US3639674A

US3639674A - Shielded cable

Info

Publication number: US3639674A
Application number: US49823A
Authority: US
Inventors: Ronald L Stier
Original assignee: Belden Corp
Current assignee: Cooper Industries LLC
Priority date: 1970-06-25
Filing date: 1970-06-25
Publication date: 1972-02-01
Anticipated expiration: 1989-02-01

Abstract

A low-noise coaxial cable is formed with an elongated inner electrical conductor about which is an elongated, dielectric insulating layer of polymeric material which may be either a solid or foamed polymeric material. A thin electroless deposited shield of metal is intimately bonded to the outer peripheral surface of the insulating layer even if the same has surface irregularities therein. The insulating layer may be made with a constant uniform cross-sectional thickness, usually being annular in cross section, and bent and flexed without experiencing discontinuities in the shield which would destroy its effectiveness. The cable may be produced with ordinary commercially feasible techniques to obtain consistently good lownoise characteristics which are maintained even with substantial use and flexing over prolonged periods of time.

Description

United States Patent 1151 3,639,674 snei- 1451 Feb. 1,1972

[54] SHIELDED CABLE 72 Inventor: Ronald L. Stier, Aurora, 111. 5;

[73] Assignee: Belden Corporation, Chicago, Ill. neyFitch, Even, Tabin and Luedeka 221 Filed: June2s,1970 [57] ABSTRACT PP 491823 A low-noise coaxial cable is formed with an elongated inner electrical conductor about which is an elongated, dielectric in- [52] M17456 174/1021}, 174/107 sulating layer of polymeric material which may be either a 511 int. c1. ..H0lb 11/06 Slid f" Wlymeric material- A elwmless 58] Field of Search ..l74/36,l02, 103,105,107, depomed Shield of metal is intimately bonded to e outer 174/ I06, l 13, l 15, 110 Peripheral surface of the insulating layer even if the same has surface irregularities therein. The insulating layer may be f made with a constant uniform cross-sectional thickness, [56] Re erences Cited usually being annular in cross section, and bent and flexed UNITED STATES PATENTS without experiencing discontinuities in the shield which would destroy its effectiveness. The cable may be produced with or- 3,287,490 1 1/1966 wl'lgl' lt 1 74/ 102 dinary commercially feasiue techniques to obtain consistently 3,315,025 4/ 1967 TPmlmson- 1 74/ 107 good low-noise characteristics which are maintained even 9 1 5/ 1962 -174/107 X with substantial use and flexing over prolonged periods of 2,258,687 10/1941 Petersonm. .....174/115 ti 3,173,990 3/1965 Lamons ..174/102 2,663,754 12/ l953 Bianco ..l74/ 102 13 Claims, 3 Drawing Figures SHIELDED CABLE This invention relates to flexible coaxial cables having an inner conductor surrounded by an insulating layer, usually of dielectric material, about which is an outer coaxial conductor which acts as a shield.

In order to providesufficient flexibility for the coaxial cable, the internal conductor and insulation layerare usually formed to flexible materials and the outer shield has been formed in various manners such as a braided metallic shield of copper or other material. Braided shields are relatively expensive and have not been totally effective in preventing extraneous electrical signals from effecting the signals carried by the inner conductors or in reducing the noise level to very low levels such as for microwave or television vision installations.

Other and more recent forms of coaxial cables have been formed with a flexible metallic foil shield spirally wrapped about .the dielectric. While still other coaxial cables have been made with an elongated foil strip extending longitudinally of the dielectricand the insulating layer with the foil formed about the insulating layer to'cover the same with longitudinally extending marginal edges of the strip overlapped at a seam. Both the braided coaxial conductor and the thin foil coaxial conductor will undergo some limited movement relative to and across the surface of the dielectric with flexing of the cable. Limitedsmall amounts of noise, e.g., to 150 millivolts may be generated with movement of electrons between the surface of these dissimilar conductor and insulating materials as in the manner of a piezoelectric phenomenon.

While it has been recognized that a more intimate bond between the dielectric and the coaxial conductor shield might be beneficial in reducing electron movement between these dissimilar surfaces, there has not been a satisfactory manner of making such a cable in a continuous commercial basis with ordinary manufacturing techniques. It has been possible to spray orbrush colloidal graphite on the outer surface of a dielectric layer. of a coaxial cable to form a conductive graphite shield. By using extraordinary careand extraordinary manufacturing techniques, it maybe possible to reduce the noise level of such a graphite shielded coaxial cable to under 0.2 millivolts. However, the bond between the dielectric and the graphite shield deteriorates with age and use to the extent that the noise level may rise to, 100 times greater than the original noise level.

It has been proposed to provide a coaxial cable with a metallic coaxial shield deposited by an electrolessmethod on an outer corrugated or grooved surface of a dielectric layer.

-The'corrugated configuration-for the dielectric is stated to provide'a stress reduction during bending of the cable and thereby prevents the electroless shield from cracking or otherwise losing its continuity. The corrugated or grooved dielectric is a limiting factor for the commercial development in that it is a nonstandard cross section for extruding, coating or otherwise forming which usually results in the dielectric being uniform in cross section along its length. Moreover, it appears that the electroless disposition according to this suggestion is limited to use on solid dielectrics as contrasted to cellular or foamed dielectrics which are often used with the thin metallic foil coaxial cable constructions.

Thus, there is a definite need for flexible coaxial cables which have an intimate bond between the dielectric layer and the metallic shield material but which do not require special configurations of the dielectric and which can be used with foamed or cellular polymer materials for the dielectrics as well as with solid polymer materials for the dielectric. Such a coaxial cable also must be-a commercially feasible product in that it ought to be capable of being produced inlarge quantities Wi t s Of extraordinary manufacturing techniques and should with reasona bleregulmity meet the desired electrical and P y s. Specifications of an approved coaxial cable.

fil'tiingly, an object of the present invention is to provide an improved flexible, low noise, coaxial cable, as contrasted with conventional coaxial cables of the foregoing kind.

These and other objects and advantages of th inventl?" will become more readily apparent from the following descriplit"! when. on connection with the drawings in which:

FIG. 1 is a perspective view, with parts broken away, of a portion of a coaxial cable constructed in accordance with the invention;

FIG. 2 is a perspective view, with parts broken away, of another embodiment of the invention; and

FIG. 3 is a perspective view, with parts broken away, of still another embodiment of the invention.

As shown in the drawings for purposes of illustration, the invention is embodied in a low noise, coaxial cable 10 having a thin electroless deposited conductor shield 11 intimately bonded to an elongated dielectric insulating layer 13 which may be a solid or foamed polymeric material such as, for example, polyethylene or polypropylene. The electroless deposit shield 11 is preferably electrical conducting copper or nickel although other materials may be used. The shield 11 may be quite thin, for example, copper shields may be in the range of 0.0005 to 0.0015 inch with good results at about one (1 mil thickness. For a nickel shield 11, the thickness has been varied from about 0.0005 to 0.002 inches with good results being obtained. Shields 11 have been deposited by electroless methods on standard, substantially cylindrical surfaces 14 of both solid and foamed polymers and have been subjected to flexing without experiencing severe cracking or discontinuities which would substantially reduce the effectiveness of the shield. The

,intimate bond; which is a chemical and electrical bond,

reduces the piezoelectric phenomena and has resulted in consistent noise reduction to within a range of 0.06 to 0.05 millivolts initially for coaxial cable of akind to be described in detail herein. Noise, as used herein, has been measured on an oscilloscope with an amplifier bandwidth of 0.1 Hz. to 0.1 mI-Iz. and a sensitivity down to 0.01 millivolt per centimeter. The coaxial cable 10 maintains good low noise capabilities despite age and use; and, when under test, to the point of mechanical destruction the noise level was still a low 2.5 millivolts for the coaxial cable 10 described in detail herein.

Referring now particularly to FIG. 1, the electric cable illustrated herein has an inner conductor 15 of copper or other suitable conductive material and the illustrated conductor 15 is asolid conductor generally circular in cross section. However, the inner conductor 15 may be formed with other cross sections and may be a stranded conductor rather than a solid conductor. Also, the dimension of the inner conductor 15 may be varied as seen in the contrast between sizes the conductor 15 illustrated in FIGS. 1, 2 and 3. v

For the purpose of insulating the inner conductor 15, the layer 13 of flexible insulating material, preferably a homogeneous polymeric material such a cellular polyethylene or polypropylene surrounds the'conductor l5 and is in engagement therewith. With the present invention, it is possible to use foamed or nonfoamed polymers, such as foamed or nonfoamed polyethylene or polypropylene for the layer 13. For a central conductor 15 having a size 18 AWG annealed copper, a suitable layer size for the insulating layer 13 of cellular polyethylene may be a 0.70-inch wall thickness having about a 0.180-inch outer diameter.

A plurality of spaced drain wires 17 may be provided to assure continuity of the shield 11 should it become broken or otherwise damaged. Preferably, the drain wires 17 are generally helically wrapped around and along the outer surface of the shield 11 and in electrical contact therewith. Thus, when the cable is flexed, the drain wires 17 on the side of the cable under compression can readily move toward each other axially along the shield while the drain wires on the opposite side of the cable under tension can move readily away from each other. 5

The cable 10 may have an outer tubular jacket 19 of insulating material which surrounds the inner conductor 15, the insulating layer 13, the conductive coaxial shield 11, and drain wires 17 to protect and insulate the same. The jacket may be comprised of vinyl or other suitable insulating material and protective material. In the cable having the conductor and sheath size, previously indicated by way of example, a satisfactory size for the jacket may be a 0.030-inch wall with a 0.242- inch outer diameter.

In accordance with the present invention, it is possible to provide a shield 11 in the form of a very thin layer or deposit which is electrically continuous and intimately bonded to the insulating layer 13 even though the surface thereof has irregularities such as from a foamed or cellular polymeric material. Usually, the outer surface of the layer 13 has a standard generally cylindrical configuration with only very small irregularities therein when the layer is formed of a foamed (either noncellular or cellular) material. The boundary areas at which the cells in foamed cellular material join one another will not be smooth or planar and likewise a foamed, but noncellular material may have small holes and'openings in its surface. A smoother surface 14 is provided for the deposition when the layer 13 is formed of a solid polymeric material. Even though the shieldis thin in cross-sectional thickness, it has been found to readily bend or otherwise flex with the insulating layer 13, and because the shield 11 is so intimately adhered to the dielectric layer 13 it doesnt readily scrape off, chip or lose its effectiveness in other manners. This is in contrast to the necessity heretofore of providing a spiral grooved outer surface and the use of a solid dielectric of homogenous polymeric material. Thus, the low noise cable 10 may be formed with a uniform cross-sectional thickness for its insulating layer, and hence with a configuration of the kind which is more readily manufactured and at a commercially competitive cost.

Turning now to a more detailed description of the electroless deposition method and in particular to the plating bath, the-latter generally contains a soluble copper salt, a complexing agent such as EDTA, Rochelle and sugar derivatives; a

A less depositing nickel and copper will now be described. When electroless depositing nickel, from a plating bath containing MACuplex19340 Nickel, the following process is used. The materials mentioned in this process are available from Mac- Derrnid, inc. 1000 Huntingdon Avenue; Waterbury, Connecticut. The polymeric layer is first cleaned in a cleaning mixture having MACuplex XD-40A which is added to water to provide a mixture having 15 percent by volume of MACuplex XD- 40A. The cleaning mixture is heated to a temperature of 150 F. and the polymeric surface is treated for -10 minutes. After treating, the polymeric surface is given a cold water rinse.

The polymeric surface is then sensitized or etched with a full strength MACuplex acid cleaner for a period of 1-2 minutes. This acid cleaner is maintained at a temperature of 135 F. Next polymeric surface is treated with MACuplex XL- 43 maintained at a temperature of l75-180 F. for a period of 5-7 minutes. Then, the polymeric surface is given two consecutive, cold water rinses and treated with MACuplex XY-l (2 percent by volume) maintained at a temperature of 180 F. plus or minus 5 F. for a period of l-3 minutes. Following this, the polymeric surface is first given a cold water rinse and then a warm water rinse with the temperature of the warm water at about 110F. I

Next the polymeric surface is treated with MACuplex XD- 34 maintained at a temperature of 8590 F. and for a time period of 3-5 minutes. The MACuplex XD-34 is mixed to percent by volume in a percent reagent grade hydrochloric acid. Next the polymeric surface is given two consecutive rinses with cold water. After rinsing, the polymeric surface is treated with an aqueous mixture of MACuplex XD-45 (5 to 10 percent by volume). This mixture is maintainedat a temperature of 120 F. plus or minus 5 F. The period of exposure to this latter mixture is 3-5 minutes.

For nickel plating of the polymeric surface, a nickel electroless plate bath having MACuplex 9340 Nickel is used. The polymeric material is immersed for 5-8 minutes in the bath which is at a temperature of F. plus or minus 5 F. Subsequent to the nickel treatment, the polymeric surface is again given a cold water rinse.

If copper plating is desired to be used with this latter process, Enplate Cu-402 (available from Enthone, lnc., Box 1900, New Haven, Connecticut) platingbath is substituted for the MACuplex 9340 Nickel bath. Each of the above described steps preparatory to plating with nickel is duplicated for the electroless deposition of copper. In this copper deposition process, the bath is made by mixing 3 parts of A, Enplate Cu- 402; 3 parts of B, Enplate Cu-402, and 4 parts of water. The bath is heated to 65-75 F. and the polymeric surface is treated for 5-10 minutes with the copper bath.

Detailed examples of electroless plating baths for use with the system are as follows:

Copper sulfate pentahydrate 7.5 g.

Sodium EDTA (Versene) 15.0 g.

NaOH 20.0 g.

NaCN I 0.1 to 1.0 g.

For copper: Cl-l,0 (40%) 40 ml. H,0 to 1000 ml. total NaI-LPO, 5-20 g.

Sodium Acetate 7.5-30 g.

For nickel: Thiourea (stabilizer) 1-50 p.p.m. pH 3.5-5.0 time 4-7 min.

temp. 1 8 5 F.

Referring now to FIG. 2, there is illustrated a further embodiment of the invention, a cable 10a, which is generally identical to the construction of FIG. 1, except that a foil strip 21 surrounds and is in contact with the electroless deposited shield 11a. reference characters with a suffix aare used to designate elements of. the cable 10a which are similar or identical to elements previously described above for the cable 10 of FIG. 1. The foil shield 21 extends longitudinally along the electroless shield 11a and insulating layer 13a and has its opposite longitudinally extending

edges

23 and 25 overlapped to form a seam thereby completely and continuously encircling the shield 11a and acting as shield along with the electroless shield lla. A plurality of helically wrapped drain wires 17a extend around, along, and in contact with the outer surface of the foil strip 21.

In accordance with this invention, the cable may vary considerably in size and in arrangement of elements. For example, as illustrated in H6. 3, a cable 10b is formed with a small internal conductor 15b of 0.0159 inch in diameter about which is a foamed polyethylene insulating layer 1312 which has an outer diameter of 0.116 inch. An electroless deposited shield 11b of about 1 mil thick nickel or copper is deposited on the layer 13b. A single drain wire 17b may be disposed intermediate the-shield 11b and a foil strip 21b. An outer sheath 19 b surrounds these internal elements and has an outer diameter of about 0.160 inch.

' Rather than using a foil strip, it is contemplated that additional shielding protection may be afiorded, i.e., in addition to the electroless deposit shield 11 or 11a, by electroplating nickel, iron, or copper onto the electroless plated shield. For instance, iron may be electroplated on the shield 11, 11a or 111; to produce a magnetic shield. On the other hand, the electroless plate shield 11a or llb may have additional metal shield material deposited thereon by conventional electroplating or vacuum deposition methods and the foil strips 21' and 21b may be eliminated. Another alternative to the use of the foil strip 21 for providing additional shieldingiprotection is to use a wire braid (not shown) in electrical contact-with and about the electroless deposit shield. A wire braid provides H good mechanical strength and electrical connections may be made to the braid with conventional techniques. The electroless deposit shield requires special clamps or techniques to make connections to it electrically. Hence, when drain wires, or foil strips or a braided shield are employed and are in contact with the electroless deposit shield, then the electrical connections may be made directly to the drain wires or shields rather than to the electroless deposit shield.

As alternative to the illustrated helically wrapped drain wires 17, a plurality of longitudinally extending drain wires (not shown) with undulations therein may be disposed in electrical contact with the electroless deposited shield 11. More specifically, the undulations may be formed by pulling an electrical conductor of a material, such a tinned copper, between the mesh of two gearlike members which form alternating crests and valleys in the conductor. The undulations in the drain wires provide the ability to stretch with reduced amount of stress in the drain wires during flexing or bending of the cable. Either the undulating drain wires or the illustrated drain wires 17 may be formed with a circular cross section, as illustrated for the wires 17, or with a thin, rectangular cross section of a ribbonlike conductor.

From the foregoing it will be seen that the present invention provides a low noise flexible cable with a metallic shield intimately bonded to the insulating layer and yet which does not require a special configuration for the insulating layer and which does not rapidly deteriorate with age and flexing. It is to be understood however, that bending or flexing of the cable may cause small cracks in the shield but the shield effectiveness is still good when compared to a conventional braid shield which may provide only 80 percent to 85 percent physical coverage. Also, the polymer insulating layer for the electroless plate shield may either be a solid polymer having a smooth surface or a foamed polymer having irregularities and a nonsmooth surface. Moreover, the cable is capable of being produced by commercial techniques to meet with regularity the desired electrical specifications including a low noise characteristic.

While a preferred embodiment has been shown and described, it will be understood that there is no intent to limit the invention by such disclosure but, rather, it is intended to cover all modifications and alternate constructions falling within the spirit and scope of the invention as defined in the appended claims.

What is claimed is:

l. A low noise coaxial cable comprising a central, elongated, flexible conductor, a dielectric insulating layer formed of a foamed polymer having an inner surface surrounding said conductor and having an outer peripheral surface, said insulating layer having a substantially uniform cross-sectional denconvolutecl thickness throughout substantially its entire length, said outer peripheral surface having surface irregularities therein as a result of its being foamed, a shield formed of an electroless deposit of conductive metal intimately bonded to and extending into and along said surface irregularities of said peripheral surface of said dielectric insulating layer, and

shield being thin in cross-sectional thickness compared to the cross-sectional thickness of said dielectric and flexing therewith and maintaining its electrical continuity during bending and a flexible protective sheath surrounding said shield, said insulating layer and said central flexible conduc- I01.

2. A coaxial in accordance with claim 1 in which said shield is substantially cylindrical in shape, is formed with copper, and has a wall thickness in the range of about 0.0005 to 0.0015 inch.

3. A coaxial cable in accordance with claim 1 in which said shield is substantially cylindrical in shape, is formed with nickel, and has a wall thickness in the range of about 0.0005 to 0.002 inch.

4. A coaxial cable in accordance with claim 1 in which the the noise level of said cable is not greater than about 0.25 millivolts.

5. A coaxial cable in accordance with claim 4 in which at least one drain conductor is disposed between said sheath and said shield and extends longitudinally along and in contact with said shield.

6. A low noise coaxial cable comprising a central, elongated, flexible conductor, a dielectric layer surrounding said conductor and having a substantially uniform cross-sectional thickness throughout substantially its entire length, and a thin electroless deposition of metal of substantially uniform crosssectional dimensions intimately bonded to the outer surface of said dielectric layer for bending therewith and for maintaining its electrical continuity with flexing of the cable.

7. A coaxial cable in accordance with claim 6 in which said dielectric layer is formed of a foamed polymeric material.

8. A coaxial cable in accordance with claim 7 in which the noise level of said cable is not greater than 0.25 millivolts.

9. A coaxial cable in accordance with claim 7 in which said electroless deposition of metal is substantially cylindrical in shape, formed of copper and has a wall thickness of about 0.0005 to 0.0015 inch.

10. A coaxial cable in accordance with claim 7 in which said electroless deposition of metal is substantially cylindrical in shape, is formed of nickel, and has a wall thickness of about 0.0005 to 0.002 inch.

11. A coaxial cable in accordance with claim 6 in which a conductive shield is disposed about and on said electroless deposition of metal to aid the latter in shielding the inner conductor.

12. A coaxial cable in accordance with claim 11 in which at least one drain conductor is provided in electrical contact with said conductive shield and said electroless deposition of metal.

13. A coaxial cable in accordance with claim 12 in which said drain wire is sandwiched between and in direct contact with said conductive shield and said electroless deposition of metal.

I UNITED STATES PATENT OFFICE CERTIFICATE OF CGRRECTEON Patent No. 74 Dated February 1, 1972 Inventor(s) Ronald L. Stier It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 9, change "to to ---of-.

Column 1, line 75, change "taken, on" to taken in-.

' Column 2, line 27, change "0.05" to --.0.2'5--.

Column 5, line 30, change "plate" to 'plated-.

Signed and sealed this 1st day of August 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM PO-10 0 USCOMM-DC 60376-P69 U 5 GOVERNMENT PRINTING OFFICE I959 O-366-334 Patent N Dated February 1,

Inventoflg) Ronald L. St1er It is certified that error appears in the above-identified patent and that. said Letters Patent are hereby corrected as shown below:

Column 5, line 44, before: "dielectric" insert non-convoluted line 48, cancel "denconvoluted" Column 6 line 23, before "dielectric" insert non-convoluted Signed and sealed this 31st day of October 1972..

(SEAL) Attest:

EDWARD M.FLETCHER,JR. I ROBERT GOTTSCHALK Attesting Officer Commissioner of Patents FORM P0-1050 (10-69) v USCOMM-DC suave-ps9 U,S GOVERNMENT PRINTING OFFICE: I969 0-36 33A,

Claims

1. A low noise coaxial cable comprising a central, elongated, flexible conductor, a dielectric insulating layer formed of a foamed polymer having an inner surface surrounding said conductor and having an outer peripheral surface, said insulating layer having a substantially uniform cross-sectional denconvoluted thickness throughout substantially its entire length, said outer peripheral surface having surface irregularities therein as a result of its being foamed, a shield formed of an electroless deposit of conductive metal intimately bonded to and extending into and along said surface irregularities of said peripheral surface of said dielectric insulating layer, and shield being thin in cross-sectional thickness compared to the cross-sectional thickness of said dielectric and flexing therewith and maintaining its electrical continuity during bending and a flexible protective sheath surrounding said shield, said insulating layer and said central flexible conductor.

6. A low noise coaxial cable comprising a central, elongated, flexible conductor, a dielectric layer surrounding said conductor and having a substantially uniform cross-sectional thickness throughout substantially its entire length, and a thin electroless deposition of metal of substantially uniform cross-sectional dimensions intimately bonded to the outer surface of said dielectric layer foR bending therewith and for maintaining its electrical continuity with flexing of the cable.