WO1992006520A1

WO1992006520A1 - Electrical connector

Info

Publication number: WO1992006520A1
Application number: PCT/GB1991/001734
Authority: WO
Inventors: Vincent Schuhl; Jean-Christian Delamotte; Bruno Lemmonier
Original assignee: Raychem S.A.; Raychem Limited
Priority date: 1990-10-05
Filing date: 1991-10-07
Publication date: 1992-04-16
Also published as: GB9021715D0

Abstract

An electrical connector (1) has at least one contact element (5) for forming an electrical connection between a pair of electrical wires, the or each contact element being surrounded by a layer (10) of high permeability metal, for example MumetalR , for reducing electromagnetic interference.

Description

Electrical Connector

This invention relates to electrical connectors, and especially to electrical connectors used for forming connections to screened electrical cables.

In recent years some electrical cables have included screens that comprise high magnetic permeability metals, normally in addition to conventional screening elements such as braids. Such cables can provide very high levels of screening against electromagnetic interference. However, their performance can be deleteriously affected by poor connection.

According to the present invention, there is provided an electrical connector which has at least one electrical contact element for forming an electrical connection between a pair of electrical wires, the or each electrical contact element being surrounded by a layer of a high permeability metal for reducing electromagnetic interference.

The particular design of the connector, and the form of the high permeability metal layer will depend on the particular form of electrical cable and the circumstances in which it is employed. For example, the connector may be designed as a simple coaxial cable connector which includes a metal shell for providing a connection between the cable screens, a central contact for the centre conductor of the cable, and a dielectric spacer between the central contact and the metal shell. In such a case the internal surface of the metal shell may be provided with a layer of the high permeability material. Another form of connector for a single coaxial cable may be in the form of a splice, eg. one in which an outer heat-recoverable sleeve contains a deformable metal sleeve such as a braid. Two coaxial cables may be spliced by cutting back their jackets to expose their screens, inserting the cable ends into the recoverable sleeve and recovering it about the cable ends to bring the braid into contact with the cable screens. If desired the braid may be impregnated with solder, for example as described in US patent No. 4,144,404, the disclosure of which is incorporated herein by reference. According to the present invention, the braid or other deformable metal sleeve in the recoverable sleeve may be formed from, or may include the high permeability metal.

Alternatively, the connector may be designed to connect a pair of cables in which a number of wires, formed singly or, for example as twisted pairs, are enclosed in a single cable shield. Such a connector will normally comprise a metal shell, an insulator plug located in the metal shell, and an insulator plug having a number of contact cavities in which are located contact elements for the wires. In this form of connector also, the internal surface of the metal shell is advantageously provided with the high permeability metal layer.

The connector may be designed instead for the connection of coaxial cables, twinaxial cables, triaxial cables or other forms of cable. In the case of a connector for connecting a number of coaxial cables, it may comprise a metal shell which contains an insulator plug having a number of contact cavities each of which contains, or is capable of containing a coaxial cable contact element. Here the coaxial cable contac element will have a centre conductor contact (male or female) and a cabl screen contact (male or female). Each coaxial cable contact is preferabl provided with a layer of the high permeability metal in order to aid th screening of the individual cables.

The high permeability metal layer may be formed in a number o ways. For example, where it is provided on a metal piece such as th metal shell of the connector or on a contact element, it may be formed b electroplating. Alternatively, a thin lining may be formed separately an pushed into place in the shell or in or on the contact elements. Instead it may be applied to the parts as a paint or lacquer by a painting, dip coating or other process. The high permeability metal need not be provided only on the metal parts of the connector. For example it may be formed on the internal surface of the contact cavities in the insulating plug, eg. by painting, dip coating or electroless deposition. The high permeability metal layer has a thickness of at least 1, more preferably at least 5 and especially at least 10 micrometres, but usually (in the case of a coating) not more than 100 micrometres. Also, it is possible for the contact elements themselves or parts thereof, or the metal shell itself to be formed from the high permeability material.

The high permeability material is preferably one having a permeability of at least 7 x 10^-3 Hm^**1, more preferably at least 0.01 Hnr¹, and especially at least 0.02 Hnr¹ (these permeability values being determined at a magnetic field strength of 1590 Am^**1). The metal should be magnetically soft. Preferred materials are those based on alloys of nickel, copper, chromium and iron, or on alloys of molybdenum, nickel and iron. The most preferred material is mumetal.

The electrical cable may be connected to the contact element by any appropriate means, for example by crimping or soldering. One preferred form of connection comprises a heat-recoverable sleeve that contains an insert formed from solder and usually in the form of a ring. The end of the contact element to be joined to the cable shield is hollow and has an aperture in its side wall, the heat-recoverable sleeve being positioned on the outside of the contact element so that the solder ring is located over the aperture, and one end region of the sleeve extending beyond the end of the contact element. The coaxial cable may be positioned in the end of the contact element after stripping the cable jacket back, so that, when the assembly is heated, the sleeve will recover about the cable and the solder will melt and flow through the aperture to form a conductive bond between the cable shield and the contact element. A similar but smaller sleeve and solder may be located adjacent to the other end of the sleeve and within the interior of the cable shield contact element for forming a solder connection between the central conductor of the cable and a further contact element for the central conductor. An example of this type of connection is described in US patent No. 3,541,495 the disclosure of which is incorporated herein by reference.

According to another aspect, the invention provides an electrical connection between a pair of screened cables, the cables each having a screen that comprises a high permeability metal, the connection being established by means of a connector which includes a layer of a high permeability metal that extends from one cable screen to the other cable screen so that a substantially continuous high permeability screen is formed.

The connection according to the invention is preferably formed by means of an electrical connector as described above. Preferably the connection is such that the high permeability material extends entirely from one screen to the other. One form of electrical connector and connection according to th present invention is now described with reference to the accompanyin drawings in which:

Figure 1 is a partially cut-away side view of an electrical connecto in accordance with the present invention;

Figure 2 is a schematic section of the connector alongthe line A- of figure 1;

Figure 3 is a graph showing the surface transfer impedance of th connector shown in figure 1; and

Figure 4 is a graph showing the surface transfer impedance of a equivalent connector that does not include the high permeabilit metal.

Referring to the accompanying drawings, Figure 1 shows a mating pair of electrical connectors 1 and 2 coupled together. Connector 1 comprises a metal shell 3 inside which is located a rubber insulating plug

4 having a number of contact cavities extending therethrough. A coaxial contact element 5 is located within each of the contact cavities. A complementary connector 2 also comprises a metal shell 6 that contains a rubber insulating plug 7, the plug containing a number of contact cavities that extend therethrough and are aligned with the contact cavities of plug

4. Each of the contact cavities contains a complementary coaxial cable con .ct element 8 which can mate with a contact element 5 of the other connector when the two connectors are coupled as shown. The two metal shells 3 and 6 are held together by means of a coupling ring 9 in conventional manner. . _

The internal surfaces of the contact cavities are coated with a 10 micrometre thick layer 10 of mumetal formed by painting a dispersion of the mumetal in an inert carrier before insertion of the contact elements 5 and 8. Coaxial cables may be connected to the contact elements in known manner by means of heat-shrinkable polyvinylidine fluoride sleeves containing solder rings as described in US patent No. 4,414,404 and/or 3,541,495. If the coaxial cables include a high permeability (mumetal) screening layer, for example as described in British patent No. 1,448,820, a substantially continuous high permeability screen is formed through the connection.

In addition, or alternatively, a high permeability layer 12 formed from mumetal may be formed on the interior surface of the metal shells 3 and 6 of the connectors, for example for use where an overall high permeability screen is employed.

Figure 3 is a graphical representation of the screening performance of the connector according to the invention, while Figure 4 is a graphical representation of the screening performance of an identical connector without the high permeability metal coatings 10 and 12. The surface transfer impedance Zt is measured in accordance with the method described in the brochure entitled "Optimised and Superscreened Cables" available from Raychem Limited, Wire & Cable Division, Faraday Road, Dorcan, Swindon, Wiltshire, England. As can be seen, the surface transfer impedance of the assembly using the connector according to the invention is considerably reduced as compared with the conventional connector, for example having a value of 0.1 mohm at 30 MHz compared with 20 mohm at 30 MHz for the conventional connector.

Claims

Claims.:

1. An electrical connector which has at least one electrical contact element for forming an electrical connection between a pair of electrical wires, the or each electrical contact element being surrounded by a layer of a high permeability metal for reducing electromagnetic interference.

2. A connector as claimed in claim 1, wherein the or each electrical contact element is surrounded by the high permeability metal along substantially its entire length.

3. A connector as claimed in claim 1 or claim 2 which has a plurality of electrical contact elements.

4. A connector as claimed in claim 3, wherein each contact element is surrounded by a separate high permeability metal layer.

5. A connector as claimed in claim 4, wherein each contact element is located in a contact cavity in an insulator plug, the internal surface of the contact cavities having been coated with the high permeability metal.

6. A connector as claimed in claim 4, wherein each contact element is coated with the high permeability metal.

7. A connector as claimed in any one of claims 1 to 6, wherein the or at least some of the contact elements are coaxial connection contacts.

8. A connector as claimed in any one of claims 1 to 7, wherein the electrical contact elements are all surrounded by a common high permeability layer.

9. A connector as claimed in claim 8, which comprises a metal shell that surrounds an insulator plug, the interior surface of the shell carrying the high permeability layer.

10. A connector as claimed in any one of claims 1 to 9, wherein the high permeability metal has a permeability of at least 7 x 10^-3 Hnr¹.

11. A connector as claimed in any one of claims 1 to 10, wherein the high permeability metal is formed from nickel, copper, chronium and iron.

12. An electrical connection between a pair of screened cables, the_ cables each having a screen that comprises a high permeability metal, the connection being established by means of a connector which includes a layer of high permeability metal that extends from one cable screen to the other cable screen so that a continuous high permeability screen is formed.

* * * * * *