JP5953799B2 - Sheet material for radio wave absorber and radio wave absorber - Google Patents

Description

  The present invention relates to a sheet material for a radio wave absorber and a radio wave absorber used for, for example, an anechoic chamber, an anechoic box, a radio wave absorption partition, and the like.

  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.

  Carbon and other foamed resin absorbers used as radio wave absorbers in the range of several GHz to several tens of GHz have a large volume, which entails enormous transportation and storage costs. There was a problem in handling such that it took a lot of work to install.

  To solve this problem, a sheet material for a radio wave absorber having a corrugated cardboard structure in which a core processed into a corrugated cross-sectional shape and a planar liner are laminated, and a radio wave absorber having a hollow three-dimensional structure (Patent) Reference 1). In addition to being able to be transported and stored in a compactly folded state, the radio wave absorber made of this sheet material is lightweight because it is hollow. However, regarding the demand for advanced absorption characteristics in the high frequency band, it has been difficult to obtain higher absorption characteristics than the foamed resin absorbent containing carbon and the like.

  In order to improve the absorption characteristics in the high-frequency band, it is proposed that a hollow external structure made of a radio wave absorbing thin material is fitted with a lattice-shaped or polygonal pyramid-shaped internal loss body made of the same radio wave absorbing thin material (Patent Documents 2 and 3). Although this radio wave absorber has improved absorption performance in the high frequency band, the assembly work is complicated because the external structure and the internal structure are made of different parts. In addition, since each part does not have a rectangular or square shape, there is a problem that a lot of parts are discarded when the part is extracted from the original thin material.

JP 2004-253760 A JP 2004-335985 A JP 2006-128454 A

  The object of the present invention is to solve the above-mentioned conventional problems, and is excellent in handling property that can be transported from a warehouse to an assembly place on a flat surface and can be constructed on site, has few waste parts, and further has a high absorption performance, particularly a few. An object of the present invention is to provide a radio wave absorber sheet material and a radio wave absorber having excellent absorption performance for radio waves in a high frequency band of GHz to several tens of GHz.

To achieve the above object, the radio wave absorber sheet material of the present invention is a dodecagon C radio wave absorber sheet material, which is an octagon formed as a result of cutting out right-angled triangles from the four corners of the rectangle A, respectively. B has a straight line F parallel to one of the two sides of the original rectangle A inside the octagon B, two vertices generated by cutting out one right triangle, and two of the straight line F When two straight lines connecting the end points closest to one of the two end points are taken as a set, the four straight lines in each of the four sets have the same length.
And the octagon B is a set of two opposite sides derived from the sides of the original rectangle A, and the two sides of each set have the same length, and the dodecagon C is an octagon B From the four sides generated by cutting out the right-angled triangle in, an isosceles triangle having these sides as the base is cut out from the octagon B or added to the octagon B.

  In the dodecagon C, the radio wave absorber sheet material connects the eight vertices of the original octagon B and the two end points of the straight line F inside the octagon B, respectively. All of the eight straight lines are mountain fold lines, and four vertices generated by cutting an isosceles triangle from the octagon B or adding it to the octagon B and the two end points of the straight line F are Of these, a sheet material in which the four straight lines connecting the closest end points are valley fold lines and the straight line F is a mountain fold line may be used.

  Furthermore, the radio wave absorber of the present invention is configured to bend the valley fold line and the mountain fold line of the radio wave absorber sheet material so that two mountain fold lines adjacent to the valley fold line overlap each other, and The straight line F is also folded in a mountain fold and has a folded solid E having four folded triangles E inside, and having a rectangular bottom.

  According to the present invention, since a thin sheet material is bent into a hollow solid body, it is lightweight and excellent in workability, and can be handled in a thin sheet state, and can be easily transported and stored. Further, since the sheet material is based on a rectangle or a square, it is possible to collect the sheet material with a high yield, and it is not necessary to assemble a large number of parts into a radio wave absorber, so that the assembling work is easy. Furthermore, by the folded triangle E inside the hollow, 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 several GHz to several tens of GHz.

(A) The top view of an example of the sheet | seat material for electromagnetic wave absorbers concerning this invention. (B) The top view which shows the shape of the rectangle A and the octagon B in the sheet | seat material of the said (a). The top view of an example of the sheet | seat material for electromagnetic wave absorbers concerning this invention, and the perspective view of the electromagnetic wave absorber obtained from the said sheet | seat material. (A) is a case where the straight line F is inside the internal rectangle D, and (b) is a case where a part of the straight line F is outside the internal rectangle D. The top view of an example of the sheet | seat material for electromagnetic wave absorbers concerning this invention. The figure which expanded one of the four corners of the rectangle A. FIG. (A) is a case where an isosceles triangle having the base of the side So is cut out from the octagon B, and (b) is a case where an isosceles triangle having the base of the side So is added to the octagon B. The perspective view which shows a part of electromagnetic wave absorber obtained from the said sheet | seat material of FIG. The perspective view of an example of the electromagnetic wave absorber concerning this invention. The perspective view of an example of the electromagnetic wave absorber concerning this invention. Both (a) and (b) show part of the folded triangle E inside the radio wave absorber. It is a perspective view of an example of the electromagnetic wave absorber concerning this invention, and shows the example of the method of hold | maintaining and fixing the hollow solid shape whose bottom face is a rectangle. The schematic diagram of the method of measuring the radio wave absorption of a radio wave absorber. The top view of the sheet | seat material for electromagnetic wave absorbers of this invention shown in Example 1, and the perspective view of the electromagnetic wave absorber obtained from it. An overhead view when the electromagnetic wave absorber is disposed in the first embodiment The top view of the sheet | seat material for electromagnetic wave absorbers shown in the comparative example 1, and the perspective view of the electromagnetic wave absorber obtained from it. The top view of the sheet | seat material for electromagnetic wave absorbers shown in Example 4. FIG. The top view of the sheet | seat material for electromagnetic wave absorbers shown in Example 5. FIG.

  Hereinafter, examples of embodiments of the present invention will be described.

  Examples of the material of the sheet material for a radio wave absorber according to the present invention include a sheet formed by containing a conductive material or a magnetic material in a substrate such as a resin or a fiber structure.

  Examples of the conductive material include conductive particles such as metal particles, carbon black, carbon nanotube particles, carbon microcoil particles, and graphite particles, and metals such as carbon fiber, stainless steel, copper, gold, silver, nickel, aluminum, and iron. Examples thereof include conductive fibers such as fibers. Moreover, what gave electroconductivity by plating, vapor-depositing, and spraying a metal to the nonelectroconductive particle or fiber can also be mentioned.

  Examples of magnetic materials include metals such as iron, nickel, and chromium, alloys such as permalloy and sendust, ferrites such as hard ferrite and soft ferrite, metal compounds such as carbonyl iron, and the like. The thing made into a fiber is mentioned. Moreover, what gave electroconductivity by plating, vapor-depositing, and spraying these magnetic materials to nonelectroconductive particle or fiber can also be mentioned.

  As a material used for the sheet material for the radio wave absorber, it is preferable to use a conductive material from the viewpoints of cost reduction, weight reduction, and easy dispersion on the base material. Among conductive materials, it is more preferable to use conductive short fibers. Since the conductive fiber has a large aspect ratio, the fibers are easily in contact with each other, and the radio wave absorption performance can be effectively obtained even in a small amount as compared with the powder. Among the conductive fibers, carbon fibers are more preferable because the fibers themselves are rigid and can be easily oriented in the substrate, and there is almost no change in performance over a long period of use.

  As a base material containing these conductive materials and magnetic materials, in the case of a resin film or film, diene rubber such as natural rubber, isoprene rubber, butadiene rubber, styrene butadiene rubber, butyl rubber, ethylene propylene rubber, Non-diene rubber such as urethane rubber and silicone rubber, polyolefin resin, polyamide resin, polyester resin, polyether resin, polyimide resin, polyurethane resin, polysiloxane resin, phenol resin, epoxy resin, acrylic resin, urea Examples thereof include resin materials such as resin, melamine resin, fluororesin, polyvinyl chloride resin, and polyphenylene sulfide resin.

  In the case of structures mainly composed of fibers such as woven fabrics, knitted fabrics, nonwoven fabrics and paper, inorganic fibers such as glass fibers and ceramic fibers, synthetic fibers, natural fibers such as cotton, hemp, wool and wood pulp, rayon, etc. Semi-synthetic fiber. 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, it is preferable to use glass fibers, aromatic polyamide fibers, polyether ether ketone fibers, polyparaphenylene benzobisoxazole fibers, polyphenylene sulfide fibers, and the like.

  The conductive material-containing layer may contain inorganic powder such as titanium oxide, barium sulfate, calcium carbonate, aluminum hydroxide, magnesium hydroxide.

  For example, flame retardance can be improved by adding aluminum hydroxide or magnesium hydroxide.

  Since the sheet material for a radio wave absorber of the present invention is folded into a hollow solid radio wave absorber, it is preferable to use a film or a nonwoven fabric, particularly paper, as a base material from the viewpoint of easy folding. In addition, resin containing conductive material or magnetic material coated on film or paper that does not contain conductive material or magnetic material, resin sheet or film containing conductive material or magnetic material, woven fabric, knitted fabric A fiber structure such as a nonwoven fabric may be laminated on a film or paper that does not contain a conductive material or a magnetic material. Furthermore, in order to obtain good strength in the hollow three-dimensional shape, the base material is preferably made of cardboard or cardboard. Among these, corrugated cardboard is more preferable because it has a sheet strength sufficient to obtain a three-dimensional shape in addition to being lightweight because it has voids in the sheet. Generally, corrugated cardboard is composed of three sheets of corrugated core paper and upper and lower liner sheets, but any of the three sheets of paper may contain conductive or magnetic materials. It may be good, or only one or two of the three may be contained. When using a paper containing a conductive material or a magnetic material for only one sheet, it is preferably used for the core paper.

  The thickness of the sheet material for a radio wave absorber of the present invention is preferably in the range of 0.2 mm to 10 mm, and more preferably in the range of 0.3 to 6 mm. This is because, by setting the thickness within this range, good strength can be obtained when the hollow three-dimensional wave absorber is formed, and bending can be easily performed.

  Further, the real part εr ′ of the complex relative permittivity at 1 GHz of the sheet material for radio wave absorber of the present invention is preferably 5 to 30, and the imaginary part εr ″ is preferably in the range of 2 to 25, and the real part εr ′ is More preferably, it is 6 to 15 and the imaginary part εr ″ is in the range of 4 to 15. 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 increases and the absorption in the ferrite tile decreases, and if it is too low, the high-frequency band in the three-dimensional absorber does not sufficiently absorb. . It is preferable to set the complex relative dielectric constant of the sheet material for a radio wave absorber of the present invention within the above-mentioned range since sufficient radio wave absorption performance can be realized for both low frequency and high frequency.

  Next, an example of an embodiment of the sheet material for a radio wave absorber of the present invention will be described with reference to the drawings.

  Fig.1 (a) shows an example of the sheet | seat material for electromagnetic wave absorbers of this invention. FIG. 1B illustrates the shapes of the rectangle A and the octagon B. FIG. Assuming a rectangle A, octagons B are formed as a result of cutting out right triangles from the four corners. Turning to FIG. 1A, the octagon B has a straight line F parallel to one of the two sides of the original rectangle A, and a right triangle is cut out from the rectangle A. Two straight lines Ln1 and Ln2 (n = a to d) connecting two vertices Pn1 and Pn2 (n = a to d) generated by having been connected to the closest end point of the two end points of the straight line F When one set is used, in each of the four sets (La1, La2), (Lb1, Lb2), (Lc1, Lc2), (Ld1, Ld2), two straight lines of each set have the same length, and eight In the square B, two opposing sides Srα and Srγ and Srβ and Srδ originating from the side of the original rectangle A are set as a pair, and the two sides of each set have the same length (Srα = Srγ). , Srβ = Srδ). Further, from the four sides Soa, Sob, Soc, and Sod resulting from cutting out right-angled triangles from the four corners of the original rectangle A, an isosceles triangle with these sides as the base is cut out from the octagon B, or an octagon The dodecagon C sheet material added to B is the sheet material for a radio wave absorber of the present invention. This electromagnetic wave absorber sheet material is formed into a predetermined shape, and then assembled into a hollow three-dimensional electromagnetic wave absorber at the construction site and applied to a wall surface or ceiling surface of an electromagnetic wave anechoic chamber or the like (this electromagnetic wave absorber sheet is Details of the radio wave absorber used will be described later). During transportation and storage before construction, the sheet can be handled in a flat sheet state, so that it is not bulky, and transportation and storage costs can be reduced. Further, since the sheet material is based on a rectangle or a square, the sheet material can be collected with a high yield. Furthermore, it is not necessary to assemble a large number of parts, and it is possible to fold a single sheet material into a radio wave absorber, so that the assembly can be facilitated.

  In the dodecagon C, the eight straight lines La1, La2, and Lb1 connecting the eight vertices of the original octagon B and the closest end points of the two end points of the straight line F inside the octagon B, respectively. , Lb2, Lc1, Lc2, Ld1, and Ld2 are all mountain fold lines, and a vertex formed by cutting an isosceles triangle from the octagon B or adding to the octagon B, and the two end points of the straight line F described above The four straight lines Ma, Mb, Mc, and Md connecting the closest end points of these are shown as valley fold lines, and the straight line F is shown as a mountain fold line. Since it becomes easy to set it as an absorber, it is preferable.

  In FIG. 2, the eight vertices of the octagon B are surrounded by four straight lines Kα, Kβ, Kγ, and Kδ that pass through two vertices that are not adjacent to each other and are orthogonal to two opposite sides derived from the side of the rectangle A. It is preferable that a straight line F is present inside the internal rectangle D (shaded portion in the figure). Although details of the radio wave absorber using the radio wave absorber sheet will be described later, the radio wave absorber sheet material is bent to form a hollow solid wave absorber having a rectangular bottom surface. At this time, a straight line F is formed on the upper side of the hollow solid, and the intersection of the perpendicular drawn from the two end points (f1, f2) of the straight line F, which is the upper side of the hollow solid, toward the bottom of the hollow solid and the bottom of the hollow solid. Are (h1, h2), respectively. FIG. 2A shows a case where the straight line F is inside the internal rectangle D, but the intersections h1 and h2 are within the bottom surface of the hollow solid. On the other hand, FIG. 2B shows a case where a part of the straight line F is outside the internal rectangle D, and one of the two intersections h1 and h2 (here, h1) is outside the bottom of the hollow solid. It becomes. The electromagnetic wave absorbers are regularly installed adjacent to each other on the wall or ceiling surface of the anechoic chamber, but if the intersections h1 and h2 are both inside the bottom surface of the square weight as shown in FIG. Since it can attach without disturbing installation of an adjacent electromagnetic wave absorber, it is preferable.

  Further, it is more preferable that the midpoint of the straight line F is at the center of the rectangle A. When this radio wave absorber sheet material is a hollow solid wave absorber having a rectangular bottom surface, the midpoint of the straight line F, which is the upper side of the hollow solid, and a perpendicular drawn from the midpoint toward the bottom surface of the hollow solid, It becomes a line-symmetric hollow solid with respect to a straight line connecting the intersection with the bottom of the hollow solid. If the symmetry of the hollow solid is high, the influence of the anisotropy of the wave absorber on the polarization plane of the incoming radio wave can be reduced, and uniform anechoic chamber performance independent of the polarization plane can be realized.

  In addition, it is preferable that the inner rectangle D is a square because the bottom of the hollow solid is a square when the hollow solid electromagnetic wave absorber is formed, and it is easy to install regularly on the wall or ceiling surface of the anechoic chamber.

  Next, FIG. 3 shows one of the four corners of the rectangle A. In FIG. 3, one of the sides generated by cutting out a right triangle from the rectangle A is defined as So, the two vertices sandwiching this are defined as P1 and P2, and the closest end point and vertex among the two end points of the straight line F The straight lines connecting P1 and P2 are L1 and L2, respectively. Further, an intersection Q between a straight line Kα orthogonal to the side of the rectangle A including the vertex P1 and passing through the straight line P1, and a straight line Kβ orthogonal to the side of the rectangle A including the vertex P2 and passing through the straight line P2; Let N be the straight line connecting the end points closest to each other. Further, a vertex generated when an isosceles triangle having the base So as a base is cut out or added is defined as P3, a side of the dodecagon C connecting the vertices P3 and P1 is connected with Sd1, and vertices P3 and P2 are connected. Let the side of the dodecagon C be Sd2. Furthermore, an angle formed by the straight line L1 and the side Sd1 is θ1, and an angle formed by the straight line L2 and the side Sd2 is θ2. At this time, it is preferable that all the angles θ1 and θ2 included in the dodecagon C are within the range of the following expression.

  FIG. 4 shows an example of a radio wave absorber made by bending the radio wave absorber sheet material of FIG. If the angles θ1 and θ2 are within this range, the bottom portion of the folded triangle E formed inside the hollow solid body can be stored without protruding from the hollow solid bottom surface when the bottom surface is a rectangular hollow solid wave absorber. In addition, it is possible to obtain sufficient absorption performance, particularly excellent absorption performance in a high frequency band of several GHz to several tens GHz.

  In addition, although the sheet | seat material for electromagnetic wave absorbers of this invention has the above-mentioned structure, as long as the effect of invention is not impaired, a part of sheet material is further cut off from a part of edge | side, A structure with an external structure can be used. A hole can be made in a part of the sheet material. Furthermore, a part or all of the sides can be formed into a waveform.

  FIG. 5 shows an example of the radio wave absorber of the present invention. The four valley fold lines (Ma, Mb, Mc, Md) and the eight mountain fold lines (La1, La2, Lb1, Lb2, Lc1, Lc2, Ld1) of the sheet material for a radio wave absorber of the present invention in FIG. , Ld2) are folded so that four pairs (La1, La2), (Lb1, Lb2), (Lc1, Lc2), and (Ld1, Ld2) overlap with two mountain fold lines adjacent to the valley fold line. The straight line F is also folded in a mountain fold so that the bottom surface having four folded triangles E inside the hollow is a rectangular hollow solid. Since this radio wave absorber is hollow, it is extremely lightweight. In addition to the radio wave absorption by the folded triangle itself, the structure having the folded triangle can absorb radio waves by multiple reflections with the outer shell part forming the hollow solid, and has a high absorption performance, particularly from several GHz to Excellent absorption performance can be obtained in a high frequency band of several tens of GHz.

  Further, it is preferable that all the four folded triangles E are perpendicular to the bottom surface of the hollow solid because radio waves can be absorbed more effectively inside the hollow solid. FIG. 6 shows an example in which the folded triangle E is perpendicular to the bottom surface of the hollow solid. FIG. 6A shows an example of a radio wave absorber in which the folded triangle E is perpendicular to the bottom surface of the hollow solid body and the bottom side of the folded triangle E is on the bottom surface of the hollow solid body. In FIG. 6B, one of the bottom sides of the folded triangle E is separated from the bottom surface of the hollow solid, but there is no problem with this structure.

  When the sheet material for a radio wave absorber according to the present invention is folded to form a hollow solid wave absorber having a rectangular bottom, any method can be used for retaining and fixing the hollow solid shape. Such an example is shown in FIG. The portion forming the folded triangle E as shown in FIG. 7 (a) is bonded with a double-sided tape (shaded portion in the figure), or the side portion of the square weight is attached to the tape (in the figure as shown in FIG. 7 (b)). 7 (c), or a hole is formed in a portion where the folded triangle E is formed as shown in FIG. 7 (c), and the overlapped hole is fastened with a pin or a string, as shown in FIG. 7 (d). Various methods can be selected, such as using a member comprising a part surrounding the outer periphery of the radio wave absorber and a part having a slit for fixing the folded triangle E.

Examples of the present invention will be described below. The performance values shown in the examples were measured by the following method.
<Radio wave absorption amount of radio wave absorber>
As shown in FIG. 8, using two antennas, a target is irradiated with radio waves from an incident antenna, and a reflected wave from the target is received by a receiving antenna to measure a reflection level. First, using a vector network analyzer (model: N5230, manufactured by Agilent Technologies), a reflection level when a radio wave is vertically applied to an aluminum plate 60 cm long × 60 cm wide × 5 mm thick as a blank is measured. Next, a radio wave absorber is placed on the aluminum plate, and the reflection level is measured. The radio wave absorption amount of the radio wave absorber is obtained from these measured values by the following formula.

Radio wave absorption (dB) = Radio wave absorber reflection level (dB) −Aluminum plate reflection level (dB)
<Complex relative permittivity of sheet material for radio wave absorber>
Measurement is performed using a vector network analyzer and a coaxial waveguide (outer diameter 39 mm, inner diameter 17 mm). The S11 (complex reflectivity) and S21 (complex transmissivity) parameters were measured in a state where a sheet material sample for an electromagnetic wave absorber having a donut shape having an outer diameter of 39 mm × an inner diameter of 17 mm was set in the coaxial waveguide. The complex dielectric constant is obtained from the value of.
[Example 1]
(Radio wave absorber sheet material)
A carbon fiber having a fiber length of 6 mm, a glass fiber having a fiber length of 6 mm, and a meta-aramid pulp having an average fiber length of 2 mm are mixed with water at a ratio of 0.8% by weight, 30% by weight, and 69.2% by weight to form a slurry. The slurry was poured into a flat surface, dehydrated and dried to obtain flame retardant paper A having a thickness of 120 μm and a basis weight of 100 g / m ² . Next, a flame retardant paper B containing no electrical loss material having a thickness of 120 μm and a basis weight of 100 g / m ^{2 in} the same manner as described above except that carbon fiber is removed from the above formulation and mixed with water to form a slurry. Got.

  Subsequently, the flame retardant paper A 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 a flat flame retardant paper B to obtain a thickness of 1. A 3 mm cardboard sheet was obtained.

  This cardboard sheet was cut into a dodecagon C shape shown in FIG. 9A by a Thomson cutter. At the time of this cutting, a mountain fold line and a valley fold line were also put in the corrugated cardboard sheet to obtain a sheet material for a radio wave absorber.

As a result of measuring the complex dielectric constant at 1 GHz of the sheet material for radio wave absorber, the real part εr ′ = 11 and the imaginary part εr ″ = 7.5.
(Radio wave absorber)
This radio wave absorber sheet material is folded along a mountain fold line and a valley fold line, and a kraft tape is applied to the side of the square weight as shown in FIG. 7B, and the folded triangle shown in FIG. A hollow three-dimensional wave absorber having a square E bottom was obtained. Further, the folded triangle E was fixed with craft tape so as to be perpendicular to the bottom surface of the hollow solid.

Four of these radio wave absorbers were prepared and mounted on an aluminum plate 60 cm long x 60 cm long x 5 mm thick, and the amount of radio wave absorption was measured. FIG. 10 shows an overhead view when four radio wave absorbers are mounted on an aluminum plate. The radio wave absorbers are arranged so that the upper sides of the hollow solid are inclined by 90 ° with respect to each other. At this time, all the four folded triangles E were fixed so as to be perpendicular to the bottom surface. The results are shown in Table 1, and it was found that they have a high radio wave absorption of 20 to 30 dB in the frequency band of 500 MHz to 6 GHz.
[Example 2]
(Radio wave absorber sheet material)
A radio wave absorbing sheet material was obtained in the same manner as in Example 1 except that carbon fiber mixed with the flame retardant paper A had a fiber length of 3 mm.

As a result of measuring the complex dielectric constant at 1 GHz of the sheet material for radio wave absorber, the real part εr ′ = 6 and the imaginary part εr ″ = 3.
(Radio wave absorber)
A radio wave absorber was obtained in the same manner as in Example 1. Further, the amount of radio wave absorption was measured in the same manner as in Example 1. The results are shown in Table 1. It was found that although the radio wave absorption amount was slightly reduced to 15 dB at frequencies of 4 and 6 GHz, the radio wave absorption amount was high at 20 dB from 500 MHz to 2 GHz.
[Example 3]
(Radio wave absorber sheet material)
A radio wave absorbing sheet material was obtained in the same manner as in Example 1 except that the mixing ratio of the carbon fiber of the flame retardant paper A and the meta-aramid pulp was 2 wt% and 68 wt%, respectively.

As a result of measuring the complex dielectric constant at 1 GHz of the sheet material for radio wave absorber, the real part εr ′ = 33 and the imaginary part εr ″ = 27.
(Radio wave absorber)
A radio wave absorber was obtained in the same manner as in Example 1. Further, the amount of radio wave absorption was measured in the same manner as in Example 1. The results are shown in Table 1. It was found that although the radio wave absorption amount was reduced to 10 to 15 dB at frequencies of 500 MHz and 2 GHz, the radio wave absorption amount was 30 to 45 dB at 4 to 6 GHz.
[Example 4]
(Radio wave absorber sheet material)
A radio wave absorbing sheet material was obtained in the same manner as in Example 1 except that the cut shape of the corrugated cardboard sheet was changed to a dodecagon C shape of the radio wave absorbing sheet material shown in FIG.
(Radio wave absorber)
The radio wave absorbing sheet material shown in FIG. 12 was assembled in the same manner as in Example 1 to obtain a radio wave absorber. Further, the amount of radio wave absorption was measured in the same manner as in Example 1. The results are shown in Table 1. It was found that although the radio wave absorption amount was slightly reduced to 15 dB at a frequency of 500 MHz, the radio wave absorption amount was 20 dB at 2 to 6 GHz.
[Example 5]
(Radio wave absorber sheet material)
A radio wave absorbing sheet material was obtained in the same manner as in Example 1 except that the cut shape of the corrugated cardboard sheet was changed to the shape of the dodecagon C of the radio wave absorbing sheet material shown in FIG.
(Radio wave absorber)
The radio wave absorbing sheet material shown in FIG. 13 was assembled in the same manner as in Example 1 to obtain a radio wave absorber. Further, the amount of radio wave absorption was measured in the same manner as in Example 1. The results are shown in Table 1. Although the amount of radio wave absorption is slightly lower than that of Example 1 or Example 4, it has a sufficient amount of radio wave absorption of 15 to 25 dB in the frequency band of 500 MHz to 6 GHz. all right.
[Comparative Example 1]
(Radio wave absorber sheet material)
A corrugated cardboard sheet produced by the same method as in Example 1 was cut with a Thomson cutter into the shape shown in FIG. At the time of this cutting, a mountain fold line was also placed on the corrugated cardboard sheet to obtain a sheet material for a radio wave absorber.
(Radio wave absorber)
The sheet material for an electromagnetic wave absorber is bent along a mountain fold line so as to form a hollow quadrangular pyramid, and the side portions of the hollow quadrangular pyramids that are not connected are attached with craft tape, and the folded triangle E shown in FIG. A hollow three-dimensional radio wave absorber having a square bottom surface with no square was obtained.

  Four of these radio wave absorbers were prepared and mounted on an aluminum plate 60 cm long x 60 cm long x 5 mm thick, and the amount of radio wave absorption was measured. Similar to Example 1, as shown in FIG. 10, the adjacent solid wave absorbers were arranged so that the upper sides of the hollow solid were inclined by 90 °. The results are shown in Table 1. In the frequency band of 500 MHz to 6 GHz, the radio wave absorption amount is about 10 to 20 dB, and it was found that the effect was small compared to the example having the folded triangle E of the present invention.

  The present invention is not limited to use in an anechoic chamber, but can also be applied as a radio wave absorber for improving the radio wave environment in various wireless communication systems.

A rectangle A
B Octagon B
C dodecagon C (sheet material for electromagnetic wave absorber)
D Internal rectangle D
E Folding triangle E

Claims (9)

A dodecagonal C wave absorber sheet material,
The octagon B resulting from cutting out right triangles from the four corners of the rectangle A has straight lines F parallel to either of the two sides of the original rectangle A inside the octagon B,
When two straight lines connecting two vertices generated by cutting out one right triangle and the two closest end points of the straight line F are set as one set, each of the four sets is each set. The two straight lines are the same length,
And the octagon B is a set of two opposite sides derived from the side of the original rectangle A, and the two sides of each set have the same length.
The dodecagon C is cut out of the octagon B from the four sides generated by cutting out the right triangle in the octagon B, or added to the octagon B. Shape,
In the dodecagon C, the eight straight lines connecting the eight vertices of the original octagon B and the two end points of the straight line F inside the octagon B are all mountain fold lines. Yes,
In addition, four straight lines connecting four vertices generated by cutting an isosceles triangle from the octagon B or adding it to the octagon B and the two end points closest to the straight line F are connected. Is the valley fold line,
A sheet material for a radio wave absorber , wherein the straight line F is a mountain fold line . The straight line F passes through two vertices that are not adjacent to each other among the eight vertices of the octagon B resulting from cutting out a right triangle from the four corners of the rectangle A, and is orthogonal to two opposite sides derived from the sides of the rectangle A. The sheet material for a radio wave absorber according to claim 1, wherein the sheet material is inside an internal rectangle D surrounded by four straight lines. The sheet material for a radio wave absorber according to claim 1 or 2 , wherein the midpoint of the straight line F is at the center of the rectangle A. An interior formed by four straight lines passing through two vertices that are not adjacent to each other among the eight vertices of the octagon B resulting from cutting out a right triangle from the four corners of the rectangle A and orthogonal to two opposite sides of the rectangle A The sheet material for a radio wave absorber according to any one of claims 1 to 3 , wherein the rectangle D is a square. One of the sides generated by cutting out a right triangle from the rectangle A is defined as So, and the two vertices sandwiching the side are defined as P1 and P2, and the two closest end points of the straight line F and the vertex P1 or P2 Let L1 and L2 be the straight lines connecting
Of the two end points of the straight line F, the intersection point Q of the straight line orthogonal to the side of the rectangle A including the vertex P1 and passing through the straight line P1 and the straight line orthogonal to the side of the rectangle A including the vertex P2 and passing through the straight line P2 Let N be the straight line connecting the nearest end points,
The vertex formed when notching or adding an isosceles triangle with the side So as the base is P3, the angle formed by the side of the dodecagon C connecting the vertices P3 and P1 and the straight line L1 is θ1, and the vertex When the angle formed by the side of the dodecagon C connecting P3 and P2 and the straight line L2 is θ2, all the angles θ1 and θ2 included in the dodecagon C are within the range of the following expression. The sheet | seat material for electromagnetic wave absorbers in any one of Claims 1-4 characterized by these.

The sheet material for a radio wave absorber according to any one of claims 1 to 5 , wherein the thickness is in a range of 0.2 to 10 mm. Complex relative permittivity at 1GHz of the wave absorber sheet material, any one of the preceding claims, characterized in that the real part .epsilon.r 'is 5-30, and the imaginary part .epsilon.r "is in the range of 2 to 25 The sheet | seat material for electromagnetic wave absorbers of description. The valley fold line and the mountain fold line of the sheet material for a radio wave absorber according to any one of claims 1 to 7 are folded so that two mountain fold lines adjacent to the valley fold line overlap each other.
The straight line F is also folded in a mountain fold, and has four folded triangles E inside.
A radio wave absorber characterized in that the bottom is a rectangular solid with a rectangular shape. 9. The radio wave absorber according to claim 8, wherein each of the four folded triangles E is perpendicular to the bottom surface of the hollow solid body.

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