JPH02184098A - Wide band radio wave absorber - Google Patents

Abstract

PURPOSE:To perform radio wave absorption in a wider frequency width with light weight by converting a radio wave incident perpendicularly to the surface of a current conversion element into a current flowing in a direction determined according to a radio wave incident direction by the current conversion element, applying a current supplied from the current conversion element to a thermal conversion element to be converted into heat to be consumed. CONSTITUTION:In order to most efficiently perform an absorption operation, a predetermined relationship is provided between the size of a current conversion element and the resistance value of a thermal conversion element. In this case, frequency is not limited. The current conversion element and the thermal conversion element are so disposed as to absorb both horizontally and vertically polarized waves. That is, the thermal conversion element is extended in a plurality of directions to convert currents flowing in various direction, supplied from the current conversion element into heats. Accordingly, a circularly polarized wave is also thermally converted. One radio wave absorber is formed in combination of a lateral thermal conversion element 2 and a pair of current conversion element 1, 2 disposed on and beneath the thermal conversion element 2, and the other radio wave absorber is formed in combination of a longitudinal thermal conversion element and a pair of current conversion elements 1, 2 disposed at the right and left sides of the thermal conversion element.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a radio wave absorption device that consumes incident radio waves as heat.

[Conventional technology]

In recent years, the proliferation of high-rise buildings has caused interference with radio waves, mainly TV waves, so the outer walls of these buildings have been covered with radio wave absorbing materials. The materials used in this case are as shown in Figure 19(a).
, (b).

In the diagram (a), an absorbing material 3 is provided on a conductive plate 1, and the absorbing material is a magnetic material such as ferrite, rubber or plastic mixed with conductive graphite, or ferrite powder and conductive graphite. There are rubber and plastic that contain both. Currently, ferrite is the thinnest anti-reflection material for TVtli waves, and the thickness of the absorption material is approximately 8 to 10 meters.
It is m.

In addition, in the case shown in FIG. 3(b), a permanent magnet 4 is inserted between the conductive plate 1 and the absorbing material 3 to modify the loss characteristics of the absorbing material. In this case, the total thickness of the magnet portion and the absorbing material portion is approximately 4 mm.

[Problem to be solved by the invention]

These radio wave absorbers have drawbacks such as heavy ferrite and magnets and high cost, which has hindered their widespread use.

Furthermore, the radio wave absorption characteristics vary depending on the frequency due to the dispersion of the magnetic permeability of the magnetic material, and radio waves can only be absorbed within a certain limited range of frequencies.

The present invention has been made in consideration of the above points, and an object of the present invention is to provide a radio wave absorbing device that is lightweight and has a wider frequency width.

[Means to solve the problem]

In order to achieve the above object, the present invention provides: 1. A plurality of current conversion elements that are made of spread conductors and convert radio waves into electric current, and a thermal conversion element that is arranged along a plurality of directions between these current conversion elements. The heat conversion element is configured to have a resistance value determined based on the distance between the current conversion elements and the length of the current conversion element along the longitudinal direction of the heat conversion element. Broadband radio wave absorber; and 2. In the radio wave absorber according to item 1 above, the current conversion elements are configured in a rectangular shape and arranged in a grid pattern, and the blank space is occupied by a heat conversion element. 3. The radio wave absorber according to item 1 above, in which the pair of heat conversion elements are arranged diagonally and orthogonally to each other within a predetermined rectangular area, and A broadband radio wave absorber in which the 7 current conversion elements are arranged in other parts,
It provides:

[For production]

The current conversion element converts a radio wave incident in a direction perpendicular to its surface into a current flowing in a direction determined by the direction of incidence of the radio wave. A heat conversion element is arranged to extend in a direction perpendicular to the direction in which the current flows, and the current supplied from the current conversion element flows into the heat conversion element and is converted into heat and consumed.

This means that radio waves are absorbed.

In order to perform this absorption operation most efficiently, a predetermined relationship is established between the dimensions of the current conversion element and the resistance value of the heat conversion element. In this case, the frequency is unlimited.

The current conversion element and the heat conversion element are arranged to absorb both horizontally and vertically polarized waves. That is, the heat conversion element extends along multiple directions and converts current flowing in various directions supplied from the current conversion element into heat. Therefore, circularly polarized waves are also converted into heat.

〔Effect of the invention〕

As described above, the present invention is configured to convert radio waves from multiple directions into heat by combining a current conversion element and a heat conversion element, so that various radio waves including horizontally polarized waves and vertically polarized waves can be can be absorbed without limit. Moreover, since the radio wave absorber of the present invention can be configured in the form of a flat plate or sheet, it can be used for a variety of purposes, from large objects such as the outer walls of buildings to small objects such as casings of electronic devices. .

[Basic theory]

FIG. 2 is an explanatory diagram of radio waves to which the present invention is applied. As shown in the figure, a radio wave can be decomposed into an electric field E represented by electric lines of force and a magnetic field H represented by magnetic lines of force. Both the electric field and the magnetic field are oriented at right angles to the propagation direction of the radio wave and at right angles to each other. There is. In the present invention, a current conversion element, that is, an element 1 made of a deck-shaped conductor that converts radio waves into current is arranged in a direction perpendicular to the electric field E.

Figure 3 shows the state in which this flat element 1 is arranged, and as the flat element 1, flat plates with a width a and an infinite length (ignoring the width d) are already arranged at intervals. ing. It is well known in electromagnetism that even if conductors are arranged perpendicular to the electric field E in this way, the electric and magnetic fields are not disturbed at all. Therefore, the way the radio waves propagate does not change before or after entering the flat element 1, and the same propagation state is obtained. This indicates that radio waves are not reflected due to the presence of the flat element 1.

FIG. 4 shows this as a transmission line model. That is, it is assumed that a pair of conductive plates 1 are arranged parallel to each other in the horizontal direction. Characteristic impedance Z in this case
c and the phase constant β are Zc-b/aE et al., -37
7b/a CΩ] −(1) β−ωr75 Kostone
[Radian/rnl...(2)
Here, ω is the angular frequency of the radio wave, ε0 is the dielectric constant of vacuum or air, and μ. is the magnetic permeability of vacuum or air.

Figures 5(a) and 5(b) are redrawn versions of the conventional device shown in Figure 19 using this transmission line model; Figure 5(a) corresponds to Figure 19(a); Figure (b) is the 19th
Corresponds to figure (b).

FIG. 6 is a diagram showing a configuration as an improvement of FIG. 5, in which a resistor R is arranged between the current conversion element 1a and the interrupting element 1b. This resistor R is a heat conversion element, and converts the current from the current conversion element 1a into heat for consumption.

FIGS. 7(a) and 7(b) show the appearance of a concrete example of the configuration shown in FIG. 6, in which a pair of current conversion elements la, la
It has a configuration in which a heat conversion element 2 is disposed at the end of the circuit, and the ends are further connected by a blocking element 1b. FIG. It shows the state where it is removed.

In this configuration, in order to absorb the propagating radio waves without reflecting them, the input impedance Zln when looking to the right from the plane along the X-X line in the conceptual diagram of FIG.
It is necessary to match c. That is, Z ln −Z c −(
3), and the conditions for satisfying this will be explained below.

The distance from the surface along the line X-X to the blocking element 1b is g
and this distance g is the wavelength λ(-2π
/β-c/f where C is the speed of light 3X108m/s
, f is the frequency. ) is very small compared to

That is, l <<λ
...(4). In FIG. 6, the circuit when viewed to the right from the plane along line XX is a lumped constant circuit, so Z in-2R-(5). This R is one of the two resistors R5R shown in FIG.

FIG. 8 shows the side profile of the radio wave absorbing device described in FIGS. 2 to 7(a) and (b).

In other words, an example is shown in which a space is formed by the current conversion element laq, the thermal transformation element laq, and the interruption element 1b, and this space is filled with air.

Figures 9(a), (b) and 10 show the above space filled with a defective conductor, and Figure 9 corresponds to the heat conversion element 2 in Figure 8. FIG. 10 shows a case in which only the space is filled, and FIG. 10 shows a case in which not only the heat conversion element 2 but also the space corresponding to the current conversion element 1a is filled.

Considering the items in FIG. 9 and FIG. 10, the length p along the direction parallel to the plane formed by the current conversion element 1g and the heat conversion element 2 of the filling 5 is the wavelength λ of the incident radio wave.
When it is sufficiently small compared to , that is, when 1 <<λ, both the one shown in FIG. 9 and the one shown in FIG. 10 can be handled in the same way. Therefore, the following discussion will focus on the one in Figure 9.

The series distributed impedance Zs of the one shown in Fig. 9
[Ω/m] and parallel distributed admittance Yp[Ω/m
] are respectively Zsmjωμ・−+R'...(6) Yp
= jωεφ − (7) where μ is the magnetic permeability of the filling, ε is the X electric constant of the filling, R′ is the resistance value for a length of 1 m of the heat conversion element 2, and a is the ftrijlif-variation. The length in the long element 1 in the direction parallel to the magnetic field component H of the current, and b is the length in the direction parallel to the electric field component E of the current.

It can be expressed as

Since a conductor is placed at the terminal end of the radio wave absorbing device shown in FIG. 9, the input impedance Z1n when looking from the left end to the right side in FIG. 9(a) is as follows.

Here, if 1 <<λ and WZsYp-47l<<l, then ta
Since nhJZsYp and j)''=JZsYpφ, 77, the above equation (8) can be rewritten as follows.

By the way, in Zs■jωμ and □ +R'...(13), up to the millimeter wave frequency, generally jωμ・□1(
<R', ZIn=Zsl'=, R' Ω
- (10) may be used.

R' is the sum of the resistance values per 1m of both the upper and lower resistances, so if the upper or lower resistance value is R', then R'R'
+R'san2R'. Therefore, Z in −2R′ Ill −
(11) Here R'l is the resistance of the length g,
It is equal to R in equation (5).

Therefore, similar to equation (5), Z In -2R- (12) becomes.

Therefore, even if the filler 5 is included, if Ω is shorter than λ, it will be the same as when there is no filler and only air.

FIG. 11 shows the shape of the heat conversion element 2 itself which should have this resistance R, and the dimensions are width a1 length g.

When the thickness is t, R-p・Illaxt-ρ/l −(1/a −Ra
A resistance R of J/a (13) is obtained. Here, ρ is the specific resistance of the resistor material, and R is the elementary resistance of the resistive film made of that material. Substituting equation (13) and equation (1) into equation (2), 377b/a-2Ro ・fl /a −
414) That is, RoJ/b-188,5[Ω]-(15) is obtained.

If R port and glb are determined so as to satisfy this relational expression, a resistor, that is, a heat conversion element 2 is obtained, which can absorb radio waves and prevent reflection. If each element is set to 18% and the distance between each element 1b is made smaller than the half wavelength λ/2 of the radio wave to be absorbed, that is, if b<λ/2, harmonics will not be generated. Furthermore, the shorter g is, the wider the frequency characteristics are because the resistor, that is, the heat conversion element 2 can be regarded as a lumped constant circuit.

-For example, if b=, 10c+n, 0-11111, R-row 188. 5X100-18850 [
:Ω] may be used as the heat conversion element 2. Although this resistive film can absorb radio waves, in practice, a current conversion element 1a made of a conductor is added to facilitate the conversion of incident radio waves into current. Furthermore, since the heat conversion element (resistive film) 2 itself can convert radio waves into current, the current conversion element 1a may be omitted in this case.

The explanation so far relates to a radio wave absorbing device constituted by a current conversion element, a heat conversion element, a blocking element, and a support element, which are the basis of the present invention.

〔Example〕

1, FIG. 1A, and FIGS. 12 to 18 are diagrams for explaining the present invention in detail. In explaining this embodiment, in order to facilitate understanding of the embodiment of the present invention, the process leading to the present invention from the content explained in the above basic theory section will be explained.

12(a) to 12(f) show one embodiment of the present invention shown in FIG. 12(r) starting from a radio wave absorption device corresponding to the specific configuration of FIG. 7 shown in FIG. 12(a). The process leading to this example is shown in sequence.

The structure shown in FIG. 1A shows the basic structure of the present invention (see Japanese Patent Application No. 63-271485), and is reproduced from FIG. 10 for convenience of explanation.

In this case, a pair of heat conversion elements 2 are provided, and each heat conversion element 2 is combined with a current conversion element 1a.

FIG. 3(b) is based on the fact that the configuration of the present invention only needs to have a current conversion element and a heat conversion element, so one of the pair of heat conversion elements in FIG. It is set up. However, the resistance value of the heat conversion element 2 is twice as high as 2R.

2C shows a configuration in which the heat conversion element 2 in the configuration shown in FIG. 1A is provided with the function of the current conversion element 1a, and its length l is shortened. The number of heat conversion elements is set to one in the same figure (d) as in the same figure (b).

FIG. 4(c) is a further development of the idea of FIG.

This is because the current conversion element 1 does not require a length in the radio wave incident direction. Therefore, specifically, it means that a sheet-like structure can be formed (Japanese Patent Application No. 63-28717
(See No. 5).

Figure (r) shows an embodiment of the present invention that further develops this idea. The present invention differs from the above six examples in that it can absorb radio waves of all polarizations. That is, in this embodiment, the heat conversion element 2 is provided in both the vertical and horizontal directions of the current conversion element 1, and the current conversion element and the heat conversion element act on both horizontally polarized waves and vertically polarized waves. do.

FIG. 1 is an expanded version of the embodiment shown in FIG. 12 ( ), in which current converting elements 1 are arranged in the form of squares, and heat converting elements 2 are arranged between the squares. The portion shown in FIG. 12(r) corresponds to that shown in FIG. 12(r).

FIG. 1A shows a state in which the current conversion element 1 in FIG. 1 is insulated for each block. That is, in FIG. 1, the distance between the center positions of the current conversion element 1 is a
In FIG. 1A, the current converting element in FIG. 1 is equally divided into two in each of the vertical and horizontal directions, and separated into four elements. These four elements are insulated from each other not only in terms of direct current but also in terms of high frequency.

FIG. 13 is an analytical view of the part within the broken line in the embodiment shown in FIG. One 7U wave absorber is formed in combination with the current conversion element 1.1, and the vertical heat conversion element shown on the right side of the figure and a pair of current conversion elements 1.1 arranged on the left and right sides thereof. 1
This shows that the other radio wave absorber is formed by the combination with .

In this case, considering that the current conversion element 1 is a so-called conductor, the resistance value that the heat conversion element should have is as follows: , R2=
377a/b is as described above. Here, dimensions a and b represent the distance between the center positions of the current conversion element 1.

FIGS. 14 and 15 are Smith charts for comparing the transmission characteristics according to the configuration forming the basis of the present invention with the transmission characteristics according to the above-described embodiments of the present invention. These characteristics are 1l
As shown in the margins of each Smith chart, the configuration of the radio wave absorber used for the 11 measurement is as follows: in Fig. 14, the heat conversion elements are oriented horizontally, and in a single tree, whereas in Fig. 15, they are oriented vertically. and one each in the horizontal direction.

This Smith chart shows that although the configuration of the present invention has two heat conversion elements, it shows almost the same transmission characteristics as the configuration that forms the basis of the present invention. This means that no problem will occur even if there are two.

FIGS. 16 to 18 show various modifications of the present invention. Among these, in FIG. 16, the intersection of the vertical heat converting element and the horizontal heat converting element is constructed with an insulator.

Further, in FIG. 17, a pair of heat conversion elements arranged diagonally and orthogonal to each other is used instead of the heat conversion elements in the vertical direction and the horizontal direction. The radio wave absorbers shown in FIGS. 16 and 18 can be formed into tiles, for example, and a large planar radio wave absorbing surface can be formed by pasting a large number of them vertically and horizontally.

On the other hand, in the case of FIG. 18, since the entire pattern must be assembled as one pattern, each tile must have a different configuration when considered in terms of tiles, which is not practical.

It can be naturally derived from distributed constant theory that the operation of the above embodiment does not change even if a dielectric material whose thickness is sufficiently thin compared to the wavelength, such as decorative tiles, ferrite, Teflon, or surface protection vinyl, is provided on the surface of the above embodiment. This is the conclusion.

Further, in the above embodiments, the current conversion elements and the heat conversion elements are arranged regularly, but they may be arranged irregularly.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing an embodiment of the present invention, FIG. 1A is a diagram showing a state in which the current conversion elements in FIG. 1 are insulated for each block, and FIG. An explanatory diagram of the radio wave to be transmitted, Figure 3 is a diagram showing a state where flat elements are arranged in this radio wave, Figure 4 is a diagram showing the state of Figure 3 as a transmission line model, and Figure 5 ( a), (b)
is a redrawing of the conventional device shown in FIG. 19 using this transmission line model, FIG. 6 is a diagram showing the configuration as an improvement on FIG. 5, and FIGS. 7(a) and (b) are FIG. 8 is a diagram showing the external appearance when the configuration of FIG. (a), (b) and Fig. 10 are diagrams showing the state in which the internal space of the device of Fig. 8 is filled with a defective conductor, Fig. 11 is a diagram showing the shape of the heat conversion element, and Fig. 12 (a) , (b), (c), (d)
, (c) and (r) are explanatory diagrams showing the process from the basic configuration of the present invention to an embodiment of the present invention, FIG. 13 is an analytical explanatory diagram of the embodiment of FIG. 1, and FIG. 14 and FIG. 15 is a Smith chart for comparing the characteristics of the configuration forming the basis of the present invention and the configuration of the present invention, FIGS. 16 to 18 are diagrams showing each embodiment of the present invention, and FIG. 1 is a diagram showing the configuration of a conventional radio wave absorption device. DESCRIPTION OF SYMBOLS 1...Conductor, 1a...Current conversion element, 1b...Blocking element, 2...Heat conversion element, 3...Absorber, 4...
・Magnet, 5...Filling, a, b, l...Dimensions. Figure 2

Claims (3)

[Claims] 1. It includes a plurality of current conversion elements made of spread conductors and converts radio waves into electric current, and heat conversion elements arranged along a plurality of directions between these current conversion elements, and the heat conversion elements A broadband radio wave absorber configured to have a resistance value determined based on the distance between current conversion elements and the length of the current conversion element along the longitudinal direction of the heat conversion element. 2. 2. The wide-band radio wave absorber according to claim 1, wherein the current converting elements are configured in a rectangular shape and arranged in a grid pattern, and the blank spaces are occupied by the heat converting elements. 3. 2. The radio wave absorber according to claim 1, wherein a pair of said heat conversion elements are disposed in a diagonal direction and perpendicular to each other in a predetermined rectangular area, and said current conversion element is arranged in another part of said rectangular area. A broadband radio wave absorber with