KR20030014787A - Wide-band ferrite electromagnetic wave absorber - Google Patents

Abstract

PURPOSE: A wideband ferrite wave absorbing device is provided to reduce manufacturing costs, while allowing equivalent permeability and equivalent dielectric permittivity to be easily controlled. CONSTITUTION: A wideband ferrite wave absorbing device comprises tile-type ferrite magnets arranged onto a reflecting plate(M); and conical ferrite magnets(F) arranged at constant intervals on the tile-type ferrite magnets. The spacing between conical ferrite magnets is shorter than the length of the wave. The expression 0 < 2r < 2R, 2r < 2R < a, 4mm <= h1 <= 8mm, 10mm <= h2 <= 20mm, 1.5mm <= h3 <= 8.5mm, is satisfied, wherein 2r and 2R indicate diameters of upper and lower sides of the conical ferrite magnet, h1 is the height of the tile-type ferrite magnet, h2 is the height of the conical ferrite magnet, and h3 is the height of a hemispherical ferrite magnet.

Description

Wideband Ferrite Wave Absorber {WIDE-BAND FERRITE ELECTROMAGNETIC WAVE ABSORBER}

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wideband ferrite radio wave absorber, and more particularly, to widening of a radio wave absorber composed of a ferrite magnetic material.

Broadband ferrite absorbers are widely used in radio darkrooms used for electromagnetic interference tests and antenna characteristic tests of electronic devices, and wall materials installed to prevent interference of TVs and radars by radio wave reflections from buildings or structures such as buildings and bridges. It is used.

A radio wave absorber composed of a sintered ferrite, which is a conventional magnetic material, has an excellent characteristic of absorbing low frequency radio waves of, for example, 30 MHz with a thin thickness of about 5 to 8 mm, and therefore, a radio wave absorber using a sintered ferrite magnetic material radiates from electronic devices. It is widely used as a wall material for preventing reflection of radio waves by radio dark rooms for measuring radio waves and buildings.

On the other hand, as a technique for widening a radio wave absorber made of a magnetic layer, for example, a technique has been proposed in which a tile-like ferrite magnetic body is floated in an air layer (actually, floated from a radio wave reflector using a foamed polyurethane plate). For example of this technique, a NiZn-based ferrite tile having a height (thickness of the tile mounting surface and the vertical direction) of 7 mm may be placed between 300 MHz and 17 mm with an air layer of 10 mm from the reflecting plate, that is, the total height of 17 mm from the reflecting plate. A radio wave absorber having a reflection attenuation of 20 dB or less can be obtained for a radio wave of 800 MHz.

In general, if the reflection coefficient of the radio wave is S on the surface of the radio absorber, the power absorption coefficient of the radio absorber Is represented by equation (1).

(One)

therefore, The smaller the value is, the better the radio absorber has.

(2)

That is, the reflection attenuation amount (-20 log S) is 20 dB or less and an absorption coefficient ≥ 0.99 is adopted.

As shown in FIG. 9, the most basic ferrite wave absorber has a structure in which a ferrite magnetic material F in a tile is attached to the reflecting plate M, and the absorption characteristics of the wave absorber having the above structure are as shown in FIG.

In Figure 10, the axis of abscissas is frequency f, and the axis of ordinates is reflection coefficient. In FIG. 10, If the lower limit and the upper limit frequency of = 0.1 are f _L and f _H , respectively, as can be seen from the figure The frequency bandwidth B that satisfies = 0.1 is represented by equation (3).

B = f _H- f _L (3)

A lot of research has already been carried out on the rental width (B). For example, (A) Ferrites used in the case where the lower limit frequency (f _L ) is set to 30 MHz are all sintered and are of NiZn or MnZn type. In general, the upper limit frequency f _H is set to 300 MHz to 400 MHz.

(B) The ferrites used when the lower limit frequency (f _L ) is 90 MHz are all sintered and of NiZn type or MnZn type. In this case, the upper limit frequency (f _H ) is generally 350 MHz to 520 MHz. do.

As an application, when applying a radio wave absorber to a wall of a radio darkroom for measuring radio waves from the above-mentioned electronic equipment, f _L = 30 MHz and f _H is the 1998 International Special Committee on Radio Interference. In the case of (A), the upper limit frequency (f _H ) is low, and in the case of (B), the upper limit frequency (f _H ) is also low because the des Perturbations Radioelectrique (II) has a regulatory range of 20 GHz. In addition, f _L = 90 MHz and f _H = 800 MHz are required in Japan in the case of wall materials for preventing reflection of TV radio waves from buildings, and the radio absorber of (B) also has insufficient characteristics.

Therefore, various attempts have been made to improve the radio wave absorber, and as an example of the recent widening of the radio wave absorber composed only of sintered ferrite, a radio wave absorber in which a ferrite is disposed in a lattice form on a reflector is disclosed in US Patent No. 5,276,448. The lattice wave absorber is obtained by f _L = 30 MHz, f _H = 800 MHz.

In addition, as an example of widening of a radio wave absorber composed of only sintered ferrite, a tile-like ferrite magnetic material is disposed on a reflecting plate, and a ferrite magnetic material of the same thickness that is repeatedly arranged in a lattice form at regular intervals on the tile-like ferrite magnetic material is overlapped with the ferrite magnetic material. A radio wave absorber in which slots are formed along a height direction at the height thereof is proposed by the present inventors in Patent No. 144802, which obtains f _L = 30 MHz and f _H = 1000 MHz.

However, the radio wave absorption characteristics of the radio wave absorber are satisfied for the wall material of the building, but the radio dark room is significantly lower than the above-regulated range, and the ferrite of a part of the structure is made relatively thin, and the width and thickness of the slot are also small. In case that the whole structure is integrally molded during actual manufacturing, the material flow may be deformed or broken during sintering due to poor material flow, poor mold release of the molded product, uneven molding pressure, etc. when the material is injected into the mold. It is easy, and manufacturing cost rises due to difficulty of setting manufacturing conditions. In particular, as interest in the electromagnetic environment (EMI / EMC) has recently increased, the radio wave absorber is also required to be widened, and in the future, the frequency to be used in the electromagnetic environment will be higher, so the above f _H will inevitably increase.

SUMMARY OF THE INVENTION In view of the above circumstances, an object of the present invention is to provide a broadband ferrite radio wave absorber which can be manufactured more economically in accordance with the demand for widening of the radio wave absorber and having good setting of manufacturing conditions.

In order to achieve the above object, the present invention arranges a tile-like ferrite magnetic material on the reflecting plate, and arranges the cutting-conical columnar protrusion-like ferrite magnetic material on the tile-like ferrite magnetic material in a longitudinal and horizontal direction at a predetermined interval, and the cutting-wistle columnar stone The hemispherical ferrite magnetic body is disposed on the vapor phase ferrite magnetic body to form a three-layer structure as a whole.

The present invention relates to a radio wave absorber in which a tile-like and a cutting cone-shaped protrusion-absorbing layer are disposed vertically and successively on a reflecting plate. As means for changing the electric constant, an equivalent permeability and an equivalent permeability to look at the protrusion by the shape change of the protrusion. The permittivity is controlled to the required set point. In other words, by adjusting the diameter of the gap, height and width of the projections it is possible to change the equivalent permeability and equivalent permittivity of the projections.

In particular, the ferrite magnetic material is formed by the projections in the vertical and horizontal direction at a predetermined interval is good moldability and easy to manufacture. And as a ferrite magnetic body, things, such as a NiZn system and MnZn system, can be used, A sintering type is preferable.

1 is a perspective view of a radio wave absorber according to the present invention

2 is a plan view of a radio wave absorber according to the present invention;

3 is a side view of a radio wave absorber according to the present invention;

Figure 4 is a unit structure diagram of the synthetic capacity of the radio wave absorber according to the present invention

5 is a synthetic capacity model of FIG.

6 is a diagram illustrating a unit structure of synthetic inductance of a radio wave absorber according to the present invention.

7 is a synthetic inductance model of FIG.

8 is a side view of a radio wave absorber when a radio wave is incident vertically;

9 is an absorption characteristic diagram of a radio wave absorber according to the present invention.

10 is a frequency characteristic of a radio wave absorber

<Description of the code used in the main part of the drawing>

M: Reflector F: Ferrite Magnetic Cu: Unit Structure

a: spacing of cutting cone column sync

2r, 2R: diameter of upper and lower sides of cutting cone column

h ₁ , h ₂ , h ₃ : height of each wave absorber layer

| S | = Reflection coefficient,

1 to 3, M represents a reflector, F represents a ferrite magnetic material, and Cu represents a unit structure (unit cell) constituting a radio wave absorption layer, and the radio wave absorption layer of the present invention has the unit structure (Cu). Are arranged side by side on the same plane to the required area in contact with each other.

According to the present invention, a tile-like ferrite magnetic body, which is a first layer, is disposed on the reflecting plate M, and a cutting winch columnar protrusion-like ferrite magnetic body, which is a second layer, is disposed on the first layer in the longitudinal and horizontal directions at the same interval (a). The heights h ₁ , h ₂ , h ₃ of the layer, the second layer, and the third layer, the diameters 2r, 2R of the upper and lower sides of the second layer, and the permeability and permittivity are adjusted so that the equivalent permeability and equivalent permittivity can be changed. will be.

In the present invention, the first layer, the second layer, and the third layer are manufactured by integrally molding, but the first layer and the second layer are separately shown in the drawings to facilitate separation, and the unit of the ferrite magnetic body (F). The structure Cu is shown by the imaginary line of FIG. 2, and the unit structure Cu may be made of the synthetic capacity and the synthetic inductance unit structure diagrams shown in FIGS. 4 and 6 by using an equivalent material integer calculation model. As the two layers are reduced in diameter only to the top side, the cross-sectional structure is the same, so that the equivalent dielectric constant (n) and the arbitrary thickness (Δt) obtained by dividing the height into 30 or more cross-sectional layers are introduced. ) And equivalent permeability ( ) Can be obtained according to the synthetic capacitance and synthetic inductance model diagrams of FIGS. 5 and 7.

Since the first layer of the present invention is formed in a tile shape, the equivalent dielectric constant ( )silver

(4)

, Equivalent permeability ( ) Is shown below.

The second layer can be obtained by the following equations by FIGS. 5 and 7.

(6)

(7)

For the third layer, the equivalent dielectric constant ( ) And equivalent permeability ( ) Is the same as Eq. (6) and Eq. (7). Only expression of is changed.

<Example>

Ferrite magnetic body (F) is all NiZn-based sintered ferrite, the relative dielectric constant , Specific permeability The height h ₁ of the first layer is 6.5 mm, the height h ₂ of the second layer is 18 mm, the height h ₃ of the third layer is 3.5 mm, and the lower side of the second layer is The diameter of 2R is 18 mm, the diameter of the upper side (2r) is 7mm, and the spacing (a) of the cutting cone-shaped projection ferrite magnetic body is 20 mm.

As shown in Fig. 8, the radio wave absorption characteristics of the present embodiment were obtained with respect to the radio wave vertically incident from the ferrite surface in the direction of the reflector, and the reflection attenuation amount of 20 dB or more was obtained in the frequency range of 30 MHz to 20 GHz. lost.

As described above, the present invention can be manufactured at low cost because the ferrite magnetic material is disposed on the reflecting plate, and the ferrite magnetic material is arranged in a vertically and horizontally at a predetermined interval thereon. In addition, since the change in the equivalent permeability and the equivalent permittivity can be easily controlled to a desired value, it is possible to exhibit the ultra-wideband wave absorption characteristics suitable for wall materials of buildings as well as radio wave dark rooms.

Claims (1)

A tile-like ferrite magnetic material is disposed on the reflecting plate, and a cutting-cone-shaped protrusion-like ferrite magnetic material is disposed on the tile-like ferrite magnetic material in the longitudinal and horizontal directions at the same interval (a), and the gap between the cutting-cone-shaped protrusion-like ferrite magnetic material (a ) Is shorter than the wavelength of radio waves to be used, and the diameters of the upper and lower sides of the cutting cone-shaped protrusion ferrite magnetic body are 2r and 2R, the height of the tile-like ferrite magnetic body is h ₁ , and When the height is h ₂ and the height of the hemispherical ferrite is h ₃ , 2r is 0 <2r <2R, 2R is 2r <2R <a, h ₁ is 4 mm ≤ h ₁ ≤ 8 mm, and h ₂ is 10 mm ≤ Broadband ferrite absorber, characterized in that h ₂ ≤ 20 mm, h ₃ is 1.5 mm ≤ h ₃ ≤ 8.5 mm.