JP2007139750A - Method and device for estimating leakage of electromagnetic wave - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electromagnetic-wave leakage estimation method and device for estimating the intensity of a leakage electromagnetic wave easily at high precision. <P>SOLUTION: The positions and shapes of current-carrying portions produced between a metal plate and another metal plate are measured in such a state that the metal plates are lapped mutually, and the intensity of an electromagnetic wave leaking through the gap between the metal plates is estimated from the maximum interval out of the intervals among the current-carrying portions, and the length of the current-carrying portions with respect to the direction of transmission of the electromagnetic wave. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an evaluation method and apparatus for leakage of electromagnetic waves from an electronic circuit incorporated in an OA / electrical product or the like.

  OA / electrical products are required to shield leakage electromagnetic waves from electronic circuits built into the products. This is because leaked electromagnetic waves may not only cause other OA / electrical products to malfunction, but may also cause electronic devices such as cardiac pacemakers to malfunction and affect people using them. is there.

  In order to reduce the strength of the leaked electromagnetic wave, it is widely performed to surround the transmission source with a conductor and block the electromagnetic wave. For example, in the case of an electromagnetic wave shielding room, walls, floors, and ceilings are covered with a conductive sheet for electromagnetic wave shielding to suppress leakage of electromagnetic waves. Further, in electronic devices such as computers, leakage of electromagnetic waves is suppressed by covering a circuit serving as a transmission source with a metal box.

  However, when the transmission source is surrounded by a metal box, there is a problem that a gap is formed unless electromagnetic waves are leaked from the overlapped portion unless a continuous joining such as welding is performed on the overlapping portion of the metal plates. In general, it is widely known that the strength of electromagnetic waves leaking can be reduced by ensuring electrical continuity at the gaps.

For example, Patent Document 1 discloses an electromagnetic wave shielding technique that suppresses leakage of electromagnetic waves by keeping the peripheral edge of the opening of the electromagnetic wave shielding chamber and the peripheral edge of the closing member energized and preventing the flow of electricity. ing. Patent Document 2 discloses a technique for covering a sheet-like conductive sheet around a sponge-like core material as an electromagnetic shielding gasket. Furthermore, Patent Document 3 discloses a technique for covering an elastic body with a conductive cloth.
Japanese Utility Model Publication No. 3-98 Japanese Patent Laid-Open No. 10-93281 JP-A-10-284869

  The techniques described in Patent Documents 1 to 3 are all for ensuring energization at the contact portion. However, although these may improve the energization at the contact portion and reduce the leakage electromagnetic wave to a considerable extent, they are generally inconsistent and cannot be said to be a complete electromagnetic wave shielding technique. This is because the mechanism of electromagnetic wave leakage is not clear, and the factors affecting electromagnetic wave leakage cannot be quantitatively evaluated. In order to evaluate these electromagnetic wave shielding technologies, leakage electromagnetic waves can be easily and accurately detected. There is a need for a technique for evaluating the influencing factors.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to provide an electromagnetic leakage evaluation method and apparatus for evaluating factors that affect leakage electromagnetic waves in a simple and highly accurate manner.

  The invention according to claim 1 of the present invention measures the position and shape of the current-carrying portion generated between the metal plates in a state where the metal plate and the metal plate are overlapped, and sets the maximum distance among the intervals between the current-carrying portions. This is an electromagnetic wave leakage evaluation method characterized by evaluating the intensity of electromagnetic waves leaking through the gaps between the metal plates.

  Further, the invention according to claim 2 of the present invention is to measure the position and shape of the current-carrying portion generated between the metal plates in a state where the metal plate and the metal plate are overlapped, and to determine the maximum interval among the intervals between the current-carrying portions. And the strength of the electromagnetic wave leaking through the gap between the metal plates based on the length of the current-carrying part with respect to the direction in which the electromagnetic wave is transmitted.

  According to a third aspect of the present invention, in the electromagnetic wave leakage evaluation method according to the first or second aspect, a current is passed between the metal plates, and a potential distribution generated on the metal plate surface is measured. It is an electromagnetic leakage evaluation method characterized by measuring the position and shape of a current-carrying part.

  The invention according to claim 4 of the present invention is the electromagnetic wave leakage evaluation method according to claim 3, wherein a plurality of conductors are connected to the surface of the metal plate, and a potential difference between the conductors is measured. An electromagnetic wave leakage evaluation method characterized by measuring a potential distribution on a metal plate surface.

  According to claim 5 of the present invention, in the electromagnetic wave leakage evaluation method according to claim 3 or 4, the current density distribution is obtained from the potential distribution on the surface of the metal plate, and the divergence of the obtained current density distribution is obtained. This is a method for evaluating electromagnetic wave leakage, wherein a portion where the value of is negative or positive is judged as an energized portion and electromagnetic wave leakage is evaluated.

  The invention according to claim 6 of the present invention is the electromagnetic wave leakage evaluation method according to any one of claims 1 to 5, wherein the metal plate is a steel plate. It is an evaluation method.

  Furthermore, the invention according to claim 7 of the present invention includes a conductive wire connected to the surface of the metal plate in a state where the metal plate and the metal plate are overlapped, a potentiometer that measures a potential difference between the conductive wires, and the potentiometer. Obtain the potential distribution on the surface of the metal plate from the measured potential difference, calculate the position and shape of the current-carrying part generated between the metal plates, and transmit the electromagnetic wave at the maximum interval among the current-carrying parts. An evaluation device for electromagnetic wave leakage, comprising: an arithmetic device that evaluates the intensity of electromagnetic waves leaking through a gap between metal plates based on the length of the energization portion with respect to a direction.

  In the present invention, the position and shape of the current-carrying part are measured, and the strength and the length of the current-carrying part are obtained to evaluate the strength of the electromagnetic wave. Therefore, the strength of the leaked electromagnetic wave can be evaluated easily and with high accuracy. .

  FIG. 1 is a diagram schematically showing an electromagnetic wave that passes through a portion where a metal plate and a metal plate are overlapped. In the figure, 1 is a metal plate, 2 is an electromagnetic wave (input), 3 is an electromagnetic wave (output), and 4 is an energizing part.

  When the electromagnetic wave permeate | transmits the part which piled up the metal plate 1 and the metal plate 1 (entering as electromagnetic wave (input) 2 and going out as electromagnetic wave (output) 3), the present inventors are with respect to the direction which electromagnetic waves permeate | transmit. Thus, it has been found that the shorter the interval d between the energization parts and the longer the length l of the energization part, the greater the attenuation of the electromagnetic wave and the weaker the intensity of the leaking electromagnetic wave. From this knowledge, it was found that the position and shape of the current-carrying part between the metal plates were specified, and the strength of the leaked electromagnetic wave could be evaluated by the maximum distance d between the current-carrying parts and the length l of the current-carrying part.

  However, in general, it is very difficult to measure an event occurring at the interface where two objects are overlapped. In this case as well, it is not possible to specify the position and shape of the current-carrying part at the interface where the metal plates overlap. It is very difficult. In order to measure the position and shape of the current-carrying part, metal plates are stacked and current is passed between them, (1) the temperature distribution on the plate surface is measured, and (2) the magnetic field distribution on the plate surface is measured. Measurement (3) A method such as measuring the potential distribution on the plate surface can be considered.

  However, in the method (1), when the area of the energization part is widened, the heat generation density is reduced due to the decrease in the current density, and the temperature rise is very small, so that measurement is often difficult. In the case of the method (2), the magnetic field generated by the current is very small, and it is very difficult to measure the magnetic field generated by the current without being affected by the geomagnetism. In addition, when measuring a magnetic field on the surface of a magnetic material such as a steel plate, the influence of the residual magnetism of the magnetic material is large, making measurement more difficult.

  When the method (3) is adopted, when the metal plate and the metal plate are overlapped, the potential of the plate placed on the upper side is made higher than the potential of the plate placed on the lower side, and a current is passed, the upper plate It is theoretically calculated that on the surface, the electric potential in the vicinity of the energized portion is lower than the surrounding area. In the case where the plate is a metal having high conductivity (low resistance), this potential difference is reduced when the value of current flowing between the metal plates is small. For example, when a current of about several A is passed between the metal plates, the potential distribution on the plate surface is measured with an accuracy of about μV.

  When the current passed between the metal plates is increased, the potential difference increases and the measurement becomes easy. In general, when a large current of about 10 A or more is passed, the power supply becomes large and the cost of measurement increases. Furthermore, since heat generation in the wiring and the board also increases, it is preferable to flow a small current.

  For measuring the potential distribution on the surface of the plate, there are a method in which the probe is brought into contact with the surface of the plate, a method in which a lead wire is directly connected to the plate surface, and a potential is measured by the lead wire. In the case of the former method, the contact resistance varies greatly depending on the contact state between the plate surface and the probe, so that the potential tends to vary greatly. On the other hand, using the latter method, the present inventors have found that the potential distribution can be measured with an accuracy of about several μV, and the position and shape of the current-carrying portion between the metal plates can be measured.

  From the measured potential distribution, the portion where the potential is minimum (or maximum) can be determined as the energized portion. A method for obtaining the energized portion more accurately will be described below.

  Let V (x, y) be a two-dimensional (x, y) potential distribution measured on the plate surface. If the conductivity of the plate is σ, the current density distribution (i (x, y)) is given by equation (1).

  Further, the divergence is obtained from the current density distribution as shown in the following equation (2).

  In the portion where the divergence value is negative, the current is absorbed, and in the portion where the divergence value is positive, the current is generated. In this way, the current density distribution is obtained from the potential distribution, and the portion where the divergence is negative (or positive) can be regarded as the energization portion.

  Example 1 of the present invention is shown below. FIG. 2 is a diagram for explaining a method for measuring leakage of electromagnetic waves and a method for evaluating a current-carrying unit. The upper diagram shows a top view and the lower diagram shows a side view. In the figure, 5 is a shield box, 6 is a transmitter, 7 is an antenna, 8 is a receiver, 9 is a welded part, 10 is an insulating part, and 11 is an energization measuring part.

  The transmitter 6 is placed in a box-shaped shield box 5 and the intensity of the electromagnetic wave 3 leaking from the edge having a width of 70 mm and a length of 50 mm is measured together with the state of the current-carrying part. (f). The material of the shield box 5 is an electrogalvanized steel sheet having a thickness of 1.2 mm. The edge part (welded part 9) of the edge is welded, and there is no leakage of electromagnetic waves from here. Further, an insulating sheet having a thickness of 50 μm was sandwiched 10 mm inside (hatched portion in the figure) from the edge so that no current was applied (insulating portion 10). The electromagnetic wave (output) 3 from the energization measuring unit 11 other than the insulating unit 10 was measured by the receiver 8 via the antenna 7 separated from the transmitter 6 by 3 m.

Next, the intensity of the electromagnetic wave is evaluated as follows. FIG. 3 is a diagram showing measurement of the reference intensity (Est (f)) of electromagnetic waves. As shown in the figure, when a 50 μm insulating sheet is sandwiched between the entire edge (width 70 mm, length 50 mm), the intensity of the electromagnetic wave measured from the edge is taken as the reference intensity. The reference intensity is measured for each frequency to be measured, and the reference intensity is set to Est (f) (f: frequency).
Here, E (f) / Est (f) (electromagnetic wave intensity / electromagnetic wave reference intensity) was used as an index for evaluating the electromagnetic wave intensity.

  Furthermore, the evaluation method of the state of a conduction point is demonstrated. First, as shown in FIG. 2, the distance (d1, 2, 3, 4) between the energization parts is obtained, and the distance (d3) farthest from the distance is set as the maximum interval between the energization parts. Further, as an example of the length of the energization part with respect to the direction in which the electromagnetic wave is transmitted, the length la of the energization part projected on the perpendicular line drawn on the straight line (13) connecting the energization parts between the largest energization parts, lb is obtained, and the shorter one (lb) is defined as the length of the energizing portion.

  FIG. 4 is a diagram illustrating a method for measuring a potential distribution. Conductive wires 12 were connected to the edge of the shield box 5 by soldering at intervals of 5 mm × 5 mm. A voltage was applied between the edge plates and a current of 4 A was applied. Then, the potential difference with respect to the conductor indicated as “Ground” in the figure was measured for each conductor to obtain the potential distribution. FIG. 5 is a diagram illustrating an example of the measurement result of the potential distribution. At points a, b, and c in the figure, the potential is a minimum value lower than that of the surroundings, and it can be seen that this is an energizing portion.

  FIG. 6 shows the relationship between the position and the shape of the energization part, the interval and length of the energization part, and the relationship between these and the intensity of the electromagnetic wave.

  Intensity of leaked electromagnetic waves due to the maximum interval d (interval between a and b in FIG. 5) when the energization portion length is 5 mm (in FIG. 5, the magnitude of a is determined at a potential of −50 μV) The change in electromagnetic wave intensity / electromagnetic wave reference intensity is shown in FIG. It turns out that the intensity | strength of electromagnetic waves becomes weak, so that the maximum space | interval of an electricity supply part becomes small.

  As described above, the position and shape of the current-carrying part between the metal plates are specified, and the relationship shown in FIG. 6 is based on the maximum distance d between the current-carrying parts and the length l of the current-carrying part obtained therefrom. The intensity of electromagnetic waves leaking indirectly can be specified instead of directly measuring electromagnetic waves leaking using an arithmetic device (not shown).

  FIG. 7 shows the change in electromagnetic wave (output) due to d (maximum distance between the energized portions) in FIG. 1 (the energized portion length l = 30 mm). When d = 0 mm, the electromagnetic wave transmitted between the plates is hardly measured. It can be seen that when the maximum distance d between the current-carrying parts is widened to 40, further 80 mm, the intensity of the transmitted electromagnetic wave increases and the lower limit value of the frequency of the transmitted electromagnetic wave decreases. Thus, when the length (= l) of the current-carrying part is 30 mm and the maximum distance d between the current-carrying parts is measured to be 0, 40, 80 mm, etc., the strength of the electromagnetic wave leaking through the gap between the plates is evaluated. it can.

As shown in FIG. 8, the potential distribution of the edge having a width of 100 mm and a length of 35 mm is measured to obtain the energized portion.
Electromagnetic waves transmitted between the plates were measured. The potential distribution in the case of (State-1) and (State-2) is shown in FIGS. It can be seen that the white arrow indicates that the potential is minimal and that the current-carrying portion is formed. The maximum distance between the energization points was 80 mm in (State-1) and 60 mm in (State-2).

  The frequency characteristics of the electromagnetic waves transmitted between the plates in each case are shown in FIGS. In the case of (State-2), the intensity of the electromagnetic wave is weaker than in the case of (State-1). That is, when the maximum distance between the energization points is reduced, the intensity of the electromagnetic wave transmitted between the plates decreases, and it is understood that the intensity of the electromagnetic wave transmitted from the maximum distance between the energization points can be evaluated.

  FIG. 13 shows the potential distribution on the plate surface measured when plates are stacked and current is passed. FIG. 14 shows the distribution of current density obtained from this potential distribution and the distribution of divergence calculated therefrom. The portion (arrow) where the divergence is negative is considered to be a current-carrying portion between the plates.

It is a figure which shows typically the mode of the electromagnetic wave which permeate | transmits the part which accumulated the metal plate and the metal plate. It is a figure explaining the measuring method of electromagnetic wave leakage, and the evaluation method of an electricity supply part. It is a figure which shows the measurement of the reference | standard intensity | strength (Est (f)) of electromagnetic waves. It is a figure explaining the measuring method of potential distribution. It is a figure which shows the example of a measurement result of electric potential distribution. It is a figure which shows attenuation | damping of the electromagnetic wave by the largest space | interval of an electricity supply part. It is a figure which shows the change of the frequency characteristic of the electromagnetic waves by the largest space | interval of an electricity supply part. It is a figure which shows the measurement conditions of electric potential distribution. It is a figure which shows electric potential distribution (state-1). It is a figure which shows electric potential distribution (state-2). It is a figure which shows the characteristic (state-1) of the measured electromagnetic wave. It is a figure which shows the characteristic (state-2) of the measured electromagnetic wave. It is a figure which shows electric potential distribution. It is a figure which shows distribution of the divergence of an electric current density.

Explanation of symbols

1 Metal plate 2 Electromagnetic wave (input)
3 Electromagnetic waves (output)
4 Current-carrying part 5 Shield box 6 Transmitter 7 Antenna 8 Receiver 9 Welding part 10 Insulating part 11 Current-measuring part 12 Conductor

Claims (7)

Measure the position and shape of the current-carrying parts that occur between the metal plates with the metal plates stacked, and leak the gaps between the metal plates based on the maximum distance between the current-carrying parts. An evaluation method of electromagnetic wave leakage characterized by evaluating the intensity of electromagnetic waves. With the metal plate and the metal plate being overlapped, the position and shape of the energization part generated between the metal plates are measured, and the maximum interval of the intervals between the energization units and the direction of transmission of the electromagnetic wave to the electromagnetic wave transmission direction. An electromagnetic wave leakage evaluation method characterized by evaluating the strength of an electromagnetic wave leaking through a gap between metal plates based on the length. In the evaluation method of electromagnetic wave leakage according to claim 1 or 2,
An electromagnetic wave leakage evaluation method characterized by measuring the position and shape of a current-carrying portion by passing a current between the metal plates and measuring a potential distribution generated on the surface of the metal plate. In the electromagnetic wave leakage evaluation method according to claim 3,
An electromagnetic wave leakage evaluation method, comprising: measuring a potential distribution on a surface of the metal plate by connecting a plurality of conductive wires to the surface of the metal plate and measuring a potential difference between the conductive wires. In the evaluation method of electromagnetic wave leakage according to claim 3 or claim 4,
An electromagnetic wave characterized in that a current density distribution is obtained from a potential distribution on the surface of a metal plate, and an electromagnetic wave leakage is evaluated by determining a portion where the divergence value of the obtained current density distribution is negative or positive as a current-carrying part. Leakage assessment method. In the electromagnetic wave leakage evaluation method according to any one of claims 1 to 5,
The method for evaluating electromagnetic wave leakage, wherein the metal plate is a steel plate. In a state where the metal plate and the metal plate are stacked, a conductive wire connected to the surface of the metal plate,
A potentiometer for measuring the potential difference between the conductors;
Obtaining the potential distribution on the surface of the metal plate from the potential difference measured by the potentiometer, calculating the position and shape of the energization portion generated between the metal plates, the maximum interval among the intervals between the energization portions, An arithmetic device that evaluates the strength of the electromagnetic wave leaking through the gap between the metal plates, based on the length of the energization part with respect to the direction in which the electromagnetic wave is transmitted;
An apparatus for evaluating leakage of electromagnetic waves, comprising: