JP2007294921A - Electromagnetic wave absorber, building material, electromagnetic wave darkroom structure, transmission/reception direction control method, and electromagnetic wave absorbing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic wave absorber which improves an electromagnetic wave absorption volume. <P>SOLUTION: The electromagnetic wave absorber is composed of a lamination of a pattern layer 5 and a loss layer. The pattern layer 5 has patterns 12 formed thereon, which are made of a conductive material, such as metal. When the area of the entire part of the pattern layer is 1, the part where the patterns 12 are formed has an area of 0.6 or more. The width of a gap formed between the patterns 12 changes in size consecutively with regard to the direction of an extension of the gap. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an electromagnetic wave absorber that captures and absorbs electromagnetic waves, and further relates to a building material and an electromagnetic wave darkroom structure including an electromagnetic wave absorber, a transmission / reception direction control method using the electromagnetic wave absorber, and an electromagnetic wave absorption method.

A communication system that constructs a wireless local area network (LAN) using microwaves and wirelessly communicates between computers as communication terminal devices is used. FWA (Fixed
2. Description of the Related Art A communication system in which a communication terminal device is connected to a wide area network called “Wireless Access” so that wireless communication can be performed is used. Furthermore, a communication system that constructs a WPAN (Wireless Personal Area Network) that performs wireless communication according to Bluetooth, which is a short-range wireless communication standard, and performs wireless communication between communication terminal devices is used. Furthermore, a communication system using a cellular phone device that constructs a wireless LAN called a VoWLAN (Voice over Wireless Local Area Network) and makes a voice call has been proposed. As one of communication systems, an RFID (Radio Frequency Identification) system using an electromagnetic wave in the UHF band has been put into practical use. Although the UHF band has not been standardized internationally, the RFID system using electromagnetic waves in the UHF band can achieve a communication distance of 7m with a passive tag and 100m with an active tag, product management, logistics management, and product traceability. Applications are expanded in a wide range of applications such as security applications.

  When an apparatus using electromagnetic waves such as a microwave oven and an anti-theft device by wireless communication is used in an environment where such a communication system for wireless communication is built close to the communication system, an electromagnetic wave called other-wave interference is used. May cause interference. In addition to this, there is a risk of erroneous transmission due to reflected waves called multipath, self-interference, and the like. As a result, a decrease in transmission speed between communication terminal devices, an increase in BER (Bit Error Rate), generation of a null point in the communication area, that is, deterioration of the communication environment, and an error in information transmission occur. In addition, there is concern about the influence on electronic devices provided around the communication system, and in the worst case, the electronic devices may malfunction.

  In order to solve these problems, an electromagnetic wave absorber including a pattern layer having a conductive pattern is used. An electromagnetic wave absorber makes an electroconductive pattern function as a receiving antenna to capture an electromagnetic wave, and the reflected electromagnetic wave is reduced by interfering the captured electromagnetic wave so as to be attenuated or canceled by the conductive pattern and the loss layer. It is configured.

As an electromagnetic wave absorber, for example, there is a radio wave reflection preventing body disclosed in Patent Document 1. The radio wave antireflection body of Patent Document 1 includes a metal radio wave reflector layer, a resin layer containing at least one powder selected from ferrite and carbon having a particle diameter of 100 μm or less, and a plurality of geometric patterns. A structure formed by sequentially laminating pattern coating layers having a volume resistivity of 10 ⁻³ to 10 ⁵ Ω · cm and a film thickness of 5 to 500 μm, which are arranged so as not to contact each other and contain metal powder. Have. The ratio of the non-coating part / coating part in the pattern of the pattern coating layer is 0.05 to 20, and the pattern coating is a checkered pattern, a polygon or a circle.

Moreover, as an electromagnetic wave absorber, there exists an electromagnetic wave reflection prevention body shown by patent document 2, for example. The radio wave prevention body of Patent Document 2 is a pattern resin that is formed in a geometric pattern and has a volume resistivity of 10 ³ Ω · cm or less, a support layer, and 25 to 70% by volume of voids. It is the structure provided with the laminated body formed by laminating | stacking a layer and a support layer one by one.

Japanese Patent No. 3209456 (JP-A-6-140787) JP-A-6-252582

  In the radio wave antireflection body shown in Patent Document 1, the pattern coating film layer is formed so that the ratio of the non-coating part / coating part in the pattern is 0.05 to 20, and the radio wave shown in Patent Document 2 In the antireflection body, the pattern resin layer is formed so that 25 to 70% by volume is a gap. As described above, the radio wave antireflection bodies of Patent Documents 1 and 2 are configured in consideration of what ratio should be formed in this case, but it is desired to further improve the amount of electromagnetic wave absorption. ing.

  The objective of this invention is providing the electromagnetic wave absorber which can improve the absorbed amount of electromagnetic waves.

The present invention provides a pattern layer on which a conductive pattern made of a conductive material is formed. When the area of the entire pattern layer region is 1, the area of the region on which the conductive pattern is formed is 0.6 or more. A pattern layer having an area ratio of
An electromagnetic wave absorber comprising a loss layer having a portion made of a material that is at least one of a magnetic loss material and a dielectric loss material.

The present invention also provides a pattern layer in which a plurality of conductive patterns made of a conductive material are formed, and at least some of the gaps formed between the conductive patterns have a width dimension of the gap. A pattern layer that continuously changes in the extending direction of
An electromagnetic wave absorber comprising a loss layer having a portion made of a material that is at least one of a magnetic loss material and a dielectric loss material.

  Further, according to the present invention, the gap in which the width dimension continuously changes has at least two approach parts having a small width dimension with an interval in the extending direction of the gap, and approaches between the approach parts. It has the separated part which has a larger width dimension than a part, It is characterized by the above-mentioned.

  Further, the invention is characterized in that at least a part of each conductive pattern has an outer shape including a curved portion.

  According to the present invention, the loss layer has a magnetic layer made of a material containing at least a magnetic substance.

In the present invention, the loss layer is
A magnetic layer made of a material containing at least a magnetic substance;
And a dielectric layer made of a material containing at least a dielectric.

  Further, the present invention is characterized in that the bandwidth of the frequency band in which the electromagnetic wave absorption amount is 15 dB or more is 70 MHz or more.

The present invention also provides an electromagnetic wave absorber for absorbing electromagnetic waves in the UHF band,
The total thickness dimension is 15 mm or less.

The present invention is also an electromagnetic wave absorber for absorbing electromagnetic waves in the 2.4 GHz band,
The total thickness dimension is 5 mm or less.

  In addition, the present invention is characterized by having an electroconductive reflection layer and having an electromagnetic wave shielding property for shielding electromagnetic waves.

In addition, the present invention is characterized by having flame retardancy, quasi-incombustibility or incombustibility.
Moreover, this invention is a building material provided with the said electromagnetic wave absorber.

Moreover, this invention is an electromagnetic wave darkroom structure using the said electromagnetic wave absorber.
The present invention also provides an RFID communication system using the electromagnetic wave absorber.

Moreover, this invention is a transmission / reception direction control method which arrange | positions the said electromagnetic wave absorber around an antenna, and controls the transmission / reception direction of an electromagnetic wave.
Moreover, this invention is an electromagnetic wave absorption method by using the said electromagnetic wave absorber.

  According to the present invention, an electromagnetic wave can be absorbed by causing the conductive pattern of the pattern layer to function as a receiving antenna, capturing an electromagnetic wave, and losing the electromagnetic wave energy in the loss layer. The pattern layer has an area ratio in which the area of the region where the conductive pattern is formed is 0.6 or more, where the area of the entire pattern layer region is 1. By forming the pattern layer in the area ratio within the above range, it is possible to increase the amount of electromagnetic wave absorption and increase the bandwidth of the frequency band where the electromagnetic wave absorption amount is large.

  Moreover, according to this invention, electromagnetic waves can be absorbed by making the electroconductive pattern of a pattern layer function as a receiving antenna, catching electromagnetic waves, and losing the electromagnetic wave energy in a loss layer. The pattern layer has a configuration in which the width dimension of at least a part of the gaps formed between the conductive patterns continuously changes with respect to the extending direction of the gaps. By forming the gaps between the conductive patterns to be continuous in this way, the amount of electromagnetic wave absorption can be increased compared to a configuration in which the gaps between the conductive patterns have a uniform width. Can do.

  Further, according to the present invention, the gap in which the width dimension continuously changes has at least two approach parts having a small width dimension and a separated part having a width dimension larger than the approach part between these approach parts. . Thus, by changing the degree of interference (coupling) between adjacent conductive patterns and making the change dense, it is possible to obtain a wide range of resonance sites according to the frequency. Therefore, it is possible to increase the bandwidth of the frequency band in which the electromagnetic wave absorption amount is large.

  According to the invention, at least a part of the conductive pattern has an outer shape including a curved portion. As a result, it is possible to improve the polarization characteristics by suppressing the frequency shift at which the amount of absorption in the polarization direction of the electromagnetic wave reaches the peak value.

  According to the present invention, since the loss layer has a magnetic layer made of a material containing at least a magnetic substance, the loss amount of electromagnetic wave energy captured by the conductive line pattern of the pattern layer is increased, and the electromagnetic wave is absorbed with a large absorption amount. Can be absorbed.

  According to the invention, the loss layer has a magnetic layer made of a material containing at least a magnetic substance and a dielectric layer made of a dielectric made of a material containing at least a dielectric. Since both the magnetic layer and the dielectric layer lose the electromagnetic wave energy captured by the conductive line pattern of the pattern layer, the loss amount can be increased and the electromagnetic wave can be absorbed with a large absorption amount.

  Further, according to the present invention, the bandwidth of the frequency band in which the electromagnetic wave absorption amount is 15 dB or more is 70 MHz or more. As described above, an electromagnetic wave absorber having an excellent absorption characteristic with a large frequency band with a large amount of electromagnetic wave absorption can be realized.

  Further, according to the present invention, the conductive pattern functions as a receiving antenna with respect to the UHF band electromagnetic wave, and can absorb the UHF band electromagnetic wave with a large absorption amount. Moreover, the total thickness dimension is 15 mm or less, and a thin electromagnetic wave absorber can be realized.

  Further, according to the present invention, the conductive pattern functions as a receiving antenna with respect to the 2.4 GHz band electromagnetic wave, and can absorb the 2.4 GHz band electromagnetic wave with a large absorption amount. Moreover, the total thickness dimension is 5 mm or less, and a thin electromagnetic wave absorber can be realized. The 2.4 GHz band is a frequency band of 2.4 GHz or more and less than 2.5 GHz.

  Further, according to the present invention, the electromagnetic wave absorber that has a conductive reflection layer and shields the electromagnetic wave can be realized. Therefore, a highly convenient electromagnetic wave absorber can be realized.

  Further, according to the present invention, the electromagnetic wave absorber has flame retardancy, quasi-incombustibility or non-flammability, and is suitably used for applications requiring flame retardancy, quasi-incombustibility or incombustibility, for example, building materials. be able to.

  Moreover, according to this invention, the outstanding building material is realizable using the above-mentioned outstanding electromagnetic wave absorber.

  In addition, according to the present invention, an electromagnetic wave anechoic chamber structure called an anechoic chamber or an anechoic box that is lightweight and excellent in handling properties can be realized using the above-described excellent electromagnetic wave absorber.

  Further, according to the present invention, an RFID communication system in a suitable communication environment can be realized by arranging the above-described excellent electromagnetic wave absorber.

  Further, according to the present invention, by arranging the above-described excellent electromagnetic wave absorber around the antenna, the transmission / reception direction of radio waves can be controlled.

  Moreover, according to this invention, electromagnetic waves can be suitably absorbed by using the above-mentioned excellent electromagnetic wave absorber.

  FIG. 1 is a front view showing a part of a pattern layer 5 of an electromagnetic wave absorber 1 according to an embodiment of the present invention. FIG. 2 is a cross-sectional view showing a part of the electromagnetic wave absorber 1. The electromagnetic wave absorber 1 is used, for example, to improve an electromagnetic environment in a space such as an office, and absorbs the electromagnetic wave in the space. The electromagnetic wave absorber 1 includes a pattern layer 5, a loss layer 7, and a conductive reflective layer (hereinafter referred to as “reflective layer”) 2 in the thickness direction in this order from the electromagnetic wave incident side which is the upper side in FIG. It is the structure laminated | stacked on. The electromagnetic wave absorber 1 has flexibility and can be bent. The electromagnetic wave absorber 1 may have a curved surface shape in a natural state where no external force acts, but in the present embodiment, the electromagnetic wave absorber 1 has a planar shape, a so-called flat plate shape.

  The pattern layer 5 has a plurality of conductive patterns (hereinafter referred to as “patterns”) 12. Each pattern 12 has a resonance frequency that depends on the shape and dimensions, and functions as a receiving antenna that receives electromagnetic waves having the resonance frequency. The pattern layer 5 is configured by forming each pattern 12 on the surface of the plate-like substrate 11 on the electromagnetic wave incident side (hereinafter referred to as “first substrate surface”). The surface of the first base material is a surface on one side in the thickness direction of the plate-like base material 11. In FIG. 1, each pattern 12 is indicated by hatching for easy understanding.

  The plate-like base material 11 is made of, for example, a dielectric that is a synthetic resin, and this plate-like base material 11 is also a dielectric material and a dielectric loss material. As a material of the plate-like substrate 11, for example, polyethylene terephthalate (PET), paper, resin, wood, glass, or the like can be used. Each pattern 12 is made of a conductive material such as metal. As a material of each pattern 12, for example, gold, platinum, silver, nickel, chromium, aluminum, copper, zinc, lead, tungsten and iron can be used. In addition, a conductive oxide such as zinc oxide or indium oxide can be used. Each pattern 12 is formed on the plate-like substrate 11 by, for example, vapor deposition, plating, metal foil sticking, etching process thereof, or screen printing.

  Each pattern 12 is a polygon called a so-called star shape. Each pattern 12 is inward by bending each side at its midpoint with each vertex of a square (hereinafter referred to as “first basic square”) 50 as shown in phantom lines in FIG. 1 fixed. The shape is deformed so as to be concave, and is an octagon. Each pattern 12 is rotationally symmetric four times, is point symmetric with respect to the center of the first base square 50, is line symmetric with respect to the two diagonal lines of the first base square 50, and passes through the center of the first base square 50. Each line is symmetrical with respect to two straight lines parallel to either side. In each pattern 12, four angles of the first angle θ1 that is an acute angle and four angles of the second angle θ2 that is an obtuse angle are alternately arranged in the circumferential direction. The sum of the first angle θ1 and the second angle θ2 is 270 degrees. The first angle θ1 is not less than 30 degrees and not more than 85 degrees, for example.

  Each pattern 12 is provided at an interval. Each pattern 12 is formed by regularly arranging and arranging in a matrix in the x direction and the y direction, with each side of the first basic square 50 being arranged in parallel with either the x direction or the y direction. The x direction and the y direction are directions along the surface of the first base material of the plate-like base material 11. In a state where the electromagnetic wave absorber 1 is planar including a natural state (hereinafter referred to as “reference state”), the first substrate surface of the plate-like substrate 11 is planar, and the x direction and the y direction are perpendicular to each other. .

  The pattern layer 5 has an area ratio in which the area of the region in which each pattern 12 is formed (hereinafter referred to as “pattern area”) is 0.6 or more when the area of the entire pattern layer region is 1. The area of the entire pattern layer area corresponds to the area of the surface of the first base material of the plate-like base material 11, and each pattern 12 is formed in a region having an area occupying 60% or more of the area. Therefore, the value obtained by dividing the pattern area by the area of the first base material surface where each pattern 12 is not formed (hereinafter referred to as “non-pattern area”) is 1.5 or more. Each pattern 12 has the same pattern dimension d1x in the x direction and pattern dimension d1y in the y direction, for example, 1 mm or more and 100 mm or less. Each pattern 12 has the same constriction part dimension d2x in the x direction and the constriction part dimension d2y in the y direction, for example, 0.1 mm or more and 99 mm or less. Each pattern dimension d1x, d1y is a dimension between vertices of corners having two adjacent first angles θ1, and each pattern dimension d1x, d1y corresponds to the length of one side of the first basic square 50. Each constriction part dimension d2x, d2y is a dimension between the vertexes of the corners having two second angles θ2 facing each other across the center of the first basic square 50.

  The width dimension ex of the gap between two patterns 12 adjacent in the x direction (hereinafter referred to as “x direction star gap”) is a gap between the minimum width dimension exmin and the maximum width dimension exmax. It changes continuously in the extending direction. The minimum width dimension exmin in the x direction is a dimension between vertices having the first angle θ1 of each pattern 12, and is, for example, 0.01 mm or more and 10 mm or less. The maximum width dimension exmax in the x direction is a dimension between vertices having the second angle θ2 of each pattern 12, and is, for example, not less than 0.01 mm and not more than 70 mm. The width dimension ey of the gap between the two patterns 12 adjacent in the y direction (hereinafter referred to as “y direction star gap”) is the gap between the minimum width dimension eymin and the maximum width dimension eymax. It changes continuously in the extending direction. The minimum width dimension eymin in the y direction is a dimension between vertices having the first angle θ1 of each pattern 12, and is the same as the minimum width dimension exmin in the x direction. The maximum width dimension eymax in the y direction is a dimension between vertices having the second angle θ2 of each pattern 12, and is the same as the maximum width dimension exmax in the x direction.

Thus, the width dimensions ex and ey of the gaps between the patterns 12 continuously change in the extending direction of the gaps. The change rate Δex of the width dimension ex between the x-direction star gaps and the change rate Δey of the width dimension ey between the y-direction star gaps are the same, for example, 0.01 or more and 9.9 or less. The change rate Δex of the width dimension ex between the x-direction star gaps is a change amount of the width dimension ex per unit dimension in the y direction between the x-direction star gaps. The change rate Δey of the width dimension ey between the y-direction star gaps is a change amount of the width dimension ey per unit dimension in the x direction between the y-direction star gaps. In the present embodiment, the change rates Δex and Δey are uniform.
The change rates Δex and Δey are expressed by the following equations (1) and (2), respectively.

  The aforementioned dimensions d1x, d1y; d2x, d2y; ex, ey; exmin, exmax; eymin, eymax; Δex, Δey and the angles θ1, θ2 with respect to each pattern 12 are the electromagnetic waves to be absorbed by the electromagnetic wave absorber 1. It is determined according to the frequency. Further, each pattern 12 is not a closed loop linear shape (strip shape) extending along the outer peripheral edge of the above-described shape, but a planar pattern in which an inner region portion is also painted. Therefore, a capacitor can be formed between the conductive reflective layer 2.

  The loss layer 7 includes a portion made of a material that is at least one of a magnetic loss material having a complex relative permeability (μ ′, μ ″) and a dielectric loss material having a complex relative permittivity (ε ′, ε ″). It is a layer having. The loss layer 7 may be a layer having only a portion made of a material that is a magnetic loss material, a layer having only a portion made of a material that is a dielectric loss material, or a magnetic loss material. It may be a layer having a portion made of a certain material and a portion made of a material that is a dielectric loss material, or may be a layer having a portion made of a material that is a magnetic loss material and is a dielectric loss material.

  In the present embodiment, the loss layer 7 has an electromagnetic wave absorption layer (hereinafter referred to as “absorption layer”) 4 and a dielectric layer 3, and is laminated in the order of the absorption layer 4 and the dielectric layer 3 from the electromagnetic wave incident side. Has been. In the present embodiment, the absorption layer 4 is made of a material that is a magnetic loss material and a dielectric loss material, and the dielectric layer 3 is made of a dielectric loss material.

  The absorbing layer 4 can be made of an insulating magnetic material. A sintered body such as ferrite, a metal oxide film, a metal polymer film, a composite of a binder and a magnetic material, and the like can be used. Such a material is a magnetic loss material and a dielectric loss material. The absorption layer 4 may be composed of only an organic polymer and a magnetic material, or other materials such as graphite and carbon fiber may be added. Thus, the absorption layer 4 is a layer made of a material containing at least a magnetic material, and corresponds to a magnetic material layer.

  The absorption layer 4 is made of, for example, a magnetic material that is a composite including a binder and soft magnetic powder, and has an electromagnetic wave absorption effect. Specifically, the following materials can be used.

(Binder)
Various organic polymer materials can be used as the binder, and examples thereof include polymer materials such as rubber, thermoplastic elastomer, and various plastics. Examples of the rubber include natural rubber, isoprene rubber, butadiene rubber, styrene-butadiene rubber, ethylene-propylene rubber, ethylene-propylene rubber, ethylene-propylene-diene rubber (EPDM rubber), ethylene-vinyl acetate rubber, and butyl rubber. , Synthetic rubbers such as halogenated butyl rubber, chloroprene rubber, nitrile rubber, acrylic rubber, ethylene acrylic rubber, epichlorohydrin rubber, fluoro rubber, urethane rubber, silicon rubber, chlorinated polyethylene rubber, hydrogenated nitrile rubber (HNBR) alone , Derivatives thereof, or those modified by various modification treatments.

  These rubbers can be used alone or in combination. In addition to vulcanizing agents, rubbers may be appropriately mixed with vulcanization accelerators, anti-aging agents, softeners, plasticizers, fillers, coloring agents, and the like that have been conventionally used as rubber compounding agents. it can. In addition to these, arbitrary additives can be used. For example, a predetermined amount of dielectric (carbon black, graphite, titanium oxide, etc.) is used to control the dielectric constant and conductivity according to impedance matching to unnecessary electromagnetic waves generated in the electronic equipment used and the temperature environment. Material design can be added. Further, processing aids (lubricants, dispersants) may be appropriately selected and added.

  Examples of thermoplastic elastomers include chlorinated polyethylenes such as chlorinated polyethylene, ethylene copolymers, acrylics, ethylene acrylic copolymers, urethanes, esters, silicones, styrenes, amides, olefins, etc. Various thermoplastic elastomers and their derivatives are mentioned.

  Further, various plastics include, for example, chlorine resins such as polyethylene, polypropylene, AS resin, ABS resin, polystyrene, polyvinyl chloride, and polyvinylidene chloride; polyvinyl acetate, ethylene-vinyl acetate copolymer, fluororesin, and silicone resin. , Thermoplastic resins such as acrylic resins, nylon, polycarbonate, polyethylene terephthalate, alkyd resins, unsaturated polyesters, polysulfones, urethane resins, phenol resins, urea resins, epoxy resins, etc., and their derivatives. . As these binders, low molecular weight oligomer types and liquid types can be used. Any material can be selected without limitation to organic materials as long as it becomes a sheet after molding due to heat, pressure, ultraviolet light, curing agent, moisture, time, force, load, and the like.

  In particular, in the present invention, the binder is preferably at least one selected from vinyl chloride resins, urethane resins, chlorinated polyethylene resins, styrene-butadiene-styrene (SBS) copolymers, and derivatives thereof.

(Soft magnetic powder)
Examples of the soft magnetic powder include magnetic stainless steel (Fe—Cr—Al—Si alloy), sendust (Fe—Si—Al alloy), permalloy (Fe—Ni alloy), silicon copper (Fe—Cu—Si alloy), Fe -Si alloy, Fe-Si-B (-Cu-Nb) alloy, Fe-Ni-Cr-Si alloy, Fe-Si-Cr alloy, Fe-Si-Al-Ni-Cr alloy Fe-based alloy, etc. It is done. Further, ferrite or pure iron particles may be used. Examples of ferrite include Mn—Zn ferrite, Ni—Zn ferrite, Mn—Mg ferrite, Mn ferrite, Cu—Zn ferrite, Cu—Mg—Zn ferrite, Ba—Ni—Co ferrite and other soft ferrites, or permanent magnet materials. Hard ferrite that is Examples of the pure iron particles include carbonyl iron powder. These metals may or may not be in an amorphous state, and may be a mixture of amorphous and crystalline materials.

  The shape (spherical shape, flat shape, fibrous shape, etc.) of the soft magnetic powder is not particularly limited, but it is preferable to use a spherical shape, a substantially spherical shape or a lump shape because it can be filled at a high filling rate. These magnetic powders may be used alone or in combination. The average particle diameter of the magnetic powder or the long diameter of the flat soft magnetic powder is 0.1 to 500 μm, preferably 1 to 200 μm. The aspect ratio of the flat soft magnetic powder is 2 to 500, preferably 10 to 100.

  The dielectric layer 3 is made of a material containing at least a dielectric, and in this embodiment, made of a dielectric. As the dielectric, for example, paper such as synthetic resin, rubber, corrugated cardboard, wood, gypsum, foam, asphalt, soil, recycled material cement, and glass can be used.

  The reflective layer 2 is a layer that has at least conductivity and reflects electromagnetic waves. The reflective layer 2 may be a plate, sheet, film, foil, woven fabric or non-woven fabric made of a conductive material, or a plate, sheet, film, foil, made of a mixed material obtained by mixing a conductive material with a synthetic resin. It may be a woven or non-woven fabric, or may be a plate, sheet, foil, woven fabric or film in which a conductive film made of a conductive material is formed on a base material made of a synthetic resin or the like. For imparting conductivity, there are methods such as plating, vapor deposition (sputtering), and printing. The conductive material forming the reflective layer 2 may be a metal or a material other than a metal such as carbon. As a conductive material for forming the reflective layer 2, a conductive material that can be used for forming each pattern 12 can be used in the same manner. In the present embodiment, the reflective layer 2 is configured by forming a metal film over the entire surface on the electromagnetic wave incident side surface of the plate-like substrate. In the reflective layer of this example, the electric field shielding property measured by the KEC method exceeds 30 dB in the UHF band.

  The electromagnetic wave absorber 1 receives an electromagnetic wave having a resonance frequency determined by each pattern 12 of the pattern layer 5 depending on the shape and dimensions thereof, stores electromagnetic wave energy between the pattern 12 and the reflective layer 2, and stores the electromagnetic wave energy. Energy is lost in the loss layer 7 including the absorption layer 4 and the dielectric layer 3. The loss of electromagnetic energy is caused by the conversion of electromagnetic energy into thermal energy. The electromagnetic wave absorber 1 attenuates the electromagnetic wave received by each pattern 12 by the interference of the electromagnetic wave by each pattern 12 and the reflective layer 2. The electromagnetic wave absorber 1 can efficiently receive an electromagnetic wave by using the pattern layer 5, and can efficiently absorb the electromagnetic wave by the above-described energy conversion and interference.

  The frequency of the electromagnetic wave absorbed by the electromagnetic wave absorber 1 depends on the shape, size, and interval of each pattern 12 and also depends on the thickness of the loss layer 7, and thus the absorption layer 4 and the dielectric layer 3. And the dimensions are selected and determined. The frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is not particularly limited, but may be a frequency in the range of 300 kHz to 3000 GHz. The electromagnetic wave absorber 1 is used, for example, to absorb electromagnetic waves particularly in the UHF band (300 MHz or more and less than 3 GHz) and 2.4 GHz band (2.4 GHz or more and less than 2.5 GHz).

  When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the 2.4 GHz band, the pattern dimensions d1x and d1y are, for example, 13 mm, the minimum width dimensions exmin, eymin are, for example, 0.25 mm, The maximum width dimensions exmax and eymax are 1.4 mm, the respective change rates Δex and Δey are, for example, 0.18, and the first angle θ1 is, for example, 80 degrees.

  The electromagnetic wave absorber 1 has flame retardancy, quasi-incombustibility, or incombustibility. The standard for flame retardancy is to obtain an evaluation of UL94V0. Although the use of the electromagnetic wave absorber 1 is not limited, for example, it is used as a constituent member of a building material. The electromagnetic wave absorber 1 having flame retardancy, quasi-incombustibility or incombustibility can suitably constitute a building material. The building material is a material used for erection of a building, for example, an interior material, a wall material, a floor material, a screen material, a top plate material, and a surface material. When imparting flame retardancy, quasi-incombustibility, or incombustibility to the electromagnetic wave absorber 1, for example, a flame retardant or a flame retardant aid is added to the electromagnetic wave absorber 1. A flame retardant or a flame retardant aid is added to the absorption layer 4 and the dielectric layer 3, for example.

  As the flame retardant, for example, phosphorus compounds, boron compounds, bromine-based flame retardants, zinc-based flame retardants, nitrogen-based flame retardants and hydroxide-based flame retardants can be used. Known flame retardants can be used alone or in combination. Examples of flame retardants include halogen flame retardants such as bromines, phosphorus compound flame retardants such as phosphate esters, zinc flame retardants such as zinc carbonate and zinc borate, triazine compounds, hindered amine compounds and melamine compounds. Using flame retardants such as nitrogen flame retardants, hydroxide flame retardants such as magnesium hydroxide and aluminum hydroxide, and flame retardant aids such as carbon black and fatty acid metal salts, achieve flame resistance such as UL94 V0. Design as much as possible.

  According to such an electromagnetic wave absorber 1, the pattern layer 5 has an area ratio in which the area of the region where the pattern 12 is formed is 0.6 or more when the area of the entire region of the pattern layer 5 is 1. is doing. By forming the pattern layer 5 in the area ratio within the above range, it is possible to increase the amount of absorption of electromagnetic waves and increase the bandwidth of the frequency band where the amount of absorption of electromagnetic waves is large. The pattern layer 5 has a configuration in which the width dimensions ex and ey of at least some of the gaps formed between the patterns 12 are continuously changed in the extending direction of the gaps. As described above, the gaps between the patterns 12 are formed so that the widths ex and ey are continuous, thereby increasing the amount of absorption of electromagnetic waves as compared with the configuration in which the widths of the gaps between the patterns 12 are uniform. be able to. In the electromagnetic wave absorber 1, the loss layer 7 includes an absorption layer 4 that is a magnetic layer made of a material containing at least a magnetic substance, and a dielectric layer 3 made of a dielectric. Since both the absorption layer 4 and the dielectric layer 3 cause the electromagnetic wave energy captured by the pattern 12 of the pattern layer 5 to be lost, the loss amount can be increased and the electromagnetic wave can be absorbed with a large absorption amount.

  In addition, the gap between the patterns 12 has at least two approach parts having a small width dimension with an interval in the extending direction of the gap, and a spaced part having a width dimension larger than the approach part between the approach parts. Have. The approaching part is a part where the width dimensions ex and ey are the minimum width dimensions exmin and eymin, and the separation part is a part where the width dimensions ex and ey are the maximum width dimensions exmax and eymax. As described above, the widths ex and ey of the gaps between the patterns 12 are formed so as to approach and separate from each other, so that the electromagnetic wave is absorbed compared to the configuration in which the widths of the gaps between the patterns 12 are uniform. Bandwidth can be increased. This is to increase the frequency that causes the resonance mode formed between the patterns 12 (ex, ey). The patterns 12 are independent, and only an insulating film, space, and other materials exist between them. However, it can be considered that the circuit is connected so that a capacitor is formed in a high frequency range. The inventors have found that the resonance frequency of the entire pattern layer 12 can be controlled by changing the coupling degree (interference degree) between the patterns 12. Specifically, the receiving frequency of the pattern 12 is widened by arranging the patterns 12 so as to repeat at least two approaches / separations, such as the patterns 12 approaching / separating / approaching between adjacent patterns 12. Can do.

  In the electromagnetic wave absorber 1, the bandwidth of the frequency band in which the electromagnetic wave absorption amount is 15 dB or more is 70 MHz or more. As described above, the electromagnetic wave absorber 1 having a large frequency band with a large amount of electromagnetic wave absorption and having excellent absorption characteristics can be realized. Furthermore, since the electromagnetic wave absorber 1 has a large amount of electromagnetic wave absorption as described above, it can be made thinner and lighter. If the electromagnetic wave absorber 1 is configured so as to be able to absorb an electromagnetic wave in the UHF band, for example, the total thickness dimension can be formed to 15 mm or less, and the thin electromagnetic wave absorber 1 can be realized. The UHF band is an ultrafine short wave and is a frequency band of 300 MHz or more and less than 3 GHz. Here, the frequency band used for communication of the RFID system is a 400 MHz band and a band of 860 MHz or more and less than 960 MHz. Further, when the electromagnetic wave absorber 1 is configured so as to be able to absorb an electromagnetic wave in the 2.4 GHz band, for example, the total thickness dimension can be formed to 5 mm or less, and the thin electromagnetic wave absorber 1 can be realized. . The 2.4 GHz band is a frequency band of 2.4 GHz or more and less than 2.5 GHz.

  The electromagnetic wave absorber 1 has a reflective layer 2 that functions as an electromagnetic wave shielding plate. Thereby, the electromagnetic wave absorber 1 has an electromagnetic wave shielding property for shielding electromagnetic waves. Therefore, the electromagnetic wave absorber 1 can not only absorb the electromagnetic wave but also shield the electromagnetic wave, and the convenience is improved. In other words, the electromagnetic wave absorber 1 of the present invention shields the electromagnetic wave but at a specific frequency, unlike the case where it is shielded like a shield material such as metal, but also reflects, and a new effect is caused by the reflected wave. On the other hand, it becomes a shield that does not generate a reflected wave. For this reason, it can be said that it is a useful material for reducing unnecessary waves and zoning in a wireless communication environment. Further, in the configuration without the reflective layer 2, the impedance of each pattern 12 functioning as a receiving antenna varies depending on whether or not an object made of a conductive material exists in the vicinity of the electromagnetic wave absorber 1, and also depending on the difference in conductivity. However, although the frequency of the receivable electromagnetic wave changes, the configuration including the reflective layer 2 can eliminate the influence of an object made of a conductive material present in the vicinity, and this is also convenient. Is improved. Moreover, the reflection layer 2 is also a structure which produces the electromagnetic wave interference which bears one wing which absorbs an electromagnetic wave inside the electromagnetic wave absorber 1 as mentioned above, and contributes also to increasing the absorption amount of an electromagnetic wave. This electromagnetic wave absorber 1 has excellent electromagnetic wave absorption characteristics.

  FIG. 3 is a cross-sectional view of an electromagnetic wave absorber 1A according to another embodiment of the present invention. This embodiment is similar to the embodiment of FIG. 1 and FIG. 2 described above, and corresponding portions are denoted by the same reference numerals, and only different configurations will be described. In this embodiment, the absorbing layer 4, the pattern layer 5, the dielectric layer 3, and the reflective layer 2 are laminated in this order from the electromagnetic wave incident side that is the upper side in FIG. Other configurations are the same as those of the above-described embodiment. In this way, the absorption layer 4 may be provided on the electromagnetic wave incident side of the pattern layer 5 and the pattern layer 5 may be sandwiched between the loss layer 7. Even with such a configuration, it is possible to achieve the same effects as those of the above-described embodiment.

  FIG. 4 is a cross-sectional view of an electromagnetic wave absorber 1B according to still another embodiment of the present invention. This embodiment is similar to the embodiment of FIG. 1 and FIG. 2 described above, and corresponding portions are denoted by the same reference numerals, and only different configurations will be described. In this embodiment, the surface layer 6 is formed on the electromagnetic wave incident side which is the upper side in FIG. The surface layer 6 is a layer made of a material that is at least one of a magnetic loss material and a dielectric loss material, and constitutes the loss layer 7. The surface layer 6 may be either the absorption layer 4 or the dielectric layer 3, or may be another layer. Other configurations are the same as those of the above-described embodiment. In this way, the surface layer 6 may be provided on the electromagnetic wave incident side of the pattern layer 5 and the pattern layer 5 may be sandwiched between the loss layer 7. Even with such a configuration, it is possible to achieve the same effects as those of the above-described embodiment.

  The electromagnetic wave absorber of the present invention only needs to have a configuration including a pattern layer and a loss layer, and the stacked configuration is not limited to the stacked configuration shown in FIGS. As an embodiment of the present invention, for example, a configuration in which the dielectric layer 3, the absorption layer 4, the pattern layer 5, the absorption layer 4, the dielectric layer 3, and the reflection layer 2 are arranged in this order from the electromagnetic wave incident side is also possible. Furthermore, as an embodiment of the present invention, the order from the electromagnetic wave incident side includes a laminate of the pattern layer 5, the absorption layer 4, and the reflective layer 2, a laminate of the pattern layer 5, the dielectric layer 3, and the reflective layer 2. . The latter is a configuration in which the absorption layer 4 is a dielectric loss layer and the dielectric layer 3 is not provided separately. Each layer may be a single layer or multiple layers, and in the case of multiple layers, it is not necessary to be exactly the same layer. It is not limited to these, The laminated body of various aspects is included. In addition, these laminates are obtained by extracting the main layers and do not necessarily have to be arranged in this manner. For example, even if an adhesive layer, an adhesive layer, a support layer or a protective layer is inserted between the layers, the same effect is obtained. Is obtained. Further, by mixing an adhesive or a pressure-sensitive adhesive into the absorption layer 4 and the dielectric layer 3, the absorption layer 4 and the dielectric layer 3 can also be configured to serve as the adhesive layer and the pressure-sensitive adhesive layer.

  Furthermore, as an embodiment of the present invention, the electromagnetic wave absorber does not include the reflective layer 2 shown in FIGS. 2 to 4, and the electromagnetic wave absorber that does not include such a reflective layer 2 is on the side opposite to the electromagnetic wave incident side. You may comprise so that the surface may be installed facing the object surface which has electromagnetic wave shielding performance. An object having electromagnetic wave shielding performance may have the same configuration as that of the reflective layer 2, for example, and may be realized by, for example, a metal plate. Such a configuration can obtain the same electromagnetic wave absorption characteristics as the electromagnetic wave absorber having the reflective layer 2.

  FIG. 5 is a front view showing a pattern layer 5C constituting an electromagnetic wave absorber according to still another embodiment of the present invention. FIG. 6 is a front view of the pattern layer 5C showing a part of FIG. 5 in an enlarged manner. This pattern layer 5C is a pattern layer used in place of the above-described pattern layer 5 shown in FIG. 1, and is similar to the above-described pattern layer 5 shown in FIG. Only the different configurations will be described. The pattern layer 5C shown in FIG. 5 is different from the pattern 5 shown in FIG. The pattern 12 in FIG. 5 has a plurality of radial patterns 30 and a plurality of substantially square patterns 31.

  Each radial pattern 30 is formed in a radial shape, and a plurality of radial patterns 30 are provided spaced apart from each other. Each radial pattern 30 is formed in a substantially cross shape that is radial along the x and y directions, and is regularly arranged in a matrix in the x and y directions. Each radial pattern 30 has a shape in which four corners 21 at a crossing portion 16 of a base 10 character (hereinafter referred to as “basic cross character”) 20 indicated by a virtual line in FIG. It is. The basic cross 20 includes a first rectangular portion 14 elongated in the x-direction and a second rectangular portion 15 elongated in the y-direction, intersecting at a right angle at an intersecting portion 16 with the centers of the rectangular portions 14 and 15 overlapped. Shape. The rectangular portions 14 and 15 are shifted by 90 degrees around the vertical axis at the intersecting portion 16 and have the same shape. Such a basic cross 20 has a shape in which four first substantially right triangles 22 are provided so that the corners of the first substantially right triangles 22 are accommodated in the four corners 21 of the intersection 16. Each first substantially right-angled triangle 22 is generally a right-angled isosceles triangle, and has a shape that is curved in an arc shape so that the hypotenuse opposite to the right-angled corner is concave toward the right-angled corner. Each radial pattern 30 is four-fold rotationally symmetric, point-symmetric with respect to the center of each rectangular portion 14, 15, and two straight lines passing through the center of each rectangular portion 14, 15 and parallel to the long side of each rectangular portion. Are symmetrical with respect to two straight lines shifted by 45 degrees with respect to two straight lines passing through the centers of the rectangular parts 14 and 15 and parallel to the long sides of the rectangular parts.

  Each substantially square pattern 31 is arranged in a region surrounded by the radial pattern 30 at a distance from the radial pattern 30 so as to fill the region surrounded by the radial pattern 30. Surrounded by four radial patterns 31 that are two radial patterns 31 adjacent to each other in the x direction and two radial patterns 31 that are combined with two radial patterns 31 adjacent to either one of the two radial patterns 31 in the y direction. The region is generally square. One substantially rectangular pattern 31 is arranged so as to fit in this region. Each substantially square pattern 31 is formed in a shape similar to the shape of the region surrounded by the four radial patterns 31.

  Each radial pattern 30 is substantially cross-shaped as described above, and each region surrounded by each radial pattern 30 is a rounded rectangle with each corner of the rectangle arcuate. The rectangle that is the basis of the rounded corner includes a rectangle having different long side and short side dimensions and a square having the same long side and short side dimensions. In this embodiment, each region surrounded by each radial pattern 30 is a substantially square corner-round rectangle, and each substantially square pattern 31 is a substantially square corner-round rectangle.

  Each substantially square pattern 31 has a shape in which four corners 26 of a square serving as a base (hereinafter referred to as a “second basic square”) are changed into an arc shape. Each substantially square pattern 31 has a shape obtained by removing four second substantially right-angled triangles 27 arranged so that the right-angled corners fit within the corners of the second foundation square 25 from the second foundation square 25. Each of the second substantially right-angled triangles 27 is generally a right-angled isosceles triangle, and has a shape that is curved in an arc shape so that the hypotenuse opposite to the right-angled corner is concave toward the right-angled corner. Each substantially square pattern 31 has the center of the second basic square 25 coincident with the center of the square formed by connecting the centers of the four basic patterns of the four radial patterns 31 around it. Each side is arranged to extend in either the x direction or the y direction. Each substantially square pattern 12 is four-fold rotationally symmetric, point-symmetric with respect to the center of the second basic square 25, and line-symmetric with respect to the two diagonal lines of the second basic square 25, and the center of the second basic square 25. Are symmetrical with respect to two straight lines passing through and parallel to either side.

  The pattern layer 5C in which each pattern 12 having the radial pattern 30 and the substantially square pattern 31 is formed is the same as the pattern layer 5 in which the star pattern 12 in FIG. 1 is formed. Where the area of each pattern 12 is formed, the area ratio (hereinafter referred to as “pattern area”) is 0.6 or more.

  The width a1y of the first rectangular portion 14 and the width a1x of the second rectangular portion 15 are equal to each other, for example, 0.05 mm or more and 10 mm or less. The length a2x of the first rectangular portion 14 and the length of the second rectangular portion 15 a2y is equal to each other, for example, not less than 1 mm and not more than 100 mm. The length of two sides sandwiching the right angle of the first substantially right-angled triangle 22, and therefore the length a3x of the two sides extending in the x direction and the length a3y of the side extending in the y direction are equal to each other, for example, 0. The curvature radius R1 of the hypotenuse of the first substantially right triangle 22 is, for example, 1 mm or more and 100 mm or less. An angle θ3 formed by two straight lines connecting the center point of the hypotenuse arc of the first substantially right triangle 22 and both ends of the hypotenuse of the first substantially right triangle 22 is not less than 5 degrees and not more than 45 degrees. The distance c2x between the first rectangular portions 14 of the two radial patterns 30 adjacent in the x direction and the distance c2y between the second rectangular portions 15 of the two radial patterns 30 adjacent in the y direction are equal to each other, For example, it is 0.1 mm or more and 100 mm or less.

  Further, the dimension b1x in the x direction and the dimension b1y in the y direction of the second basic square 25 are equal to each other, for example, 1 mm or more and 100 mm or less. The dimensions b1x and b1y of the second basic square 25 are the dimension in the x direction and the dimension in the y direction of the substantially square pattern 31, respectively. The length of two sides sandwiching the right angle of the second substantially right triangle 27, and therefore the length b2x of the two sides extending in the x direction and the length b2y of the side extending in the y direction are equal to each other. The radius of curvature R2 of the hypotenuse of the second substantially right triangle 27 is 1 mm or more and 100 mm or less.

  Further, the width dimension c1 of the gap between the radial pattern 30 and the substantially rectangular pattern 31 (hereinafter referred to as “radial square gap”) is continuous in the extending direction of the gap between the minimum width dimension c1min and the maximum width dimension c1max. To change. The minimum width dimension c1min between the radial square gaps is a dimension to the substantially rectangular pattern 31 at the longitudinal ends of the rectangular portions 14 and 15 of the radial pattern 30, and is, for example, 0.1 mm or more and 20 mm or less. The maximum width dimension c1max between the radial square gaps is a dimension along a straight line that bisects the right angle of each of the substantially right triangles 22 and 27, and is, for example, 0.2 mm or more and 50 mm or less.

As described above, the width dimension c1 between the radial square gaps continuously changes in the extending direction of the gap. The change rate Δc1 of the width dimension c1 between the radial square gaps is, for example, not less than 0.001 and not more than 10. The change rate Δc1 of the width dimension c1 between the radial square gaps is a change amount of the width dimension c1 between the radial square gaps per unit dimension along the edge of the radial pattern 30. In the present embodiment, the rate of change Δc1 is not uniform, and decreases from the position of the minimum width dimension c1min toward the position of the maximum width dimension c1max.
The change rate Δc1 is expressed by Expression (3).

  When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the UHF band, the widths a1x and a1y of the rectangular portions 14 and 15 are, for example, 1 mm, and the lengths a2x and a2y of the rectangular portions 14 and 15 are The length a3x, a3y of two sides sandwiching the right angle of the first substantially right triangle 22 is, for example, 6.5 mm, and the curvature radius R1 of the hypotenuse is 6.5 mm. When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the UHF band, the dimensions b1x and b1y of the second basic square 25 are, for example, 25 mm, and the length of the two sides sandwiching the right angle of the second substantially right triangle 27. The length b2x, b2y is, for example, 10.5 mm, and the curvature radius R2 of the hypotenuse is 10.5 mm. When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the UHF band, the minimum width dimension c1min of the width dimension c1 between the radial square gaps is, for example, 0.5 mm, and the maximum width dimension c1max is, for example, 2 mm. Yes, the rate of change Δc1 is, for example, 0.15. When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the UHF band, the distances c2x and c2y between the radial patterns are, for example, 7 mm.

  When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the 2.4 GHz band, the widths a1x and a1y of the rectangular portions 14 and 15 are, for example, 0.5 mm, and the lengths of the rectangular portions 14 and 15 are, respectively. a2x and a2y are, for example, 17.5 mm, the lengths a3x and a3y of the two sides sandwiching the right angle of the first substantially right triangle 22 are, for example, 5 mm, and the curvature radius R1 of the hypotenuse is 5 mm. When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the 2.4 GHz band, the dimensions b1x and b1y of the second basic square 25 are, for example, 20.5 mm and sandwich the right angle of the second substantially right triangle 27. The lengths b2x and b2y of the two sides are, for example, 8 mm, and the curvature radius R2 of the hypotenuse is 8 mm. When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the 2.4 GHz band, the minimum width dimension c1min of the width dimension c1 between the radial square gaps is, for example, 0.5 mm, and the maximum width dimension c1max is, for example, For example, the change rate Δc1 is 0.14. When the frequency of the electromagnetic wave to be absorbed by the electromagnetic wave absorber 1 is in the 2.4 GHz band, the distances c2x and c2y between the radial patterns are, for example, 2.5 mm.

  The electromagnetic wave absorber provided with the pattern layer 5C in which each pattern 12 having the radial pattern 30 and the substantially square pattern 31 is formed is the electromagnetic wave absorber 1, 1A, 1B provided with the pattern layer 5 of FIG. The same effect can be achieved. In the pattern layer 5C of FIGS. 5 and 6, at least a part of the patterns 12 has an outer shape including a curved portion. In the present embodiment, all patterns 12 have an outer shape including a curved portion. In such a pattern 12, the resonance current when electromagnetic waves are received flows smoothly in the curved portion.

  FIG. 7 is a front view of the pattern P showing the influence of the direction of the pattern P on the electric field generated in the pattern P when the pattern P receives an electromagnetic wave that is a TE wave. FIG. 7 shows a case of normal incidence in which electromagnetic waves are incident on the pattern P perpendicularly. FIG. 7A shows how the electric field is generated when the square pattern P is placed in a positional relationship facing the front. FIG. 7B shows how the electric field is generated when the pattern P is displaced by 45 degrees (°) from the positional relationship shown in FIG. FIG. 7 (3) shows how an electric field is generated in the case of a circular pattern P. FIG. 7 (4) shows how the electric field is generated when the R-added square pattern P is placed in a directly-facing positional relationship as in FIG. 7 (1). FIG. 7 (5) shows how the electric field is generated when the pattern P is displaced by 45 degrees (°) from the positional relationship of FIG. 7 (4).

  The positional relationship in FIG. 7A is a positional relationship of a square pattern P having sides parallel or perpendicular to the direction of the electric field in the electromagnetic wave (hereinafter referred to as “polarization direction”). In the positional relationship in FIG. 7 (2), the rectangular pattern P similar to that in FIG. 7 (1) is angularly displaced by 45 degrees (°) around the axis perpendicular to the pattern P from the positional relationship in FIG. Each side has a positional relationship that forms an angle of 45 degrees (°) with respect to the polarization direction. A square is a quadrangle whose four interior angles are right angles. The positional relationship in FIG. 7 (4) is the positional relationship of the R-added square pattern P in which sides parallel or perpendicular to the polarization direction exist. The positional relationship in FIG. 7 (5) is the same as that in FIG. 7 (4), but the square pattern P with R is displaced by 45 degrees (°) around the axis perpendicular to the pattern P from the positional relationship in FIG. 7 (4). And each side forms a 45 ° (°) angle with respect to the polarization direction. The square with R is a substantially rectangular shape having a straight line and a curved line in which a corner portion of the square has a curvature and is rounded. Each pattern P in FIG. 7 corresponds to a conductive pattern.

  As shown in FIG. 7, when the electromagnetic wave is received by the pattern P, the direction E of the electric field generated in the pattern P varies depending on the shape of the pattern P. In the case of the square pattern P, the pattern with respect to the polarization direction of the electromagnetic wave It depends on the positional relationship of P. In the case of FIG. 7A, the direction E of the electric field generated in the pattern P is a linear direction parallel to one side. In the case of FIGS. 7 (2), 7 (3) and 7 (5), the direction E of the electric field generated in the pattern P is substantially hyperbolic.

  When the direction E of the generated electric field changes, the resonance frequency with respect to the electromagnetic wave changes. When electromagnetic waves, particularly TE waves and TM waves are received in the square pattern P, if the arrangement shown in FIG. 7A is adopted, a resonance current tends to flow along the sides. On the other hand, in the case of FIG. 7 (2) in which the square pattern P is displaced by 45 degrees (°) from FIG. 7 (1) and in the case of FIG. 7 indicates that the resonance current cannot be concentrated near the side as the P is used as shown in FIG. Therefore, the pattern used to receive the electromagnetic wave changes depending on the pattern such as a circular pattern in which the reception state is constant and the polarization direction of the electromagnetic wave, regardless of the polarization direction of the electromagnetic wave. There are patterns like square patterns.

  The pattern P in FIGS. 7 (4) and 7 (5) has a substantially rectangular shape with R at the corner. The difference in the path length and distribution of the resonance current between the case of FIG. 7 (4) and FIG. 7 (5), the path length of the resonance current between the case of FIG. 7 (1) and the case of FIG. When the difference in distribution is compared, the difference between the case of FIG. 7 (4) and the case of FIG. 7 (5) is more than the difference between the case of FIG. 7 (1) and the case of FIG. 7 (2). It is getting smaller. Therefore, the square pattern P with R in FIGS. 7 (4) and 7 (5) has a lower resonance frequency cyst against the polarization than the square pattern P in FIGS. 7 (1) and 7 (2). it can. This R-shaped square pattern shape is basically a square pattern, but has the effect of incorporating the polarization-resistant characteristics of a circular pattern.

  In an actual environment where electromagnetic wave absorbers are used, not only linearly polarized electromagnetic waves such as TE waves and TM waves, but also circularly polarized electromagnetic waves exist. It is not always the same direction, and electromagnetic waves with different polarization directions must be absorbed. Therefore, it is necessary to suppress the polarization dependence in which the reception state varies depending on the polarization direction. Improving sex is an important issue. The present invention can solve this problem.

  Furthermore, according to the analysis of the tendency of electromagnetic wave absorption characteristics due to the shape of the pattern in the electromagnetic wave absorber that receives the electromagnetic wave by the pattern and loses energy in the loss layer, the amount of electromagnetic wave absorption is improved and the polarization dependence is reduced This improvement in polarization characteristics is not compatible, but rather contradictory. When the shape of the pattern is a polygon, regardless of whether it is linear or planar, if the outer shape of the pattern has sharp corners called edges, the peak value of electromagnetic wave absorption is Although it becomes higher, the frequency shift at which the absorption amount reaches the peak value increases depending on the direction of the electric field of the electromagnetic wave. In addition, when the pattern shape is a circle, regardless of whether the pattern is linear or planar, the frequency at which the amount of absorption reaches the peak does not shift depending on the polarization direction of the electromagnetic wave, but the peak value of the electromagnetic wave absorption amount Will be lower.

  A pattern having sharp corners such as a polygon has a higher Q value than a circular pattern. The Q value can be expressed by a resonance frequency and a bandwidth, and Q = resonance frequency / bandwidth. The bandwidth is a width of a band having a predetermined reception intensity, for example, a reception intensity that is one half or more of the reception intensity at the resonance frequency ω0. Therefore, assuming that the resonance frequency is ω0 and the frequencies on both sides sandwiching the resonance frequency at which the reception intensity is a half of the reception intensity at the resonance frequency ω0 are ω1 and ω2 (> ω1), respectively, Q = ω0 / (ω2-ω1 ).

  In order to show the electromagnetic wave absorption characteristics of the patterned electromagnetic wave absorber, this Q value is expressed by applying it to the peak value of the electromagnetic wave absorption amount. A high Q value means that the frequency band of electromagnetic waves to be absorbed (hereinafter sometimes referred to as “absorption band”) is small, but the peak value of the high electromagnetic wave absorption amount (hereinafter sometimes simply referred to as “absorption amount”). It represents having. A low Q value means that the peak value of the absorption amount is small but has a large absorption band width. The absorption band is the frequency of electromagnetic waves that are absorbed with an absorption amount that is greater than or equal to a predetermined absorption amount.

  A pattern with sharp corners has a high Q value, so the peak value of the absorption amount is high, but the width of the absorption band is narrowed and the resonance frequency shifts due to the difference in polarization direction. become. In the case of FIG. 7 (1), a strong current is generated along the side of the pattern P, and resonance occurs in that portion, whereas in the case of FIGS. 7 (2) and 7 (3), a strong current is generated. As is clear from the case of FIG. 7A, the path through which the current flows is not concentrated along the side. In other words, it can be said that by expanding the current path, the region where the half-wave wave related to resonance is distributed is expanded and the conditions for resonance increase. As a result, the width of the absorption band is increased. In the case of a square pattern, if it is arranged as shown in FIG. 7 (1), an electric field in a straight direction parallel to the side is generated. However, if it is displaced by 45 degrees (°) as shown in FIG. Since the electric field is generated in the direction of drawing, the distribution is clearly different. That is, the configuration using the square pattern has polarization dependency although the electromagnetic wave absorption characteristic is enhanced as a result of concentrated resonance. Such a characteristic is not limited to a rectangular shape, and similarly has a configuration using a polygonal pattern.

  On the other hand, the rectangular pattern P with R in FIGS. 7 (4) and 7 (5) is from the rectangular pattern P in FIGS. 7 (1) and 7 (2) in terms of anti-polarization characteristics. It is improved so as to approach the circular pattern P in FIG. 7 (3), and the difference in absorption frequency caused by the polarization direction of the radio wave is reduced. As for the Q value, the high value of the square pattern can be maintained even a little. Designed.

  The pattern layer 5C of the present embodiment shown in FIGS. 5 and 6 has a substantially square pattern 31 having the same shape as the square pattern P with R shown in FIGS. 7 (4) and 7 (5). In the electromagnetic wave absorber provided with the pattern layer 5C of FIGS. 5 and 6, the polarization dependency is small and the electromagnetic wave absorption amount can be increased. In order to improve the above-described drawbacks when using a polygonal pattern, the pattern shape is basically a polygonal shape, but at least one corner is formed in a curved shape. The effect of imparting R to the corner, that is, the curved surface, is that the resonance current easily flows without stagnation at the corner, and further, the resonance region is widened. As a result, the Q value slightly decreases. By exhibiting broadband performance, the polarization characteristics are improved.

  Accordingly, it is possible to suppress a shift in frequency at which the absorption amount reaches a peak value depending on the polarization direction of the electromagnetic wave. Accordingly, it is possible to realize an electromagnetic wave absorber having an excellent electromagnetic wave absorption characteristic in which the peak value of the electromagnetic wave absorption amount is high and the frequency shift at which the absorption amount reaches the peak value depending on the polarization direction of the electromagnetic wave is small. The electromagnetic wave absorber provided with the pattern layer 5C of FIGS. 5 and 6 can realize such an excellent electromagnetic wave absorber.

  The inventors of the present invention confirmed the usefulness of the present invention through simulation and actual measurement. Table 1 shows the characteristics of the electromagnetic wave absorbers of Examples 1 to 6. Table 2 shows the characteristics of the electromagnetic wave absorbers of Examples 7 to 10. Table 3 shows the characteristics of the electromagnetic wave absorbers of Examples 11 to 22. Table 4 shows the characteristics of the electromagnetic wave absorbers of Examples 27 to 31 and Comparative Examples 1 to 7. Table 5 shows the characteristics of the electromagnetic wave absorbers of Examples 4 and 31 and Comparative Example 2. Table 6 shows the characteristics of the electromagnetic wave absorbers of Examples 10, 13, and 23 to 26.

  The electromagnetic wave absorbers of Examples 1 to 6 are intended to absorb electromagnetic waves having a frequency of 2.4 GHz band, include the pattern layer 5 having the star pattern 12 shown in FIG. 1, and have the laminated structure shown in FIG. The electromagnetic wave absorbers of Examples 7 to 10 are provided with a pattern layer 5C that is intended to absorb an electromagnetic wave having a frequency of 2.4 GHz band, and that has a radial pattern 30 and a substantially square pattern 31 with curved corners shown in FIG. 2 has a laminated structure shown in FIG. The electromagnetic wave absorbers of Examples 11 to 22, 25, and 26 are intended to absorb electromagnetic waves having a frequency of UHF band, and have a pattern layer 5C having a radial pattern 30 and a substantially square pattern 31 with curved corners shown in FIG. And has a laminated structure shown in FIG. However, in Examples 25 and 26, the width dimension of the gap between the radial pattern 30 and the substantially rectangular pattern 31 has a constant configuration. In each table, when the width dimension of the gap interval changes continuously, the continuous change of the conductor interval is indicated as “present”, and when the gap interval is constant, the continuous change of the conductor interval is indicated as “no”.

  The electromagnetic wave absorbers of Examples 27 to 31 and Comparative Examples 1 and 2 are intended to absorb electromagnetic waves having a frequency of 2.4 GHz, and the square pattern 40 shown in FIG. The pattern layer 5 is formed in the same arrangement, and has a stacked structure shown in FIG. The electromagnetic wave absorbers of Comparative Examples 3 to 7 are intended to absorb electromagnetic waves having a frequency of 2.4 GHz band, and a pattern in which the circular pattern 41 shown in FIG. The layer 5 is provided and has the laminated structure shown in FIG. The electromagnetic wave absorber of Example 10 is provided with a pattern layer 5C that is intended to absorb electromagnetic waves having a frequency of 2.4 GHz band, and has a radial pattern 30 and a substantially square pattern 31 with curved corners shown in FIG. 2 has a laminated structure. The electromagnetic wave absorbers of Examples 23 and 24 are substantially the same as the electromagnetic wave absorbers of Examples 7 to 10, except that the width dimension of the gap between the radial pattern 30 and the substantially rectangular pattern 31 is constant. The point is different.

  In Examples 1 to 6, the conductor interval (max) is the maximum width dimension exmax, eymax, the conductor interval (min) is the minimum width dimension exmin, eymin, and the conductor width (max) is each pattern. The dimensions are d1x and d1y, and the conductor width (min) is the respective constriction part dimensions d2x and d2y. In Examples 27 to 31 and Comparative Examples 1 and 2, since the width interval f of the gap between the patterns 40 is constant, the width dimension f is set as the conductor interval (max), and the conductor interval (min) is omitted. Yes. Furthermore, in Examples 27 to 31 and Comparative Examples 1 and 2, the pattern 40 is square, the length of one side is the conductor width (max), and the conductor width (min) is omitted. In Comparative Examples 3 to 7, the conductor interval (max) is the maximum value gmax of the width dimension of the gap between the patterns 41 as shown in FIG. 9, and the conductor interval (min) is the pattern as shown in FIG. This is the minimum value gmin of the width dimension of the gap between 41. Furthermore, in Comparative Examples 3 to 7, the pattern 41 is circular, the outer diameter is the conductor width (max), and the conductor width (min) is omitted. In Examples 1 to 6 and Comparative Examples 1 to 7, the conductor width / interval (max) is a value obtained by dividing the conductor width (max) by the conductor interval (min), and the conductor width / interval (min) is It is a value obtained by dividing the conductor width (max) by the conductor interval (max). In Examples 27 to 31 and Comparative Examples 1 and 2, since there is no conductor interval (min), the conductor width / interval (min) is omitted.

  In Examples 7 to 26, Rcp is the radius of curvature R1 of the hypotenuse of the first substantially right triangle 22, Rsp is the radius of curvature R2 of the hypotenuse of the second substantially right triangle 27, Dsc is C1min, and Lcp is , A2x, a2y, and Lsp is b1x, b1y.

  In Examples 1 to 31 and Comparative Examples 1 to 7, the absorption layer thickness is the thickness dimension of the absorption layer 4, and the dielectric layer thickness is the thickness dimension of the dielectric layer 3. In Examples 1 to 31 and Comparative Examples 1 to 7, the peak frequency is the frequency at which the amount of absorption of electromagnetic waves is maximized, the peak absorption amount is the maximum value of the amount of absorption of electromagnetic waves, and the 15 dB bandwidth is This is the frequency width at which an absorption amount of 15 dB or more is obtained. In Examples 1 to 31 and Comparative Examples 1 to 7, the non-pattern of the area ratio is the value of the area of the region where the pattern 12 is not formed when the area of the entire pattern layer region is 1, and the area ratio This pattern is the value of the area of the region in which the pattern 12 is formed, where the area of the entire pattern layer region is 1. In Examples 1 to 22, the magnetic material is a magnetic substance contained in the absorption layer 4.

  FIG. 10 is a graph showing the absorption characteristics of Examples 1-6. FIG. 11 is a graph showing the absorption characteristics of Examples 7 to 10. FIG. 12 is a graph showing the absorption characteristics of Examples 11 to 16. FIG. 13 is a graph showing the absorption characteristics of Examples 17-22. 10 to 13, the horizontal axis indicates the frequency, and the vertical axis indicates the reflection loss. The reflection loss is a loss due to absorption by the electromagnetic wave absorber, and the value corresponding to the absolute value of the reflection loss is the amount of absorption by the electromagnetic wave absorber. As is apparent from Tables 1 to 3 and FIGS. 10 to 13, the electromagnetic wave absorber according to the present invention has excellent absorption characteristics with a large maximum absorption amount.

  FIG. 14 is a graph showing the relationship between the pattern area ratio and the amount of absorption. FIG. 15 is a graph showing the relationship between the pattern area ratio and the absorption bandwidth. In FIG. 14, the horizontal axis indicates the percentage of the area where the pattern is formed in the entire pattern layer region, and the vertical axis indicates the maximum value of the amount absorbed by the electromagnetic wave absorber. In FIG. 15, the horizontal axis indicates the percentage of the area where the pattern is formed in the entire pattern layer region, and the vertical axis indicates the bandwidth of the frequency where the amount of absorption by the electromagnetic wave absorber is 15 dB or more. The bandwidth of the frequency where the absorption amount is 15 dB or more is a value obtained by subtracting the lowest frequency from the highest frequency in the continuous frequency band where the absorption amount is 15 dB or more.

  14 and 15 show the results of designing as an electromagnetic wave absorber in the 2.4 GHz band. In creating this figure, those whose absorption frequency (peak frequency) deviates from 2.45 GHz to 3.0 GHz cannot be a 2.4 GHz band electromagnetic wave absorber, and for this reason, Comparative Example 2 is excluded from FIGS. 14 and 15. is doing. In FIGS. 14 and 15, Examples 1 to 6 using the star-shaped pattern 12 are indicated by crosses, and a radial pattern and a substantially square pattern (curvature cross patch) pattern as shown in FIGS. 5 and 6 are used. Examples 7 to 10 using 12 are indicated by ◯, Examples 27 to 31 using the square pattern 40 as shown in FIG. 8 and Comparative Examples 1 and 2 are indicated by ◆, and as shown in FIG. Comparative Examples 3 to 7 using a simple circular pattern 41 are indicated by ■.

  As is apparent from Tables 1 and 4 and FIGS. 14 and 15, as the pattern area ratio increases, the amount of absorption increases, and the bandwidth for obtaining an amount of absorption of 15 dB or more increases. When the area of the entire pattern layer region is 1, when the area of the region where the pattern is formed is 0.6 or more, the maximum absorption amount is large, and the absorption amount is as high as 15 dB or more, and the 15 dB band. The width becomes as wide as 70 MHz or more. Further, as in Examples 1 to 22, the pattern 12 has a star shape or a combination of a radial shape and a substantially square shape (curvature cross patch), and the width dimension of the gap between adjacent patterns 12 changes continuously. There is a tendency that the bandwidth having a high absorption amount becomes wide and shows a broadband characteristic. In the case of a circle, when the area of the entire pattern layer is set to 1, it is difficult to increase the area of the region where the pattern is formed, the maximum value of the electromagnetic wave absorption amount is small, and between the adjacent patterns 41 Even if the width dimension of the gap changes continuously, the bandwidth with high absorption is small. That is, as in Examples 1 to 6, when the area of the entire pattern layer region is 1, the area of the region where the pattern is formed is 0.6 or more and the width dimension of the gap between the adjacent patterns 12 is continuous. By adopting such a configuration, the peak value of the absorption amount of electromagnetic waves is high, and the bandwidth in which a high absorption amount band, for example, an absorption amount of 15 dB or more can be obtained can be increased. In Examples 1 to 22, when the area of the entire pattern layer region is 1, the area of the region where the pattern is formed is 0.69 or more, the peak value of the electromagnetic wave absorption is 17 dB or more, and 15 dB or more. As shown in FIG. 12, for example, the bandwidth for obtaining a large amount of absorption is 70 MHz or more, and an excellent electromagnetic wave absorber is realized over the entire UHF band. In Examples 18, 20, 21 and the like, the 15 dB bandwidth may be less than 70 dB. This is a result of designing the electromagnetic wave absorber around 1 GHz to be significantly thinned, and a configuration in which thinning is given top priority. Is the result of

  FIG. 16 is a graph showing the relationship between the change in the width dimension of the gap between the patterns shown in Table 5 and the absorption characteristics in a star pattern and a square pattern. In FIG. 16, the horizontal axis indicates the frequency, and the vertical axis indicates the reflection loss. In FIG. 16, the characteristics of Example 4 are indicated by a two-dot chain line, the characteristics of Example 31 are indicated by a solid line, and the characteristics of Comparative Example 2 are indicated by a dotted line. As apparent from Table 5 and FIG. 16, when the area of the entire pattern layer region is 1, the area of the region where the pattern is formed is 0.6 or more, and the width dimension of the gap between the patterns is continuous. In the configuration that changes to, the peak value of the amount of electromagnetic wave absorption can be increased regardless of whether the width dimension is large or small compared to the case where the width dimension of the gap between patterns is constant.

  FIG. 17 shows the relationship between the change in the width of the gap between the patterns shown in Table 6 and the absorption characteristics. The frequency to be absorbed is in the 2.4 GHz band, and the gap between the radial pattern and the substantially rectangular pattern is It is a graph which compares and shows the case where it changes, and a fixed case. FIG. 18 shows the relationship between the change in the width of the gap between the patterns shown in Table 6 and the absorption characteristics. The frequency of the absorption target is the UHF band, and the gap between the radial pattern and the substantially square pattern changes. It is a graph which compares and shows a case and a fixed case. 17 and 18, the horizontal axis indicates the frequency, and the vertical axis indicates the reflection loss. In FIG. 17, the characteristic of Example 10 is shown by a solid line, the characteristic of Example 23 is shown by a two-dot chain line, and the characteristic of Example 24 is shown by a dotted line. In FIG. 18, the characteristic of Example 13 is shown by a solid line, the characteristic of Example 26 is shown by a two-dot chain line, and the characteristic of Example 25 is shown by a dotted line.

  As is apparent from Table 6 and FIGS. 17 and 18, even in the configuration in which the radial pattern 30 and the substantially rectangular pattern 31 are combined, the area where the pattern is formed when the area of the entire pattern layer area is 1. The configuration in which the area of the gap is 0.6 or more and the width dimension of the gap between the patterns is continuously changed is larger or smaller than the case where the width dimension of the gap between the patterns is constant. Regardless, the peak value of the electromagnetic wave absorption can be increased. Moreover, this effect can be achieved regardless of the frequency of the electromagnetic wave to be absorbed. Such an effect causes the resonance phenomenon to be more strongly expressed with respect to the electromagnetic wave by continuously changing the width dimension of the gap between the patterns, that is, by continuously controlling the coupling between the pattern conductors. It is thought that electromagnetic waves can be attenuated more.

  The actual measurement results are described below. An electromagnetic wave absorber 1 having the configuration shown in FIG. 2 was produced. The pattern shape of Example 16 was used as the pattern layer 5 from the aluminum vapor-deposited PET sheet, and the sheet was formed by etching. The absorption layer 4 was obtained by heat-kneading ferrite powder 445 phr into 100 phr vinyl chloride resin and calendering. The created sheet was used. In this absorption layer, the real part (μ ′) of the complex relative permeability in the 950 MHz band is 2.6, the imaginary part (μ ″) is 1.0, the real part (ε ′) of the complex relative permittivity is 31, A sheet having an imaginary part (ε ″) of 2 is used with a thickness of 1.5 mm. Furthermore, 5.5 mm of polypropylene resin foam as the dielectric layer 3 (no magnetism, real part (ε ′) of complex relative permittivity in 950 MHz band is 1.25, imaginary part (ε ″) is 0.05)) Thickness was used and an aluminum vapor-deposited PET sheet was used as the reflective layer 2. After lamination with an adhesive, an electromagnetic wave absorber for UHF band with a total thickness of 7.5 mm and a weight of 7.5 kg and a size of 900 mm × 1,800 mm was obtained. It was.

  The reflective layer 2 used in the present invention is an aluminum vapor-deposited PET sheet having an aluminum vapor-deposited layer of 400 to 500 mm. When the shielding property of the sheet at 1 GHz by the KEC method was measured, the electric field shielding property was 45 dB, and the magnetic field shielding property was 28 dB.

  FIG. 19 is a graph showing a simulation result and an actual measurement result of the electromagnetic wave absorption amount of the electromagnetic wave absorber 1. In FIG. 19, the horizontal axis indicates the frequency, and the vertical axis indicates the reflection loss. As shown in FIG. 19, it can be seen that there is no significant difference between the simulation result and the actual measurement result. As a result of the actual measurement, the peak value of the absorption frequency was 960 MHz, the absorption amount was 24 dB, and the absorption band indicating the 15 dB absorption amount was 70 MHz. The electromagnetic wave absorption measurement is performed in an anechoic chamber, the sample size is a square shape corresponding to 5λ on each side, the distance from the double-ridged antenna for radio wave transmission / reception to the sample is separated by 10λ, and connected to the network analyzer HP8720ES with a coaxial cable. , Based on the so-called free space method.

  In an RFID system, long-distance wireless communication between a reader / writer and a transponder is possible by using an electromagnetic wave in the UHF band for communication between the reader / writer and the transponder. When UHF band electromagnetic waves are used, information can be collectively managed for products on forklifts, carts, or belt conveyors, for example, by attaching IC tags as transponders to the products. Reading and writing information from the IC tag is performed by a reader / writer built in a device called an IC gate installed at a predetermined installation location.

  When introducing such an RFID system, there are objects made of conductive materials such as metals around the reader / writer installation location, and objects made of concrete with deck plates and wires inside. The communication environment deteriorates due to the interference of the reflected waves, leading to a decrease in reading rate and writing rate by the reader / writer. Also, if another reader / writer exists such as another IC gate around the reader / writer installation location, the communication environment deteriorates due to direct wave interference from the other reader / writer, and the reader / writer The reading rate and writing rate due to the above will be reduced. These are obstacles to the introduction of the IC tag system (RFID system).

  In distribution agencies that handle large quantities of products, it is desired to introduce RFID systems that use UHF band electromagnetic waves that can manage large quantities of products in a batch, but the introduction is realized without solving the problem of electromagnetic interference. Not. In general, locations and distribution centers with distribution departments that handle collection and delivery functions are inevitably in an environment with many metal objects such as warehouses, containers, and trucks, and they are operated without sufficient spacing. This is because even if an IC tag system (RFID system) is to be introduced later, the problem of electromagnetic interference as described above cannot be avoided.

  In order to improve the communication environment of such an RFID system, the electromagnetic wave absorbers 1, 1 </ b> A, 1 </ b> B of the present invention absorb reflected waves from an object near the reader / writer, and two reader / writers that are close to each other. It can be used to absorb electromagnetic waves so that the electromagnetic waves from the writer do not interfere. Thus, the RFID system including the electromagnetic wave absorber is a suitable system having a high reading rate and writing rate.

FIG. 20 is a perspective view schematically showing an experimental apparatus 50 for an experiment for confirming the communication improvement effect of the RFID system by the electromagnetic wave absorber 1. FIG. 21 is a graph showing an experimental result of an experiment for confirming the communication improvement effect of the RFID system by the electromagnetic wave absorber 1. FIG. 21 shows a comparison of electric field intensity distributions when the electromagnetic wave absorber 1 is used on the floor 51 and when it is not used. In FIG. 21, the horizontal axis indicates the distance between the antennas, and the vertical axis indicates the received power. In order to confirm the effect of improving the communication of the RFID system using the electromagnetic wave in the UHF band by the electromagnetic wave absorber 1 of the present invention, an experiment was performed in an anechoic chamber using the experimental device 50. The anechoic chamber used was a 3 m anechoic chamber. In the anechoic chamber, pyramid-shaped wave absorbers are installed on five surfaces, but the floor surface 51 is a rectangular metal surface having a long side dimension L51 of 4 m and a short side dimension W51 of 2 m. The electromagnetic wave absorber 1 of the present invention was used as a floor material in order to suppress the influence of the floor surface 51. First, in a state where the electromagnetic wave absorber 1 is not provided, a transmitting antenna (reader: circularly polarized patch antenna, Fujitsu TFU-RW351) 52 and a receiving antenna (dipole antenna) are located at a height H50 = 1.2 m from the floor 51. Advantest TR1722) 53 was installed, and the received power value was measured while changing the distance L50 between the antennas. Similarly, the electromagnetic wave absorber 1 manufactured with the pattern layer of Example 16 was spread over the entire floor surface 51, and the received power value was measured while changing the inter-antenna distance L50 in the same manner. For the sake of comparison, a theoretical value indicating a free space propagation loss is obtained by Friis's equation (5) and is shown in FIG. In the formula (5), _{P R} is the received power, _{P T} is the transmission power.

  It can be seen from FIG. 20 that when the electromagnetic wave absorber 1 is not used (when the floor surface is made of metal), the theoretical value greatly deviates alternately in the vertical direction, and a standing wave is generated. Although this is due to the interference between the direct wave and the reflected wave, reading failure occurs when the area where the electric field strength of the standing wave is lower than the reading sensitivity of the tag. Under these conditions, 10 UHF band IC tags were installed at the position of the dipole antenna, and the reading test was conducted. When the distance from the reader (distance between the antennas) L50 was 1.5 to 1.7 m, the reading rate was It was 10 to 70%.

  From the results when the electromagnetic wave absorber 1 is used as the flooring in FIG. 20, it can be seen that standing wave generation is suppressed. This is because the electromagnetic wave absorber 1 suppresses reflected waves. When the tag reading rate was evaluated in this state, a reading rate of 98% or more could be obtained.

  The electromagnetic wave absorber 1 of the present invention has a reflective layer 2, and does not reflect or transmit incident electromagnetic waves from the pattern layer 5 side, but reflects but does not transmit electromagnetic waves incident from the reflective layer 2 side. , Which has resistance to electromagnetic wave transmission. As a result, by installing the electromagnetic wave absorber 1 in the path of direct waves and reflected waves from other readers, it is possible to greatly suppress the arrival of those unnecessary radio waves. In particular, since the radio wave absorber 1 that shields electromagnetic waves of a specific frequency but does not reflect it is thin and lightweight, it can be installed even in a narrow gap between adjacent IC gates and used as an effective measure for reducing unnecessary radio waves. Became possible. In addition, it is effective to use two electromagnetic wave absorbers stacked together with the back side so that the electromagnetic wave incident side of the radio wave absorber faces the gates facing each other, but the limited space ( The thickness of the electromagnetic wave absorber has been an important issue for use within a width of about 25 cm. For the first time, the electromagnetic wave absorber 1 of the present invention can achieve thinning and can be evaluated and examined as an actual application. Thus, the electromagnetic wave absorbers 1, 1 </ b> A, 1 </ b> B of the present invention can improve the communication environment of such an RFID system.

  FIG. 22 is a perspective view showing a partition 57 using the electromagnetic wave absorber 1. The electromagnetic wave absorber 1 of the present invention can be used as it is as a wall material, a floor material or the like. For example, the electromagnetic wave absorber 1 is held by a frame 55 and a caster 56 is attached to the frame 55 as shown in FIG. Alternatively, a self-supporting partition 57 may be formed. In addition to the partition 57, a panel in which the electromagnetic wave absorber 1 is held by the frame 55 can be formed. The frame 55 and the casters 56 can be made of a material such as resin, wood, or metal. Further, for example, it can be used for the purpose of suppressing leaked radio waves by using an opening / closing mechanism (shutter, door, curtain, etc.) of an entrance / exit portion connected from the heater of the microwave heater to the outside.

  FIG. 23 is a perspective view showing an electromagnetic wave darkroom structure 60 formed using the electromagnetic wave absorber 1. In FIG. 23, a part is notched and the inside is shown and the apparatus used for the electric field strength measurement in the electromagnetic wave anechoic structure 60 is also shown. The electromagnetic anechoic chamber structure 60 is called an anechoic chamber or an anechoic box, and is a structure that forms an internal space in which electromagnetic waves are blocked. Hereinafter, the anechoic chamber structure 60 is referred to as an anechoic box 60. The electromagnetic wave absorber 1 was assembled in a box shape in such a manner that the electromagnetic wave absorbing surface (the surface on the upper side in FIG. 2 and the side opposite to the reflective layer 2) was directed to the inner side, thereby producing a UHF band compatible anechoic box 60. The anechoic box 60 has a width dimension L60 of 1800 mm, a depth dimension W60 of 800 mm, and a height dimension H60 of 800 mm.

  FIG. 24 is a graph showing the results of measuring the electric field strength distribution in the internal space of the anechoic box 60 formed using the electromagnetic wave absorber 1. In FIG. 24, the first axis represents received power, the second axis represents the horizontal axis movement distance, and the third axis represents the vertical axis movement distance. In the anechoic box 60, as shown in FIG. 22, the same transmission antenna 52 and reception antenna 53 as those in FIG. 22 are placed at a distance L50 = 1.5 m between the antennas in the first horizontal direction α parallel to the floor surface. Opened. The transmission antenna 52 is fixed at a position where the height H52 from the floor surface is 1.2 m, and the reception antenna 53 includes a horizontal second direction β orthogonal to the first direction α, and first and second directions α, It was movably provided in a third vertical direction γ perpendicular to β. While the receiving antenna 53 was moved in the second direction β and the third direction γ, the received electric field strength was measured with a test receiver ESS manufactured by Rhode & Schwarts.

  The results are shown in FIG. FIG. 24 shows the electric field strength (reception voltage) distribution in a plane perpendicular to the communication direction (first direction) when the communication distance (inter-antenna distance L50) is 1.5 m. In FIG. 24, the position of the receiving antenna 53 in the second direction β is indicated by the distance (in the second direction β from the reference point where the receiving antenna 53 is aligned with the transmitting antenna 52 on a straight line parallel to the first direction α) ( The position of the receiving antenna 53 in the third direction γ is indicated by the distance from the reference point to one side in the third direction γ (vertical movement distance).

  As shown in FIG. 24, the electric field strength is stable in the anechoic box 60, and is a level that can be sufficiently used as a simple anechoic box 60. The anechoic box 60 is not affected by unnecessary electromagnetic waves such as disturbance noise and other-wave interference due to the shielding effect of the reflective layer 2, and performs quality inspection (communication distance evaluation) and product development of tags and readers / writers therein. It becomes possible to carry out. When combining in a room or box shape, it is important to reduce the weight and thickness of the electromagnetic wave absorber 1. This is because weight reduction can contribute to reducing the cross-sectional area of the frame and angle used in the anechoic box, and the reinforcing bar, which makes it possible to reduce the cost. Thinning leads to effective use of the internal space (test space). Because it will be. Thus, the anechoic chamber structure configured using the electromagnetic wave absorber can be preferably used.

  FIG. 25 is a perspective view showing a transmission / reception direction control device 70 formed using the electromagnetic wave absorber 1. FIG. 25 (1) shows the transmission / reception antenna 71 in a state where the electromagnetic wave absorber 1 is not used, and FIG. 25 (2) shows the transmission / reception direction control device 70 formed using the electromagnetic wave absorber 1 as a side wall. The state transmission / reception antenna 71 is shown. As shown in FIG. 25 (2), the transmission / reception direction control device 70 directs the electromagnetic wave absorber 1 to the inner side with the electromagnetic wave absorbing surface (the surface on the upper side in FIG. 2 opposite to the reflective layer 2). This is a device that is formed in a cylindrical shape, for example, a square cylindrical shape, is attached to the side surface of the transmitting / receiving antenna 71 at one end in the axial direction, and is provided so that the other end in the axial direction protrudes in the transmitting / receiving direction. The axial direction dimension L70 is 20 cm.

  FIG. 26 is a graph showing the results of a test for evaluating the performance of the transmission / reception direction control device 70. The solid line in FIG. 26 is the result of FIG. 25 (1), and the dotted line in FIG. 26 is the result of FIG. 25 (2). FIG. 26 shows the result of measuring the directivity of the transmission / reception antenna 71. In FIG. 26, the horizontal axis represents the measurement angle, and the vertical axis represents the received power received by the reception antenna, with the transmission / reception antenna 71 being a transmission antenna. The measurement angle is 0 ° at the position where the transmission / reception antenna 71 faces the front (reception antenna), makes a right turn, and returns to the 0 ° position at 360 °. Place the received power measuring device in a positional relationship facing directly at 0 ° (360 °) where the position facing away from the receiving antenna is 180 °, and measure the change in received power according to the direction of the antenna (measurement angle) Yes. The angle range from the received power value at 0 ° (360 °) to the 3 dB (50%) drop is evaluated as the antenna radio wave directivity angle.

  In this test, as shown in FIG. 25 (2), a transmission / reception direction control device 70 is provided on the side wall of the transmission antenna (Fujitsu reader / writer TFU-RW351) 71, and the transmission / reception direction control device 70 as shown in FIG. A test for confirming the directivity was conducted as compared with the case where no pattern was provided. The results are shown in FIG. This usage uses the electromagnetic wave absorber 1 for uses such as a corner reflector in which a metal plate is used. Since the electromagnetic wave absorber 1 is close to the transmission / reception antenna 71, sufficient electromagnetic wave absorptivity cannot be exhibited. However, since the electromagnetic wave absorber 1 has the reflective layer 2, it has excellent electromagnetic shielding properties. Thereby, the side rope generated from the transmission / reception antenna 71 can be suppressed, and the interference in the lateral direction can be reduced. As shown by a solid line in FIG. 26, the half-value angle is a radio wave directing angle at which the received power at 0 degree (°) is 76.14 dBμV and the received power level is halved (decreased by 3 dB) when the electromagnetic wave absorber 1 is not disposed. What is 60 degrees (°) is that the electromagnetic wave absorber 1 (transmission / reception direction control device 70) is arranged, so that the received power at 0 degree (°) is 70.76 dBμV, as shown by the broken line in FIG. The half-value angle was 52 degrees (°). Although the communication distance is shortened by suppressing the reflected wave, the directivity can be controlled. As described above, the transmission / reception direction control device 70 can suitably control the transmission / reception direction.

  Since the application example of the radio wave absorber 1 shown in FIGS. 20 to 26 is the electromagnetic wave absorber 1 that is thin and lightweight, it is easier to handle and can be provided at low cost. The pattern layer of the electromagnetic wave absorber 1 used in these application examples may be any pattern layer as long as it conforms to the present invention. Further, not only the electromagnetic wave absorber 1 but also electromagnetic wave absorbers 1A and 1B having different layer configurations can be used. Furthermore, the use of the electromagnetic wave absorbers 1, 1A, 1B of the present invention is not limited to the above-described applications, and any product is applicable as long as the electromagnetic wave absorber of the present invention is used.

  The above-described embodiment is merely an example of the present invention, and the configuration can be changed. For example, each pattern 12 may be formed directly on the surface of the loss layer 7 such as the absorption layer 4 or the dielectric layer 3, and the plate-like substrate 11 may not be used. The loss layer 7 does not necessarily include both the absorption layer 4 and the dielectric layer 3. The loss layer 7 includes only one of them, for example, includes only the absorption layer 4 and does not include the dielectric layer 3. It may be a configuration. The loss layer 7 may be configured to include one or more other layers in addition to the absorption layer 4 and the dielectric layer 3. There may also be a configuration without the reflective layer 2. You may combine the structure of the 2 or more form of each above-mentioned form.

It is a front view which shows a part of pattern layer 5 of the electromagnetic wave absorber 1 of one Embodiment of this invention. 1 is a cross-sectional view showing a part of an electromagnetic wave absorber 1. It is sectional drawing of the electromagnetic wave absorber 1A of the other form of implementation of this invention. It is sectional drawing of the electromagnetic wave absorber 1B of further another form of implementation of this invention. It is a front view which shows 5 C of pattern layers which comprise the electromagnetic wave absorber of the further another form of implementation of this invention. It is a front view of pattern layer 5C which expands and shows a part of FIG. In the pattern P, it is a front view of the pattern P which shows the influence which the direction of the pattern P at the time of receiving the electromagnetic waves which are TE waves has on the electric field which arises in the pattern P. FIG. 3 is a front view showing a square pattern 40. FIG. 4 is a front view showing a circular pattern 41. FIG. It is a graph which shows the absorption characteristic of Examples 1-6. It is a graph which shows the absorption characteristic of Examples 7-10. It is a graph which shows the absorption characteristic of Examples 11-16. It is a graph which shows the absorption characteristic of Examples 17-22. It is a graph which shows the relationship between the area ratio of a pattern, and absorption amount. It is a graph which shows the relationship between the area ratio of a pattern, and an absorption bandwidth. It is a graph which shows the relationship between the change of the width dimension of the clearance gap between patterns, and an absorption characteristic by comparing with a star-shaped pattern and a square pattern. The relationship between the change in the width dimension of the gap between the patterns and the absorption characteristics is as follows: the frequency of the absorption target is 2.4 GHz band, and the gap between the radial pattern and the substantially rectangular pattern changes or is constant. It is a graph shown in comparison. The relationship between the change in the width of the gap between the patterns and the absorption characteristics is compared between the case where the absorption target frequency is the UHF band and the gap between the radial pattern and the substantially square pattern changes, and when the gap is constant. It is a graph shown. 14 is a graph showing a comparison between a simulation result and an actual measurement result of the electromagnetic wave absorber 1 having the pattern layer of Example 16. FIG. It is a perspective view which simplifies and shows the experimental apparatus 50 for the experiment which confirms the communication improvement effect of the RFID system by the electromagnetic wave absorber.

It is a graph which shows the experimental result of the experiment which confirms the communication improvement effect of the RFID system by the magnetic wave absorber. It is a perspective view which shows the partition 57 using the electromagnetic wave absorber 1. FIG. It is a perspective view which shows the electromagnetic wave anechoic structure 60 formed using the electromagnetic wave absorber 1. FIG. 4 is a graph showing the result of measuring the electric field strength distribution in the internal space of the anechoic box 60 made of the electromagnetic wave absorber 1. It is a perspective view which shows the transmission / reception direction control apparatus 70 formed using the electromagnetic wave absorber 1. FIG. It is a graph which shows the result of the test which evaluates the performance of the transmission / reception direction control apparatus.

Explanation of symbols

1, 1A, 1B Electromagnetic wave absorber 2 Conductive reflective layer 3 Dielectric layer 4 Electromagnetic wave absorption layer 5, 5C Pattern layer 11 Plate-like substrate 12 Pattern 30 Radial pattern 31 Substantially square pattern

Claims (16)

A pattern layer in which a conductive pattern made of a conductive material is formed, and when the area of the entire pattern layer region is 1, the area ratio of the region where the conductive pattern is formed is 0.6 or more. Having a pattern layer;
An electromagnetic wave absorber comprising: a loss layer having a portion made of a material that is at least one of a magnetic loss material and a dielectric loss material. A pattern layer in which a plurality of conductive patterns made of a conductive material are formed, and among the gaps formed between the conductive patterns, the width dimension of at least some of the gaps is related to the extending direction of the gaps. A continuously changing pattern layer;
An electromagnetic wave absorber comprising: a loss layer having a portion made of a material that is at least one of a magnetic loss material and a dielectric loss material.   The gap in which the width dimension changes continuously has an interval in the extending direction of the gap, and has at least two approach parts having a smaller width dimension, and the width dimension is smaller than the approach part between the approach parts. The electromagnetic wave absorber according to claim 2, wherein the electromagnetic wave absorber has a large separation portion.   The electromagnetic wave absorber according to claim 1, wherein at least some of the conductive patterns have an outer shape including a curved portion.   The electromagnetic wave absorber according to claim 1, wherein the loss layer has a magnetic layer made of a material containing at least a magnetic substance. The loss layer is
A magnetic layer made of a material containing at least a magnetic substance;
The electromagnetic wave absorber according to claim 1, further comprising a dielectric layer made of a material containing at least a dielectric.   The electromagnetic wave absorber according to any one of claims 1 to 6, wherein a frequency band having an electromagnetic wave absorption amount of 15 dB or more is 70 MHz or more. An electromagnetic wave absorber for absorbing electromagnetic waves in the UHF band,
The total thickness dimension is 15 mm or less, The electromagnetic wave absorber as described in any one of Claims 1-7 characterized by the above-mentioned. An electromagnetic wave absorber for absorbing 2.4 GHz band electromagnetic waves,
The electromagnetic wave absorber according to any one of claims 1 to 7, wherein a total thickness dimension is 5 mm or less.   The electromagnetic wave absorber according to any one of claims 1 to 9, wherein the electromagnetic wave absorber has an electroconductive reflection layer and has an electromagnetic wave shielding property for shielding electromagnetic waves.   The electromagnetic wave absorber according to any one of claims 1 to 10, which has flame retardancy, quasi-incombustibility, or incombustibility.   A building material comprising the electromagnetic wave absorber according to any one of claims 1 to 11.   An electromagnetic wave darkroom structure using the electromagnetic wave absorber according to any one of claims 1 to 11.   The RFID communication system using the electromagnetic wave absorber as described in any one of Claims 1-11.   The transmission / reception direction control method which arrange | positions the electromagnetic wave absorber as described in any one of Claims 1-11 around an antenna, and controls the transmission / reception direction of an electromagnetic wave.   The electromagnetic wave absorption method by using the electromagnetic wave absorber as described in any one of Claims 1-11.

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