JP4420253B2 - Radio wave absorber and anechoic chamber - Google Patents

Description

  The present invention relates to a radio wave absorber having broadband characteristics and an anechoic chamber using the same.

  An anechoic chamber is widely used as a test site for measuring electromagnetic noise radiated from various electronic devices and evaluating the resistance of electronic devices to external electromagnetic noise. In recent years, there has been a movement to use an anechoic chamber as a place (CALTS = Calibration Test Site) for calibrating an antenna for measuring radiation noise.

  An electromagnetic wave absorber is installed on the ceiling and walls of such an anechoic chamber (EMC anechoic chamber) to realize a space in which electromagnetic wave reflection from other than the floor (metal surface) is extremely small.

  The performance of the electromagnetic anechoic chamber for EMC is evaluated by measuring site attenuation. Site attenuation is a radio wave attenuation characteristic between transmitting and receiving antennas measured by a method determined in a measurement field, and is measured in a frequency range of 30 MHz to 1 GHz (or 18 GHz). Compared with the measured site attenuation in an anechoic chamber and the ideal site attenuation (theoretical value), the smaller the difference, the higher the performance of the anechoic chamber. Usually, if the difference from the theoretical value is within the range of ± 4 dB, it is considered suitable as a measurement field for radiated noise. However, the smaller the difference from the theoretical value, the more accurate the radiated noise can be measured. In many cases, about ± 3 dB is required, and there is also a high performance requirement of ± 1 dB to ± 2 dB. When the measurement accuracy in an anechoic chamber increases, it becomes possible to reduce the margin for the standard value when electronic equipment manufacturers measure the radiation noise of the product and confirm that it is below the standard value. There is an advantage that can be suppressed.

  On the other hand, when used as an antenna calibration field, high-accuracy measurement is required, so that high performance is required such that the difference from the theoretical value is about ± 1 dB to ± 1.5 dB.

  The characteristics required for electromagnetic wave absorbers installed on the ceiling and walls of an electromagnetic anechoic chamber for EMC are said to be approximately 20 dB or more at 30 MHz to 18 GHz, but depend on the required anechoic chamber performance (difference from the theoretical value of site attenuation) Not only does this depend on the size of the anechoic chamber, measurement distance, frequency, etc. In particular, in the case of a 10 m method anechoic chamber (measurement distance 10 m), it is necessary to improve the absorption characteristics at a low frequency of 30 to 100 MHz than the characteristics at a high frequency of 100 MHz or more. This is due to the measurement conditions of site attenuation. In the case of horizontal polarization, the received electric field intensity at a low frequency of 30 to 100 MHz is smaller than the received electric field intensity at a high frequency of 100 MHz or higher. This is because the difference from the theoretical value is likely to be large.

  As the electromagnetic wave absorber used for the ceiling and walls of these electromagnetic wave anechoic chambers for EMC, as shown in FIG. 11, a ferrite sintered body 1 as an electromagnetic wave absorber made of a magnetic loss material and a dielectric as an electromagnetic wave absorber containing a conductive material. A composite type electromagnetic wave absorber combined with a property loss material 2 (sometimes referred to as an ohmic loss material) is currently widely used.

  The ferrite sintered body absorbs radio waves due to magnetic loss, and has excellent characteristics at a low frequency of about 30 to 400 MHz while being as thin as several millimeters. On the other hand, the dielectric loss material is made of a material in which a conductive material such as carbon or graphite is contained in a base material (low dielectric constant dielectric) such as expanded polystyrene or expanded polyurethane, and absorbs radio waves due to the ohmic loss of the conductive material. The higher the frequency, the better the characteristics.

  The composite type electromagnetic wave absorber is a combination of a ferrite sintered body with excellent low-frequency characteristics and a dielectric loss material with excellent high-frequency characteristics. Compared to a radio wave absorber, the length of the radio wave absorber can be reduced to half or less.

  The dielectric loss material is usually tapered such as a pyramid shape or a wedge shape. The reason for the tapered shape is to absorb and absorb radio waves efficiently while suppressing reflection by gradually changing the impedance of radio waves incident from free space.

  The length of the dielectric loss material is usually about 0.5 to 2 m, but the longer the length, the higher the performance. Therefore, depending on the required anechoic chamber performance, a length of 3 m or more is used. There is also. Therefore, in order to reduce the cost by reducing the weight and reducing the material, a radio wave absorber in which a dielectric loss material is hollowed as shown in Patent Document 1 below has been put into practical use. As the shape of the hollow dielectric loss material, there are a hollow pyramid shape of FIGS. 12A and 12B and a hollow wedge shape of FIGS. 13A and 13B.

Furthermore, the applicant proposes a shape (FIG. 14) in which an opening is provided at the tip of a hollow cone-shaped body as a radio wave absorber that can obtain good low-frequency characteristics with a short length and has no difference in polarization plane characteristics. (Patent Document 1 below).
JP 2005-340730 A

  As described in Patent Document 1, a problem with a radio wave absorber having a shape in which an opening is provided at the end of a hollow cone-shaped body is that radio waves pass through the opening and reach the ferrite sintered body at a high frequency of several GHz or higher. Therefore, the radio wave absorption characteristic is lowered. Therefore, Patent Document 1 discloses that a bottom absorbent material (including a tapered portion) is added to improve high-frequency characteristics as shown in FIG. 15, but if the bottom absorbent material is thick, the merit of hollowing is sufficient. I can't make use of it.

  The present invention has been made in recognition of such a situation, and the object thereof is light weight and low cost, there is no difference in polarization characteristics compared to a wedge-shaped structure, and a short length compared to the conventional one. An object of the present invention is to provide a radio wave absorber capable of obtaining good radio wave absorption characteristics over a wide range from a low frequency to a high frequency, and an anechoic chamber using the same.

One embodiment of the present invention is a radio wave absorber. This radio wave absorber
A first electromagnetic wave absorber made of a magnetic loss material;
A second radio wave absorber including a conductive material disposed on the front surface of the first radio wave absorber;
The second radio wave absorber has a hollow pyramid or a side surface forming part having a shape provided with an opening at the tip of the hollow pyramid, and one side line of the side surface forming part protrudes from the side surface forming part on the same surface. There is an extended extension, and there is only one extension for one ridgeline.

  In the radio wave absorber according to an aspect, the extension portion may have a shape in which a width decreases from a tip of the hollow pyramid or a shape in which an opening is provided at a tip of the hollow pyramid toward a bottom.

  In this case, the extension portion may have a width of 0 at the bottom portion.

  In the radio wave absorber of a certain aspect, the side surface forming portion and the extension portion on the same surface are preferably integrated to form a single radio wave absorber.

  In a certain aspect of the radio wave absorber, the second radio wave absorber may have a configuration including a conductive material therein or a configuration including a conductive layer containing the conductive material on the surface.

  In the radio wave absorber according to an aspect, a bottom support member may be disposed between the first radio wave absorber and the second radio wave absorber.

  In the radio wave absorber according to an aspect, the bottom support material may include a conductive material.

  In the radio wave absorber according to an aspect, the first radio wave absorber may be a ferrite sintered body.

  Another aspect of the present invention is an anechoic chamber. In the anechoic chamber, a plurality of the radio wave absorbers are arranged on at least one of the indoor side wall surface and the ceiling surface so that the front surface of the first radio wave absorber is on the indoor side.

  It should be noted that any combination of the above components is also effective as an aspect of the present invention.

  According to the present invention, since the second radio wave absorber has a hollow structure, the second radio wave absorber has a light weight and a low cost as compared with a structure in which the second radio wave absorber is not hollow. Further, since the side surface forming portion forms a hollow pyramid or a side surface having an opening at the tip of the hollow pyramid, there is no difference in polarization plane characteristics as compared with the conventional wedge shape. Furthermore, since there is only one extension portion extending from one side surface forming portion so as to protrude one ridge line of each side surface forming portion on the same surface, there is no extension portion in Patent Document 1. As compared with the radio wave absorber, the opening size can be reduced or zero (no opening at the tip) if the tip width is the same. For this reason, good radio wave absorption characteristics can be obtained over a wide range from low frequency to high frequency.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. In addition, the same code | symbol is attached | subjected to the same or equivalent component, member, process, etc. which are shown by each drawing, and the overlapping description is abbreviate | omitted suitably. In addition, the embodiments do not limit the invention but are exemplifications, and all features and combinations thereof described in the embodiments are not necessarily essential to the invention.

(First embodiment)
FIG. 1 is an explanatory view of the shape of a radio wave absorber 100 according to a first embodiment of the present invention, where (A) is a front view and (B) is a side view. FIG. 2 is an explanatory view of the shape of the extension 23 of the radio wave absorber 100 shown in FIG. In this figure, the extension 23 is shown highlighted with diagonal lines.

  The radio wave absorber 100 includes a first radio wave absorber 10 made of a magnetic loss material and a conductive material disposed on the front surface (radio wave arrival side) of the first radio wave absorber 10 (for example, fixed with an adhesive or the like). 2 radio wave absorber 20. The first radio wave absorber 10 is a flat radio wave absorber formed by laminating plate-like ferrite sintered bodies 11 as magnetic loss materials without gaps to form a flat wall body. The second radio wave absorber 20 has a side surface forming part 22 and an extension part 23. The side surface forming part 22 forms each side surface having a shape in which an opening 25 is provided at the tip of a hollow pyramid (in the figure, a hollow regular quadrangular pyramid is illustrated). The extension part 23 is extended so that one ridgeline 24 (refer FIG. 2) of each side surface formation part 22 may protrude from each side surface formation part 22 on the same surface. As is clear from FIG. 2, the extension 23 has a shape that decreases in width from the tip of the shape in which an opening is provided at the tip of the hollow pyramid toward the bottom, and preferably has a width of zero at the bottom. Further, the extension 23 preferably has a shape that does not protrude from the bottom surface of the shape in which an opening is provided at the tip of the hollow pyramid when viewed from the front. The side surface forming portion 22 and the extension portion 23 on the same surface are preferably integrated and form one plate-like dielectric loss material 21 (a radio wave absorbing plate). In this case, the second electromagnetic wave absorbing material 20 can be configured by combining a predetermined number (four in the illustrated case) of plate-like dielectric loss materials 21 having the same shape and integrating them by bonding or the like. The plate-like dielectric loss material 21 is obtained by containing a conductive material such as carbon or graphite in a base material such as foamed polystyrene or foamed polyurethane. Note that a radio wave transparent surface material can be attached to the tip of the second radio wave absorber 20, and the anechoic chamber can be made brighter by making the surface material a bright color such as white.

  FIG. 3 is an exemplary shape comparison diagram (No. 1) between the radio wave absorber 100 of the present embodiment shown in FIG. 1 and the radio wave absorber (conventional example) described in Patent Document 1 described above. In this figure, both wave absorbers have a front end width of 400 mm, a bottom end width of 600 mm, a length of 925 mm, and a plate thickness of 40 mm. In this case, the tip opening size of the wave absorber described in Patent Document 1 is 320 mm, whereas the tip opening size of the wave absorber 100 of the present embodiment is 220 mm, which is smaller by the width of the extension 23. .

  FIG. 4 is a comparison diagram of radio wave absorption characteristics in the case shown in FIG. As is clear from this figure, the radio wave absorber 100 of the present embodiment and the radio wave absorber described in Patent Document 1 are equally good in low-frequency characteristics because the tip width is the same. On the other hand, since the radio wave absorber 100 of the present embodiment has a smaller opening size than the radio wave absorber described in Patent Document 1, the high frequency characteristics (from 2 GHz) are remarkably improved.

  FIG. 5 is an exemplary shape comparison diagram (No. 2) between the radio wave absorber 100 of the present embodiment shown in FIG. 1 and the radio wave absorber (conventional example) described in Patent Document 1 described above. In this figure, the tip widths of both wave absorbers are 300 mm, the bottom end width is 600 mm, the length is 925 mm, and the plate thickness is 40 mm (that is, other than the tip width is the same as in FIG. 3). In this case, the tip opening size of the wave absorber described in Patent Document 1 is 220 mm, whereas the tip opening size of the wave absorber 100 of the present embodiment is that the width of the extension 23 does not contribute to the opening size. Only small 120mm.

  FIG. 6 is a comparison diagram of radio wave absorption characteristics in the case shown in FIG. As is clear from this figure, the radio wave absorber 100 of the present embodiment and the radio wave absorber described in Patent Document 1 are equally good in low-frequency characteristics because the tip width is the same. On the other hand, since the radio wave absorber 100 of the present embodiment has a smaller opening size than that of the radio wave absorber described in Patent Document 1, the high frequency characteristics (from 6 GHz to 10 GHz in particular) are remarkably improved.

  According to the radio wave absorber 100 of the present embodiment, the following effects can be achieved.

(1) Since the second radio wave absorber 20 employs a hollow structure, the second radio wave absorber 20 is lighter and less expensive than the case where the second radio wave absorber 20 is not hollow.

(2) Since the side surface forming portion 22 forms each side surface having an opening at the tip of the hollow pyramid, there is no difference in polarization plane characteristics as compared with the conventional wedge shape. In addition, the extended portions 23 are arranged so that the front surface shape is the same even when the radio wave absorber 100 is rotated by 90 °, and there is no difference in polarization plane characteristics.

(3) Since there is only one extended portion 23 extending from each side surface forming portion 22 so that one ridge line of each side surface forming portion 22 protrudes on the same surface with respect to one ridge line 24 (see FIG. 2). As compared with the case where the extension portion 23 does not exist as in the radio wave absorber of Patent Document 1, the opening size can be reduced with the same tip width (see FIGS. 3 and 5). For this reason, good radio wave absorption characteristics can be obtained over a wide range from low frequency to high frequency.

(4) If the side surface forming part 22 and the extension part 23 on the same surface are integrated to form a single plate-like dielectric loss material 21 (a radio wave absorbing plate), a predetermined number of plate-like dielectric loss materials 21 ( 4) The second electromagnetic wave absorber 20 can be configured by combining and integrating by bonding or the like, and is easy to manufacture. Further, since the plate-like dielectric loss material 21 may have the same shape, it is excellent in mass productivity.

(5) The extension 23 has a shape in which an opening is provided at the tip of the hollow pyramid, the width of the extension 23 decreases from the tip toward the bottom and becomes zero at the bottom, and opens at the tip of the hollow pyramid when viewed from the front. If the shape of the bottom surface of the shape provided with a shape that does not protrude from the bottom, the adjacent ones do not get in the way when the plurality of radio wave absorbers 100 are arranged.

(Second Embodiment)
FIG. 7 is an explanatory view of the shape of the radio wave absorber 200 according to the second embodiment of the present invention, in which (A) is a front view and (B) is a side view. In this figure, the extension 23 is highlighted with diagonal lines. Compared with the radio wave absorber 100 of the first embodiment shown in FIG. 1, the radio wave absorber 200 of the present embodiment has a hollow pyramid (a case of a hollow regular quadrangular pyramid is illustrated in the figure). Are different, that is, there is no opening at the tip of the second radio wave absorber 20, and the other points are the same.

  According to the radio wave absorber 200 of the present embodiment, since there is no opening at the tip, it is possible to further improve the high frequency characteristics as compared with the first embodiment. However, when the extension 23 has a shape that does not protrude from the bottom of the hollow pyramid when viewed from the front, the maximum value of the tip width of the plate-like dielectric loss material 21 is the bottom end. Since it is limited to the sum of the half of the width and the plate thickness, the configuration of the first embodiment may be adopted when it is necessary to secure a tip width larger than that.

(Third embodiment)
FIG. 8 is an explanatory view of the shape of the radio wave absorber 300 according to the third embodiment of the present invention, in which (A) is a front view and (B) is a side view. FIG. 9 is an explanatory view of the shape of the plate-like dielectric loss material 21 of FIG. 8, (A) is a front view, and (B) is a side view. Compared with the radio wave absorber 100 of the first embodiment shown in FIG. 1, the radio wave absorber 300 of the present embodiment has a jagged shape 26 at the tip of the plate-like dielectric loss material 21. The plate-like dielectric loss material 21 has a convex portion 28 formed on the side edge and a concave portion 29 (see FIG. 9) formed on the inner surface, and is fitted to each other, and the first radio wave absorber 10. The bottom support member 30 is disposed (intervened) between the second wave absorber 20 and the second radio wave absorber 20, and the other points are the same.

  The jagged shape 26 is formed by a series of small tapered shapes (substantially conical or mountain-shaped). This jagged shape 26 suppresses reflection in the high frequency region in the operating frequency range such as an anechoic chamber.

  The bottom support member 30 is preferably a dielectric loss material in which a conductive material such as carbon or graphite is contained in a base material such as foamed polystyrene or foamed polyurethane similarly to the second radio wave absorber 20, and the second radio wave absorption material. A tapered portion 31 is provided so as to be located in the hollow portion of the material 20. The tapered portion 31 is, for example, a set of small square pyramids. The convex portion 27 of the base (bottom side) of the plate-like dielectric loss material 21 is fitted into the hole 32 (concave portion) on the top surface of the bottom support member 30 so that the plate-like dielectric loss material 21 is supported by the bottom support member 30.

  In this case, first, the first electromagnetic wave absorber 10 made of the plate-like ferrite sintered body 11 and the bottom support member 30 covering the first electromagnetic wave absorber 300 are mounted on the conductor plate wall surface of the anechoic chamber to which the electromagnetic wave absorber 300 is to be attached. Then, it becomes possible to assemble the projection part 27 of the second radio wave absorber 20 base portion by inserting it into the hole 32 on the bottom support member 30 side, and the second radio wave absorber 20 can be easily attached to the wall surface. There is. Further, since the bottom support member 30 covers the front surface of the flat plate wave absorber 10 composed of a large number of plate-like ferrite sintered bodies 11, if the bottom support member 30 is a dielectric loss material as described above, a high frequency The reflection from the surface of the plate-like ferrite sintered body 11 can be suppressed. In addition, by providing the tapered portion 31 on the bottom support member 30, the effect of suppressing reflection at high frequencies can be further enhanced. However, as described above, since the high frequency characteristics are improved as compared with the radio wave absorber of Patent Document 1, even when the bottom support member 30 is provided, the thickness is thinner than that of the bottom absorber described in Patent Document 1. Is enough.

(Fourth embodiment)
In the present embodiment, an anechoic chamber using the radio wave absorber 100 according to the first embodiment will be described.

  10A is a front view and FIG. 10B is a side sectional view of an anechoic chamber 400 according to the fourth embodiment of the present invention. In this figure, a large number of electromagnetic wave absorbers 100 are arranged and fixed adjacent to each other on the indoor side surface of a shield panel 450 (a panel provided with a conductive plate on one or both sides) constituting the inner wall surface of the anechoic chamber. . In this case, the front side of the first radio wave absorber 10 (the side where the second radio wave absorber 20 is disposed) is the indoor side. Usually, the side wall surface and the ceiling surface of the anechoic chamber are configured as shown in FIG.

  According to the anechoic chamber of the present embodiment, since the radio wave absorber 100 shown in the first embodiment is used, good radio wave absorption characteristics can be obtained over a wide range from a low frequency to a high frequency. In addition, it is also possible to use the thing of the structure shown to the 2nd or 3rd embodiment as a radio wave absorber arrange | positioned indoors of the shield panel 450. FIG.

  The present invention has been described above by taking the embodiment as an example. However, it will be understood by those skilled in the art that various modifications can be made to each component of the embodiment within the scope of the claims. Hereinafter, modifications will be described.

  In the embodiment, it has been described that the side surface forming portion 22 and the extension portion 23 are preferably integrated and form a single plate-like dielectric loss material 21 (radio wave absorbing plate). However, the side surface forming portion 22 and the extension portion 23 are described. Even if they are separate, the same electromagnetic wave absorption characteristics can be obtained. In this case, first, the side surface forming portion may be combined to form a hollow pyramid or an opening at the tip of the hollow pyramid, and the extension portion may be fixed to the side edge of the side surface forming portion later by bonding or the like.

  In the embodiment, the second radio wave absorber 20 is not only configured to include a conductive material inside the base material such as foamed polystyrene or foamed polyurethane, but also configured to include a conductive layer containing the conductive material on the surface of the base material. May be.

  In the embodiment, the shape of the second radio wave absorber 20 is exemplified by a hollow regular quadrangular pyramid or a shape in which an opening is provided at the tip of the hollow regular quadrangular pyramid. Or a shape having an opening at its tip. In this case, the second radio wave absorber 20 can be configured by combining three or more plate-like dielectric loss materials 21.

It is shape explanatory drawing of the electromagnetic wave absorber which concerns on the 1st Embodiment of this invention, (A) is a front view, (B) is a side view. It is shape explanatory drawing of the extension part of the electromagnetic wave absorber shown by FIG. 1 (extension part is emphasized with the oblique line). FIG. 2 is an exemplary shape comparison diagram (part 1) between the radio wave absorber of the present embodiment shown in FIG. 1 and the radio wave absorber described in Patent Document 1 described above. FIG. 4 is a comparison diagram (frequency characteristic diagram) of radio wave absorption characteristics in the case shown in FIG. 3. FIG. 3 is an exemplary shape comparison diagram (part 2) between the radio wave absorber according to the present embodiment shown in FIG. 1 and the radio wave absorber described in Patent Document 1 described above. FIG. 6 is a comparison diagram (frequency characteristic diagram) of radio wave absorption characteristics in the case shown in FIG. 5. It is shape explanatory drawing of the electromagnetic wave absorber which concerns on the 2nd Embodiment of this invention, (A) is a front view, (B) is a side view. It is shape explanatory drawing of the electromagnetic wave absorber which concerns on the 3rd Embodiment of this invention, (A) is a front view, (B) is a side view. It is shape explanatory drawing of the plate-shaped dielectric loss material of FIG. 8, (A) is a front view, (B) is a side view. (A) is a front view and (B) is a sectional side view of an anechoic chamber according to a fourth embodiment of the present invention. It is shape explanatory drawing of the conventional electromagnetic wave absorber (non-hollow). It is shape explanatory drawing of the conventional electromagnetic wave absorber (hollow pyramid shape), (A) is a front view, (B) is a side view. It is shape explanatory drawing of the conventional electromagnetic wave absorber (hollow wedge shape), (A) is a front view, (B) is a side view. It is shape explanatory drawing of the electromagnetic wave absorber of patent document 1, (A) is a front view, (B) is a side view. It is shape explanatory drawing of the electromagnetic wave absorber (with bottom part absorber) of patent document 1, (A) is a front view, (B) is a side view.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 1st electromagnetic wave absorber 11 Plate-shaped ferrite sintered body 20 2nd electromagnetic wave absorber 21 Plate-like dielectric loss material 22 Side surface formation part 23 Extension part 24 Edge line 25 Opening 26 Jagged shape 30 Bottom part support material 31 Tapered shape part 100,200 , 300 radio wave absorber

Claims (9)

A first electromagnetic wave absorber made of a magnetic loss material;
A second radio wave absorber including a conductive material disposed on the front surface of the first radio wave absorber;
The second radio wave absorber has a hollow pyramid or a side surface forming part having a shape provided with an opening at the tip of the hollow pyramid, and one side line of the side surface forming part protrudes from the side surface forming part on the same surface. An electromagnetic wave absorber having an extended extension and having only one extension for one ridgeline.   2. The radio wave absorber according to claim 1, wherein the extension portion has a shape whose width decreases from a tip of the hollow pyramid or a shape in which an opening is provided at a tip of the hollow pyramid toward a bottom portion.   The radio wave absorber according to claim 2, wherein the extension portion has a width of 0 at the bottom portion.   4. The radio wave absorber according to claim 1, wherein the side surface forming portion and the extension portion on the same surface are integrated to form a single radio wave absorber. 5.   5. The radio wave absorber according to claim 1, wherein the second radio wave absorber is configured to include a conductive material therein, or to have a conductive layer containing a conductive material on a surface thereof. Radio wave absorber.   The radio wave absorber according to any one of claims 1 to 5, wherein a bottom support member is disposed between the first radio wave absorber and the second radio wave absorber.   The radio wave absorber according to claim 6, wherein the bottom support material includes a conductive material.   The radio wave absorber according to any one of claims 1 to 7, wherein the first radio wave absorber is a ferrite sintered body.   A plurality of the radio wave absorbers according to any one of claims 1 to 8 are arranged on at least one of the indoor side wall surface and the ceiling surface so that the front surface of the first radio wave absorber is on the indoor side. There is an anechoic chamber.

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