JP4909832B2 - Radio wave absorber and radio wave anechoic chamber using the same - Google Patents

Description

  The present invention relates to a radio wave absorber capable of absorbing both radio waves and sound waves and a radio wave anechoic chamber using the same.

  An anechoic chamber (an anechoic chamber) is used as an evaluation facility for measuring radio noise radiated from electronic equipment and testing the resistance of electronic equipment to external radio waves. On the other hand, an acoustic anechoic chamber is used as an evaluation facility for performing an acoustic test.

  These anechoic chambers and sonic anechoic chambers are expensive to construct, so the cost burden is considerable to own each of the test chambers. Therefore, if both tests are to be carried out, the cost burden can be reduced by constructing a radio-acoustic anechoic chamber that also serves as both. Further, when examining the state of sound when an electronic device is irradiated with radio waves, it is necessary to perform a test in an environment in which neither radio waves nor sound waves are reflected, so a radio wave anechoic chamber is required.

  As a radio wave absorber used for the wall surface of such a radio wave anechoic chamber, the radio wave absorber of Patent Document 1 has been proposed.

As shown in FIG. 11, the radio wave acoustic wave absorber disclosed in Japanese Patent Publication No. 6-35518 includes a foamed polystyrene radio wave absorber 1 in which a plurality of wedge-shaped projections 2 are arranged, and front and rear. And the acoustic absorption part 3 of glass wool formed into a wedge shape, and the wedge-shaped protrusion 4 on the rear side of the acoustic absorption part 3 is fitted between the wedge-shaped protrusions 2 of the radio wave absorption part 1 to form a single unit. The wedge-shaped protruding portion 5 in front of is protruded from the tip of the radio wave absorbing portion 1.

  In the radio wave absorber of Patent Document 1, the radio wave absorber 1 of the foamed polystyrene reflects sound waves. Therefore, when exposed to the sound wave arrival surface, the acoustic characteristics are adversely affected. For this reason, the acoustic absorption part 3 is arrange | positioned in the front surface (sound wave arrival side), and it makes it protrude from the front-end | tip of the electromagnetic wave absorption part 1, and it can eliminate the bad influence to the acoustic characteristic by the electromagnetic wave absorption part 1. Further, the acoustic absorption part 3 of glass wool is almost transparent to radio waves and does not adversely affect the radio wave absorption characteristics. However, there is a problem in that the length of the entire radio wave absorber is increased by the amount of protrusion of the acoustic absorber 3 and the effective space in the room is reduced. Further, if the entire length of the radio wave absorber is simply shortened to increase the effective space, the radio wave absorption characteristic and the sound wave absorption characteristic do not satisfy the required performance.

  The present invention has been made in view of such problems, and uses a radio wave acoustic wave absorber that is excellent in radio wave absorption characteristics and sound wave absorption characteristics, can be downsized, and thus can increase the effective space in a room, and the same. The purpose is to provide an anechoic chamber.

  Other objects and novel features of the present invention will be clarified in embodiments described later.

  In order to achieve the above object, a radio wave acoustic wave absorber according to an aspect of the present invention includes a first sound wave absorber substantially free of radio wave reflection on the front side of the first radio wave absorber and the first sound wave. A second radio wave absorber that substantially does not reflect sound waves and that surrounds at least the side surface of the outer surface of the absorber is arranged.

  In the radio wave absorber, a second sound absorber having substantially no radio wave reflection may be disposed so as to surround at least a side surface of the outer surface of the second radio wave absorber.

  In the radio wave acoustic wave absorber, the second radio wave absorber may have a shape in which an opening is provided at a tip of a hollow cone.

  In the radio wave absorber, the first radio wave absorber has a cylindrical part having an opening at a tip of a hollow cone, and the leading edge of the cylindrical part is the second radio wave absorber. They may touch or be close.

  In the radio wave absorber, the first and second sound absorbers may be glass fiber mats.

  In the radio wave acoustic absorber, the second radio wave absorber may be a conductive glass fiber mat containing a conductive material.

  In the radio wave absorber, the first radio wave absorber may be a foamed resin containing a conductive material.

  In the radio wave absorber, a third radio wave absorber made of a magnetic loss material may be disposed on the back surface of the first radio wave absorber.

  In a radio wave anechoic chamber according to another aspect of the present invention, the radio wave acoustic wave absorber is arranged on at least one of the indoor side wall surface and the ceiling surface so that the front side of the first radio wave absorber is the indoor side. It is characterized by that.

  According to the radio wave acoustic wave absorber according to the present invention, it is possible to improve the radio wave absorption characteristic and the sound wave absorption characteristic and to reduce the size of the shape.

  Moreover, the radio wave anechoic chamber using the radio wave absorber according to the present invention can increase the effective space in the room because the radio wave absorber is small and sufficiently good characteristics can be obtained.

  Hereinafter, as a best mode for carrying out the present invention, a radio wave absorber and a radio wave anechoic chamber using the same will be described with reference to the drawings.

  FIGS. 1A and 1B show a radio wave absorber according to Embodiment 1 of the present invention. In this figure, the radio wave absorber 10 includes a radio wave absorber 20 made of a dielectric loss material such as foamed resin containing a conductive material, a sound wave absorber 30 substantially free of radio wave reflection such as a glass fiber mat, A radio wave absorber 40 such as a conductive glass fiber mat containing a conductive material and having substantially no sound wave reflection is provided, and a flat radio wave absorber 50 made of a magnetic loss material. Note that “substantially no radio wave reflection” means that the radio wave reflection is negligibly small in applications such as an anechoic room, and “substantially no sound wave reflection” means that the sound wave reflection can be ignored. It can be said that it is small.

  As shown in FIGS. 2A and 2B, a radio wave absorber 20 containing a conductive material, such as foamed resin, rises from a flat bottom 21 and an edge of the front surface (radiation surface of radio waves and sound waves). A cylindrical portion 22 having an opening at the tip of a hollow quadrangular pyramid and a number of tapered portions 23 provided inside the cylindrical portion 22 and provided on the front surface of the flat bottom portion 21 are integrally formed. Have. For example, the flat bottom portion 21, the cylindrical shape portion 22, and the tapered shape portion 23 are integrally molded with each other by an adhesive or the like. Carbon, graphite, or the like can be used as the conductive material, and the conductive material is contained in a foamed resin such as foamed polystyrene or foamed polyurethane.

  As the acoustic wave absorber 30 such as a glass fiber mat, for example, a short fiber glass fiber mat (glass wool) can be used, which has substantially no radio wave reflection, for example, has a characteristic of being transparent to radio waves (transmitting radio waves). It is. The average fiber diameter of the glass fiber used for the short fiber glass fiber mat is preferably 1 μm to 20 μm, and more preferably 5 μm to 10 μm. A short glass fiber porous structure (mat) having such a fiber diameter can be produced by a known method such as a flame method or a centrifugal method. For example, it is generally used as a heat insulating material or a sound absorbing material for residential use or industrial use. Is used. Since this porous structure may loosen the fibers if no treatment is performed, it is preferable to bind the fibers with a binder. Examples of the binder for binding include acrylic resin, melamine resin, urea resin, and phenol resin. The sound wave absorber 30 is disposed on the front side of the radio wave absorber 20, that is, on the front side of the tapered portion 23 and partly housed inside the cylindrical portion 22.

  As the radio wave absorber 40 such as a conductive glass fiber mat containing a conductive material, for example, a long fiber (continuous fiber) conductive glass fiber mat can be used, and there is substantially no sound wave reflection, for example, against sound waves. It has transparency (transmits sound waves). The average fiber diameter of the long glass fiber used for the long fiber glass fiber mat is preferably 1 μm to 50 μm. A long-fiber porous structure (mat) having such a fiber diameter can be produced by a known method, and is already generally used as, for example, an automotive battery insulator or a ventilation fan filter. If the porous structure is not subjected to any treatment, the fibers may be loosened. Therefore, the porous structure is preferably bound with a binder. Examples of the binder for binding include acrylic resin, melamine resin, urea resin, and phenol resin. The radio wave absorber 40 has a shape that surrounds (covers) the side surface on the front end side of the sound wave absorber 30 protruding from the cylindrical portion 22 and has an opening at the front end of the hollow quadrangular pyramid. . The rear edge of the radio wave absorber 40 is in contact with or close to the front edge of the cylindrical portion 22 of the radio wave absorber 20, and a longer cylindrical shape is formed by the cylindrical portion 22 of the radio wave absorber 20 and the radio wave absorber 40. Is configured.

  The flat wave absorber 50 made of a magnetic loss material is made of, for example, sintered ferrite tiles, and is disposed on the back surface of the radio wave absorber 20 (the surface opposite to the arrival surface of radio waves and sound waves).

  Note that, as indicated by a dotted line in FIG. 1B, a cloth 55 such as polyclar fiber may be provided to cover the periphery of the radio wave absorber 20, the sound wave absorber 30, and the radio wave absorber 40 in a bag shape. This bag-like cloth 55 can integrate the three more reliably and prevent separation.

  The cloth 55 such as polyclar fiber has a bag shape, and an edge thereof is fixed on the back side of the radio wave absorber 20 with an adhesive or the like. As a specific product name of the cloth 55, Cordelan (registered trademark) manufactured by Kojin Co., Ltd. may be mentioned. Corderan contains polyvinyl chloride and polyvinyl alcohol as main components and a part of kraft polymer. The feature of Corderan is that the fiber itself is flame retardant and self-extinguishing, and the toxicity of smoke and gas generated by combustion is very low.

  3A and 3B show Comparative Example 1 in which the radio wave absorber 40 having substantially no sound wave reflection in the first embodiment is removed (the same reference numerals are used for the same parts as those in the first embodiment). This is prepared for comparison with the effect of the first embodiment.

FIG. 4 shows the frequency characteristics of radio wave return loss (dB) in the first embodiment and the first comparative example. In the case of the first embodiment, the measurement conditions are a height L1 from the back surface of the radio wave absorber 20 to the tip of the sound wave absorber 30 = 640 mm, and a height L2 from the back surface of the radio wave absorber 20 to the tip of the cylindrical portion 22. = 450 mm and the thickness of the cylindrical portion 22 were 45 mm. Further, the height L3 = 190 mm, the bottom width W = 600 mm, and the thickness 25 mm of the radio wave absorber 40 (using a long-fiber conductive glass fiber mat), the glass fiber average fiber diameter 20 μm, and the carbon density 0.5 kg / It was m ^3. Comparative Example 1 has the same dimensions, shape, and material as those of Embodiment 1 except that the radio wave absorber 40 is not provided.

  According to FIG. 4, in the case of the first embodiment, the return loss is sufficiently higher than the target performance line indicated by a thick straight line in the required frequency range of 30 MHz or more, and the first embodiment is particularly from 30 MHz. It can be seen that better characteristics than Comparative Example 1 are obtained in the range of 60 MHz and around 200 MHz.

  In addition, the reflection attenuation amount of the sound wave is not substantially different between the first embodiment and the comparative example 1. In any case, the normal incident sound pressure reflectance at a frequency of 125 to 1000 Hz is approximately 0.3 or less, and the sound absorber is Since the structure can easily increase the volume, it is possible to obtain a sound wave reflection attenuation amount superior to the conventional example of Patent Document 1.

  According to the first embodiment, the following effects can be obtained.

(1) When the characteristics of the radio wave acoustic absorber 10 with respect to the incoming radio wave are considered, the conductive material is substantially contained in front of the radio wave absorber 20 of dielectric loss material such as foamed resin containing the conductive material. By arranging the radio wave absorber 40 such as a long fiber conductive glass fiber mat that does not reflect sound waves, an opening is provided at the tip of the hollow quadrangular pyramid by the cylindrical portion 22 of the radio wave absorber 20 and the radio wave absorber 40. Thus, it is possible to construct a sufficiently long cylindrical shape, and it is possible to improve radio wave absorption characteristics (especially radio wave absorption characteristics in a low frequency region). Further, the sound absorber 30 such as a short fiber glass fiber mat (glass wool) does not substantially reflect radio waves and does not deteriorate radio wave absorption characteristics.

(2) By arranging the flat wave absorber 50 made of a magnetic loss material such as sintered ferrite and tile on the back surface of the radio wave absorber 20, it is possible to further improve the radio wave absorption characteristics in the low frequency region. The radio wave absorber 20 can be downsized.

(3) When the characteristics of the radio wave absorber 10 with respect to the incoming sound wave are considered, the sound absorber 30 can be disposed in the hollow portion of the radio wave absorber 20, the volume of the sound absorber 30 can be sufficiently increased, and the sound absorption The characteristics can be improved. Further, the radio wave absorber 40 such as a long fiber conductive glass fiber mat does not substantially reflect sound waves, and does not deteriorate sound wave absorption characteristics even when exposed to the sound wave arrival side surface.

(4) When a radio wave absorber is composed only of a conductive glass fiber mat radio wave absorber and a glass fiber mat sound wave absorber, it is difficult to attach to the wall because the material is soft, but the foam contains a conductive material. By using the resin wave absorber 20 at the bottom, it is easy to attach to the wall surface.

  5A and 5B show a radio wave absorber according to the second embodiment of the present invention. In this figure, the radio wave absorber 10A includes a radio wave absorber 20A made of a dielectric loss material such as a foamed resin containing a conductive material, and a sound wave absorber 30A substantially free of radio wave reflection such as a glass fiber mat, A radio wave absorber 40A such as a conductive glass fiber mat that does not substantially reflect sound waves containing a conductive material, a sound wave absorber 60 that does not substantially reflect radio waves such as glass fiber mats, and a flat plate made of a magnetic loss material. The electromagnetic wave absorber 50 is provided.

  As shown in FIGS. 6A and 6B, a radio wave absorber 20A such as a foamed resin containing a conductive material rises from the flat bottom 21A and the edge of the front surface (the arrival surface of radio waves and sound waves). A cylindrical portion 22A provided with an opening at the tip of a hollow quadrangular pyramid and a number of tapered portions 23A provided inside the cylindrical portion 22A and provided on the front surface of the flat bottom portion 21 are integrally formed. Have. This radio wave absorber 20 </ b> A corresponds to a tube in which the length of the cylindrical portion 22 of the radio wave absorber 20 of the first embodiment is shortened.

  The sound wave absorber 30A such as a glass fiber mat is made of the same material as that of the sound wave absorber 30 of the first embodiment, is disposed on the front side of the radio wave absorber 20A, that is, on the front side of the tapered portion 23, and absorbs radio waves. The side surface is surrounded by the body 40A. The radio wave absorber 40A is made of the same material as the radio wave absorber 40 of the first embodiment, and has a shape in which an opening is provided at the tip of a hollow quadrangular pyramid. The rear edge of the radio wave absorber 40A is in contact with or close to the front edge of the cylindrical portion 22A of the radio wave absorber 20A. The longer cylindrical shape is formed by the cylindrical portion 22A of the radio wave absorber 20A and the radio wave absorber 40A. Is configured.

  The sound wave absorber 60 substantially free of radio wave reflection is made of the same material as the sound wave absorber 30A inside the wave wave absorber 40A, and is disposed so as to surround at least the side surface of the wave absorber 40A (wave wave absorption). The configuration may also cover the entire outer surface of the body 40A).

  Other configurations are the same as those of the first embodiment described above, and the same or corresponding parts are denoted by the same reference numerals and description thereof is omitted.

  FIGS. 7A and 7B show a comparative example 2 in which the radio wave absorber 40A substantially free of sound wave reflection in the second embodiment is removed, and the sound wave absorber 30B (sound wave) is disposed on the front side of the radio wave absorber 20A. (The same outer peripheral shape as the absorber 60) (the same reference numerals are given to the same parts as those of the second embodiment), and are prepared for comparison with the effects of the second embodiment.

FIG. 8 shows the frequency characteristics of the return loss (dB) in the second embodiment and the second comparative example. In the case of Embodiment 2, the measurement conditions are as follows: height L1 from the back surface of the radio wave absorber 20A to the tip of the sound wave absorber 30A = 640 mm, and height L2 from the back surface of the radio wave absorber 20A to the tip of the cylindrical portion 22A. = 230 mm and the thickness of the cylindrical portion 22A were 45 mm. Further, the height L3 of the radio wave absorber 40A (using a long-fiber conductive glass fiber mat) is set to 410 mm, the bottom width W is 600 mm, and the thickness is 25 mm. The glass fiber has an average fiber diameter of 20 μm and a carbon density of 0.5 kg / It was m ^3. In Comparative Example 2, the same size, shape, and material as in Embodiment 2 were used except that the radio wave absorber 40A was not provided.

  According to FIG. 8, in the case of the second embodiment, the return loss is sufficiently higher than the target performance line indicated by a thick straight line in the required frequency range of 30 MHz or more, and in the second embodiment, particularly from 30 MHz. It can be seen that better characteristics than those of Comparative Example 1 are obtained in the range of 50 MHz and in the range of about 150 MHz to about 450 MHz.

  In addition, the reflection attenuation amount of the sound wave is not substantially different between the second embodiment and the comparative example 2, and the normal incident sound pressure reflectance at the frequency of 125 to 1000 Hz is almost 0.3 or less, and the sound absorber is Since the structure can easily increase the volume, it is possible to obtain a sound wave reflection attenuation amount superior to the conventional example of Patent Document 1.

  FIG. 9 shows a radio wave absorber according to the third embodiment of the present invention. In this figure, the radio wave absorber 10B includes a radio wave absorber 70 made of a dielectric loss material such as foamed resin containing a conductive material, a sound wave absorber 80 substantially free of radio wave reflection such as a glass fiber mat, A radio wave absorber 90 having substantially no sound wave reflection, such as a conductive glass fiber mat containing a conductive material, and a flat radio wave absorber 50 made of a magnetic loss material are provided.

  In this case, the radio wave absorber 70 includes a flat bottom portion 71 and wedge-shaped protrusions 72 formed in a wedge shape on the front surface (arrival surface of radio waves and sound waves) and arranged in a wedge shape. 1 is the same as that of the first electromagnetic wave absorber 20.

  The sound wave absorber 80 having substantially no radio wave reflection is formed in a wedge shape in the front and rear, and the material is the same as that of the sound wave absorber 30 of the first embodiment. Then, the wedge-shaped protrusion 81 on the rear side of the sound absorber 80 is fitted and integrated between the wedge-shaped protrusions 72 of the radio wave absorber 70.

  The radio wave absorber 90 having substantially no sound wave reflection is disposed so as to surround (cover) the side surface of the wedge-shaped protruding portion 82 in front of each sound wave absorber 80 protruding from the radio wave absorber 70, and the material thereof is that of the first embodiment. This is the same as the radio wave absorber 40.

  Also in the case of the third embodiment, a longer protrusion can be formed by the wedge-shaped protrusion 72 of the radio wave absorber 70 and the radio wave absorber 90 having substantially no sound wave reflection, and the wedge-shaped protrusion 72 is made longer. Similar effects can be obtained. In general, the longer the length of the radio wave absorber, the better the radio wave absorption characteristic. Therefore, the addition of the radio wave absorber 90 can improve the radio wave absorption characteristic, particularly in the low frequency region. In addition, since the wedge-shaped protrusion 72 of the radio wave absorber 70 that actually reflects sound waves can be shortened while obtaining substantially the same effect as the length of the wedge-shaped protrusion 72, the overall shape can be reduced in size. In addition, sound absorption characteristics are also improved.

  Note that the structure of covering the radio wave absorber and the sound wave absorber in a bag shape with the cloth 55 indicated by the dotted line in the first embodiment can also be applied to the second and third embodiments.

  FIG. 10 is a fourth embodiment of the present invention, and shows a radio wave anechoic chamber using the radio wave absorber 10 shown in the first embodiment. In FIG. 10, a large number of radio wave absorbers 10 are arranged adjacent to each other on a room-side surface of a shield panel (panel on which one or both sides of a conductive plate is provided) 100 constituting the inner wall surface of a radio wave anechoic chamber. It is fixed. In this case, the front side of the radio wave absorber 20 is the indoor side. Usually, the side wall surface and the ceiling surface of the radio wave anechoic chamber are configured as shown in FIG.

  According to the configuration of this radio wave anechoic chamber, the radio wave absorber 10 shown in the first embodiment is used, and even if the total length is small, the radio wave and sound wave absorption characteristics are good. Is possible.

  In addition, it is also possible to use the thing of the structure shown in Embodiment 2 or Embodiment 3 as a radio wave acoustic wave absorber arrange | positioned indoors of the shield panel 100. FIG.

  Although the embodiments of the present invention have been described above, it will be obvious to those skilled in the art that the present invention is not limited to these embodiments, and various modifications and changes can be made within the scope of the claims.

BRIEF DESCRIPTION OF THE DRAWINGS It is Embodiment 1 of the radio wave absorber based on this invention, Comprising: (A) is a front view, (B) is a sectional side view. It is a radio wave absorber of dielectric loss material used in Embodiment 1, and (A) is a front view and (B) is a sectional side view. It is the comparative example 1 for performance comparison, Comprising: (A) is a front view, (B) is a sectional side view. 6 is a graph showing frequency characteristics of return loss of Embodiment 1 and Comparative Example 1. It is Embodiment 2 of the electromagnetic wave absorber which concerns on this invention, Comprising: (A) is a front view, (B) is a sectional side view. It is an electromagnetic wave absorber of the dielectric loss material used in Embodiment 2, Comprising: (A) is a front view, (B) is a sectional side view. It is the comparative example 2 for performance comparison, Comprising: (A) is a front view, (B) is a sectional side view. 5 is a graph showing frequency characteristics of return loss of Embodiment 2 and Comparative Example 2. It is a sectional side view which shows Embodiment 3 of the radio wave absorber based on this invention. It is a sectional side view of the radio wave anechoic chamber using the radio wave absorber according to the present invention. It is a sectional side view of the electromagnetic wave absorber of a prior art example.

Explanation of symbols

10, 10A, 10B Radio wave absorber 20, 20A, 40A, 50, 70, 90 Radio wave absorber 21, 21A, 71 Flat bottom portion 22, 22A Tubular portion 23, 23A Tapered portion 30, 30A, 30B, 60 , 80 Sound absorber 55 Cloth 72, 81, 82 Wedge-shaped protrusion 100 Shield panel

Claims (9)

  A first acoustic wave absorber substantially free of radio wave reflection on the front side of the first radio wave absorber and a second substantially free of acoustic wave reflection surrounding at least the side surface of the outer surface of the first acoustic wave absorber. An electromagnetic wave absorber comprising a radio wave absorber.   2. The radio wave absorber according to claim 1, wherein a second sound wave absorber substantially free of radio wave reflection is disposed so as to surround at least a side surface of the outer surface of the second radio wave absorber.   The radio wave absorber according to claim 1 or 2, wherein the second radio wave absorber has a shape in which an opening is provided at a tip of a hollow cone.   The first radio wave absorber has a cylindrical part having an opening at a tip of a hollow cone, and a leading edge of the cylindrical part is in contact with or close to the second radio wave absorber. Item 4. The radio wave absorber according to Item 3.   The radio wave absorber according to claim 1, 2, 3, or 4, wherein the sound absorber is a glass fiber mat.   6. The radio wave absorber according to claim 1, 2, 3, 4 or 5, wherein the second radio wave absorber is a conductive glass fiber mat containing a conductive material.   The radio wave absorber according to claim 1, 2, 3, 4, 5, or 6, wherein the first radio wave absorber is a foamed resin containing a conductive material.   The radio wave absorber according to claim 1, 2, 3, 4, 5, 6 or 7, wherein a third radio wave absorber made of a magnetic loss material is disposed on a back surface of the first radio wave absorber.   The radio wave acoustic wave absorber according to any one of claims 1 to 8 is disposed on at least one of the indoor side wall surface and the ceiling surface so that the front side of the first radio wave absorber is the indoor side. Radio wave anechoic chamber characterized by.

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