JPH04317399A - Electromagnetic shield - Google Patents

Abstract

PURPOSE:To obtain a sufficient shielding effect for leakage of an electromagnetic wave for use in a seam of a metal housing or a periphery of a door. CONSTITUTION:One row or a plurality of rows of grooves are formed partly on a contact part with a conductor in a conductive shielding material 3 having an elasticity for suppressing leakage of an electrostatic field in contact with the conductor, and a rodlike magnetic element 2 is so buried integrated as to coincide with the groove. Since the part fill with the element 2 is increased in its surface impedance, a high frequency current to be leaked from the contact surface can be suppressed.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to an electromagnetic shield for suppressing unnecessary electromagnetic waves emitted from electronic equipment and for use in electromagnetic shielding rooms to prevent leakage and intrusion of electromagnetic waves, particularly at joints of metal casings. The present invention relates to an electromagnetic shielding body that is used in the door of an electromagnetic shielding room to suppress electromagnetic waves leaking from joints or gaps around the door.

0002

[Prior Art] When providing electromagnetic shielding, generally conductors such as metals have low conductivity in some areas where they come into contact with each other.
Electromagnetic waves tend to leak, and it is necessary to install electromagnetic shields at the contact points between conductors such as metal to suppress leaking electromagnetic waves.

Conventionally, this type of electromagnetic shielding body has a shielding finger 1 formed of a comb-shaped metal piece as shown in FIG.
1, or a conductive shielding material such as an EMI gasket 12 made of conductive rubber in the form of a tube as shown in FIG. The electromagnetic shield shown in Fig. 6 uses the spring action of a metal piece, and the electromagnetic shield shown in Fig. 7 uses the elasticity of conductive rubber to connect the conductors to each other. The aim was to improve its electrical conductivity.

0004

[Problem to be solved by the invention] However, FIGS. 6 and 7
The conductive electromagnetic shield shown in FIG.
1. The contact resistance between the gasket 12 and the housing, the attachment part of the electromagnetic shielding room, or the shield finger 11 or the conductor part that comes into contact with the gasket 12 affects the electromagnetic wave leakage effect, so the contact is strengthened. A mechanism was needed to do so.

Furthermore, when the shield fingers 11 and gaskets 12 are used, changes in spring action and elasticity over time have led to a decrease in the shielding effect.

[0006] Furthermore, when a low-impedance electromagnetic wave source of a large current and low voltage type is used, the shielding effect becomes smaller in the low frequency band (see Institute of Electronics, Information and Communication Engineers, Environmental Electromagnetic Engineering Research Group Technical Research Report, EMCJ90-48). There were problems such as:

An object of the present invention is to provide an electromagnetic shield for use around the joints and doors of metal casings to suppress leakage of electromagnetic waves, which does not require any special mechanism to strengthen contact. Another object of the present invention is to provide an electromagnetic shielding body capable of obtaining a sufficient shielding effect in a low frequency band even against a low-impedance electromagnetic wave source.

[0008]

[Means for Solving the Problems] In order to achieve the above object, an electromagnetic shielding body according to the present invention is an electromagnetic shielding body having a conductive shielding material and a rod-shaped magnetic body, the electromagnetic shielding body comprising:
The conductive shielding material has elasticity and is installed in the gap formed between the conductors, and the rod-shaped magnetic material is
It is provided integrally with a contact portion of a conductive shielding material that comes into contact with a conductor, and places the contact portion in a state where a surface impedance is loaded.

[0009]

[Operation] As shown in FIG. 5(a), the conductive shielding material 10
is in contact with the conductor 14, the conductive shielding material 1
At the contact portion between 0 and the conductor 14, the contact resistance is greater than the resistance on the surface of the conductor. This is shown in an equivalent circuit in Figure 5 (
b) Since the contact resistance Rc between the conductive shielding material 10 and the conductor 4 is larger than the surface resistance Rs of the conductor 14 surface, most of the high frequency current Ie flowing through the conductor surface is
Flows on the surface of a conductor with low resistance. This high frequency current Ie causes leakage electromagnetic waves. In the structure in which the magnetic material 2 is embedded in a part of the part of the conductive shielding material 1 that contacts the conductor 4 as shown in FIG. 4(a), the contact part has a surface as shown in the equivalent circuit of FIG. Impedance (Rf+jXf:j=√
-1) is equivalent to the loaded state. If a material with high magnetic permeability is used as the magnetic body, the surface impedance will increase, and most of the high frequency current Ie flowing on the conductor surface will be guided to the conductive shielding material side, making it possible to suppress leakage of electromagnetic waves. Since the surface impedance (Rf+jXf) is almost determined by the characteristics of the magnetic material used, the influence of contact resistance on leakage current is small. Since the shielding body according to the present invention has a greater effect of suppressing leakage current than conventional conductive shielding materials, it can significantly improve the shielding effect of low-impedance wave sources that are relatively likely to generate induced currents.

0010

Embodiments Hereinafter, embodiments of the present invention will be described with reference to the drawings.

(Embodiment 1) FIG. 1 is a perspective view showing Embodiment 1 of the present invention.

In the figure, the electromagnetic shielding body 1 of this embodiment has an elastic conductive shielding material 3 having a rectangular cross section, and a row of long grooves 3b are formed in the contact end surface 3a of the conductive shielding material 3 with the conductor. It has a structure in which the rod-shaped magnetic body 2 is embedded and integrated into the long groove 3b. The rod-shaped magnetic body 2 is made of a sintered ferrite material, a polymer material mixed with ferrite powder, and a magnetic alloy such as a magnetic amorphous alloy or permalloy. A sintered ferrite material with small deterioration is suitable. The conductive shielding material 3 is made of a conductive gasket material having a structure in which conductive rubber or polyurethane foam material is coated with silver-deposited cloth, or an elastic conductive material such as a conductive finger. The shielding effect is greater when a large number of magnetic bodies 2 are arranged with a smaller cross-sectional area per magnetic body.

FIG. 2 is a sectional view showing a state in which the shield 1 according to this embodiment is applied to a gap formed between two conductors 4. As shown in FIG.

In this embodiment, since the magnetic material 2 is not provided at the attachment part 5 of the shielding body 1 to the conductor 4, the electromagnetic shielding body 1 and the conductor part 4 are connected by frequently tightening screws during attachment. It is necessary to ensure contact and suppress leakage of high frequency current from this part. The conductive shielding material 3 may have a circular cross-sectional shape, an L-shape, or other shapes. In this case, a structure is used in which a groove is provided in the part that contacts the conductor and a magnetic material is embedded.

(Embodiment 2) FIG. 3 is a perspective view showing Embodiment 2 of the present invention.

In this embodiment, long grooves 6c are provided in opposing end surfaces 6a and 6b in the cross section of the conductive shielding material 6, and the long grooves 6c are
A rod-shaped magnetic body 2 is embedded inside to form an integrated structure. The shielding body 7 according to this embodiment has a structure in which the rod-shaped magnetic material 2 is also embedded in the part where it is attached to the conductor, and the surface resistance of the attachment part becomes large, so the method of attaching the shielding body 7 is greatly simplified. can. As in the first embodiment, the conductive shielding material 6 may have a circular cross-sectional shape, an L-shape, or other shapes.

[0017]

[Effects of the Invention] As explained above, the electromagnetic shield according to the present invention has a small effect of contact, so when applied to gaps or joints of metal casings, there is no need for a mechanism to strengthen contact. , it has the effect of being able to take efficient shielding measures. Further, since the shielding body according to the present invention has a greater effect of suppressing leakage current than conventional conductive shielding materials, a significant improvement can be achieved in shielding a low impedance wave source that is likely to generate an induced current.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a first embodiment of the present invention.

FIG. 2 is a perspective view showing a state in which the electromagnetic shield according to the present invention is applied to a conductor gap.

FIG. 3 is a perspective view showing a second embodiment of the present invention.

FIG. 4 is a diagram for explaining the effect of the electromagnetic shield of the present invention.

FIG. 5 is a diagram for explaining the effect of a conventional electromagnetic shield.

FIG. 6 is a diagram showing an electromagnetic shield according to the prior art.

FIG. 7 is a diagram showing an electromagnetic shield according to the prior art.

[Explanation of symbols]

1 Electromagnetic shielding body 2 Rod-shaped magnetic body 3 Elastic conductive shielding material 4 Conductor 5 Contact portion between conductive shielding material and conductor 6 Elastic conductive shielding material 7 Electromagnetic shielding body 10 Conductive shielding material 11 Shield Finger 12 Conductive gasket 14 Conductor

Claims (1)

[Claims] [Claim 1] An electromagnetic shielding body comprising a conductive shielding material and a rod-shaped magnetic body, the conductive shielding material having elasticity and being installed in a gap formed between conductors. An electromagnetic shield characterized in that the rod-shaped magnetic body is integrally provided at a contact portion of a conductive shielding material that contacts a conductor, and the contact portion is loaded with surface impedance. body.