JPS63200075A - Method and apparatus for measuring shield effect of electrically conductive material - Google Patents

Abstract

PURPOSE:To reduce the effect of a power feeding part on a measuring result, by vertically installing a pair of antennae on the surface of an earthed metal plate at a predetermined interval and generating imaging effect on the rear surface side of the metal plate. CONSTITUTION:A pair of semi-loop antennae 8a, 8b are vertically installed on the surface of an earthed metal plate 2 at a predetermined interval. A power is fed to the feeding point of the antenna 8a from the back surface side of the metal plate 2 through a connector 10a so that imaging effect is generated on the back surface side of the metal plate 2 and the receiving output from the receiving point of the antenna 8b is taken out from the back surface side through a connector 10b. Then, shield effect is evaluated on the basis of the ratio of the receiving output in such a state that a test sample is not arranged and the space between the antennae 8a, 8b continues and the receiving output in such a state that the test sample 1 composed of a cup-shaped half-split body made of a conductive material is arranged and the space between the antennae 8a, 8b is blocked by the test sample 1. Further, a monopole antenna is used in the measurement of magnetic field shielding effect.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a measuring method and a measuring device for measuring the shielding effect of a conductive material against electric field waves and magnetic field waves.

[Conventional technology]

The N constant 11 d of the shielding effect of the shield housing is determined by the MILSTD-285 method, which is known to measure both near and far electromagnetic fields and both horizontal and vertical return waves. In this method, the transmitting and receiving antennas are placed opposite each other at a predetermined reference distance to measure the reference level S0, and then the shield wall is measured at the same distance to obtain the measured level S, and the shielding effect is determined by 56-S□. That is. There is also a method called the plane wave method (radio wave method), which calculates the electric field strength inside and outside the ceiling room as S, , S, respectively.
The shielding effect is defined as 50-S. In addition to this, there are auxiliary methods such as a sniffer method, a search coil method, and a high frequency C'R method. The sniffer method is a method in which a shield wall is excited with a low frequency of about 100 kl [z, the wall surface is swept with a par antenna, and leakage is searched for by reading the relative level. The search coil method is a method in which radio waves are radiated onto a shield wall and a search coil is used to search for leakage from the wall surface. In the high-frequency CT method, equipment isolated from the earth, the shield room floor, a ground plane, etc. are grounded at a single point, and a high-frequency current transformer is inserted into the ground wire to determine changes in shielding effectiveness.

[Problem that the invention seeks to solve]

The above-mentioned conventional techniques are all methods for measuring the shielding effect of the shield housing or the shield chamber itself, and evaluate the shielding effect of the material itself, which can also be called the characteristics of the conductive material that constitutes the shield structure. A measurement method for this has not yet been established.

When measuring the characteristics of a material, a test sample is usually taken from the conductive material to be measured and the sample is measured. One possible measurement method that directly estimates the shielding effect is to measure the shielding effect of a spherical shielding material. It is necessary to compare the electromagnetic field strength of However, there is a problem in that the portion affects the shielding effect, making accurate measurement impossible.

In view of the above-mentioned disadvantages, it is an object of the present invention to reduce the influence of the power feeding part on a test sample molded into a predetermined shape, and to obtain measurement results substantially equivalent to those of a spherical shield material using a half-split test sample. An object of the present invention is to provide a method and apparatus for measuring the shielding effect of a conductive material.

[Means for solving problems]

In order to achieve the above-mentioned problems in the method for measuring the shielding effect of conductive materials of the present invention, a pair of micro antenna elements are erected on the surface of a grounded metal flat plate at a predetermined interval, and each In order to produce an image effect on the back side of the antenna element, power is supplied from the back side of the metal plate to the feed point near the surface of the metal flat plate of one antenna element, and an electric or magnetic field is radiated to the front side of the metal plate, and the electric field or magnetic field is radiated to the front side of the metal flat plate. The received output from the power receiving point near the metal flat plate surface of the element is similarly taken out from the metal flat plate 11 side, and a cup-shaped half body made of a conductive material of the shot to be measured is placed on top of one of the antenna elements. A test sample consisting of is placed concentrically with the feeding point of the antenna element, and the entire circumference of the mouth edge of the sample is grounded to a metal flat plate. The shielding effect is evaluated based on the ratio of the received output to the received output when the test sample is placed and the space between both antenna elements is blocked by the test sample.

Preferably, the measurements are carried out continuously over a predetermined frequency range; in one embodiment, the magnetic field shielding effect is measured using a half-loop antenna for both antenna elements, and in another embodiment for both antenna elements. Monoball 7
The electric field shielding effect is measured using the antenna.

Further, the measuring device for carrying out the above-mentioned measuring method of the present invention includes:
A sample consisting of a cup-shaped half body made of a conductive material to be measured, a metal flat plate having an opening that matches the outer circumference shape of the mouth edge of the sample, and a metal plate that matches the inner circumference shape of the mouth edge of the test sample. A metal fitting that has a flat upper surface with an external shape and is attached to the flat metal plate from the back side of the metal flat plate so that the upper surface is flush with the surface of the metal flat plate, and the metal fitting is removably fixed to the metal flat plate from the back side. and a connecting mechanism capable of clamping and fixing the entire periphery of the sample mouth rim in a fixed state in the gap between the sample opening and the upper surface of the opening, and a central portion of the upper surface of the metal fitting so as to produce an image effect on the back side of the metal plate. a first micro antenna element erected; and a first micro antenna element erected at a predetermined distance away from the center of the opening on the surface of the flat metal plate so as to similarly produce an image effect on the back side of the flat metal plate; The second minute antenna element and the first minute antenna of the metal fitting are fed from the back side of the flat metal plate with the Furukawa wave signal. signal feeding means for extracting the received output from the power receiving point near the surface of the metal flat plate of the second micro antenna element on the back side of the metal flat plate; and a signal for supplying the high frequency signal to the signal feeding means. Receiving outputs from the transmitting means and the signal extracting means, receiving outputs when the space between both antenna elements is continuous without placing the test sample, and receiving output when the space between the two antenna elements is continuous with the test sample being placed. analysis means for evaluating the shielding effect based on the ratio to the received output in a state where the space of the test sample is blocked by the test sample;

In a preferred embodiment of the invention, the test sample of the conductive material to be measured is formed into a hemispherical shape on the surface of a flat metal plate; in another aspect, the test sample is formed on the surface of a flat metal plate into half a cube form a shape.

According to one implementation of the device of the invention, both seven antenna elements are half-loop antennas, and according to another implementation, both antenna elements are monopole antennas.

[Effect]

As a method to evaluate the shielding effect of a shielding structure made of conductive material, consider a spherical shell made of a lossy (conductive) medium, and insert a minute Wa current source J or a minute magnetic current source JffI into the shell.
When the spherical shell exists, the electromagnetic field outside the spherical shell is determined, and the ratio to the electromagnetic field at the same distance when the spherical shell does not exist is calculated and used as the evaluation value of the shielding effect. In this case, when the wave source is a microcurrent, the shielding effect of the electric field is required, and when the wave source is a micromagnetic current, the shielding effect of the magnetic field is required. This is because a normal shielding housing covers the circuit or component with a cubic cover, so we introduced a spherical structure as a way to imitate this housing, and by adopting this structure, we can improve the actual shielding effect. It is now possible to understand quantitatively to a certain extent, and theoretically an exact solution exists. However, in the present invention, the shield housing is not limited to a spherical shape, and may be a cube itself, but for convenience of explanation, a spherical shape will be described here.

In the present invention, half of the spherical shield housing is used as a sample shape imitating the above-mentioned spherical shield housing, and the image effect on the ground plane is used to obtain measurement results equivalent to those of the spherical sample. By using a half body for the sample, it is possible to feed power from the back side of the ground plane to the wave source at the center of the sample via a cable, and also to make it possible to take out the reception output from the receiving point outside the sample using a cable from the back side of the ground plane. This reduces the influence of the feeding part of the antenna on measurements to a negligible extent due to the imaging effect.

In order to further clarify the features and advantages of the present invention, preferred embodiments of the present invention will be described below with reference to the drawings.

〔Example〕

Fig. 1 shows the configuration of the main parts of the apparatus according to the present invention for measuring the magnetic field shielding effect, and Fig. 2 shows the structure of the main parts of the apparatus according to the present invention for measuring the electric field shielding effect. show. FIG. 3 is a block diagram of the measurement system.

In Figures 1 and 2, 1 is a test sample having the shape of a cup-shaped half formed by molding the conductive material to be measured, and the test sample 1 fits into the circular opening 3 of the flat metal plate 2. A hemispherical shell having the same outer diameter as the aperture is formed on the surface of the flat metal plate. Reference numeral 4 denotes a metal fitting, which is screwed into a socket 5 fixedly installed on the back surface of the metal flat plate 2 and attached to the opening 3, and crimps the lip flange portion 6 of the sample 1 to the back surface of the metal flat plate with its peripheral shoulder. The upper surface portion 7 is formed to be flush with the surface of the metal flat plate 2 in a fixed state. In this case, the outer diameter of the upper portion 7 is sized to match the inner diameter of the sample 1, and the opening 3 of the metal flat plate 2 is dimensioned to match the inner diameter of the sample 1.
The rim of the sample is held between them. still,
In order to ensure electrical contact between the flat metal plate 2, the sample 1, and the metal fitting 4, it is preferable to interpose mesh-like metal fittings made of a conductive material on the front and back surfaces of the mouth flange portion 6 of the sample 1. The center of the upper surface part 7 has a magnetic field shielding effect! 1! A half-loop antenna 8a as shown in FIG. 1 is used for measurement.

Alternatively, for measuring the electric field shielding effect, a monopole antenna 9a as shown in FIG. Monopole antenna 9 shown in Figure 2
b is erected.

The spacing between the antenna elements inside and outside the sample must be within a range that does not cause mutual induction between the antenna elements on the outside and the sample if the spacing is too narrow, and that the received output level is sufficient within the measurement frequency range. Set the reception sensitivity level.

The feeding points of these antenna elements are all located at the surface level of the metal flat plate, and connectors Ion, b, lla, and b are connected to these feeding points from the back side of the metal flat plate. Metal fittings 4
The connectors 10a and 11a in the antenna 10a transmit high frequency signals for measurement from the transmitter/receiver set 22 amplified by the power amplifier 21 shown in FIG.
, 11°. In FIG. 3, the system of FIGS. 1 and 2 is shown as a measurement chamber 20. In FIG. Receiving side antenna 8b
, 9b is sent to the signal analyzer 23 shown in FIG. 3 by a cable via connectors 10b and 11b.
Here, it is used to evaluate the shielding effect. The measurement results are recorded by a recording device 24.

Here, the evaluation calculation of the shielding effect by the analyzer 23 is as follows:
For example, you can do it as follows.

-How to find the electromagnetic field radiated from the antenna in m? Yo,
For example, the well-known Stratton's magnetic theory (J, Man, 5tratton + Electromagnet
ic Theory-McGrow 1lill 1
Using the vector wave function described in 941),
For the general solution of the wave equation in coordinates adapted to the target system,
It is obtained by introducing a boundary condition that satisfies the discontinuity of the faal field in the medium that exists there. Here, the electromagnetic field strength at any coordinate point is determined by applying a boundary condition that the tangential components of the electromagnetic field at the boundary surface are equal to the wave equation in polar coordinates.

In this invention, as mentioned above, the surface of the metal flat plate 2 provides a ground plane, and the half-shaped system including the sasiple on the front side and both antenna elements appears on the back side due to the image effect, with this ground plane as a boundary. Therefore, the half-split sample can be treated as a spherical sample. Therefore, the calculation of the electromagnetic field strength described above is performed when the conductive material to be measured is applied as a spherical shell, and when the conductivity is zero and the dielectric constant ε7=1. The relative magnetic permeability is μm-1, that is, the shielding effect is evaluated by taking the ratio of the magnetic field strength of both m and that of free space.
Let it be Jt1.

In other words, the magnetic field shielding effect S b is the magnetic field strength H0 when there is no sample and the magnetic field strength ■1 when there is a sample.
From ゜, Sh-201ag1. ) (t-t I/II
o). Similarly, the electric field shield effect SL,
From the magnetic field strength H when there is no sample and the magnetic field strength H0 when there is a sample, S , = 20 l
oguo (Et/Eo).

In addition, in the present invention, the dimensions of the sample and the dimensions of the antenna elements are such that each antenna element can be regarded as a minute antenna within the frequency range to be measured, and a resonance state does not occur.
It is desirable that the transmission characteristics between the antennas be determined so as to ensure as wide a dynamic range as possible.

FIGS. 4 and 5 show the results of measurements performed on a hemispherical sample with an inner diameter of 50 mm, which is a 3IIIm thick plastic sample coated with conductive paste. Although the solid lines in the figure are calculated values, good agreement can be seen when compared with measured values.

〔Effect of the invention〕

As mentioned above, 1. According to the present invention, the sample shape of the conductive material is made into a half body, and measurement is performed using the image effect on the ground plane, so that the cable connection to the antenna element is usually This method has the advantage that it is easy to perform and the influence of the power supply part is less likely to appear in the measurement results.
It is possible to provide a versatile measuring method and device for evaluating the shielding effectiveness of various conductive materials.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the configuration of the main parts of an apparatus according to an embodiment of the present invention for measuring magnetic field shielding effects, and FIG. 2 is a sectional view showing the main parts of an apparatus according to an embodiment of the invention for measuring electric field shielding effects. A sectional view showing the configuration, Figure 3 is a block diagram of the measurement system, and Figure 4 is a block diagram of the measurement system.
5 and 5 are diagrams showing an example of measurement results obtained by the method and apparatus of the present invention. In the figures, the same reference numerals indicate the same or equivalent parts, l is the test sample, 2 is the metal flat plate, 3 is the opening, 4 is the metal fitting, 5 is the socket, 1-16 is the flush part, 7 is the top part, 8a
, 8b is a half-loop antenna, 9a, 9b are monopole antennas, 10a, b and lla, b are connectors, 20
21 is a measurement chamber, 21 is a power amplifier, 22 is a transceiver set, 23 is an analysis device, and 24 is a recording device.

Claims (1)

[Scope of Claims] 1. A pair of micro antenna elements are erected at a predetermined distance on the surface of a grounded metal plate, and one of the antennas is arranged so as to produce an image effect on the back side of the metal plate. Power is fed from the back side of the metal flat plate to the power feeding point near the surface of the flat metal plate of the element, and an electric field or magnetic field wave is radiated to the front side of the metal flat plate, while receiving output from the power receiving point near the surface of the metal flat plate of the other antenna element. Similarly, take it out from the back side of the metal flat plate,
Furthermore, a test sample consisting of a cup-shaped half body made of a conductive material to be measured is placed on top of the one antenna element concentrically with the feeding point of the antenna element, and the entire periphery of the sample is covered with a metal flat plate. Reception output when grounded and the space between both antenna elements is continuous without placing the test sample, and when the test sample is placed and the space between both antenna elements is blocked by the test sample. A method for measuring the shielding effect of conductive materials, characterized by giving an evaluation of the shielding effect based on the ratio of the received output of the . 2. The measurement method according to claim 1, which continuously measures over a preset frequency range. 3. The measurement method according to claim 1, wherein the magnetic field shielding effect is measured using half-loop antennas for both antenna elements. 4. The measurement method according to claim 1, wherein the electric field shielding effect is measured using monopole antennas for both antenna elements. 5. A test sample consisting of a cup-shaped half body made of a conductive material to be measured, a metal flat plate having an opening that matches the outer circumference shape of the mouth edge of the sample, and a test sample that matches the inner circumference shape of the mouth edge of the test sample. A metal fitting that has a flat upper surface with an external shape and is attached to the flat metal plate from the back side of the metal flat plate so that the upper surface is flush with the surface of the metal flat plate, and the metal fitting is removably fixed to the metal flat plate from the back side. and a connecting mechanism capable of clamping and fixing the entire periphery of the sample mouth rim in a fixed state in the gap between the sample opening and the upper surface of the opening, and a central portion of the upper surface of the metal fitting so as to produce an image effect on the back side of the metal plate. a first micro antenna element erected; and a first micro antenna element erected at a predetermined distance away from the center of the opening on the surface of the flat metal plate so as to similarly produce an image effect on the back side of the flat metal plate; a second micro antenna element; a signal feeding means for feeding a high frequency signal from the back side of the metal flat plate to a feeding point near the surface of the metal flat plate of the first micro antenna element of the metal fitting; and the second micro antenna. Signal extraction means for extracting the received output from the power receiving point near the surface of the metal flat plate of the element on the back side of the metal flat plate; Signal output means for supplying the high frequency signal to the signal feeding means; Receiving the reception output from the signal extraction means. , Reception output when the test sample is not placed and the space between both antenna elements is continuous, and reception when the test sample is placed and the space between both antenna elements is blocked by the test sample. An apparatus for measuring the shielding effect of a conductive material, comprising: an analysis means for evaluating the shielding effect based on the ratio to the output. 6. The measuring device according to claim 5, wherein the test sample has a hemispherical shape on the surface of a flat metal plate. 7. The measuring device according to claim 5, wherein the test sample has a half-cubic shape on the surface of a flat metal plate. 8. The measuring device according to claim 5, wherein both antenna elements are half-loop antennas. 9. The measuring device according to claim 5, wherein both antenna elements are monopole antennas.