JPH03228398A - Ferrite radio wave absorber - Google Patents

Abstract

PURPOSE:To obtain a ferrite radio wave absorber having a small weight by arranging ferrite blocks at a predetermined interval in one direction on a conductive flat plate. CONSTITUTION:Ferrite rectangular parallelepiped bodies F each having a height lare so arranged in parallel at a predetermined interval S on a metal plate M that the longitudinal directions are directed in the same direction. This radio wave absorber is so mounted that the longitudinal directions of the bodies coincide with a magnetic field direction of a radio wave, and the blocks F are so disposed that the centers of the blocks F in the thickness direction are opposed to parallel flat plates up to the centers of the adjacent blocks in the thickness direction.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a radio wave absorber constructed using a ferrite magnetic material, and particularly to a radio wave absorber constructed by arranging ferrite blocks at predetermined intervals on a flat plate. Regarding.

[Conventional technology]

Ferrite is widely used for various purposes.

One of these uses is to absorb radio waves, and it is called a ferrite radio wave absorber.

As shown in FIG. 9, the conventional ferrite radio wave absorber has a structure in which a flat ferrite plate F is lined with a metal plate M, which is arranged in a direction perpendicular to the radio waves. FIG. 10 shows this using a transmission line model. If Z is the impedance when looking to the right of the line AA' in FIG. 10, and Rc is the characteristic impedance of the transmission line, then FIG. 11 is obtained.

This impedance Z changes depending on the material, thickness d1, frequency fo, and can be expressed as a series circuit of a resistance RO, an inductance Lo, and a capacitance Co, as shown in FIG.

Ro - Rc...
...When the relationship (1) holds, all radio waves are absorbed as TEM waves, and there is no reflection. On the other hand, reflection occurs when these equations (1) and (2) are not satisfied.

FIG. 13 shows the contents expressed by these equations (1) and (2), with the frequency plotted on the horizontal axis and the amount of reflection plotted on the vertical axis. As shown in this figure, the amount of reflection is 0 at frequency fo, and increases as the distance from frequency fo increases.

Since this flat ferrite radio wave absorber is a funeral plate, it simultaneously makes zero reflection for vertically polarized waves shown in Figure 14 (a) and horizontally polarized waves shown in Figure 14 (b). It is characterized by being able to.

[Invention or problem to be solved]

This flat radio wave absorber has a structure in which a thick ferrite plate is pasted over a flat conductor.
It has the disadvantage of being heavy.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a ferrite radio wave absorber that is light in weight.

[Failure to solve the problem]

To achieve the above object, the present invention provides a radio wave absorber in which ferrite blocks are arranged in one direction at predetermined intervals on a conductive flat plate; A radio wave absorber arranged in two directions orthogonal to each other is provided.

[For production]

Each radio wave absorber is constructed by arranging ferrite magnetic bodies at predetermined intervals on a conductive flat plate.

In a radio wave absorber in which ferrite blocks are arranged in one direction, the ferrite blocks are arranged so that the longitudinal direction of the ferrite blocks coincides with the direction of the magnetic field of the radio waves, that is, the width direction of the ferrite blocks coincides with the direction of the electric field of the radio waves. Therefore, for horizontally polarized waves, if the ferrite blocks are rectangular parallelepipeds, they are arranged so that the longitudinal direction is in the vertical direction, and for vertically polarized waves, they are arranged so that the longitudinal direction is in the horizontal direction.

Furthermore, in a radio wave absorber in which ferrite blocks are arranged in two directions, the ferrite blocks are arranged so that their longitudinal directions are orthogonal to each other.

As a result, radio waves incident as TEM waves are converted into TM waves and absorbed on the side surfaces of the ferrite.

〔Effect of the invention〕

As mentioned above, the present invention is made by arranging ferrite blocks at predetermined intervals on a conductive flat plate, so it does not absorb TEM waves as they are like the conventional ferrite plates arranged on one side. The frequency absorption band is wide because it converts to TM waves.

The configuration in which ferrite blocks are arranged in one direction is intended only for specific polarized waves such as television radio waves or in-building communication, and the conventional flat ferrite board is pasted all over the conductor. The volume and weight are reduced compared to structural ones.

The configuration in which ferrite blocks are arranged in two directions is horizontal,
It can be used for both vertical polarization and has a wide frequency absorption band.

〔Example〕

FIG. 1 shows an embodiment of the present invention, which is configured to absorb either horizontally or vertically polarized waves. This is because, for example, when using a radio wave absorber as a measure against the reflection of television radio waves by buildings, it is sufficient to consider only horizontal polarization, which is the case for most television radio waves.

As shown in the figure, in this embodiment, a height Ω is placed on the metal plate M.
The ferrite rectangular parallelepipeds F are arranged in parallel at a predetermined interval S so that their longitudinal directions face in the same direction. The radio wave absorber is installed so that the longitudinal direction of the ferrite rectangular parallelepiped corresponds to the direction of the radio wave magnetic field.

Fig. 2 shows the embodiment shown in Fig. 1 viewed from the end face in the longitudinal direction.The radio wave is incident from the left side in the figure, and the magnetic field is perpendicular from the front side of the page to the back side. It goes downwards.

In this radio wave absorber, a radio wave incident eastward in the height direction of the ferrite rectangular parallelepiped block is converted into a TEM wave or a TM wave due to the presence of block F in the figure and is absorbed.

This point is different from the conventional radio wave absorbers that absorb TEM waves shown in FIGS. 9 and 10.

FIG. 3 shows an equivalent transmission line model by cutting out only one section of the embodiment shown in FIGS. The figure shows parallel flat plates facing each other up to the center in the viewing direction. Note that even with this parallel plate interposed, there is no change in the radio wave absorber and its operation.

Therefore, the two blocks F in the figure each have a thickness of t/2.

Figure 4 is a representation of Figure 3 as a transmission line model, and is shown as an equivalent circuit where Z' is the input impedance when looking to the right from line B-B', and Rc' is the characteristic impedance of the transmission line. There is.

FIG. 5 shows a more detailed representation of the equivalent circuit shown in FIG. That is, a signal source having a frequency fo is connected to loads having input impedances Zl and Z2 via a line having a characteristic impedance Rc'.

Figure 6 shows the human power impedance Zl in Figure 4.

It shows that it can be decomposed into Z2, resistance R1, R2, inductance LIL2, and capacitance CI C2.

These resistances R1, R2, inductance L1. L
2 and capacitance CI, C2, radio frequency fo
When the relationship R1+R2-Rc' (3) holds between RcO and characteristic impedance RcO, all radio waves are absorbed and no longer reflected.

Furthermore, the major difference between the absorbent body of the present invention and the conventional absorbent body is that the absorbent body of the present invention is shown in FIG. , 21 in Figure 6
, or Z2, that is, even if one of the upper and lower ferrite blocks in FIG. 3 is missing, it can still function as an absorber.

In Figure 7, the thickness is t-2mm, the height is l-20mm, and the interval is 5.
This shows the results of an experiment using a NiZn-based ferrite rectangular parallelepiped block with =2Q+n+s and magnetic permeability tt-700.

According to this, when looking at the return loss ff120[dB] level, the conventional example has a return loss of 700[MHzl to 1500[MHz].
zl range, whereas in the present invention the range is 200 [MHz
It extends from 1 to 1700 MHz.

Furthermore, when looking at the return loss ff115 [dB] level,
In the conventional example, the frequency is 600 [MHz to 1600 [MHz].
However, in the present invention, the range is significantly expanded to 100 [MHz] to 2800 [-MHz].

This experimental example shows that the present invention can provide a radio wave absorber with a much wider absorption frequency band than the conventional example.

FIG. 8 shows another embodiment of the present invention, in which rectangular ferrite blocks are arranged in two directions. The basic configuration is the same as the embodiment shown in FIGS. 1 and 2, except that the blocks are arranged in two directions, so detailed explanation will be omitted.

[Brief explanation of drawings]

Fig. 1 is an explanatory diagram showing an embodiment of the present invention, Fig. 2 is an illustration showing the arrangement direction for radio waves in the embodiment, Fig. 3 is an explanatory diagram showing the middle part of the embodiment, and Fig. 4 is an explanatory diagram showing an embodiment of the present invention. The figure is an explanatory diagram of the radio wave transmission operation for the part shown in Fig. 3, Fig. 5 is a circuit diagram of Fig. 4 rewritten as an equinodal circuit, Fig. 6 is an exploded diagram showing the impedance Z1z2 in Fig. 4, FIG. 7 is a diagram showing the actual measurement results of the characteristics of the radio wave absorber according to the present invention, FIG. 8 is a diagram showing another embodiment of the present invention, FIG. 9 is a cross-sectional view showing the structure of a conventional radio wave absorber, and FIG. Figure 10 is a diagram showing the radio wave absorption operation of the absorber in Figure 9, Figure 11 is an equivalent circuit diagram showing the state in Figure 10, and Figure 12 is the impedance Z in Figure 11.
Figure 13 is a diagram showing the absorption characteristics of the absorber in Figure 9, and Figures 14 (a) and (b) show the magnetic field component and the radio wave absorbed by the absorber in Figure 9. This shows the electric field components. M...metal plate, F...ferrite, S...spacing, 1...height, t...thickness, 2...
...Impedance, Rc, Re' Characteristic impedance. Figure 6 Figure 7 Figure 8 Figure 13 ((1) (b) Figure 14

Claims (4)

[Claims] 1. A radio wave absorber made by arranging ferrite blocks in one direction at predetermined intervals on a conductive flat plate. 2. In the radio wave absorber according to claim 1, a parallel plate line is passed through approximately the center of the width of the ferrite block with respect to the direction of arrival of the radio wave, one end of the parallel plate line is opened, and the other end is short-circuited with a conductive flat plate. A radio wave absorber. 3. A radio wave absorber made by arranging ferrite blocks at predetermined intervals in two directions orthogonal to each other on a conductive flat plate. 4. In the radio wave absorber according to claim 3, a parallel plate line is passed through approximately the center of the width of the ferrite block with respect to the direction of arrival of the radio wave, one end of the parallel plate line is opened, and the other end is short-circuited with a conductive flat plate. A radio wave absorber.