Strain-tolerant conductor assemblies and methods of manufacture

Abstract

A method and system of forming a sensor includes coupling a mid-point of a conductor to a substrate and rotating the substrate to draw the conductor from a spool, forming a wound region. The wound region includes conductors extending respectively to spools. A filar is coupled to the substrate, and the spools are rotated to form a twisted pair around the filar. Tension applied to the twisted pair is at least partially transferred to the filar to reduce strain on the conductors. The sensor may be incorporated into a medical device having an elongated body. The sensor includes a coil with a wound region, a filar coupled to the wound region, and a twisted pair wrapped or braided around the filar. This construction improves mechanical durability, enables use of thinner or higher-conductivity conductors, and supports compact, modular integration into medical devices such as catheters or endoluminal tools.

Description

STRAIN-TOLERANT CONDUCTOR ASSEMBLIES AND METHODS OF MANUFACTUREFIELD

[0001] This disclosure relates to the field of conductor assemblies used in medical devices, and more particularly to strain-tolerant conductor assemblies and methods of manufacture for sensor integration and signal transmission in catheters and endoluminal instruments.BACKGROUND

[0002] Medical procedures such as endoscopic procedures or minimally invasive procedures are commonly used to treat conditions affecting organs including the liver, brain, heart, lungs, gall bladder, kidneys, and bones. To guide these procedures, clinicians frequently rely on imaging modalities, such as magnetic resonance imaging (MRI), ultrasound imaging, computed tomography (CT), cone-beam computed tomography (CBCT), and fluoroscopy (including 3D fluoroscopy) to identify and to navigate to areas of interest within a patient and ultimately target sites for biopsy or treatment.

[0003] For example, an endoscopic approach has proven useful in navigating to areas of interest within a patient. To enable the endoscopic approach, endoscopic navigation systems have been developed that use previously acquired MRI data or CT image data to generate a three-dimensional (3D) rendering, model, or volume of a body part such as a lung. In some applications, the acquired MRI data or CT image data may be acquired during the procedure (perioperatively). The resulting volume is used to create a navigation plan to facilitate the advancement of the endoscope (or other suitable medical device) within the patient anatomy to an area of interest. In some cases, the volume may be used to update a previously created navigation plan. A locating or tracking system, such as an electromagnetic (EM) tracking system, or fiber-optic sensing system (e.g., shape sensing system) may be utilized in conjunction with, for example, CT data, to facilitate guidance of the endoscope to the area of interest.

[0004] The medical device navigated within the luminal network of the patient may include a sensor, such as an electromagnetic sensor, at the distal end of the medical device that interacts with the EM tracking system to enable positioning and tracking of the distal end of the medical device as the medical device is navigated to the area of interest. However, airways of the luminal network are often small and narrow, increasingly so towards the terminal bronchioles.Larger access devices, for example, may have difficulty navigating to the area of interest if the area of interest is located adjacent to small or narrow airways.

[0005] The overall dimensions, or outer diameter, of the medical device may be driven in part by the size of the chosen electromagnetic sensor or coil. Using lighter-gauge or smaller- diameter conductors may help reduce the overall size of the electromagnetic coil. However, the size of the conductors used is limited by the forces exerted on the conductors during manufacturing, such as winding, and during operation of the medical device. As such, conductor size can be a limiting factor when reducing the overall dimensions of medical devices used to navigate to, and treat, target tissue within a patient’s luminal network. These mechanical limitations may restrict conductor selection and, in turn, limit the device’s size, flexibility, and manufacturability, especially when conductors are routed along the device wall or offset from the neutral bending axis.SUMMARY

[0006] This disclosure generally relates to strain-tolerant conductor assemblies for medical devices, including constructions that allow conductors to stretch and flex without compromising signal integrity or mechanical durability. The techniques enable conductors to be helically wound around cores that decouple mechanical strain from the conductive elements, improving manufacturability, reliability, and miniaturization.

[0007] A conductor assembly may include a twisted pair, a flexible printed circuit board assemblies (PCBA), or single filar conductors wound helically around a substrate, which may be rigid or highly extensible. In certain aspects, the extensible substrate (or core) provides both mechanical support during winding and strain relief under load. A method of forming such a conductor assembly includes coupling a mid-point of wire to a substrate, rotating the substrate about its axis to draw wire from a first wire spool and form a wound region on the substrate, the wound region including a first wire and a second wire, the first wire extending to the first wire spool and the second wire extending to a second wire spool, coupling a filar to a portion of the substrate, and rotating the first wire spool concomitantly with the second wire spool to form a twisted pair of wires, the twisted pair of wires wrapping around the filar, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.

[0008] In aspects, coupling the filar to a portion of the substrate may include coupling the filar to a notch formed within a portion of the substrate.

[0009] In certain aspects, coupling the filar to a portion of the substrate may include wrapping the filar around the substrate by doubling back and forming a loop.

[0010] In other aspects, coupling the filar to a portion of the substrate may include bonding the filar to the substrate.

[0011] In certain aspects, coupling the filar to a portion of the substrate may include temporarily coupling the filar to the substrate.

[0012] In aspects, the method may include bonding the filar to the wound region.

[0013] In other aspects, the method may include decoupling the filar from the substrate.

[0014] In certain aspects, the method may include removing the substrate from the wound region.

[0015] In aspects, the method may include threading the filar through a through-bore formed through a spindle of a twist former, the spindle rotatably supporting the first wire spool and the second wire spool.

[0016] In other aspects, the method may include frictionally engaging a portion of the filar to impart tension on the filar.

[0017] In accordance with another aspect of the disclosure, a system for manufacturing a sensor coil includes a substrate, a twist former, the twist former rotatably supported on a shaft, wherein rotation of the shaft effectuates rotation of the twist former, a spool of wire, the spool of wire supported on the twist former, a filar source, a second spool supported on the twist former, wherein the second spool is disposed in spaced relation to the spool of wire, and a motor, the motor operably coupled to the twist former, wherein the motor effectuates rotation of the spool of wire concomitantly with the second spool about the filar from the filar source to form a twisted pair of wires, the twisted pair of wires wrapping around the filar, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.

[0018] In certain aspects, the substrate may include a notch, the notch configured to receive a portion of the filar.

[0019] In aspects, the notch may be formed adjacent to a wound region of wire, the wound region of wire formed on the substrate.

[0020] In certain aspects, the spool of wire may include a first half of a length of wire and the second spool includes a remaining half of the length of wire.

[0021] In other aspects, the substrate may be removable from the wound region of wire and the filar.

[0022] In accordance with another aspect of the disclosure, a medical device includes an elongated body, the elongated body extending between a proximal end portion and an opposite, distal end portion, and a sensor, the sensor operably coupled to the elongated body, the sensor including a coil of wire disposed adjacent to the distal end portion of the elongated body,wherein the coil of wire includes a wound region, a filar operably coupled to the wound region, and a twisted pair of wires wrapped around the filar, wherein the twisted pair of wires and the filar extend in a proximal direction along the elongated body, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.

[0023] In aspects, the sensor may include a potting material, the potting material encapsulating the wound region, a distal portion of the filar, and a distal portion of the pair of wires.

[0024] In certain aspects, the distal portion of the filar may include an anchor. The anchor may be encapsulated within the potting material and may be configured to secure the filar to the potting material.

[0025] In other aspects, the filar may be bonded to the wound region.

[0026] In certain aspects, the filar may be operably coupled to a substrate, wherein the wound region is disposed on the substrate.

[0027] In aspects, the medical device may include a first protrusion member may be coupled to the substrate and disposed adjacent to the distal end portion of the wound region. The medical device may include a second protrusion member coupled to the substrate and configured to define a loop-back radius of an inner layer conductor of the coil. The second protrusion member may be a cylindrical protrusion member. The first and second protrusion members may be an integral part of the substrate.

[0028] In aspects, the at least one filar may be braided with the twisted pair. The at least one filar may include a pair of filars braided with the twisted pair.

[0029] In aspects, the at least one filar may include a pair of filars defining two valleys along a length of the pair of filars, and two conductors of the length of the twisted pair may be disposed in or adjacent to respective valleys.

[0030] In aspects, the at least one filar may have a cross-sectional area greater than a cross- sectional area of a conductor of the twisted pair.

[0031] In aspects, the at least one filar may have a rigidity greater than a rigidity of a conductor of the twisted pair.

[0032] In aspects, the at least one filar may be formed into a knot with a pair of conductors of the coil. The knot may be a hitch-type knot disposed about a substrate. The hitch-type knot may be a cow hitch knot.

[0033] In aspects, the medical device may include a saddle member coupled to the substrate. The saddle member may include a ridge and a saddle horn defining a groove. The wound region may be disposed on a portion of the groove adjacent to the ridge. The saddlehorn may define a loop-back radius of an inner layer conductor of the coil in a coil to twisted pair zone.

[0034] In accordance with still another aspect of the disclosure, a method of forming a sensor assembly includes winding a first conductor about a substrate to form a first layer of a wound region, winding a second conductor about the substrate to form a second layer of the wound region; coupling a filar to a portion of the substrate, forming a loop back of the first conductor according to a predetermined radius, and forming a twisted pair with the first conductor, the second conductor, and the filar.

[0035] In aspects, coupling the filar to the portion of the substrate may include forming a knot on the substrate with the filar. Forming a knot with the filar on the substrate may include forming a hitch-type knot on the substrate with the first conductor, the second conductor, and the filar. Forming the twisted pair may include braiding the first conductor, the second conductor, and two portions of the filar.

[0036] In aspects, forming a loop back of the first conductor includes looping back the first conductor using a first protrusion member coupled to the substrate. Winding the first and second conductors about the substrate may include winding the first and second conductors using a second protrusion member. Forming the substrate with the first and second protrusion members may define a groove, a portion of which includes the wound region.

[0037] In aspects, the method may include winding the twisted pair about the substrate.

[0038] In accordance with still another aspect of the disclosure, a strain-tolerant conductor assembly includes an elastic core, the elastic core including elastic strands extending longitudinally, and a twisted pair conductor helically wound about the elastic core, wherein the elastic core is configured to elongate under a tensile load and return to a relaxed state upon load removal, wherein a pitch of the helically-wound twisted pair conductor increases in response to elongation of the elastic core, and wherein the increase in pitch reduces axial strain on the twisted pair conductor.

[0039] In aspects, the elastic core may include two or more elastic strands.

[0040] In certain aspects, the two or more elastic strands may be twisted or braided together.

[0041] In aspects, the twisted pair conductor may include two individually insulated wires each having a diameter less than 0.1 mm.

[0042] In aspects, the twisted pair conductor may be helically wound onto the elastic core while the elastic core is maintained under longitudinal tension during fabrication.

[0043] In accordance with still another aspect of the disclosure, a medical device includes an elongated flexible body and a conductor assembly disposed along the elongated body, the conductor assembly including an extensible elastic core including elastic filaments, and a twisted pair of conductors helically wound about the extensible elastic core, wherein the conductor assembly is configured to stretch and contract in coordination with articulation or elongation of the elongated flexible body while minimizing axial strain on the twisted pair of conductors.

[0044] In aspects, the conductor assembly may be embedded within a wall of the elongated body and disposed radially outward from a neutral bending axis of the elongated body.

[0045] In aspects, the elastic core may be bonded to the elongated body along at least a portion of the length of the elastic core.

[0046] In aspects, the elastic core may include an elastane strand, a nylon strand, a polyester strand, a copolymer strand, or a fluorocarbon strand.

[0047] In aspects, the twisted pair of conductors may be secured to the extensible elastic core using an adhesive or heat-fused overwrap.BRIEF DESCRIPTION OF DRAWINGS

[0048] Various aspects of the disclosure are described hereinbelow with references to the drawings, wherein:

[0049] FIG. l is a side view of a medical device in accordance with the disclosure;

[0050] FIG. 2 is a cross-sectional view of the medical device of FIG. 1 taken along section line 2-2 of FIG. 1;

[0051] FIG. 3 is a cross-sectional view of the medical device of FIG. 1 taken along section line 3-3 of FIG. 1;

[0052] FIG. 4 is an enlarged view of the area of detail indicated in FIG. 1;

[0053] FIG. 5 is a perspective view of a sensor and twisted wire pair formed in accordance with the disclosure;

[0054] FIG. 6 is a side view of a twisted pair conductor a sensor of the medical device of FIG. 1 formed in accordance with the disclosure, illustrating the twisted wire pair forming a first angle relative to a longitudinal axis;

[0055] FIG. 7 is a side view of another example of a twisted pair conductor formed in accordance with the disclosure, illustrating the twisted wire pair forming a second angle relative to a longitudinal axis;

[0056] FIG. 8 is a perspective view of a sensor forming device in accordance with the disclosure;

[0057] FIG. 9 is a front view of the sensor forming device of FIG. 8;

[0058] FIG. 10 is a perspective view of the sensor forming device of FIG. 8 including a filar spool in accordance with the disclosure;

[0059] FIG. 11 is a perspective view of another example of the sensor forming device of FIG. 11 including a filar spool in accordance with the disclosure;

[0060] FIG. 12 is a perspective view of yet another example of the sensor forming device of FIG. 11 including a filar spool in accordance with the disclosure;

[0061] FIG. 13 is a perspective view of still another example of the sensor forming device of FIG. 11 including a filar guide in accordance with the disclosure;

[0062] FIG. 14 is a perspective view of a coil formed in accordance with the disclosure over a form having an anchor for a filar;

[0063] FIG. 15 is a perspective view of another example of a coil formed in accordance with the disclosure over a fixed core;

[0064] FIG. 16 is a perspective view of the coil of FIG. 15 shown joined to a twisted wire pair and filar;

[0065] FIG. 17A is a flow diagram of a method of forming a twisted pair coil having a filar in accordance with the disclosure;

[0066] FIG. 17B is a continuation of the flow diagram of FIG. 17A;

[0067] FIG. 18A is a perspective view of a coil that illustrates an example of a strain relief strand knot incorporated into the coil to twisted pair transition;

[0068] FIG. 18B is a side view of the coil to twisted pair transition of FIG. 18 A;

[0069] FIG. 19 is a diagram that illustrates an example of a strain relief strand knot incorporated into the coil to twisted pair transition;

[0070] FIGS. 20 A and 20B are diagrams that illustrate another example of a strain relief strand knot incorporated into the coil to twisted pair transition;

[0071] FIG. 21 is a diagram that illustrates an example of a tool used to set a loop-back radius in a coil conductor;

[0072] FIG. 22 is a perspective view of a twisted conductor assembly that illustrates a strain relief filar braided with two conductors;

[0073] FIG. 23 is a perspective view of another twisted conductor assembly that illustrates two strain relief filars braided with two conductors;

[0074] FIG. 24A is a perspective view of another twisted conductor assembly that illustrates two strain relief filars braided with two conductors;

[0075] FIG. 24B is a cross-sectional view of the twisted conductor assembly of FIG. 1; and

[0076] FIG. 25 is a cross-sectional side view of a coil assembly that illustrates examples of coil assembly features to control the coil edge and control the loop-back radius of the inner coil conductor.

[0077] FIG. 26 is a perspective view of a strain-tolerant conductor assembly including a twisted pair wire helically wrapped about an elastic core formed from elastic threads.

[0078] FIG. 27A is a side view of the conductor assembly of FIG. 26 in a relaxed state.

[0079] FIG. 27B is a side view of the conductor assembly of FIG. 27A that illustrates the extension and contraction of the conductor assembly.DETAILED DESCRIPTION

[0080] Devices such as endoscopes, catheters, and surgical probes have long integrated conductors for imaging, sensing, and therapy delivery. In conventional designs, conductors are routed with sufficient mechanical clearance and preferably close to the device’s neutral bending axis to reduce strain during articulation. For example, in a 6 mm bronchoscope with a 2.8 mm working channel, conductors for a chip-on-tip camera may be routed interior to the insertion tube, adjacent to the working channel tubing. Similarly, cardiac ablation catheters route therapy and sensing conductors through central lumens. These arrangements minimize strain on the conductors during bending.

[0081] Unlike traditional catheter-based sensors that require long conductor windings routed through central lumens or around the full device length, the disclosed system supports modular sensor construction. These sensor modules may be fabricated independently with conductors helically wound around stretchable cores, then inserted as subassemblies into the walls of medical devices. This modular approach reduces complexity, improves manufacturability, and enhances robustness against mechanical strain.

[0082] The disclosed strain-tolerant conductor assemblies address a key technical challenge in high-resolution localization systems, such as electromagnetic (EM) tracking, used across cardiac rhythm management (CRM) and surgical platforms. In comparison to fiber optic shape sensing techniques, the disclosed constructions enable lower-cost, higher-yield manufacturing. Traditional EM solutions often encounter reliability challenges when conductors are routed through thin catheter walls, where strain-induced failure is a concern. By incorporating strain-relief structures and modular assembly techniques, the disclosed conductorassemblies and the corresponding methods of manufacture improve durability, supports device miniaturization, and reduces overall development and production costs.

[0083] When conductors are routed in or on the walls of catheter shafts, away from the neutral bending axis, they undergo increased elongation and bending strain, particularly in highly articulated sections. This mechanical loading elevates the risk of fatigue and failure, which limits the extent to which devices can be miniaturized or made more flexible.

[0084] However, modern device designs reduce cross-sectional profiles and working channels for tool delivery, which increasingly forces conductors to be routed in, on, or under the device wall, substantially offset from the neutral axis. This leads to significantly greater mechanical strain, particularly in highly deflected or articulated segments. When strain exceeds the tolerances of fine-gauge conductors, risks of conductor failure, signal degradation, or fatigue increase. Accordingly, there is a need for conductor assemblies that tolerate such strain while supporting miniaturization and functionality.

[0085] As medical device profiles shrink, and designers seek to retain central working lumens for instruments or imaging, traditional strategies for conductor routing, such as central lumens, become impractical. Conductors must instead be routed along the periphery or within thin shaft walls, making strain tolerance an essential design requirement. These trade-offs affect the mechanical design, electrical integrity, and manufacturability of modem devices.

[0086] To address this challenge, this disclosure presents conductor assemblies that endure elevated strain without compromising size or performance. In particular, the disclosure is directed to a system and method for forming sensors, especially electromagnetic sensors, which incorporate strain-relief structures into conductor assemblies. The disclosure is directed to a system and method for forming sensors, particularly electromagnetic sensors. As can be appreciated, electromagnetic sensors used in medical devices and other small devices or tools utilize thin conductors that are easily broken during manufacture or during operation of the device. As such, the thickness of conductors that can be used to form these sensors is limited by the mechanical properties of the conductors, including the alloy from which the conductor is formed.

[0087] A filar (i.e., strain relief strand) may be incorporated into the twisted pair manufacturing process to transfer tension and other stresses and strains away from the conductors to the filar. As can be appreciated, transferring a portion of these forces to the filar reduces failure of the conductors during manufacture as well as during operation of the device as compared to a sensor not incorporating a filar.

[0088] Additionally, reducing the forces on the conductors enables the use of thinner gauge wires and / or alloys having increased conductivity (which may have reduced ultimate strength compared to other alloys), thereby increasing the efficiency and accuracy of the sensor relative to larger gauge wires or less conductive alloys. Examples of thinner-gauge wires and / or alloys having increased conductivity that may be used include: silver-plated copper (SPC); nickel- plated copper (NPC), copper alloys such as tin bronze (CuSn), beryllium copper (CuBe), or phosphor bronze; silver alloys such as silver-palladium (AgPd) or silver-copper (AgCu); and / or high-conductivity annealed copper, including oxygen-free high-conductivity (OFHC) and electrolytic tough pitch (ETP) copper. Additionally, plating can impart desirable properties such as increased conductivity, solderability, and corrosion resistance when combined with an alloy substrate.

[0089] The filar may be coupled to a substrate upon which the sensor coil is formed. In this manner, the filar may be introduced into the sensor after forming a wound region of wire on the substrate before forming the twisted pair of wires. The filar may be coupled to a notch formed on the substrate, bonded or otherwise mechanically coupled to the substrate (e.g., by using knots, loops, or adhesives such as epoxy, cyanoacrylate, or other suitable potting materials), or braided into the conductor itself. It is envisioned that a spool of filar may be rotatably supported on a twisted pair former, on a wire guide adjacent to the substrate, or on a pair of arms of the twisted pair former without departing from the scope of the disclosure. In aspects, a support shaft coupling the pair of arms of the twisted pair former to a motor may include a through-bore, through which the filar may be threaded.

[0090] These and other aspects of the disclosure will be described in further detail hereinbelow. Although generally described herein with reference to electromagnetic coils, it is envisioned that the systems and methods herein may be used with any devices and / or systems requiring the use of very thin conductors.

[0091] Turning now to the drawings, FIG. 1 illustrates a medical device in accordance with the disclosure is described and generally identified by reference numeral 10. The medical device 10 is configured for navigation through a luminal network of a patient. The medical device 10 includes a handle assembly 20, a telescopic channel 30, and an elongated body 40 extending between a proximal end portion 42 and a distal end portion 44. The handle assembly 20 is coupled to the proximal end portion 42 of the elongated body 40 to permit a clinician to manipulate the medical device 10. The telescopic channel 30 is positioned between the handle assembly 20 and the proximal end portion 42 of the elongated body 40 to provide lateral support for the elongated body 40. The telescopic channel 30 includes a proximal or first end portion32 that is coupled to a distal end portion 24 of the handle assembly 20 and a distal or second end portion 36 that is configured to couple the medical device 10 to a bronchoscope (not shown) or other medical device. The telescopic channel 30 includes an extendable body portion 34 between the first end portion 32 and the second end portion 36 that is expandable along a longitudinal axis and substantially rigid transverse to the longitudinal axis. The extendable body portion 34 allows the first end portion 32 to translate along and rotate about the longitudinal axis relative to the second end portion 36. When the first end portion 32 is coupled to the handle assembly 20, the proximal end portion 42 of the elongated body 40 translates and rotates with the first end portion 32 of the telescopic channel 30.

[0092] Continuing with FIG. 1 and with additional reference to FIGS. 2 and 3, the elongated body 40 defines an extended working channel (EWC) 46 along a length thereof. The EWC 46 allows instruments (not shown) to be inserted through the elongated body 40 to treat target tissue adjacent to the distal end portion 44 of the elongated body 40. The elongated body 40 includes an inner liner 48, a braid 50, and an outer coating 52. The inner liner 48 defines the EWC 46 that passes entirely through the elongated body 40. It is contemplated that the elongated body 40 may be constructed without the inner liner 48 such that the braid 50 defines the EWC 46.

[0093] With additional reference to FIG. 4, as will be described in further detail hereinbelow, a sensor 70 is formed of one continuous wire 72 wrapped over the braid 50 and covered by the outer coating 52 to form the sensor 70. The wire 72 includes a first lead 74 and a second lead 76, which together form a twisted pair 78 that is coiled about the braid 50 along the proximal end portion 42 of the elongated body 40. It will be appreciated that while the portions of the wire 72 (e.g., the first lead 74 and the second lead 76) are discussed individually herein, the wire 72 is monolithically formed (e.g., the wire 72 is one continuous wire without any solder joints between different portions thereof). By forming the sensor 70 from one continuous monolithic wire 72, the robustness of the sensor 70, and therefore the elongated body 40, is increased as compared to sensors formed from multiple wires 72.

[0094] The inner liner 48 and the outer coating 52 are formed from polymer tubes, as detailed hereinbelow, which in aspects are made from a reflowable polymer material (e.g., thermoplastic polymers or polytetrafluoroethylene (PTFE)) which may bond to the braid 50, the wire 72, and to one another. The braid 50 is constructed of a mesh of between 16 and 32 of similar or varying material cords woven together (e.g., stainless steel, polyethelene naphthalate (PEN), polyethylene terephthalate (PET), and insulated electrical wire). The wire 72 is a solid core magnetic wire with a thin dialectic coating (e.g., a copper wire with a polyimide coating).

[0095] Continuing with FIG. 4 and with additional reference to FIG. 5, the sensor 70 may be formed of a wound region 80 having a plurality of wraps of a conductive wire 72. On a proximal end of the sensor 70, the windings terminate and the first and second leads 74, 76 extend away from the wound region 80. To eliminate interference and noise in electrical systems associated with the medical device 10, the first and second leads 74, 76 are formed into a twisted pair 78. A proximal end (not shown) of the twisted pair 78 can be connected to terminals (not shown) that are connectable to a navigation system (not shown). As can be appreciated, the navigation system includes an electromagnetic field generator. By placing the sensor 70 in the electromagnetic field, a current is generated in the wound region 80, which is transmitted to the navigation system via the twisted pair 78 of wires.

[0096] Historically, the wound region 80 of the sensor 70 would be formed in one step and the twisted pair 78 in a second step. These two components then require soldering, or another mechanical connection, to electrically connect the components. However, a medical device, such as for example, a catheter or biopsy tool, is required to bend and twist for navigation and also survive the stresses induced by movement of the medical device due to respiration. Additionally, medical devices are becoming smaller in order to reach further within luminal networks and treat target tissue located adjacent to increasingly smaller lumens. As such, the components that make up the medical device necessarily need to be reduced in size to accommodate the reduction in size of the medical device.

[0097] However, the reduction in size of certain components, such as the sensor 70, is limited by the mechanical properties of extremely thin-gauge wire. Extremely thin-gauge wire, or wire formed from certain high conductivity alloys, is prone to breakage due to tension loads or other stress and strain induced by movement and / or flexing of the medical device during normal operation. For example, conductor strain is much higher than in typical applications when the medical device is highly articulated or when conductors are bound to the shaft or wall of the medical device at positions radially offset from the neutral axis or centerline of the medical device.

[0098] Further, tension applied to the wire 72 during the manufacturing process may cause undesired failure of the wire 72, resulting in waste and reduced production yields. For example, the forces involved in placing, routing, and stringing (e.g., pulling through a lumen) very fine wires may exceed the ultimate tensile strength of the material. Such conditions may inhibit efforts to reduce the size of the sensor 70, which, in turn, may inhibit efforts to reduce the size of the medical device, and may also preclude the use of high-conductivity alloys and / or thinnergauge wire 72 that would increase the efficiency and accuracy of the sensor 70.

[0099] With reference to FIGS. 6 and 7, it is envisioned that the tension loads and / or other stress and strain imparted on the wire 72 of the sensor 70 during manufacture and during normal operation can be mitigated by using a reinforcement strand or filar 82. In this manner, a portion of the stress and strain experienced by the sensor 70 and / or the twisted pair 78 is transferred to the filar 82, reducing stresses imparted on the wire 72 itself. The filar 82 may be formed from any suitable material, such as for example, a metallic material, a non-metallic material, and combinations thereof. In aspects, the filar 82 maybe formed from Kevlar, Teflon, Nitinol, carbon fiber, steel, copper, and combinations thereof.

[0100] As can be appreciated, the use of the filar 82 allows for using smaller gauge wire during the manufacture of the sensor 70, reducing the size of the sensor 70 as well as increasing the robustness of the sensor 70, the wire 72, and the twisted pair 78, and enables the use of conductors formed from high conductivity alloys having reduced ultimate strength as compared to lower conductivity alloys. In aspects, the filar 82 is interposed between each of the first lead 74 and the second lead 76 as the first lead 74 and the second lead 76 are twisted to form the twisted pair 78. Those having skill in the art will recognize that the size of the first and second leads 74, 76 and the filar 82 impacts the overall size of the twisted pair 78. First and second leads 74, 76 and / or a filar 82 having a first overall dimension causes the twisted pair 78 to form a first angle a relative to a longitudinal axis extending along the length of the twisted pair 78. First and second leads 74, 76 and / or a filar 82 having a second overall dimension that is greater than the first overall dimension causes the twisted pair 78 to form a second angle p. It is envisioned that the size of the wire 72 forming the twisted pair 78 may be reduced, the size of the filar 82 can be reduced, or both the size of the wire 72 and the filar 82 can be reduced depending upon the design needs of the sensor 70. Although generally described as being interposed between the first and second leads 74, 76 of the twisted pair 78, it is envisioned that the filar 82 may be braided or otherwise interwoven into the wire 72 itself. As can be appreciated, braiding the filar 82 into the wire 72 may reduce the angle a of each of the first and second leads 74, 76, reducing the overall dimensions of the twisted pair 78. In aspects, multiple filars 82 may be utilized without departing from the scope of the disclosure.

[0101] Turning to FIGS. 8 and 9, a winding machine for forming a sensor coil is illustrated and generally identified by reference numeral 100. The winding machine 100 defines a first axis 102 and a second axis 104 that is oriented generally perpendicular to the first axis 102. On the first axis 102 is a carriage 106 which rides on a first rail 108. The carriage 106 supports two head stocks 110. Each headstock 110 includes a chuck 112 or other suitable structure or assembly for grasping a mandrel or another substrate 62 or structure that spans a gap betweenthe two chucks 112 (FIG. 9). Either or both chucks 112 may be driven by a motor 114. In one implementation of the winding machine 100, both chucks 112 are synchronously driven by motors 114; however, in other implementations one of the chucks 112 is merely passive and not itself motor driven but rather is rotatably coupled to the driven chuck 112 through the substrate 62. In aspects, if the substrate 62 is sufficiently rigid, the second headstock 110 and chuck 112 can be eliminated and only a single headstock 110 and chuck 112 is employed.

[0102] A separate motor (not shown) is connected to a linear screw 116, which interfaces with and drives the carriage 106 along the first axis 102 defined by the first rail 108. Mounted on one of the chucks 112, such that it rotates with the chuck 112, is a spool support 118 which is configured to receive a spool of wire, the use of which will be described in greater detail hereinbelow. A wire guide 119 is configured to have the wire 72 pass therethrough. As can be appreciated, the wire guide 119 helps ensure that each successive coil of wire 72 butts up against the prior coil to form a cohesive wound region 80. In one non-limiting example, the wire guide 119 remains stationary while the headstocks 110 are advanced along the first axis 102 by the linear screw 116. Alternatively, the wire guide 119 may be mounted on the carriage 106, such that the linear screw 116 moves the wire guide 119 while the chucks 112 rotate but are otherwise fixed in location. It is contemplated that both the wire guide 119 and the headstocks 110 may be motor driven and move either in concert or independently.

[0103] It is envisioned that the substrate 62 that spans the gap between the two chucks 112 can be formed of a variety of materials. In one non-limiting example, the substrate 62 is a material that has rigidity when under tension between the two chucks 112, but once the tension is released, loses its rigidity and can be easily removed from the wound region 80 of the sensor 70. In aspects, the substrate 62 may be a rigid, reusable mandrel, such as, for example, a rod of steel or other material that can be removed from the wound region 80 of the sensor 70 for incorporation into a medical device, such as, for example, a catheter and a tool. In one nonlimiting example, the substrate 62 is a solid core that is configured to be bonded or otherwise affixed to the wound region 80.

[0104] It is contemplated that the substrate 62 may be a polymeric or metal material and intended to form a component of the medical device, such as for example, the medical device 10. For example, if formed from a polymeric material, the substrate 62 may be formed from a similar heat flowable material as other components of the medical device 10 and joined with these materials thought the medical device manufacturing process, as described in detail hereinabove. Similarly, where the substrate 62 is formed from a metal or other material resistant to piercing, the sensor 10, formed on the substrate 62, can be joined with other portionsof the medical device 10, such that when a tool (not shown) is inserted into the medical device 10, the substrate 62 protects the sensor 70, and in particular, the wound region 80 from being pierced by the tool as it navigates the internal lumen of the medical device 10, which in aspects, may be the EWC 56. It is envisioned that the substrate 62 may be formed from materials such as, for example, steel, Nitinol, titanium, PTFE, Arnitel®, polyether ether ketone (PEEK), and combinations thereof.

[0105] Although generally described as axially aligned, it is envisioned that the headstocks 110 may be as much as 20 to 30 degrees out of axial alignment. As can be appreciated, where the substrate 62 is flexible or very thin in diameter (e.g., 0.005-0.010 inches in diameter), even with axially aligned headstocks 110, rotation of the substrate 62 results in radial bowing of the substrate 62 as it rotates between the headstocks 110. This bowing can be countered locally by allowing or forcing the substrate 62 to contact the wire guide 119. In aspects, the wire guide 119 may be treated with molybdenum or PTFE to act as a bearing surface. Rotation of the substrate 62 and tension applied to the substrate 62 by the wire and a tensioner 140 forces the substrate 62 against the wire guide 119, which then acts as a bearing, which produces a portion of the substrate 62 to be substantially straight near the wire guide 119, thus allowing the formation of a wound region 80 on a straight portion of the substrate 62, despite the outward bowing caused by the rotation of the substrate 62. By placing the headstocks 110 out of alignment, the formation of the flat portion can be adjusted as needed. Although generally described herein as having coils of the wound region 80 formed with the wire 72 disposed orthogonal to the substrate 62, other angular orientations are contemplated herein without departing from the scope of the disclosure. In aspects, the coils may be formed at any angle between 20 and 70 degrees askew relative to the longitudinal axis of the substrate 62.

[0106] With continued reference to FIGS. 8 and 9, the second axis 104 of the winding machine 100 is defined by a second rail 120. The second rail 120 supports a second carriage 122, on which a post 124 is mounted. The post 124 supports a twisted pair former 126 and a spool pre-winder 128. The spool pre-winder 128 includes a motor 130 and a spindle 132 connected thereto. The spool pre-winder 128 is configured to receive a second spool 131, as will be described in further detail hereinbelow. The twisted pair former 126 includes a twisting assembly including two arms 134 extending from a shaft 136. A motor 138 connects to the two arms 134 via the shaft 136. Each arm of the two arms 134 includes a respective tensioner 140 disposed proximate to an end portion of the two arms 134 that is located radially outward from the shaft 136. Each tensioner 140 is operably coupled to a respective twist spindle 142, 144, which are configured to receive a respective spool 141, as will be described in further detailhereinbelow. A motor 146 moves the second carriage 122 and the post 124 along the second axis 104 defined by the second rail 120 as the twisted pair former 126 rotates forming a twisted pair 78 of wires.

[0107] With additional reference to FIG. 10, to accommodate the placement of the filar 82 within the twisted pair 78, the winding machine 100 may include a filar spool 150. The filar spool 150 is supported by a filar spool support 152. The filar spool support 152 is rotatably supported on a portion of the shaft 136 of the twisted pair former 126 such that the filar spool support 152 remains in a generally vertical orientation (e.g., does not rotate with the shaft 136 or the two arms 134). In this manner, it is envisioned that the filar spool support 152 may include a bearing or bushing 154 operably coupled to the shaft 136. In aspects, the filar spool support 152 includes a weight 156 for maintaining an orientation of the filar spool support 152 relative to the twisted pair former 126 as the shaft 136 rotates.

[0108] With reference to FIG. 11, it is envisioned that the filar spool 150 may be disposed proximate the motor 138 of the twisted pair former 126. A through-bore 158 is defined through the shaft 136 to receive the filar 82 and enable the filar 82 to exit the shaft 136 and be coupled to the sensor 70. As can be appreciated, routing the filar 82 through the through-bore 158 defined through the shaft 136 enables the shaft 136 to rotate without being encumbered by the filar spool 150 or the filar 82. It is contemplated that the filar spool 150 may be supported using any suitable means and may be disposed at any suitable location permitting the filar 82 to be received within the through-bore 158.

[0109] Turning to FIG. 12, in aspects, the filar spool 150 may be rotatably supported on a portion of the wire guide 119. In this manner, a guide bushing 160 is interposed between each guide-post of the wire guide 119 to support the filar 82 when transitioning from the filar spool 150 to the sensor 70. It is envisioned that the guide bushing 160 may be any suitable device capable of supporting the filar 82, such as for example, a bearing, a fixed rod, a rotatable rod, an eyelet, and combinations thereof.

[0110] Referring to FIG. 13, it is envisioned that the filar 82 may be unspooled or otherwise disposed at a location remote from the winding machine 100. As can be appreciated, without a spool to support the filar 82, a force or tension must be applied to the filar 82 to maintain a generally linear shape of the filar 82 along its length between the source of the filar 82 and the sensor 70 (e.g., inhibit sagging of the filar 82). To tension the filar 82 and / or create drag on the filar 82, a friction tensioner 162 is operably coupled to the shaft 136 or a portion of the two arms 134, although it is contemplated that the friction tensioner 162 may be disposed at any suitable location, such as for example, on the wire guide 119. The friction tensioner 162 maybe any suitable device capable of imparting drag or otherwise tensioning the filar 82, such as for example, a spring clip, a friction wheel, and combinations thereof. Although generally illustrated as being routed through the through-bore 158 of the shaft 136, those having skill in the art will recognize that the filar 82 may be routed in any suitable fashion without departing from the scope of the disclosure.

[0111] In operation, a first spool of wire 141 is placed on one of the twist spindles 142, 144 and a second spool 131 is placed on the spindle 132 of the spool pre-winder 128. Because the diameter and length of the wound region 80 are known, as is a desired length of the twisted pair 78 of wires, the overall length of the wire 72 needed to form the sensor 70 is known. Approximately half of the length of wire 72 needed to form the sensor 70 is fed from the first spool of wire 144 to the second spool supported by the spindle 132. As can be appreciated, this can be accomplished using the motor 130 to rotate the empty spool (e.g., the second spool) while a tensioner 140 connected to the twist spindle 142 on which the first spool of wire 144 is secured. The tensioner 140 ensures that proper tension is maintained on both the twist spindle 142 and the spindle 132 to prevent breakage of the wire 72 by over tensioning or the loose winding of the wire 72 on the empty spool as it is driven by the motor 130. Those of skill in the art will recognize that in lieu of pre-winding the secondary spool, the secondary spool may be pre-loaded with wire 72.

[0112] Once approximately half the length of wire 72 needed for formation of the sensor 70 is transferred from the first spool of wire 144 to the second spool of wire 131, a portion of the wire 72 is threaded through the wire guide 119 and affixed to the substrate 62 supported by the two chucks 112 and spanning the gap therebetween. It is envisioned that the wire 72 may be affixed to the substrate 62 using a clip, tape, skive, or a slot without departing from the scope of the disclosure. In aspects, the substrate 62 may be a mandrel of appropriate diameter, a thin piece of tubing, a catheter liner (e.g., PTFE), or another structure capable of supporting the wire 72 and rotating on its axis between the chucks 112. With the wire 72 affixed to the substrate 62 at approximately its midpoint, the second spool of wire 131 is moved from the spindle 132 to the spool support 118 on the head piece 110. In aspects, the filar 82 may be coupled to the substrate 62 before the wire 72 from the first spool of wire 144 is wound about the substrate 62. In this manner, the filar 82 is fed through the wire guide 119 in a similar manner to the wire 72 from the first spool 144. It is envisioned that the filar 82 may be coupled to the substrate 62 using any suitable means, such as for example, adhesives, potting material, mechanical fasteners (e.g., a clip, tape, skive, and a slot) and combinations thereof. In one nonlimiting example, the filar 82 is wrapped around the substrate 62 by doubling back and forminga loop. After the filar 82 is coupled to the substrate 62, the chucks 110 are caused to rotate. As the chucks 110 are caused to rotate, the wire 72 is drawn from the first spool 144 secured in the twist spindle 142 and the tensioner 140 ensures that the wire 72 is always under tension as it is being wound about the substrate 62, while ensuring that the wire 72 is not over-tensioned.

[0113] Once the wound region 80 is formed, which in aspects, may be formed by first wrapping 64 (FIG. 3) of the wire 72 on the medical device 10 in a first direction and then a second wrapping 66 (FIG. 3) of the wire 72 over the first wrapping 64, the wound region 80 and the portions of the wire 72 therein, is bonded to itself to form a cohesive wound region 80. It is envisioned that this bonding may be a heat bond, a solvent bond, a varnish, a wicking adhesive, and combinations thereof, amongst others. As can be appreciated, by forming the wound region 80 by wrapping the wire 72 in a first direction and then by forming a second layer by wrapping in a second direction, the wire 72 extending from the wound region 80 is proximate the portion of the wire 72 leading to the secondary spool.

[0114] Although generally described in connection with a two-layer wound region 80, the disclosure is not so limited. As can be appreciated, an even number of layers will result in the portion of the wire 72 leading to the secondary spool and to the first spool of wire 141 on the twist spindle 142 being disposed proximate one another, allowing for easy formation of the twisted pair 78 of wire. However, odd numbers of layers may also be employed in the wound region 80. To achieve an odd number of layers, either an under layer (e.g., under the wound region 80) or an over layer (e.g., over the wound region 80) of wire 72 is employed to bring the wire 72 into position for forming the twisted pair 78 of wire. The overlayer or the underlayer, which in aspects is a straight section of wire 72 oriented generally perpendicular to the coils of the wound region 80, can be accommodated in a final construction of the medical device 10, as the polymeric materials of the medical device 10, when reflowed, conform to this slight incongruity of shape.

[0115] Next, the second spool is (a) transferred from the spool support 118, (b) threaded through the wire guide 119 to one of the twist spindles 142, 144 such that there are two wires 72 extending from the wound region 80 through the wire guide 119, and (c) connected to the first spool 144 and the second spool, each of which is secured to a twist spindle 142. If the filar 82 has not yet been coupled to the substrate 62, the filar 82 is threaded through the wire guide 119 and coupled to the substrate 62 using any suitable method, structure, and / or material. In one non-limiting example, the filar 82 is coupled to a notch or slot 170 (FIG. 14) formed within the substrate 62. It is envisioned that the filar 82 may be coupled to the notch 170 using anysuitable structure and / or material, such as adhesives, potting, mechanical fasteners, and combinations thereof.

[0116] With the filar 82 coupled to the substrate 62 and threaded through the wire guide 119, the motor 138 rotates the two arms 134 via the shaft 136, causing the wires 72 to twist and form a twisted pair 78 about the filar 82 (e.g., the wires 72 are wrapped around the filar 82. The carriage drive motor 146 operably coupled to the second carriage 122 draws the twist former 128 along the second axis 104 and away from the first axis 102 until a twisted pair 78 of sufficient length has been formed or until the first spool of wire 144 or the secondary spool are exhausted of wire 72, at which point the procedure ends. It is envisioned that the filar 82 may be removed from the substrate 62 if the substrate 62 is removable or may remain with the substrate 62 if the substrate 62 is solid or is intended to remain with the wound region 12.

[0117] Once the sensor 70 has been formed, the wound region 12 can be removed from the substrate 62 and made ready for incorporating into a medical device. As can be appreciated, the sensor 70 is formed from a single length of wire 72 with no transitions or mechanical connections. In this manner, the sensor 70 need not be formed on the medical device 10 as a part of the medical device manufacturing process, but rather, can be a component added to the buildup of the medical device 10 layers. One advantage of this is that the twisted pair 78 need not be wrapped around the medical device 10, but rather, can be inserted into longitudinal spacing in the layers of the medical device 10, reducing the amount of wire 72 needed and reducing the likelihood of the wire 72 breaking during manufacturing. Although generally described as being utilized for medical devices, the disclosure is not so limited. It is envisioned that the sensor 78 may be incorporated into any device that uses electromagnetic location systems.

[0118] With reference to FIGS. 15 and 16, in aspects where the substrate 62 is a solid core, as described hereinabove, after forming the wound region 80, two wires 172 and 174 are left extending from the wound region 80. A first conductor 74 is coupled to the first wire 172 at a first joint 176 and a second conductor 76 is coupled to the second wire 172 at a second joint 178 using any suitable means, such as for example, mechanical fasteners, adhesives, solder, and combinations thereof. A bar anchor or knot 180 is formed on an end portion of the filar 82 adj acent to the wound region 80. At this point, a protective coating and / or potting 182 is applied to the wound region 80 that encapsulates the wound region 80, the first wire 172 and the first joint 176, and the second wire 174 and the second joint 178. In this manner, each of the first conductor 74, the second conductor 76, and the filar 82 are anchored to the sensor 70. With the potting 182 applied to the wound region 80, the first conductor 74 and the second conductor76 are wound about the filar 82 to create a twisted pair 78 as described in detail hereinabove. Although generally described as being formed after the potting 182 has been applied, it is envisioned that the twisted pair 78 may be formed at any suitable time without departing from the scope of the disclosure.

[0119] Turning to FIGS. 17A and 17B, and referring again to FIGS. 8 and 9, a method of forming a sensor is described and generally identified by reference numeral 200. Initially, at step 202, a first spool of wire 141 is placed in one of the twist spindles 142, 144 of a winding machine 100. At step 204, a second spool 131 is placed in a spindle 132 of a spool pre-winder 128. At step 206, approximately half the length of wire required to form a sensor is fed from the first spool of wire 141 to the second spool 131 supported by the spindle 132 of the spool pre-winder 128. As can be appreciated, steps 204 and 206 may be omitted and / or are optional, and the second spool 131 may be pre-loaded with wire so that no pre-winding is required.

[0120] Once approximately half the length of wire needed to form the sensor has been transferred from the first spool of wire 141 to the second spool 131, a portion of the wire is threaded through a wire guide of the winding machine 100 and affixed to a substrate supported by two chucks of the winding machine 100 and spanning a gap formed between the two chucks at step 208. In aspects, a filar may be threaded through the wire guide and affixed to the substrate at step 210. With the wire affixed to the substrate at approximately its midpoint, at step 212, the second spool 131 is moved from the spindle of the spool pre-winder 128 to a spool support 118 on a head piece of the winding machine 100. Those having skill in the art will recognize that the order of steps 208-212 may be reversed without departing from the scope of the disclosure.

[0121] At step 214, the chucks are rotated in a first direction to draw wire from the first spool of wire 141 secured in the twist spindle 142, 144, and in aspects where a filar is affixed to the substrate, filar from a filar spool, to form a wound region of the sensor. With the wound region formed, at step 216, the wound region is bonded to itself to form a cohesive wound region. At step 218, the second spool 131 is transferred from the spool support 118, threaded through the wire guide to one of the twist spindles 142, 144 such that there are two wires extending from the wound region, through the wire guide, and connecting to the first spool of wire 141 and the second spool 131, each of which is secured to a twist spindle 142, 144.

[0122] In aspects, where the filar has not yet been affixed to the substrate, at step 220, a filar is threaded through the wire guide and affixed to a portion of the substrate adjacent to the two wires extending from the wound region. At step 222, a motor rotates the two arms of the twisted pair former causing the wires to twist and form a twisted pair about the filar. At step224, a carriage drive motor causes the twisted pair former along a longitudinal axis until a twisted pair of sufficient length has been formed, or until the first spool 141 or the second spool 131 are exhausted of wire, at which point the procedure ends at 226. Those having skill in the art will recognize that the various steps of the above described method may be performed in any order and the above described method may be repeated any number of times without departing from the scope of the disclosure.

[0123] As described above with reference to FIGS. 4 and 5, extremely thin gauge wire, or wire formed from certain high conductivity alloys, is prone to break due to tension loads or other stress or strain induced by movement and / or flexing of a medical device during normal operation. Additionally, the region of transition from the coil to the twisted pair may be susceptible to strain and / or fracture. In aspects, strain relief may be provided through loop-back radius control and stranding that supports robustness of the twisted pair and uniformly forms and supports the region for transition from the coil to the twisted pair.

[0124] In one aspect, strain relief may be provided by setting a controlled loop-back radius in the inner-layer conductor as illustrated in FIG. 5. This controlled loop-back radius also allows for minimal size and space constraints within the system.

[0125] In another aspect, strain relief may be provided by a stranding knot integrated into the coil to twisted pair transition. The stranding knot may be a hitch-type knot, such as a “cow hitch” knot. Using a hitch-type knot may allow for anchoring that integrates strain relief stranding into the coil to twisted pair transition without additional special adhesive or component placement. An example of a hitch-type knot is shown in FIGS. 18A and 18B. FIG. 18A illustrates a stranding knot 1821 before a twisted pair is formed with a pair of conductors 1801, 1802 and a pair of strain relief strands 1811, and 1812. FIG. 18B illustrates the stranding knot 1821 after the twisted pair 1822 is formed with the pair of conductors 1801, 1802 and the pair of strain relief strands 1811, 1812.

[0126] FIG. 19 illustrates an example of how a strain relief strand may be formed into a hitch-type knot and integrated into the coil to twisted pair transition. Specifically, a strain relief strand is manipulated around the substrate 62 in the form of a hitch-type knot having two halves 1903 and 1906. A coil inner layer conductor 1901 is partially looped around the substrate 62, passed through the hitch-type knot, and looped back into the twisted pair formed by strand portions 1904 and 1905 (which, for example, is illustrated in FIG. 20B). A coil outer layer conductor 1902 is passed through the hitch-type knot into the twisted pair.

[0127] FIGS. 20A and 20B illustrate another example of how a strain relief strand may be formed into a hitch-type knot and integrated into the coil to twisted pair transition. Specifically,a strain relief strand is formed into a loop 2011, which is wound once around the substrate 62 and through which the strain relief strand halves 2003 and 2004 are passed. The coil outer and inner layer conductors 2001 and 2002 are also passed through the loop 2011 and, as illustrated in FIG. 20B, are formed into a twisted pair 2020 with the strain relief strand halves 2003, 2004.

[0128] FIG. 21 illustrates another example of how strain relief stranding may be integrated into the twisted pair. An outer layer conductor 2102 and an inner layer conductor 2103 are wound around a substrate 62 in the coil zone 2110. Alternatively, the substrate 62 may be a core, a mandrel, or other structure suitable for supporting sensor functions. A strain relief strand, which is defined by a first half strand 2101 and a second half strand 2104, is also wound around the substrate 62 in the coil zone 2110. The first and second half strands 2101, 2104 are twisted within the twisted pair of the inner and outer layer conductors 2102, 2103 in the twisted pair zone 2120.

[0129] FIG. 21 also illustrates a loop-back tool 2105 used to set a controlled loop-back radius in the coil inner layer conductor 2102 within the coil to twisted pair transition zone 2115. The controlled loop-back radius allows for minimal size and space constraints within the system. The loop-back tool 2105 holds an optimal radius in the inner and outer layer conductors 2102, 2103 and the strain relief strands 2101, 2104 as the twisted pair is first being formed. The loop-back tool 2105 is then moved away before the remaining bulk of the twisted pair (in zone 2120) is formed.

[0130] The twisted pair strain relief stranding described herein may take the form of a weave- or twisted pair-type geometry. The twisted pair-type geometry may be in the form of a three or four strand braid. For example, FIG. 22 illustrates a three-strand braid model 2200 in which a strain relief filar 2201 is braided into a pair of conductors 2202, 2204 of a twisted pair. FIG. 23 illustrates a four-strand braid 2300 in which a pair of strain relief filars 2201 are braided into a pair of conductors 2202, 2204 of a twisted pair. Alternatively, a single doubled-back filar may be used in place of the two strain relief filars 2201. The four-strand braid 2300 may be an optimal balance of strain relief to space / size profile.

[0131] If strain relief strands are greater in size and / or rigidity than the conductors, the conductors may tend to coil around the strain relief strands rather than twist uniformly about the strain relief strands. In aspects, as illustrated in FIGS. 24A and 24B, strain relief strand and / or conductor control may be applied to place the conductors 2401, 2402 in the valleys 2413, 2414 of the larger strain relief strands 2411, 2412 to achieve optimal twist uniformity.

[0132] FIG. 25 is a cross-sectional side view of a coil assembly that illustrates examples of coil assembly features to control the edge of the coil in the wound region 80 and control theloop-back radius of the coil inner layer conductor. In aspects, to couple the strain relief strand to the coil and / or substrate 62, a saddle 2510 with a saddle horn or cylindrical protrusion 2516 may be employed. The saddle 2510 may include ridges 2511, 2512 defining a groove 2514. The ridge 2511 may define an edge which may provide uniform coil edge control during manufacture. The cylindrical protrusion 2516 may be used to control the radius of the loop back of the coil inner layer conductor 2501.

[0133] A strain-tolerant conductor assembly may include a twisted pair of conductors, a flexible printed circuit board assembly (PCBA), or a single filar wound helically around a highly extensible substrate. The extensible substrate, which is referred to herein as an elastic core, may serve dual roles: (1) it acts as a structural base for the winding process, and (2) it provides a compliant, spring-like structure that absorbs mechanical strain by elongating and recoiling. By accommodating tensile loading through geometric deformation rather than material stretching, the conductor assembly helps maintain the integrity and electrical continuity of the conductors.

[0134] This disclosure further enables modular sensor subassemblies within catheter systems without requiring continuous conductor windings along the entire device length. These modular units, which may be pre-wound onto extensible substrates, can be incorporated into the catheter wall or shaft during manufacturing. The extensible substrate provides both a winding base and a compliant core that elongates under strain and recoils upon load removal, thereby preserving the geometry and function of the wound conductors.

[0135] FIG. 26 shows an example of a strain-tolerant conductor assembly 2600, which includes an elongate, elastic core 2602 formed from a bundle of elastic strands 2602a-2602c (e.g., elastic threads or monofilaments). A twisted pair 2606, including wires 2606a, 2606b, is helically wrapped around the elastic core 2602 to form a compact, flexible subassembly suitable for incorporation into a catheter or other endoluminal device. The extensible elastic core 2602 serves as both a winding substrate during fabrication and a strain-relief element in the final strain-tolerant conductor assembly 2700 shown in FIGS. 27A and 27B.

[0136] During fabrication, a removable metal mandrel 2604 is inserted alongside the elastic core 2602 to suppress bowing and enable precise winding of the twisted pair 2606. In some aspects, the metal mandrel 2604 is a nitinol wire that functions as both an axial and rotational stiffener, facilitating controlled winding around the highly elastic core strands. Once the winding process is complete, the metal mandrel 2604 is removed, yielding the strain-tolerant conductor assembly 2700 of FIGS. 27A and 27B.

[0137] As shown in FIG. 27A, the conductor assembly 2700 is shown in an unloaded or relaxed state. The twisted pair 2606, including two insulated conductors 2606a, 2606b twisted together, is helically wrapped along the length of the elastic core 2602 with a relatively tight pitch. The helical pitch and winding density of the conductors on the elastic substrate may be varied depending on the application requirements. The helical configuration provides mechanical strain decoupling by allowing the twisted pair 2606 to deform geometrically rather than elastically during extension. The elastic core 2602 provides tensile compliance and acts as a central strain-relief element. In the prototype, insulated conductors 2606a, 2606b with a diameter of approximately 0.0404 mm are helically wrapped around the elastic core 2602 formed from a bundle of three elastic threads 2602a-2602c. The elastic core 2602 is stabilized by a removable steel mandrel during winding and then released to produce a stretchable, strain- tolerant conductor assembly 2700. In aspects, the helical wrap may be more tightly spaced to extend the available strain range. However, this comes with the trade-off of greater material cost and conductor length, which, in turn, may increase resistance and reduce signal-to-noise ratio, especially for electromagnetic sensing or other applications involving small signal transmission.

[0138] In FIG. 27B, the conductor assembly 2700 is illustrated in both relaxed (2711, 2713) and extended (2712) states. Under longitudinal tensile load 2714, the elastic core 2602 elongates, causing the helical pitch of the twisted pair 2606 to increase. This geometric change accommodates axial deformation of the conductor assembly 2700 while minimizing direct tensile strain on the conductor wires 2606a, 2606b. When the tensile force is removed 2713, the elastic core 2602 recoils, returning the twisted pair 2606 toward its original pitch and configuration 2711. This elongation behavior under a load was directly observed in the fabricated prototype, confirming that geometric deformation of the winding accommodates mechanical strain while preserving electrical continuity.

[0139] The extensible nature of the elastic core 2602 allows the conductor assembly 2700 to elongate and contract in response to mechanical forces while preserving electrical continuity and minimizing stress concentration within the conductor. This construction is advantageous for routing conductors along regions of a medical device that experience frequent bending or elongation, such as steering sections of catheters, or shaft walls offset from the neutral bending axis.

[0140] The assembly shown in FIGS. 26, 27A, and 27B can be fabricated using the winding processes and equipment described in detail with reference to FIGS. 8-13. The elastic core 2602 may be tensioned during winding to ensure uniform placement of the twisted pair 2606,and the resulting assembly may be integrated into device structures either as a modular component or as part of an over molded shaft layer. The helical winding of the twisted pair 2606 over the elastic core 2602 enables both strain tolerance and compact routing of high- signal-integrity conductors in constrained geometries.

[0141] This assembly offers significant advantages over traditional conductor routing techniques that rely on helically wrapping conductors along the entire length of a medical device. Instead of forming continuous, device-long helical wraps, the disclosed modular conductor assemblies may be fabricated independently and integrated into localized sections of the device where sensing or signal transmission is needed. These modular conductor assemblies are especially beneficial in the highly and acutely articulated sections of the catheter, such as bidirectional bending regions and sections designed with small bend radii (e.g., 10 mm bend radius in a lung catheter) where mechanical strain is most pronounced. This modular approach simplifies manufacturing, enables selective repair or replacement of conductor segments, and can improve production yield by isolating potential failure points to discrete subassemblies.

[0142] In addition to manufacturing benefits, the modular conductor assembly 2700 provides a mechanically robust and electrically reliable solution that supports miniaturization, flexibility, and durability, which are critical for advanced catheter-based and endoluminal systems. The use of extensible substrates and localized integration allows devices to maintain performance in constrained geometries and in highly-articulated sections.

[0143] One illustrative example of this solution is a strain-tolerant conductor assembly, which includes one or more conductors, such as twisted pair copper wires, e.g., 46-gauge copper wires, which are helically wound around an extensible elastic core formed of extensible strands such as stretchable fishing line or elastic sewing thread (e.g., elastic spun or felted sewing cord). Alternatively, the elastic core may be implemented using other materials, including loosely knit or woven-style filars, where extensibility is achieved through slack between individual filars rather than through elastic deformation of the filars themselves.

[0144] In another alternative, the extensible core may combine both structural and material extensibility, such as a loosely knit or woven-style filar formed from an elastically deformable material. In some aspects, the filar may include a polymer light pipe, allowing the elastic core to serve multiple functions, such as mechanical strain relief and light transmission, within the allocated cross-sectional area. As described herein, this extensible elastic core may function both as a winding substrate and as a strain-absorbing element during bending or elongation, allowing the conductor assembly to maintain electrical continuity under mechanical stress.

[0145] The extensibility of the core may also be attributed to the construction of the material itself. For example, elastic sewing thread may be formed as a deliberate entanglement of many very fine threads. The unfilled spaces among these threads and their tortuous pathways enable a significant elastic range compared to a monofilament or homogeneous filar structure. In other examples, felted or electrospun materials may be used to achieve similar extensibility through geometric rearrangement of fibers (e.g., microfibers or nanofibers), rather than through material elongation alone. In some aspects, the construction of the threads or cords may be tailored to achieve desired strain relief profile.

[0146] In some aspects, the conductor assembly described herein may incorporate one or more twisted pairs, shielding elements, or bundled subassemblies disposed on a common extensible core. For example, multiple twisted pairs may be helically wound about a shared elastic substrate or arranged in parallel with individual strain-relief filars. Shielding layers, such as foil wraps or conductive braids, may be included to reduce electromagnetic interference in high-sensitivity applications. These multi-conductor or shielded constructions may be advantageous where signal integrity must be maintained during repetitive flexing or elongation.

[0147] In some aspects, the twisted pair conductors may retain a residual undulating or waveform geometry resulting from prior spooling on a small-radius mandrel during manufacture. This undulation may contribute to strain relief by introducing geometric slack that accommodates initial elongation before axial loading is transferred to the twisted pair conductors. The waveform geometry may be imparted by over- wrapping, coiling, or compressive storage techniques, and may provide durability in regions subject to frequent extension and contraction. This pre-strain geometry may supplement the helical winding strainrelief features described herein.

[0148] To construct the conductor assembly 2700, a mid-point of the twisted pair 2606 is affixed to the elastic core 2602. For assemblies incorporating highly extensible elastic cores, a rigid mandrel (e.g., a metal mandrel) may be used in conjunction with the elastic core materials (e.g., elastic threads) to provide sufficient structural support for winding. Without a rigid mandrel, application of the twisted pair onto the elastic core may not be feasible because of the flexibility of the elastic core material. For example, the elastic threads may be paired with the metal mandrel and rotated together, enabling winding of the twisted pair onto the surface of the combined mandrel and elastic thread structure. In some implementations, the elastic member may be installed under partial longitudinal tension, allowing the final conductor assembly to accommodate bidirectional strain (i.e., both tensile and compressive strain) during operation.

[0149] In one aspect, a winding fixture (e.g., the winding machine 100 illustrated in FIGS. 8-9) may include a mandrel or shaft on which the elastic core 2602 is tensioned. A temporary steel mandrel may be inserted alongside or within the elastic core 2602 to inhibit bowing or rotation during the winding process. The mandrel and elastic core 2602 may be rotated about a central axis, drawing the twisted pair 2606 from supply spools (e.g., spools 131, 141) and forming a helical wound region along the length of the elastic core 2602.

[0150] The winding pitch and density may be varied depending on the desired electrical performance and mechanical flexibility. For applications requiring high strain tolerance and electrical continuity under extension, a low-pitch, high-turns-per-length configuration may be employed. This allows the helically-wound conductors to uncoil elastically when axial strain is applied, reducing direct tensile loading on the conductor elements.

[0151] Once the winding is complete, the steel mandrel may be removed, leaving the twisted pair wire helically wound around the elastic substrate. In certain aspects, the wound conductor assembly may be encapsulated in a polymeric jacket or integrated into a catheter wall using thermoplastic bonding techniques, such as reflow of a surrounding polymer sleeve. For example, polytetrafluoroethylene (PTFE) or poly ether ether ketone (PEEK) tubes may be employed to encase the conductor and fuse around the wound structure, thereby providing environmental protection and positional stability.

[0152] This modular conductor assembly enables localized assembly of sensor or electrode arrays (e.g., the sensor 70 illustrated in FIG. 4) within catheter shafts or flexible instruments. Unlike whole-device helical wraps, the conductor winding may not need to extend along the entire device length but may be formed as discrete modules that are subsequently integrated into the final device.

[0153] In some aspects, the elastic core may also serve as a mechanical strain relief or “filar” as described in greater detail herein. The elastic core provides distributed support along the length of the twisted pair and absorbs tensile forces during flexure. The resulting assembly provides improved mechanical durability under bending, elongation, or torsion, especially when the conductors are positioned radially away from a neutral bending axis within thinwalled catheter or endoscopic devices.

[0154] From the foregoing and with reference to the various figures, those skilled in the art will appreciate that certain modifications can be made to the disclosure without departing from the scope of the disclosure.

[0155] The invention may be further described by reference to the following numbered paragraphs:1. A method of forming a sensor, comprising: coupling a mid-point of wire to a substrate; rotating the substrate about its axis to draw wire from a first wire spool and form a wound region on the substrate, the wound region including a first wire and a second wire, the first wire extending to the first wire spool and the second wire extending to a second wire spool; coupling a filar to a portion of the substrate; and rotating the first wire spool concomitantly with the second wire spool to wrap a twisted pair of wires around the filar, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.2. The method according to paragraph 1, wherein coupling the filar to a portion of the substrate includes coupling the filar to a notch formed within a portion of the substrate.3. The method according to paragraph 1 , wherein coupling the filar to a portion of the substrate includes wrapping the filar around the substrate by doubling back and forming a loop.4. The method according to paragraph 1, wherein coupling the filar to a portion of the substrate includes bonding the filar to the substrate.5. The method according to paragraph 1, wherein coupling the filar to a portion of the substrate includes temporarily coupling the filar to the substrate.6. The method according to any of the preceding paragraphs, further comprising bonding the filar to the wound region.7. The method according to any of the preceding paragraphs, further comprising decoupling the filar from the substrate.8. The method according to any of the preceding paragraphs, further comprising removing the substrate from the wound region.9. The method according to any of the preceding paragraphs, further comprising threading the filar through a through-bore formed through a spindle of a twist former, the spindle rotatably supporting the first wire spool and the second wire spool.10. The method according to any of the preceding paragraphs, further comprising frictionally engaging a portion of the filar to impart tension on the filar.11. A system for manufacturing a sensor coil, comprising: a substrate; a twist former rotatably supported on a shaft, wherein rotation of the shaft effectuates rotation of the twist former; a first spool supported on the twist former, wherein the first spool includes a conductor; a filar source; a second spool supported on the twist former, wherein the second spool is disposed in spaced relation to the first spool; and a motor operably coupled to the twist former, wherein the motor effectuates rotation of the first spool concomitantly with the second spool about a filar from the filar source to wind a twisted pair of wires around the filar, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.12. The system according to paragraph 11, wherein the substrate includes a notch configured to receive a portion of the filar.13. The system according to paragraph 12, wherein the notch is formed adjacent to wire formed on the substrate in a wound region.14. The system according to paragraph 13, wherein the first spool includes a first half of a length of the wire and the second spool includes a remaining half of the length of the wire.15. The system according to paragraph 13, wherein the substrate is removable from the wire and the filar in the wound region.16. A medical device comprising:an elongated body extending between a proximal end portion and an opposite, distal end portion; and a sensor, the sensor operably coupled to the elongated body, the sensor including: a coil disposed adjacent to the distal end portion of the elongated body, wherein the coil includes a wound region; a filar operably coupled to the wound region; and a twisted pair braided with the filar, wherein the twisted pair and the filar extend in a proximal direction along the elongated body, wherein a portion of tension applied to the twisted pair is transferred to the filar.17. The medical device according to paragraph 16, wherein the sensor includes potting material, and wherein the potting material encapsulates the wound region, a distal portion of the filar, and a distal portion of the twisted pair of wires.18. The medical device according to paragraph 17, wherein the distal portion of the filar includes an anchor, and wherein the anchor is encapsulated within the potting material and is configured to secure the filar to the potting material.19. The medical device according to paragraph 16, wherein the filar is bonded to the wound region.20. The medical device according to paragraph 16, wherein the filar is coupled to a substrate, and wherein the wound region is disposed on the substrate.21. The medical device according to paragraph 20, further comprising a first protrusion member coupled to the substrate and disposed adjacent to the distal end portion of the wound region.22. The medical device according to paragraph 21, further comprising a second protrusion member coupled to the substrate and configured to define a loop-back radius of an inner layer conductor of the coil.23. The medical device according to paragraph 22, wherein the second protrusion member is a cylindrical protrusion member.24. The medical device according to paragraph 22, wherein the first and second protrusion members are an integral part of the substrate.25. The medical device according to any of the preceding paragraphs, wherein the at least one filar is braided with the twisted pair.26. The medical device according to paragraph 25, wherein the at least one filar includes a pair of filars braided with the twisted pair.27. The medical device according to any of the preceding paragraphs, wherein the at least one filar includes a pair of filars defining two valleys along a length of the pair of filars, and wherein two conductors of the length of the twisted pair are disposed in or adjacent to respective valleys.28. The medical device according to any of the preceding paragraphs, wherein the at least one filar has a cross-sectional area greater than a cross-sectional area of a conductor of the twisted pair.29. The medical device according to any of the preceding paragraphs, wherein the at least one filar has a rigidity greater than a rigidity of a conductor of the twisted pair.30. The medical device according to any of the preceding paragraphs, wherein the at least one filar is formed into a knot with a pair of conductors of the coil.31. The medical device according to paragraph 30, wherein the knot is a hitch-type knot disposed about a substrate.32. The medical device according to paragraph 30, wherein the hitch-type knot is a cow hitch knot.33. The medical device according to paragraph 20, further comprising a saddle member coupled to the substrate, wherein the saddle member includes a ridge and a saddle horn defining a groove, wherein the wound region is disposed on a portion of the groove adjacent to the ridge, and wherein the saddle horn defines a loop-back radius of an inner layer conductor of the coil in a coil to twisted pair zone.34. A method of forming a sensor assembly, comprising: winding a first conductor about a substrate to form a first layer of a wound region; winding a second conductor about the substrate to form a second layer of the wound region; coupling a filar to a portion of the substrate; forming a loop back of the first conductor according to a predetermined radius; and forming a twisted pair with the first conductor, the second conductor, and the filar.35. The method according to paragraph 34, wherein coupling the filar to the portion of the substrate includes forming a knot on the substrate with the filar.36. The method according to paragraph 35, wherein forming a knot with the filar on the substrate including forming a hitch-type knot on the substrate with the first conductor, the second conductor, and the filar.37. The method according to paragraph 36, wherein forming the twisted pair includes braiding the first conductor, the second conductor, and two portions of the filar.38. The method according to any of the preceding paragraphs, wherein forming a loop back of the first conductor includes looping back the first conductor using a first protrusion member coupled to the substrate.39. The method according to paragraph 38, wherein winding the first and second conductors about the substrate includes winding the first and second conductors using a second protrusion member.40. The method according to paragraph 39, further comprising forming the substrate with the first and second protrusion members defining a groove, a portion of which includes the wound region.41. The method according to any of the preceding paragraphs, further comprising winding the twisted pair about the substrate.42. A strain-tolerant conductor assembly comprising: an elastic core including elastic strands extending longitudinally; and a twisted pair conductor helically wound about the elastic core, wherein the elastic core is configured to elongate under a tensile load and return to a relaxed state upon load removal, wherein a pitch of the helically-wound twisted pair conductor increases in response to elongation of the elastic core, and wherein the increase in pitch reduces axial strain on the twisted pair conductor.43. The strain-tolerant conductor assembly according to paragraph 42, wherein the elastic core includes two or more elastic strands.44. The strain-tolerant conductor assembly according to any of the preceding paragraphs, wherein the two or more elastic strands are twisted or braided together.45. The strain-tolerant conductor assembly according to any of the preceding paragraphs, wherein the twisted pair conductor includes two individually insulated wires each having a diameter less than 0.1 mm.46. The strain-tolerant conductor assembly according to any of the preceding paragraphs, wherein the twisted pair conductor is helically wound onto the elastic core while the elastic core is maintained under longitudinal tension during fabrication.47. A medical device comprising: an elongated flexible body; anda conductor assembly disposed along the elongated body, the conductor assembly including: an extensible elastic core including elastic filaments; and a twisted pair of conductors helically wound about the extensible elastic core, wherein the conductor assembly is configured to stretch and contract in coordination with articulation or elongation of the elongated flexible body while minimizing axial strain on the twisted pair of conductors.48. The medical device according to paragraph 47, wherein the conductor assembly is embedded within a wall of the elongated body and disposed radially outward from a neutral bending axis of the elongated body.49. The medical device according to any of the preceding paragraphs, wherein the elastic core is bonded to the elongated body along at least a portion of the length of the elastic core.50. The medical device according to any of the preceding paragraphs, wherein the elastic core includes an elastane strand, a nylon strand, a polyester strand, a copolymer strand, or a fluorocarbon strand.51. The medical device according to any of the preceding paragraphs, wherein the twisted pair of conductors is secured to the extensible elastic core using an adhesive or heat- fused overwrap.

Claims

WHAT IS CLAIMED IS:

1. A method of forming a sensor, comprising: coupling a mid-point of wire to a substrate; rotating the substrate about its axis to draw wire from a first wire spool and form a wound region on the substrate, the wound region including a first wire and a second wire, the first wire extending to the first wire spool and the second wire extending to a second wire spool; coupling a filar to a portion of the substrate; and rotating the first wire spool concomitantly with the second wire spool to wrap a twisted pair of wires around the filar, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.

2. The method according to claim 1, wherein coupling the filar to a portion of the substrate includes coupling the filar to a notch formed within a portion of the substrate, wrapping the filar around the substrate by doubling back and forming a loop, bonding the filar to the substrate, or temporarily coupling the filar to the substrate.

3. The method according to any of the preceding claims, further comprising bonding the filar to the wound region, decoupling the filar from the substrate, or removing the substrate from the wound region.

4. The method according to any of the preceding claims, further comprising threading the filar through a through-bore formed through a spindle of a twist former, the spindle rotatably supporting the first wire spool and the second wire spool.

5. The method according to any of the preceding claims, further comprising frictionally engaging a portion of the filar to impart tension on the filar.

6. A system for manufacturing a sensor coil, comprising: a substrate; a twist former rotatably supported on a shaft, wherein rotation of the shaft effectuates rotation of the twist former; a first spool supported on the twist former, wherein the first spool includes a conductor; a filar source;a second spool supported on the twist former, wherein the second spool is disposed in spaced relation to the first spool; and a motor operably coupled to the twist former, wherein the motor effectuates rotation of the first spool concomitantly with the second spool about a filar from the filar source to wind a twisted pair of wires around the filar, wherein a portion of tension applied to the twisted pair of wires is transferred to the filar.

7. The system according to claim 6, wherein the substrate includes a notch configured to receive a portion of the filar, and wherein the notch is formed adjacent to wire formed on the substrate in a wound region.

8. The system according to any of the preceding claims, wherein the first spool includes a first half of a length of the wire and the second spool includes a remaining half of the length of the wire.

9. The system according to any of the preceding claims, wherein the substrate is removable from the wire and the filar in the wound region.

10. A medical device comprising: an elongated body extending between a proximal end portion and an opposite, distal end portion; and a sensor, the sensor operably coupled to the elongated body, the sensor including: a coil disposed adjacent to the distal end portion of the elongated body, wherein the coil includes a wound region; a filar operably coupled to the wound region; and a twisted pair braided with the filar, wherein the twisted pair and the filar extend in a proximal direction along the elongated body, wherein a portion of tension applied to the twisted pair is transferred to the filar.

11. The medical device according to claim 10, wherein the sensor includes potting material, wherein the potting material encapsulates the wound region, a distal portion of the filar, and a distal portion of the twisted pair of wires, wherein the distal portion of the filar includes an anchor, andwherein the anchor is encapsulated within the potting material and is configured to secure the filar to the potting material.

12. The medical device according to any of the preceding claims, wherein the filar is bonded to the wound region.

13. The medical device according to any of the preceding claims, wherein the filar is coupled to a substrate, and wherein the wound region is disposed on the substrate.

14. The medical device according to any of the preceding claims, further comprising: a first protrusion member coupled to the substrate and disposed adjacent to the distal end portion of the wound region; a second protrusion member coupled to the substrate and configured to define a loop- back radius of an inner layer conductor of the coil, wherein the second protrusion member is a cylindrical protrusion member, and wherein the first and second protrusion members are an integral part of the substrate.

15. The medical device according to any of the preceding claims, wherein the at least one filar is braided with the twisted pair, and wherein the at least one filar includes a pair of filars braided with the twisted pair.

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