Electromagnetic Shielding Mesh

This invention relates to a mesh, particularly knitted or braided, electromagnetic shielding material for shielding electromagnetic waves irradiated to or from electronic components or signal conductors.

These days, office equipment such as electronic typewriters and printers, household appliances such as washing machines and vacuum cleaners, automobiles equipped with electronic control systems for fuel injection and the like increasingly use electronic components such as microcomputers. Thus, the number of microcomputers is increasing, and so is the clock frequency of microcomputers. Electronic components are generating increasing amounts of electromagnetic noise, which leaks through gaps in the housing of the electronic components and may be transmitted through signal conductors to other electronic components, thus causing malfunctions or damage to the other electronic components.

To solve the above-mentioned problem, conventionally, a meshed metal is formed by knitting or braiding metallic wires or metal-clad non-metallic wires and this mesh metal is wrapped around an electrical wire or the like which is to be electromagnetically shielded. Alternatively, a meshed gasket is formed by coating an elastomer with the meshed metal, and this gasket is attached to gaps in the housing of electronic components, thus preventing electromagnetic waves from being irradiated into or from the electronic components.

Conventionally in the prior art, to prevent the meshed metal from loosening or disentangling, the ends of the meshed metal needed to be soldered or taped, or the entire meshed metal needed to be coated with resin or embedded in an elastic body. To secure the meshed gasket to the housing of the electronic equipment, the housing required a groove for receiving the meshed gasket.

Wherefore, an object of the invention is to provide a mesh, including knitted or braided, electromagnetic shielding material which can be easily secured to electronic equipment without the shielding material loosening or disentangling.

Other objects and benefits of the invention will become apparent from the detailed description which follows hereinafter when taken in conjunction with the drawing figures which accompany it.

To solve this and other objects, the invention provides a knitted or braided electromagnetic shielding material attached to an electronic component or a signal conductor for shielding electromagnetic waves generated by or irradiated to the electronic component or the signal conductor. The knitted or braided electromagnetic shielding material comprises a plurality of metallic linear materials or metal-clad linear non-metallic materials which are plated with solder layers and interwoven to form the knitted or braided electromagnetic shielding material.

The invention will now be described, by way of example, with reference to the accompanying drawings, in which:

FIG. 1 is a cross-sectional view of a wire rod used for composing an electromagnetic shielding material of a first embodiment according to the invention;

FIG. 2 is an explanatory view showing an electromagnetic shielding material formed by knitting the wire rods shown in FIG. 1;

FIG. 3 is an explanatory view showing an electromagnetic shielding material formed by braiding the wire rods shown in FIG. 1;

FIG. 4 is a front view of a meshwork having a screwing hole formed in the electromagnetic shielding material shown in FIG. 2;

FIG. 5 is an explanatory view showing the operation of the meshwork shown in FIG. 4;

FIG. 6 is a perspective view of an electromagnetic shielding gasket clad with the electromagnetic shielding material shown in FIG. 2;

FIG. 7 is an explanatory view showing the electromagnetic shielding gasket attached to the housing of electronic equipment; and

FIG. 8 is a cross-sectional view showing the housing with its lid member closed.

As shown in FIG. 1, a wire rod 1 comprises a core 2 and a solder-plated layer 3. The core 2 is formed of a tinned copper wire, a welded copper wire, a Monel metal wire, a stainless steel wire, an aluminum wire, a tinned copper foil wire, or the like. A Monel metal is, as is known, an alloy mainly composed of nickel and copper. The tinned copper foil wire is formed by winding a tinned copper foil helically around polyester fibers, aramid fibers or polyimide fibers.

FIG. 2 shows a knitted material 4 having an electromagnetic shielding effect and formed by knitting the wire rod 1 shown in FIG. 1. FIG. 2 is divided into upper and lower portions by a break strip: the lower portion shows the knitted material 4 before a heat treatment; and the upper portion shows the knitted material 4 after the heat treatment. As shown in the upper portion, the heat treatment of the knitted material 4 causes the wire rods 1 to be soldered and secured to one another at contact portions 5. Since the knitted material 4 is composed of the wire rods 1 having on their surfaces the solder-plated layers 3, by heating given points of the knitted material 4, the wire rods 1 are securely soldered to one another at the given points. Therefore, if cut or punched portions of the knitted material 4 are heated, the knitted material 4 is prevented from loosening or disentangling. By securely soldering the wire rods 1 to one another, the knitted material 4 is also prevented from contracting or expanding. In addition, the contact resistance among the wire rods 1 is reduced, thus enhancing the electromagnetic shielding effect of the knitted material 4. Therefore, the mesh size of the knitted material 4 can be made constant. The contact resistance in the extending direction of the wire rods 1 (corresponding to the lateral direction in FIG. 2) is different from that in the direction orthogonal to the extending direction (corresponding to the vertical direction in FIG. 2). Therefore, the electromagnetic shielding effect differs with the knitting direction of the knitted material 4. Such a difference in the contact resistance can be reduced when the wire rods 1 are securely soldered to one another.

As shown in FIG. 3, a braided material 6 has an electromagnetic shielding effect and is formed by braiding the wire rods 1 shown in FIG. 1. In the same way as the knitted material 4, by heating the braided material 6, the wire rods 1 can be securely soldered to one another. Therefore, the braided material 6 is prevented from loosening or disentangling and can provide a high electromagnetic shielding effect.

As shown in FIG. 4, the knitted material 4 forms a strip-shaped meshwork 7 having a screwing hole 8 punched in one end of the meshwork 7. The knitted material 4 is heated before punching the screwing hole 8, such that the wire rods 1 are securely soldered to one another and the knitted material 4 is prevented from loosening or disentangling. A peripheral edge 9 of the screwing hole 8 is thus reinforced.

In operation, the meshwork 7 is first wrapped around a signal conductor (not shown) or other portions which need to be shielded from electromagnetic waves. As shown in FIG. 5, by inserting a small screw 12 with a washer 11 through the screwing hole 8, the end of the meshwork 7 is secured to a rim of a housing 10 of electronic components. When the signal conductor is wrapped in the knitted material 4 which is conductive, the knitted material 4 is electrically connected to the housing 10. Therefore, electromagnetic waves generated by the electronic components in the housing 10 or entering the housing 10 from the signal conductor are reflected and absorbed by the knitted material 4. The electronic components and the signal conductor are thus protected from the influence of electromagnetic waves.

As shown in FIG. 6, a gasket 13 having an electromagnetic shielding effect is composed of an elastic body 14 clad with the knitted material 4 which is partially shown. The elastic body 14 is formed of silicone rubber, fluoro-silicone rubber, fluoro-rubber or other elastic material. Since the knitted material 4 is formed of the wire rods 1 having on their surfaces the solder-plated layers 3, a ground 15 can be easily attached to any portion of the gasket 13.

In operation, as shown in FIG. 7, the gasket 13 is attached to a rim of a housing 16 which encloses electronic components. By using the solder-plated layers 3 of the wire rods 1, the knitted material 4 of the gasket 13 can be easily secured to any given portion of the housing 16 by melting the knitted material 4 thereto. Thus, the housing 16 requires no grooves for securely receiving the gasket 13. Furthermore, since the wire rods 1 of the knitted material 4 are soldered and electrically connected to the housing 16, a higher electrical conductivity is established between the gasket 13 and the housing 16 as compared to a conventional gasket which is attached by a groove in a housing. When a lid 17 is closed, as shown in FIG. 8, electromagnetic waves generated by the electronic components in the housing 16 are reflected and absorbed by the knitted material 4 of the gasket 13, thus preventing the electromagnetic waves from leaking outside. At the same time, the electronic components are protected in the housing 16 from electromagnetic waves outside.

The invention has been described above with reference to a preferred embodiment as shown in the drawings. Modifications and alterations may become apparent to one skilled in the art upon reading and understanding the specification. Despite the use of embodiments for illustration purposes, however, it is intended to include all such modifications and alterations within the scope and spirit of the appended claims.