ELECTRICAL SIGNAL LINE CABLE ASSEMBLY

Abstract: The invention relates to an electrical signal cable assembly (10) having a subcable assembly (40, 60) cylindrically arranged around a central axis (15). The subcable assembly (40, 60) comprises a plurality of flat cables (45), each one of which has at least three electrical signal conductors (130) encased within and separated at a pitch distance (a) from each other by a flat cable insulator (120). In use one of the three electrical signal conductors (130) carries a ground signal and the two other coplanar electrical signal conductors (130) carry a signal. The flat cables (45) are either cylindrically braided or cylindrically surfed about the central axis (15). The flat cable insulator (120) is formed in the preferred embodiment of the invention from an upper insulator (120a) laminated to a lower insulator (120b) and is made from expanded polytetrafluoroethylene (ePTFE).

Description: E l e c t r i c a l S i g n a l L i n e C a b l e A s s e m b l y Field of the Invention The invention relates to an electrical signal cable assembly. Prior Art Electrical signal lines are known, for example, from European Patent Application EP-A-0 735 544 (Cartier et al.) assigned to Hewlett-Packard Company. This patent application describes an ultrasound system with a transducer cable for providing an electrical connection between a transducer and a display processor. The third embodiment of the transducer cable in this application uses three layers of extruded ribbon assemblies separated from each other by shield conductors comprising thin strips of bare copper. The stack of ribbon assemblies and shield conductors are extruded with a ribbon jacket to form a desired length of the transducer cable. US-A-4 847 443 (Basconi) assigned to the Amphenol Corporation teaches another example of an electrical signal line cable formed from a plurality of generally flat electrical signal line segments stacked together in an interlocking relationship. Each electrical signal line segment of this prior art cable contains at least one signal conductor surrounded on either side by ground conductors. The plurality of ground conductors effectively form a ground plane which inhibit the cross-talk between the adjacent signal conductors. The insulating materials in which the conductors are disposed is extruded over the individual signal conductors. European Patent EP-B-0 605 600 (Springer et al.) assigned to the Minnesota Mining and Manufacturing Company teaches a ribbon cable and a lamination method for manufacturing the same. The ribbon cable manufactured comprises a plurality of evenly spaced flexible conductors surrounded by an insulator which is a microporous polypropylene. US Patent US-A-4 847 443 (Crawley et al.) assigned to W.L.Gore & Associates teaches a multi- conductor flat ribbon cable having a plurality of electrical conductors disposed within an insulator consisting of expanded polytetrafluoroethylene (ePTFE). PCT patent application WO- A-91/09406 (Ritchie et al) teaches an electrical wiring composed of elongated electrically conductive metal foil strips laminated between opposing layers of insulating films by means of adhesive securing the foil strips between the laminating films. German patent application DE-A-24 24 442 assigned to Siemens teaches a cable assembly which comprises a plurality of flat cables laminated between insulating films. In German Patent Application DE-A-31 41 636 (Fischer) assigned to Siemens a flat cable having a plurality of individual signal conductors which is wrapped around a central core in a spiral manner or longitudinally. The central core has a central conductor which is separated from a braided shield by an insulation layer. A further braided shield is provided to shield the individual signal conductors in the flat cable from stray electromagnetic fields. This patent application does not teach any method of providing any form of shielding between the individual signal conductors in the flat cable. In a similar construction, European Patent Application EP-A-0 089 541 (Tillmanns) assigned to W.L.Gore & Associates GmbH teaches a flat cable having a plurality of individual signal conductors wrapped around a central core in a helical manner. A braided shield is provided to shield the individual signal conductors in the flat cable from stray electromagnetic fields. This patent application does not teach any method of providing any form of shielding between the individual signal conductors in the flat cable. PCT patent application WO-A-80/00389 (Clarke) assigned to Square D company of Palatine, Illinois, teaches an input/output data cable for use with programmable controllers. The cable has a ground conductor, a logic level voltage conductor and a number of signal tracks. The conductors are disposed on two or three layers of flexible plastics material in specified ways to give high immunity to interference and low inductive losses. The layers are glued together to form a laminate structure. W.L.Gore & Associates, Inc., in Phoenix, Arizona, sell a round cable under the part number 02-07605 which comprises 132 miniature co-axial cables enclosed within a braided shield of tin-plated copper and a jacket tube of PVC. Summary of the Invention It is an object of the invention to provide an improved electrical signal cable assembly having a plurality of flat cables containing individual signal conductors. It is a further object of the invention to reduce the cross talk between individual signal conductors in an electrical signal cable assembly containing a plurality of flat cables . It is a further object of the invention to provide a lightweight electrical signal cable assembly which can be attached to a hand-held sensor device, such as an ultrasound probe, for easy handling. It is a further object of the invention to provide an electrical signal cable assembly which has a high flexlife. These and other objects of the invention are solved by providing an electrical signal cable assembly comprising at least one subcable assembly being cylindrically arranged around a central axis in which the at least one subcable assembly comprises a plurality of flat cables and each of said flat cables has a at least two electrical signal conductors encased within and separated at a pitch distance a from each other by an flat cable insulator. In use at least two of the coplanar electrical signal conductors carries a signal such as a measurement signal and another one of the coplanar electrical signal conductors carries a ground signal and separates the at least two of the coplanar electrical signal conductors. The separation of the two signal-carrying electrical signal conductors from each other by a signal conductor carrying a ground signal substantially reduces the cross-talk between the two signal- carrying electrical signal conductors. In one embodiment of the invention, this allows one to dispense with the presence of cylindrical shields in the electrical cable assembly to separate the flat cables from each other, thus saving weight in the entire construction. The cylindrical arrangement of the flat cables around the central axis of the assembly allows the assembly to bend easily in multiple directions and thus any sensor device, such as an ultrasound probe, can be easily put into a position by an operator. The cylindrical arrangement of the flat cables furthermore ensures a high flex life since any stresses within the assembly are distributed over the whole of the assembly rather than being concentrated in certain longitudinal planes. In one embodiment of the invention, the flat cables are cylindrically braided about the central axis and in a further embodiment of the invention the flat cables are cylindrically surfed or wrapped about the central axis. In order to ensure that the signal conductors within the assembly are shielded from interfering magnetic fields, an outer shield is disposed about said at least one subcable assembly , . A plurality of said at least one subcable assemblies can be cylindrically arranged around a central axis and in such a case are preferably separated from each other by a separating cylindrical shield. The use of a plurality of flat cables within the assembly, each of which contains a limited number of signal conductors, has the advantage that flexlife and handling of the cable is improved since each of the flat cables has a degree of freedom to move within the assembly. The separating cylindrical shield is used to shield the subcable assemblies from one another such that the stray electromagnetic fields created by signals in the individual signal conductors of one subcable assembly do not interfere with the signals in the individual signal conductors of a further subcable assembly. Furthermore the separating cylindrical shield serves as a reference impedance potential. A tubular spacer is disposed within said at least one subcable assembly and serves as a filler or stabiliser about which the flat cables are cylindrically arranged. The tubular spacer is constructed from a solid material, from a stranded material or is in the form of a hollow tube. In the latter case the interior of the tubular spacer can carry fluids or further electric leads, for example for control signals or power. Preferably an inner cylindrical shield is disposed between the tubular spacer and the at least one subcable assembly to provide further protection against interfering electromagnetic fields when the interior of the tubular spacer carries further electric leads and also acts as a reference ground potential. In another embodiment of the invention an outer cylindrical shield is disposed between an outer one of said at least one subcable assembly and the outer ground shield and is separated from the outer ground shield by a first insulation layer. A second insulation layer is further disposed between said outer ground shield and a jacket. These shields, insulation layers and outer jacket protect the interior of the assembly from mechanical damage and also from external interfering magnetic fields. The flat cables in the assembly are constructed from an upper insulator attached to a lower insulator which is, in the preferred embodiment of the invention, laminated to each other. In another embodiment of the invention, the upper insulator is adhered to the lower insulator by an adhesive is selected from the group of thermoplastic adhesives comprising polyester or polyurethane. Furthermore a coating of adhesion promoters made from fluorinated copolymers, such as fluorinated ethylene/propylene and perfluoroalkoxy, from epoxy resind adhesives, from amino resin adhesives, from phenolic resin adhesives or from silicone adhesives can be used to bond the layers together. The insulator is formed from the group of insulating materials consisting of polyester, perfluoralkoxy, fluoroethylene-propylene, polyolefins including polyethylene and polypropylene, polymethylpentene, polytetrafluoroethylene or expanded polytetrafluorethylene. Preferably a fluoropolymer is used and most preferably the upper insulator and the lower insulator are formed from expanded polytetrafluorethylene (ePTFE). Expanded PTFE has a very low dielectric constant and is light in weight. This ensures that the electrical properties of the assembly are extremely good and also that the assembly constructed using an ePTFE dielectric material is light in weight which allows for easy handling of the cable. Furthermore the flexlife properties of cables made from ePTFE are known to be good and thus the assembly constructed using this dielectric material also has good flexlife properties. The assembly could also be constructed using an extruded polymer or a foamed polymer. Description of the Drawings Fig. la shows an electrical signal cable assembly of the invention. Fig. lb shows another embodiment of the electrical signal cable assembly of the invention. Fig. 2 shows a cross section of a flat cable used in the inventive electrical signal cable assembly. Fig. 3 shows a method of manufacturing the plurality of subcable assemblies for the inventive electrical signal cable assembly. Fig. 4 shows a sintering device used in the manufacture of the subcable assemblies. Fig. 5 shows a diagram of an apparatus for testing the flexlife of the electrical signal cable assemblies: Fig. 6 shows a further embodiment of the invention. Fig. 7 shows a further embodiment of the invention. Fig. 8 shows a further embodiment of the invention. Detailed Description of the Invention Figs, la and lb show a cylindrical electrical signal cable assembly 10 according to the invention having a central axis 15. The term cylindrical used in this context does not imply that the assembly be geometrically cylindrical. Rather an assembly 10 whose dimensions are substantially cylindrical is also covered. Such an assembly 10 could be formed when outside forces exert pressure on the surface of the assembly 10 and "squash" one side of the assembly 10 to form an assembly 10 with an oval cross-section. In all figures, like numerals are used to denote like elements. The assembly 10 comprises an optional tubular spacer 20 forming the central core of the assembly 10. The tubular spacer 20, if present, is surrounded by a cylindrically arranged inner cylindrical shield 30 onto which is disposed a first subcable assembly 40. The structure of the subcable assembly 40 will be described later. The tubular spacer 20 is made from permeable ePTFE, PTFE, polyamide, polyurethane, persion or any other suitable material. The tubular spacer 20 may be solid or have a hollow interior to carry cooling fluids, electrical control lines, electrical power lines, gases etc. The tubular spacer 20 may further be made from a braided material. In the embodiment of the invention depicted in Figs, la and lb, the first subcable assembly 40 is disposed within a second subcable assembly 60 and is separated from the second subcable assembly 60 by a separating cylindrical shield 50. The second subcable assembly 60 has the same structure as the first subcable assembly 40. It is possible to conceive of an embodiment of the invention in which no further subcable assemblies are present. It is also possible to conceive of an embodiment in which further subcable assemblies are disposed about the second subcable assembly 60 and separated from the second subcable assembly 60 by further separating cylindrical shields. An outer cylindrical shield 70 is disposed about the outermost one of the subcable assemblies 40, 60. In the embodiment of Fig. 1 the outer cylindrical shield 70 is disposed about the second subcable assembly 60. A first insulating layer 80 is arranged about the outer cylindrical shield 70 and on this is disposed an outer shield 90. The outer shield 90 is grounded and shields the subcable assemblies 40, 60 within the assembly 10 from interfering electromagnetic fields. A second insulating layer 100 is disposed about the outer ground shield 90 and the assembly 10 is then placed within a jacket 110. The first insulating layer 80 and the second insulating layer 100 are made, for example, from PTFE, ePTFE, FEP or polyester. Preferably the first insulating layer 80 and the second insulting layer 100 are made from sintered GORE-TEX® tape which is obtainable from W.L.Gore & Associates and is wrapped about the assembly 10 using known wire-wrapping techniques. The inner cylindrical shield 30 and the separating cylindrical shield 50 are braid, foil, surfed, woven or wire shields made from a metal or a metallised polymer, such as copper, aluminium, tin-plated copper, silver-plated copper, nickel-plated copper, alloys or aluminised polyester. Later embodiments of the invention will be described in which no inner cylindrical shield 30 or separating cylindrical shield 50 are present. The outer ground shield 90 is a braid, foil or wire shield made from a metal or a metallised polymer, such as copper, aluminium, tin-plated copper, silver-plated copper, nickel-plated copper, alloys or aluminised polyester. In one embodiment of the invention, the outer ground shield 90 is made from a copper braid with a braiding angel of about 35°. In some applications, the outer ground shield 90 can be omitted. The jacket 110 is made from silicone or polyolefins such as polyethylene, polypropylene or polyethylpentene; fluorinated polymers such as fluorinated ethylene/propylene (FEP); fluorinated alkoxypolymer such as perfluoro(alkoxy)alkylanes, e.g. a co-polymer of TFE and perfluorproplyvinyl ether (PFA); polyurethane (PU), polyvinylchloride (PVC), silicone, polytetralfluoroethylene (PTFE) or expanded PTFE. In one embodiment of the invention the jacket 1 10 was made from PVC. In a further embodiment of the invention the jacket is made from ePTFE reinforced with silicone. As can be seen by close inspection of Fig. la the first subcable assembly 40 and the second subcable assembly 60 are made from a plurality of flat cables 45 which are braided together in a first embodiment of the invention. Braiding techniques are known in the art and suitable machines are available from Ratera in Manresa, Spain, SPIRKA Maschinenbau GmbH in Alfeld (Leine), Germany, Magnatech International, Inc., in Sinking Spring, USA, and Steeger GmbH & Co., Wuppertal, Germany. In the second embodiment of the invention depicted in Fig. lb, the first subcable assembly 40 and the second subcable assembly 60 are formed respectively from two layers 42a and 42b and 62a and 62b respectively. Each of the two layers 42a, 42b, 62a, 62b is formed of one or a plurality of flat cables 45 which are wrapped or surfed in opposite directions around the electrical signal cable assembly 10. Surfing the flat cables 45 in opposite directions has the advantage that cross-talk between the individual signal conductors 130 in the different flat cables 45 is reduced. A first one of the layers 42a, 62a is wrapped in a first direction. A second one of the layers 42b, 62b is wrapped in a second direction as shown in the Fig. Wrapping techniques are known in the art and suitable machines are available from Ridgeway & Co., Leicester, UK, Roblon, Denmark, Innocable, France or Stolberger, Germany. Fig. 2 shows a cross-sectional view of the flat cable 45. The flat cable 45 is made up of a plurality of individual signal conductors 130 arranged in a parallel plane and surrounded by an upper insulating layer 120a and a lower insulting layer 120b. In this example sixteen individual signal conductors 130 are shown spaced at a pitch distance a of 0.35 mm. However, this is not limiting of the invention and different pitch distances a of number of individual signal conductors 130 could be used. The upper insulating layer 120a and the lower insulating layer 120b are laminated together as will be explained later. Whilst the flat cable 45 is shown in this embodiment as being laminated, it would be possible to use extrusion techniques to extrude the individual signal conductors 130 for example within a polyurethane, an FEP-based or a polyester layer. Alternatively foamed or solid polyethylene could be used. Furthermore the upper insulating layer 120a and the lower insulating layer 120b could be adhered together using a thermoplastic adhesive such as a polyester adhesive or a polyurethane adhesive. The individual signal conductors 130 can be made from any conducting material such as copper, nickel-plated copper, tin-plated copper, silver-plated copper, tin-plated alloys, silver-plated alloys or copper alloys. The individual signal conductors 130 may be lacquered. Preferably the individual signal conductors used in the invention are made from round alloy wire. It would also be possible to use flat conductors. The number of individual signal conductors 130 depicted in Fig. 2 is not intended to limiting of the invention. The axes of the individual signal conductors 130 are separated by a first pitch distance a which is in the range of 0,1 to 1 mm. The upper insulating layer 120a and the lower insulating layer 120b can be made of any insulating dielectric material such as polyethylene, polyester, perfluoralkoxy, fluoroethylene-propylene, polypropylene, polymethylpentene, polytetrafluoroethylene or expanded polytetrafluorethylene. Preferably expanded polytetrafluoroethylene such as that described in US-A-3 953 556, US-A-4 187 390 or US-A-4 443 657 is used. Manufacture of the flat cable 45 is illustrated in Fig. 3 for the embodiment in which the upper insulating layer 120a and the lower insulating layer 120b are made from expanded PTFE. This method is essentially the same as that taught in US-A-3082292 (Gore). A plurality of individual signal conductors 130, an upper insulator 120a located above the plurality of individual signal conductors 130, and a lower insulator 120b located below the plurality of individual signal conductors 130 were communally passed between two heated contra-rotating pressure rollers 400a and 400b at a lamination temperature sufficient to achieve bonding between the lower insulator 120b and the upper insulator 120a, e.g. between 327°C and 410 °C. The flat cable 45 was thereby formed. For this purpose, the upper pressure roller 400a is provided with a number of upper peripheral grooves 410a each separated by an upper peripheral rib 420a which are lined up at a distance from one another along the circumference of the pressure rollers 400a. Similarly, the lower pressure rollers 400b is provided with a number of lower peripheral grooves 410b each separated by a lower peripheral rib 420b which are lined up at a distance from one another along the circumference of the pressure roller 400b. Each upper peripheral groove 410a of the upper pressure roller 400a together with the adjacent upper peripheral ribs 420a lines up with one of the lower peripheral grooves 410b with the adjacent lower peripheral ribs 420b of the lower pressure roller 400b to form a passageway channel for one of the electrical signal conductors 130. The distance (a) between the two pressure rollers 400a, 400b and the peripheral grooves 410a, 410b are designed in terms of their dimensions in such a way that a single conductor 410 and the upper insulator 420a and the lower insulator 420b pass continuously between a pair consisting of one of the upper peripheral grooves 410a and one of the lower peripheral grooves 410b. The upper peripheral ribs 420a and the lower peripheral ribs 420b have such a small separation from one other that the upper insulator 420a and the lower insulator 420b are firmly pressed together at these positions to form an intermediate zone 440 in the flat cable 45. In order to improve their adhesion of the upper insulator 420a to the lower insulator 420b to the individual signal conductors 130 and with each other within the flat cable 45, the flat cable 45 was led through a sintering device in which the flat cable 45 is heated such that one achieves intimate joining in the intermediate zones 140 of the flat cable 45. If using an upper insulator 420a and a lower insulator 420b made of PTFE, use is made of a sintering temperature in the range from 327° to 410°C. An example of an embodiment of a sintering device in the form of a sintering oven 150 comprising a salt bath is illustrated in a schematic and simplified form in Figure 4. In this example flat cable 45 is continually passed through the sintering oven 150. Flex-life measurements are made using an apparatus as shown in Fig. 5. A one metre long sample of the electrical signal cable assembly 10 to be tested is attached to a movable attachment 520 and hung with a weight 540 of 500g. The movable attachment 520 could swing a 30 cm long first end 525 of the electrical signal cable assembly 10 through an angle of ±90° as shown by the arrow in Fig. 5. The bending radius was 50 mm. A cycle counter 530 is used to count the number of cycles through which the first end 525 of the electrical signal cable assembly 10 was swung, i.e. from the zero, upright position to +90°, back to the zero position, to the -90° position and then back to the zero position. Stops 510a, 510b prevent the other end of the electrical signal cable assembly 10 from being swung. A measurement of the ohmic resistance of the individual signal conductors 130 within the electrical signal cable assembly 10 was carried out by connecting sixteen individual signal conductors 130 in one flat cable 45 in parallel with each other. Eight flat cables 45 were connected in series with each other. The total ohmic resistance of the electrical signal cable assembly 10 comprising eight flat cables 45 each with sixteen individual signal conductors 130 was measured at the beginning of the measurement cycles and then the number of measurement cycle carried out until the ohmic resistance had increased by 10%. A maximum of 180 000 cycles was, however, carried out and then by plotting the results obtained to the end of the measurement, the number of cycles required to increase the ohmic resistance by 10% was calculated by plotting a curve on the graph. The measurements are carried out a temperature of 22±2°C. Further details of the test are found in German National Standard DIN 0472 603 test F. Examples Example 1 This was constructed as shown in Fig. la. The tubular spacer 20 was made of a polyurethane tube and had an outer diameter of 4.0 mm. The inner cylindrical shield 30 (outer diameter 4.4 mm), the separating cylindrical shield 50 (outer diameter 6.0 mm) and the outer cylindrical shield 70 (outer diameter 7.6 mm) were made of a copper-plated polyamid fabric supplied by the Statex company of Bremen, Germany under the trade name KASSEL. The first subcable assembly 40 (outer diameter 5.6 mm) and the second subcable assembly 60 (outer diameter 7.2 mm) were both made from four flat cables 45 each containing sixteen individual signal conductors 130 of AWG 4007 made from PD 135 alloy obtainable from Fhelps Dodge in Irvine, California, at a pitch distance of 0.35 mm laminated between ePTFE with a dielectric constant of 1.3. These were braided at a braiding angle of 20-22°. The first insulation 80 (outer diameter 7.7 mm) and the second insulation 100 (outer diameter 8.2 mm) were made of an ePTFE GORE-TEX binder available from W.L.Gore & Associates. The outer shield 90 was made from braided bare alloy wire constructed with a braiding angle of approx. 40° using 36 bobbins with eight ends at 10 picks/inch (2.54 cm). The jacket 110 was made from PVC and had an outer diameter of 10.0 mm. Flexlife tests carried out on the electrical signal cable array showed that the ohmic resistance increased by 10% after only 6000 and 60 000 cycles. This was thought to be due to the extremely sharp braiding angle of the subcable assemblies 40 and 60. Example 2 This was constructed as shown in Fig. lb. The tubular spacer 20 was made of a ePTFE joint sealant filler (JSF 50) obtainable from W.L.Gore & Associates, Putzbrunn, Germany, having an outer diameter of 4.0 mm. The inner cylindrical shield 30 (outer diameter 4.4 mm), the separating cylindrical shield 50 (outer diameter 6.0 mm) and the outer cylindrical shield 70 (outer diameter 7.6 mm) were made of a copper-plated polyamid fabric supplied under the trade name KASSEL by the Statex company of Bremen, Germany. The first subcable assembly 40 (outer diameter 5.6 mm) and the second subcable assembly 60 (outer diameter 7.2 mm) were both made from two flat cables 45 each containing 32 individual signal conductors 130 of AWG 4207 made from PD135 alloy at a pitch distance of 0.35 mm laminated between ePTFE with a dielectric constant of 1.3. The first layers 42a, 62a of the first and second subcable assemblies 40, 60 were formed from one of the flat cables 45. The second layers 42b, 62b of the first and second subcable assemblies 40, 60 were formed from the other one of the flat cables 45. These were wrapped at a wrapping angle of 40°. The first insulation 80 (outer diameter 7.7 mm) and the second insulation 100 (outer diameter 8.2 mm) were made of an ePTFE GORE-TEX binder available from W.L.Gore & Associates. The outer shield 90 (outer diameter 8.1 mm) was made from braided bare alloy wire with a braiding angle of 40°. The jacket 110 was made from silicone-reinforced ePTFE obtainable from W.L.Gore & Associates, Phoenix, Arizona, under the name SILKORE and had an outer diameter of 10.5 mm. Flexlife tests carried out on the electrical signal cable array showed that the ohmic resistance increased by 10% after between 25 000 and 110 000 cycles. The capacitance between one of the individual signal conductors 130 and the outer shield 90 was 57 pF/m. Example 3 This is constructed as shown in Fig. 6. This example has a first subcable assembly 40 which is identical to the first subcable assembly of Example 2 and having an outer diameter of 5.6 mm. The example has, however, two second subcable assemblies 60' and 60" each containing flat cables 45 with forty-eight individual signal conductors 130 of AWG 4207 laminated in the same manner as the flat cables 45 of example 2 and separated by a further cylindrical separating shield 50'. The outer diameter of the first one of the second subcable assemblies 60' has an outer diameter of 7.4 mm and the second one of the second subcable assemblies 60" has an outer diameter of 9.0 mm. The further cylindrical separating shield 50' has an outer diameter of 7.8 mm. As a result of the incorporation of the two second subcable assemblies 60' and 60", the outer diameter of some of the outer layers of the electrical signal cable assembly 10 changes as follows. The outer cylindrical shield 70 has an outer diameter of 9.4 mm, the first insulation 80 had an outer diameter of 9.5 mm and the second insulation 100 had outer diameter of 9.9 mm whilst the outer shield's 90 outer diameter was 9.8. Finally the jacket 1 10 had an outer diameter of 1 1.4 mm. In this example an electrical signal cable assembly 10 with 256 individual signal conductors 130 is formed. Example 4 This was constructed as shown in Fig. 7. The tubular spacer 20 was made of an ePTFE joint sealant filler (JSF50) obtainable from W.L.Gore & Associates with an outer diameter of 4.0 mm. In contradistinction to Example 1, there was no inner cylindrical shield 30, the separating cylindrical shield 50 and the outer cylindrical shield 70. A first subcable assembly 40' and two second subcable assemblies 60' and 60" were both made from four flat cables 45 each containing sixteen individual signal conductors 130 made from PD 135 alloy of AWG 4207 at a pitch distance of 0.35 mm laminated between ePTFE with a dielectric constant of 1.3. These were braided at a braiding angle of approx. 40°. The subcable assemblies 40', 60' and 60" had outer diameter of 5.2 mm, 6.4 mm and 7.6 mm respectively. The outer shield 90 had an outer diameter of 8.0 mm and was made from braided PD 135 alloy wire of AWG 4001 obtainable from Fhelps Dodge in Irvine, California, and was braided using 36 bobbins with eight ends at 10 picks per inch (2.54 cm) with a braiding angle of approx. 35°. The jacket 110 was made from reinforced ePTFE sold under the name SILKORE by W.L.Gore & Assoicates in Phoenix, Arizona, with a wall thickness of approx. 1mm and had an outer diameter of 10.5 mm. The subcable assemblies 40', 60' and 60" together with the outer shield formed a core which was pulled into the jacket 110. Grounding between individual signal conductors 130 in this example is achieved by using every second individual signal conductor 130 as a ground conductor 130. Flexlife tests carried out on the electrical signal cable array showed that the ohmic resistance increased by substantially less than 10% after 180 000 cycles at which point the flexlife test was stopped Example 5 This example is identical with that of Example 1 except that the flat cables 45 made from individual signal conductors of AWG 4207 (0.07 mm diameter) made from PD135 alloy were braided at an angle of 20° and the tubular spacer 20 was made of polyurethane. Example 6 This example is identical with that of Example 4 except that the flat cables 45 were braided at an angle of 20° and individual signal conductors 130 of AWG 4007 (0.08 mm diameter) made from PD135 alloy were used. Flexlife tests carried out on the electrical signal cable array 10 showed that the ohmic resistance increased by substantially less than 10% after 240 000 cycles at which point the flexlife test was stopped Example 7 This example was identical with that of Example 4 except that the flat cables 45 were surfed or wrapped at an angle of 20° instead of being braided and individual signal conductors 130 of AWG 4007 (0.08 mm diameter) made from PD135 alloy were used. A polyurethane tube was used as the tubular spacer 20. Flexlife tests carried out on the electrical signal cable array 10 showed that the ohmic resistance increased by substantially less than 10% after 240 000 cycles at which point the flexlife test was stopped Example 8 This example was identical with that of Example 2 except that individual signal conductors 130 of ■ AWG 4007 (0.08 mm diameter) made from PD135 alloy were used and a polyurethane tube was used as the tubular spacer 20. Flexlife tests carried out on the electrical signal cable array showed that the ohmic resistance increased by substantially less than 10% after 180 000 cycles at which point the flexlife test was stopped Example 9 This example is illustrated in Fig. 8. The tubular spacer 20 was made of an ePTFE joint sealant filler (JSF 50) obtainable from W.L.Gore & Associates. The first subcable assembly 40 was contructed from four flat cables 45, denoted LI, L2, L3 and L4, each containing sixteen individual signal conductors 130 of AWG 4007 (0.08 mm diameter) made from PD 135 alloy at a pitch distance of 0.35 mm laminated between ePTFE with a dielectric constant of 1.3. The outer cyclindrical shield 70 was made from the KASSEL foil obtainable from the Statex company of Bremen, Germany. The first insulating layer 80 was made from an ePTFE GORE-TEX binder obtainable from W.L.Gore & Associates, Putzbrunn, Germany. Example 10 This example was identical with that of Example 2 except that a polyurethane tube was used as the tubular spacer 20 and the jacket was made of PVC. Flexlife tests carried out on the electrical signal cable array showed that the ohmic resistance increased by substantially less than 10% after 180 000 cycles at which point the flexlife test was stopped Example 11 This example was identical with that of Example 2 except that the individual signal conductors were made of wire of AWG 4007 and the jacket was made of PVC. Flexlife tests carried out on the electrical signal cable array showed that the ohmic resistance increased by substantially less than 10% after 180 000 cycles at which point the flexlife test was stopped Further Examples using different dielectric materials Further examples are carried out using the structures taught above but using different dielectric materials with different constants. These require different thickness of the upper inulsation layer 120a and the lower insulation layer 120b when the pitch distance is 0.35 mm. Table 1 illustrates the case when an impedance of the electrical signal cable assembly 10 is designed to be 80 Ω. Table 2 illustrates the case when an impedance of the electrical signal cable assembly 10 is designed to be 50 Ω. Table 1 Dielectric constant Dielectric Material AWG size conductor Thickness of one of the 130 inulation layers 120a, 120b [mm] 1.4 ePTFE, foamed PE, 4207 0.1 foamed FEP/PFA 2.1 FEP, PFA, PE 42 0,16 3.5 Polyester 42 0,3 1.4 ePTFE, foamed PE, 4007 0.122 foamed FEP/PFA 2.1 FEP, PFA, PE 40 0,193 3.5 Polyester 40 0,363 1.4 ePTFE, foamed PE, 3807 0.1255 foamed FEP/PFA 2.1 FEP, PFA, PE 38 0,24 3.5 Polyester 38 0,44 1.4 ePTFE, foamed PE, 4407 0.076 foamed FEP/PFA 2.1 FEP, PFA, PE 44 0,116 3.5 Polyester 44 0,22 Table 2 Dielectric constant Dielectric Material AWG size conductor Thickness of one of the 130 inulation layers 120a, 120b [mm] 1.4 ePTFE, foamed PE, 4207 0.05 foamed FEP/PFA 2.1 FEP, PFA, PE 42 0.066 3.5 Polyester 42 0,11 1.4 ePTFE, foamed PE, 4007 0.053 foamed FEP/PFA 2.1 FEP, PFA, PE 40 0.078 3.5 Polyester 40 0,128 1.4 ePTFE, foamed PE, 3807 0.07 foamed FEP/PFA 2.1 FEP, PFA, PE 38 0.1 3.5 Polyester 38 0,165 1.4 ePTFE, foamed PE, 4407 0.033 foamed FEP/PFA 2.1 FEP, PFA, PE 44 0.048 3.5 Polyester 44 0,08 Experimental Results The impedance and capacitance of the electrical signal cable assembly 10 was measured. The attenuation between an individual signal conductor 130 carrying a signal and the separating cyclindrical shields 30, 50, 70 joined together were measured and also the attenuation between an individual signal conductor 130 carrying a signal and an individual signal conductor 130 serving as a ground conductor. Table 3 Example 1 2 4 5 8 9 Impedance (Ohm) 97 91 125 100 93 140 Capacitance (pF/m) 52.4 57 38 46 59 39 Attenuation (dB/m) -0.73 -1 -0.87 -0.81 -0.73 Signal-Shield Attenuation (dB/m) Ground-Shield -20.3 0 -0.5 -0.57 Cross-Talk (dB/m) Cross-talk measurements were also carried out and are illustrated in the following table. In this table S indicated an individual signal conductors 130 carrying a signal, G an individual signal conductor 130 serving as a ground conductor in the same flat cable 45. x indicates an individual signal conductor 130 separating the individual signal conductors 130 on which the measurements are made. The last six entries in the table illustrate the cross-talk measurements made between individual signal conductors 130 in different layers of flat cables 45. The first three of these entries show the cross-talk between individual signal conductors 130 of different flat cable layers (L1-L2; L1-L3; L1-L4) in which separating cylindrical shields were at ground potential. The last three of these entries show the crosstalk between individual conducts 130 of different flat cable layers (L1-L2; L1-L3; L1-L4) in which some of the individual signal conductors 130 served as ground conductors. In the case of Examples 1, 2, 5, 8 and 9 the separating cylindrical shields were also at ground potential. Table 4 Measurement Points Example Number 1 2 4 5 8 9 S-S -20.3 -20.4 -19.9 -20.5 -16.8 S x S -24.5 -19.2 S x x S -26.4 -21.6 S x x x S -26.8 -23.1 G S S G -16.9 -22.2 -19.7 G S G S -38.6 -32 -35.4 SS: L1-L2 -51.4 -53.5 -46.6 -51.8 -41.2 SS: L1-L3 -48.8 -45.6 -51.1 -43.6 -36.1 SS: L1-L4 -49.5 -52 GS: L1-L2 -50.1 -42.2 -52.7 -53.6 -48 GS: L1-L3 -51.5 -42 -42.7 GS: L1-L4 -43 -50.

Claims: C L A I M S 1. Electrical signal cable assembly (10) comprising - at least one subcable assembly (40, 60) cylindrically arranged around a central axis (15), said at least one subcable assembly (40, 60) comprises a plurality of flat cables (45), each of said flat cables (45) having at least three electrical signal conductors (130) encased within and separated at a pitch distance (a) from each other by a flat cable insulator (120) and wherein at in use least one of said at least three coplanar electrical signal conductors is a ground signal conductor and carries a ground signal and in use at least at least two of said at least three coplanar electrical signal conductors (130) are signal-carrying conductors and carry a signal, and wherein the two signal-carrying conductors (130) are separated in the flat cable (45) by the ground signal condcutors. 2. Electrical signal cable assembly (10) according to claim 1 wherein said flat cables (45) are cylindrically braided about the central axis (15). 3. Electrical signal cable assembly (10) according to claim 1 wherein said flat cables (45) are cylindrically surfed about the central axis (15). 4. Electrical signal cable assembly (10) according to claim 1 wherein an outer shield (90) is disposed about said at least one subcable assembly (40, 60). 5. Electrical signal cable assembly (10) according to claim 1 wherein a plurality of said at least one subcable assembly (40, 60) are cylindrically arranged around a central axis (15). 6. Electrical signal cable assembly (10) according to claim 5 wherein said plurality of said at least one subcable assembly (40, 60) are separated from each other by a separating cylindrical shield (50, 70). 7. Electrical signal cable assembly (10) according to claim 1 wherein a tubular spacer (20) is disposed within said at least one subcable assembly (40, 60). 8. Electrical signal cable assembly (10) according to claim 7 wherein said tubular spacer (20) is constructed from a solid material. 9. Electrical signal cable assembly (10) according to claim 7 wherein said tublular spacer is in the form of a hollow tube. 10. Electrical signal cable assembly (10) according to claim 7 wherein said tubular spacer s made from a stranded material. 1 1. Electrical signal cable assembly (10) according to claim 3 wherein an inner cylindrical shield (30) is disposed between said tubular spacer (20) and said at least one subcable assembly (40, 60). 12. Electrical signal cable assembly (10) according to claim 1 wherein an inner cylindrical shield (30) is disposed within said at least one subcable assembly (40, 60). 13. Electrical signal cable assembly (10) according to claim 1 wherein an outer cylindrical shield (70) is disposed between an outer one of said at least one subcable assembly (40, 60) and said outer shield (90). 14. Electrical signal cable assembly (10) according to claim 13 wherein said outer cylindrical shield (70) is separated from said ground shield (90) by a first insulation layer (80). 15. Electrical signal cable assembly (10) according to claim 1 wherein a second insulation layer (100) is disposed between said outer ground shield (90) and said jacket (110). 16. Electrical signal cable assembly (10) according to claim 1 wherein said flat cable insulator (120) comprises an upper insulator (120a) attached to a lower insulator (120b). 17. Electrical signal cable assembly (10) according to claim 16 wherein said flat cable insulator (120) comprises an upper insulator (120a) laminated to a lower insulator (120b). 18. Electrical signal cable assembly (10) according to claim 16 wherein said flat cable insulator (120) comprises an upper insulator (120a) adhered to a lower insulator (120b) by an adhesive. 19. Electrical signal cable assembly (10) according to claim 18 wherein said adhesive is selected from the group of thermoplastic adhesives comprising polyester, polyurethane or fluorinated ethylene/propylene. 20. Electrical signal cable assembly (10) according to claim 16 wherein said flat cable insulator (120) comprises an upper insulator (120a) attached to a lower insulator (120b) by means of an adhesion promoter. 21. Electrical signal cable assembly (10) according to claim 20 wherein said adhesion promoter is selected from the group of fluorinated copolymers comprising fluorined ethylene/propylene and perfluoralkoxy. 22. Electrical signal cable assembly (10) according to claim 16 wherein said upper insulator (120a) and said lower insulator (120b) are formed from the group of insulating materials consisting of perfluoralkoxy, fluoroethylene-propylene, polyester, polyolefin including polyethylene and polypropylene, polymefhylpentene, polytetrafluoroethylene or expanded polytetrafluorethylene. 23. Electrical signal cable assembly (10) according to claim 22 wherein said upper insulator (120a) and said lower insulator (120b) are formed from expanded polytetrafluorethylene. 24. Electrical signal cable assembly (10) according to claim 1 wherein said flat cable insulator ( 120) comprises an extruded polymer. 25. Electrical signal cable assembly (10) according to claim 24 wherein said flat cable insulator comprises a foamed polymer. 26. Electrical signal cable assembly (10) according to claim 1 wherein a jacket (110) is disposed about the outside of said electrical signal cable assembly (10).

Inventors: HOFFMANN HEIKE, HOFFMANN, HEIKE
Applicants: GORE W L & ASS GMBH, HOFFMANN HEIKE, HOFFMANN, HEIKE, W.L. GORE & ASSOCIATES GMBH
Application year: 1999
Main classification: H01B7
IPC codes: H01B7, H01B11