JP2001320190A - Electromagnetic-wave absorbing material and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic-wave absorbing material and its manufacturing method wherein its electromagnetic-wave absorbing ability is large and its absorbing performance for absorbing an electromagnetic wave projected on its incidence plane as forming an angle with its incidence plane is excellent too. SOLUTION: In inner walls 4 of continuous pores 3 of a porous ceramics (ceramic sintered material) 10 of the electromagnetic-wave absorbing material which has the continuous pores 3, carbon films 5a are formed. Further, the porous ceramics 10 has an inclined structure wherein both the abundance ratios of its carbon films 5a and its dielectric losses become large as proceeding from the side of its incidence plane 1a to the side of the opposite plane thereto (its reflection plane) 1b. Also, by subjecting the porous ceramics 10 to a smoke processing, the carbon films 5a are formed in the inner walls 4 of the continuous pores 3. Also, the porous ceramics 10 is so constituted that its void ratios generated by the continuous pores 3 become small and its permittivity becomes large, as proceeding from its incidence plane 1a to its opposite plane thereto 1b.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to an electromagnetic wave absorber and a method of manufacturing the same, and more particularly, to an electromagnetic wave absorber made of a ceramic material and a method of manufacturing the same.

[0002]

2. Description of the Related Art In recent years, in order to prevent the influence of electromagnetic waves,
Electromagnetic wave absorbers are being developed and applied. This electromagnetic wave absorber solves the problem of radio interference caused by the irregular reflection of television waves by high-rise buildings, increases the speed and capacity of mobile communication systems, wireless LANs, anti-collision radars, remote sensing, etc. With the development of new wireless technology, it is used for the purpose of solving various problems such as ghosts and code errors caused by multiple reflections of electromagnetic waves that have been brought up close, In order to solve such problems, building materials and paints having low electromagnetic wave reflectance and good electromagnetic wave absorption are used.

As a conventional electromagnetic wave absorber, for example, there is a radio wave absorber disclosed in Japanese Utility Model Laid-Open No. 60-48294. In this radio wave absorber, a laminated dielectric plate arranged so that its dielectric constant gradually increases from one side to a deep portion is used. The dielectric plate located on one side has a dielectric constant of about 1, and a thin film of a synthetic resin made of polycarbonate or the like is formed on the entire outer surface of the dielectric plate on one side. It is integrally coated.

[0004]

However, in the above-mentioned conventional radio wave absorber, the radio wave absorbing ability is not always sufficient.

Although electromagnetic waves are incident from all directions, conventional electromagnetic wave absorbers do not always have the ability to absorb electromagnetic waves obliquely incident on the incident surface of the electromagnetic wave absorber. An electromagnetic wave absorber that is not sufficiently considered and has excellent absorption performance of an electromagnetic wave obliquely incident on an incident surface is desired.

The present invention solves the above-mentioned problems, and provides an electromagnetic wave absorber having a large electromagnetic wave absorbing capability and excellent in absorbing electromagnetic waves obliquely incident on an incident surface, and a method of manufacturing the same. The purpose is to provide.

[0007]

In order to achieve the above object, an electromagnetic wave absorber of the present invention (claim 1) is an electromagnetic wave absorber configured so that a predetermined surface becomes an electromagnetic wave incident surface. (A) a porous ceramic having continuous pores, and (b) carbon is present in the continuous pores, and the proportion of the carbon increases from the incident surface to the opposite surface. And (c) an inclined structure in which the dielectric loss increases from the incident surface toward the opposite surface.

The electromagnetic wave absorber according to the first aspect of the present invention comprises:
It is formed from porous ceramics having continuous pores, and carbon is present in the continuous pores, and the proportion of carbon increases from the incident surface to the opposite surface, and dielectric loss is reduced. Has an inclined structure that increases toward the opposite surface, so that the incident electromagnetic wave causes heat loss inside, is consumed as heat energy, and the electromagnetic wave incident from the incident surface is efficiently absorbed Is done. Note that there is no particular limitation on the ceramic that can be used in the electromagnetic wave absorber of the present invention, and various ceramic materials can be widely used. In the electromagnetic wave absorber of the present invention, there are no particular restrictions on the specific shape of the continuous pores, the state of carbon present in the continuous pores, and the like.

Further, in the electromagnetic wave absorber according to the present invention, the main part of carbon in the continuous pores is subjected to a smoke treatment (a high-temperature gas generated by incomplete combustion of a carbon-containing substance) from the opposite side. A carbon film formed on the inner wall of the continuous pores by performing a process of forming a carbon film on the contact surface by bringing the carbon film into contact with the inner wall of the continuous pores.

[0010] By performing the smoking process, carbon is introduced into the continuous pores, the main part of the carbon is held as a carbon film on the inner wall of the continuous pores, etc., and the abundance ratio from the incident surface to the opposite surface is reduced. This makes it possible to efficiently and reliably form a tilted structure in which the dielectric loss increases from the incident surface toward the opposite surface. It can be effective. The smoking process is, for example, a process in which a high-temperature gas generated by incomplete combustion of a carbon-containing substance such as a hydrocarbon gas is brought into contact with the inner wall of the continuous pores to form a carbon film on the contact surface. In general, gas generated by incomplete combustion of a carbon-containing substance often contains some soot-like carbon. However, the presence or absence of soot-like carbon and its abundance ratio There are no special restrictions.

The electromagnetic wave absorber according to a third aspect of the present invention is characterized in that the electromagnetic wave absorber has an inclined structure such that the porosity of the continuous pores decreases from the incident surface to the opposite surface.

When the porosity due to the continuous pores is inclined so that the porosity decreases from the incident surface to the opposite surface, the dielectric constant increases from the incident surface to the opposite surface. Therefore, the dielectric loss increases from the incident surface to the opposite surface, and the dielectric constant also increases from the incident surface to the opposite surface, so that impedance matching with air is improved and electromagnetic waves are absorbed more efficiently. It becomes possible to do.

The electromagnetic wave absorber according to claim 4 is characterized in that a plurality of layers having different carbon abundances are laminated.
The present invention is characterized in that the existence ratio of carbon is inclined so as to increase stepwise from the incident surface to the opposite surface.

The method of forming a structure in which the proportion of carbon is inclined is not limited to the case where the proportion of carbon is inclined in one layer, and a plurality of layers having different proportions of carbon are arranged in a predetermined order. Also by laminating, it is possible to incline the existing ratio of carbon as a whole so as to increase stepwise from the incident surface to the opposite surface. By doing so, it is possible to improve the degree of freedom of the configuration.

In the electromagnetic wave absorber according to a fifth aspect of the present invention, by stacking a plurality of layers having different carbon content ratios and porosity due to the continuous pores, the carbon content ratio can be reduced from the incident surface to the opposite surface. , And the porosity is inclined so as to gradually decrease from the incident surface toward the opposite surface.

When a plurality of layers having different carbon content ratios and porosity due to continuous pores are laminated, the carbon content ratio (ie, dielectric loss) is gradually increased from the incident surface to the opposite surface. Incline to be larger,
The porosity can be graded so as to gradually decrease from the incident surface to the opposite surface, and in a multi-layer structure, both the carbon abundance (ie, dielectric loss) and the porosity are graded. , And the degree of freedom of the configuration can be further improved.

In the electromagnetic wave absorber according to a sixth aspect of the present invention, a porous ceramic layer having a low dielectric constant and having no carbon introduced into the pores is joined to the incident surface side, and the surface of the ceramic layer is incident. It is characterized by having a surface.

[0018] No carbon is introduced into pores on the incident surface side of the electromagnetic wave absorber according to any one of claims 1 to 5,
When a porous ceramic layer having a small dielectric constant is joined, and the surface of the ceramic layer is configured as an incident surface,
This makes it possible to reliably reduce the dielectric constant of the surface, improve impedance matching with air, and more efficiently absorb electromagnetic waves.

Further, the electromagnetic wave absorber according to claim 7 is characterized in that a conductor layer functioning as an electromagnetic wave reflection layer is provided on the opposite surface side.

When a conductor layer functioning as a reflection layer of electromagnetic waves is provided on the opposite surface side, electromagnetic waves that have not been absorbed until reaching the conductor layer from the incident surface are reflected by the conductor layers, and the electromagnetic waves are again reflected. Since the electromagnetic waves pass through the absorber and are absorbed in the process, the electromagnetic waves can be more efficiently absorbed.

The method of manufacturing an electromagnetic wave absorber according to the present invention (claim 8) is a method of manufacturing an electromagnetic wave absorber having an electromagnetic wave incident surface, wherein (a) a porous ceramic sintered body having continuous pores is provided. (B) performing a smoking process from one surface of the ceramic sintered body (the surface opposite to the surface serving as the incident surface) so that the proportion of carbon present in the ceramic sintered body is reduced. Forming a carbon film on the inner wall of the continuous pores so as to increase from the surface to the opposite surface (smoke-treated surface).

After a porous ceramic sintered body having continuous pores is formed, one of the surfaces (the surface opposite to the surface serving as the incident surface) is subjected to a smoking treatment to reduce the carbon content. It is possible to form a carbon film on the inner wall of the continuous pores so as to increase from the incident surface toward the opposite surface (smoke-treated surface), and to efficiently manufacture the electromagnetic wave absorber of the present invention. Becomes possible.

According to a ninth aspect of the present invention, the step of forming a porous ceramic sintered body having continuous pores includes the steps of: (a) rhyolite, feldspathic rock, tribute, slate 100 parts by weight of at least one ceramic raw material selected from the group consisting of perlite, obsidian and expanded clay; (b)
0.1 to 5 parts by weight of at least one foaming agent selected from the group consisting of silicon carbide, manganese dioxide and iron oxide, (c)
10 to 200 parts by weight of a foamed hollow body having a particle size of 5 mm or less, which is at least one selected from natural pumice and artificially heated obsidian, perlite and tribute, and (d) an organic binder. 0.3 to 3.5 parts by weight, and inorganic binder 5-2
The process is characterized in that 0 parts by weight of each component are mixed, fired, and foamed to form a porous ceramic sintered body having continuous pores.

The above-described components (a) to (d) are mixed, fired, and foamed to form a ceramic sintered body, whereby a porous ceramic sintered body having continuous pores can be efficiently produced. In addition, it is possible to reliably produce the present invention, and the present invention can be made more effective.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, the features of the present invention will be described in more detail by showing embodiments of the present invention. [Embodiment 1] FIG. 1 is a sectional view showing a schematic structure of an electromagnetic wave absorber according to an embodiment of the present invention. The electromagnetic wave absorber 1 according to this embodiment is made of, for example, a ceramic sintered body 10, and the characteristics of the dielectric constant and the dielectric loss gradually increase from the incident surface 1a to the opposite surface (reflection surface) 1b. It has a so-called inclined structure that is inclined so as to be inclined. On the opposite side (reflection surface) 1b side of the ceramic sintered body 10, a conductor layer (a carbon film (reflection surface side carbon film) in this embodiment) 2 is provided.

The ceramic sintered body 10 has a porous structure having continuous pores 3, and the porosity of the continuous pores 3 changes from the incident surface 1a to the opposite surface (reflection surface) 1b.
, Thereby giving a slope characteristic such that the dielectric constant increases from the incident surface 1a toward the opposite surface (reflection surface) 1b.

In this electromagnetic wave absorber 1,
The carbon 5 is present inside the continuous pores 3, and a main part of the carbon 5 is held as a carbon film 5 a on the inner wall 4 of the continuous pores 3. In addition, the proportion of carbon 5 present is inclined so as to increase from the incident surface 1a toward the opposite surface (reflection surface) 1b, thereby reducing the dielectric loss.
From the surface to the opposite surface (reflection surface) 1b.

In the electromagnetic wave absorber 1 of this embodiment, in the region from the incident surface 1a to the middle,
No carbon film is formed on the inner wall 4 of the continuous pores 3, and the opposite surface (reflection surface) 1 b extends from substantially the center of the ceramic sintered body 10.
In the region leading to the inner wall 4, the carbon film 5 a
In addition, it is formed to be inclined so that the thickness gradually increases toward the opposite surface (reflection surface) 1b. Therefore, in the electromagnetic wave absorber 1 of this embodiment, the region from the incident surface 1a to the middle is a region that functions as a buffer layer that promotes the electromagnetic wave to enter the electromagnetic wave absorber 1.

In the electromagnetic wave absorber 1 of the present invention, the inner wall 4 of the continuous pores 3 is formed so that the carbon amount is inclined in the entire region from the opposite surface (reflection surface) 1b to the incident surface 1a. It is also possible to form a carbon film.

Next, a method of manufacturing the electromagnetic wave absorber 1 will be described. <Preparation of Ceramic Sintered Body> First, the following raw materials (a) to (d) are mixed, fired under a predetermined temperature condition (about 1150 ° C. in this embodiment), and foamed, thereby obtaining FIG. Ceramic sintered body 10 having continuous pores 3 as shown in FIG.
Is prepared. (a) 100 parts by weight of at least one ceramic raw material selected from the group consisting of rhyolite, feldspathic rock, tribute, slate, perlite, obsidian and expanded clay; (b) silicon carbide, manganese dioxide and 0.1 to 5 parts by weight of at least one foaming agent selected from the group consisting of iron oxides (c) natural pumice and artificially heated foamed obsidian,
At least one selected from pearlite and tribute,
10 to 200 parts by weight of a hollow foam having a particle size of 5 mm or less (d) 0.3 to 3.5 parts by weight of an organic binder and 5 to 20 parts by weight of an inorganic binder

As shown conceptually in FIG. 3 (a), each of the above-mentioned raw materials (a) to (d) is mixed, and an organic binder 1 is provided around the mixture.
1 and a blended raw material in which a ceramic raw material 14 coexists with a foamed hollow body 13 to which an inorganic binder 12 is attached,
By firing under a temperature condition of 50 ° C., as shown conceptually in FIG. 3B, continuous pores in which a foamed hollow body 13 a that has grown and expanded and an opening 15 is formed, and a ceramic raw material 14 are mixed. Is formed (FIG. 2).

As shown in FIG. 2, the porosity of the continuous pores 3 of the ceramic sintered body 10 constituting the electromagnetic wave absorber 1 (FIG. 1) of this embodiment is changed from the incident surface 1a to the opposite surface ( Although the ceramic sintered body 10 having such a tilted structure has a structure that is gradually reduced toward the (reflection surface) 1b, as shown in FIG.
As a compounding raw material in which the above-mentioned respective raw materials are compounded, compounding materials having different particle sizes are prepared in stages, and a first material having a large particle size and a high porosity is spread on the first layer 10a.
A compounding material having a smaller particle size than the layer 10a and having a low porosity is spread as the second layer 10b, and a compounding material having a smaller particle size and a lower porosity than the second layer 10b is formed on the second layer 10b. Is spread as a third layer 10c, pressed under predetermined conditions, and fired. In addition, by continuously laying compounding materials having different particle sizes, it is possible to obtain a ceramic sintered body having a porosity that is not stepwise but continuously inclined. There is no particular limitation on the method of manufacturing the ceramic sintered body 10 having a structure in which the porosity is inclined so as to decrease from the incident surface 1a toward the opposite surface (reflection surface) 1b.
Various other methods can be used.

<Smoking Treatment of Ceramic Sintered Body> The ceramic sintered body 10 (FIG. 2) manufactured as described above was sealed with the incident surface 1a side and the side surface 1c side. By performing a smoking process from the opposite surface (reflection surface) 1b side, a carbon film 5a is deposited on the inner wall 4 of the continuous pore 3 as shown in FIG.

In the smoking process, for example, on the opposite surface (reflection surface) 1b side of the ceramic sintered body 10, a high-temperature gas generated by incomplete combustion of a hydrocarbon gas under predetermined conditions is subjected to ceramic firing. It is performed by introducing into the continuous pores 3 of the united body 10 and contacting the inner wall 4 of the continuous pores 3.
By this smoking process, the high-temperature gas is turned to the opposite surface (reflection surface) 1b.
From the side to the incident surface 1a side, and the thickness of the carbon film 5a is large on the opposite surface (reflection surface) 1b side, and the incident surface 1a
The carbon film 5a is formed on the inner wall 4 of the continuous pore 3 in an inclined state such that the thickness of the carbon film 5a decreases toward the side.
In this way, as shown in FIG. 1, the electromagnetic wave absorber 1 inclined such that the proportion of the carbon 5 present increases from the incident surface 1a side to the opposite surface (smoke treated surface) 1b side is obtained. Can be

In this embodiment, in the above-mentioned smoking process, a carbon film (reflection surface side carbon) functioning as a conductor layer for reflecting electromagnetic waves is provided on the opposite surface (reflection surface) 1b side of the ceramic sintered body 10. (Film) 2 was formed.

The electromagnetic wave absorber 1 thus manufactured
In the above, the carbon film 5a is formed on the inner wall 4 of the continuous pores 3, and the proportion of the carbon film 5a (carbon 5) increases from the incident surface 1a toward the opposite surface (reflection surface) 1b. And the dielectric loss is increased from the incident surface 1a toward the opposite surface (reflection surface) 1b, so that the incident electromagnetic wave causes heat loss inside and becomes heat energy. And efficiently consumed, it is possible to efficiently absorb incident electromagnetic waves.
In addition, since the conductor layer (reflection surface side carbon film) 2 that functions as a reflection layer of electromagnetic waves is disposed on the opposite surface (reflection surface) 1b of the entrance surface 1a, the conductor layer 2 from the entrance surface 1a to the conductor layer 2 is provided. The electromagnetic wave that has not been absorbed is reflected by the conductor layer 2, passes through the electromagnetic wave absorber 1 again, and is further absorbed in the process, so that the electromagnetic wave can be more efficiently absorbed.

With respect to the electromagnetic wave absorber 1 of the first embodiment, the electromagnetic wave absorption characteristics (the relationship between the incident angle of the electromagnetic wave and the amount of electromagnetic wave absorption) were examined, and the performance as the electromagnetic wave absorber was evaluated. As shown in FIG. 5, the measurement of the absorption characteristics of the electromagnetic wave was performed using an arch-shaped measuring device having a radius of 1 m, with the electromagnetic wave absorber 1 to be measured placed on the sample support 21 positioned at the center of the device. , Radiation horn antenna (transmission antenna) 2
The position of the antenna 2 and the receiving horn antenna (receiving antenna) 23 on the circumferential orbit were changed, and the relationship between the incident angle (θi) and the amount of electromagnetic wave absorption was examined.

In the measurement, the influence of the direct wave between the radiation horn antenna (transmission antenna) 22 and the reception horn antenna (reception antenna) 23 is removed by slightly moving the electromagnetic wave absorber (measurement sample) 1 up and down. (Herein referred to as electrolysis vector method). In measurement, a radiation horn antenna (transmitting antenna) 2
2, the incident angle θi of the electromagnetic wave to the electromagnetic wave absorber (measurement sample) 1 was changed from 10 degrees to 60 degrees, and the amount of absorption including oblique incidence was measured. FIG. 6 shows the measurement results of the absorption amount at the measurement frequency of 10 GHz.

As shown in FIG. 6, this electromagnetic wave absorber 1
It can be seen that the sample has an electromagnetic wave absorbing ability even at an oblique incidence of an electromagnetic wave at an incident angle of 10 to 60 degrees, and has a sufficient absorption amount.

[Embodiment 2] FIG. 7 is a view showing an electromagnetic wave absorber 31 according to another embodiment of the present invention. The electromagnetic wave absorber 31 is composed of a plurality of layers formed by subjecting a ceramic sintered body to a smoking process and having different carbon porosity and porosity due to continuous pores (in the second embodiment, the first
In addition to the absorption layer 31b and the second absorption layer 31c) having a higher percentage of carbon than the first absorption layer 31b and having a low porosity due to continuous pores, the incident surface 1a side contains carbon. There is provided a ceramic sintered layer 31a which is not provided, and further has a structure in which, for example, a copper plate 32 is provided as a conductor layer on the reflection surface 1b side.

The electromagnetic wave absorber 31 having such a multilayer structure
Can be manufactured by separately preparing each of the above-mentioned layers, that is, the ceramic sintered layer 31a not containing carbon, the first absorption layer 31b, the second absorption layer 31c, and the copper plate 32, and joining them. it can.

In the case of a multi-layer structure, by preparing a plurality of predetermined types of absorbing layers, it is possible to provide desired absorbing characteristics only by combining arbitrary absorbing layers. In some cases, the degree of freedom in designing and manufacturing can be improved.

In the first and second embodiments, the method of smoking is used as a method of retaining carbon in the continuous pores of the ceramic sintered body. The carbon distribution is determined by a method of firing (carbonization firing) under the condition that the substance is carbonized, and then firing (oxidation firing) from the predetermined surface side under the condition that the carbon is oxidized and removed with a gradient. An inclined structure is also possible, and other methods can be used.

The present invention is not limited to the above embodiment in other respects. The present invention relates to the number of layers in the case of a multi-layer structure, the type and composition of the raw material constituting the ceramic sintered body, and the like. Various applications and modifications can be made within the scope of the gist.

[0045]

As described above, the electromagnetic wave absorber of the present invention (Claim 1) is made of porous ceramic having continuous pores. Has an inclined structure such that the dielectric loss is increased from the incident surface toward the opposite surface, so that the incident angle is wide. , And can sufficiently absorb electromagnetic waves.

Also, as in the electromagnetic wave absorber of claim 2,
By performing the smoking process, carbon is introduced into the continuous pores, the main part of the carbon is held as a carbon film on the inner wall of the continuous pores, etc., and its abundance increases from the incident surface to the opposite surface. It is possible to efficiently and reliably form a tilted structure in which the dielectric loss increases from the incident surface to the opposite surface, and the present invention can be further effectively demonstrated. be able to.

Also, as in the electromagnetic wave absorber of claim 3,
When the porosity due to the continuous pores is configured such that the porosity decreases from the incident surface to the opposite surface, the dielectric constant increases from the incident surface to the opposite surface. Therefore, the dielectric loss increases from the incident surface to the opposite surface, and the dielectric constant also increases from the incident surface to the opposite surface, so that impedance matching with air is improved and electromagnetic waves are absorbed more efficiently. It becomes possible to do.

The method of forming a structure in which the proportion of carbon is inclined is not limited to the case where the proportion of carbon is inclined in one layer, but a plurality of layers having different proportions of carbon are arranged in a predetermined order. Also by laminating, it is possible to incline the existing ratio of carbon as a whole so as to increase stepwise from the incident surface to the opposite surface. By doing so, the degree of freedom of the configuration can be improved.

Further, when a plurality of layers having different carbon content ratios and porosity due to continuous pores are laminated, the carbon content ratio is increased from the incident surface to the opposite surface. And the porosity can be gradually decreased from the incident surface to the opposite surface. Both the dielectric loss) and the porosity can be made to have an inclined structure, and the degree of freedom of the configuration can be further improved.

Further, as in the electromagnetic wave absorber of claim 6,
A porous, low dielectric constant ceramic layer in which carbon is not introduced into pores is joined to the incident surface side of the electromagnetic wave absorber according to any one of claims 1 to 5, and the surface of the ceramic layer is incident. In the case of a configuration having a plane, the dielectric constant of the surface can be reliably reduced, impedance matching with air can be improved, and electromagnetic waves can be absorbed more efficiently.

Also, as in the electromagnetic wave absorber of claim 7,
When a conductor layer functioning as an electromagnetic wave reflection layer is provided on the opposite surface (reflection surface) side, electromagnetic waves that have not been absorbed before reaching the conductor layer from the incident surface are reflected by the conductor layer and again. Since the electromagnetic wave passes through the electromagnetic wave absorber and is absorbed in the process, the electromagnetic wave can be more efficiently absorbed.

Further, according to the method of manufacturing an electromagnetic wave absorber of the present invention (claim 8), after forming a porous ceramic sintered body having continuous pores, one of the surfaces (opposite to the surface serving as the incident surface) is formed. Side)), so that the smoking process is applied.
The carbon film can be formed on the inner wall of the continuous pores so that the proportion of carbon increases from the incident surface to the opposite surface (smoke-treated surface). It can be manufactured efficiently.

According to a ninth aspect of the present invention, there is provided a method of manufacturing an electromagnetic wave absorber, in which the above-described components (a) to (d) are mixed, fired and foamed to form a ceramic sintered body. Therefore, it is possible to efficiently and reliably produce a porous ceramic sintered body having continuous pores,
The present invention can be made more effective.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating a schematic configuration of an electromagnetic wave absorber according to an embodiment (Embodiment 1) of the present invention.

FIG. 2 is a sectional view of a ceramic sintered body constituting the electromagnetic wave absorber according to the first embodiment of the present invention.

3A and 3B are diagrams for explaining the method of manufacturing the electromagnetic wave absorber according to the first embodiment of the present invention, wherein FIG. 3A is a diagram conceptually showing a state of a compounding material before firing, and FIG. It is a figure which shows notionally a part of ceramic sintered compact after.

FIG. 4 is a diagram illustrating a method for manufacturing a ceramic sintered body constituting the electromagnetic wave absorber according to the first embodiment of the present invention.

FIG. 5 is a diagram showing a method for measuring the absorption characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention.

FIG. 6 is a diagram illustrating electromagnetic wave absorption characteristics of the electromagnetic wave absorber according to the first embodiment of the present invention.

FIG. 7 is a diagram schematically showing a configuration of an electromagnetic wave absorber according to another embodiment (Embodiment 2) of the present invention.

[Description of Signs] 1 Electromagnetic wave absorber 1a Incident surface 1b Opposite surface (reflective surface) 1c Side surface of electromagnetic wave absorber 2 Conductor layer (reflective surface side carbon film) 3 Continuous pores 4 Inner wall of continuous pores 5 Carbon 5a Carbon Film 10 Ceramic sintered body 10a First layer 10b Second layer 10c Third layer 11 Organic binder 12 Inorganic binder 13 Foamed hollow body 13a Hollow foamed body after firing 14 Ceramic raw material 15 Opening 21 Sample support 22 Radiation Horn antenna (transmitting antenna) 23 Receiving horn antenna (receiving antenna) 31 Electromagnetic wave absorber 31a Ceramic sintered layer not containing carbon 31b First absorbing layer 31c Second absorbing layer 32 Copper plate θi Incident angle

 ──────────────────────────────────────────────────続 き Continuation of the front page (71) Applicant 000006231 Murata Manufacturing Co., Ltd. 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto (72) Inventor Toshihide Kitazawa 7-7-112 Wakakusa, Kusatsu-shi, Shiga (72) Invention Person Masao Miyashiro 498, Nagano, Shigaraki-cho, Koka-gun, Shiga Prefecture Inside the Shigara Ceramics Technical Testing Center, Shiga Prefectural Institute of Technology ) Inventor Kikuo Wakino 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto F-term in Murata Manufacturing Co., Ltd. (Reference) 5E321 BB22 BB25 BB51 BB60 GG05 GG11 5J020 EA04 EA05 EA08 EA10 EA10

Claims (9)

[Claims] 1. An electromagnetic wave absorber having a predetermined surface serving as an electromagnetic wave incident surface, comprising: (a) a porous ceramic having continuous pores; and (b) carbon in the continuous pores. Is present, and the proportion of the carbon increases from the incident surface to the opposite surface, and (c) the slope is such that the dielectric loss increases from the incident surface to the opposite surface. An electromagnetic wave absorber having a structure. 2. A main portion of carbon in the continuous pores is subjected to a smoldering treatment (a hot gas generated by incomplete combustion of a carbon-containing substance from the opposite side to contact an inner wall of the continuous pores or the like). 2. The electromagnetic wave absorber according to claim 1, wherein the carbon film is formed on the inner wall of the continuous pores by performing a process of forming a carbon film on the contact surface. 3. The electromagnetic wave absorber according to claim 1, wherein the electromagnetic wave absorber has an inclined structure such that the porosity of the continuous pores decreases from the incident surface toward the opposite surface. 4. The method according to claim 1, wherein a plurality of layers having different carbon abundances are laminated so that the carbon abundance is gradually increased from the incident surface to the opposite surface. The electromagnetic wave absorber according to any one of claims 1 to 3. 5. A method of laminating a plurality of layers having different carbon content ratios and porosity due to the continuous pores so that the carbon content ratio increases stepwise from the incident surface to the opposite surface. The electromagnetic wave absorber according to any one of claims 1 to 3, wherein the porosity is inclined so that the porosity gradually decreases from the incident surface to the opposite surface. 6. A porous ceramic layer having a low dielectric constant, wherein no carbon is introduced into pores, is joined to the incident surface side, and the surface of the ceramic layer serves as an incident surface. The electromagnetic wave absorber according to claim 1. 7. The electromagnetic wave absorber according to claim 1, wherein a conductor layer functioning as an electromagnetic wave reflection layer is provided on the opposite surface side. 8. A method for producing an electromagnetic wave absorber having an electromagnetic wave incident surface, comprising: (a) forming a porous ceramic sintered body having continuous pores; and (b) forming the ceramic sintered body. By performing the smoking process from one surface (the surface opposite to the surface that becomes the incident surface), the proportion of carbon present increases from the incident surface toward the opposite surface (the smoked surface). Forming a carbon film on the inner wall of the continuous pores as described above. 9. The step of forming a porous ceramic sintered body having continuous pores comprises: (a) rhyolite, feldspathic rock, tribute, slate, perlite, obsidian and expanded clay. 100 parts by weight of at least one ceramic raw material selected from the group; (b) 0.1 to 5 parts by weight of at least one foaming agent selected from the group consisting of silicon carbide, manganese dioxide and iron oxide; Natural pumice and obsidian artificially heated and foamed,
At least one selected from pearlite and tribute,
10 to 200 parts by weight of a foamed hollow body having a particle size of 5 mm or less, (d) 0.3 to 3.5 parts by weight of an organic binder, and 5 to 20 parts by weight of an inorganic binder are mixed, and calcined. 9. The method for producing an electromagnetic wave absorber according to claim 8, wherein the step is a step of forming a porous ceramic sintered body having continuous pores by foaming.