JP2016146374A - Electromagnetic wave absorber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber, having high level electromagnetic wave absorption performance, particularly excellent electromagnetic wave absorption performance to an electromagnetic wave of a high frequency band of 1 GHz to 3 GHz, suitably used in an anechoic chamber and such, for instance.SOLUTION: The electromagnetic wave absorber has a quadrangular truncated pyramid shape having a top face, a bottom face, and four inclined faces. An angle between the bottom face and the inclined faces is greater than or equal to 64° and less than or equal to 68°. A height of the absorber is greater than or equal to 35 cm and less than or equal to 105 cm.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a radio wave absorber.

  An anechoic chamber is a measurement facility that performs evaluation of electromagnetic noise radiated from electronic devices, immunity evaluation of electronic devices against external electromagnetic noise, evaluation of antenna characteristics, and the like. A radio wave absorber is used on the wall or ceiling surface of the anechoic chamber, and the absorption frequency band required for the radio wave absorber is several tens of MHz to several GHz. In general, as a radio wave absorber, a ferrite tile that absorbs tens to several hundreds of MHz, a foamed urethane containing carbon or graphite that supports absorption in the GHz band, a pyramid type or wedge type absorption made of expanded polystyrene. It is used in combination with a three-dimensional absorber such as a body.

  In recent years, electronic devices have been increasing in frequency with the increase in the amount of information transmitted, and the required performance of an anechoic chamber for evaluating it has increased from several GHz to several tens of GHz. The role of radio wave absorbers responsible for band absorption is becoming increasingly important.

  In recent years, there has been proposed a radio wave absorber that regularly has a pyramid and a trapezoidal trapezoid having both radio wave absorption characteristics and noise reduction performance (Patent Document 1).

  Moreover, in order to manufacture a lightweight and non-combustible radio wave absorber with high productivity, a radio wave absorber in which a square pyramid made of a calcium silicate plate and a small square pyramid are combined has been proposed (Patent Document 2).

  Furthermore, a radio wave absorber made of a sheet material that has excellent radio wave absorption performance and excellent handling properties such as transportability and on-site workability has been proposed (Patent Document 3).

JP 2003-241761 A JP-A-10-163670 JP 2012-191183 A

  Although the electromagnetic wave absorber disclosed in Patent Document 1 adopts a cone or a trapezoidal trapezoidal shape, the angle and height between the lower surface and the inclined surface are inappropriate, and it is required as an anechoic chamber. In particular, there is a problem that the absorption performance is inferior in a high frequency band of 1 GHz to 3 GHz.

  Further, the radio wave absorber disclosed in the above-mentioned Patent Document 2 adopts a quadrangular pyramid shape in which a small quadrangular pyramid is coupled to the upper portion of the quadrangular pyramid, but the angle and height between the lower surface and the slope are different. It is inadequate and is inferior in absorption performance in a high frequency band of 1 GHz to 3 GHz which is required as an anechoic chamber. Further, the height of the electromagnetic wave absorber is as high as 956 mm, and there is a problem that the effective use volume that can be used as the electromagnetic wave anechoic chamber becomes small after being attached to the wall surface or ceiling surface of the electromagnetic wave anechoic chamber.

  Although the electromagnetic wave absorber disclosed in Patent Document 3 adopts a shape similar to a quadrangular pyramid trapezoid, the angle and height between the lower surface and the inclined surface are inappropriate, and it is required as an anechoic chamber. In particular, there is a problem that the absorption performance is inferior in a high frequency band of 1 GHz to 3 GHz.

  Then, this invention makes it a subject to provide the radio wave absorber which has the high radio wave absorption performance, especially the radio wave absorption performance excellent with respect to the high frequency band of 1 GHz-3 GHz.

In order to solve the above problems, the present invention has the following configuration. That is,
(1) A quadrangular frustum-shaped radio wave absorber having an upper surface, a lower surface, and four inclined surfaces, wherein an angle between the lower surface and the inclined surface is not less than 64 ° and not more than 68 °, and a height is not less than 35 cm and not more than 105 cm. Absorber,
(2) The radio wave absorber according to (1), wherein the quadrangular pyramid is a regular quadrangular pyramid.
(3) The radio wave absorber according to (1) or (2), comprising a radio wave absorber sheet material having radio wave absorption performance,
(4) The radio wave absorber according to (3), wherein the complex relative permittivity at 3 GHz of the radio wave absorber sheet material is real part εr ′ of 7 to 18 and imaginary part εr ″ of 4 to 15.

  According to the present invention, it is possible to obtain a radio wave absorber having high radio wave absorption performance, particularly excellent radio wave absorption performance for radio waves in a high frequency band of 1 GHz to 3 GHz.

The perspective conceptual diagram which shows an example of the electromagnetic wave absorber of this invention. The side surface conceptual diagram which shows an example of the electromagnetic wave absorber of this invention. The conceptual diagram which shows the mechanism of the electromagnetic wave absorption by two electromagnetic wave absorbers whose angle of a lower surface and a slope is 64 degrees or more and 68 degrees or less. The conceptual diagram which shows the mechanism of the electromagnetic wave absorption by the two electromagnetic wave absorbers whose angle of a lower surface and a slope is less than 64 degrees.

  Hereinafter, embodiments of the present invention will be described in detail. The radio wave absorber of the present invention is a quadrangular pyramid shaped radio wave absorber. By adopting a quadrangular pyramid shape, the wave absorber has high absorption performance, particularly excellent absorption performance for radio waves in the high frequency band of 1 GHz to 3 GHz, while suppressing the height of the absorber lower than that of the pyramid shape. Can be obtained. Here, FIG. 1 is a perspective conceptual diagram illustrating an example of the radio wave absorber of the present invention, and FIG. 2 is a side conceptual diagram illustrating an example of the radio wave absorber of the present invention. The radio wave absorber of the present invention has a quadrangular pyramid shape and has a quadrangular upper surface 1, a quadrangular lower surface 2 and four trapezoidal slopes 3. The height B of the radio wave absorber of the present invention is the distance between the upper surface 1 and the lower surface 2 and is within a specific range as will be described later. Furthermore, the radio wave absorber of the present invention has four slopes 3, and the angle A between the lower surface 2 and the slope 3 is within a specific range as described later. Moreover, an example of the radio wave absorber of the present invention is produced by bending the radio wave absorber sheet material 4 as described later, and has a hollow structure.

  The shape of the radio wave absorber of the present invention is a quadrangular pyramid, but it is preferably a regular quadrangular pyramid from the viewpoint of obtaining stable radio wave absorption performance.

  In the radio wave absorber of the present invention, the angle between the lower surface and the slope is in the range of 64 ° to 68 °. By making the angle between the lower surface of the radio wave absorber and the slope of the radio wave absorber within the above range, most of the radio waves incident from above the radio wave absorber can enter the radio wave absorber and reach the lower surface thereof. Therefore, the radio wave absorption efficiency of the radio wave absorber of the present invention is excellent. When the angle between the lower surface and the slope is less than 64 °, when at least two radio wave absorbers of the present invention are used and arranged adjacent to each other, the incident radio wave incident from above the radio wave absorber is the first radio wave. Because it is reflected by the slope of the absorber and then reflected by the slope of the adjacent second radio wave absorber, a part of the incident radio wave is not absorbed by the radio wave absorber and becomes a radiated radio wave emitted above the radio wave absorber. The radio wave absorption performance of the radio wave absorber is significantly reduced. On the other hand, when the angle between the bottom surface and the slope exceeds 68 °, the mechanism is not clear, but the incident angle between the radio wave incident from above the radio wave absorber and the slope of the radio wave absorber becomes large, and as a result Since the reflectance at the surface of the radio wave absorber increases and the proportion of radio waves entering the radio wave absorber decreases, it is presumed that the radio wave absorption performance of the radio wave absorber is significantly reduced. From the above viewpoint, the lower limit of the angle between the lower surface and the inclined surface of the radio wave absorber is preferably 65 ° or more, and the upper limit is preferably 67 ° or less, more preferably 66 ° or less.

  Here, FIG. 3 is a conceptual diagram showing a mechanism of radio wave absorption by two radio wave absorbers having an angle between the lower surface and the slope of 64 ° to 68 °, and FIG. 4 shows an angle between the lower surface and the slope. It is a conceptual diagram which shows the mechanism of the electromagnetic wave absorption by two electromagnetic wave absorbers which are less than 64 degrees. When a radio wave absorber having an angle between the lower surface and the slope of 64 ° or more and 68 ° is used, a part of the incident radio wave 5 from above the radio wave absorber is first on the slope of the first radio wave absorber 6. Enter the radio wave absorber 6. Further, the incident radio wave 5 that has not entered the first radio wave absorber 6 becomes a reflected radio wave 8, and a part thereof enters the second radio wave absorber 7 and reaches the lower surface of the second radio wave absorber 7. Further, the reflected radio wave 8 that has not entered the second radio wave absorber 7 becomes a reflected radio wave 9, and the reflected radio wave 9 reaches the slope of the first radio wave absorber 6 again. Here, when a radio wave absorber whose angle between the lower surface and the slope is less than 64 ° is used, a part of the incident radio wave 5 from above the radio wave absorber is first on the slope of the first radio wave absorber 6. Enters the electromagnetic wave absorber 6. Further, the incident radio wave 5 that has not entered the first radio wave absorber 6 becomes a reflected radio wave 8 and reaches the slope of the second radio wave absorber 7. Here, a part of the reflected radio wave 8 is reflected by the slope of the second radio wave absorber 7 and becomes a radiated radio wave 10 radiated above the radio wave absorber without being absorbed by the radio wave absorber. Here, the incident angle M of the incident radio wave 5 and the reflection angle N of the reflected radio wave 8 vary depending on the angle between the lower surface of the radio wave absorber and the inclined surface.

  The radio wave absorber of the present invention has a height of 35 cm or more and 105 cm or less. By setting the height of the radio wave absorber to 35 cm or more, it is possible to obtain a radio wave absorber having high absorption performance, particularly excellent absorption performance for radio waves in a high frequency band of 1 GHz to 3 GHz. There is a correlation between the height of the radio wave absorber and the frequency range where the radio wave absorption performance is enhanced, that is, the wavelength of the radio wave, and in the shape of the present invention, an attempt is made to obtain a high absorption performance particularly for radio waves in the high frequency band of 1 GHz to 3 GHz. In this case, the height of the radio wave absorber needs to be 35 cm or more. From the above viewpoint, the lower limit of the height of the radio wave absorber of the present invention is preferably 45 cm or more. On the other hand, by setting the height of the radio wave absorber to 105 cm or less, it is possible to obtain a radio wave absorber having high absorption performance, particularly excellent absorption performance for radio waves in a high frequency band of 1 GHz to 3 GHz. From the above viewpoint, the upper limit of the height of the radio wave absorber of the present invention is preferably 55 cm or less. In addition, by setting the height of the electromagnetic wave absorber of the present invention to 55 cm or less, it becomes possible to increase the effective use volume in the anechoic chamber when it is attached to the wall or ceiling surface of the anechoic chamber. In the practical use of the anechoic chamber, the convenience is greatly improved. As described above, when the height of the radio wave absorber is less than 35 cm or exceeds 105 cm, high radio wave absorption performance cannot be obtained particularly for radio waves in a high frequency band of 1 GHz to 3 GHz.

  The relationship between the height of the radio wave absorber and the radio wave absorption performance of the radio wave absorber, and the relationship between the angle between the lower surface and the slope of the radio wave absorber and the radio wave absorption performance of the radio wave absorber is as described above. The radio wave absorber of the present invention has an angle between the lower surface and the slope of 64 ° to 68 ° and a height of 40 cm to 105 cm, so that the radio wave absorber of the present invention absorbs radio waves particularly in a high frequency band of 1 GHz to 3 GHz. We have found that the performance is remarkably superior.

  When the radio wave absorber of the present invention is a regular quadrangular pyramid trapezoid, the lower surface is square, and the size of one side is preferably 50 cm or more and 70 cm or less, and the lower limit is more preferably 55 cm or more. The upper limit is more preferably 65 cm or less. By setting it as such a size, affixing to the wall surface and ceiling surface of an anechoic chamber becomes easy, and workability improves. By setting the length of one side to 50 cm or more, the number of radio wave absorbers required for construction is reduced, and the time required for the radio wave absorber assembly process and the radio wave absorber attachment process can be further reduced. . On the other hand, by setting the length of one side to 70 cm or less, the size of the radio wave absorber can be made small, and when the radio wave absorber is attached to the wall or ceiling surface of the anechoic chamber, Handling is improved.

  The radio wave absorber of the present invention is preferably composed of a radio wave absorber sheet material having radio wave absorption performance. By making the radio wave absorber of the present invention composed of the above sheet material, the interior of the radio wave absorber can be made hollow, and the inside containing carbon, graphite or the like is made of solid foamed urethane Compared to a radio wave absorber or the like, it is light and has good workability, and is easy to transport and store. The radio wave absorber of the present invention may be composed only of a radio wave absorber sheet material having radio wave absorption performance, or a member other than the radio wave absorber sheet material within a range that does not impair the effects of the present invention. You may have.

  Examples of the radio wave absorber sheet material having radio wave absorbing performance include a radio wave absorber sheet material containing a material for imparting radio wave absorbing performance to the radio wave absorber sheet material. Examples of the material for imparting radio wave absorption performance to the radio wave absorber sheet material used for the radio wave absorber sheet material include conductive materials and magnetic materials. It is preferable to use a conductive material because it can be easily dispersed uniformly. Among conductive materials, it is more preferable to use conductive short fibers. Since the conductive short fibers have a large aspect ratio, the fibers are easily brought into contact with each other, and the radio wave absorber sheet material can be effectively imparted with radio wave absorbing performance even in a small amount as compared with the powder. Among conductive short fibers, carbon fibers are more preferable because the fibers themselves are rigid and easy to be oriented in the base material, and there is almost no change in performance over a long period of use.

  Moreover, as a form of said sheet | seat material for electromagnetic wave absorbers, there are a resin film, a film, a nonwoven fabric, a woven fabric, a knitted fabric, paper, a corrugated cardboard based on paper, a resin plate, or a foam boat. In addition, the above-mentioned sheet material for the wave absorber is folded into a hollow three-dimensional wave absorber, so that film, non-woven fabric, woven fabric, knitted fabric, paper, or paper is used from the viewpoint of easy folding. It is preferable to use corrugated cardboard as a base material.

  In addition, the above-described electromagnetic wave absorber sheet material may be obtained by adding a conductive material to a material constituting a film and the like, and forming the film into a film or the like. A film containing no conductive material or magnetic material may be coated with the contained resin, or a film containing a conductive material or the like may be coated with a film containing no conductive material or magnetic material. It may be laminated on the like. Of course, a film containing a conductive material or the like may be laminated on a resin plate that does not contain a conductive material or a magnetic material.

  As a base material containing a conductive material or a magnetic material, natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber when the above-mentioned sheet material for radio wave absorber is a resin film or film Rubber materials such as diene rubber such as butyl rubber, ethylene propylene rubber, urethane rubber and silicone rubber, polyolefin resin, polyamide resin, polyester resin, polyether resin, polyimide resin, polyurethane resin, poly Resin materials such as siloxane resin, phenol resin, epoxy resin, acrylic resin, urea resin, melamine resin, fluorine resin, polyvinyl chloride resin, and polyphenylene sulfide resin can be used.

  In addition, in the case where the form of the sheet material for the radio wave absorber is a woven fabric, a knitted fabric, a non-woven fabric, or a structure mainly composed of fibers such as paper, a base material containing a conductive material or a magnetic material is used. Examples thereof include inorganic fibers such as glass fibers and ceramic fibers, synthetic fibers, natural fibers such as cotton, hemp, wool, and wood pulp, and semi-synthetic fibers such as rayon. Furthermore, examples of the polymer forming the synthetic fiber include polyethylene terephthalate, polybutylene terephthalate, polylactic acid, and copolymer polyester obtained by copolymerizing the acid component of those polyesters with isophthalic acid, 5-sodium sulfoisophthalic acid, adipic acid, and the like. Polyester, nylon 6, nylon 66, nylon 12, nylon 46, polyamide such as copolymerized polyamide obtained by copolymerizing nylon 6 and nylon 66, polyvinyl alcohol, aromatic polyamide, polyether ether ketone, Examples include paraphenylene benzobisoxazole, polyphenylene sulfide, polyethylene, and polypropylene. From the viewpoint of improving flame retardancy, glass fibers, aromatic polyamide fibers, polyether ether ketone fibers, polyparaphenylene benzobisoxazole fibers, polyphenylene sulfide fibers, etc. should be used among the above-mentioned base material materials. Is preferred. Moreover, a flame retardance can also be improved by adding inorganic powders, such as aluminum hydroxide and magnesium hydroxide, to the material of a base material.

  Among the forms of the electromagnetic wave absorber sheet material described above, the corrugated cardboard is light in weight because it has voids in the electromagnetic wave absorber sheet material, and has sufficient sheet strength to form a three-dimensional shape. The form of the above-mentioned electromagnetic wave absorber sheet material is particularly preferable. In addition, when the sheet material for the radio wave absorber is made of corrugated cardboard, from the viewpoint of productivity, a paper containing a conductive material or a magnetic material is manufactured and processed into a corrugated cardboard by corrugating. A configuration is preferably used. Generally, corrugated cardboard is composed of three sheets of corrugated core paper and upper and lower liner sheets, but any of the three sheets may contain conductive or magnetic materials. It is good, and any one of the three or only two may be contained. When paper containing a conductive material or magnetic material is used for only one sheet, it is preferably used for a core paper, and when only two sheets are used, it is preferably used for upper and lower liner paper.

  When the above-mentioned sheet material for radio wave absorber is a corrugated cardboard based on resin film, film, nonwoven fabric, woven fabric, knitted fabric, paper or paper, its thickness may be in the range of 0.05 mm or more and 5 mm or less. preferable. This is because, by setting the thickness within this range, good strength can be obtained and a bending process can be easily performed when a hollow three-dimensional electromagnetic wave absorber is obtained.

  When the form of the sheet material for a radio wave absorber is a resin plate or a foam board, the thickness is preferably 1 mm or more and 30 mm or less, more preferably 2 mm or more as a lower limit, and 10 mm or less as an upper limit. Is more preferable. By setting the thickness within this range, it is possible to obtain a satisfactory strength that can be used even when a radio wave absorber that particularly requires strength is required.

  The complex relative permittivity at 3 GHz of the sheet material for radio wave absorber of the present invention is preferably such that the real part εr ′ is in the range of 7 to 18 and the imaginary part εr ″ is in the range of 4 to 15. Particularly preferably. The lower limit of the real part εr ′ is more preferably 8 or more, and the upper limit thereof is more preferably 16. The lower limit of the imaginary part εr ″ is more preferably 5 or more, and the upper limit thereof is More preferably, it is 13 or less. By assembling a sheet material for a radio wave absorber having a complex relative dielectric constant in such a range and making it the shape of the above-mentioned square pyramid trapezoid, it has excellent absorption performance, particularly excellent absorption for radio waves in a high frequency band of 1 GHz to 3 GHz. A radio wave absorber having performance can be obtained. Generally, in an anechoic chamber, a ferrite tile that is responsible for absorption in the low frequency band of several tens to several hundreds of MHz is combined with a three-dimensional type absorber such as a pyramid type or wedge type absorber that is responsible for absorption in the high frequency band of GHz. Used. If the complex relative permittivity of the three-dimensional absorber is too high, reflection in the low frequency band is increased and the radio wave absorption performance of the ferrite tile is lowered. On the other hand, if the complex dielectric constant is too low, the three-dimensional absorber tends to be unable to sufficiently absorb radio waves in the high frequency band. By setting the complex dielectric constant of the sheet material for a radio wave absorber of the present invention within the above range, it is preferable because sufficient radio wave absorption performance can be realized.

  The measurement method used in this example will be described later.

(1) Complex relative dielectric constant of sheet material for radio wave absorber On the upper surface of an aluminum plate having a length of 30 cm, a width of 30 cm and a thickness of 5 mm, a styrofoam spacer (thickness: 14 mm) having the same size and shape as the aluminum plate and a foaming ratio of 70 times On top of this spacer, a sheet material for a radio wave absorber having the same size as the aluminum plate is further placed, and the center point of the polystyrene foam spacer (on the surface opposite to the aluminum plate side surface of the polystyrene foam spacer and Set the transmitting and receiving antennas to a position just 1.4m away from the intersection of two diagonal lines of polystyrene foam spacers) so that the incident angle of radio waves is 7 °, and sample radio waves in the frequency range of 2 to 4 GHz. The vector network analyzer (model: N5230, manufactured by Agilent Technologies) ) Was used to measure the input impedance. After that, remove the wave absorber sheet material and measure the input impedance with the wave absorber sheet material removed as above, and the difference between the input impedance with and without the wave absorber sheet material. From this, the complex relative permittivity of the sheet material for the radio wave absorber was calculated, and the real part εr ′ and the imaginary part εr ″ of the complex relative dielectric constant at the frequency of 3 GHz were read. = 3, for each radio wave absorber sheet material, the real part εr ′ and the imaginary part εr ″ of the complex relative permittivity in the direction parallel to the one side and the direction perpendicular to the one side are obtained. The average values of the six measured values of the real part εr ′ and the imaginary part εr ″ of the complex relative dielectric constant were defined as the real part εr ′ and the imaginary part εr ″ of the complex relative dielectric constant.

(2) Radio wave absorption amount of radio wave absorber Four aluminum plates having a length of 60 cm, a width of 60 cm, and a thickness of 5 mm were arranged in a square shape so as to be 120 cm long and 120 cm wide. The incident angle of the radio wave is set between the transmitting and receiving antennas at a position 2.7 m away from the center point (on the surface of one surface of an aluminum plate 120 cm long × 120 cm wide and the intersection of the two diagonal points). It set so that it might become 7 degrees, the electromagnetic wave of the frequency range of 1-3 GHz was injected into the aluminum plate, and the reflection level of the aluminum plate was measured using the vector network analyzer (model: N5230, Agilent Technologies). Next, on the aluminum plate, four regular quadrangular pyramid shaped wave absorbers having a size of 60 cm × 60 cm on the lower surface are placed so as to cover the entire one surface of the aluminum plate, and reflection of the wave absorber is performed. Level was measured. From these measured values, the radio wave absorption amount (reflection attenuation amount) of the radio wave absorber was obtained by the following equation, and the minimum value and the maximum value at 1 to 3 GHz were read.
Radio wave absorption (dB) = reflection level (dB) of aluminum plate−reflection level (dB) of radio wave absorber
Example 1
(Radio wave absorber sheet material)
Polyacrylonitrile-based carbon fiber with an average fiber length of 3 mm (“Torayca” (registered trademark) manufactured by Toray Industries, Inc.), glass fiber with an average fiber length of 4 mm, wood pulp, core-sheath type heat-sealable polyester short fiber with an average fiber length of 3 mm ( “Safmet” (registered trademark) manufactured by Toray Industries, Inc.) and aluminum hydroxide were mixed in water at a ratio of 1% by mass, 19% by mass, 7% by mass, 3% by mass, and 70% by mass, respectively. The slurry was poured into a flat surface, dehydrated and dried to obtain flame retardant paper I having a thickness of 130 μm and a basis weight of 100 g / m ² .

In the same manner, the ratio of the glass fiber having an average fiber length of 4 mm was changed to 20% by mass with the composition excluding the polyacrylonitrile-based carbon fiber, and the same method as described above, the thickness of 130 μm and the basis weight of 100 g / m ² was difficult. Fuel paper II was obtained.

  Subsequently, the flame retardant paper II is processed into a corrugated shape with a hot press roll to form a corrugated core portion having a corrugated cardboard three-layer structure, and both sides thereof are bonded to the planar flame retardant paper I to have a thickness of 3.0 mm. Corrugated sheet material was used.

  As a result of measuring the complex dielectric constant at 3 GHz of the sheet material for radio wave absorber, the real part εr ′ = 11.3 and the imaginary part εr ″ = 6.5.

(Radio wave absorber)
This radio wave absorber sheet material is cut and bent, and the kraft tape is attached to the sides of the slope and the sides of the top and bottom surfaces, and the angle between the bottom surface and the slope is 65.2 °. , Height is 35.0 cm, upper base size is 27.7 x 27.7 cm square, upper base diagonal length is 39.2 cm, lower base is 60.0 x 60.0 cm square, lower base diagonal A square wave trapezoidal wave absorber having a length of 84.9 cm was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 1, and it was found that the radio wave absorption amount was a minimum of 18 dB and a maximum of 35 dB in the frequency band of 1 to 3 GHz.

(Example 2)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 65.2 °, the height is 40.0 cm, and the top surface A square with a size of 23.2 × 23.2 cm, a diagonal length of the upper bottom surface of 32.9 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 1. It was found that the radio wave absorption amount was a minimum of 19 dB and a maximum of 36 dB in the frequency band of 1 to 3 GHz.

(Example 3)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 65.2 °, the height is 45.0 cm, and the top surface A square with a size of 19.4 × 19.4 cm, a diagonal length of the upper base of 27.4 cm, a lower base of 60.0 × 60.0 cm and a diagonal length of the lower base of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 1, and it was found that they have a high radio wave absorption amount of 20 dB minimum and 38 dB maximum in the frequency band of 1 to 3 GHz.

Example 4
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 66.7 °, the height is 45.0 cm, and the top surface A square with a size of 21.6 × 21.6 cm, a diagonal length of the upper bottom surface of 30.5 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 1, and it was found that they have a high radio wave absorption amount of 16 dB minimum and 32 dB maximum in the frequency band of 1 to 3 GHz.

(Example 5)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 68.0 °, the height is 45.0 cm, and the top surface A square with a size of 23.4 × 23.4 cm, a diagonal length of the upper bottom surface of 33.1 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 1, and it was found that they have a high radio wave absorption amount of 15 dB minimum and 29 dB maximum in the frequency band of 1 to 3 GHz.

(Example 6)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 64.3 °, the height is 50.0 cm, and the top surface A square with a size of 11.8 × 11.8 cm square, a diagonal length of the upper bottom surface of 16.7 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 1, and it was found that they have a high radio wave absorption amount of 17 dB minimum and 35 dB maximum in the frequency band of 1 to 3 GHz.

(Example 7)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 65.2 °, the height is 50.0 cm, and the top surface A square with a size of 13.8 × 13.8 cm square, a diagonal length of the upper bottom surface of 19.5 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 2. It was found that the radio wave absorption amount was a minimum of 24 dB and a maximum of 41 dB in the frequency band of 1 to 3 GHz.

(Example 8)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 66.7 °, the height is 50.0 cm, and the top surface A square with a size of 17.2 × 17.2 cm, a diagonal length of the upper bottom surface of 24.3 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 2, and it was found that the radio wave absorption amount was a minimum of 15 dB and a maximum of 37 dB in the frequency band of 1 to 3 GHz.

Example 9
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side portion. The angle between the bottom surface and the slope is 68.0 °, the height is 50.0 cm, and the top surface. A square with a size of 19.4 × 19.4 cm, a diagonal length of the upper base of 27.4 cm, a lower base of 60.0 × 60.0 cm and a diagonal length of the lower base of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 2, and it was found that the radio wave absorption amount was a minimum of 15 dB and a maximum of 31 dB in the frequency band of 1 to 3 GHz.

(Example 10)
(Radio wave absorber sheet material)
In the same manner as in Example 1, polyacrylonitrile-based carbon fiber having an average fiber length of 3 mm (“Torayca” (registered trademark) manufactured by Toray Industries, Inc.) and glass fiber having an average fiber length of 4 mm were each 0.6 mass% and 19. A flame retardant paper III having a thickness of 130 μm and a basis weight of 100 g / m ² was obtained in the same manner as the flame retardant paper I except that the content was changed to 4% by mass.

  Subsequently, by processing the flame retardant paper II used in Example 1 into a corrugated shape with a hot press roll, forming a corrugated core portion of a corrugated cardboard three-layer structure, and laminating both sides thereof with the planar flame retardant paper III, A corrugated sheet material having a thickness of 3.0 mm was used.

  As a result of measuring the complex relative dielectric constant at 3 GHz of the sheet material for radio wave absorber, the real part εr ′ = 6.0 and the imaginary part εr ″ = 3.5.

(Radio wave absorber)
The above electromagnetic wave absorber sheet material is cut, bent, and craft tape is attached to the sides. The angle between the bottom surface and the slope is 65.2 °, the height is 50.0 cm, and the size of the top surface. Is a square square frustum with 13.8 × 13.8 cm square, diagonal length of the upper bottom surface of 19.5 cm, lower bottom surface of 60.0 × 60.0 cm square, and diagonal length of the lower bottom surface of 84.9 cm A shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 2, and have a minimum 14 dB and a maximum 27 dB absorption in the frequency band of 1 to 3 GHz, which is slightly inferior to the other examples, but has a high radio wave absorption. all right.

(Example 11)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 65.2 °, the height is 55.0 cm, and the top surface A square with a size of 9.2 × 9.2 cm square, a diagonal length of the upper bottom surface of 13.0 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 2, and it was found that they have a high level of radio wave absorption of a minimum of 21 dB and a maximum of 39 dB in the frequency band of 1 to 3 GHz.

(Example 12)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 65.2 °, the height is 64.0 cm, and the top surface A square with a size of 0.9 × 0.9 cm square, a diagonal length of the upper bottom surface of 1.3 cm, a lower bottom surface of 60.0 × 60.0 cm square and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 2, and it was found that the radio wave absorption amount was a minimum of 19 dB and a maximum of 38 dB in the frequency band of 1 to 3 GHz.
(Comparative Example 1)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 63.4 °, the height is 45.0 cm, and the top surface A square with a size of 15.0 × 15.0 cm square, a diagonal length of the upper bottom surface of 21.2 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3, and the radio wave absorption amount is a minimum of 11 dB and a maximum of 24 dB in the frequency band of 1 to 3 GHz, which is inferior to the radio wave absorber of the example.

(Comparative Example 2)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 63.4 °, the height is 50.0 cm, and the top surface A square with a size of 10.0 × 10.0 cm square, a diagonal length of the upper bottom surface of 14.1 cm, a lower bottom surface of 60.0 × 60.0 cm square and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3, and the radio wave absorption amount is 10 dB minimum and 26 dB maximum in the frequency band of 1 to 3 GHz, which is inferior to the radio wave absorber of the example.

(Comparative Example 3)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 68.5 °, the height is 45.0 cm, and the top surface Is a square having a size of 24.4 × 24.4 cm, a diagonal length of the upper bottom surface of 34.5 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3, and the radio wave absorption amount is 10 dB minimum and 24 dB maximum in the frequency band of 1 to 3 GHz, which is inferior to the radio wave absorber of the example.

(Comparative Example 4)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 68.5 °, the height is 50.0 cm, and the top surface A square with a size of 20.5 × 20.5 cm, a diagonal length of the upper bottom surface of 29.0 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3, and the radio wave absorption amount is a minimum of 11 dB and a maximum of 25 dB in the frequency band of 1 to 3 GHz, which is inferior to the radio wave absorber of the example.

(Comparative Example 5)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, the angle between the bottom surface and the slope is 65.2 °, the height is 30.0 cm, and the top surface A square with a size of 32.4 × 32.4 cm square, a diagonal length of the upper bottom surface of 45.8 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3, and the radio wave absorption amount is 9 dB minimum and 25 dB maximum in the frequency band of 1 to 3 GHz, which is inferior to the radio wave absorber of the example.

(Comparative Example 6)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 65.2 °, the height is 115.0 cm, and the top surface A square with a size of 13.8 × 13.8 cm square, a diagonal length of the upper bottom surface of 19.5 cm, a lower bottom surface of 120.0 × 120.0 cm square, and a diagonal length of the lower bottom surface of 169.7 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 240 cm x length of 240 cm and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3. The radio wave absorption amount is 12 dB minimum and 26 dB maximum in the frequency band of 1 to 3 GHz, which is inferior to the radio wave absorber of the example.

(Comparative Example 7)
The electromagnetic wave absorber sheet material of Example 1 is cut, bent, and craft tape is pasted on the side, and the angle between the bottom surface and the slope is 63.4 °, the height is 30.0 cm, and the top surface A square with a size of 30.0 × 30.0 cm, a diagonal length of the upper bottom surface of 42.4 cm, a lower bottom surface of 60.0 × 60.0 cm square, and a diagonal length of the lower bottom surface of 84.9 cm A frustum-shaped wave absorber was obtained.

Four of these radio wave absorbers were prepared and placed on an aluminum plate having a length of 120 cm, a length of 120 cm, and a thickness of 5 mm, and the amount of radio wave absorption was measured.
The results are shown in Table 3, and the radio wave absorption amount is 7 dB minimum and 18 dB maximum in the frequency band of 1 to 3 GHz, which is very inferior to the radio wave absorber of the example.

  The radio wave absorber of the present invention has high radio wave absorption performance, particularly excellent radio wave absorption performance for radio waves in a high frequency band of 1 GHz to 3 GHz, and is preferably used in, for example, an anechoic chamber.

1: upper surface 2: lower surface 3: slope 4: sheet material for radio wave absorber 5: incident radio wave 6: first radio wave absorber 7: second radio wave absorber 8: reflected radio wave 9: reflected radio wave 10: radiated radio wave A : Angle B between bottom surface and slope B: Height of radio wave absorber M: Incident angle N: Reflection angle

Claims (4)

A quadrangular pyramid shaped wave absorber having an upper surface, a lower surface and four inclined surfaces;
The angle between the lower surface and the slope is 64 ° or more and 68 ° or less,
A radio wave absorber having a height of 35 cm to 105 cm.   2. The radio wave absorber according to claim 1, wherein the quadrangular frustum is a regular quadrangular frustum. The radio wave absorber according to claim 1 or 2, comprising a radio wave absorber sheet material having radio wave absorption performance. 4. The radio wave absorber according to claim 3, wherein the complex relative permittivity at 3 GHz of the sheet material for the radio wave absorber has a real part εr ′ of 7 to 18 and an imaginary part εr ″ of 4 to 15. 5.

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