JPWO2007108478A1 - Electromagnetic wave absorber and absorbed electromagnetic wave control method - Google Patents

Abstract

The electromagnetic wave absorber having variable absorption wavelength range and / or absorption amount according to the present invention is characterized in that a fluid containing conductive carbon having a high aspect ratio is filled between electrodes. Also, the method for controlling an absorbed electromagnetic wave according to the present invention, a method for controlling the wavelength range and / or the amount of absorption of an electromagnetic wave transmitted through an electromagnetic wave absorber, and a fluid containing conductive carbon having a high aspect ratio is filled between electrodes. The conductive carbon is oriented by applying an electric field between the electrodes of the electromagnetic wave absorbing device.

Description

  The present invention relates to a novel electromagnetic wave absorber and an absorbed electromagnetic wave control method.

  2. Description of the Related Art In recent years, various electromagnetic wave absorbing sheets that absorb electromagnetic waves corresponding to each have been provided due to the increase and diversification of communication devices such as mobile phones (Patent Document 1, etc.).

  For example, Patent Document 1 provides a sheet of dielectric loss material containing a specific amount of microcoiled carbon fibers having a specific fiber length.

  However, the electromagnetic wave absorbing sheet of Patent Document 1 and the conventional electromagnetic wave absorbing materials are fixed in advance in the wavelength range and the amount of absorption, and after installation or installation in a building or the like, the wavelength range and the amount of absorption are fixed. It can not be changed. Therefore, there is a problem that when the wavelength range or the like to be absorbed changes, the wavelength range or the like cannot be handled.

Therefore, it is desired to develop a device that can control the wavelength range and / or the amount of absorption of electromagnetic waves after manufacturing or installation.
JP 2001-77583 A

  The main object of the present invention is to provide a device capable of changing the absorption wavelength range and / or the amount of absorption of electromagnetic waves, and a control method therefor.

  As a result of intensive studies in view of the above prior art, the present inventors have completed the present invention by using an apparatus having a specific structure. That is, the present invention relates to the following apparatus and control method.

  Item 1. An electromagnetic wave absorber having a variable absorption wavelength range and / or absorption amount, wherein a fluid containing conductive carbon having a high aspect ratio is filled between electrodes.

  Item 2. Item 2. The electromagnetic wave absorber according to Item 1, wherein the conductive carbon has an aspect ratio of 2 or more.

  Item 3. Item 3. The electromagnetic wave absorber according to Item 1 or 2, wherein the conductive carbon is at least one selected from the group consisting of carbon nanocoils, carbon nanotubes, carbon nanofibers, and carbon nanotwists.

  Item 4. Item 4. The electromagnetic wave absorber according to any one of Items 1 to 3, wherein the conductive carbon content is 0.001 to 50 parts by weight with respect to 100 parts by weight of the fluid.

Item 5. Item 5. The electromagnetic wave absorber according to any one of Items 1 to 4, wherein the fluid has a viscosity of 1 to 100,000 cPs (25 ° C).

Item 6. A method for controlling the wavelength range and / or the amount of absorption of electromagnetic waves that pass through an electromagnetic wave absorbing device, wherein a fluid containing conductive carbon having a high aspect ratio is filled between the electrodes. Orienting the conductive carbon by applying an electric field to
A method for controlling absorbed electromagnetic waves.

  Item 7. Item 7. The absorbed electromagnetic wave control method according to Item 6, wherein the electromagnetic wave is an electromagnetic wave having a wavelength range equal to or greater than a microwave.

  Item 8. Item 7. The absorbed electromagnetic wave control method according to Item 6, wherein the electromagnetic wave is an electromagnetic wave having a wavelength range equal to or less than infrared rays.

Item 9. A method for controlling the wavelength range and / or the amount of absorption of electromagnetic waves transmitted through an electromagnetic wave absorbing device,
9. Absorption characterized by changing the orientation state of the conductive carbon by applying flow, vibration or heat to the fluid containing the conductive carbon oriented by the method according to any one of items 6 to 8 above. Electromagnetic wave control method.

  The electromagnetic wave absorber (also referred to as “electromagnetic wave modulator”) of the present invention is characterized in that a fluid containing conductive carbon having a high aspect ratio is filled between electrodes.

  Examples of the conductive carbon having a high aspect ratio include carbon microcoils having a diameter of less than 1 μm and carbon microcoils having a diameter of 1 μm or more, such as carbon nanotubes, carbon nanofibers, carbon nanocoils, and carbon nanotwists. Among these, from the viewpoint of good orientation response characteristics to an electric field, at least one of carbon nanotubes, carbon nanofibers, carbon nanocoils, and carbon nanotwists is preferable, and carbon nanocoils are most preferable.

  Although the aspect ratio (fiber length / fiber diameter) of the conductive carbon is not limited, for example, the average is 2 or more, and preferably about 10 to 5000000 on average.

  The fiber length of the conductive carbon is not limited and may be appropriately determined from a wide range of, for example, an average of about 50 nm to 1 mm. The fiber diameter (diameter) is not limited, but is preferably 1 nm or more and less than 1 μm on average.

  When the shape of the conductive carbon is a coil, that is, a carbon nanocoil or a carbon nanotwist, the coil length is preferably about 50 nm to 1 mm on average, and more preferably about 0.5 to 100 μm on average. The coil diameter (diameter) is preferably about 10 nm to 10 μm on average, more preferably about 50 nm or more and less than 1 μm.

  The fluid containing conductive carbon is not particularly limited as long as it has fluidity and can disperse conductive carbon. For example, water; monovalent or polyhydric alcohols such as isopropyl alcohol, ethanol, glycerin, ethylene glycol, polyethylene glycol, and sorbitol; organic solvents such as benzene, hexane, chloroform, and acetone.

  In the present invention, a substance having fluidity when heated (for example, about 60 to 250 ° C.) is also included in the fluid. As such a fluid, a thermoplastic resin etc. are mentioned suitably, for example. Specifically, polyvinyl alcohol (PVA), polyethylene (PE), polypropylene (PP), etc. other than styrene resin, acrylic resin, and (meth) acrylic resin are mentioned. Also included are paraffin, wax, oligomers and the like. By using such a resin as a fluid, for example, the fluid is heated to about 60 to 250 ° C. to make the fluid fluid, and then an electric field is applied to orient the conductive carbon. The orientation state can be maintained by returning to normal temperature and losing the fluidity of the fluid. Furthermore, it can be heated again to have fluidity, and then an electric field can be applied to bring the conductive carbon into a new orientation state again.

  Moreover, the substance which has fluidity | liquidity by sending electric currents, such as a liquid crystal, is also contained in the fluid of this invention.

  These fluids may be used alone or in combination of two or more.

  In the present invention, alcohol and thermoplastic resin are particularly preferable among these fluids.

  The fluid may contain various additives such as polycyclic aromatic compounds such as anthracene, pyrene and porphyrin; polymer compounds such as carboxymethyl cellulose, gelatin, polycarbonate and polyimide; and surfactants.

  The fluidity of the fluid has a viscosity at 25 ° C. of usually about 1 cPs to 100,000 cPs, preferably about 2 cPs to 10,000 cPs. By setting it as this range, the dispersion and orientation state of the conductive carbon can be controlled more easily. In addition, about the substance which has fluidity | liquidity when heated or when an electric current is sent, what is necessary is just to have the viscosity of the said range at the time of the said heating (for example, 60-250 degreeC) or electricity supply. In the present invention, the viscosity is measured by a viscosity measuring device.

  The fluid is preferably an insulator from the viewpoint of electromagnetic wave permeability, and usually has a relative dielectric constant of about 1 to 200 (normal temperature 25 ° C.).

  The content of conductive carbon in the fluid is appropriately determined according to the type of conductive carbon, the type of fluid, the viscosity, and the like. For example, about 0.001 to 50 parts by weight with respect to 100 parts by weight of the fluid The amount is preferably about 0.01 to 30 parts by weight.

A well-known or commercially available electrode can be used. Examples of the material include metals such as gold, platinum, silver, copper, aluminum, titanium, nickel, chromium, cobalt, indium, tin, and zinc, or alloys thereof, ITO (Indium Tin Oxide), IZO (In ₂ ). O ₃ —ZnO), SnO _{2 and} other oxides, carbon, and the like can also be used.

  The shape of the electrode may be a thin line or a thin film. Further, it may be a comb electrode in which a plurality of fine wires are arranged in parallel.

  When the electrode is made into a thin film, it is necessary to transmit electromagnetic waves through the thin film electrode (see FIG. 1 described later). Therefore, if the surface resistance of the electrode is made larger than the radio wave impedance (about 377Ω) in free space. Good. Generally, it is about 400Ω or more, preferably about 1000Ω or more, more preferably about 3000Ω or more. The upper limit is not limited, but may be about 100,000Ω, for example.

  In the case of a comb-shaped electrode, the electromagnetic wave is transmitted through the substrate between the electrodes, and thus the radio wave impedance is not particularly limited.

  The substrate is not limited as long as it is a material that can transmit electromagnetic waves, and examples thereof include a glass substrate, a quartz substrate, a plastic substrate, and a ceramic substrate.

  The area of the substrate and electrodes, the distance between the electrodes, and the like may be appropriately determined according to the content of conductive carbon in the fluid, the strength of the electric field, and the like.

  The power source connected to the electrode is not limited, and a known or commercially available power source can be used.

As a typical example of the electromagnetic wave absorbing device according to the present invention, at least one selected from the group consisting of an absorption wavelength region and an absorption amount is variable.
i) As shown in FIG. 1, two thin film electrodes laminated on a substrate are arranged so as to face each other, and a fluid containing conductive carbon having a high aspect ratio is filled between the two electrodes. apparatus,
ii) As shown in FIG. 2, two sets of comb-shaped electrodes stacked on the substrate are arranged so that the thin wire electrodes constituting the opposing comb-shaped electrodes are parallel to each other, and between the two sets of comb-shaped electrodes. A device filled with a fluid containing conductive carbon having a high aspect ratio,
iii) As shown in FIG. 3, two sets of comb-shaped electrodes stacked on a substrate are arranged so that each thin wire electrode of the facing comb-shaped electrodes is vertical (relationship of twist) and has a high aspect ratio. Examples thereof include an apparatus filled with a fluid containing conductive carbon.

  In particular, in the apparatus shown in FIGS. 1 to 3, when the electromagnetic wave to be transmitted is visible light, a transparent substrate may be used. In this case, in FIG. 1, the thin film electrode is also a transparent electrode, that is, ITO, IZO or the like.

  In order to redisperse the oriented conductive carbon (in an unoriented state), a dispersing device may be provided between the electrodes or between the electrodes. Specifically, if a known or commercially available flow, vibration device (for example, liquid feed pump, stirrer, sonic device, etc.), heating device (electric heater, infrared lamp, halogen lamp, etc.) is installed between the electrodes. Good.

  Since the present invention employs the above-described structure, an electromagnetic wave is transmitted through the electrodes by causing the electric current to flow between the electrodes and generating an electric field between the electrodes to orient the conductive carbon between the electrodes at a desired angle. The area and / or the amount of absorption (transmittance or reflectivity) can be changed.

  The orientation of the present invention means that individual conductive carbons are arranged in a specific direction, and includes plane orientation as well as uniaxial orientation.

  The electromagnetic wave absorbed by the device of the present invention can be absorbed in a wide wavelength range of about 200 nm to 300 mm. Specifically, microwaves (about 300 mm to 10 mm, about 1 GHz to 30 GHz), millimeter waves (10 mm) About 1 mm, about 30 GHz to about 300 GHz), terahertz wave (about 1 mm to about 10 μm, about 0.3 THz to about 30 THz), infrared light (about 100 μm to about 800 nm), visible light (about about 830 nm to about 360 nm), ultraviolet light (about about 400 nm to about 14 nm) ).

  Among these, particularly in visible light and ultraviolet light, by changing the amount of absorption (transmittance or reflectance), a switch function (on / off function of light absorption represented by an optical shutter or the like) can be suitably exhibited. Therefore, it can be suitably used as an electromagnetic wave absorber.

  In microwaves, millimeter waves, terahertz waves, infrared rays, etc., in addition to the above-mentioned absorption amount, the absorption wavelength range can be changed in a multi-stage (stepwise) manner. In addition to the switch function, the variable wavelength function (absorption wavelength range) And the modulation function (the function of changing the transmittance (or reflectivity) or the polarization plane (or polarization component) of the electromagnetic wave in multiple stages) can be suitably exhibited. Therefore, it can be suitably used not only as an electromagnetic wave absorber but also as a variable wavelength electromagnetic wave absorber.

2. Control Method The method according to the first aspect of the present invention is a method for controlling the wavelength range and / or the amount of absorption of electromagnetic waves that pass through the electromagnetic wave absorber, and the fluid containing conductive carbon having a high aspect ratio is between the electrodes. The conductive carbon is oriented by applying an electric field between the electrodes of the electromagnetic wave absorber filled in the electrode.

  As the electromagnetic wave absorbing device, the above-described electromagnetic wave absorbing device with variable absorption wavelength range and / or absorption amount of the present invention is used.

  Hereinafter, a preferable method will be described using the above-described typical electromagnetic wave absorber.

i) In the case of an apparatus in which two thin film electrodes laminated on a substrate are arranged to face each other, and a fluid containing conductive carbon having a high aspect ratio is filled between the two electrodes. As described above, when an AC voltage is applied to the bipolar electrodes, the conductive carbon in the fluid is oriented in a direction perpendicular to the electrode substrate plane. In addition, by appropriately adjusting the voltage, it is possible to appropriately adjust the angle of the conductive carbon until it is oriented in the vertical direction. By these, the wavelength range and / or absorption amount of the electromagnetic wave transmitted between the electrodes of the device can be controlled.

  To explain this mechanism in detail, for example, when carbon nanocoils are used as conductive carbon, the dielectric constant of the fluid in which carbon nanocoils are dispersed when carbon nanocoils are unoriented (the orientation is irregular) The anisotropy is averaged and is isotropic as a whole. On the other hand, when an AC voltage is applied between the transparent electrodes, the carbon nanocoils in the fluid are oriented perpendicular to the transparent electrodes. When carbon nanocoils are in an oriented state, dielectric anisotropy develops, the dielectric constant and dielectric loss for an electric field perpendicular to the orientation direction decrease, and the dielectric constant and dielectric loss for an electric field parallel to the orientation direction increase. . Since the electric field of the electromagnetic wave perpendicularly incident on this device is perpendicular to the orientation direction of the carbon nanocoil, the absorption peak frequency of the electromagnetic wave increases due to the decrease in dielectric constant, and the transmission loss of the electromagnetic wave decreases due to the decrease in dielectric loss. In addition, when the wavelength of the incident electromagnetic wave is smaller than the size of the carbon nanocoil, the transmittance (transmittance) increases due to the reduction of the geometric optical shielding area.

ii) Two sets of comb-shaped electrodes stacked on the substrate are arranged so that the electrodes constituting the opposing comb-shaped electrodes are parallel to each other, and the conductivity having a high aspect ratio is set between the two sets of comb-shaped electrodes. In the case of an apparatus filled with a fluid containing carbon As shown in FIG. 5, when an alternating voltage is applied to the comb-shaped electrode, the conductive carbon in the fluid is interposed between the individual thin wire electrodes constituting the comb-shaped electrode. , Orienting so as to be perpendicular to the fine wire electrode and parallel to the electrode substrate. Note that, by appropriately adjusting the voltage, the angle of the conductive carbon until it is vertically aligned can be appropriately adjusted. By these, the wavelength range and / or absorption amount of the electromagnetic wave transmitted between the electrodes of the device can be controlled.

  This mechanism will be described in detail. The electromagnetic wave perpendicularly incident on this device can be considered by dividing it into a polarization component whose electric field is parallel to the comb teeth and a polarization component whose electric field is perpendicular to the comb electrodes. With respect to the polarization component in which the electric field is parallel to the comb electrode, an increase in dielectric constant and an increase in dielectric loss cause a decrease in absorption peak frequency and an increase in transmission loss.

  With respect to the polarization component in which the electric field is perpendicular to the comb electrode, the absorption peak frequency increases and the transmission loss decreases due to the decrease in the dielectric constant and the decrease in the dielectric loss. In addition, when the wavelength of the incident electromagnetic wave is smaller than the size of the carbon nanocoil, the transmittance (transmissivity) increases due to an increase in the geometric optical shielding area.

iii) A fluid containing conductive carbon having a high aspect ratio in which two sets of comb-shaped electrodes stacked on a substrate are arranged so that each of the opposing comb-shaped electrodes is vertical (twisted relationship) A) When a voltage is applied to the upper and lower comb electrodes, the conductive carbon is oriented perpendicular to the electrode substrate plane (in the Z direction) as shown in FIG.
b) When a voltage is applied only to the upper comb-shaped electrode, the conductive carbon is oriented in the Y direction between the thin wire electrodes of the upper comb-shaped electrode, as shown in FIG.
c) When a voltage is applied only to the lower comb electrode, as shown in FIG. 8, the conductive carbon is oriented in the X direction between the thin wire electrodes of the lower comb electrode.

  Note that, by appropriately adjusting the voltage, the angle of the conductive carbon until it is vertically aligned can be appropriately adjusted. Thus, it is possible to control the wavelength range and / or the amount of absorption (transmittance or reflectivity) of the electromagnetic wave transmitted between the electrodes of the device. These mechanisms are the same as described above. From the above method, an optimal control method may be taken in accordance with the use and purpose of the final product.

  In particular, when the electromagnetic waves are visible light and ultraviolet light, the amount of absorption (transmittance or reflectance) of the electromagnetic waves is changed by orienting the conductive carbon by the above method, and the switch function (represented by an optical shutter or the like). The function as an on / off function of light absorption is effectively exhibited.

  When the electromagnetic waves are microwaves, millimeter waves, terahertz waves, infrared rays, etc., by aligning the conductive carbon by the above method, the absorption wavelength region and the like can be changed in multiple stages in addition to the above absorption amount. In addition to the switch function, a variable wavelength function (a function for changing the absorption wavelength range in a multistage manner) and a modulation function (a function for changing the transmittance (or reflectance) of electromagnetic waves in a multistage manner) can be suitably exhibited.

  The voltage, application time, etc. may be determined as appropriate according to the conductive carbon, fluid, type of the above device, as well as the distance between the electrodes, etc., and the degree of orientation of the conductive carbon by appropriately changing the voltage, application time, etc. As a result, the absorption wavelength region and / or the amount of absorption of electromagnetic waves can be appropriately adjusted.

  If the fluid between the electrodes of the device is a resin, depending on the type of the resin, there is a case where the conductive carbon does not align due to lack of fluidity at room temperature. In this case, the conductive carbon may be oriented by applying an electric field after imparting fluidity to the resin by heating. By using as a fluid a resin that does not have fluidity at room temperature but will have fluidity upon heating, the absorption wavelength range and / or absorption amount of transmitted electromagnetic waves can be changed after installation of the device. At the same time, it is possible to provide an electromagnetic wave absorber that can firmly stabilize the orientation of the conductive carbon at room temperature.

  The method according to the second aspect of the present invention is a method for controlling the wavelength region and / or the amount of absorption of an electromagnetic wave transmitted through an electromagnetic wave absorber, and is a conductive material having a high aspect ratio oriented by the method of the first invention. The oriented conductive carbon is dispersed by applying flow, vibration, or heat to a fluid containing carbon. Thereby, the orientation state of the conductive carbon once oriented can be changed.

  Specific examples include a method of causing a fluid to flow with a liquid feed pump, a method of vibrating a fluid with an ultrasonic device, a method of stirring the fluid with a stirrer, a method of heating the fluid with an electric heater, etc. For example, a method of indirectly flowing, vibrating, stirring, and heating the fluid by virtue of vibration, heating, or the like can be used. In addition, when the fluid is a resin that does not have fluidity at room temperature, the above method may be employed after the fluidity is imparted by heating the resin.

  Since the electromagnetic wave absorption device of the present invention has a structure in which a fluid containing conductive carbon having a high aspect ratio is filled between electrodes, the absorption wavelength region and / or absorption amount of electromagnetic waves can be adjusted. For this reason, the absorption wavelength region and / or the amount of absorption can be appropriately changed after production or after installation at a desired location, and can be used for various applications.

  In addition, according to the control method of the present invention, the absorption wavelength region and / or the amount of absorption of electromagnetic waves can be adjusted by adjusting the electric field (voltage, etc.).

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples. In addition, this invention is not limited to a following example.

Example 1
<Example of horizontal alignment of nanocoil by electric field>
A dispersion liquid in which carbon nanocoils were dispersed in an isopropyl alcohol solution (viscosity at 25 ° C .: 2 cPs) was prepared. The average coil length of the nanocoils in the dispersion was 1 to 40 μm, and the concentration of the carbon nanocoils in the dispersion was 0.0127% by weight.

  Two thin wire electrodes (copper wires) were arranged in parallel at intervals of 0.9 mm to produce an electrode device (for horizontal facing). The electromagnetic wave absorber of Example 1 was manufactured by filling the dispersion liquid between the two electrodes. An electric field having a frequency of 100 kHz and an electric field strength of 63 kV / m was applied to this apparatus for 1 minute.

  The results observed with an optical microscope before and after the application of the electric field are shown in FIG.

  When the amount of transmitted light of the fluid between the electrodes before and after the application of the electric field was measured, a change of 0.91% occurred. As a result, it was found that there was a switch function.

  A white LED (manufactured by Nichia Corporation, model number: NSPW500CS) was used as the light source. The rate of change in the amount of transmitted light was determined as follows.

  A small CCD camera (Logitech Q Cam Pro 4000) that can be directly connected to a personal computer was attached to the eyepiece of a bright field microscope (manufactured by Olympus), and the state of electrophoresis (orientation) was recorded as a color moving image by collimated photography. Color still images before and after the start of alignment were extracted from the recorded moving images, and the average luminance of all pixels in the region where the alignment of the carbon nanocoils between the electrodes was calculated.

  Luminance (Y) was calculated from the levels (0 to 255) of the red (R), green (G), and blue (B) components of one pixel using the following formula.

Y = 0.29891 × R + 0.58661 × G + 0.11448 × B
The change rate between the average value of the luminance after orientation calculated by the above formula and the average value of the luminance before orientation was defined as the change rate of the transmitted light amount.

Example 2
<Example of vertical alignment of nanocoil by electric field>
A dispersion in which carbon nanocoils were dispersed in an isopropyl alcohol solution (viscosity at 25 ° C .: 2 cPs) was used. The coil length of the carbon nanocoil in the dispersion was 1 to 40 μm, and the concentration of the nanocoil in the dispersion was 0.006% by weight.

  By placing two ITO glass substrates on which ITO electrodes (manufactured by Sanyo Vacuum Industry Co., Ltd.) are laminated on a glass substrate at an interval of 0.22 mm so that the ITO layer is on the inside, an electrode device (for vertical facing measurement) is installed. Produced. The electromagnetic wave absorbing device of Example 2 was manufactured by filling the electrode device with the dispersion. An electric field having a frequency of 1 kHz and an electric field strength of 256 kV / m was applied for 1 minute.

    The result observed with the optical microscope is shown in FIG.

  When the transmitted light quantity of the fluid between the electrodes before and after the application of the electric field was measured, a change of 8% occurred. As a result, it was found that there was a switch function.

Example 3
<Example of horizontal orientation of nanocoil in high viscosity fluid>
A dispersion in which carbon nanocoils were dispersed in a glycerin solution (viscosity at 25 ° C .: 800 cPs) was prepared. The coil length of the carbon nanocoil in the dispersion was 1 to 40 μm, and the concentration of the nanocoil in the dispersion was 0.006% by weight. The electromagnetic wave absorber of Example 3 was manufactured by filling the electrode device manufactured in Example 1 with the dispersion. An electric field having a frequency of 1 kHz and an electric field strength of 63 kV / m was applied to this apparatus.

  The results observed with an optical microscope before and after the application of an electric field are shown in FIG.

  When the transmitted light quantity of the fluid between the electrodes before and after the application of the electric field was measured, a change of 0.7% occurred. As a result, it was found that there was a switch function.

Example 4
A coil-containing resin in which 0.05% by weight of carbon nanocoil was dispersed in an acrylic ultraviolet curable resin (manufactured by TESK, model number A-1836, viscosity 10 cPs at 25 ° C.) was prepared. Two ITO glass substrates (22 mm x 33 mm) obtained by laminating ITO electrodes (manufactured by Sanyo Vacuum Industry Co., Ltd.) on a glass substrate are parallel so that the ITO layer is on the inside and the electrode interval is 0.5 mm. A cell was prepared by placing and fixing with a spacer. The electromagnetic wave absorbing device of the present invention was produced by filling the cell with 0.4 g of a coil-containing resin.

  The carbon nanocoils in the obtained electromagnetic wave absorber were oriented, and the complex dielectric constant before and after the orientation was measured. FIG. 12 shows a measurement circuit.

First, an AC voltage (voltage 20 V, frequency 100 kHz) is applied to the electromagnetic wave absorber immediately after the cell is filled with the coil-containing resin, and the cell impedance before orientation is measured using a two-phenomenon oscilloscope (manufactured by Tektronix, model number TDS3024B). Z and the phase difference φ between the voltage waveform and the current waveform were measured. As a result of the measurement, the impedance Z was 54.3 kΩ, and the phase difference φ was −78.2 °. From this result, the complex relative dielectric constant ε _r before orientation was calculated to be 2.23-j0.466.

  Next, the applied voltage was raised and an AC voltage of 200 V (frequency: 100 kHz) was applied to the electromagnetic wave absorbing device, so that the carbon nanocoils in the device were oriented perpendicular to the electrode plane.

Thereafter, the applied voltage is lowered, an AC voltage of 20 V (frequency 100 kHz) is applied, and the cell impedance Z ′ after orientation, voltage waveform and current waveform are measured using a two-phenomenon oscilloscope (manufactured by Tektronix, model number TDS3024B). The phase difference φ was measured. As a result of the measurement, the impedance Z was 48.0 kΩ, and the phase difference φ was −77.9 °. From this result, the complex relative dielectric constant ε _r after orientation was calculated to be 2.53-j0.527.

  For this reason, both the values of the imaginary part and the real part of the complex relative permittivity after orientation were larger than the complex relative permittivity before orientation. Thereby, it turned out that the electromagnetic wave absorber of this invention can change an electromagnetic wave absorption characteristic (an absorption wavelength range and absorption amount).

Comparative Example 1
<Electromagnetic wave absorption characteristics of microwave band in carbon black>
A dispersion was prepared by dispersing carbon black (average particle size 25 nm, manufactured by Tokai Carbon Co., Ltd., “Conductive Talker Black # 5500”) in an isopropyl alcohol solution (viscosity at 25 ° C .: 2 cPs). The concentration of carbon black in the dispersion was 0.0127% by weight.

  Two thin wire electrodes (copper wires) were arranged in parallel at intervals of 0.9 mm to produce an electrode device (for horizontal facing). The device of Comparative Example 1 was manufactured by filling the dispersion between the two electrodes.

  An electric field having a frequency of 100 kHz and an electric field strength of 63 kV / m was applied to this apparatus for 1 minute. When the amount of light transmitted through the fluid between the electrodes before and after the application of the electric field was measured, no change occurred. As a result, it was found that the switch function was not exhibited.

FIG. 1 shows an example of an electromagnetic wave absorber according to the present invention. FIG. 2 shows an example of the electromagnetic wave absorber of the present invention. FIG. 3 shows an example of the electromagnetic wave absorber of the present invention. FIG. 4 shows an example of the mechanism of the electromagnetic wave control method of the present invention. FIG. 5 shows an example of the mechanism of the electromagnetic wave control method of the present invention. FIG. 6 shows an example of the mechanism of the electromagnetic wave control method of the present invention. FIG. 7 shows an example of the mechanism of the electromagnetic wave control method of the present invention. FIG. 8 shows an example of the mechanism of the electromagnetic wave control method of the present invention. FIG. 9 shows the observation results before and after applying the electric field of the electromagnetic wave absorber of Example 1. FIG. 10 shows the observation results before and after applying the electric field of the electromagnetic wave absorber according to the second embodiment. FIG. 11 shows the observation results before and after applying the electric field of the electromagnetic wave absorbing device of Example 3. FIG. 12 shows a measurement circuit of the variable wavelength electromagnetic wave absorber used in the fourth embodiment.

Claims (9)

  An electromagnetic wave absorber having a variable absorption wavelength range and / or absorption amount, wherein a fluid containing conductive carbon having a high aspect ratio is filled between electrodes.   The electromagnetic wave absorber according to claim 1, wherein the conductive carbon has an aspect ratio of 2 or more.   The electromagnetic wave absorber according to claim 1, wherein the conductive carbon is at least one selected from the group consisting of carbon nanocoils, carbon nanotubes, carbon nanofibers, and carbon nanotwists.   The electromagnetic wave absorber according to claim 1, wherein the content of the conductive carbon is 0.001 to 50 parts by weight with respect to 100 parts by weight of the fluid.   The electromagnetic wave absorber according to claim 1, wherein the fluid has a viscosity of 1 to 100,000 cPs (25 ° C.). A method for controlling the wavelength range and / or the amount of absorption of electromagnetic waves transmitted through an electromagnetic wave absorbing device,
Orienting the conductive carbon by applying an electric field between the electrodes of an electromagnetic wave absorbing device in which a fluid containing conductive carbon having a high aspect ratio is filled between the electrodes;
A method for controlling absorbed electromagnetic waves.   The method for controlling an absorbed electromagnetic wave according to claim 6, wherein the electromagnetic wave is an electromagnetic wave having a wavelength range of microwaves or more.   The method for controlling an absorbed electromagnetic wave according to claim 6, wherein the electromagnetic wave is an electromagnetic wave having a wavelength range equal to or less than infrared. A method for controlling the wavelength range and / or the amount of absorption of electromagnetic waves transmitted through an electromagnetic wave absorbing device,
The orientation state of the conductive carbon is changed by applying flow, vibration or heat to the fluid containing the conductive carbon oriented by the method according to claim 6.
A method for controlling absorbed electromagnetic waves.