WO2002079841A1

WO2002079841A1 - Conductive elastomer shielding strain relief

Info

Publication number: WO2002079841A1
Application number: PCT/US2002/009779
Authority: WO
Inventors: Kenneth Robinson; Mohamed Ait-El-Cadi
Original assignee: Laird Technologies, Inc.
Priority date: 2001-03-29
Filing date: 2002-03-28
Publication date: 2002-10-10

Abstract

The strain relief (10) is a conductive boot made from molded conductive-particle filled elastomer, or a non-conductive elastomer coated with a thin coating of low durometer conductive particle filled elastomer. The conductive boot shields by reducing aperture size (60) and by the waveguide-beyond-cutoff principle. Additionally, the conductive boot is proportioned so that the length is typically at least five times the width, thereby acting as a waveguide and blocking EMI with destructive interference.

Description

CONDUCTIVE ELASTOMER SHIELDING STRAIN RELIEF

BACKGROUND OF THE INVENTION

1. Field of the Invention This invention pertains to a cable strain relief boot made from conductive coated elastomer or conductive elastomer and used to shield around a connector and/or connector opening .

2. Description of the Prior Art The apertures for fiber optic connectors and transceivers are well-known sources of EMI (electromagnetic interference) leakage. As the frequencies in use have exceeded 20GHz, EMI leakage has only worsened. In particular, connector apertures are large, thereby- causing leakage problems . When many prior art strain reliefs operate at higher frequencies, such as 20 GHz and beyond, even an aperture which is the width of 12 conductor fiber-optic ribbon cable will be so large as to cause unacceptable leakage levels.

Prior art references include U.S. Patent No. 6,158,899 entitled "Method and Apparatus for Alleviating ESD Induced EMI Radiating from I/O Connector Apertures" issued on December 21, 2000 to Arp et al . ; U.S. Patent No. 6,134,370 entitled "Fiber Optic Cable Guide" issued on October 17, 2000 to Childers et al . ; U.S. Patent No. 5,915,056 entitled "Optical Fiber Strain Relief Device" issued on June 22, 1999 to Bradley et al . ; U.S. Patent No. 5,886,294 entitled "Interference Suppressing Cable Boot Assembly" issued on March.23, 1999 to Scrimpshire et al . ; and U.S. Patent No. 5,631,443 entitled "Inter erence Suppressing Cable Boot Assembly" issued on May 20, 1997 to Scrimpshire et al .

OBJECTS AND SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide a strain relief which can operate at frequencies as high as or exceeding 20 GHz while minimizing EMI leakage.

It is therefore a further object of the present invention to provide a strain relief which is suitable for use with electrical and optical fiber connectors and cables .

It is therefore a still further object of the present invention to provide a strain relief which can be manufactured in various sizes to fit a variety of standard connectors and cables .

It is therefore a still further object of the present invention to provide a strain relief which can be. installed inside or outside a shielded enclosure and can be mounted in a variety of ways.

It is therefore a still further object of the present invention to provide a strain relief which can be manufactured economically.

These and other objects are attained by providing a strain relief which is a conductive boot made from molded conductive-particle filled elastomer, or a non-conductive elastomer coated with a thin coating of low durometer conductive particle filled elastomer. The conductive boot shields by reducing aperture size and by the waveguide- beyond-cutoff principle. Additionally, the conductive boot is proportioned so that the length is typically at least five times the width, thereby acting as a waveguide and blocking EMI with destructive interference.

The conductive boot can be mounted in different ways. For instance, the boot can be part of a fiber cable assembly and slide over the connector after the connector is plugged into a transceiver port . Alternately, the boot can be located inside an enclosure and mounted onto the rear of a bulkhead adapter.

BRIEF DESCRIPTION OF THE DRAWINGS

Further objects and advantages of the invention will become apparent from the following description and claims, and from the accompanying drawings, wherein:

Figure 1 is a perspective view of the installed configuration • of the strain relief of the present invention;

Figure 2 is a front perspective view of the strain relief of the present invention;

Figure 3 is a rear perspective view of the strain relief of the present invention;

Figure 4 is a top plan view, partially in phantom, of the strain relief of the present invention;

Figure 5 is a side plan view, partially in phantom, of the strain relief of the present invention; Figure 6 is a rear plan view, partially in phantom, of the strain relief of the present invention;

Figure 7 is a front plan view, partially in phantom, of the strain relief of the present invention;

Figure 8 is a cross-sectional view of the strain relief of the present invention taken along plane 8-8 of

Figure 5 ; Figure 9 is a cross-sectional view of the strain relief of the present invention taken along plane 9-9 of Figure 4 ;

Figure 10 is a cross-sectional view of the strain relief of the present invention taken along plane 10-10 of Figure 5 ;

Figure 11 is a cross-sectional view of a perimeter contact method of mounting the strain relief of the present invention; and Figure 12 is a cross-sectional view of a face contact method of mounting the strain relief of the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to the drawings in detail wherein like numerals indicate like elements throughout the several views, one sees that Figure 1 is a perspective view of the installed position of strain relief 10 of the present invention, while Figures 2 and 3 are perspective views of the strain relief 10 from different angles.

Strain relief 10 is made from molded conductive particle filled elastomer or, alternatively, a non- conductive elastomer coated with a thin coating of low durometer conductive particle filled elastomer. A typical material is EcE 93 silicone with nickel graphite, although those skilled in the art will recognize a range of equivalent substitutions.

As shown in Figure 4 and the other various figures, strain relief 10 includes rearward portion 12 with a square or rectangular cross-section formed from walls 14,

16, 18, 20 thereby forming a square-shaped or rectangular- shaped rearward opening 22. As shown in Figure 8, while the exterior of walls 14, 16, 18, 20 are orthogonal with each other, the interior of walls 14, 16, 18, 20 is inclined at an angle of 0.7° so that walls 14, 16, 18, 20 progressively thicken as the walls extend away from rearward opening 22.

Rearward portion 12 is integral with intermediate oblique portion 24 which is formed by oblique walls 26, 28, 30, 32. As shown in Figure 8, the interior of walls 26, 30 typically form an 18.5° angle therebetween. A similar angle is typically formed between walls 28 and 32. Likewise, walls 14 and 26 typically form an angle of 6.3° therebetween. Similar angles are typically formed between the various walls of rearward portion 12 and intermediate oblique portion 24. Forward nose chamfer 40 is formed by walls 42, 44, 46, 48. As shown in Figure 8, wall 42 typically forms a 33.3° angle with respect to the exterior of wall 14.

Forward portion 50 extends integrally from forward nose chamfer 40 and is formed by walls 52, 54, 56, 58 thereby forming cable aperture 60 therebetween. Cable aperture 60 is configured and arranged to fit tightly over a cable 302. As shown in Figure 8, the interior of walls 52 and 54 are typically parallel with each other with the exterior of wall 52 typically forming an angle of 3.1° with the interior of wall 52. However, as shown in Figure 9, the interior of walls 54, 58 include portions 62, 64 of reduced thickness, respectively, thereby causing increased distance therebetween. All angles given are typical angles and those skilled in the art will recognize a range of equivalent substitutions .

The proportions of a length typically at least five times the width causes a waveguide-beyond-cutoff phenomena and blocks EMI by destructive interference. This, along with the reduced size of cable aperture 60 greatly increases the shielding of strain relief 10. Additionally, the physical structure of strain relief 10 provides for reduced curvature and hence, less strain on cables passing therethrough, which is particularly important for fiber optic installations.

The details of two methods of mounting are shown in Figures 11 and 12. Both methods of mounting involve an electronic or fiber optic transceiver 100 mounted on a P.C. board 102. Transceiver 100 protrudes through opening 202 in conductive enclosure wall 200. Fiber optic transceiver 100 receives connector 300 which is fastened to cable 302. Cable 302 extends through cable aperture 60. Additionally, in both Figures 11 and 12, the portion of transceiver 100 protruding through opening 202 in conductive enclosure wall 200 along with connector 300 and a portion of cable 302 are enclosed and thereby shielded within strain relief 10. In Figure 11, perimeter contact mounting is used wherein opening 202 of conductive enclosure wall 200 includes an orthogonal portion 204 through which transceiver 100 extends and which is received by square-shaped rearward opening 22 of strain relief 10. The inherent elasticity of the material from which strain relief 10 is formed forms a relatively strong lateral contact between orthogonal portion 204 and rearward portion 12 of strain relief 10. Similarly, the conductivity of orthogonal portion 204 and of strain relief 10 leads to a low impedance electrical connection therebetween which is virtually essential for effective shielding. Similarly, in Figure 12, the orthogonal portion 204 of conductive enclosure wall 200 is omitted and walls 14, 16, 18, 20 form an out-turned lip which makes physical and electrical contact with conductive enclosure wall 200. Thus the several aforementioned objects and advantages are most effectively attained. Although preferred embodiments of the invention have been disclosed and described in detail herein, it should be understood that this invention is in no sense limited thereby.

Claims

WHAT IS CLAIMED IS:

1. A strain relief comprising: walls formed of an elastic material, said elastic material being conductive on at least a portion of a surface thereof, said walls forming a first end and a second end, said first end including a rearward opening and said second end including a cable aperture, said walls further forming a tapered portion between said first end and said second end, said tapered portion forming a waveguide .

2. The strain relief of Claim 1 wherein said elastic material is a molded conductive particle filled elastomer.

3. The strain relief of Claim 1 wherein said elastic material is a substantially non-conductive elastomer with a coating of conductive particle filled elastomer.

4. The strain relief of Claim 2 wherein a length of the strain relief is at least five times a width of the strain relief .

5. The strain relief of Claim 4 wherein said waveguide blocks electromagnetic interference with destructive interference .

6. The strain relief of Claim 5 wherein said rearward opening is square or rectangularly shaped.

7. The strain relief of Claim 6 wherein said cable aperture is configured and arranged to fit tightly over a cable by minimizing the size of said aperture, thereby to maximize the shielding effectiveness of said strain relief.

8. The strain relief of Claim 3 wherein a length of the strain relief is at least five times a width of the strain relief.

9. The strain relief of Claim 8 wherein said waveguide blocks electromagnetic interference with destructive interference .

10. The strain relief of Claim 9 wherein said rearward opening is square or rectangularly shaped.

11. The strain relief of Claim 10 wherein said cable aperture is configured and arranged to fit tightly over a cable .