JP3064861B2 - Radio wave absorber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a radio wave absorber, and more particularly to a radio wave absorber for an anechoic chamber.

[0002]

2. Description of the Related Art In recent years, the use of the millimeter wave band has been activated in various communication fields including the data communication field such as wireless LAN, and accordingly, the millimeter wave band has been used in addition to the microwave band conventionally used. There is a demand for an anechoic chamber that can also be used.

[0003]

An anechoic chamber used as an evaluation facility in various communication fields is intended to perform high-precision measurement, and is required to have high-performance anti-reflection characteristics. Therefore, a radio wave absorber used in the anechoic chamber is also required to have high-performance absorption characteristics. The required absorption characteristics vary depending on the intended use of the anechoic chamber, but are generally 40 dB or more in the microwave band and 50 dB or more in the millimeter wave band.

[0004] Current radio wave absorbers for anechoic chambers are intended for frequencies below the microwave band, and have not been designed to include the millimeter wave band. Therefore, when a conventional radio wave absorber is used, the absorption characteristics are degraded in the millimeter wave band due to surface reflection caused by the material and the shape. It has been reported that the band is reduced to about 43 dB. As a result, it was very difficult to obtain a high-performance anechoic chamber in the millimeter wave band.

[0005] The present invention relates to a microwave band of 40 dB or more,
It is an object of the present invention to provide a high-performance radio wave absorber having a return loss of 50 dB or more in a millimeter wave band.

[0006]

According to the present invention, there is provided a first radio wave introducing section constituted by arranging a plurality of quadrangular pyramid-shaped protrusions made of a dielectric loss material, and the first radio wave introducing section. A second radio wave introduction part made of a dielectric loss material having a wedge shape or a quadrangular pyramid shape in a radio wave arrival direction, provided between the respective projecting portions of the portion,

(Equation 3) To

(Equation 4) Provided is a radio wave absorber in which ε _r2 ′ ≦ 1.8 ε _r2 ″ ≦ 0.4 at 2 GHz and ε _r2 ≦ 1.3 0.03 ≦ ε _r2 ″ ≦ 0.2 at 100 GHz. Is done.

A wedge-shaped or pyramid-shaped low dielectric material is provided at a valley portion of a first radio wave introducing portion (hereinafter referred to as a base absorber) comprising a plurality of quadrangular pyramid-shaped protrusions having high-performance absorption characteristics in a microwave band. By inserting a second radio wave introduction part (hereinafter referred to as an absorber element) made of a low-loss material with low efficiency, a high-performance absorption characteristic can be obtained in a wide frequency range from microwaves to millimeter waves. Can be

In the millimeter wave band, the wavelength is shorter than that in the microwave band, so that the directivity of the radio wave is further improved. In the case of only the base absorber, the radio wave is repeatedly reflected multiple times in the valley portion and a part of the wave is reflected. Is reflected on the front surface of the absorber, but by inserting the absorber element into the valley portion of the base absorber, the multiple reflection components in the valley portion of the base absorber are absorbed by the absorber element. Is suppressed. However, such a technique of inserting the absorber element into the valley portion of the base absorber is known from Japanese Utility Model Application Laid-Open No. 2-67699.

In the present invention, the real part ε _r2 ′ of the complex relative permittivity at 2 GHz of the dielectric loss material constituting the absorber element is provided.
Is 1.8 or less, and the imaginary part ε _r2 ″ is 0.4 or less, so that the influence of the absorber element in the microwave band is reduced. Since the dielectric constant of the absorber element is small, it has almost no effect on radio waves in the microwave band, so that the absorption characteristics in the microwave band reflect the characteristics of the base absorber as they are, so that high performance is achieved. Characteristics are realized.

Further, the real part ε _r2 ′ of the complex relative permittivity at 100 GHz of the dielectric loss material constituting the absorber element is set to 1.3 or less, and the imaginary part ε _r2 ″ is set to 0.03 or more and 0.2 Because of the following, the radio wave in the millimeter wave band is sufficiently attenuated and the reflection is suppressed, and the radio wave in the millimeter wave band is 50 dB.
The above-described high-performance characteristic of return loss is realized.

Further, since the base absorber has a quadrangular pyramid shape, there is no directionality in the absorption characteristics due to the polarization of radio waves.

Furthermore, the rate of change in the longitudinal direction of the cross-sectional area perpendicular to the longitudinal direction of the quadrangular pyramid is a higher rate of change than the square of the general rate of change of the pyramid, for example, 2.5 or 3
It is preferably a power. Thereby, the absorption characteristics in the millimeter wave band can be improved.

[0013]

Embodiments of the present invention will be described below with reference to the drawings. FIG. 1 is a perspective view schematically showing the configuration of one embodiment of the radio wave absorber of the present invention.

In FIG. 1, reference numeral 10 denotes a flat base. On the base 10, a base absorber composed of a plurality of quadrangular pyramid-shaped protrusions (corresponding to a first radio wave introduction unit of the present invention).
11 is fixed (adhered in this embodiment) so as to be integrated with the base 10. An absorber element having a quadrangular pyramid shape (pyramid shape) between the respective projecting portions of the base absorber 11 in a radio wave arrival direction (corresponding to a second radio wave introduction unit of the present invention)
12 are provided integrally.

The base 10, the base absorber 11, and the absorber element 12 are all formed of the same type of dielectric loss material in this embodiment. However, they may be formed of dielectric loss materials having different dielectric constants.

In this embodiment, foamed polyethylene mixed with carbon powder is used as the dielectric loss material. In addition, as the dielectric loss material, foamed polyurethane mixed with carbon powder, foamed polyurethane impregnated in a carbon liquid, foamed polystyrene in which particles are coated with carbon, or the like can be applied.

Further, in this embodiment, the base 10 having a height of 50 mm is used, and
A 50 mm square pyramid-shaped absorber is used, and the absorber element 12 is a square pyramid having a height of 150 mm.

In this embodiment, the complex relative permittivity at 2 GHz of the material constituting the base absorber 11 is a real part ε _r1 ′.
Is 2.16 and the imaginary part ε _r1 ″ is 1.76. The complex relative permittivity of the material forming the absorber element 12 at 2 GHz is 1.35 for the real part ε _r2 ′ and imaginary part ε _r2. Is 0.08, and the complex relative permittivity at 100 GHz is 1.11 for the real part ε _r2 ′ and 0.05 for the imaginary part ε _r2 ″.

2 GHz and 10 GHz of the radio wave absorber of this embodiment
The absorption performance at normal incidence at 0 GHz is 2 GHz.
Absorption performance of 44 dB or more at z and 54 dB or more at 100 GHz is obtained.

FIG. 2 is a perspective view showing a modified form of the projecting portion of the base absorbent body 11. The protruding portion of the base absorber 11 has a pyramid shape, and its taper shape (expressed by a change in cross-sectional area with respect to height) may have a squared taper change rate as in the conventional case, but may have a squared taper change rate. Higher rate of change,
For example, by setting it to the 2.5th power or the 3rd power, more excellent absorption characteristics can be obtained. In the example of FIG. 2, the taper change rate is the third power.

In general, as the ratio (cell size / wavelength) of the unit size (hereinafter referred to as cell size) of one peak of the pyramid to the wavelength increases, the equivalent relative permittivity in the height direction of the radio wave absorber changes and the return loss increases. May decrease. For this reason, by setting the taper change rate to a higher order than the square, the change in the equivalent relative permittivity with respect to the pyramid height occurring at such a high frequency is improved. FIG. 3 is a characteristic diagram showing the return loss with respect to the rate of change of the tapered shape of the protrusion of the base absorber at 100 GHz. From the figure, it can be seen that the return loss is improved by about 3 dB in the case of 2.5 power.

FIG. 4 is a perspective view schematically showing the configuration of another embodiment of the radio wave absorber of the present invention.

In FIG. 1, reference numeral 40 denotes a flat base, on which a base absorber composed of a plurality of quadrangular pyramid-shaped protrusions (corresponding to a first radio wave introducing section of the present invention).
41 is fixed (adhered in this embodiment) so as to be integrated with the base 40. Absorber elements (corresponding to a second radio wave introduction section of the present invention) 42 each having a wedge shape in a radio wave arrival direction are provided integrally between the respective projecting portions of the base absorber 41.

The base 40, the base absorber 41, and the absorber element 42 are formed of the same type of dielectric loss material in this embodiment. However, they may be formed of dielectric loss materials having different dielectric constants.

In this embodiment, foamed polyethylene mixed with carbon powder is used as the dielectric loss material. In addition, as the dielectric loss material, foamed polyurethane mixed with carbon powder, foamed polyurethane impregnated in a carbon liquid, foamed polystyrene in which particles are coated with carbon, or the like can be applied.

In this embodiment, the base 40 having a height of 50 mm is used, and the height of the base absorber 41 is 3 mm.
A quadrangular pyramid-shaped absorber of 00 mm is used, and a wedge-shaped absorber having a height of 150 mm is used as the absorber element 42. As shown in FIG. 2, the projecting portion of the base absorbent body 41 is
A taper change rate higher than the second power, for example, a taper shape of 2.5 power or 3 power may be used.

In this embodiment, the complex relative permittivity at 2 GHz of the material constituting the base absorber 41 is the real part ε _r1 ′.
Is 2.16 and the imaginary part ε _r1 ″ is 1.76. The complex relative permittivity of the material forming the absorber element 42 at 2 GHz is 1.35 for the real part ε _r2 ′ and 1.35 for the imaginary part ε _r2 ″. 0.08
Where the complex relative permittivity at 100 GHz is the real part ε
_r2 ′ is 1.11 and the imaginary part ε _r2 ″ is 0.05.

2 GHz and 10 GHz of the radio wave absorber of this embodiment
The absorption performance at normal incidence at 0 GHz is 2 GHz.
Absorption performance of 43 dB or more at z and 54 dB or more at 100 GHz is obtained.

FIGS. 5 to 8 show that the return loss of the radio wave absorber according to the present invention is expressed by the real part ε _r2 ′ and the imaginary part ε _r2 ″, 100, of the complex relative permittivity of the material constituting the absorber element at 2 GHz.
It shows how the complex relative permittivity changes in response to changes in the real part ε _r2 ′ and the imaginary part ε _r2 ″ at GHz.

As apparent from these figures, the real part ε _r2 ′ of the complex relative permittivity at 2 GHz of the dielectric loss material constituting the absorber elements 12 and 42 is 1.8 or less, and the imaginary part ε _r2 ″ is not more than 1.8. By setting the ratio to 0.4 or less, the radio wave influence of the absorber elements 12 and 42 in the microwave band is reduced, and as a result, the absorption characteristics in the microwave band are the same as those of the base absorbers 11 and 41. Is reflected as it is, so 2GHz
, A high-performance absorption characteristic of 40 dB or more is realized.

On the other hand, the real part ε _r2 ′ of the complex relative permittivity at 100 GHz of the dielectric loss material forming the absorber elements 12 and 42 is 1.3 or less, and the imaginary part ε _r2 ″ is 0.03 or more and 0.2. By making the following, 100 millimeter wave band
An absorption characteristic of 50 dB or more at GHz is obtained.

The embodiments described above all illustrate the present invention by way of example and not by way of limitation, and the present invention can be embodied in various other modified and modified forms. Therefore, the scope of the present invention is defined only by the appended claims and their equivalents.

[0033]

As described above in detail, according to the present invention, the radio wave absorber comprises a first radio wave introduction portion formed by arranging a plurality of quadrangular pyramid-shaped protrusions made of a dielectric loss material;
A second radio wave introducing portion, which is provided between the projecting portions of the first radio wave introducing portion, has a wedge shape or a quadrangular pyramid shape in a radio wave arrival direction, and is made of a dielectric loss material; The real part of the complex relative permittivity of the constituent material of the
_r2 ′ and the imaginary part is ε _r2 ″, at 2 GHz,
ε _r2 ′ ≦ 1.8, ε _r2 ″ ≦ 0.4, 100 GH
At z, ε _r2 ′ ≦ 1.3, 0.03 ≦ ε _r2 ″ ≦ 0.
Since it is set to 2, it has high-performance absorption characteristics in a wide frequency range from microwaves to millimeter waves. Therefore,
By using the electromagnetic wave absorber of the present invention in an anechoic chamber, a high-performance anechoic chamber covering a microwave band to a millimeter wave band can be realized.

[Brief description of the drawings]

FIG. 1 is a perspective view schematically showing a configuration of one embodiment of a radio wave absorber of the present invention.

FIG. 2 is a perspective view illustrating a modified form of a protruding portion of a base absorbent body.

FIG. 3 is a characteristic diagram showing a return loss with respect to a change rate of a taper shape of a protrusion of a base absorber.

FIG. 4 is a perspective view schematically showing a configuration of another embodiment of the radio wave absorber of the present invention.

FIG. 5 is a characteristic diagram showing how the return loss of the radio wave absorber of the present invention changes with respect to the real part ε _r2 ′ of the complex relative permittivity at 2 GHz of the material forming the absorber element. .

FIG. 6 is a characteristic diagram showing how the return loss of the radio wave absorber of the present invention changes with respect to the imaginary part ε _r2 ″ of the complex relative permittivity at 2 GHz of the material forming the absorber element. .

FIG. 7 is a characteristic diagram showing how the return loss of the radio wave absorber of the present invention changes with respect to the real part ε _r2 ′ of the complex relative permittivity at 100 GHz of the material constituting the absorber element. .

FIG. 8 is a characteristic diagram showing how the return loss of the radio wave absorber of the present invention changes with respect to the imaginary part ε _r2 ″ of the complex relative permittivity at 100 GHz of the material forming the absorber element. .

[Explanation of symbols]

 10, 40 Base 11, 41 Base absorber 12, 42 Absorber element

Continuing from the front page (72) Yasuo Hashimoto Inventor, TDK Corporation, 1-13-1 Nihonbashi, Chuo-ku, Tokyo (72) Inventor Kenichi Ichihara, 1-13-1 Nihonbashi, Chuo-ku, Tokyo (72) Inventor Takashi Tanaka 1-13-1 Nihombashi, Chuo-ku, Tokyo Inside TDK Corporation (56) References JP-A-4-206999 (JP, A) JP-A-63-14498 (JP, A) JP-A-57-66699 (JP, A) JP-A-62-183599 (JP, A) JP-A-57-17202 (JP, A) JP-A-58-199000 (JP, A) JP-A-2-250398 (JP, A) Hikaru Hei 2-67699 (JP, U) (58) Field surveyed (Int. Cl. ⁷ , DB name) H05K 9/00

Claims (2)

(57) [Claims] 1. A first radio wave introduction part configured by arranging a plurality of quadrangular pyramid-shaped protrusions made of a dielectric loss material, and provided between the respective protrusions of the first radio wave introduction part. And a second radio wave introducing portion made of a dielectric loss material having a wedge shape or a quadrangular pyramid shape in a radio wave arrival direction, and a complex relative permittivity of a constituent material of the second radio wave introducing portion. To _Εr2 ′ ≦ 1.8 _εr2 ″ ≦ 0.4 at 2 GHz and _εr2 ′ ≦ 1.3 0.03 ≦ _εr2 ″ ≦ 0.2 at 100 GHz. Radio wave absorber. 2. A rate of change in a length direction of a cross-sectional area perpendicular to a length direction of a quadrangular pyramid of a protruding portion of the first radio wave introduction portion is set to a higher rate than a square. The radio wave absorber according to claim 1, wherein: