JPH08316679A - Electromagnetic shielding box and electric equipment having this case - Google Patents

Abstract

PURPOSE: To lessen radiation and entering of electromagnetic waves through opening sections without increasing the number of components by forming conductive structures which are so located as to surround the openings and which are electrically connected to the material which a case is made of. CONSTITUTION: An electromagnetic shielding case 1 is formed of such material as to have a conductivity. Openings of the case 1 are in the shape of a slit and are formed, for example, in three places in a left rear part of the box 1. On edges of each opening 2, plate-like conductive structures 3 are so formed as to be projecting inside the case 1 and surround the opening 2. These structures 3 are made, for example, by bending edges of the opening 2 inside the case 1 when making the opening 2 and thereby they are electrically connected to the case 1. In other words, the structures 3 are made of the same material as that of the case 1. By forming the structures 3 in this manner, there is no necessity of manufacturing or installing new components and the time and cost can be saved in manufacturing.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electric device and a housing thereof, and more particularly to an electric device having a function of preventing unnecessary electromagnetic radiation and a function of shielding an external electromagnetic wave and an electromagnetic shield housing thereof.

[0002]

2. Description of the Related Art Unwanted electromagnetic waves are radiated from electronic equipment such as information processing devices. This unnecessary electromagnetic wave propagates in the space and enters the surrounding equipment or oneself either directly or through a cable. As a result, noise may be generated and the information may be distorted, or the device may malfunction. Therefore, there are various regulations in and outside Japan regarding electromagnetic wave radiation from electronic devices that can be a noise source.

In Japan, information processing devices such as personal computers are subject to the Voluntary Control Council for Interference of Information Processing Devices (VCC
I) regulates radiated electromagnetic waves. If the electromagnetic wave emitted from the information processing device exceeds this regulation, it cannot be put on the market as a product. 2. Description of the Related Art In recent years, information processing devices have become faster and smaller, and noise is likely to occur, making it difficult to take measures against noise. Therefore, it takes time and money to develop and manufacture, and it has become difficult to provide a product satisfying the regulations of VCCI at low cost in a short period of time.

There is an electromagnetic shield as a means for reducing unnecessary electromagnetic radiation from electronic equipment such as an information processing apparatus and preventing external electromagnetic waves from entering the inside. A general electromagnetic shield is a method of covering a device or an electromagnetic wave source with a metal having good conductivity. The metal box for this is called a housing. Normally, the housing is made of metal plates, but there are always joints of metal plates, opening and closing parts such as doors, openings for intake of power supply / signal cables and ventilation / heat dissipation, and electromagnetic waves leak from here. It radiates or intrudes and becomes a gateway for noise. Therefore,
How to reduce leakage, radiation, and intrusion of interfering electromagnetic waves from such openings is a key point in designing the housing.

Conventional countermeasures against electromagnetic noise have been dealt with by using parts and members therefor. For example, in the prior arts described in Japanese Utility Model Laid-Open No. 1-116492, Japanese Patent Laid-Open No. 2-246200, and Japanese Patent Laid-Open No. 5-136592, a non-conductive material such as ferrite is provided in a wiring outlet formed in a housing made of a conductive plate. A member in which the magnetic material is formed in a ring shape is fitted and the wiring is inserted into the non-conductive magnetic material ring. However, such a conventional technique has a problem in that a member made of a material different from that of the housing has to be separately prepared, which increases cost. Further, this non-conductive magnetic material ring plays the role of a so-called noise filter, and eddy currents induced by high-frequency noise components flowing in the wiring flow into the non-electric ferrite and are attenuated, thereby reducing noise flowing in the wiring. It is a thing. That is, the noise that enters the electronic device through the wiring is reduced, and the effect of reducing the noise radiated from the electronic device is small.

Further, Japanese Patent Laid-Open No. 5-206671 discloses a structure in which the shield effect is improved by providing a shield material or a supporting member on the end surface of the door that is opened and closed so as to cover the opening of the housing. ing. In this structure, it is necessary to form a reinforcing portion on the end face portion of the door, further to provide a groove at a predetermined position of the reinforcing portion, and to hold the shield material by the groove, which makes the structure very complicated.

[0007] Japanese Patent Laid-Open No. 5-13979 discloses an electromagnetic shield as a means for suppressing leakage of electromagnetic waves by using it around a joint of a metal housing or around a door. This shield is made of a conductor having a groove formed therein and a magnetic body arranged in the groove. If this means is used as a countermeasure against electromagnetic noise, such a shield must be purposely manufactured and attached to the housing.

Japanese Unexamined Patent Publication No. 5-67892 discloses a high-frequency shield housing. In this high-frequency shield housing, a frame having an opening for housing and fixing an electronic device requires an outer case and an outer cover for housing them, in addition to a shield cover for closing the frame. In other words, this casing does not cover the electronic device doubly, and is not an efficient shield method.

As described above, in these conventional examples, it is necessary to create a new part for the shield and to attach the part to the housing. Therefore, the cost and process for developing and manufacturing the device ， Time has increased, housing,
Furthermore, it has the drawback that the equipment and devices become complicated and large.

[0010]

In a shield housing of an information processing apparatus such as a personal computer, it is necessary to prevent the electromagnetic wave from leaking, radiating or entering through the opening. On the other hand, small size,
Light weight and low cost devices are desired. In the conventional technology, it was necessary to create a new component for the shield or attach the component to the housing. In order for the device to satisfy the legal regulations and operate normally, it is essential to prevent the electromagnetic wave from leaking, radiating, and invading, but for that reason, the development / manufacturing cost, process, and time increase, and It is not desirable that the body and equipment become complicated and large. That is, it is necessary to reduce the leakage, radiation, and intrusion of electromagnetic waves by a low cost, a short development and production period, a small number of parts, an easy method, and an effective method.

An object of the present invention is to provide an electromagnetic shield housing and an electric device which can reduce the emission and intrusion of electromagnetic waves from the opening portion by a simple method without increasing the number of parts.

[0012]

SUMMARY OF THE INVENTION The above object is to provide an electromagnetic device having an electric device (for example, CPU, RAM, HDD, FDD, power source, etc.) therein and having at least one opening formed of a conductive plate material. The present invention is achieved by a personal computer having an electromagnetic shield housing, which is arranged so as to surround the opening and has a conductive structure electrically connected to a material forming the opening in the shield housing. .

Preferably, the conductive structure is made of the same material as the case. Preferably, the height of the conductive structure is 0.11 times or more the maximum dimension of the opening. Preferably, the conductive structure is provided at the edge of the opening.

[0014]

In the electromagnetic shield case made of a conductive material, when an electromagnetic wave enters the case, a current flows on the wall surface of the case. If there is an opening on the wall surface of the housing, the flow of the current is cut off there, and positive and negative charges are accumulated at both ends of the opening. In this case, the opening becomes a slot antenna, which becomes a new electromagnetic wave source and re-radiates the electromagnetic wave. In particular, the maximum size of the opening (for example,
In the slit-shaped opening, the emission is remarkably increased for electromagnetic waves having a wavelength such that the length of the slit) is half the wavelength.

Therefore, in order to reduce the emission of electromagnetic waves,
It is necessary to prevent the current flow on the surface of the housing from being interrupted by the opening. In the present invention, the structure having conductivity and electrically connected to the material forming the opening is arranged so as to surround the opening, so that current flows through the conductive structure. So that it is not cut off at the opening. That is, the current that has reached the opening flows through the conductive structure and flows around the opening. As a result, electric charge is not accumulated at both ends of the opening, and electromagnetic radiation by the slot antenna is prevented.

Further, if the electromagnetic shield housing has an opening, electromagnetic waves leak or enter through the opening. The leakage or invasion of electromagnetic waves can be reduced by arranging a conductive structure, which is electrically connected to the material forming the opening, so as to surround the opening, as in the present invention.

[0017]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the present invention will be described below with reference to the drawings. First, prior to the description of specific examples, the principle that the leakage or intrusion of electromagnetic waves from the opening can be reduced by providing the above-described conductive structure in the opening will be described.

When the conductive structure is regarded as a short waveguide, electromagnetic waves having a wavelength longer than a cutoff wavelength determined by the size of the waveguide are attenuated in the waveguide and cannot propagate. Therefore, when a waveguide of a certain length is attached to the opening, the electromagnetic wave is attenuated in the waveguide and does not leak or enter through the opening of the housing.

Specifically, the wavelength λ is the cutoff wavelength λ.
Electromagnetic waves above c are attenuated by exp (-ad) in the rectangular waveguide. Here, d is the distance traveled by the electromagnetic wave, and a is the attenuation constant represented by the following equation.

[0020]

[Equation 1]

In the rectangular waveguide, the longest cutoff wavelength λc
Is L, where L is the length of the longer side of the waveguide cross section.
There is a 2L relationship. Generally, it is recognized that the electric field is significantly attenuated when it is attenuated by 3 dB. Cutoff wavelength λc
In order for an electromagnetic wave having a longer wavelength λ to be attenuated by 3 dB, the electromagnetic wave must travel a distance d = 0.11L considering the limit when the wavelength λ is sufficiently long. On the contrary, if the wavelength λ is longer than the cutoff wavelength λc, no matter how long the wavelength of the electromagnetic wave is, it is 3 dB when traveling a distance of d = 0.11L.
Decay. In addition, since the length L is the length of the longer side of the waveguide cross section, in the case of the opening of the housing, replace with the maximum size of the opening (for example, the length of the slit in the slit-shaped opening). To be That is, the maximum dimension L of the opening is 0.11
If a structure with a height more than double is attached, all electromagnetic waves with a wavelength of λ = 2L or more will be attenuated by 3dB or more.

In order to confirm the above operation, the result of a numerical simulation example performed on an electromagnetic shield casing having a slit-shaped opening will be described. In this simulation example, an electromagnetic wave source is arranged inside an electromagnetic shield casing 1 made of a conductor as shown in FIG.
The amount of electric field leaking is calculated at a point 3 m away from the housing 1.

Calculation results of this simulation example are shown in FIG.
Shown in The horizontal axis represents the frequency, and the vertical axis represents the shield amount, that is, the electric field amount reduced by the housing 1. For comparison, the calculation results when the structure 3 is not installed on the edge of the opening 2 are also shown. The white circle marks are used in this embodiment, and the opening 2
The calculation results for the electromagnetic shield housing having the structure 3 arranged on the edge of the, and the black circles indicate the calculation results for the electromagnetic shield housing in which the structure is not installed. Looking at the case where there is no structure (black circle), it can be seen that there is no shielding effect at a frequency of 500 MHz and electromagnetic waves are radiated and leaked significantly from the slit. This is
This is because the opening radiates (resonates) most electromagnetic waves as a slot antenna at 500 MHz.

On the other hand, looking at the results when the structure 3 is present (white circles), there is a shielding effect of about 10 dB at 500 MHz, and when the structure is not installed, the opening that is remarkably seen at this frequency is seen. It can be seen that the radiation and leakage from is reduced. Compared to the case where there is no structure at frequencies other than 500 MHz, the shielding effect is improved, and the above-mentioned effect was confirmed. Even if the size or shape of the opening is different from that of this simulation example, it is not possible to obtain the same effect of reducing the radiation / leakage of electromagnetic waves based on the above action, only by the frequency at which the opening resonates. no change.

According to this simulation result, the structure having conductivity and electrically connected to the material forming the opening is arranged so as to surround the opening, whereby the electromagnetic wave at the opening is prevented. It can be seen that radiation, leakage and intrusion can be prevented and reduced.

FIG. 1 is a perspective view of an electromagnetic shield housing used in an electronic device according to an embodiment of the present invention, as viewed from the front right diagonally above. As shown in the schematic diagram of FIG. 4, electronic devices provided inside include a board 11 on which a CPU and a RAM are mounted, an HDD 12, an FDD 13, and a power supply 14, which are connected to each other. The housing 1 surrounds them, but the opening 2 is provided for heat dissipation and ventilation.
There is also a cable 16 for connecting to an external CRT 15 or the like.

In FIG. 1 and the figures used in the following description,
Parts inside the housing, wiring, external CR
T and cables are omitted, and a perspective view of only the housing is shown. For easier viewing, the opening of the housing and the conductive structure are shown in an exaggerated and larger size than they actually are.

In the embodiment shown in FIG. 1, the electromagnetic shield casing 1 is made of a conductive material, and the opening 2 has a slit shape, and there are three places on the left rear side of the casing 1. Plate-shaped conductive structures 3 are provided on the respective edges of the openings 2 so as to surround the openings 2 so as to project inside the housing 1. The structure 3 is formed, for example, by bending the edge of the structure 2 inside the housing 1 when forming the opening 2, and is electrically connected to the housing. That is, the structure 3 is made of the same material as the case 1. When the structure 3 is formed in this way, there is no need to manufacture or attach new parts, and the manufacturing does not take time or cost. Further, by such a simple method, it is possible to prevent the current flow on the housing surface from being interrupted, and as a result, it is possible to reduce the radiation, leakage, and intrusion of electromagnetic waves from the opening 2.

It should be noted that when the opening 3 is punched out with a mold, what is called a burr can be formed on the edge, but a normal burr has a low height and does not have an electromagnetic shielding effect. That is, the burr is lower than 0.11 times the length L of the long side of the opening, and the electromagnetic shield does not work in principle.

In this embodiment, the conductive structure 3 is formed by bending the edge of the opening 2 of the housing 1. However, the same material as that of the housing or another conductive plate material is used to form the opening. It may be electrically connected to the housing 1 by brazing the edge of the portion later. Further, the conductive structure 3 shown in FIG. 1 has a strip shape, but is not limited to this shape. For example, the edge of the opening may be surrounded by a wall-shaped or convex member that is thicker than the band. In this case, all of the wall-shaped member and the convex member may be formed of a conductive member, or only the surface thereof may be coated with a conductive paint. The same applies to the following embodiments.

FIG. 5 is a perspective view of an electromagnetic shield casing according to the second embodiment of the present invention. In this embodiment, three openings 2 of the electromagnetic shield casing 1 are collectively formed into a conductive structure 3.
Surrounded by. The structure 3 is made of the same conductive material as the case, and is electrically connected to the case. As described above, even if the plurality of openings are collectively surrounded by the structure, the amount of electromagnetic waves radiated by the above-described action can be reduced. Of course, the number of openings is not limited to three, and two or more openings may be enclosed together in the same manner. The structure 3 may be electrically connected to the housing by using another conductive material different from the housing.

FIG. 6 is a perspective view of an electromagnetic shield casing according to the third embodiment of the present invention. In this embodiment, the electromagnetic shield housing 1 is provided with a plurality of circular openings 4.
Even if the opening has a circular shape as in this embodiment, as shown in FIG. 6, the circular opening 4 is surrounded by the structure 3 made of a conductive material and electrically connected to the housing 1. You can do it.

FIG. 7 is a perspective view of an electromagnetic shield casing according to the fourth embodiment of the present invention. In this embodiment, the opening 5 is
An example is shown in which two of the six planes forming the electromagnetic shield housing 1 are straddled. Also in this case, similarly to the above-described embodiment, the structure 3 made of a conductive material may be provided so as to surround the opening 5 and be electrically connected to the housing. As described above, the present invention is effective not only when the opening is on one plane but also when it is present over a plurality of planes. In the present embodiment, the number of planes over which the opening 5 extends is two, but the number of planes over which the opening 5 extends is not limited to this, and may be three or more.

FIG. 8 is a perspective view of an electromagnetic shield casing according to the fifth embodiment of the present invention. In this embodiment, the structure 3 is installed outside the electromagnetic shield housing 1. FIG. 8 shows such a state by a diagram as seen from diagonally above the back right of the housing. Also in this embodiment, as in the above-described embodiments, the structure 3 made of a conductive material surrounds the opening 2 and is electrically connected to the housing 1. Even when the structure is installed outside the housing as in the present embodiment, there is an effect of reducing the radiation, leakage and intrusion of electromagnetic waves.

In each of the above embodiments, the shape of the structure 3 is band-shaped, but the shape is not limited to this. The side of the structure 3 that is not connected to the electromagnetic shield housing 1 may be a straight line, a curved line, a polygonal line, or the like. That is, the height of the structure 3 does not have to be constant. Further, the thickness of the structure 3 does not have to be constant. The structure 3 may be made of a conductive material and may be electrically connected to the electromagnetic shield housing 1. Furthermore, the electromagnetic shield housing 1 and the structure 3 do not necessarily have to be formed of only a conductive material (for example, aluminum). For example, plastic may be plated, conductive paint may be applied, conductive tape or sheet may be attached, etc., and may be formed of a conductive material so that an electric current flows on the surface. Good. Further, in the above embodiment, the opening has a slit shape or a circular shape, but the shape is not limited to this. Whatever the shape of the opening, it is sufficient if the structure exists so as to surround the opening and is electrically connected to the housing. Further, the shape of the electromagnetic shield housing is not limited to the rectangular parallelepiped shape as in the above embodiment,
The effect of the present invention can be obtained in any shape and size.

[0036]

According to the present invention, the radiation, leakage, and intrusion of electromagnetic waves from the opening of the electromagnetic shield housing can be reduced easily without increasing the number of parts, and in an effective way without spending time and cost. It becomes possible to do.

[Brief description of drawings]

FIG. 1 is a perspective view of an electromagnetic shield housing according to a first embodiment of the present invention.

FIG. 2 is a diagram of an electromagnetic shield housing in a numerical simulation performed to confirm the operation of the present invention.

FIG. 3 is a graph showing a result of a numerical simulation example performed for confirming the operation of the present invention.

FIG. 4 is a schematic diagram showing an example of an internal configuration of an electronic device.

FIG. 5 is a perspective view of an electromagnetic shield housing according to a second embodiment of the present invention.

FIG. 6 is a perspective view of an electromagnetic shield housing according to a third embodiment of the present invention.

FIG. 7 is a perspective view of an electromagnetic shield housing according to a fourth embodiment of the present invention.

FIG. 8 is a perspective view of an electromagnetic shield housing according to a fifth embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Electromagnetic shield housing, 2 ... Opening part, 3 ... Conductive structure, 4 ... Circular opening part, 5 ... Opening part which extends over two planes, 11 ... CPU, RAM mounting board, 12 ... HDD,
13 ... FDD, 14 ... Power supply, 15 ... CRT, 16 ... Cable.

Claims (14)

[Claims] 1. An electromagnetic shield housing formed of a conductive plate material for accommodating electric parts therein, wherein the opening provided in the conductive plate material and the conductive material standing upright so as to surround the edge of the opening. And a strip-shaped conductive structure that makes electrical contact with the flexible plate material, and the height of the conductive structure is at least 0.11 times the maximum dimension of the opening. 2. The electromagnetic shield housing according to claim 1, wherein a wall-shaped or convex conductive structure having a thickness is used instead of the band-shaped conductive structure. 3. The electromagnetic shield housing according to claim 1 or 2, wherein the conductive structure is formed by bending the conductive plate material forming the electromagnetic shield housing. 4. The conductive structure according to claim 1 or 2, wherein the conductive structure is formed as a member different from the conductive plate material forming the electromagnetic shield casing and is attached to the opening. Characteristic electromagnetic shield housing. 5. The electromagnetic shield housing according to claim 4, wherein the main body of the conductive structure is made of a non-conductive member and the surface thereof is coated with a conductive material. 6. An electromagnetic shield housing formed of a conductive plate material for housing electric parts therein, wherein a plurality of adjacent openings provided in the conductive plate material and a plurality of adjacent openings are surrounded inside. And a strip-shaped conductive structure that stands upright and makes electrical contact with the conductive plate material. 7. The electromagnetic shield casing according to claim 6, wherein a wall-shaped or convex conductive structure having a thickness is used instead of the strip-shaped conductive structure. 8. The electromagnetic shield housing according to claim 1 or 2, wherein the conductive structure is formed by bending the conductive plate material forming the electromagnetic shield housing. 9. The electromagnetic shield casing according to claim 6 or 7, wherein the conductive structure is formed as a member different from the conductive plate material forming the electromagnetic shield casing. body. 10. The electromagnetic shield casing according to claim 9, wherein the main body of the conductive structure is made of a non-conductive member and the surface thereof is coated with a conductive material. 11. The electromagnetic shield casing according to claim 6, wherein the height of the conductive structure is at least 0.11 times the maximum dimension of the opening. 12. An electric device comprising the electromagnetic shield casing according to claim 1 and an electric component mounted inside the electromagnetic shield casing. 13. The electric device according to claim 12, wherein the electric component includes an electronic device that operates at a high frequency. 14. The electric component according to claim 12, wherein the electric component is C
An electric device comprising a personal computer including a PU, a RAM, a HDD, an FDD, and a power supply.