Electrical signal bundle

Abstract: The invention is an electrical signal bundle (40) which is placed within an outer jacket (50) for use, for example, in a catheter. The electrical signal bundle (40) has a plurality of coplanar electrical signal conductors (70) encased within an insulator (80). A shielding strip (90) is placed on one side of the insulator (80) to shield the signal conductors (70) from interfering electromagnetic fields. The bundle assembly (40) is then helically twisted around a central axis (60). The electrical signal conductors (70) have a characteristic impedance in the range of 50 Ω to 200 Ω. Preferably the insulator (80) is made from expanded polytetrafluororethylene (ePTFE) and is formed from two insulators (80a, 80b) laminated onto each other.

Description: Field of the Invention The invention relates to an electrical cable having an electrical signal bundle for placing within an outer jacket. 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 multiconductor 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. 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. Summary of the Invention It is an object of the invention to provide an improved electrical signal bundle which may be placed in an outer jacket. It is furthermore an object of the invention to provide an electrical signal bundle offering easy termination to termination board. It is furthermore an object of the invention to provide an electrical signal bundle whose conductors offer coaxial properties. It is furthermore an object of the invention to provide an electrical signal bundle for use in a catheter. These and other objects of the invention are solved by providing an electrical signal bundle for placing within an outer jacket and a plurality of coplanar electrical signal conductors encased within an insulator and which form a bundle assembly. The insulator has an insulator top side and an insulator bottom side and a shielding strip is placed on one of the insulator top side or the insulator bottom side. The bundle assembly is helically twisted around a central axis and at least one of the said electrical signal conductors has a characteristic impedance in the range of 50 to 200 Ω. The encasing of the plurality of coplanar electrical signal conductors in an insulator allows the electrical signal conductors to be easily manipulated and connected to a termination board. This offers substantially improved handling over the prior art methods of using a plurality of individual coaxial conductors within a tube in which each conductor must be individually identified and matched to the appropriate connection on a termination board. The insulator ensures that all of the signal conductors within the bundle remain at a known position and thus can be easily identified. The shielding strip is used to shield at least some of the conductors from interfering electromagnetic field which are generated outside of the bundle or are generated by signals passing through other ones of the signal conductors. The shielding strip is advantageously made from the group of electrically conducting compounds consisting of metallised textile, a metal layer, metal foil, metal braid, conducting fluoropolymer filled with metal particles or a combination thereof. Preferably the metal is copper, aluminium, gold or silver or an alloy thereof and most preferably the metal is copper. In one embodiment of the invention the insulator comprises an upper insulator attached to a lower insulator. This allows the signal conductors to be placed on the surface of one of the insulators in a defined position and then the other insulator is placed on top of the conductors to hold them in a fixed position. In the preferred embodiment of the invention the upper insulator is laminated to said lower insulator. However, other attachment methods such as the use of adhesive can be used. It is, of course, possible to extrude the insulation with the signal conductors. Preferably the upper insulator and said lower insulator are formed from the group of insulating materials consisting of perfluoralkoxy, fluoroethylene-propylene, polyolefin including polypropylene and polyethylene, polymethylpentene, polytetrafluoroethylene or expanded polytetrafluorethylene and most preferably from expanded polytetrafluorethylene (PTFE). Expanded PTFE has a very low dielectric constant and, as a result, offers extremely good electrical signal properties to the bundle. The shielding strip is attached to said insulator preferably by lamination although other methods such as the use of adhesives can be used.. In order to allow the electrical signal conductors to be attached to a termination board, electrical signal conductors are exposed at one end of the electrical signal bundle. Most preferably the electrical signal conductors have a pitch distance which is matched to the distance between termination points on said termination board. This allows simple connection of the individual termination points to the signal conductors within the bundle. The electrical signal bundle of the invention can be advantageously used in a catheter. Description of the Figures Fig. 1 shows an electrical cable according to the invention. Fig. 2 shows a circuit board to which the electrical cable is to be connected Fig. 3 shows a perspective drawing of the electrical cable with the coplanar electrical signal conductors and having the shield on a first side of the electrical signal bundle. Fig. 4 shows a perspective drawing of the electrical cable with the coplanar electrical signal conductors and having the shield on a second side of the electrical signal bundle. Fig. 5 shows a manufacturing apparatus for the coplanar electrical signal conductors. Fig. 6 shows a sintering oven for the electrical signal conductors. Fig. 7 shows an apparatus for carrying out flexlife measurements. Detailed Description of the Invention Fig. 1 shows an electrical signal cable 10 forming a catheter according to the invention. The electrical signal cable 10 is connected at one end to a termination board 20 and at the other end to connectors 30a and 30b. The termination of the electrical signal cable 10 to the termination board 20 and to the connectors 30a and 30b is merely illustrative of possible terminations of the electrical signal cable of the invention and is not intended to be limiting of the invention. The electrical signal cable comprises an electrical signal bundle 40 having a first end 45a and a second end 45b and an outer jacket 50. The outer jacket has a outer jacket ends 55a and 55b. The electrical signal bundle 40 extends beyond the outer jacket ends 55a, 55b. Fig. 2 shows one example of the termination board 20 to which the electrical signal cable 10 at the second end 45b may be connected. The termination board 20 has a plurality of contacts 60a and 60b to which each of the electrical signal conductors within the electrical signal cable 10 is connected. The electrical signal conductors will be depicted in later figures. The termination board 20 may be connected to probes 65 used in a medical application. Other applications are contemplated and the use is in a medical device is not limiting of the invention. The contacts 60a and 60b have a pitch distance which is preferably matched to the pitch distance of the electrical signal conductors within the electrical signal cable 10. Fig. 3 shows the electrical signal cable 10 of the invention. It depicts the electrical signal bundle 40 within the outer jacket 50. The electrical signal bundle 40 is manufactured - as will be described later - as a planar insulation 80 within which are encased a plurality of coplanar electrical signal conductors 70 having a pitch distance from each other. The planar insulation 80 has a top side 84 and a bottom side 86. A shielding strip 90 is then attached to one of the top side 84 or the bottom side 86 of the planar insulation 80. The electrical signal bundle 40 is then helically wound around a central axis 60 and placed within the outer jacket 50. In the embodiment depicted in Fig. 3, the shielding strip 90 is placed on the top side 84 of the planar insulation and thus forms an external circumference of the helically wound electrical signal bundle 40. It could also be placed on the bottom side 86 of the planar insulation 80 to form an internal circumference of the helically wound electrical signal bundle 40 as is depicted in Fig. 4. The outer jacket 50 furthermore contains a drain wire 100. The electrical signal conductors 70 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. Preferably the electrical signal conductors 70 are made of round copper wire. It would also be possible to use flat conductors. The number of electrical signal conductors 70 depicted in Figs. 3 and 4 are not intended to be limiting of the invention. The axes of the electrical signal conductors 70 are separated by a first pitch distance a which is in the range of 0,1 to 1 mm. The insulator 80 comprises an upper insulating layer 80a and a lower insulating layer 80b which 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. The electrical signal bundle 40 is connected at its first end 45a to the connectors 30a, 30b by exposing the electrical signal conductors 70 within the electrical signal bundle by removing all or past of the insulator 80. The electrical signal bundle 40 is connected at its second end 45b by unbundling or untwisting the electrical signal bundle 40 and then exposing at least some of the electrical signal conductors 70 by preferably removing one of the upper insulating layer 80a or the lower insulating layer 80b. This allows direct connection of the exposed conductors 70 to the conductors on the termination board 20. In one embodiment of the invention the electrical signal bundle 40 has twenty-one electrical signal conductors 70. Sixteen of the electrical signal conductors 70 carry electrical measurement signals from the probes 65 attached to the termination board 20. Five of the electrical signal conductors 70 carry electrical control signals to the probes 65. The sixteen electrical signal conductors carrying measurement signals need to be shielded from electromagnetic fields outside the electrical signal cable 10 and from electromagnetic fields generated from the electrical control signals. In the embodiment of Fig. 3, the electrical signal conductors 70 carrying the measurement are situated on the outer circumference of the electrical signal bundle 40 so that the shielding strip 90 shields them from stray electromagnetic fields. In the embodiment of Fig. 4, the electrical signal conductors 70 carrying the electrical measurement signals are situated in the inner of the electrical signal bundle 40 where the shielding strip 90 shields them from stray electromagnetic fields from outside the signal bundle 40 and those generated by the electrical control signals. The outer jacket 50 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, polyvinylchloride (PVC) or polytetrafluoroethylene (PTFE) or reinforced expanded PTFE (ePTFE). In one embodiment of the invention the outer jacket 50 was made from polyethylene or expanded PTFE reinforced with silicone. The latter outer jacket 50 is available from W.L.Gore & Associates in Phoenix, Arizona, under the trade name SILKORE. Manufacture of the electrical signal bundle 40 is illustrated in Fig. 5 for the embodiment in which the upper insulating layer 80a and the lower insulating layer 80b are made from expanded PTFE. This method is essentially the same as that taught in US-A-3082292 (Gore). The same reference numerals are used to denote the components of the electrical signal bundle 40 in this figure as those used for the components of the electrical signal bundle 40 in the embodiments of the invention depicted in Figs. 3 and 4. A plurality of individual signal conductors 70, an upper insulator 80a located above the plurality of individual signal conductors 70, and a lower insulator 80b located below the plurality of individual signal conductors 70 as well as a shielding strip 90 were communally passed between two contra-rotating pressure rollers 110a and 110b at a lamination temperature sufficient to achieve bonding between the lower insulator 80b and the upper insulator 80a, e.g. between 327°C and 410 °C. In the manufacturing embodiment depicted in Fig. 5, the shielding strip 90 is placed on the top side 84 of the insulator 80. However, the same apparatus could be used to place the shielding strip 90 on the bottom side 86 of the insulator 80. The electrical signal bundle 40 was thereby formed. For this purpose, the upper pressure roller 110a is provided with a number of upper peripheral grooves 120a each separated by an upper peripheral rib 130a which are lined up at a distance from one another along the circumference of the pressure rollers 110a. Similarly, the lower pressure rollers 110b is provided with a number of lower peripheral grooves 120b each separated by a lower peripheral rib 130b which are lined up at a distance from one another along the circumference of the pressure roller 110b. Each upper peripheral groove 120a of the upper pressure roller 110a together with the adjacent upper peripheral ribs 130a lines up with one of the lower peripheral grooves 120b with the adjacent lower peripheral ribs 130b of the lower pressure roller 110b to form a passageway channel for one of the electrical signal conductors 70. The distance between the two pressure rollers 110a, 110b and the peripheral grooves 120a, 120b are designed in terms of their dimensions in such a way that a single conductor 70 and the upper insulator 80a and the lower insulator 80b pass continuously between a pair consisting of one of the upper peripheral grooves 120a and one of the lower peripheral grooves 120b. The upper peripheral ribs 130a and the lower peripheral ribs 130b have such a small separation from one other that the upper insulator 80a and the lower insulator 80b are firmly pressed together at these positions to form an intermediate zone 140 in the electrical signal bundle 40. In order to improve their adhesion of the upper insulator 80a to the lower insulator 80b to the individual signal conductors 70 and with each other within the electrical signal bundle 40, the electrical signal bundle 40 was led through a sintering device in which the electrical signal bundle 40 is heated such that one achieves intimate joining in the intermediate zones 140 of the electrical signal bundle 40. If using an upper insulator 80a and a lower insulator 80b 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 6. In this example electrical signal bundle 40 is continually passed through the sintering oven 150. Examples Table 1 shows the pitch distance a for an electrical signal bundle 40 having a characteristic impedance of 50 Ω compared with electrical signal conductors 70 of AWG (American Wire Gauge) 3801 (outer diameter 0.102 mm), 4001 (outer diameter 0.079 mm), 4201 (outer diameter 0.063 mm) and 4401 (outer diameter 0.051) and insulators made of ePTFE (dielectric constant 1.3), PTFE (dielectric constant 2.1), PES (dielectric constant 3.3). The electrical signal conductors are made of a single strand of copper wire. The shielding strip 90 is formed from a perforated silver-plated copper foil. It should be noted that the dielectric constant of PTFE is identical to that of PFA and FEP and as a result the pitch distance a obtained for PTFE will be identical to that of PFA and FEP. Pitch distance in mm AWG: 3801 4001 4201 4401 Insulator: ePTFE 0.23 0.17 0.12 0.09 PTFE 0.3 0.22 0.17 0.13 PES 0.42 0.31 0.24 0.19 Table 2 shows the same material used to obtain an electrical signal bundle 40 having a characteristic impedance of 75 Ω. Pitch distance in mm AWG: 3801 4001 4201 4401 Insulator: ePTFE 0.39 0.30 0.23 0.18 PTFE 0.58 0.44 0.34 0.27 PES 0.94 0.72 0.57 0.45 Table 3 shows the use of different insulators 80 to obtain pitch distance a of specified values. Pitch Distance a (mm) Insulator AWG Impedance (Ω) 0.1 ePTFE 4401 52 0.175 ePTFE 4001 51 0.35 ePTFE 3801 70 0.5 PTFE 3801 69 0.635 PES 4001 71 A further example of an electrical signal cable of was constructed using electrical signal conductors 70 made of AWG 4207 copper wire spaced at a pitch distance of 0.35 mm within an ePTFE insulation 80 having a dielectric constant of 1.3. A shielding strip 90 was made from copper-coated polyamide foil obtainable from the Statex company of Bremen, Germany. The characteristic impedance of the electrical signal cable 10 was 50 Ω. Flexlife measurements gave a result of around 30 000 cycles. The crosstalk between the first one of the electrical signal conductors 70 and the planar insulation was measured to be 19 dB/2.5m Assembly length at 10 MHz and 22.6 dB/2.5 m assembly length at 5 MHz. The impedance of the first one of the electrical signal conductors 70 was measured to be 85 Ω. The attenuation was measured to be 2.25 dB at 10 MHz and 1.88 dB at 5 MHz. Although a few exemplary embodiments of the present invention have been described in detail above, those skilled in the art readily appreciate that many modifications are possible without materially departing from the novel teachings and advantages which are described herein. Accordingly, all such modifications are intended to be included within the scope of the present invention, as defined by the following claims.

Claims: Electrical signal bundle (40) for placing within an outer jacket (50) and having an outer side, the electrical signal bundle (40) having a plurality of coplanar electrical signal conductors (70) encased within an insulator (80) and forming a bundle assembly (40), wherein the insulator has an insulator top side (84) and an insulator bottom side (86), a shielding strip (90) placed on one of the insulator top side or the insulator bottom side, wherein said bundle assembly (40) is helically twisted around a central axis (60) and at least one of the said electrical signal conductors (70) has a characteristic impedance in the range of 50 Ω to 200 Ω. Electrical signal bundle (40) according to claim 1 wherein said shielding strip (90) is made from the group of electrically conducting compounds consisting of metallised textile, a metal layer, metal foil, metal braid, conducting fluoropolymer filled with metal particles or a combination thereof. Electrical signal bundle according to claim 2 wherein said metal is copper, aluminium, gold or silver or an alloy thereof. Electrical signal bundle according to claim 3 wherein said metal is copper. Electrical signal bundle (40) according to claim 1, wherein the insulator (80) comprises an upper insulator (80a) attached to a lower insulator (80b). Electrical signal bundle (40) according to claim 5, wherein said upper insulator (80a) is laminated to said lower insulator (80b). Electrical signal bundle (40) according to claim 1, wherein said upper insulator (80a) and said lower insulator (80b) are formed from the group of insulating materials consisting of polyester, perfluoralkoxy, fluoroethylene-propylene, polyolefin including polypropylene and polyethylene, polymethylpentene, polytetrafluoroethylene or expanded polytetrafluorethylene Electrical signal bundle (40) according to claim 7, wherein said upper insulator (80a) and said lower insulator (80b) are formed from expanded polytetrafluorethylene. Electrical signal bundle (40) according to claim 1, wherein said shielding strip (90) is attached to said insulator (80). Electrical signal bundle (40) according to claim 9, wherein said shielding strip (90) is laminated to said insulator (80). Electrical signal bundle (40)according to claim 1 wherein the outer diameter of the electrical signal bundle (40) is less than 1,6 mm. Electrical signal bundle (40) according to claim 11 wherein said electrical signal bundle (40) has at least twenty one electrical signal conductors (70). Electrical signal bundle (40) according to claim 1 wherein said electrical signal bundle (40) has at least eight electrical signal conductors (70) with matched characteristic impedance. Electrical signal bundle (40) according to claim 13 wherein said electrical signal bundle (40) has at least sixteen electrical signal conductors (70) with matched characteristic impedance Electrical signal bundle (40) according to claim 1 wherein said electrical signal conductors (70) have an outer diameter of 0,07 mm. Electrical signal bundle (40) according to claim 1 wherein said has a first end (45a) and a second end (45b) and at the first end (45a) the electrical signal conductors (70) are exposed. Electrical signal bundle according to claim 1 wherein at the second end (45b) the bundles is untwisted and the electrical signal conductors (70) are connected to a termination board (20). Electrical signal bundle according to claim 17 wherein the electrical signal conductors (70) have a pitch distance (a) and the distance between termination points on said termination board (20) is matched to said pitch distance (a). Electrical signal bundle (40) according to claim 1 wherein the shielding strip (90) is placed on the insulator top side (84) such that the external circumference of the electrical signal bundle (40) is shielded. Electrical signal bundle (40) according to claim 1 wherein the electrical signal conductors are separated from each other by a pitch distance a and said pitch distance (a) is between 0,1 mm and 10 mm. Electrical signal bundle (40) according to claim 20 wherein said pitch distance (a) is 0,35 mm. Catheter (10) having an outer tube (50), the outer tube having a first tube outer end (55a) and a second tube outer end (55b), within which the electrical signal bundle of one of claims 1 to 20 is placed. Catheter (10) according to claim 21 wherein the bundle (40) first end (45a) extends beyond the first tube outer end (55a). Catheter according to claim 21 wherein the bundle second end (45b) and the termination board (20) extends beyond the second tube outer end (55b).

Inventors: SIEGERSCHMIDT HELMUT, SIEGERSCHMIDT, HELMUT
Applicants: GORE W L & ASS GMBH, W.L. GORE & ASSOCIATES GMBH
Application year: 1998
Main classification: H01B7
IPC codes: H01B7