle marks in FIG. 5 shows that the shape of the matching body is a rectangular parallelepiped. A certain case is shown, and the data connected by square marks show the case where the pyramid is subjected to mountain processing, and the reflection attenuation amount due to these differences is shown. As shown in FIG. 5, it has been conventionally known that the electromagnetic wave absorption characteristics change when the shape of the matching body is different, but until the completion of the present invention, a general rectangular parallelepiped as shown in FIG. Not only Yamagata and Yamagata, we are conducting experiments based on a wide variety of shapes. For example, a urethane sheet and a carbon fiber mixed paper are laminated to form a solid sandwich, or a urethane sheet without carbon impregnation and a carbon fiber mixed paper are laminated to form a cylinder obtained by rolling. With such shapes, it was not possible to obtain good electromagnetic wave absorption characteristics. Further, an experiment was also conducted on a shape obtained by processing a carbon fiber mixed paper into a honeycomb shape. As a result, although good electromagnetic wave absorption characteristics could be obtained, there was a problem in mass productivity.

FIG. 6 is a graph for comparing return loss with a carbon fiber-containing radio wave absorber according to the present invention containing a powder magnetic material and with other configurations not containing a powder magnetic material. Is. The data connected by triangles shows the return loss in the ferrite tile type absorber 10, and the data connected by circles shows the return loss of the ferrite tile type absorber 10 and the carbon fiber-containing radio wave absorber according to the present invention. The amount of return loss in the combination is shown, and the data connected by square marks are the return loss in the case where the ferrite tile type absorber 10 and the carbon fiber-containing radio wave absorber according to the present invention are further combined with the powder magnetic material 31. Shows the amount. The shape and height of the combined matching body are the same. As shown in FIG. 6, it can be seen that by using the powder magnetic material 31 together, the performance is improved although it is several dB.

FIG. 7 is an embodiment explanatory diagram showing an embodiment of a structure in which a carbon fiber-containing radio wave absorber according to the present invention has a plane 50 parallel to the traveling direction of radio waves in parallel. More specifically, the solid three-dimensional urethane absorbent layer 23 and the styrofoam material layer 24 having no dielectric loss are formed so that the solid three-dimensional urethane absorbent layer 23 has a shape that engages with the shape of the styrofoam material layer. FIG. 3 is an explanatory diagram illustrating a carbon fiber-containing radio wave absorber 1 having a configuration in which the urethane foam absorber 20 is foam-cured and is integrated with the styrofoam layer 24 in the process of foam-curing, and a method for manufacturing the same. 7A shows a layer 24 of a polystyrene foam material having no dielectric loss, FIG. 7B shows a layer 23 of a solid three-dimensional urethane absorbent, and FIG. 7C shows a solid three-dimensional urethane absorbent. The layer 23 and the layer 24 of styrofoam material without dielectric loss are shown in combination.

As shown in FIG. 7, by combining the layer 23 of the solid three-dimensional urethane absorber and the layer 24 of styrofoam material having no dielectric loss, and having the plane 50 perpendicular to the traveling direction of the radio wave in parallel, the protrusion on the floor or the wall is formed. The electromagnetic wave absorber can be arranged without causing a particulate matter. Moreover, in the carbon fiber-containing radio wave absorber 1 according to the present invention, since the matching body is made of hard urethane foam, it is strongly bonded to the target object by directly foaming on the surface of the target object. Since it has an excellent feature of self-adhesiveness that foam materials do not have, it can be firmly bonded to the layer 24 of styrofoam material that is easily dissolved by a solvent, and is strongly bonded to the ferrite tile type absorber 10 without using an adhesive. be able to.

In the configuration that combines the ferrite sintered body and the matching radio wave absorber, which was used as a conventional radio wave absorber, there is a trade-off relationship that cancels the absorption performance of the ferrite sintered body due to the effect of surface reflection by the carbon fine particles. It was difficult to improve. The present invention has solved this problem and made it possible to provide excellent electromagnetic wave absorption performance in a wide frequency band, and thus contributes to avoiding electromagnetic interference to electronic equipment such as ETC as well as anechoic chambers. It is considered highly available.

1 Megahertz Band to Gigahertz Band Radio Wave Absorber 10 Ferrite Tile Type Absorber 20 Solid Three-dimensional Foam Hard Urethane Absorber 21 Polyol 22 Polyisocyanate 23 Solid Three-dimensional Foam Hard Urethane Absorber Layer 24 Styrofoam Layer 30 Carbon Fiber 31 Powdered magnetic material 40 Carbon fiber coating type absorber 50 Flat surface

Claims (6)

A method of manufacturing a radio wave absorber in the megahertz band to the gigahertz band,
A ferrite tile type absorber (10),
A solid three-dimensional foamed rigid urethane absorber (20),
It is configured by combining
When molding the solid three-dimensional foamed rigid urethane absorbent (20), the carbon fiber (30) is foamed by mixing the polyol (21) and the polyisocyanate (22) with the carbon fiber (30) and foaming the mixture. A method (2) for producing a carbon fiber-containing radio wave absorber, which comprises uniformly dispersing the carbon fiber. When molding the solid three-dimensional foamed rigid urethane absorber (20), the polyol (21) and the polyisocyanate (22) are mixed with carbon fiber (30) and powder magnetic material (31) to foam. A method (2) for producing a radio wave absorber containing carbon fiber according to claim 1 . A method for manufacturing a radio wave absorber in the megahertz to gigahertz band having a plane (50) parallel to a traveling direction of radio waves, the method comprising:
A layer (23) of the solid three-dimensional foamed hard urethane absorbent composed of the solid three-dimensional foamed hard urethane absorbent (20) and a layer of styrofoam material (24) composed of the styrene foam material having no dielectric loss. In the process of molding
The solid three-dimensional foamed rigid urethane absorbent body (20) is foamed and hardened so as to have a shape that engages with the shape of the foamed polystyrene material layer (24), and in the foaming and hardening step, the foamed polystyrene material layer (24) is formed. (2) The method for producing a carbon fiber-containing radio wave absorber according to claim 1 or 2 , characterized in that (2). The carbon fiber-containing radio wave absorber manufacturing method (2) according to any one of claims 1 to 3 , wherein the carbon fiber (30) has a length of 5 mm to 7 mm. Method for producing a carbon fiber-containing wave absorber according to claims 1 to any one of claims 4, characterized in that to change the frequency band to be absorbed by adjusting the content of the carbon fibers (30) (2). The styrofoam layer (24) is formed to have a plurality of shapes in which the area of the cross section in the vertical direction gradually decreases in the traveling direction of radio waves.
In the layer (23) of the solid three-dimensional foamed hard urethane absorbent body (23) composed of the solid three-dimensional foamed hard urethane absorbent body (20), the cross-sectional area in the direction perpendicular to the traveling direction of the radio wave is gradually increased. The method (2) for producing a carbon fiber-containing radio wave absorber according to claim 3 , wherein the carbon fiber-containing radio wave absorber is molded so as to have a plurality of increasing matching bodies.