JP2006140298A - Coated-bar array type electric wave absorber, and manufacturing method for coated-bar for electric wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electric wave absorber which shows better electric wave absorbing characteristics than a conventional resonant single layer sheet in broader bands, and is remarkably thinner than a conventional pyramidal electric wave absorber for a microwave chamber having broad-band characteristics. <P>SOLUTION: According to the coated-bar array type electric wave absorber, an array of columnar conductor cores 1 coated with an electric absorbing material (coated bars) are formed on the electric wave incident side of a conductor reflective plate 2 or a conductor reflective plate 2 coated with an electric wave absorbing material. The diameter of each columnar conductor cores 1 is 1/20 of the wavelength of the incident electric wave or larger, and a gap at each coated bar 1 is equal to the wavelength of the incident electric wave or smaller. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a coated rod array type radio wave absorber and a method for producing a coated rod for a radio wave absorber, and in particular, is excellent in radio wave absorption characteristics and broadband properties, and is thin and has a coated rod array type radio wave absorber. The present invention relates to a body and a method of manufacturing a covering rod constituting the radio wave absorber.

  In recent years, the use of wireless digital data communication such as wireless LAN, ETC, and cellular phone has rapidly spread, and accordingly, problems such as radio wave interference and information leakage are becoming social problems. One of the countermeasure techniques for such problems is the use of a radio wave absorber.

  The radio wave absorber used for the above-mentioned applications has, as characteristics, absorption characteristics of radio waves and broadband properties (absorption characteristics necessary in a wide frequency range. Generally, 20 dB or more; absorption of 99% or more of incident radio waves). It is required that a wide frequency region exhibiting absorption of 20 dB or more is one guideline for the performance of the absorber), being lightweight or thin, and having weather resistance when used outdoors, Although it can be mentioned that it is inexpensive when used for an area, there are merits and demerits of currently used radio wave absorbers, and an absorber that satisfies all the above requirements has not yet been realized.

As currently used as a radio wave absorber,
(A) A flat-plate-type absorber in which a monolithic or multilayered product is formed by dispersing or adhering a ferrite powder, carbon powder or other electromagnetic wave absorber to a sintered ferrite tile, resin, rubber, or fiber. ,
(B) Polystyrene foam or the like contains carbon, etc., molded into a pyramid shape or wedge shape, and there are pyramid type and wedge type absorbers, etc., which are arranged side by side, depending on the required performance and usage environment. Yes.

The flat plate absorber further includes
(A-1) a rubber or resin impregnated with carbon or ferrite, or a composite sheet type absorbent body in which carbon is deposited on resin fibers and laminated into a plate shape;
(A-2) a resistance film type absorber coated with a resistance film, fiber, or conductive paint,
(A-3) Transparent wave absorbers and the like in which glass is coated with a transparent conductive film such as ITO have been put into practical use.

  Of the radio wave absorbers currently in wide use, this flat type absorber is simple in shape and easy to make thin, and it is easy to make a relatively large area at a low cost. Is used.

  As a generally used flat plate type absorber, there is one having a structure composed of an absorption layer made of a loss medium of radio waves and a back reflector. Such a structure is also called a matching type, and its absorption principle is as follows.

  That is, when radio waves are incident on the absorption layer, a part of it is reflected on the surface of the absorption layer and the rest is absorbed in the absorption layer due to the difference between the radio wave refractive index of the air layer and the radio wave refractive index of the absorption layer. Then, the light reaches the back reflector and is reflected. The radio wave reflected by this reflector travels again through the absorption layer, part of it is reflected by the surface of the absorption layer and travels through the absorption layer again, and part of it is emitted from the surface of the absorption layer to the air layer. The

  The radio wave of the absorber so that the radio wave radiated from the surface of the absorption layer out of the reflected wave primarily reflected on the surface of the absorption layer and the reflected wave reflected after reaching the back reflector is mutually cancelled. If the refractive index, thickness, etc. are adjusted, the radio wave intensity reflected on the surface of the absorption layer disappears, and is completely absorbed inside the absorption layer and converted to heat.

  This condition is called a matching condition, and the control of the condition is a basic design method for a flat plate type absorber and a sheet type absorber. However, as apparent from the principle, when the wavelength or incident angle of the incident radio wave changes, that is, when the matching condition is lost, the reflection attenuation characteristic of the radio wave deteriorates. Therefore, a single-layer absorber having a simple structure is generally limited to a narrow band and has a large characteristic deterioration with respect to oblique incidence. As a technique for improving this defect, it is common to increase the area by multilayering the absorption layer. However, if the number of layers is increased, the design of each layer, quality stability, and margin design of characteristics become difficult, and this leads to cost increase.

  The pyramidal and wedge-shaped wave absorbers are widely used as absorbers constituting the inner wall of an anechoic chamber used for performance evaluation of various antennas and communication devices because they exhibit broadband characteristics.

  The radio wave absorption principle of this type of absorber is as follows. In other words, by arranging pyramidal absorption elements with sharp tips, the impedance discontinuity at the radio wave incident interface is eliminated, reflection on the surface is suppressed, and the cross-sectional area of the absorption layer is continuously increased to increase the loss factor. By raising it, it gradually absorbs the radio waves that have entered the interior without being reflected by the surface.

  In this structure, the impedance to the radio wave is gradually changed from the impedance of the air in order to suppress the surface reflection of the incident radio wave, so a pyramid or wedge shape with a sharp tip is formed, and gradually as the radio wave enters the inside. It has a structure that attenuates and absorbs radio waves. Therefore, even when a change in the wavelength of the radio wave or a change in the incident angle occurs, the impedance at the incident interface on the surface of the absorption layer continuously changes from the impedance of the air, so that the absorption characteristics do not greatly deteriorate. Therefore, it can cope with a wide frequency range, has high angle characteristics, and exhibits high absorption performance. However, this type of absorber has the disadvantage that the structure becomes large.

  In addition, cylindrical wave absorbers and string-like wave absorbers have also been proposed. The cylindrical radio wave absorber is provided with a coating layer including a radio wave absorber on the surface of a cylindrical conductor that reflects radio waves, and suppresses radio wave reflection from the cylindrical conductor. A number of radio wave absorption structures in which a plurality of cylindrical radio wave absorbers are arranged to suppress radio wave reflection have been proposed.

  Cylindrical radio wave absorbers are cylindrically shaped, so even if radio waves are reflected on the surface, they are not strongly reflected backwards like flat type absorbers, compared to flat type ones. , Scattered around. Therefore, the shape itself is a convenient form for suppressing radio wave reflection. And the reflection intensity | strength can be reduced more by covering and arranging the absorption layer (antireflection layer) which suppresses radio wave reflection to them. However, in such a structure, the incident radio wave is transmitted through the gap between the cylindrical absorbers, so that the radio wave cannot be sufficiently absorbed.

  In general, in order to suppress transmission of radio waves, for example, when metal conductor wires or the like are assembled in a mesh pattern, the interval between the wires needs to be sufficiently smaller than the radio wave wavelength. Specifically, if the distance between the wires is about 1/10 or less of the radio wave wavelength, the radio wave transmission intensity can be reduced to about 10 dB or less. However, when a radio wave absorption layer is formed on the conductor surface, radio wave transmission is promoted. Therefore, in order to sufficiently reduce the radio wave transmission intensity, it is necessary to further reduce the interval between the wires. Even if the metal conductors are arranged in close contact with each other, the metal conductors cannot be brought into close contact with each other, and since the incident radio wave passes through the absorption layer existing between the metal conductors, the transmission cannot be completely suppressed. Therefore, it is difficult to sufficiently absorb the incident radio wave even if the radio wave absorption covering rods simply covering the absorption layer are arranged.

  As specific examples of the various radio wave absorbers, for example, Patent Document 1 proposes a cylindrical radio wave absorber in which an epoxy resin and a carbon resin are coated on the surface of a cylinder. By covering the outer surface of the cylinder with a layer that exhibits electromagnetic wave absorption characteristics, it has been shown that the electromagnetic wave absorber that has been applied only to a plane can be applied to the mast of a ship having a curved surface. Yes. In this case, it is shown that the reflection of radio waves can be effectively reduced by coating with an appropriate absorber, but it is intended to suppress reflection from a single cylinder and absorb radio waves in a wide area. is not.

  Further, Patent Document 2 proposes a radio wave absorber of a magnetic material coated metal wire array in which a plurality of composite wires each having a magnetic loss material coated around a metal wire are arranged. Specifically, parallel line arrays of metal wires coated with magnetic powder, or absorbers in which they are overlapped with each other in a lattice shape are exemplified. By adopting such a structure, air permeability and light can be obtained. It is shown that it is possible to combine the permeability.

  In principle, by coating a metal wire with a magnetic material, the reflection intensity of the radio wave is reduced as compared with an uncoated metal wire array or grating, and therefore, a certain level of radio wave absorptivity is exhibited. However, since the magnetic-coated metal wire arrays are arranged at intervals, the reflection of radio waves can be reduced, but the transmission intensity of radio waves passing through the opening increases conversely, so that the incident radio wave power is effectively reduced. It can be said that it is insufficient for absorption. In addition, the relationship between the spacing and thickness of the line arrays and the radio wave reflection suppression effect has not been specifically studied, and the effective absorption performance is considered to be low.

  In Patent Document 3, a radio wave absorber in which powdered ferrite is bonded or painted to a core material made of a conductive material, an absorber using carbon fiber as a core material, and further, this is made into a string shape, a string shape, A knitted radio wave absorber and the like are shown. Further, it is shown that when the core material is not conductive, it needs to be combined with a terminal short-circuit plate of a conductor.

  In the above-mentioned document, it is shown that air permeability can be ensured by adopting the lattice shape, and the radio wave absorption characteristics can be changed by adjusting the thickness and interval of the strings. In addition, a radio wave absorber having air permeability by combining a radio wave absorption layer having a ventilation structure in which carbon is impregnated with a yarn and an absorption layer formed by forming a string-like absorber in a lattice shape, and combining a wire mesh as a terminal short-circuit conductor It can be configured.

  In practice, however, powdered absorbent material is attached to or impregnated into thread or string, and this is collected to make an absorbent body. The structure is the same as that of the absorbent body in which the absorbent body is dispersed and formed into a plate shape and a terminal short circuit plate is provided on the back surface. In other words, the shape and thickness of the core are not specifically studied, and it is difficult to say that sufficient radio wave absorption performance is obtained.

  Patent Document 4 discloses a method for changing matching characteristics of a radio wave absorber and a radio wave absorption wall using the method. Specifically, radio wave absorption materials with different characteristics are divided and mounted on the surface of a flat plate, triangular prism, or cylindrical object made of a conductive material, these are arranged closely, and each element is rotated as necessary to generate radio waves. It is shown that the matching characteristics can be changed by changing the surface on the side where the light is incident. Although this case is an effective method for dealing with radio waves of different wavelengths, the effect of the size of the radio wave absorber on the radio wave absorption characteristics has not been specifically studied.

  Patent Document 5 describes a radio wave shield and an absorber, and specifically proposes a radio wave absorber that can transmit light. As a wave absorber, a wire, rod, cylinder, tape, or cotton impregnated with carbon or ferrite is used as a wave absorber and placed on a planar conductor plate. It is described that it can be a radio wave absorber. It has been proposed that if a conductive thread such as a wire mesh or carbon fiber is used as the planar conductor plate, air permeability can be secured, and if a conductive light-transmitting film is used, a light-transmitting property can also be obtained.

  Patent Document 6 proposes a radio wave absorber including a metal plate and a honeycomb core provided on the metal plate with the core axis substantially vertical, and ferrite and carbon powder are contained in the honeycomb core. A broadband electromagnetic wave absorber that is filled with a predetermined continuous concentration change in the core axis direction is disclosed.

  By continuously changing the concentration of ferrite and carbon powder, it reduces the impedance discontinuity for radio waves entering from the air, suppresses surface reflection, and efficiently absorbs radio waves that have entered the interior. However, this is considered to be configured based on an absorption principle similar to that of a pyramid-type or wedge-type electromagnetic wave absorber, or an absorption principle of a multi-layered plate-type absorber.

Although the thickness of the structure is not described in the above document, it is considered that the thickness is the same as that of the pyramidal absorber. Further, it is presumed that, like the multilayer type absorber, it is difficult to control the characteristics of each layer, and problems such as lack of quality stability in practice occur.
Japanese Patent Laid-Open No. 2517849 JP 47-24253 A Japanese Patent Laid-Open No. 4-122098 Japanese Patent No. 2914436 JP-A-6-235281 JP-A-5-90832

  Existing flat plate absorbers, pyramid-type and wedge-type wave absorbers have limitations in meeting all the requirements such as radio wave absorption characteristics, wide bandwidth, thin and light weight, and low cost. No other type of absorber that satisfies all these requirements has been proposed. This invention is made | formed in view of such a situation, The objective is to provide the manufacturing method of the coating rod which comprises the electromagnetic wave absorber which satisfy | fills the said characteristic simultaneously, and this electromagnetic wave absorber.

  The coated rod array type electromagnetic wave absorber according to the present invention is a coated rod array composed of a cylindrical conductor core wire (hereinafter referred to as “coated rod”) coated with a radio wave absorber, and is coated with a conductor reflector or a radio wave absorber. A radio wave absorber formed on the radio wave incident side of the conductor reflecting plate, wherein the diameter of the cylindrical conductor core wire is 1/20 or more of the target radio wave wavelength, and the interval between the adjacent coating rods ( (Pitch) is characterized by being equal to or less than the target radio wave wavelength.

  It is preferable that the plurality of the covering rod rows are formed on the radio wave incident side of the conductor reflecting plate or the conductor reflecting plate coated with the radio wave absorber because higher radio wave absorbing performance can be obtained. Further, it is preferable to use a material containing flat iron oxide powder having an average thickness of 30 μm or less as the radio wave absorber because the radio wave can be efficiently absorbed in the coated bar array or the conductor reflector coated with the radio wave absorber.

  The present invention also stipulates a method of manufacturing a covering rod that constitutes the covering rod array type electromagnetic wave absorber, and the method includes applying the mixture of the electromagnetic wave absorbing material and the binder to the cylindrical conductor core wire by an extrusion method. It is characterized by where it is coated.

  According to the present invention, a radio wave absorber that exhibits good radio wave absorption characteristics in a wide band as compared with a conventional resonance type single-layer sheet, and is significantly thinner than a conventional pyramid type radio wave absorber for an anechoic chamber having wide band characteristics. Can provide. In addition, the radio wave absorber of the present invention can exhibit a confinement effect and reliably improve radio wave absorption characteristics even when radio waves are incident on the reflecting surface of the reflector from an oblique direction.

  The inventors of the present invention have intensively studied to realize a radio wave absorber that can absorb incident radio waves with almost no reflection / transmission. As a result, a coated bar array composed of cylindrical conductor core wires (hereinafter referred to as “coated bars”) coated with a radio wave absorber is placed on the radio wave incident side of the conductor reflector or the conductor reflector coated with the radio wave absorber. It was found that radio wave absorption characteristics can be improved reliably by forming and absorbing radio waves with a covering rod and confining radio waves between the covering rod array and the reflecting plate.

  This mechanism is considered as follows. First, a part of the radio wave incident on the front covering rod row is absorbed by the surface of the covering rod row, and the rest is scattered in the direction and side where the radio wave has entered. Moreover, a part of incident wave permeate | transmits from between covering rod rows. Radio waves that are not absorbed by the covering rod row and scattered or transmitted between the covering rod rows are reflected by a reflector placed behind the covering rod row when viewed from the incident direction, and reflected in the direction in which the radio wave enters. Is done. The radio wave reflected by the reflecting plate is incident on the covering rod row again, a part is absorbed by the surface of the covering rod, and the rest is scattered again. FIG. 1 shows a multiple scattering state of radio waves in the radio wave absorber in which the covering bar array and the back reflector are arranged with a space therebetween. FIG. 1 exemplifies a propagation path of radio waves. When incident radio waves are confined in a space between a large number of coating rods and reflectors, multiple reflections occur and the radio waves can be absorbed very efficiently. It becomes possible.

  In order to effectively confine radio waves in the space between the covering rod row and the reflecting plate or the absorbing plate and efficiently absorb it, the reflection attenuation characteristics of the radio waves of the target frequency on the surface of one covering rod are sufficiently enhanced, It is important to optimize the core wire diameter of the covering rod and the spacing between the adjacent covering rods.

  In the present invention, as described above, the cylindrical rod is used as the covering rod type absorber, so that the incident angle dependency is suppressed, and the radio wave can be sufficiently absorbed even when incident from an oblique direction.

  First, it is important to control the core wire diameter of the covering rod. The reason for this is that if the core wire diameter of the coating rod is extremely small, the radio wave incident on one coating rod is scattered almost isotropically, and the probability that the radio wave is incident is increased. It is mentioned that a sufficient absorption performance cannot be obtained as a result. When it confirmed by experiment, when the core wire diameter of the coating rod was less than 1/20 of a wavelength, it turned out that the absorption effect as a whole falls large. In the present invention, if the core wire diameter of the covering rod is increased to 1/20 or more of the wavelength, the incident radio wave is greatly diffracted and enters the space between the reflector and the covering rod row arranged on the radio wave incident side. It was found that the light was effectively absorbed by multiple reflection in the space. Preferably, the core wire diameter of the covering rod is set to 1/15 or more of the target wavelength. On the other hand, the effect is saturated even if the core wire diameter of the covering rod is too large, and the relationship between the interval (pitch) between the covering rods described later is less than 1/2 of the target wavelength, preferably 1/3 or less. .

  It is also important to control the interval (pitch) between the covering rods as described above. When the intervals between the covering rod rows become extremely large and sparse, it is a matter of course that radio waves are transmitted between the covering rods and reflected by the reflecting plate, so that the overall absorption performance is significantly reduced. However, when the interval between the covering rod rows is a certain value or less, the transmitted wave that has entered between the covering rod rows and the reflecting plate or the wave absorbing plate can be confined in the space and transmitted between the covering rod rows. Thus, the intensity of the radio wave reflected by the reflecting plate can be sufficiently reduced.

  Multiple reflections occur when the reflected wave reflected by one coating rod enters the other coating rod on the side. At this time, the pitch is set so that the phase of the reflected wave from each coating rod is random. If selected, it is possible to further promote a reduction in the intensity of the reflected wave. In order to realize this function and effect, it is necessary to set the interval between the coating rods to a wavelength or less. In this way, by setting the distance between the coating rods to be equal to or less than the wavelength, the incident radio wave can be effectively confined in the space between the coating rod array and the reflector, and effective radio wave absorption is caused by the internally generated multiple scattering. Furthermore, it is possible to enhance the attenuation effect by the phase cancellation of the scattered waves from the covering rod, and to attenuate the radio wave intensity comprehensively.

  The radio wave absorber according to the present invention preferably has a plurality of the covering rod rows arranged on the radio wave incident side of the conductor reflector or the conductor reflector coated with the radio wave absorber. For example, when two rows of covered rods are arranged on the radio wave incident side of a conductor reflector or a conductor reflector coated with a radio wave absorber, a part of the radio waves is first covered by the first covered rod row on which radio waves are incident. Absorbed and transmitted transmitted waves are absorbed by the next coating rod row (second coating rod row), and in addition, between the first coating rod row and the second coating rod row, Because radio waves are confined in a two-layer space between the two coated rod rows and the reflector placed behind it, the absorption effect increases due to multiple internal scattering, or the absorption characteristics for polarized waves in various directions It is possible to realize a higher-performance absorber by isotropy.

  By arranging a plurality of the covering rod rows in this way, it is possible to absorb the transmitted wave transmitted between the covering rod rows with a gap, but the second covering rod row absorbs as much as the first covering rod row. Even if the performance is not exhibited, if there is a certain reflection attenuation performance, sufficient absorption characteristics as a whole can be obtained. Furthermore, even if the reflecting plate is a simple metallic reflecting plate, as described above, in addition to controlling the diameter of the cylindrical conductor core wire of the covering rod and the spacing between the covering rods, the distance between the covering rod row and the metal plate is set as follows. If it is controlled within an appropriate range, sufficiently high absorption characteristics can be realized.

  In the case of controlling the distance between the covering rod row and the metal plate, it can be specifically performed as follows. That is, it is important to control the phase of the reflected wave reflected on the metal plate to an optimum value, and the overall reflection intensity vibrates with a half-wavelength period with respect to the distance between the covering rod row and the metal plate. The distance between the covering rod row and the metal plate is preferably adjusted so that the overall reflection intensity takes a minimum value and the thickness of the entire absorber is not too thick.

  The intervals between the coating rods in the coating rod array need not be the same among all the coating rods, and a predetermined effect can be obtained if the intervals between the coating rods are within the specified range of the present invention. Further, they may be arranged in a zigzag pattern or in a curved line instead of being arranged in a straight line. Further, when the reflecting plate is curved, as shown in FIGS. 2A and 2B, the reflecting plate may be arranged even if the covering rods are arranged along the wall surface of the reflecting plate. And the absorption effect by multiple scattering can be obtained.

  The covering rod is formed by covering a cylindrical metal conductor, a cylindrical (hollow) metal pipe, or a radio wave-reflecting cylindrical support whose surface is subjected to metal plating or the like with a radio wave absorption layer having a certain thickness. can do. The absorbing layer can be formed by dispersing a general electromagnetic wave loss material such as carbon or ferrite in plastic, rubber, or other resin and applying it to the surface of the cylindrical conductor. In particular, the proposed flat iron oxide powder having an average thickness of 30 μm or less (for example, Japanese Patent Application Laid-Open No. 2004-96084) is suitable as the radio wave absorber covering the reflector. The flat iron oxide powder has a large dielectric constant, magnetic permeability, and large loss term due to the orientation of the powder parallel to the direction of the electric field and magnetic field of the incident radio wave, and it is easy to obtain sufficient absorption characteristics with a thin film. is there.

  As a method for producing a coated rod by coating the conductor core wire with the absorbent material, it is preferable to employ, for example, an extrusion coating method used as a flux coating method for a coated arc welding rod. In the above-described flux coating of the coated arc welding rod, a very dense coating with a uniform thickness can be formed by extruding the core wire together with the flux in the axial direction into a die while supplying the flux from the surroundings. In the present invention, if this method is also used to coat the conductor core wire with the absorbent, the thickness of the entire circumference becomes uniform, and the flat iron oxide powder used as the radio wave absorber becomes a core wire by a strong axial axial shearing force. It is strongly oriented parallel to the surface and can absorb the electric and magnetic fields near the cylindrical conductor surface very effectively.

  In addition, the absorption layer in the covering rod is designed so that the return loss rate of the radio wave of the target frequency is as large as possible (specifically, the three factors of the material of the absorbent, the filling rate [volume ratio], and the thickness are controlled) However, increasing the reflection attenuation characteristic of the characteristic covering rod does not improve the radio wave absorption characteristic of the entire structure in proportion, and as described above, the diameter of the cylindrical conductor core wire of the covering rod In addition, it is important to control the spacing between adjacent covering rods, and if these conditions are controlled, the absorption layer can be designed and the distance between the reflecting plate and the covering rod row can be further reduced. The body performance can be further enhanced. In addition, since the thickness of the absorption layer is generally proportional to the wavelength, the optimum value may be determined according to the wavelength of the target radio wave.

  In manufacturing the covering rod, as the binder to be mixed with the radio wave absorbing material, epoxy resin, silicone resin, acrylic resin, alkyd resin, unsaturated polyester resin, etc. can be used. It is preferable to set it as 20 to 90 volume%. This is because when the amount is less than 20% by volume, the binding force tends to be insufficient, and when the amount exceeds 90% by volume, the amount of the absorbent added is relatively insufficient.

  Moreover, as a reflecting plate, the metal plate which consists of various metals can be used, for example, the metal plate which consists of aluminum can be used.

  EXAMPLES Hereinafter, the present invention will be described more specifically with reference to examples. However, the present invention is not limited by the following examples, but may be appropriately modified within a range that can meet the purpose described above and below. It is also possible to implement, and they are all included in the technical scope of the present invention.

  A coated rod was formed using flat iron oxide powder having an average thickness of 10 μm as a radio wave absorber. Specifically, the flat iron oxide powder and water glass as a binder are first kneaded, and an approximately 1.5 mm absorbing layer is coated on a 500 mm long and 8 mm soft iron core wire by extrusion coating using a φ11 mm die. After that, it was dried, and then an epoxy coating was applied to prevent moisture absorption to obtain a radio wave absorbing coated rod. The mass ratio of water glass and flat iron oxide powder was 100: 350. The volume ratio of the flat iron oxide powder in the absorbent layer was calculated to be about 50% by actually measuring the mass of the absorbent layer immediately after coating and the final absorbent layer thickness.

  As shown in FIG. 3, the obtained covering rod 14 is arranged (mounted) on the aluminum plate 15 which is a radio wave reflecting plate at regular intervals, and the radio wave is emitted from the upper part toward the covering rod row. The radio wave reflection characteristics were measured. The measurement of the radio wave absorption characteristic is a general method (specifically, using a network analyzer 11 and a horn antenna 12 with a dielectric lens 13 to calibrate the reflection characteristic at one port using the reflection characteristic from a reference metal plate ( The free space method). The measurement results are shown in FIGS.

  4 and 5 show the results when the covering rods are arranged as shown in FIG. 8 (E is the electric field direction and H is the magnetic field direction. The same applies to FIG. 9). These show the results when the covering rods are arranged as shown in FIG.

  4 to 7, it can be seen that the reflection attenuation characteristics are greatly improved by arranging the covering rods so that the interval (pitch) of the covering rods is less than the target radio wave wavelength (about 50 mm with respect to 6 GHz). On the other hand, when the pitch is larger than the target wavelength, the return loss is greatly reduced to about 5 dB, regardless of whether the covering rod is arranged in parallel with the electric field direction, and the incident radio wave is not absorbed by the radio wave absorber. It is considered that the light is mainly reflected by the reflecting plate and released to the outside of the radio wave absorber.

  In the same manner as in Example 1, a coated rod was formed using flat iron oxide powder having an average thickness of 10 μm as a radio wave absorber. Specifically, water glass, which is a binder, and flat iron oxide powder are kneaded, and an about 1 mm absorption layer is coated on a 500 mm long, 20 mm long soft iron core wire by an extrusion coating method using a φ22 mm die, followed by drying. Then, an epoxy-based coating was applied to prevent moisture absorption to obtain a radio wave absorption covering rod. The mass ratio of water glass and flat iron oxide powder was 100: 350, the same as in Example 1. Further, the volume ratio of the flat iron oxide powder in the absorbing layer was about 50% as in Example 1.

  The obtained covering rods were placed on an aluminum plate as a radio wave reflector at regular intervals, and the radio wave reflection characteristics were measured in the same manner as in Example 1. The measurement results are shown in FIGS.

  10 and 11 show the results when the covering rods are arranged as shown in FIG. 8, and FIGS. 12 and 13 show the results when the covering rods are arranged as shown in FIG.

  From FIG. 10 to FIG. 13, the reflection attenuation characteristics can be greatly improved if the covering rods are arranged so that the interval (pitch) of the covering rods is less than the target radio wave wavelength (about 32 mm with respect to 9.4 GHz). Recognize. On the other hand, when the pitch is larger than the target wavelength, the return loss is greatly reduced to about 5 dB, regardless of whether the covering rod is arranged in parallel with the electric field direction, and the incident radio wave is not absorbed by the radio wave absorber. It is considered that the light is mainly reflected by the reflecting plate and released to the outside of the radio wave absorber.

  In this example, the reflection attenuation effect with respect to the radio frequency of 5.8 GHz circularly polarized wave used for ETC was investigated (hereinafter the same applies to Examples 4 to 8). The radio wave absorber used and the method for producing the covering rod were the same as in Example 1. In addition, various types of core wire diameters were prepared as soft iron core wires, and various coating rods were prepared by adjusting the coating thickness so that the thickness of the absorbing layer to be coated was maximized in the amount of return loss near 5.8 GHz. . Specifically, for the core wire diameters of φ2 mm, φ3 mm, and φ5 mm, the absorption layer was coated relatively thick in order to make the absorption frequency close to 5.8 GHz. Further, the core wire having a larger core wire diameter was covered with an absorption layer having a thickness of 1.5 mm. The reflection attenuation amount is obtained by comparing the reflection intensity from one coated rod obtained in this way and the reflection intensity from an uncoated bare wire, and is 1 m away from the coated rod. The amount of attenuation with respect to the bare wire was determined. The electric field and the core wire were parallel. These measurement results are shown in Table 1.

  From Table 1, it can be seen that the absorption frequency can be adjusted to around 5.8 GHz for each core wire diameter. However, when the diameter is 2 mm, it is less than 1/20 of the wavelength, so that the scattering to the rear of the covering rod (in the direction in which the radio wave enters) is large and the return loss is low.

  Further, the obtained covering rod was placed on an aluminum plate with the pitch changed, and the radio wave reflection characteristics were measured. Radio wave absorption characteristics are measured using a network analyzer and two circularly polarized antennas with dielectric lenses for transmission and reception, and the reflection characteristics at an incident angle of 15 ° are calibrated using the reflection characteristics from a standard metal plate. It was done by the method. Table 2 shows the measured values of the core wire diameter, the distance between the coating rods (wire pitch), and the return loss at 5.8 GHz circular polarization.

  FIG. 14 is a graph showing the dependence of the return loss on the wire pitch when a covering rod having a core wire diameter of 8 mm and a covering thickness of 1.5 mm obtained by arranging the data in Table 2 is arranged. Further, FIG. 15 shows the dependency of the reflection attenuation amount of the covering rod row on the core wire diameter and the pitch, and FIG. 16 shows the dependency of the reflection attenuation amount on the core rod diameter after the coating rod interval optimization.

  From the results of FIGS. 15 and 16, it can be seen that a practical return loss of 20 dB or more can be achieved by controlling the interval (pitch) of the covering rods, except when the core wire diameter is 2 mm. That is, if the core diameter is a certain value or more, by controlling the interval between the covering rods, it is possible to obtain a sufficient absorption characteristic by maximizing the confinement effect of the incident radio wave between the covering rod row and the reflecting plate, When the core wire diameter is 2 mm, which is extremely small compared to the radio wave wavelength, more radio waves are transmitted through the covering rod row and reflected by the reflecting plate. Therefore, even if the interval between the covering rods is optimized, a sufficient absorption effect can be obtained. I can't understand. From these results, it was found that the core wire diameter must be 1/20 or more of the wavelength in order to achieve practical absorption characteristics.

  It was also found that if the spacing (pitch) between the covering rods exceeds a certain value, a sufficient return loss cannot be achieved even if the core wire diameter is controlled. The target wavelength at this time is about 50 mm. If the interval (pitch) of the coating rods is 50 mm or less of the target wavelength, the core wire diameter and the coating thickness are optimized as other conditions, so that the reflection attenuation characteristics are sufficiently excellent. Is obtained.

  The covering rods produced in the same manner as in Example 3 were arranged on the aluminum plate at regular intervals to produce a covering rod array type electromagnetic wave absorber A. Specifically, a coated rod array absorber A in which a coating rod having a length of 500 mm and a diameter of 8 mm coated on a core wire having a diameter of 11 mm and disposed on an aluminum plate at an interval of 25 mm is provided. It was. Then, radio waves were incident on the aluminum plate from an oblique direction, and the radio wave reflection characteristics at the oblique incidence of the coated bar array type radio wave absorber A were measured. The incident surface of the radio wave (the surface including the wave number vector of the incident wave and the reflected wave) and the covering rod row were set to be vertical.

  Specifically, the radio wave absorption characteristics are measured using a network analyzer and two circularly polarized antennas with dielectric lenses for transmission and reception, and the return loss at each incident angle is the reflection intensity from the reference metal plate. It was obtained by comparison with. Specifically, the reflection intensity of the circularly polarized wave was measured when the direction of the circularly polarized wave indicated by the arrow in FIG.

  As a result of the measurement, the reflection attenuation spectrum at an incident angle of 15 ° is shown in FIG. 18, and the reflection attenuation spectrum at each incident angle is shown in FIG. FIG. 20 shows the incident angle dependence of the return loss at 5.8 GHz. The return loss characteristics at an incident angle of 0 ° in FIG. 20 were estimated from the return loss amount at the normal incidence of linearly polarized waves.

  From these results shown in FIGS. 18 to 20, the coated bar array type radio wave absorber of this example shows an excellent absorption characteristic with a return loss of 25 dB or more in the range of the incident angle of the radio wave from 0 ° to 60 °. Recognize. In this way, even when the incident angle of the radio wave is oblique, it exhibits excellent absorption characteristics because the shape of the covering rod is cylindrical, which shows a radio wave response equivalent to normal incidence, and high absorption due to radio wave confinement This is thought to be due to the fact that the characteristics were secured.

  The covering rods produced in the same manner as in Example 3 were arranged on the aluminum plate at regular intervals to produce a covering rod array type electromagnetic wave absorber B. Specifically, a coating rod having a diameter of 11 mm is applied to a core wire having a diameter of 8 mm by placing a coating rod having a diameter of 11 mm on an aluminum plate at an interval of 25 mm. Further, as shown in FIG. The coated bar array type absorbent body B was disposed at a right angle to the first coated bar array disposed at 90 mm intervals. Then, radio waves were incident on the aluminum plate from an oblique direction, and the radio wave reflection characteristics at the oblique incidence of the covered bar array type radio wave absorber B were measured. The radio wave incident surface (the surface including the wave number vectors of the incident wave and the reflected wave) was parallel to the lower covering rod row.

  Specifically, the radio wave absorption characteristics are measured using a network analyzer and two circularly polarized antennas with dielectric lenses for transmission and reception, and the return loss at each incident angle is the reflection intensity from the reference metal plate. It was calculated by comparison.

  As a measurement result, a reflection attenuation spectrum at an incident angle of 15 ° is shown in FIG. Further, FIG. 23 shows the incident angle dependence of the return loss at 5.8 GHz. The reflection attenuation characteristics at an incident angle of 0 ° in FIG. 23 were estimated from the reflection attenuation amount at normal incidence of linearly polarized waves.

  From these results of FIGS. 22 and 23, the reflection attenuation characteristics of the coated rod array type electromagnetic wave absorber B of this example are the same as those of the coated rod array type absorber A of Example 4 in which the coated rod array is one layer. FIG. 22 shows a large return loss of 60 dB at an incident angle of 15 °, and a return loss of 20 dB or more over a wide band of frequencies from 5 GHz to 7 GHz. FIG. 23 also shows that the absorption characteristics are excellent even when the incident angle is in the range of 0 ° to 60 ° and the return loss is 20 dB or more and oblique incidence.

  By overlapping two layers of the covering rod row in this way, the characteristics such as the absorption frequency band and the amount of absorption are greatly improved, but this is enhanced by the effect of confinement of radio waves and the effect of multiple scattering inside. This is probably because the absorption characteristics were realized.

  In the same manner as in Example 5, a coated bar array type radio wave absorber laminated in two layers in directions orthogonal to each other was produced, and the absorption characteristics were evaluated. Specifically, as shown in FIG. 24, a coating rod having a diameter of 11 mm by coating a core wire having a diameter of 8 mm with a diameter of 11 mm is placed on the aluminum plate at an interval of 40 mm below the target radio wave wavelength of 50 mm. A coated bar array type absorber C was obtained in which the above-mentioned coated rods were disposed at right angles to the first layer coated rods at intervals of 40 mm. Then, radio waves were incident on the aluminum plate from an oblique direction, and the radio wave reflection characteristics at the oblique incidence of the coated bar array type radio wave absorber C were measured. The radio wave incident surface (the surface including the wave number vectors of the incident wave and the reflected wave) was perpendicular to the lower covering rod row.

  Specifically, the radio wave absorption characteristics are measured using a network analyzer and two circularly polarized antennas with dielectric lenses for transmission and reception, and the return loss at each incident angle is the reflection intensity from the reference metal plate. It was calculated by comparison.

  As a measurement result, the reflection attenuation spectrum at an incident angle of 15 ° is shown in FIG. FIG. 26 shows the incident angle dependence of the return loss at 5.8 GHz. The reflection attenuation characteristics at an incident angle of 0 ° in FIG. 26 were estimated from the reflection attenuation amount at normal incidence of linearly polarized waves.

  From the results of FIGS. 25 and 26, the reflection attenuation characteristics of the coated bar array type radio wave absorber C of this example are the same as those of the coated bar array type radio wave absorber B even when it is incident obliquely at 5.8 GHz. It can be seen that even in the case where the incident angle is in the range of 0 ° to 60 ° and the return loss is 20 dB or more and oblique incidence, excellent absorption characteristics are exhibited.

  Further, it can be seen that when the interval between the covering rod rows is set to be equal to or smaller than the radio wave wavelength as defined in the present invention, high radio wave absorption performance can be obtained due to the effect of confinement of radio waves and internal multiple scattering.

  A coating rod array in which the arrangement of the coating rod array of the coated rod array type wave absorber of Example 4 was changed was prepared. Specifically, a covering rod array type absorber D in which the covering rods are arranged in a zigzag manner as shown in FIG. 27 and the average interval of the covering rods is 25 mm as in Example 4 was prepared. Here, the distance between the covering rods is obtained by measuring the distance between a and b in FIG. 28 and obtaining (a + b) / 2.

  Then, in the same manner as in Example 4, radio waves were incident on the aluminum plate from an oblique direction, and the radio wave reflection characteristics at the oblique incidence of the coated bar array type radio wave absorber D were measured. The incident surface of the radio wave (the surface including the wave number vectors of the incident wave and the reflected wave) was perpendicular to the average direction of the covering rod row shown in FIG.

  As a measurement result, the reflection attenuation spectrum at an incident angle of 15 ° is shown in FIG. 30, and the incident angle dependence of the return loss at 5.8 GHz is shown in FIG. Note that the return loss characteristics at an incident angle of 0 ° in FIG. 31 were estimated from the return loss amount at the normal incidence of linearly polarized waves.

  From the results of FIGS. 30 and 31, even if the arrangement of the covering rods is slightly changed as in the covering rod array type electromagnetic wave absorber D of this embodiment, the average interval of the covering rods is within the specified range of the present invention. It can be seen that the reflection attenuation characteristics are substantially the same as those of the coated rod array type electromagnetic wave absorber A of the fourth embodiment.

  A coated bar array type absorber E in which the reflecting plate of the coated bar array type radio wave absorber A of Example 4 was changed to a reflecting plate whose surface was coated with the radio wave absorber was prepared. The radio wave absorber coated on the surface of the reflecting plate is a type in which carbon black is mixed with 50 PHR in rubber and has a thickness of 2.5 mm. FIG. 32 shows the reflection attenuation characteristics of the linearly polarized wave and the normal incidence of the reflector coated with the carbon-containing rubber sheet absorber. From FIG. 32, it can be seen that this absorption plate exhibits a reflection attenuation characteristic of about 10 dB at maximum in the region of 5 GHz to 7 GHz.

  Using the coated rod type absorber E with the absorber plate disposed on the back surface, similarly to the fourth embodiment, a radio wave is incident on the aluminum plate from an oblique direction, and the coated rod array type electromagnetic wave absorber E The radio wave reflection characteristics at oblique incidence were measured. The incident surface of the radio wave (the surface including the wave number vector of the incident wave and the reflected wave) and the covering rod row were set to be vertical.

  As a result of the measurement, the reflection attenuation spectrum at an incident angle of 15 ° is shown in FIG. 33, and the incident angle dependence of the return loss at 5.8 GHz is shown in FIG. In FIG. 33, the return loss characteristic at an incident angle of 0 ° was estimated from the return loss amount at the normal incidence of linearly polarized waves.

  From the results shown in FIGS. 33 and 34, the maximum value of the return loss can be obtained by applying the radio wave reflection attenuation performance to the reflection plate arranged on the back surface as compared with the case of using the metal reflection plate as in the fourth embodiment. It can be seen that increases. In addition, even when incident obliquely at 5.8 GHz, the reflection attenuation characteristic was remarkably excellent with a return loss of 30 dB or more in an incident angle range of 0 ° to 60 °. This is presumably because radio waves were absorbed more effectively by providing reflection attenuation characteristics to the reflection plate in the multiple reflection between the covering rod row and the reflection plate.

It is the schematic diagram which showed the multiple scattering state of the electromagnetic wave in the electromagnetic wave absorber which consists of a covering rod row | line | column and a back reflector. It is the upper surface schematic diagram which illustrated arrangement | positioning of the covering stick | rod when the reflecting plate is curving. It is the top view which showed typically the measuring method of the electromagnetic wave reflection characteristic in an Example. It is a graph (linearly polarized wave, electric field direction and covering rod perpendicular) showing the frequency / pitch dependence of the return loss. 6 is a graph showing the pitch dependence of return loss (linear polarization, electric field direction and covering rod perpendicular). It is a graph (linear polarization, electric field direction and covering rod are parallel) showing the frequency / pitch dependence of the return loss. It is a graph (linearly polarized wave, electric field direction and covering rod are parallel) showing the pitch dependence of the return loss. 4 is a top view schematically showing the arrangement of the covering rods in Example 1. FIG. 6 is a top view schematically showing another arrangement of the covering rods in Example 1. FIG. It is a graph (linearly polarized wave, electric field direction and covering rod perpendicular) showing the frequency / pitch dependence of the return loss. 6 is a graph showing the pitch dependence of return loss (linear polarization, electric field direction and covering rod perpendicular). It is a graph (linear polarization, electric field direction and covering rod are parallel) showing the frequency / pitch dependence of the return loss. It is a graph (linearly polarized wave, electric field direction and covering rod are parallel) showing the pitch dependence of the return loss. It is a graph which shows the pitch dependence of the return loss when a fixed-shaped covering rod is used. It is a graph which shows the core wire diameter and pitch dependence of a return loss. It is a graph which shows the core wire diameter dependence of return loss. It is a side view which shows the positional relationship of the covering rod row | line | column in Example 4 and a polarized wave. The reflection attenuation spectrum in the incident angle of 15 degrees in Example 4 is shown. The reflection attenuation spectrum in each incident angle in Example 4 is shown. It is a graph which shows the incident angle dependence of the return loss in 5.8 GHz in Example 4. FIG. 10 is a top view schematically showing the arrangement of covering rods in Example 5. 10 shows a reflection attenuation spectrum at an incident angle of 15 ° in Example 5. It is a graph which shows the incident angle dependence of the return loss in 5.8 GHz in Example 5. It is the perspective view which showed typically the covering rod row absorber in Example 6, and the incident / reflection direction of an electromagnetic wave. The reflection attenuation spectrum in Example 6 in the incident angle of 15 degrees is shown. It is a graph which shows the incident angle dependence of the return loss in 5.8 GHz in Example 6. The arrangement | sequence of the covering rod row | line | column in Example 7 is shown. It is a figure which shows the length of a and b in calculation of the space | interval [(a + b) / 2] between covering rods. It is a figure which shows the average direction of the covering rod row | line | column arrange | positioned at a zigzag. The reflection attenuation spectrum in Example 7 in the incident angle of 15 degrees is shown. It is a graph which shows the incident angle dependence of the return loss in 5.8 GHz in Example 7. The reflection attenuation characteristic of the carbon containing rubber sheet absorber in Example 8 is shown. 10 shows a reflection attenuation spectrum at an incident angle of 15 ° in Example 8. It is a graph which shows the incident angle dependence of the return loss in 5.8 GHz in Example 8.

Explanation of symbols

1,14,21 Cover rod 2 Reflector 3 Radio wave propagation path 11 Network analyzer 12 Horn antenna 13 Derivative lens 15 Reflector (aluminum plate)
22 Rear aluminum plate

Claims (4)

  A covered bar array composed of a cylindrical conductor core wire (hereinafter referred to as a “cover bar”) coated with a radio wave absorber is formed on the radio wave incident side of the conductor reflector or the conductor reflector coated with the radio wave absorber. The diameter of the cylindrical conductor core wire is 1/20 or more of the target radio wave wavelength, and the interval (pitch) between the adjacent coating rods is equal to or less than the target radio wave wavelength. Coated bar array type electromagnetic wave absorber.   The coated rod array type radio wave absorber according to claim 1, wherein the plurality of coated rod arrays are formed on a radio wave incident side of a conductor reflector or a conductor reflector coated with a radio wave absorber.   The coated radio wave absorber according to claim 1 or 2, wherein the radio wave absorber contains flat iron oxide powder having an average thickness of 30 µm or less.   It is a manufacturing method of the covering rod which comprises the covering rod row | line | column type | formula electromagnetic wave absorber in any one of the said Claims 1-3, Comprising: The mixture of the said electromagnetic wave absorber and a binder is coat | covered by the extrusion method. A method for producing a covering rod for a radio wave absorber, comprising:

Images