JP2005231931A - Cement type radio wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a cement type radio wave absorber showing an absorption property stable in a high-frequency band of 1 GHz or higher, having workability with fluidity, and the like, and a strength and a radio wave absorption property together, being thin and light with a high dielectric constant and a dielectric loss, being durable in outdoor use for a long term because of nonflammability and no degradation with ultraviolet rays, being no need for a back metal, being inexpensive, excellent in reliability, able to relieve sizing accuracy, workable with direct adhesion on sprayed mortar like a usual tile and being excellent in workability and reliability with direct spraying or mortar coating, or the like, on an optional substrate. <P>SOLUTION: A flat iron oxide powder whose mean thickness is 30 μm or less and where the weight ratio of particles having a shortest size in a face of more than 25 μm is 50% or more is mixed with a hydrated and solidified inorganic material to form the cement type radio wave absorber. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a cement-type radio wave absorber excellent in practicality that exhibits stable absorption characteristics in a high frequency band of GHz or higher.

Conventionally, in order to prevent reception of terrestrial analog TV, so-called ghost countermeasures, the installation of ferrite tile-type or ferrite mortar-type radio wave absorbers has been effective for the prevention of TV radio wave reflection on the outer wall of buildings. ing. On the other hand, portable communication devices that use electromagnetic waves in the high-frequency region of 1 GHz or higher, wireless LAN, or wireless usage related to ITS such as ETC, DSRC, etc. are rapidly spreading. Problems such as communication failure due to unnecessary electromagnetic wave reflection, malfunction of equipment, etc. are highlighted and countermeasures are required. As a technique for avoiding these obstacles, it is effective to apply an electromagnetic shield or an electromagnetic wave absorbing material. Ferrite, which is a typical electromagnetic wave absorbing material that is being widely used, contains iron oxide as a main component and a part of iron as Mn, It is a ferromagnetic oxide replaced with Ni, Zn, etc., and is generally used in the form of rubber ferrite. Ferrite tiles are sintered bodies formed by firing ferrite powder after compression molding, and mortar ferrite is a radio wave absorber made by pulverizing ferrite with a diameter of several millimeters in cement as an aggregate, both of which are 1 GHz or less. Excellent electromagnetic absorption characteristics at VHF to UHF. In addition, since it has a certain level of electrical insulation, unlike metals, it is effective as an absorption material in the GHz band, especially in the state of fine powder of several μm to submicron, and rubber ferrite in which ferrite fine powder is kneaded with rubber is used. Widely used as a radio wave absorbing material that can be used in high frequency bands.

  There have already been many reports of radio wave absorbers containing such ferrite in cementitious dielectric materials.

  First, Patent Documents 1, 2, and 3 report a precast electromagnetic wave absorber in which ferrite particles are contained in concrete as an aggregate.

  In Patent Document 1, there is a report of a precast electromagnetic wave absorber in which ferrite particles are contained in concrete. In this report, it is composed of an absorption layer that is laminated in two layers by containing 70% by weight or more of particles such as MnZn, MgZn, NiZn ferrite, etc. with a particle size of 0.1 mm to several mm, and further containing carbon fiber in concrete. It has been reported that the absorber exhibits good radio wave absorption characteristics in the VHF band.

  Patent Document 2 discloses a radio wave absorber containing 75 to 90 wt% of coarse ferrite particles having a particle diameter of 0.5 to 7 mm and an epoxy resin and a carbon fiber reinforcing material, and a curtain wall configured using the same. A report has been made. In this report, it has been shown that a curtain wall using a relatively thin wave absorption layer of 28 mm can obtain excellent wave absorption characteristics of 20 dB or more with UHF and VHF.

  Further, Patent Document 3 reports a ferrite-containing mortar wave absorber having high absorption performance over the entire UHF band. In this report, the size of ferrite particles used as a radio wave absorber and mortar aggregate is 50% by volume or more of ferrite as ferrite particles having a particle size of 2 mm or more, and the volume ratio of ferrite particles in mortar is 35% to Broadband absorption characteristics with an absorption performance of 15 dB or more effective for ghost disturbance of TV radio waves in the entire UHF band have been reported by precast concrete radio wave absorbers with a 60% ferrite mortar absorption layer and a decorative panel on the surface. .

  Patent Document 4 reports an absorption band in which magnetic powder is contained in a water-curable inorganic binder. Cement, mortar, calcium silicate, gypsum and the like are used as the water-curable inorganic binder, and the use of metal oxide magnetic powder as the magnetic powder has been reported. An example of a radio wave absorber dispersed and contained in calcined gypsum using NiZn ferrite with a particle size of 0.24 mm to 1 mm and MnZn ferrite with a particle size of 0.3 mm to 2 mm as magnetic powder is shown. It has been shown that it is possible to effectively absorb electromagnetic waves in the 10-1000 MHz band by using.

  In these reports, the target radio frequency band is VHF, UHF, which is a TV radio wave, or a radio frequency band of 1000 MHz or less, which is noise from a general personal computer, AV, or audio equipment, and the ferrite particle size used is as large as possible. The thing is advantageous also from the point of a radio wave absorption characteristic. Concrete containing such large ferrite particles is close to the size of a general fine aggregate used in mortar, and the mortar structure having relatively good strength can be formed. It is possible.

  However, on the other hand, it is necessary for these cement-type radio wave absorbers to contain a large amount of ferrite in order to obtain sufficient absorption characteristics, and reinforcing materials such as carbon fibers and glass fibers to prevent a decrease in the strength of concrete. There is also a need for strengthening, leading to increased costs.

  In addition, when using the above coarse aggregate and ferrite with a fine aggregate level particle size, it is good as a mortar aggregate, but a frequency band higher than GHz, that is, a mobile phone that has been rapidly spreading in recent years, When using coarse-grained ferrite of a few millimeters in the S-band and C-band frequency bands above GHz used for digital wireless communications represented by wireless LAN, ITS-related bidirectional communications such as ETC, ferrite It is difficult to obtain sufficient absorption characteristics due to a decrease in magnetic loss.

  When ferrite is used in such a high frequency band, generally, pulverized ferrite of several μm to several tens of μm or submicron ferrite formed by a wet process typified by a coprecipitation method is dispersed in rubber. Rubber ferrite is generally used. The use of fine powdered ferrite increases the magnetic loss in the high-frequency region and enables it to be used as an effective absorbing material. It is extremely difficult to contain such a fine powdered ferrite in concrete in a sufficient amount, for example, at a volume ratio of about 50% used in rubber ferrite. When rubber or resin is used as a binder, even if the number of parts of rubber and resin is reduced to the maximum to increase the filling rate of ferrite, they can function as a binder in a small amount and evenly mix by mixing the polymer and ferrite sufficiently. Ferrite fine powder is dispersed and can be formed into a sheet by subsequent extrusion, pressing, or the like. However, when finely divided ferrite is dispersed in concrete, if the amount of cement is decreased to increase the ferrite filling rate, unlike the kneading with a resin such as rubber, the finely divided ferrite particles are surrounded by a small amount. Since it is difficult to connect them together, it is difficult to sufficiently increase the filling rate of ferrite.

  Further, when the ferrite powder is refined, it is necessary to greatly increase the amount of water added to the cement in order to increase the fluidity of the cement and obtain a certain workability, so-called workability. As a result, the amount of water added to the concrete, or the water-powder ratio, which is the ratio of water to the powder component, will greatly increase beyond the appropriate value. Density and density are significantly reduced. Particularly in the case of a radio wave absorber, a large number of voids is undesirable because it leads to an increase in water absorption.

  On the other hand, if the amount of ferrite fine powder to be added is reduced, such workability deterioration and strength reduction can be avoided, but the necessary radio wave absorption characteristics cannot be obtained. As described above, if the ferrite grain size is coarse, workability and strength as concrete or mortar can be obtained, but it also hinders the maintenance of the absorption characteristics in the high frequency region.

  Examples of absorbers in which ferrite is dispersed in concrete in the GHz band are reported in Patent Documents 5 and 6 and the like.

  Patent Document 5 reports an electromagnetic wave absorbing fire wall material in which a calcium silicate plate is laminated on the surface of a radio wave absorption layer in which 10-70 wt% of ferrite is added to cement. In this report, radio wave absorption performance and manufacturing efficiency are improved compared to the prior art (a radio wave absorber having a calcium silicate plate laminated on its surface (JP-A-6-24077, JP-A-7-74494). The structure consists of a calcium silicate plate laminated on the surface and a ferrite-containing radio wave absorber formed under the plate.The absorber material used for the radio wave absorber is 0.1-2 mm MnZn ferrite with a solid content of 60% by weight. In addition, it is shown that a high mechanical strength and a radio wave absorption characteristic of 20 dB or more can be obtained in the vicinity of 1 GHz by using an absorption layer containing 5% graphite powder and 7% by weight pulp and polypropylene fiber as a reinforcing material. Yes.

  Patent Document 6 reports an example of an electromagnetic wave absorber for ETC of 5.8 GHz as an application example. In this example, the thickness of the upper layer calcium silicate and the thickness of the lower absorption layer are controlled to realize a high absorption characteristic of 50 dB at 5.8 GHz. However, the ferrite used in these examples is still coarse ferrite with a grain size of 0.1-2 mm, so it is difficult to achieve high-frequency characteristics by itself, graphite is added, and the thickness of the absorption layer is 7 mm. By doing so, a predetermined radio wave absorption characteristic is obtained. In addition, it is necessary to add a reinforcing material such as organic, inorganic, glass, and metal fiber in order to prevent a decrease in strength.

  In the above report example, that is, in the prior art, it is indispensable to install a radio wave reflector layer on the back surface as an absorber structure, and a metal mesh, metal foil, carbon fiber sheet or the like is embedded or adhered by adhesion or the like. . Such a metal reflective layer is necessary to improve radio wave absorption characteristics, but there are many problems such as deterioration problems such as corrosion, reliability problems such as peeling, or cost increases and productivity decreases. If so, it is desirable not to use it. In particular, in the case of a radio wave absorber for the GHz band, the thickness control is inevitably strict and precise processing is required. This is a serious problem when using a material that is difficult to obtain precise dimensional accuracy, such as cement, because the resonator type radio wave absorber with a radio wave reflector layer on the back side requires particularly high accuracy. It becomes. Moreover, post-processing is absolutely necessary to obtain sufficient accuracy, leading to an increase in cost. Therefore, in the case of cement-type absorbers, it is desirable to design such that the characteristics do not depend much on the dimensional system of the product.

  Ferrite powder is generally manufactured by sintering ferrite or by a wet process such as coprecipitation. However, it is expensive to manufacture, and the cost of raw materials such as Ni is high. The powder is expensive.

  As an electromagnetic wave absorbing material that is inexpensive and excellent in performance instead of such an expensive ferrite, the present inventors have already filed Japanese Patent Application No. 2000-203028 in which flat iron oxide powder (simply referred to as flat iron oxide powder is sometimes used. It has been disclosed that a radio wave absorber including a certain material in a dielectric has better radio wave absorption performance than a conventional absorber using a raw material such as ferrite. This flat iron oxide powder is a flaky iron oxide powder with a large aspect ratio, and by mixing the powder having such a shape into rubber, resin, etc., and molding it into a sheet shape, excellent radio waves It was clarified to show absorption characteristics. The flat iron oxide powder used here has an average thickness of 30 μm or less and an average aspect ratio which is a ratio of thickness to maximum diameter of 5 or more. A radio wave absorber characterized in that it is a flaky powder obtained by peeling a scale by a mechanical descale method and is kneaded and contained in resin and rubber has been proposed previously.

  Such a flat iron oxide powder has both conductivity and magnetism mainly composed of magnetite and wustite, and has an appropriate electrical conductivity and magnetic loss possessed by carbon or the like used in dielectric loss type radio wave absorbers. This is an excellent absorbing material that combines both the magnetic loss of a ferrite of the type, and because of its flat shape, it has a high dielectric constant and magnetic permeability by orienting the powder parallel to the sheet surface of the sheet type absorber. It is an excellent absorbent material that can be obtained and can be thinned as a result, and has high electrical resistance compared to metal flat powder and can effectively infiltrate radio waves even at high frequencies and maintain high absorption performance.

  By the way, the previously proposed radio wave absorber in which such flat iron oxide powder is contained in rubber or resin also has the following problems.

In other words, due to the flat shape, when dispersed in a dielectric material such as rubber, the adhesion with the compound is worse than when dispersing a conventional spherical (unshaped) ferrite powder, acting as an inclusion, and the strength of the molded product is remarkably increased. It may deteriorate, and since it is flat, the powder is oriented in the processing direction by roll kneading, rolling, and extrusion, which is generally performed to disperse it in a dielectric and form it into a sheet. Anisotropy tends to occur in characteristics. Furthermore, because it was dispersed in a low dielectric constant material such as rubber or resin, the high dielectric properties brought about by the flat powder and the high dielectric loss exhibited by the conductive powder were completely eliminated. It is not demonstrated. In addition, when dispersed in a flammable base material such as rubber or resin, there is a problem that flame retardancy or incombustibility cannot be obtained, and improvement is required.
JP-A-8-18273 JP-A-10-209667 JP 2000-294900 A JP 2000-269680 A JP 2001-220198 A JP 2003-229893 A

  The present invention has been made in view of the above situation, and the technical problem is a cement-type absorber that exhibits stable absorption characteristics in a high frequency band of GHz or higher, workability such as fluidity, and strength. It is a cement-type absorber that combines radio wave absorption characteristics, and is a thin and lightweight cement-type absorber that has a high dielectric constant and dielectric loss. It is nonflammable, has no UV degradation, and can withstand long-term outdoor use. In addition, no back metal is required, it is inexpensive, has excellent reliability, can reduce dimensional accuracy, and can be applied directly onto sprayed mortar like normal tiles, or can be directly sprayed or applied to any substrate. The object is to provide a radio wave absorber excellent in workability and reliability that can be constructed by, for example.

The present invention has been completed to solve such a problem, and the gist of the present invention is as follows.
(1) Cement-type radio wave absorber formed by mixing and molding flat iron oxide powder having an average thickness ≦ 30 μm and the in-plane shortest portion size> 25 μm weight ratio of 50% or more with hydrated solidified inorganic material (Claim 1).
(2) The cement-type electromagnetic wave absorber according to claim 1, wherein the volume ratio of the flat iron oxide powder is 5% or more and 40% or less (claim 2).
(3) The cement-type radio wave absorber according to (2), further comprising carbon and / or titanium oxide mixed in a volume ratio of 0.5% to 10%.
(4) The cement-type radio wave absorber according to any one of claims 1 to 3, wherein the cement-type radio wave absorber is formed into a single-layer or multi-layer plate shape, and a radio wave reflector layer is formed on a surface opposite to the radio wave arrival direction. (Claim 4).
(5) A single-layer or multi-layered plate is formed, and a radio wave reflector layer is provided on the surface opposite to the radio wave arrival direction, and one or more surface dielectric layers made of a dielectric material are provided on the radio wave arrival side surface. The cement-type electromagnetic wave absorber according to claim 4 (claim 5).
(6) The cement-type radio wave absorber according to claim 5 having no radio wave reflector layer (Claim 6).
(7) The real part n _R (n _R = Real (√ (εr · μr), εr: complex relative permittivity, μr: complex relative permeability, n _R ; refractive index)) of the radio wave refractive index of the surface dielectric layer The thickness t is the radio wave wavelength (wavelength in vacuum) of the target radio frequency or the radio wave wavelength λ of the center frequency in the target radio frequency region.
4n _R × t / λ ≦ 1.1
The cement-type radio wave absorber according to claim 5 or 6, wherein the refractive index n (n = √ | εr · μr |, | A | is the absolute value of the complex number A) is 2.5 or less. Item 7).
(8) The cement-type radio wave absorber according to any one of claims 5 to 7, wherein the surface dielectric layer has a water absorption of 5% or less.
(9) The cement-type radio wave absorber according to any one of claims 1 to 8, wherein a part or all of the surface is waterproofed.

(1) According to the present invention, a cement-type absorber that exhibits stable absorption characteristics in a high-frequency band of GHz or higher, has a workability such as fluidity, and has both strength and radio-wave absorption characteristics. Can be provided.
(2) Further, according to the present invention, a thin and light cement-type radio wave absorber having a high dielectric constant and dielectric loss can be provided.
(3) Furthermore, according to the present invention, it is possible to provide a cement-type radio wave absorber that is nonflammable, has no ultraviolet deterioration, and can sufficiently withstand long-term outdoor use.
(4) In addition, according to the present invention, no back metal is required, and it is inexpensive, excellent in reliability, can reduce dimensional accuracy, and can be directly applied onto sprayed mortar like a normal tile, or can be applied arbitrarily. It is possible to provide a cement type radio wave absorber excellent in workability and reliability that can be applied by spraying or mortar coating directly on the ground.

The flat iron oxide powder scale powder used in the electromagnetic wave absorber of the present invention is obtained by collecting and applying a scale generated by hot working of steel, and particularly preferably 2 of the wire surface formed by wire processing of steel. Next scale. Here, the secondary scale referred to by the present inventors is an iron oxide scale formed on the surface of the wire during hot working or cooling after working. This is different from a so-called primary scale formed in a heating furnace during heating before hot working and peeled off before working. The secondary scale formed on the surface of the wire has a small thickness and is usually peeled and removed by pickling or mechanical descaling before secondary processing such as wire drawing.

  The scale formed on the surface of the wire and peeled off by mechanical descaling is a flake-like powder with a thickness of several tens of μm, it is thin and flat, like the iron oxide powder that has been used in conventional radio wave absorption materials In Japanese Patent Application No. 2002-203028, which was filed earlier, it has a very different form from that of a spherical, needle-shaped or rod-shaped, and has excellent radio wave absorption characteristics.

  However, when such flat iron oxide powder is dispersed in a dielectric material such as rubber, it is a flat-shaped powder, and therefore has better adhesion to a rubber compound than when conventional spherical (unshaped) ferrite powder is dispersed. Unfortunately, it has been found that it acts as an inclusion and may significantly deteriorate the strength of the molded body. In addition, because of its flat shape, the powder is oriented in the processing direction by roll kneading, rolling, and extrusion, which is commonly performed to form a sheet by dispersing it in a dielectric, and the radio wave absorption characteristics are anisotropic in the plane. It has also been found that it has a drawback that tends to occur.

  Furthermore, the large dielectric loss due to the high dielectric constant and the conductive loss, which is a characteristic of the flat iron oxide powder having electrical conductivity, is dispersed in a matrix having a relatively low dielectric constant such as rubber or resin. Since the dielectric constant is low, the overall dielectric constant is greatly reduced, and it has become clear that the characteristics of the original flat iron oxide powder cannot be fully exhibited. Due to the low dielectric constant of the base material, the capacitive coupling between the conductive flat powders dispersed in the base material is lowered, and it is difficult to obtain a sufficient conductive loss.

  On the other hand, those using concrete, mortar cement or gypsum as the base, ie cement (Portland cement, alumina cement, magnesia cement, etc.), calcium silicate, calcium sulfate, lime and other hydrated solidified materials (cement binder) and aggregate When a cement-type solidified material mixed with water and water is used, the dielectric constant of rubber or resin is around 3 in the GHz band and has a higher value of 5 or more, so it has conductivity. In principle, it is advantageous to increase the dielectric constant or dielectric loss of the molded product in which the flat powder is dispersed. Actually, according to the composite dielectric law, when the volume filling factor of the absorbent material powder is about 30%, the dielectric constant of the molded body can be increased from about 20 to about 30 by increasing the dielectric constant of the matrix from 3 to 5. It can be predicted theoretically. In addition, due to the high dielectric constant of the base material, especially when flat powders are dispersed, local capacitors are formed between the flat powders and strongly capacitively coupled. Can be converted to a very large conductive loss. That is, it becomes an extremely large dielectric loss material and can exhibit high radio wave absorption performance. The flat iron oxide powder has not only electrical conductivity but also magnetism, and since it has a flat shape, it has a high magnetic permeability and a high magnetic loss, and exhibits a greater radio wave absorption performance.

  Thus, by dispersing the flat iron oxide powder in the cement having a high dielectric constant, the original performance is exhibited, and a thin absorber can be obtained. Such characteristics cannot be obtained using existing ferrite powders. Since a general ferrite powder is not a flat powder but an irregular shape, high dielectric properties due to the shape effect cannot be expected in the first place. Moreover, it is difficult to obtain a large conductive loss because there is no appropriate conductivity such as iron oxide powder. Furthermore, when such a shaped powder is dispersed in concrete, the capacitive coupling between the powders is small, and further loss of conductivity cannot be expected.

  Therefore, when using a general ferrite, it is necessary to sufficiently increase the filling rate of the ferrite, and to supplement the insufficient dielectric constant by adding carbon or the like that is effective for increasing the dielectric constant. In order to improve the characteristics at high frequencies above GHz, fine powder of several μm to several tens of μm is preferable, but such a fine powder has a very large specific surface area and forms a solidified molded body such as mortar using cement. If you do, it will cause quality degradation. That is, if an attempt is made to contain a sufficient amount of ferrite with respect to the cement, it is necessary to increase the fluidity at the time of kneading and inevitably increase the amount of water in order to ensure a certain workability. A large problem arises due to a decrease in density of the molded body, and consequently a decrease in strength.

  Such strength reduction can be improved to some extent by adding reinforcing materials such as carbon fiber and glass fiber to the molded product, but the addition of the reinforcing material imposes some restrictions on the filling rate of the ferrite powder as an absorbent. In addition, it is necessary to design the material in consideration of the electromagnetic wave response characteristics of the reinforcing material, which causes a disadvantage that the design becomes complicated. Increasing the size of the ferrite improves the quality such as workability and mechanical strength of the cement solidified body, but in this case, particularly, the electromagnetic wave absorption characteristics are deteriorated due to a decrease in magnetic loss.

  The use of flat iron oxide powder is effective as a method for overcoming such a trade-off. Although the flat iron oxide powder obtained by mechanical de-scaling of hot-rolled wire that we can use is as thin as several tens of μm, the size is as large as several tens of μm to 100 μm, and the ratio of water to powder, the so-called water powder ratio It is possible to knead with cement relatively easily even when the ratio is low. As a result, it is a perfect form for realizing high radio wave absorption characteristics by being dispersed in cement without impairing the density or strength of the molded body. Although the in-plane size is large, since the size of the minimum portion, that is, the thickness is several tens of μm or less, the radio wave absorption characteristic shows a good value.

  Although it is a flat iron oxide powder having a form suitable for dispersion in cement as described above, if the size is too small, the fluidity deteriorates due to kneading with cement, and solidification molding due to an increase in the water powder ratio It is not preferable because it reduces the strength of the body.

  As a method for avoiding this quality deterioration, it is necessary to remove fine powder from the flat iron oxide powder raw material to be used or to use a raw material with a low proportion of fine powder. Specifically, as proved by the examples described later, when screened with a mesh and selected, if the proportion of particles of 25 μm or less exceeds 50%, workability in cement kneading such as fluidity deteriorates. Therefore, it is necessary to make the weight ratio of the particles whose in-plane shortest part size exceeds 25 μm 50% or more. Moreover, as shown in the prior application, good radio wave absorption characteristics can be obtained by setting the average thickness of the flat iron oxide powder to 30 μm or less.

  Using a flat iron oxide powder raw material prepared for such a cement-type radio wave absorber, dispersed in a hydrated and solidified inorganic material such as cement, mortar, gypsum, etc., molded into a plate shape, and further a metal reflector on the back By using a standard resonator-type absorber provided with, the thickness can be reduced as compared with a conventional absorber using ferrite, and in addition, the strength of the molded body can be greatly improved.

  The volume filling rate of the flat iron oxide powder in the molded body is 5% or more and 40% or less. When the volume filling rate is less than 5%, it is difficult to obtain sufficient characteristics as a radio wave absorber, and when it exceeds 40%, the strength is remarkably lowered.

  Also, it is known that when flat iron oxide powder is used compared to the case of using conventional ferrite, the filling rate for obtaining equivalent characteristics can be greatly reduced, which is effective in improving the dielectric constant. Carbon or / and titania powder can be further added. In addition to the use of flat iron oxide powder alone, the addition of carbon or titania powder increases the overall dielectric constant and makes the absorber thinner. The real part and the imaginary part of the material cannot be controlled independently, but by adding these additives, it can be controlled independently, increasing the degree of freedom in material design and making it easier to optimize the electromagnetic wave absorption characteristics. is there.

  As the amount of carbon and / or titania to be added, the effect of substantially increasing the dielectric constant can be obtained by adding 0.5% or more by volume. The maximum filling rate is 10% by volume.

  As a configuration of the radio wave absorber, a multi-layer type can be used in addition to a general single-layer type. Multi-layer type includes absorbent layers containing flat iron oxide powder in concrete, mortar, gypsum, etc., or other types of absorbent materials such as common ferrite and carbon May be laminated with different base materials such as those containing rubber in a rubber or the like, or a radio wave absorption layer of different absorbing materials. Further, it may be laminated with a dielectric layer made of a general dielectric material (a material having a dielectric constant larger than 1) that is not a radio wave absorbing material.

  Moreover, it is also possible to perform surface treatment for imparting designability and functionality such as painting, resin plate bonding, tile bonding, rubber bonding, and glass bonding on the surface.

  These surface treatments or surface laminates do not affect the electromagnetic absorption characteristics when they are extremely thin, but if they are thick, they have a significant effect on the absorption characteristics. Therefore, it is necessary to control the physical properties of the lower radio wave absorption layer, that is, the complex dielectric constant, the complex magnetic permeability, and the thickness. The physical properties of the absorbent layer are mainly adjusted by adjusting the composition of the absorbent material. However, when the flat iron oxide powder of the present invention is used, the dielectric constant and dielectric loss are large as described above. In addition, the dielectric constant of the absorber can be changed and the control area is wide. Moreover, it can be adjusted by adding additional additives such as carbon and titanium oxide as required.

  In addition, the radio wave absorbing material of the present invention, that is, a radio wave having a large dielectric loss, dielectric loss, and porcelain loss, in which flat iron oxide powder adjusted to a predetermined particle size is contained in a cement base material such as concrete, mortar, or gypsum In a laminated body using an absorbing material and having a dielectric layer as the uppermost layer, a radio wave reflector layer (hereinafter sometimes simply referred to as a reflector or a back metal) used in a normal resonator type radio wave absorber. Can be made unnecessary. The radio wave reflector layer can be anything as long as it is placed on the opposite side of the radio wave arrival direction and normally reflects radio waves completely, such as metal plates, metal meshes, metal foils such as aluminum foil, conductive paste, conductive Carbon fiber is used, but it not only leads to cost increase, but when used in harsh outdoor environments, there are many problems in terms of durability and reliability, and resonator type absorption Factors that hinder productivity in terms of adhesive thickness management and bonding process when bonding the reflector layer to the absorber layer, and increase the cost of the radio wave absorber as a whole and lower the reliability. It has become.

  In the case of a normal resonator-type electromagnetic wave absorber, the mechanism for suppressing radio wave absorption, that is, reflection of radio waves from the surface is as follows. That is, when a radio wave is incident on the radio wave absorber from the air, the refractive index of the radio wave absorber is different from the refractive index 1 of the air, so that the refractive index is discontinuous at the boundary surface and the radio wave is always reflected. On the other hand, the radio wave that has entered the inside without being reflected on the surface reaches the radio wave reflector layer on the back side while being partially absorbed by the radio wave absorption layer, and is reflected there in the reverse direction. The radio wave reflected by the radio wave reflector layer travels again through the radio wave absorption layer, and part of the radio wave is transmitted outside from the surface, and part of the radio wave is reflected again by the surface and returns to the inside. The incident radio wave is finally reflected from the surface in the direction opposite to the incident direction while repeating this process, and the other part is absorbed while repeating the multiple reflection in the radio wave absorption layer.

  In the resonator type absorber, the non-reflection state is realized by removing the radio wave intensity reflected from the former absorber surface in the direction opposite to the incident direction by phase cancellation. In this case, if there is no reflector, a reflected wave that cancels out the radio wave reflected on the surface cannot be obtained, so that the radio wave reflection intensity always becomes a finite value and no reflection condition can be obtained.

  The absorber without a reflector of the present invention can be obtained by the following method. In other words, the dielectric constant, the dielectric loss, and the porcelain loss of the cement-type radio wave absorbing material of the present invention, that is, the cement-based base material such as concrete, mortar, gypsum and the like containing flat iron oxide powder adjusted to a predetermined particle size. A large wave-absorbing material is used, and a laminated body in which a dielectric layer (surface dielectric layer) is provided on the uppermost layer. As the dielectric layer, that is, the surface dielectric layer, paint, resin, rubber, ceramics, porcelain, cement, glass, and other various organic and inorganic dielectric materials can be used.

  With this configuration, the radio wave reflected from the outermost surface and the radio wave reflected from the second interface, that is, the interface between the upper dielectric layer and the lower radio wave absorption layer are canceled out to suppress radio wave reflection from the surface. can do.

  Furthermore, in order to eliminate the need for the radio wave reflector layer, it is necessary to always have the same absorption characteristics regardless of the structure behind the absorber or the material such as air. Otherwise, the absorption characteristics change depending on the base material on which the absorber is applied. To avoid this, it is necessary to redesign the absorber for each base, and the meaning of removing the reflector is lost.

  In order to realize this, the radio wave absorbing material of the present invention can be used. In other words, the only way to prevent the absorber base material from being affected at all is to ensure that radio waves are completely absorbed by the absorber layer before it enters the absorber layer and reaches the back of the absorber. For this purpose, the large dielectric loss and magnetic loss of the absorber of the present invention are extremely effective.

  Here, various conditions for producing a radio wave absorber using the radio wave absorber material of the present invention and not requiring a radio wave reflector layer provided with an upper dielectric layer will be described.

  First, although there are restrictions on the physical properties of the upper dielectric layer, it is not preferable that the incoming electromagnetic wave is reflected very strongly on the surface. This is because a certain amount of radio waves penetrates from the surface and is reflected by the second interface (the interface between the upper dielectric layer and the lower radio wave absorption layer), and the reflected wave is superimposed on the reflected wave reflected by the surface. This is because the reflected radio wave is canceled. This condition does not hold when the reflection intensity at the surface increases. Of course, by controlling the dielectric constant or permeability of the lower absorption layer to control the reflection coefficient at the second interface, it becomes possible to design corresponding to the difference in dielectric constant of the upper dielectric layer. There is a limit. The range that can be dealt with using the radio wave absorbing material of the present invention is limited to the case where the absolute value of the refractive index of the upper dielectric layer is 2.5 or less.

  Here, the refractive index n is expressed as n = √ | εr · μr | using the complex relative permittivity εr and complex relative permeability μr of the material at the target frequency. When the absolute value of the refractive index n exceeds 2.5, the amplitude of the primary reflection at the surface becomes too large, and even if the radio wave absorbing material of the present invention is used, it is not possible to cancel the reflection from the second interface. It becomes impossible.

Next, regarding the thickness of the upper dielectric layer, if the thickness does not satisfy the following formula, it is difficult to obtain an absorber without a reflector layer using the radio wave absorbing material of the present invention. n _R indicates the real part of the radio wave refractive index of the upper dielectric layer.

4n _R × t / λ ≦ A
Here, A is 1.1, more preferably 1.0.

  If the thickness does not satisfy this formula and becomes thick, the incident radio wave is incident from the surface, the phase shift received by the second interface and reflected again from the surface becomes too large, The control range of the phase control of the reflected wave at the interface using the radio wave absorbing material is exceeded, making it impossible to cope with it. Although a method of increasing the thickness of the upper dielectric layer by about half a wavelength in the dielectric so that the phase becomes the next matching condition is also conceivable, it is disadvantageous because the entire thickness is increased.

  The conditions of n and A are of course not only in the absorber without the radio wave reflector layer provided with the upper dielectric layer, but also in the absorber with the radio wave reflector layer provided with the upper dielectric layer. Adoption is preferred.

  A cement-type radio wave absorber without a radio wave reflector layer provided with a dielectric layer as the uppermost layer has the following merits. That is, in the case of cement-type absorbers such as concrete, mortar, and plaster, there is a drawback that water easily enters the absorber from the outside and the dielectric constant fluctuates greatly. The simplest way to solve this drawback is to apply waterproofing to the surface, but this is not always a satisfactory method in terms of long-term reliability and cost.

  On the other hand, in the case of a cement-type radio wave absorber without a radio wave reflector layer provided with a dielectric layer as the uppermost layer of the present invention, a sufficiently large margin can be obtained with respect to fluctuations in the dielectric constant of the lower layer absorber and water intrusion It is possible to prevent the characteristics from changing. This is because the absorption itself is designed to be completely formed by the radio wave absorption layer, so that even if water enters, the radio wave absorption is improved but not deteriorated. In the case of a single-layer absorber, the absorption frequency shifts because the dielectric constant fluctuates due to water penetration, but in this method, the dielectric constant and thickness of the upper dielectric layer dominate the absorption frequency. Therefore, unless these characteristics are changed, the absorption frequency does not change greatly. Of course, when the upper dielectric layer absorbs water, the dielectric constant increases and the absorption frequency fluctuates. Therefore, it is necessary to use a material having a low water absorption rate, or to waterproof itself. However, unlike cement, a dielectric material having a low water absorption rate can be obtained relatively easily, and there is often no need for special waterproof treatment.

  The water absorption rate of the upper dielectric layer needs to be 5% or less, preferably 2% or less, more preferably 1% or less. If it exceeds 5%, if the dielectric constant of the material used as the upper dielectric layer is a refractive index of 2.5 or less used in the present invention, the absorption frequency is shifted by about 20% or more when designed for the C band absorption band. Resulting in. If the water absorption is 1% or less, the fluctuation can be suppressed to 5% or less.

  Furthermore, a cement-type radio wave absorber without a radio wave reflector layer provided with a dielectric layer as the uppermost layer has the following merits. That is, the thickness of the lower cement-type absorption layer only needs to have a thickness necessary for radio waves to be sufficiently absorbed before reaching the back surface, and even if the thickness is larger than that, the absorption characteristics are not affected. The fact that it is not necessary to strictly control the thickness is particularly advantageous for a cemented product in which precise control of the thickness is difficult. Since it is sufficient to set the thickness to a certain level or more, for example, a ceramic tile with a predetermined thickness that does not absorb water by acting as an upper dielectric layer on an existing wall surface with sprayed mortar and having a certain thickness or more applied to it. It is also possible to obtain the necessary electromagnetic wave absorbing wall simply by arranging

Finally, the method for producing the absorbent material of the present invention will be briefly described.
First of all, it is a manufacturing method of flat iron oxide powder used in the present invention, a mechanical descale method in which a steel wire is rolled and a secondary scale formed on the surface of the wire during cooling is performed before secondary processing such as wire drawing. Use the one peeled off. The thickness, size, and the like of the obtained peeling scale can be controlled by hot working of the wire and mechanical descaling method, and a thinner and finer descaling powder is obtained as the processing temperature is lower and the cooling rate is faster. Also, the scale size varies depending on the difference in mechanical descale method, that is, reverse bending, torsion type mechanical descale method, operating conditions thereof, and the like.

  The flat iron oxide powder used in the present invention has an average thickness of 30 μm or less, and a large size in which the weight ratio of particles having an in-plane shortest portion size of 25 μm or more is 50% or more, and controls the rolling conditions and descaling conditions. Or, select and collect from rolling mills and steel types that are operated under optimum conditions, and use fine particles after sieving and adjusting the particle size as necessary.

  As a method of incorporating such flat iron oxide powder into a so-called cement-based base material such as concrete, mortar, or gypsum, the flat iron oxide powder is hydrated and solidified inorganic material in the same manner as the placing method generally used in concrete. This is mixed with dry cement, and the required amount of water is added and kneaded. When sufficient fluidity cannot be obtained, vibration casting, press molding, or extrusion can be employed. Moreover, you may add aggregates, such as sand, as needed.

  In the solidification process, room temperature solidification, steam curing, autoclave curing, and the like can be used as in the case of a general cement-based material hydration process. When attaching a radio wave reflector layer to the back side, a member that reflects radio waves, such as a metal plate or metal mesh such as an aluminum foil, an aluminum plate, an iron plate, or other radio wave reflector layer is attached to the back side with an adhesive, Alternatively, in the case of a mesh or the like, it may be embedded in cement and solidified in advance.

  When making a multilayer structure, mix and solidify one layer at a time, solidify and paste together with an adhesive after solidification, or pour it into the mold layer by layer, so that the interface is not disturbed and semi-solidified so as not to make a cold joint After that, it is integrated by pouring the next layer.

  In the case where a dielectric layer is provided on the surface layer, the absorbing layer can be prepared first, and then adhered to the dielectric layer, or the dielectric layer can be bonded and solidified and bonded as it is before solidifying in the manner of applying a tile.

  Finally, a part of the surface or the front surface is waterproofed as necessary. As the waterproofing treatment, a method of applying or impregnating an organic material such as a room temperature curable resin, a thermosetting resin or an ultraviolet curable resin, or an inorganic material such as water glass to the surface is used.

Now, many examples will be shown below to clarify the excellent effects of the present invention.
(Example 1)
The secondary scale formed on the low-carbon steel φ5.5 wire was peeled and collected by mechanical descale (reverse bending method).

The composition of the wire is
C; 0.035, Si; 0.71, Mn; 1.35, Ti; 0.03, S; 0.009, Al; 0.007, Cu; 0.011, P; 0.008, Zr; 0.01
Met.

The hot working condition of the wire is billet heating temperature: 950 ℃
Finished wire diameter: φ5.5mm
Mounting (winding) temperature: 900 ° C
Conveyor speed: 10m / sec
Cooling method: Cover cooling.

  The obtained scale was first embedded in a resin and polished, and thickness data of 20 powders were obtained by SEM observation to obtain an average value. The average thickness was 8.5 μm.

  Further, in order to measure the magnetism of the obtained scale powder, the magnetization was measured by applying a maximum applied magnetic field of 10 kOe using a vibrating sample magnetometer, and it was 56.8 emu / g. The scale is generally a mixture of iron oxides of FeO, Fe3O4, and Fe2O3, of which about 65% is magnetite because Fe3O4 shows magnetism and shows a value of about 65% for the magnetite magnetization 87.43emu / g. It is estimated that

  Next, 7 types of flat iron oxide powders for radio wave absorbers with different particle sizes obtained by partially removing fine particles with a powder size of 25 μm or less from the collected scale powder or by intentionally adding powders of 25 μm or less A raw material sample was obtained. The obtained seven kinds of raw materials were obtained by sieving the weight ratio of particles having an in-plane shortest portion size> 25 μm by a method according to JISZ8801.

  For comparison, a coarsely pulverized raw material of MnZn ferrite pulverized by a dry method was prepared. The average particle size of the powder was about 5 μm.

  These powders were mixed with general Portland cement to produce a strength test molded body (mortar) having a final volume ratio of 18% to 21% after solidification.

  For the mixing of water for each raw material, after mixing cement and raw material powder, add water to investigate the optimal water mixing that gives fluidity and does not cause breathing. A molded body for measurement was produced.

  The volume ratio of the flat iron oxide powder or ferrite in the compact is determined by the mixing ratio of cement, iron oxide powder and ferrite, water, compact weight, compact size (volume) and true density of powder (flat iron oxide powder 5.26 From MnZn ferrite 5.1), the following calculation was performed.

Weight of compact x (weight of flat iron powder / total weight) / true specific gravity of flat iron powder / volume of compact
Samples for the cement bending test and compression test were filled in a mold for measurement (40 mm x 40 mm x 160 mm, φ100 mm x 200 mml) with the mixed mortar, placed while tapping and dried overnight. It was taken out and further cured with an autoclave at 10 atm for 24 hours.

  The cement bending test and compression test were determined according to JIS A1106 central loading method and JIS A1108, respectively.

  These test results are shown in Table 1, FIG. 1 and FIG.

  When the flat iron oxide powder is used, high compressive strength can be realized when the weight ratio of the powder having the shortest in-plane size of 25 μm or more is 50% or more. When the weight ratio of the powder of 25 μm or more is less than 50% and the weight ratio of the powder of 25 μm or less is increased, the amount of water for obtaining the required workability is increased, and as a result, the compressive strength is lowered. The MnZn ferrite powder (Table 1 sample number 8) used for comparison had a low workability when mixed with cement and a high water-powder ratio, resulting in a low compressive strength.

Also, when using flat iron oxide powder, high bending strength can be realized when the weight ratio of the powder having the shortest in-plane size of 25 μm or more is 50% or more. If the weight ratio of the powder of 25 μm or more is less than 50% and the weight ratio of the powder of 25 μm or less increases, the amount of water for obtaining the required workability increases, and as a result, the bending strength decreases. The MnZn ferrite powder (Table 1 sample number 8) used for comparison had a low workability when mixed with cement and a high water-powder ratio, resulting in low bending strength.
(Example 2)
(Characteristics of single layer material with back metal)
A flat iron oxide powder was contained in the cement, and a single-layer absorber with a back metal on the back was prepared. The weight percent of the flattened iron oxide powder raw material used in which the minimum part size was 25 μm or more was 93.3%.

  Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, filled into a 200 mm × 200 mm × 3 mm mold, solidified, removed from the mold 24 hours later, and further cured at room temperature for 30 days. Thereafter, an aluminum adhesive sheet was affixed on one side, and the other surface was dry-ground with a grindstone to optimize the absorption frequency to 5.8 GHz, which is an ETC frequency, and the radio wave absorption characteristics were measured. The radio wave absorption characteristics were measured using a network analyzer and a horn antenna with a dielectric lens, using a general method (free space method) to calibrate the reflection characteristics at one port using the reflection characteristics from a standard metal plate. .

  These conditions and measurement results are shown in Table 2 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 21.1%. At this time, good absorption characteristics with a thickness of 2.85 mm and an absorption of 30 dB were obtained.
(Comparative Example 1)
(Characteristics of single layer material with back metal)
A single-layer absorber in which MnZn ferrite was contained in cement and a back metal was installed on the back was prepared. As the MnZn ferrite, coarsely pulverized one having an average particle diameter of 5 μm was used.

  Cement, ferrite, and water were mixed according to the composition shown in the table, filled into a 200 mm × 200 mm × 3 mm mold, solidified, removed from the mold after 24 hours, and further cured at room temperature for 30 days. Thereafter, an aluminum pressure-sensitive adhesive sheet was affixed on one side, and the other side was dry-ground with a grindstone to adjust the thickness to the same level as in the examples, and the radio wave absorption characteristics were measured. The measurement of the radio wave absorption characteristics is the same as that in the first embodiment.

  These conditions and measurement results are shown in Table 3 and FIG.

The ferrite content in the cement was significantly increased compared to the examples, but the workability was poor and the water powder ratio had to be increased. Therefore, the volume ratio of the molded body was 17.9%, and the absorption characteristics at this time were about 16 dB at 8 GHz. In order to lower the absorption frequency, it is necessary to increase the thickness of the absorber further, and in order to improve the absorption amount, it is necessary to increase the filling amount of the ferrite powder, but it is difficult.
(Example 3)
(Characteristics of single layer material with back metal)
A flat iron oxide powder was contained in the cement, and a single-layer absorber with a back metal on the back was prepared. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%.

  Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, filled into a 200 mm × 200 mm × 6 mm mold, solidified, taken out of the mold 24 hours later, and further cured at room temperature for 30 days. Thereafter, an aluminum adhesive sheet was attached to one side, and the other side was dry-ground with a grindstone to optimize the absorption frequency to 2.4 GHz which is a wireless LAN (IEEE802.11b) frequency, and the radio wave absorption characteristics were measured. The radio wave absorption characteristics were measured using a network analyzer and a horn antenna with a dielectric lens, using a general method (free space method) to calibrate the reflection characteristics at one port using the reflection characteristics from a standard metal plate. .

  These conditions and measurement results are shown in Table 4 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 17.5%. At this time, good absorption characteristics with a thickness of 5.8 mm and an absorption of 20 dB or more were obtained.
(Comparative Example 2)
(Characteristics of single layer material with back metal)
A single-layer absorber in which MnZn ferrite was contained in cement and a back metal was installed on the back was prepared. As the MnZn ferrite, the same coarsely pulverized one as in Comparative Example 1 having an average particle diameter of 5 μm was used.

  The cement, ferrite, and water are mixed at the maximum with the raw material ferrite used, and are the same as in Comparative Example 1. After mixing, the mixture is filled into a 200 mm × 200 mm × 6 mm mold and solidified. It was removed from the frame and cured at room temperature for 30 days. Thereafter, an aluminum pressure-sensitive adhesive sheet is attached to one side, and the other side is dry-ground with a grindstone to adjust the thickness to the same level as in the example, and the thickness of the molded body is adjusted to 5.8 mm as in Example 3. The radio wave absorption characteristics were measured. The measurement of the radio wave absorption characteristics is the same as that in the first embodiment.

  These conditions and measurement results are shown in Table 5 and FIG.

The volume ratio was 17.9%, and the absorption characteristic at this time was about 14 dB at 3.2 GHz. As with Comparative Example 1, it is necessary to increase the thickness of the absorber further to lower the absorption frequency, and to further increase the filling amount of ferrite powder to improve the absorption amount, but it is difficult.
(Example 4)
(Characteristics of single layer material with back metal)
A flat iron oxide powder was contained in the cement, and a single-layer absorber with a back metal on the back was prepared. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%.

  Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, filled into a 200 mm × 200 mm × 3 mm mold, solidified, taken out of the mold 24 hours later, and further autoclaved. Conditions for autoclave treatment were 10 atm and 180 ° C for 24 hours. Then, the aluminum adhesive sheet was affixed on one side, and the electromagnetic wave absorption characteristic was measured.

  These conditions and measurement results are shown in Table 6 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 17.5%. At this time, good absorption characteristics with a thickness of 2.96 mm and an absorption of 25 dB were obtained.
(Example 5)
(Characteristic of single layer material with back metal, graphite added)
A flat iron oxide powder was contained in the cement, and a single-layer absorber with a back metal on the back was prepared. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. Further, graphite was added for the purpose of increasing the dielectric constant and making the absorber thinner. The graphite used was natural graphite having an average particle size of 80 μm.
Cement, flat iron oxide powder, and graphite water were mixed in the composition shown in the table, filled into a 200 mm × 200 mm × 3 mm mold, solidified, taken out of the mold 24 hours later, and further autoclaved. The conditions for the autoclave treatment were the same as in Example 4. Then, the aluminum adhesive sheet was affixed on one side, and the electromagnetic wave absorption characteristic was measured.

  These conditions and measurement results are shown in Table 7 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 16.7%, and the volume ratio of graphite was 4.6%. At this time, good absorption characteristics with a thickness of 2.93 mm, absorption at 4.8 GHz and an absorption of 25 dB were obtained. The matching frequency can be greatly reduced as compared with Example 4, and as a result, it has been found that the thickness of ETC 5.8 GHz can be reduced to about 2.4 mm.
(Example 6)
(Characteristics of single-layer material with back metal added titanium oxide)
A flat iron oxide powder was contained in the cement, and a single-layer absorber with a back metal on the back was prepared. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. Titanium oxide was added for the purpose of increasing the dielectric constant and making the absorber thinner. The average particle size of the titanium oxide used was 1 μm or less.

  Cement, flat iron oxide powder, and graphite water were mixed in the composition shown in the table, filled into a 200 mm × 200 mm × 3 mm mold, solidified, taken out of the mold 24 hours later, and further autoclaved. The conditions for the autoclave treatment were the same as in Example 4. Then, the aluminum adhesive sheet was affixed on one side, and the electromagnetic wave absorption characteristic was measured.

  These conditions and measurement results are shown in Table 8 and FIG.

The volume fraction of the flat iron oxide powder in the cement was 15.4%, and the volume fraction of titanium oxide was 3.5%. At this time, good absorption characteristics with a thickness of 3 mm, 5.3 GHz and an absorption of 30 dB were obtained. The matching frequency can be greatly reduced as compared with Example 4, and as a result, it was found that the thickness of ETC 5.8 GHz can be reduced to about 2.7 mm.
(Example 7)
(Characteristics of single layer with back metal, X band)
A flat iron oxide powder was contained in the cement, and a single-layer absorber with a back metal on the back was prepared. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%.

  Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, filled into a 200 mm × 200 mm × 2 mm mold, solidified, removed from the mold 24 hours later, and further cured at room temperature for 30 days. Thereafter, an aluminum pressure-sensitive adhesive sheet was attached to one side, and the radio wave absorption characteristics were measured.

  These conditions and measurement results are shown in Table 9 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 11.4%. At this time, good absorption characteristics with a thickness of 1.95 mm, a frequency of 9.5 GHz and an absorption of 35 dB were obtained.
(Example 8)
(Characteristics of single layer with back metal, C band using plaster)
A flat iron oxide powder was contained in gypsum, and a single-layer absorber with a back metal on the back was prepared. The weight% of the flattened iron oxide powder raw material used in which the minimum part size was 25 μm or more was 87.3%.
Gypsum, flat iron oxide powder, and water are mixed in the composition shown in the table, filled into a 200mm x 200mm x 8mm mold, and stirred further to prevent the raw material from settling. Then, the surface was finished by using and left at room temperature. After 24 hours, it was removed from the mold and cured at room temperature for 30 days. After that, an aluminum adhesive sheet was affixed on one side, and the other side was dry-ground with a grindstone to optimize the absorption frequency to 2.4GHz, which is the frequency for wireless LAN. The results are shown in Table 10 and FIG.

The volume ratio of the flat iron oxide powder in gypsum was 13.1%. At this time, good absorption characteristics with a thickness of 6.2 mm and an absorption amount of 30 dB were obtained.
Example 9
(Characteristics of single-layer material with back metal, adhesion of surface dielectric layer, for wireless LAN)
A flat iron oxide powder was contained in the cement, a back metal was placed on the back, and a two-layer absorber having a dielectric layer on the surface was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, a commercially available ceramic tile having a thickness of 6.5 mm was used. The dielectric constant of the tile was 3.9 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water were mixed according to the composition shown in the table, filled into a 152 mm × 152 mm × 5 mm mold, solidified, taken out of the mold 24 hours later, and further cured by autoclave. Thereafter, an aluminum adhesive sheet was affixed on one side, and a tile was affixed with a cement adhesive for commercial tiles on the surface and the radio wave arrival side to measure the radio wave absorption characteristics.

  These conditions and measurement results are shown in Table 11 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 24.4%, and good absorption characteristics with an absorption of 35 dB at a frequency of 2.4 GHz were obtained.
(Example 10)
(Characteristics of single layer with back metal, surface dielectric layer, for ETC)
A flat iron oxide powder was contained in the cement, a back metal was placed on the back, and a two-layer absorber having a dielectric layer on the surface was produced. The weight% of the flattened iron oxide powder raw material used in which the minimum part size was 25 μm or more was 59.3%. As the dielectric layer, a commercially available ceramic tile having a thickness of 6.5 mm was used as in Example 9. The dielectric constant of the tile was 3.9 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water are mixed in the composition shown in the table. After 24 hours, it was removed from the mold and further cured by autoclaving and integrated. The autoclave conditions were 10 atm and 180 ° C for 24 hours. Thereafter, an aluminum adhesive sheet was attached to the surface opposite to the tile, and the radio wave absorption characteristics were measured.

  These conditions and measurement results are shown in Table 12 and FIG.

The volume ratio of the flat iron oxide powder in the cement was 29.1%. At this time, good absorption characteristics with an absorption amount of 25 dB were obtained near a frequency of 5.8 GHz. In addition, the absorption characteristics are broadened by laminating tiles, which is a favorable characteristic. Absorber material containing flat iron oxide powder in cement has a sufficiently high dielectric loss and magnetic loss, and it is laminated with other dielectrics to design a broadband absorber with excellent characteristics. It was confirmed that it was possible.
(Example 11)
(Characteristics of single layer with back metal, thin surface dielectric layer, for ETC)
A flat iron oxide powder was contained in the cement, a back metal was placed on the back, and a two-layer absorber having a dielectric layer on the surface was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, a commercially available ceramic tile having the same material as in Example 9 and a thickness of 4 mm was used. The dielectric constant of the tile was 3.9 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, the mixture was filled into a 200 mm × 200 mm × 10 mm mold, solidified, taken out of the mold after 24 hours, and then cured with an autoclave. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 11.4% and the thickness was 8.8 mm. A 97 mm × 97 mm tile was adhered to the surface with an adhesive for four tiles, and an aluminum adhesive sheet was attached to the opposite surface to measure the radio wave absorption characteristics.

  These conditions and measurement results are shown in Table 13 and FIG.

As the absorption characteristic, a good absorption characteristic with a frequency of 5.8 GHz and an absorption amount of 25 dB was obtained. It was found that the electromagnetic wave absorber for ETC can be produced using small and thin ceramic tiles for commercial interior.
(Example 12)
(Characteristics of single layer material with and without back metal, with thin surface dielectric layer, for ETC example, surface dielectric layer thickness 6.2 mm)
A flat iron oxide powder was contained in the cement, and an absorber having a dielectric layer on the surface with and without a back metal was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. The dielectric layer was the same as in Example 8, and a slightly thin commercially available ceramic tile was used. The dielectric constant of the tile was 3.9 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water were mixed according to the composition shown in the table, the mixture was filled in a 152 mm × 152 mm × 20 mm mold, solidified, taken out of the mold after 24 hours, and then cured by autoclave. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 18.0% and the thickness was about 18 mm. A 152 mm × 152 mm tile was adhered to the surface with an adhesive for tiles, and an aluminum pressure-sensitive adhesive sheet was not first attached to the opposite surface, but then attached, and the radio wave absorption characteristics were measured.

  These conditions and measurement results are shown in Table 14 and FIG.

As the absorption characteristic, a very good absorption characteristic with an absorption amount of 35 dB at a frequency of 5.8 GHz was obtained. Further, it can be seen that there is almost no difference in radio wave reflection characteristics with and without the back surface aluminum reflection layer, and a radio wave absorber exhibiting stable radio wave absorption characteristics independent of the back material is obtained. Even if there is no back reflective layer, there is no difference in reflection characteristics even if it is present, so the radio wave clearly does not reach the back surface, and as a result, an absorber that can realize stable characteristics regardless of the base material It has become.
(Example 13)
(Example of the characteristics of a two-layer absorber with or without a back metal, with a thin surface dielectric layer, for ETC, with a thickness of 4 mm for the surface dielectric layer)
A flat iron oxide powder was contained in the cement, and an absorber having a dielectric layer on the surface with and without a back metal was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. The absorption layer was a two-layer laminate in which flat iron oxide powder was contained in cement at different volume ratios. As the dielectric layer, a commercially available ceramic tile of the same type as that of Example 8 and made thinner with the same material was used. The dielectric constant of the tile was 3.9 as measured by the S parameter method.

  First, mix the first layer (the layer opposite to the direction of arrival of radio waves) with cement, flat iron oxide powder, and water in the composition shown in the table, fill it into a 152mm x 152mm x 10mm mold, and 24 hours later from the mold It was taken out and further cured with an autoclave. In the second layer (layer in the direction of arrival of radio waves), cement, flat iron oxide powder, and water are mixed in the composition shown in the table, filled into a 152mm x 152mm x 3mm mold, and taken out from the mold 24 hours later. Cured with crepe. The autoclave conditions were 10 atm and 180 ° C for 24 hours. After autoclaving, the surfaces of the first and second layers were dry-ground to obtain a flat surface, and then a 4 mm thick ceramic tile was attached with an adhesive in the order of the second and first layers to form a radio wave absorber. The volume ratio of the flat iron oxide powder in the cement was 29.7% for the first layer and the thickness was 10.2 mm, 5.64% for the second layer, and the thickness was 2.5 mm. The adhesive sheet made of aluminum was not first attached to the surface opposite to the direction of arrival of radio waves, but was then applied to measure the radio wave absorption characteristics.

  These conditions and measurement results are shown in Table 15 and FIG.

As absorption characteristics, good absorption characteristics with an absorption of 20 dB or more at a frequency of 5.8 GHz were obtained. Further, it can be seen that there is almost no difference in radio wave reflection characteristics with and without the back surface aluminum reflection layer, and a radio wave absorber exhibiting stable radio wave absorption characteristics independent of the back material is obtained.
(Example 14)
(Example of single layer material with or without back metal, with thin surface dielectric layer, for ETC, surface dielectric layer thickness of 6.9mm)
An absorber using a surface dielectric layer of a ceramic tile made of the same material as in Example 12 was prepared by using flat iron oxide powder in cement and with or without a back metal, and the characteristics were evaluated. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, a slightly thick 6.9 mm ceramic tile was used as in Example 8. The dielectric constant of the tile was 3.9 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water are mixed in the composition shown in the table, and the mixture is partially filled into a 152mm x 152mm x 30mm mold, solidified, taken out from the mold after 24 hours, and then cured by autoclave. did. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 12.8% and the thickness was about 25 mm. A 152 mm × 152 mm tile was bonded to the surface with a tile adhesive, and an aluminum adhesive sheet was not first bonded to the opposite surface, but was then bonded to measure radio wave absorption characteristics.

  These conditions and measurement results are shown in Table 16 and FIG.

  As absorption characteristics, good absorption characteristics were obtained with an absorption of 40 dB at a frequency of 5.4 GHz and an absorption of 20 dB at a frequency of 5.8 GHz. Moreover, there is almost no difference in the radio wave reflection characteristics with and without the back surface aluminum reflective layer, and a radio wave absorber exhibiting stable radio wave absorption characteristics independent of the back material is obtained.

  Next, four absorbers having the same size of 152 × 152 mm were prepared, and these were closely adhered to each other, and the absorption characteristics at oblique incidence with 5.8 GHz circular polarization were evaluated. The evaluation results are shown in FIG.

By using a surface dielectric layer with a surface protective layer thickness of 6.9 mm and 4 nt / λ of 1.05, the amount of absorption is 20 dB at the target frequency, and the oblique incidence characteristic also shows a value of 20 dB or more over the entire incident angle range. I understood.
(Comparative Example 3)
(Characteristics of single-layer material with and without back metal, bonding surface dielectric layer)
On the other hand, Table 17 and FIG. 19 show the conditions and measurement results when using a surface dielectric layer having a surface protective layer thickness of 6.9 mm and 4 nt / λ of 1.22 under the same conditions as in the above examples.

Since 4 nt / λ of the surface dielectric layer exceeded 1.1, the matching frequency was greatly reduced, and the absorption at 5.8 GHz was below 20 dB.
(Example 15)
(Characteristics of single layer material with and without back metal, with thin surface dielectric layer, for ETC, porcelain tile with surface dielectric layer thickness of 5.5mm)
A flat iron oxide powder was contained in the cement, and an absorber having a dielectric layer on the surface with and without a back metal was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, a commercially available thin ceramic tile was used. The dielectric constant of the tile was 5.1 as measured by the S-parameter method.
Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, and the mixture was filled into a 152 mm × 152 mm × 15 mm mold, solidified, taken out from the mold after 24 hours, and then cured by autoclave. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 31.4% and the thickness was about 15 mm. A 152 mm × 152 mm porcelain tile was attached to the surface with an adhesive for tiles, and an aluminum adhesive sheet was not attached to the opposite side first, but then attached, and the radio wave absorption characteristics were measured.

  These conditions and measurement results are shown in Table 18 and FIG.

As the absorption characteristic, a very good absorption characteristic with an absorption amount of 60 dB at a frequency of 5.8 GHz was obtained. Moreover, there is almost no difference in the radio wave reflection characteristics between the case with the back surface aluminum reflective layer (Comparative Example 5) and the case without this (Example), and a radio wave absorber exhibiting stable radio wave absorption characteristics independent of the back material is obtained. I understand that.
(Example 16)
(Characteristics of single layer with back metal, thin surface dielectric layer, for ETC, alumina with surface dielectric layer of 4.95mm)
A flat iron oxide powder was contained in cement, an absorber having a back metal and a dielectric layer on the surface was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, an alumina-based porcelain plate having a thickness of 4.95 mm was used. The porcelain plate used had a dielectric constant of 7.8 as measured by the S-parameter method.

  Cement, flat iron oxide powder, and water were mixed in the composition shown in the table, the mixture was filled into a 152 mm × 152 mm × 6 mm mold, solidified, taken out of the mold after 24 hours, and then cured by autoclave. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 9.7% and the thickness was 5.9 mm. A 152 mm × 152 mm alumina porcelain plate was attached to the surface with a tile adhesive, and an aluminum adhesive sheet was first attached to the opposite surface to measure the radio wave absorption characteristics.

These conditions and measurement results are shown in Table 19 and FIG.
As absorption characteristics, good absorption characteristics with an absorption of 30 dB at a frequency of 5.8 GHz were obtained.
(Comparative Example 4)
(Characteristics of single layer material with and without back metal, with thin surface dielectric layer, for ETC, alumina with surface dielectric layer thickness of 5.2 mm)
A flat iron oxide powder was contained in the cement, and an absorber having a dielectric layer on the surface with and without a back metal was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, an alumina-based porcelain plate having a refractive index of 2.79 and a thickness of 5.2 mm was used. The dielectric constant of the alumina porcelain plate was 7.8 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water are mixed in the composition shown in the table, the mixture is filled into a 152mm x 152mm x 3mm mold, solidified, taken out from the mold after 24 hours, and then cured by autoclave. It was dry-ground and finished to a thickness of 2.5 mm. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 9.7%. A 152 mm × 152 mm alumina porcelain plate was attached to the surface with an adhesive for tiles, and an aluminum adhesive sheet was not first attached to the opposite side, and then applied to measure the radio wave absorption characteristics.

  These conditions and measurement results are shown in Table 20 and FIG.

In the case of no back metal, a good absorption characteristic with an absorption of 30 dB at a frequency of 5.8 GHz was obtained as the absorption characteristic. On the other hand, in the case of the back metal, the absorption frequency increased significantly and showed an absorption amount of about 20 dB at about 9 GHz. In this example, the dielectric constant of the alumina-based porcelain plate is large, and the value of 4nt / λ is 1.12 at 5.8GHZ. If there is no back metal, it could be a 5.8GHz absorber for ETC. Thus, it was not possible to obtain an absorber having the same radio wave absorption characteristics.
(Comparative Example 5)
(Characteristics of single layer material with and without back metal, with thin surface dielectric layer, for ETC, alumina with surface dielectric layer thickness of 5.2 mm, the same as Example 17 except for different thickness of absorption layer)
A flat iron oxide powder was contained in the cement, and an absorber having a dielectric layer on the surface with and without a back metal was produced. The weight percent of the flattened iron oxide powder raw material used in which the shortest part size was 25 μm or more was 77.8%. As the dielectric layer, an alumina-based porcelain plate having a refractive index of 2.79 and a thickness of 5.2 mm was used. The dielectric constant of the alumina porcelain plate was 7.8 as measured by the S parameter method.

  Cement, flat iron oxide powder, and water are mixed in the composition shown in the table, the mixture is filled in a 152mm x 152mm x 6mm mold, solidified, taken out from the mold after 24 hours, and then cured by autoclave. It was dry-ground and finished to a thickness of 5.7 mm. The autoclave conditions were 10 atm and 180 ° C for 24 hours. The volume ratio of the flat iron oxide powder in the cement was 9.7%. A 152 mm × 152 mm alumina porcelain plate was attached to the surface with an adhesive for tiles, and an aluminum adhesive sheet was not first attached to the opposite side, and then applied to measure the radio wave absorption characteristics.

These conditions and measurement results are shown in Table 21 and FIG.
In the case of back metal, good absorption characteristics with an absorption of 28 dB at a frequency of 5.8 GHz were obtained. On the other hand, in the case of no back metal, the absorption frequency was significantly reduced, and the absorption amount was about 20 dB at about 4 GHz. In this example, the dielectric constant of the alumina-based porcelain plate is large, and the value of 4nt / λ is 1.12 at 5.8GHZ. If there is a back metal, it could be used as a 5.8GHz absorber for ETC. Thus, it was not possible to obtain an absorber having the same radio wave absorption characteristics.
(Example 17)
With or without back metal, characteristics of wall material with mortar + surface porcelain tile, for ETC, porcelain tile with surface dielectric layer of 5.7mm thickness)
Absorbing walls with dielectric tiles on the surface were prepared with cement containing flat iron oxide powder and without back metal. The weight% of the flattened iron oxide powder raw material used in which the minimum part size was 25 μm or more was 87.3%. As the dielectric layer, a commercially available porcelain tile having a refractive index of 2.26 and a thickness of 5.7 mm was used. The dielectric constant of the tile was 5.1 as measured by the S-parameter method.

  Cement, flat iron oxide powder, water mixed in the table composition, on a concrete plate of 40cm x 40cm x 5cm thickness and on a steel plate of 40cm x 40cm x 5mm thickness as a back metal with a thickness of 14-15mm A mortar was applied with a thickness, and a porcelain tile was attached on top of the mortar. The panel was then cured at room temperature for 30 days to simulate a radio wave absorption wall. The volume ratio of the flat iron oxide powder in the cement was evaluated by preparing a sample poured into a small formwork separately, and the volume filling ratio was 17.2%.

  These conditions and measurement results are shown in Table 22 and FIG. As absorption characteristics, good absorption characteristics with an absorption of 30 dB at a frequency of 5.6 GHz were obtained.

  Next, the absorption characteristics at 5.8 GHz circular polarization at oblique incidence were evaluated. The evaluation results are shown in FIG.

  From these results, by using a surface dielectric layer with a surface protective layer thickness of 5.7 mm and 4 nt / λ of 0.995, the amount of absorption is 20 dB or more at the target frequency regardless of the presence or absence of back metal. It was found that the incident characteristics also showed a value of 20 dB or more over the entire incident angle.

The graph which shows the relationship between the weight ratio of the in-plane shortest part size of 25 micrometers or more of the flat iron oxide powder which concerns on this invention Example 1, and the compressive strength of a cement-type electromagnetic wave absorber. The graph which shows the relationship between the weight ratio of the in-plane shortest part size of 25 micrometers or more of the flat iron oxide powder which concerns on this invention Example 1, and the bending strength of a cement type electromagnetic wave absorber. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on Example 2 of this invention. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on the comparative example 1. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on Example 3 of this invention. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on the comparative example 2. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on Example 4 of this invention. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 5. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 6. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 7. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on Example 8 of this invention. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 9. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 10. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 11. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 12. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on Example 13 of this invention. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on this invention Example 14. The graph which shows the electromagnetic wave absorption characteristic seen from the circular polarization angle of the cement-type electromagnetic wave absorber which concerns on Example 14 of this invention. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on the comparative example 3. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on this invention Example 15. FIG. The graph which shows the electromagnetic wave absorption characteristic of the cement type electromagnetic wave absorber which concerns on this invention Example 16. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on the comparative example 4. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on the comparative example 5. The graph which shows the electromagnetic wave absorption characteristic of the cement-type electromagnetic wave absorber which concerns on Example 17 of this invention. The graph which evaluated the absorption characteristic in the 5.8-GHz circularly polarized wave based on this invention Example 17 at oblique incidence.

Claims (9)

A cement-type radio wave absorber formed by mixing and molding a flat iron oxide powder having an average thickness ≦ 30 μm and a weight ratio of particles having an in-plane shortest portion size> 25 μm of 50% or more with a hydrated solidified inorganic material. The cement-type electromagnetic wave absorber according to claim 1, wherein the volume ratio of the flat iron oxide powder is 5% or more and 40% or less. The cement-type radio wave absorber according to claim 2, further comprising carbon and / or titanium oxide mixed in a volume ratio of 0.5% to 10%. 4. The cement-type radio wave absorber according to claim 1, wherein the cement-type radio wave absorber is formed into a single-layer or multi-layer plate, and a radio wave reflector layer is formed on a surface opposite to a radio wave arrival direction. A single-layer or multi-layered plate that has a radio wave reflector layer on the surface opposite to the radio wave arrival direction and one or more surface dielectric layers made of dielectric material on the radio wave arrival side surface The cement-type electromagnetic wave absorber according to claim 4. The cement-type radio wave absorber according to claim 5, which has no radio wave reflector layer. The real part n _R (n _R = Real (√ (εr · μr), εr: complex relative permittivity, μr: complex relative permeability, n _R ; refractive index)) and thickness t of the surface dielectric layer For the radio wave wavelength (wavelength in vacuum) of the target radio frequency or the radio wave wavelength λ of the center frequency in the target radio frequency range
4n _R × t / λ ≦ 1.1
The cement-type radio wave absorber according to claim 5 or 6, wherein a refractive index n (n = √ | εr · μr |, | A | is an absolute value of a complex number A) is 2.5 or less. 8. The cement-type radio wave absorber according to claim 5, wherein the surface dielectric layer has a water absorption of 5% or less. 9. The cement-type radio wave absorber according to claim 1, wherein a part or all of the surface is waterproofed.

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