JP2010021459A - Radio wave absorber and radio wave absorption wall - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a radio wave absorber superior in radio wave absorption performance. <P>SOLUTION: A plurality of structural components are combined to provide this radio wave absorber. In each structural component, a block 1 is configured by adhering a conductor such as a carbon and metal fine powder, etc., to a synthetic resin while dispersing and causing appropriate dielectric loss, and two blocks arranged in parallel at a constant interval are used in pairs. These pairs of blocks are divided into relatively upper stage pairs and lower stage pairs to arrange at least two pairs of blocks in the upper and lower stages, and the pairs of blocks in the upper and lower stages are coupled in the direction perpendicular to each other, and two or more pairs of blocks are combined in a double cross. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a radio wave absorber used in an anechoic chamber or an anechoic chamber, and a radio wave absorption wall formed by combining a plurality of radio wave absorbers and placing them in an anechoic chamber or an anechoic chamber.

  The radio wave absorber is provided on the ceiling surface, the side wall surface, or in some cases, the floor surface of the room in order to configure an anechoic chamber that performs measurement of radiated electromagnetic waves of electronic devices and measurement of resistance to external electromagnetic waves. As a radio wave absorber, a dielectric loss body in which a conductive material such as carbon / metal fine powder is uniformly dispersed in a synthetic resin in a three-dimensional shape is formed into a pyramid or wedge shape.

  Furthermore, for the purpose of cost reduction and transportation cost reduction, there is also known a structure in which materials are carried into the site and assembled into a hollow pyramid or wedge shape at the site.

  By the way, when an electromagnetic wave absorber with a hollow pyramid or wedge structure is used for an anechoic chamber that requires a wide range of operating frequencies, the dielectric loss material becomes irregular in the space area occupied by the electromagnetic wave absorber. As a result, the surface reflection of the dielectric loss body partially increases, and it is difficult to obtain good radio wave absorption characteristics.

In addition, in the radio wave absorber used for such applications, a thickness of about 1/5 wavelength of the lower limit frequency to be operated is required, and a conductor is synthesized with the constituent members of the radio wave absorber so as to satisfy the condition. When a dielectric loss body dispersed and fixed to a resin is used, there is a problem that its volume becomes excessively large.
JP 2000-59067 A JP-A-7-86783 JP-A-7-22769

  The problem to be solved is that a wave absorber installed on a wall such as an anechoic chamber requires a thickness of about 1/5 wavelength of the lower limit frequency to be operated. When a dielectric loss body in which a conductor is dispersedly fixed to a synthetic resin is used as the constituent member, the volume becomes excessively large.

  In the present invention, the dielectric loss of the dielectric loss body is set to a high value, and the dielectric loss body and the free space are regularly mixed in the space region occupied by the absorber, so that the dielectric loss of the entire space occupied by the absorber is equivalent. The greatest feature is that the volume of the necessary dielectric loss body is suppressed to about half despite having a thickness that can cope with a low frequency with a long wavelength by lowering.

  According to the radio wave absorber of the present invention, good absorption performance can be obtained in a very wide frequency band. In addition, by combining the structural members with a cross beam, the proportion of the dielectric loss body in the volume of the radio wave absorber can be reduced to 50% or less, and the process of dispersing and fixing the conductor to the synthetic resin and its materials are reduced. There is an advantage that it is possible to achieve a significant cost reduction.

  Despite having a thickness that can handle low wavelengths with long wavelengths, the purpose of reducing the volume of the required dielectric loss material to about half is to disperse and fix a conductive material such as carbon or metal fine powder on the synthetic resin. This was realized by combining a block having an appropriate dielectric loss or a plate having an appropriate sheet resistance value by adhering carbon fibers to the surface in a cross-beam shape.

  The present invention is a radio wave absorber in which a plurality of constituent members are combined. The constituent member is a standard dielectric loss body in which a conductor such as carbon or metal fine powder is dispersed or a sheet resistance value is retained on the surface. A plurality of constituent members are combined at an angle, and dielectric loss bodies and free space are regularly mixed in the region occupied by the constituent members and the space region, and the dielectric loss as a whole is reduced equivalently. It is characterized by that.

  FIG. 1 shows an example in which a block is used as a constituent member of a radio wave absorber. Blocks 1 shown in FIGS. 1A and 1B are obtained by dispersing a conductive material such as carbon in a synthetic resin and solidifying it into a regular rectangular parallelepiped. In this embodiment, for convenience of explanation, the description will be made by distinguishing the upper and lower sides of the block in a posture with the long side of the rectangular parallelepiped as the upper and lower edges. Block 1 has two opposing sides, and in this embodiment, the two sides on the long side are divided into five equal lengths L, and convex at both ends and the center at three intervals of L / 5. By forming the concave portions 3 at two locations between the portion 2 and both convex portions, the square convex portions 2 and the concave portions 3 are alternately formed on the upper and lower edges of the block 1, respectively.

  In the present invention, the recess 3 is a notch for engaging the block arranged in the upper stage and the block arranged in the lower stage as will be described later, and the interval (L / 5) The thickness d is adjusted. FIG. 2 shows an example in which two or more blocks are combined in a cross pattern. Fig.2 (a) is a front view of the electromagnetic wave absorber which combined the group of blocks to the upper and lower stages, and FIG.2 (b) is the side view.

  2 (a) and 2 (b), two blocks (first set of blocks) 1a arranged in parallel with each other, with the respective concave portions facing each other in the perpendicular direction at the lower position. (Second Block Set) 1b are arranged in parallel, and the recesses of the blocks of the second block set 1b are engaged with the recesses of the blocks of the first block set 1a, and the first block set 1a and The second block set 1b is vertically connected to each other, and similarly, the two third block sets 1c are arranged in parallel by facing each concave portion from a right angle to the lower position of the two second block sets 1b. Then, the second block set 1b and the third block set 1c are connected vertically by engaging the recesses of the third block set 1c with the recesses of the second block set 1b block.

  Similarly, by connecting the third block set and the fourth block set in the same manner, the N-1th block and the Nth block (where N is a positive integer) are connected in order, as shown in FIG. As shown in Fig. 3, at least two sets of blocks are connected in the upper and lower stages, and in this embodiment, the upper and lower stages are connected in three stages. As shown in FIG. To do.

  The wave absorbers combined in the form of a cross-girder are stacked on the ferrite sintered body as they are and installed on a wall such as an anechoic chamber. Alternatively, the wave absorbers combined in the form of a cross-girder are shown in FIG. The case 5 is housed in a case 5 of a radio wave transparent body, and further, if necessary, the opening of the case 5 is closed with a cover 5a as shown in FIG. FIG. 6 shows an example in which the obtained prismatic radio wave absorber units 6 are stacked on a ferrite sintered body plate (not shown) and arranged vertically and horizontally and installed on the wall surface of an anechoic chamber.

  FIG. 7 shows an example in which a plate is used as a constituent member of the radio wave absorber. The plate 7 is a flat plate having a coating film on the surface with carbon fibers fixed to the surface and having an appropriate sheet resistance value. By dispersing a conductive material such as carbon in a synthetic resin and solidifying it into a flat plate shape. Can also be obtained.

  In FIG. 7, the plate 7 used in this embodiment is a vertically long rectangle, and two slits 10 having a width corresponding to the thickness of the plate 7 are arranged in parallel from the upper edge (or lower edge) of the short side to the central portion. It is an opening.

  When assembling the plate 7 of FIG. 7, as shown in FIG. 8, first, two plates are arranged in parallel as a first plate set 7a at a predetermined interval, and then a plate whose top and bottom directions are reversed is arranged. As the second plate, the posture of the second plate set 7b is arranged parallel to the first plate set 7a in a perpendicular direction at a fixed interval, and the slits opened in both sets of plates are vertically oriented. From above and combined in a cross pattern as shown.

  Although not shown, in this embodiment as well, a set of radio wave absorbers combined in a cross beam shape is accommodated in a case of a radio wave transparent body, and further, if necessary, the opening is closed with a cover and a prismatic radio wave absorber. The points obtained by finishing the unit and arranging the obtained radio wave absorber units vertically and horizontally on the ferrite sintered body plate and installing them on the wall surface of the anechoic chamber are the same as in the previous embodiment.

  According to the radio wave absorber according to the present invention, electromagnetic waves can be efficiently absorbed by setting the dielectric loss of the constituent member higher in the high frequency region where the gap of the cross beam formed by assembling the constituent member is larger than the wavelength. Furthermore, in the low frequency range where the gap between the cross beams <wavelength, it is considered that there is no gap between the cross beams, acting as a radio wave absorber composed of dielectric loss bodies rather than the actual dielectric constant, and the surface deteriorating the radio wave absorption performance Reflection is reduced.

  Therefore, according to the radio wave absorber of the present invention, good absorption performance can be obtained in a very wide frequency band. In addition, the radio wave absorption characteristics of the radio wave absorber of the present invention can be determined by selecting the dielectric constant of the dielectric loss body, the volume ratio of the dielectric loss body in the radio wave absorber, and the number of stages in which blocks constituting the radio wave absorber are stacked. It can be adjusted.

  In addition, by combining the structural members in a cross beam, dielectric loss bodies and free space are mixed in the space area occupied by the radio wave absorber, and the proportion of the dielectric loss body in the volume of the radio wave absorber is 50% or less. Is possible. Next, examples of the present invention will be described with reference to the drawings with specific examples.

  Ten blocks shown in FIG. 9 were used, and two blocks were assembled as a set into a five-stage grid-shaped radio wave absorber as shown in FIG. 10, and the radio wave absorption characteristics were measured. The blocks used in this example and the assembled radio wave absorber are as follows.

(1) Block The block is obtained by fixing carbon to a foamed urethane base material with latex and forming recesses at two locations on the upper and lower edges. The fixed amount of carbon is 0.3 g / L with respect to the volume of the urethane foam base material.
Block size 580mm x 484mm x 116mm
The width of the recess was 116 mm, and the depth was 75 mm. Two portions were formed on the edge of the long side of the block.

(2) Radio wave absorber On the ferrite sintered body plate, radio wave absorbers assembled in a five-stage grid pattern as shown in FIG. 10 were stacked. At this time, the volume of the block contained in the height 1820 mm (volume of about 0.612 m ³ ) of the radio wave absorber stacked in five steps on the bottom surface 580 mm × 580 mm ferrite sintered plate 13 is 0.284 m ^3. The volume ratio of the dielectric loss body in the absorber is about 46%.

(3) Measuring method The characteristics in the low frequency region were measured by the stripline method using the network analyzer 15 shown in FIG. In the measurement, a rectangular stripline waveguide having a length of 600 mm and a width of 7200 mm was used. Reference numeral 8 denotes an outer conductor of the stripline waveguide, and reference numeral 9 denotes an inner conductor inserted into the outer conductor 8.

An object to be measured was set within the measurement area (60 cm × 120 cm) of this waveguide, and the radio wave absorption performance of 30 MHz to 300 MHz was measured.
The characteristics in the high frequency region (0.7 GHz to 4.5 GHz) were measured by the free space method using the network analyzer 16 shown in FIG. In the measurement, the DUT M was placed at a position of 3000 mm below the transmission horn antenna 11 and the reception horn antenna 12. A radio wave absorber 14 for removing unnecessary reflected waves is placed around the object to be measured M.

(4) Measurement results Prior to the measurement of the radio wave absorption performance of the radio wave absorber, the radio wave absorption performance of a single ferrite sintered plate was measured. FIG. 13A shows the measurement result of the single ferrite sintered body plate in the low frequency region, and FIG. 13B shows the measurement result in the high frequency region. Next, as Example 1, the radio wave absorber was placed on this ferrite sintered body single plate, and the radio wave absorption performance was measured. The measurement results in the low frequency range and the high frequency range are shown in FIGS. 14 (a) and 14 (b), respectively. As is apparent from the figure, it can be seen that the low frequency and high frequency regions have characteristics as a radio wave absorber without impairing the absorption characteristics of the sintered ferrite plate. Further, as apparent from comparison between FIG. 13 and FIG. 14, the attenuation amount according to Example 1 in which the radio wave absorbers assembled in a five-stage grid pattern are stacked on the ferrite sintered body plate is low. It was shown to increase significantly over a wide range from the frequency range to the high frequency range.

  The same shape as the block used in Example 1, and the amount of carbon adhering is 10 blocks with 0.4 g / L of the foamed urethane base material volume. It was assembled into a five-stage grid-shaped radio wave absorber, stacked on a ferrite sintered plate, and its radio wave absorption characteristics were measured.

  The volume ratio of the dielectric loss body is about 46%. As Example 2, the measurement results of the radio wave absorption performance of the radio wave absorber placed on the ferrite sintered body single plate are shown in FIG. FIG. 15A shows the measurement result in the low frequency region, and FIG. 15B shows the measurement result in the high frequency region (the same applies hereinafter). Also in this example, it can be seen that, as in Example 1, it has characteristics as a radio wave absorber in the low frequency and high frequency regions without impairing the absorption characteristics of the sintered ferrite plate. Further, compared with the result of Example 1, since the carbon fixing amount is increased, it can be confirmed that the characteristics in the high frequency region are improved by about 5 to 10 dB.

  The same shape as the block used in Example 1, and the amount of carbon adhering was 10 blocks with 0.4 g / L of the foamed urethane base material volume. It was assembled into a stepped cross-shaped wave absorber and stacked on the ferrite sintered plate 13 to measure the wave absorption characteristics. The volume ratio of the dielectric loss body is about 44%.

  FIG. 17 shows a measurement result of the radio wave absorption performance of the radio wave absorber placed on the ferrite sintered body plate alone as Example 3. As is apparent from the figure, this example also has characteristics as a radio wave absorber in the low and high frequency regions without impairing the absorption characteristics of the ferrite sintered body plate. Moreover, although the amount of carbon adhering to the block of Example 2 is the same, in Example 3, since −26 dB is −18 dB at 30 MHz, it can be confirmed that the characteristics are deteriorated in the low frequency region. This is because the height of the radio wave absorber itself has decreased.

  The amount of carbon adhering is 0.8 g / L with respect to the volume of the urethane foam base, and 10 blocks shown in FIG. 18 are used. Assembled and stacked on a ferrite sintered body plate, and its radio wave absorption characteristics were measured. The volume ratio of the dielectric loss body is about 21%.

  The block used in this example had dimensions, 580 mm × 484 mm × 116 mm, and two recesses (width 16 mm, depth 75 mm) on the long edge of the block.

  As Example 4, the measurement result of the radio wave absorption performance of the radio wave absorber placed on the ferrite sintered body plate alone is shown in FIG. Also in this embodiment, it can be seen that the low frequency and high frequency regions have characteristics as a radio wave absorber without impairing the absorption characteristics of the sintered ferrite plate. Further, it can be confirmed that the volume of the dielectric can be reduced to 1/2 (46% → 21%) by doubling the carbon fixing amount as compared with Example 2.

A block having the same shape as the block used in Example 1 and having carbon fibers fixed to the surface of the expanded polystyrene base material was used. The amount of carbon fiber attached was 0.3 g / m ³ with respect to the volume of the foamed urethane substrate. The apparent volume ratio of the dielectric loss body is about 60%.

  Ten blocks were used as a set, and each block was assembled into a 5-stage grid-shaped wave absorber in the same manner as in Example 1, and stacked on a ferrite sintered body plate to measure the wave absorption characteristics.

  As Example 5, the measurement results of the radio wave absorption performance of the radio wave absorber placed on the ferrite sintered body plate alone are shown in FIG. As is apparent from the figure, it can be seen that the low frequency and high frequency regions have characteristics as a radio wave absorber without impairing the absorption characteristics of the sintered ferrite plate. Also, from this result, it can be confirmed that the performance is almost the same as the case where a material in which carbon is uniformly dispersed and fixed in a dielectric is used.

  Example 6 is an example in which a plate is used as a constituent member of a radio wave absorber. As shown in FIG. 22, this plate is a vertically long rectangle with a total length of 1820 mm and a width of 580 mm, in which carbon fibers are dispersed on the surface of a low dielectric constant material (synthetic resin), and the upper edge of the short side. Two slits having a length corresponding to the thickness of the plate and a length of 910 mm are opened in parallel from (or the lower edge) to the central portion.

The fixed amount of carbon fiber is 0.3 g / m ² . These two plates are arranged in parallel as a set of the first plate at a certain interval, and then the plate with the up and down direction reversed is set as the second plate, and the posture of the set of the second plate is set as the set of the first plate. On the other hand, they are arranged in parallel at regular intervals in a posture in a right angle direction, and the slits opened in both sets of plates are engaged with each other from above and below and combined in a cross-beam shape as viewed from above as shown in FIG. Are stacked on the ferrite sintered body plate 13.

  As Example 6, the measurement results of the radio wave absorption performance of the radio wave absorber placed on the ferrite sintered body plate alone are shown in FIG. As is apparent from the figure, this example also has characteristics as a radio wave absorber in the low frequency and high frequency ranges without impairing the absorption characteristics of the sintered ferrite plate.

  As described above, the absorption performance of the radio wave absorber according to the present invention in which the blocks or plates as the constituent members are stacked in the shape of a cross beam, as is apparent from each example, has characteristics comparable to those of the conventional radio wave absorber. Compared with conventional wave absorbers that have the same height, the volume of dielectric loss bodies used can be reduced to half or less, greatly reducing manufacturing costs, and transport and storage. -In terms of construction, it is far more advantageous than conventional construction of electromagnetic wave absorbers.

  The present invention provides a radio wave absorber that is installed in a anechoic chamber that performs measurement of radiated electromagnetic waves of an electronic device and measurement of resistance to external electromagnetic waves, etc., and can obtain good radio wave absorption performance over a wide frequency range, and in particular, the volume of the radio wave absorber. Good radio wave absorption characteristics can be obtained by keeping the ratio of the dielectric loss body in the layer to 50% or less.

It is a figure which shows the example which uses a block for the structural member of an electromagnetic wave absorber, (a) is a three-view figure, (b) is a perspective view. (A) is a front view of the electromagnetic wave absorber which combined the group of the block on the upper and lower stages, (b) is the same side view. It is a top view of the state which combined the upper and lower stage block in the shape of a cross. It is a top view of the state which accommodated the electromagnetic wave absorber combined in the shape of a cross in the case of an electromagnetic wave transparent body. It is a figure which shows the state which closed the opening of the case with the cover. It is a figure which shows the example which piled up the prismatic electromagnetic wave absorber unit on the ferrite sintered compact board, arranged vertically and horizontally, and installed in the wall surface etc. of the electromagnetic wave anechoic chamber. It is a figure which shows the example which uses a plate for the structural member of an electromagnetic wave absorber. It is a figure which shows the state which assembled the plate. 3 is a three-sided view of a block of Example 1. FIG. It is a figure which shows the state which assembled the block of Example 1 to the 5-stage grid-shaped electromagnetic wave absorber. It is the schematic of the measurement system used for the electromagnetic wave absorption performance of 30 MHz-500 MHz in this invention. It is the schematic of the measurement system used for the electromagnetic wave absorption performance of 0.7 GHz-4.5 GHz in this invention. It is a measurement result of the ferrite sintered compact board in Example 1, (a) is a figure which shows the measurement result of a low frequency area, (b) is a figure which shows the measurement result of a high frequency area. It is a measurement result of the electromagnetic wave absorber in Example 1, (a) is a figure which shows the measurement result of a low frequency region, (b) is a figure which shows the measurement result of a high frequency region. It is a measurement result of the electromagnetic wave absorber in Example 2, (a) is a figure which shows the measurement result of a low frequency area, (b) is a figure which shows the measurement result of a high frequency area. It is a figure which shows the state which assembled the block of Example 3 to the three-stage grid-shaped electromagnetic wave absorber. It is a measurement result of the electromagnetic wave absorber in Example 3, (a) is a figure which shows the measurement result of a low frequency area, (b) is a figure which shows the measurement result of a high frequency area. FIG. 6 is a three-sided view of a block of Example 4. It is a figure which shows the state which assembled the block of Example 4 to the 5-stage grid-shaped electromagnetic wave absorber. It is a measurement result of the electromagnetic wave absorber in Example 4, (a) is a figure which shows the measurement result of a low frequency region, (b) is a figure which shows the measurement result of a high frequency region. It is a measurement result of the electromagnetic wave absorber in Example 5, (a) is a figure which shows the measurement result of a low frequency area, (b) is a figure which shows the measurement result of a high frequency area. It is a figure which shows the example which uses a plate for the structural member of the electromagnetic wave absorber of Example 6. FIG. It is a figure which shows the state which assembled the plate. It is a measurement result of the electromagnetic wave absorber in Example 6, (a) is a figure which shows the measurement result of a low frequency region, (b) is a figure which shows the measurement result of a high frequency region.

Explanation of symbols

1 Block 1a, 1b, 1c Block set 2 Convex part 3 Concave 4 Radio wave absorber 5 Case 5a Cover 6 Radio wave absorber unit 7 Plate 7a, 7b Plate set 8 Outer conductor 9 Inner conductor 10 Slit 11 Transmitting horn antenna 12 Reception Horn antenna 13 Ferrite sintered plate 14 Radio wave absorbers 15 and 16 for removing unnecessary reflected waves Network analyzer M Device under test

Claims (4)

A radio wave absorber combining a plurality of components,
The component member is a standard dielectric loss body in which a conductor such as carbon or metal fine powder is dispersed or a sheet resistance value is retained on the surface.
A plurality of constituent members are combined at an angle, and by regularly mixing dielectric loss bodies and free spaces in the cross section of the region occupied by the constituent members and the space region, and continuously existing in the height direction, An electromagnetic wave absorber characterized by equivalently reducing the overall dielectric loss. The structural member is a block in which a conductive material such as carbon or metal fine powder is dispersed and fixed to a synthetic resin to have an appropriate dielectric loss,
Two blocks arranged in parallel at regular intervals are made into one set, and each block set is divided into an upper set and a lower set, and at least two sets of blocks are arranged in the upper and lower stages. The radio wave absorber according to claim 1, wherein the sets of upper and lower blocks are connected in a direction orthogonal to each other and two or more sets of blocks are combined in a cross-beam shape.   A radio wave absorbing wall, wherein a plurality of the radio wave absorbers according to claim 1 are stacked on a ferrite sintered body plate and installed on the inner walls of an anechoic chamber and an anechoic chamber.   4. The radio wave absorber wall according to claim 3, wherein the radio wave absorbers combined in a grid pattern are accommodated in a case of a radio wave transparent body and arranged on a wall surface as a radio wave absorber unit.

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