JP2007073662A - Wave absorber - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a wave absorber with reflective attenuation capability capable of preventing a communication failure caused by reflection of electromagnetic waves and the like, thinning, reducing weight and also possessing the characteristics of absorbing electric waves of two or more frequencies. <P>SOLUTION: The wave absorber comprises a conductive layer consisting of a conductor, a dielectric layer consisting of a dielectric composed of one layer or two or more layers, and a pattern layer having two or more patterns consisting of a conductor. Each pattern in the pattern layer is constituted such that at least one loop groove 102 is formed in the inside of a patch pattern 101. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a radio wave absorber, and more particularly, to a radio wave absorber that can prevent communication failure due to reflection of electromagnetic waves and the like and can be reduced in thickness and weight.

  In recent years, with the development of wireless communication systems such as mobile phones, wireless LAN (Local Area Network), and ITS (Intelligent Transport Systems), it is necessary to protect communication information and prevent crosstalk and miscommunication. For the purpose of mainly protecting communication information, indoor and outdoor radio waves are blocked by an electromagnetic shielding material in order to shield external radio waves and shield radio waves emitted from the communication device itself. However, in this case, radiated radio waves from the communication device itself remain in the room due to reflection, which may cause deterioration in communication quality due to interference between the reflected wave and a desired communication radio wave. In order to prevent such communication quality deterioration and communication failure such as interference / miscommunication, a radio wave absorber that absorbs electromagnetic waves and converts them into heat is used.

  As a general radio wave absorber, a magnetic powder such as ferrite or soft magnetic metal is mixed and dispersed in an insulating matrix such as rubber or plastic and molded into a sheet or block (for example, see Patent Document 1) In addition, a product obtained by impregnating a dielectric loss powder such as carbon black into foamed polyurethane or the like and processing it into a pyramid shape or a wedge shape (for example, see Patent Document 2) is used.

  These electromagnetic wave absorbers described in Patent Document 1 and Patent Document 2 generally exhibit electromagnetic wave absorption characteristics over a wide frequency band. However, in a radio wave absorber formed by mixing and dispersing magnetic powder such as ferrite or soft magnetic metal in an insulating matrix such as rubber or plastic as disclosed in Patent Document 1, a certain degree is required when high radio wave absorption performance is required. Therefore, since a material having a large specific gravity is used, the weight is increased. In addition, in the electromagnetic wave absorber processed by impregnating foamed polyurethane or the like with a dielectric loss powder such as carbon black as described in Patent Document 2, the absorption performance depends on the thickness, so that desired performance is obtained. However, there is a problem that a device having a pyramid shape or a wedge shape or a considerable thickness in the absorption direction is required.

On the other hand, a plurality of conductive loops are regularly arranged as a thin and light wave absorber that solves the problems of weight and thickness in the wave absorber described in Patent Document 1 and Patent Document 2. There has also been proposed a radio wave absorber (see, for example, Patent Document 3) that includes a periodic loop pattern, an intermediate layer, and a conductive reflective layer, and whose thickness is 0.027 times or more the absorption target wavelength.
JP 2001-308584 A JP 10-051180 A JP 2001-352191 A

  However, as disclosed in Patent Document 3, it is composed of a periodic loop pattern in which a plurality of conductive loops are regularly arranged, an intermediate layer, and a conductive reflective layer, and the thickness thereof is 0.027 times or more the absorption target wavelength. A wave absorber with a structure in which single-size patterns are arranged periodically is basically designed for a specific (single) frequency, and has a narrow band characteristic with a limited frequency band. Therefore, it has been difficult to realize radio wave absorption for a plurality of frequencies.

  The present invention has been made in view of the above-described problems, and has a reflection attenuation capability that can prevent communication failure due to reflection of electromagnetic waves, etc., can be reduced in thickness and weight, and has a plurality of frequencies. An object of the present invention is to provide a radio wave absorber having multi-frequency radio wave absorption characteristics that can absorb the radio wave of the above.

 In order to solve the above problems, the radio wave absorber of the present invention has a conductor layer (11) made of a conductor, a dielectric layer (12) made of one or more dielectric layers, and a plurality of patterns made of a conductor. A pattern layer (13), and each pattern in the pattern layer (13) is a pattern in which at least one loop slot (102, 202, 302) is formed inside the patch pattern (101, 201, 301). It is characterized by being.

  Each pattern in the pattern layer may be a pattern in which one loop slot is formed in the patch pattern, or a pattern in which two or more loop slots are formed in the patch pattern. Patch pattern shapes include circles (including perfect circles and ellipses), square shapes (including squares, rectangles, and rounded vertices thereof), and polygonal shapes (polygons such as triangles, and the like) Any shape such as a rounded vertex may be used.

  The loop slot may be a closed loop configured by a closed curve or a broken line having the same start point and end point, or may be configured by a curved line or a broken line that is partially different from the start point and the end point. It may be an open loop. The shape of the loop slot may be any shape such as a circular shape, a square shape, and a polygonal shape.

 According to the radio wave absorber of the present invention, the pattern of the pattern layer functions as an antenna to receive radio waves, and electromagnetic waves leak to the dielectric layer during reception, which is caused by the dielectric loss component of the dielectric layer. Electromagnetic waves are converted into heat and consumed. In addition, even if the radio wave was not received by the pattern layer, the radio wave that passed through the pattern layer and the dielectric layer was received by the pattern layer after being totally reflected by the conductor layer and converted to heat by the dielectric layer. Being consumed. Thus, the radio wave absorber of the present invention can absorb and consume radio waves. Further, since each pattern in the pattern layer is a pattern in which at least one loop slot is formed inside the patch pattern, the pattern layer can receive radio waves of a plurality of frequencies. Therefore, according to the present invention, multi-frequency radio wave absorption has a reflection attenuation capability that can prevent communication failure due to reflection of electromagnetic waves, can be reduced in thickness and weight, and can absorb radio waves of multiple frequencies. A radio wave absorber having characteristics can be provided.

  In the radio wave absorber of the present invention, each pattern in the pattern layer (13) has one loop slot (102, 202, 302) formed in the patch pattern (101, 201, 301). It is a pattern.

  Further, in the radio wave absorber of the present invention, each pattern in the pattern layer (13) has one rectangular shape as the loop slot inside the rectangular patch pattern (101, 201, 301) as the patch pattern. It is a pattern in which loop slots (102, 202, 302) are formed.

In the radio wave absorber of the present invention, the outermost circumference of the patch pattern (101, 201, 301) corresponds to one frequency of the absorbed radio wave, and the circumference of the loop slot (102, 202, 302). Corresponds to one other frequency of the absorbed radio wave.
According to the radio wave absorber of the present invention, the frequency band of the radio wave received by each of the patch pattern and the loop slot can be matched to the radio wave to be absorbed, and absorption characteristics can be obtained for a plurality of frequencies. Therefore, according to the radio wave absorber of the present invention, communication failure due to reflection of electromagnetic waves can be effectively prevented.

The radio wave absorber of the present invention changes only the size or shape of the loop slot (102, 202, 302) without changing the size and shape of the patch pattern (101, 201, 301). Thus, the radio wave absorption characteristics can be changed.
According to the radio wave absorber of the present invention, absorption characteristics can be obtained for a plurality of frequencies, and the radio wave absorption characteristics to be absorbed can be changed without changing the pattern position of each pattern in the pattern layer. An electromagnetic wave absorber that can be easily changed can be provided.

  According to the present invention, a multi-frequency radio wave absorption characteristic that has a reflection attenuation capability that can prevent communication failure due to reflection of electromagnetic waves, can be reduced in thickness and weight, and can absorb radio waves of multiple frequencies. A radio wave absorber having the same can be provided.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. The radio wave absorber of the present embodiment is suitable for a radio wave absorber that prevents communication failure in, for example, a wireless LAN (Local Area Network) system. Wireless LAN systems include those that communicate using radio waves in the 2.45 GHz band and those that communicate using radio waves in the 5.2 GHz band. Therefore, the radio wave absorber of the present embodiment is suitable for absorbing unnecessary radio waves of the plurality of wireless LAN systems and avoiding communication errors of such systems. For example, it is preferable to install the radio wave absorber of the present embodiment on the ceiling (the lower surface of the ceiling) or the side wall surface in a conference room or the like equipped with a wireless LAN access point.

(First embodiment)
First, a first embodiment of the present invention will be described. FIG. 1 is a cross-sectional view illustrating a schematic configuration of the radio wave absorber according to the present embodiment. The radio wave absorber of this embodiment includes a conductor layer 11 (entire conductor layer) formed of a copper foil having a thickness of 18 μm, and a dielectric substrate 12 having a relative dielectric constant of 4.3, a dielectric loss of 0.1, and a thickness of 3 mm. (Dielectric layer) and a pattern layer 13 in which a plurality of patterns formed of copper foil are periodically arranged are sequentially stacked. The conductor layer 11 has a function of totally reflecting radio waves, and may be a grid-like conductor layer formed of a grid pattern of conductors. The dielectric substrate 12 is composed of one layer of dielectric, but may be composed of a plurality of layers of dielectric.

  FIG. 2 is a partial plan view of the radio wave absorber shown in FIG. 1 and shows a detailed configuration of the pattern layer. The pattern layer 13 is composed of a plurality of patterns in which one square loop slot 102 is formed inside a square patch pattern 101 having a side of 18 mm. The patch pattern 101 has patterns 101 a and 101 b that are spaced apart from each other by the loop slot 102. The patch pattern 101 is made of a copper foil, and is periodically arranged on the upper surface of the dielectric substrate 12 (that is, regularly with a constant interval). Each patch pattern 101 is arranged such that the center distance between the center points of adjacent patch patterns 101 is 22 mm. The loop slot 102 has a slot width of 1 mm and a center loop length of 44 mm.

  The pattern layer 13 having the patch pattern 101 and the loop slot 102 is formed by patterning a dielectric substrate 12 having a copper foil formed on the surface thereof with a ferric chloride etchant using a photoresist mask. Can do.

  Next, a method for measuring the radio wave absorption characteristics of the radio wave absorber of the present embodiment having the above structure will be described. First, a pyramid cone type wave absorber having a reflection amount of −40 [dB] or less with respect to radio waves in the frequency range to be measured is installed on the wall surface, floor, and measurement surface side in the measurement chamber. Then, the transmission horn antenna is arranged so that the incident angle of the radio wave with respect to the measurement sample (this radio wave absorber) is a predetermined angle (for example, 5 degrees from the front), and the electromagnetic wave emitted from the transmission horn antenna is measured. The receiving horn antenna is installed in the direction reflected by the light (the direction of optical reflection). These transmission / reception horn antennas are connected to a vector network analyzer, and the S parameter (S21) is measured by separating only the radio waves reflected and received from the measurement sample (radio wave absorber) using the free space time domain method.

  A metal reflector (Cu plate) is installed at a position at a predetermined distance from each horn antenna, a radio wave having a predetermined frequency and a predetermined intensity is emitted from the transmitting horn antenna, and the reception level of the receiving horn antenna is measured. In addition, a measurement sample (radio wave absorber) having the same size as the metal reflector (Cu plate) is installed at the same position as the metal reflector (Cu plate), and the same radio wave as that emitted to the metal reflector (Cu plate). Is emitted from the transmitting horn antenna, and the reception level of the receiving horn antenna at that time is measured. The difference (power ratio) between the reception level for the metal reflector (Cu plate) and the reception level for the radio wave absorber measured in this way is evaluated as the return loss. The evaluation results of this measurement are shown in FIG. From FIG. 3, the absorption characteristics in two frequency bands of about 2.7 GHz on the low frequency side corresponding to the outermost peripheral length of 72 mm of the patch pattern 101 and 5.9 GHz on the high frequency side corresponding to the 44 mm peripheral length of the loop slot 102. It can be seen that

(Second Embodiment)
Next, a second embodiment of the present invention will be described. FIG. 4 is a partial plan view of the radio wave absorber according to the present embodiment, and shows a detailed configuration of the pattern layer. The laminated structure of this embodiment is the same as the structure shown in FIG. The pattern layer 13 is composed of a plurality of patterns in which one square loop slot 202 is formed inside a square patch pattern 201 having a side of 18 mm. The patch pattern 201 has patterns 201 a and 201 b that are spaced apart from each other by the loop slot 202. The patch pattern 201 is made of copper foil, and is periodically arranged on the upper surface of the dielectric substrate 12 (that is, regularly with a constant interval between each other). Each patch pattern 201 is arranged such that the center distance between the center points of adjacent patch patterns 201 is 22 mm. The loop slot 202 has a slot width of 1 mm and only the center loop length is changed to 36 mm.

  The pattern layer 13 having the patch pattern 201 and the loop slot 202 was formed by the same method as in the first embodiment. Further, the method for measuring the radio wave absorption characteristics was also evaluated by measuring the return loss in the same manner as in the first embodiment.

  The evaluation results of this measurement are shown in FIG. FIG. 5 shows that absorption characteristics are shown in two frequency bands of about 2.9 GHz and 7 GHz. In the present embodiment, it can be seen that the absorption on the high frequency side shifts to 7 GHz, which is a shorter wavelength, corresponding to the one circumferential length of 36 mm of the loop slot 202 which is shorter than that of the first embodiment. Under the influence, the absorption on the low frequency side corresponding to the outermost peripheral length of 72 mm of the patch pattern 201 is also shifted to 2.9 GHz. According to the above, absorption characteristics can be obtained for a plurality of frequencies, and the radio wave absorption characteristics to be absorbed can be changed without changing the pattern position of each pattern in the pattern layer. I can see that

(Third embodiment)
Next, a third embodiment of the present invention will be described. FIG. 6 is a partial plan view of the radio wave absorber according to the present embodiment, and shows a detailed configuration of the pattern layer. The laminated structure of this embodiment is the same as the structure shown in FIG. The pattern layer 13 includes a plurality of patterns in which one square loop slot 302 is formed inside a square patch pattern 301 having a side of 18 mm. The patch pattern 301 has patterns 301 a and 301 b that are spaced apart from each other by the loop slot 302. The patch pattern 301 is made of a copper foil, and is periodically arranged on the upper surface of the dielectric substrate 12 (that is, regularly with a fixed interval). Each patch pattern 301 is arranged such that the center distance between the center points of adjacent patch patterns 301 is 22 mm. The loop slot 302 has a slot width of 1 mm and a center loop length changed to 52 mm.

  The pattern layer 13 having the patch pattern 301 and the loop slot 302 was formed by the same method as in the first embodiment. Further, the method for measuring the radio wave absorption characteristics was also evaluated by measuring the return loss in the same manner as in the first embodiment.

  The evaluation results of this measurement are shown in FIG. FIG. 7 shows that absorption characteristics are shown in two frequency bands of approximately 2.6 GHz and 5 GHz. In the present embodiment, it can be seen that the absorption on the high frequency side shifts to a longer wavelength of 5 GHz corresponding to the circumference of 52 mm of the loop slot 302 which is longer than that of the first embodiment. Under the influence, the absorption on the low frequency side corresponding to the outermost peripheral length of 72 mm of the patch pattern 301 is also shifted to 2.6 GHz. According to the above, absorption characteristics can be obtained for a plurality of frequencies, and the radio wave absorption characteristics to be absorbed can be changed without changing the pattern position of each pattern in the pattern layer. I can see that

(Comparative example)
Next, differences between the conventional radio wave absorber (comparative example) and the above-described radio wave absorbers according to the first to third embodiments of the present invention will be described with reference to FIGS.

  FIG. 8 is a partial plan view of a conventional radio wave absorber, and shows a detailed configuration of the pattern layer 13. The laminated structure of this comparative example is the same as the structure shown in FIG. The pattern layer 13 is composed only of a square patch pattern 401 having a side of 18 mm. The patch pattern 401 is made of a copper foil, and is periodically arranged on the upper surface of the dielectric substrate 12 (that is, regularly with a constant interval). Each patch pattern 401 is arranged so that the center interval between the center points of adjacent patch patterns 401 is 22 mm.

  The pattern layer 13 having these patch patterns 401 was formed by the same method as in the first embodiment. Further, the method for measuring the radio wave absorption characteristics was also evaluated by measuring the return loss in the same manner as in the first embodiment.

  The evaluation results of this measurement are shown in FIG. From FIG. 9, it can be seen that the conventional radio wave absorber exhibits absorption characteristics only in the frequency band of about 3.2 GHz. In other words, the radio wave absorber according to the first to third embodiments of the present invention can obtain absorption characteristics with respect to a plurality of frequencies, unlike the conventional radio wave absorber, while reducing the thickness and weight. It can be an electromagnetic wave absorber. Therefore, it can have sufficient performance as a radio wave absorber used in a wireless LAN system or the like in which a plurality of frequency bands are used. Further, the radio wave absorption characteristics can be changed by changing only the size or shape of the loop slots 102, 202, 302 without changing the size and shape of the patch patterns 101, 102, 103. The radio wave absorber according to the first to third embodiments is a radio wave absorber that can be easily changed in design.

  As described above, the embodiments of the present invention have been described in detail with reference to the drawings. However, the specific configuration is not limited to these embodiments, and includes design changes and the like without departing from the gist of the present invention. . For example, the patch patterns 101, 201, and 301 of the pattern layer 13 in the radio wave absorber of the first to third embodiments are rectangular patch patterns, and the shapes thereof are circular (including perfect circles and ellipses). , Square shapes (including squares, rectangles and rounded vertices thereof), and polygonal shapes (including polygons such as triangles and rounded vertices thereof).

  The loop slots 102, 202, and 302 are rectangular loop slots, but their shapes may be any shape such as a circular shape, a square shape, and a polygonal shape. Furthermore, the loop slots 102, 202, and 302 are closed loops configured by closed curves or broken lines having the same start point and end point. However, the start points and the end points are different and partially broken curves or broken lines. May be an open loop.

  Each pattern in the pattern layer 13 may be a pattern in which one loop slot is formed in the patch pattern, or a pattern in which two or more loop slots are formed in the patch pattern. Also good.

  In the above embodiment, an example in which the radio wave absorber of the present invention is applied to a wireless LAN system has been described. However, the present invention is not limited to this and can be applied to other than a wireless LAN system. That is, the frequency and band of radio waves to be absorbed can be changed by adjusting the shape, size, and arrangement of the patch pattern and loop slot, or by adjusting the thickness, surface resistance value, constituent material, etc. of each layer. Can do.

It is sectional drawing of the electromagnetic wave absorber by the 1st Embodiment of this invention. It is a fragmentary top view which shows the detailed structure of the pattern layer which the electromagnetic wave absorber same as the above has. It is a reference figure which shows the electromagnetic wave absorption characteristic of an electromagnetic wave absorber same as the above. It is a fragmentary top view which shows the detailed structure of the pattern layer which the electromagnetic wave absorber by the 2nd Embodiment of this invention has. It is a reference figure which shows the electromagnetic wave absorption characteristic of an electromagnetic wave absorber same as the above. It is a fragmentary top view which shows the detailed structure of the pattern layer which the electromagnetic wave absorber by the 3rd Embodiment of this invention has. It is a reference figure which shows the electromagnetic wave absorption characteristic of an electromagnetic wave absorber same as the above. It is a fragmentary top view which shows the detailed structure of the pattern layer which the conventional electromagnetic wave absorber (comparative example) has. It is a reference figure which shows the electromagnetic wave absorption characteristic of an electromagnetic wave absorber same as the above.

Explanation of symbols

DESCRIPTION OF SYMBOLS 11 ... Conductor layer, 12 ... Dielectric substrate (dielectric layer), 13 ... Pattern layer, 101, 201, 301, 401 ... Patch pattern, 101a, 101b, 201a, 201b, 301a, 301b ... pattern, 102, 202, 302 ... loop slot

Claims (5)

A conductor layer made of a conductor, a dielectric layer made of one or more dielectric layers, and a pattern layer having a plurality of patterns made of a conductor;
Each pattern in the pattern layer is a pattern in which at least one loop slot is formed inside a patch pattern.   2. The radio wave absorber according to claim 1, wherein each pattern in the pattern layer is a pattern in which one loop slot is formed inside the patch pattern.   2. Each pattern in the pattern layer is a pattern in which one square loop slot as the loop slot is formed inside a square patch pattern as the patch pattern. 2. The radio wave absorber according to 2.   The outermost circumference of the patch pattern corresponds to one frequency of the absorbed radio wave, and the one circumference of the loop slot corresponds to another frequency of the absorbed radio wave. 4. The radio wave absorber according to any one of items 3. 5. The radio wave absorption characteristic can be changed by changing only the size or shape of the loop slot without changing the size and shape of the patch pattern. The electromagnetic wave absorber described in the paragraph.

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