Flexible shielded position sensor

Abstract

The present invention is entitled "Flexible Shielded Position Sensor." In one embodiment, a medical device includes an instrument including a distal end configured for insertion into a body part; and a position sensor including a flexible printed circuit comprising alternating conductive and dielectric layers wrapped around the distal end of the instrument, the conductive layers comprising: at least one inner layer patterned with traces to form a coil; and a plurality of outer layers covering the at least one inner layer and configured to connect to an electrical ground to shield the coil from electromagnetic interference.

Description

Technical Field

[0001] The present invention relates to medical devices and, in particular, but not exclusively, to position sensors for medical devices. Background Art

[0002] A large number of medical procedures involve placing probes such as guidewires and catheters within the patient's body. Position sensing systems have been developed to track such probes. Magnetic position sensing is a method known in the art. In magnetic position sensing, a magnetic field generator is typically placed at a known position outside the patient's body. A magnetic field sensor within the distal end of the probe generates electrical signals in response to these magnetic fields, which are processed to determine the coordinate position of the distal end of the probe. These methods and systems are described in U.S. Patents No. 5,391,199, No. 6,690,963, No. 6,484,118, No. 6,239,724, No. 6,618,612, and No. 6,332,089, in PCT International Patent Publication No. WO 1996 / 005768, and in U.S. Patent Application Publication No. 2003 / 0120150 and No. 2004 / 0068178, the disclosures of which are incorporated herein by reference in their entirety.

[0003] U.S. Patent Publication 2013 / 0131496 to Jenkins et al. describes an MRI-compatible catheter that reduces local heating caused by induced currents in an MRI scanner and includes an elongated flexible shaft having a distal end portion and an opposing proximal end portion. A handle is attached to the proximal end portion and includes an electrical connector interface configured to be electrically connected to the MRI scanner. One or more RF tracking coils are positioned adjacent to the distal end portion of the shaft. Each RF tracking coil includes a conductive lead, such as a coaxial cable, that extends between the RF tracking coil and the electrical connector interface and electrically connects the RF tracking coil to the MRI scanner. In some embodiments, the conductive lead has a length sufficient to define an odd harmonic / multiple of a quarter wavelength of the operating frequency of the MRI scanner and / or includes a series of pre-shaped round-trip segments along its length.

[0004] US Patent Publication 2013 / 0235550 to Stevenson et al. describes a shielded three-terminal flat-through EMI / energy dissipation filter that includes an active electrode plate through which circuit current flows between a first terminal and a second terminal, a first shield plate on a first side of the active electrode plate, and a second shield plate on a second side of the active electrode plate opposite the first side. The first shield plate and the second shield plate are conductively coupled to a third terminal that is grounded. In some embodiments, the active electrode plate and the shield plate are at least partially provided with a hybrid flat-through substrate that can include a flexible cable segment, a rigid cable segment, or both. Summary of the Invention

[0005] According to an embodiment of the present disclosure, a medical device is provided, comprising: an instrument, the instrument including a distal end configured for insertion into a body part; and an orientation sensor, the orientation sensor including a flexible printed circuit, the flexible printed circuit including alternating conductive layers and dielectric layers and wrapped around the distal end of the instrument, the conductive layer including: at least one inner layer, the at least one inner layer patterned with traces to form a coil; and multiple outer layers, the multiple outer layers covering the at least one inner layer and configured to be connected to an electrical ground to shield the coil from electromagnetic interference.

[0006] Additionally, according to embodiments of the present disclosure, the combined thickness of the outer layers is in the range of 100 microns to 300 microns.

[0007] Additionally, according to an embodiment of the present disclosure, the instrument includes a proximal end, the position sensor includes two electrical connectors electrically connecting the coil to the proximal end, and the plurality of outer layers include elongated sections covering the electrical connectors to shield the electrical connectors from electromagnetic interference.

[0008] Additionally, in accordance with an embodiment of the present disclosure, the coil includes a major surface at least 90% of which is shielded by the plurality of outer layers.

[0009] Furthermore, according to an embodiment of the present disclosure, each outer layer of the plurality of outer layers includes a major surface at least 90% of which is covered by the metal foil.

[0010] Additionally, according to an embodiment of the present disclosure, the thickness of each of the plurality of outer layers is in a range of 40 micrometers to 100 micrometers.

[0011] In addition, according to an embodiment of the present disclosure, a coil is formed of a plurality of layers connected by vias.

[0012] Additionally, in accordance with an embodiment of the present disclosure, the distal end of the instrument is formed as an elongated metal tool.

[0013] According to another embodiment of the present disclosure, a method of manufacturing a medical device is also provided, the method including forming a position sensor from a flexible printed circuit, the flexible printed circuit including alternating conductive layers and dielectric layers, the conductive layers including: at least one inner layer, the at least one inner layer being patterned with traces to form a coil; and a plurality of outer layers covering the at least one inner layer and being configured to be connected to an electrical ground to shield the coil from electromagnetic interference; wrapping the position sensor around a distal end of an instrument configured for insertion into a body part; and adhering the position sensor to the distal end.

[0014] Furthermore, according to embodiments of the present disclosure, the combined thickness of the outer layers is in the range of 100 microns to 300 microns.

[0015] Additionally, according to an embodiment of the present disclosure, a method includes forming the flexible printed circuit such that the plurality of outer layers include an elongated portion covering electrical connections from the coil to the proximal end of the instrument to shield the electrical connections from electromagnetic interference.

[0016] Additionally, in accordance with an embodiment of the present disclosure, the coil includes a major surface at least 90% of which is shielded by the plurality of outer layers.

[0017] Additionally, according to embodiments of the present disclosure, each outer layer of the plurality of outer layers includes a major surface at least 90% of which is covered by the metal foil.

[0018] Furthermore, according to an embodiment of the present disclosure, the thickness of each of the plurality of outer layers is in a range of 40 micrometers to 100 micrometers.

[0019] In addition, according to an embodiment of the present disclosure, a coil is formed of a plurality of layers connected by vias.

[0020] Additionally, in accordance with an embodiment of the present disclosure, the distal end of the instrument is formed as an elongated metal tool. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The present invention will be understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

[0022] Figure 1 is a schematic diagram of a medical surgical system according to an embodiment of the present invention;

[0023] Figure 2 is a schematic diagram of a magnetic field radiation component used in a medical surgery system according to an embodiment of the present invention;

[0024] Figure 3 For use Figure 1 A schematic diagram of the medical devices in the system;

[0025] Figure 4 Shown Figure 3 Handles and interchangeable heads of medical devices;

[0026] Figure 5 For Figure 3 A plan view of a sensor used with a medical device;

[0027] Figure 6 To set in Figure 3 An interchangeable head on one of the interchangeable heads of a medical device Figure 5 Schematic diagram of the sensor;

[0028] Figure 7 Taken along line AA Figure 5 A cross-sectional view of the sensor;

[0029] Figure 8 for Figure 5 a plan view of one of the plurality of layers of the sensor; and

[0030] Figure 9 for Figure 5 An exploded view of the sensor; and

[0031] Figure 10 is a flow chart including steps in a method of manufacturing a medical device according to an embodiment of the present invention. DETAILED DESCRIPTION

[0032] Overview

[0033] In medical devices such as cardiac catheters that use magnetic coil sensors for navigation, the coil may be covered with one or more metal electrodes, such as ablation electrodes or mapping electrodes, which, in addition to performing their primary function (e.g., ablation or mapping), also act as radio frequency (RF) shielding for the magnetic sensor in the device. However, for other medical devices such as ENT tools or guidewires that do not include metal electrodes covering the magnetic sensor, the magnetic sensor may be exposed to unwanted electromagnetic interference (e.g., from an RF source). For example, if the sensor operates at 20 kHz and a nearby analog-to-digital converter switches at 120 kHz, some of the switching frequency signals may be collected by the sensor. This interference significantly reduces the efficiency of the sensor. In addition, since the signal amplitude of the interference may be much higher than the signal amplitude of the magnetic signal used for tracking the magnetic sensor, the use of an electronic low-pass filter may not be sufficient to remove the interference from the signal detected by the sensor. Although covering the magnetic sensor with a metal cover can provide some shielding, in many implementations, it may be impractical to fix the metal cover to the magnetic sensor.

[0034] Embodiments of the present invention address the aforementioned problems by providing a medical device comprising an instrument and a position sensor comprising a flexible printed circuit having alternating conductive and dielectric layers, the position sensor being wrapped around and adhered to a distal end of the instrument. The conductive layer comprises at least one inner layer patterned with traces to form a coil and a plurality of outer layers covering the inner layer, the at least one inner layer being patterned with traces to form a coil, the plurality of outer layers being connected to an electrical ground during operation of the medical device to shield the coil from electromagnetic interference. Each of the outer conductive layers is disposed on one of the dielectric layers and can be formed from a "raw" printed circuit board (PCB) layer comprising a dielectric substrate, such as a polymer, covered with a conductive layer, such as copper foil.

[0035] When the outer layers are connected and grounded, these layers effectively act as a single thick conductive layer that provides electromagnetic shielding depending on the thickness of the combined outer layers. In some embodiments, the combined thickness of the outer layers ranges from 100 microns to 300 microns. In other embodiments, the combined thickness of the outer layers may be less than 100 microns or greater than 300 microns. The penetration of electromagnetic signals into the outer layers varies with the signal frequency (for a given thickness of conductor, the higher the frequency, the shorter the distance the signal can penetrate). Therefore, the thickness and / or number of outer layers can be selected so that the operating frequency of the sensor (e.g., 20 kHz) sufficiently penetrates the outer layers, while higher "interference" frequencies (e.g., 120 kHz) are sufficiently attenuated. For example, the "skin depth" of copper, which reduces the current density to approximately 1 / e of its initial value, is approximately 188 microns at 120 kHz and 460 microns at 20 kHz. Therefore, using four copper layers, each 50 microns thick, will significantly reduce the 120 kHz signal picked up by the coil (to approximately 1 / e), while allowing a significant amount of the 20 kHz signal to be detected by the coil. The plurality of connected outer layers effectively acts as a physical low-pass filter, allowing low-frequency signals to pass and blocking (or reducing) higher-frequency signals. Thus, the plurality of layers acts as a frequency-selective RF shield for the position sensor. The thickness and / or number of outer conductive layers can be selected while still maintaining sufficient flexibility of the flexible printed circuit to allow the flexible printed circuit to be wrapped around the distal end.

[0036] In some embodiments, the distal end of the instrument is formed as an elongated metal tool. In other embodiments, the distal end can be formed from any suitable material.

[0037] The coil can be formed as a single layer coil or a multi-layer coil having different PCB layers connected by vias. In some embodiments, the coil includes a major surface, at least 90% of which is shielded by multiple outer layers. In some embodiments, each outer layer includes a major surface, at least 90% of which is covered by a metal foil, such as copper foil. By way of example only, the thickness of each of the outer conductive layers can be in the range of 40 microns to 100 microns. The term "major surface" as used in this specification and claims is defined herein as a surface parallel to the plane of the various layers of the flexible printed circuit before the flexible printed circuit is wrapped around the distal end of the instrument.

[0038] In some embodiments, the position sensor includes two electrical connectors electrically connecting the coil to the proximal end of the instrument, while the outer layer includes an elongated section that covers the electrical connectors to shield the electrical connectors from electromagnetic interference.

[0039] In some embodiments, the medical device may further include one or more magnetic field radiators to radiate at least one alternating magnetic field of at least one frequency for detection by the coil. The number and / or thickness of the outer conductive layers of the position sensor may be selected so as to configure the outer layer as a low-pass filter that filters out at least some of the electromagnetic interference while still allowing transmission of signals at the frequency (or frequencies) radiated by the magnetic field radiators. Additionally or alternatively, the number and / or thickness of the outer conductive layers may be selected to minimize electromagnetic interference while still maintaining sufficient flexibility of the flexible printed circuit to allow the flexible printed circuit to be wrapped around the distal end.

[0040] System Description

[0041] Documents incorporated herein by reference are to be considered an integral part of this application, except that, to the extent any term is defined in these incorporated documents in a manner that contradicts a definition explicitly or implicitly set forth in this specification, only the definition in this specification shall prevail.

[0042] Turning now to the drawings, according to an embodiment of the present invention, reference is now made to Figure 1 , which is a schematic diagram of the medical surgical system 20, and reference Figure 2 , which is a schematic diagram of a magnetic field radiating component location pad 24 for use in system 20. The medical surgical system 20 is typically used during invasive and / or exploratory surgery on a patient 22's sinuses or other body parts, such as the brain.

[0043] For this procedure, the magnetic field radiation assembly 24 can be positioned behind and / or around the head of the patient 22, for example, by securing the magnetic field radiation assembly 24 to a chair 25 (or bed) on which the patient sits (or lies). The magnetic field radiation assembly 24 in the illustrated example includes five magnetic field radiators 26 secured in a horseshoe-shaped frame that is positioned under or around the patient 22 so that the magnetic field radiators 26 surround the head of the patient 22. Alternatively, a smaller or larger number of radiators 26 in various configurations can be used. The magnetic field radiators 26 are configured to radiate an alternating magnetic field at a corresponding frequency into an area 30 where a body part is located, the area being adjacent to the magnetic field radiation assembly 24 and including the head of the patient 22.

[0044] The alternating magnetic field induces signals in position sensor 32 and position sensor 36. Position sensor 32 is shown as being disposed on medical device 28 to track the position of medical device 28. Position sensor 36 is shown as being disposed on patient 22 (e.g., on the forehead of patient 22 or any other suitable body part) to track the position of patient 22 (e.g., to track the position of patient 22's head) to compensate for movement of the patient relative to magnetic field radiating assembly 24. By way of example only, medical device 28 may include any one or more of the following: a probe for insertion into a body part, an endoscope, and / or a surgical tool (such as an ENT tool, a suction tool, a minimally invasive instrument, or a razor).

[0045] The position of the distal end of the medical device 28 and the position of the patient 22 can be tracked using a tracking subsystem that tracks the position and orientation coordinates of a position sensor 32 and a position sensor 36 mounted at the distal end, respectively. The position sensors 32, 36 are configured to output signals indicating the positions of the sensors 32, 36, respectively. The signals are processed by the tracking subsystem running on processing circuitry 38 to track the position of the distal end of the medical device 28 and the position of the patient 22 over time. In embodiments where the tracking subsystem is a magnetic tracking subsystem, the position sensor 32 and / or the position sensor 36 include at least one coil, as described with reference to FIG. Figure 5-9 Using the tracking subsystem, the physician 54 advances the distal end of the medical instrument 28 within the body part, as will be described in more detail below.

[0046] In some embodiments, the medical device 28 is attached to and held by a robotic arm 40, which is configured to manipulate the medical device 28. The robotic arm 40 includes a plurality of robotic joints configured to control movement of the robotic arm 40 and manipulate the medical device 28. In other embodiments, the medical device 28 is held and manipulated by a physician 54.

[0047] As described in more detail below, the position sensor 32 is attached to the medical device 28, and determination of the position and orientation of the position sensor 32 enables tracking of the position and orientation of the distal end 34 (or other location) of the medical device 28, which can be reversibly inserted into a body part of the patient 22 (a living subject).

[0048] Similarly, determination of the position and orientation of position sensor 36 enables tracking of the position and orientation of a portion of patient 22 (e.g., the head). Figure 1 2 is shown as being disposed on the forehead of the patient 22. The position sensor 36 may be disposed on any other suitable body part of the patient 22 to track the position / movement of the patient 22.

[0049] Systems for tracking objects inserted into a patient using magnetic field radiators, such as magnetic field radiator 26, are described in U.S. Patent Publication No. 2016 / 0007842 to Govari et al., which is incorporated herein by reference. Additionally, a system manufactured by Biosense Webster (33 Technology Drive, Irvine, CA 92618 USA) The system uses a tracking system similar to that described herein to find the position and orientation of the coil in an area irradiated by a magnetic field.

[0050] The robotic arm 40 typically has its own robotic coordinate system. The robotic coordinate system is aligned with the magnetic coordinate system of the magnetic field radiator 26, or vice versa. Alignment of the robotic coordinate system with the magnetic coordinate system can be performed, for example, by moving the robotic arm 40 or the medical device 28 attached to the robotic arm 40 to one or more known positions of the magnetic field radiator 26, such as positions on the magnetic field radiating assembly 24, or to the orientation sensor 36, or to one or more other known positions on the patient 22. Once the robotic coordinate system has been aligned with the magnetic coordinate system, the position in the magnetic coordinate system can be translated into the robotic coordinate system in order to properly manipulate the robotic arm 40.

[0051] The elements of the system 20, including the radiator 26, can be controlled by a processing circuit 38, which includes a processing unit in communication with one or more memories. Typically, the elements can be connected to the processing circuit 38 via a cable, for example, the radiator 26 can be connected to the processing circuit 38 via a cable 58. Alternatively or in addition, the elements can be coupled to the processing circuit 38 wirelessly. The processing circuit 38 can be mounted in a console 50, which includes operating controls 51, which typically include a keypad and / or a pointing device such as a mouse or trackball. The console 50 is also connected to other elements of the medical surgical system 20, such as the proximal end 52 of the medical instrument 28. The physician 54 interacts with the processing circuit 38 using the operating controls 51 while performing the procedure, and the processing circuit 38 can present the results generated by the system 20 on a display 56.

[0052] In some embodiments, prior to performing a medical procedure, a CT image of patient 22 is acquired. The CT image is stored in a memory (not shown) for subsequent retrieval by processing circuitry 38. Figure 1 , a display 56 is shown showing various views 59 of a previous CT scan (or other suitable scan) that can be used as an aid to the physician 54 in guiding the medical instrument 28 in the body part. The display screen 56 also shows an image 61 captured by a camera (not shown) of the medical instrument 28. The CT image can be registered with the magnetic coordinate system so that a representation of the medical instrument 28 can be displayed on the display screen 56 along with the CT image.

[0053] In implementation, some or all of the functions of the processing circuit 38 may be combined in a single physical component, or alternatively, implemented using multiple physical components. These physical components may include hard-wired or programmable devices, or a combination of the two. In some embodiments, at least some of the functions of the processing circuit may be implemented by a programmable processor under the control of appropriate software. The software may be downloaded to the device in electronic form over a network, for example. Alternatively or in addition, the software may be stored in a tangible, non-transitory computer-readable storage medium, such as an optical, magnetic, or electronic memory.

[0054] Now see Figure 3 , which is used for Figure 1 Schematic diagram of a medical device 28 in the system 20. The medical device 28 includes a handle 62 into which a plurality of different rigid interchangeable heads 64 are individually and reversibly insertable. Figure 3 One of the interchangeable heads 64 is shown inserted into the handle 62. The other of the interchangeable heads 64 is shown in FIG. Figure 4 as described below. Figure 3The illustrated medical device 28 also includes an irrigation or drainage tube 66. Each interchangeable head 64, representing the distal end of the medical device 28, can be formed as an elongated tool formed from any suitable material, such as, but not limited to, a metal such as stainless steel or a plastic such as a biocompatible plastic. In some embodiments, the interchangeable head 64 can be flexible or bendable.

[0055] Figure 3 The illustrated medical device 28 is shown before any position sensors are added to the medical device 28. In fact, in some embodiments, the medical device 28 can be implemented using off-the-shelf medical devices that are commercially available without position sensors and with position sensors added at appropriate locations, as will be discussed below with reference to Figure 5 Description. For example, Bien The S120 handpiece and interchangeable reusable blades (available without a position sensor) can be adapted to provide the medical device 28 described below. In other embodiments, the medical device 28 can be implemented as a purpose-built medical device with an integrated position sensor.

[0056] Now see Figure 4 , which shows Figure 3 The medical device 28 includes a handle 62 and a plurality of different interchangeable heads 64. Figure 4 The illustrated handle 62 and interchangeable heads 64 are also shown without the orientation sensor.The interchangeable heads 64 differ from one another with respect to head shape and / or head size.

[0057] Each interchangeable head 64 includes a plastic proximal end 68 that inserts into a socket 70 of the handle 62. The socket 70 of the handle 62 includes multiple rotational positions for inserting different rigid interchangeable heads 64. For example, using the S120 handpiece, the reusable blade can be inserted into eight different rotational orientations. In some embodiments, the interchangeable head 64 can be inserted into the socket 70 in a single rotational position.

[0058] The handle 62 includes a plurality of rotational positions into which the differently rigid interchangeable heads 64 are rotated. Thus, once one of the interchangeable heads 64 is inserted into the socket 70, the inserted interchangeable head 64 can be rotated into the plurality of rotational positions using the rotation adjustment gear 72. In other embodiments, the inserted interchangeable head 64 cannot be rotated into another position.

[0059] exist Figure 4In the example of FIG, each of the interchangeable heads 64 is implemented with an elongated shaft 74 having a distal end 76, the interchangeable head including at least one cutting element 78 disposed at the distal end 76 of the elongated shaft 74. The cutting element 78 may include a shaving bar (e.g., a roughened surface cylindrical or spherical element) or a shaving blade that rotates within the elongated shaft 74 or any other suitable cutting element.

[0060] Now refer to Figure 5 , which is Figure 3 A plan view of a sensor 82 for use with a medical device 28. The sensor 82 includes a distal end 84 including at least one coil ( Figure 5 The shielding layer is used to shield the coil from electromagnetic interference, as shown in FIG. Figure 7-9 The sensor 82 may be a single-axis sensor, a dual-axis sensor, or a tri-axis sensor using one, two, or three coils, respectively. The sensor 82 also includes an elongated section 86 that includes shielded electrical connectors that electrically connect the one or more coils to the proximal end of the medical device 28, as further described with reference to FIG. Figure 7-9 The sensor 82 is attached to one of the interchangeable heads 64 ( Figure 4 ), such that the distal end 84 of the sensor 82 is wrapped around the distal end 76 of the interchangeable head 64 as shown by arrow 88, and the elongated section 86 extends from the distal end 76 of the interchangeable head 64 toward the proximal end 68 of the interchangeable head 64, as shown Figure 6 As used in this specification and claims, the term "wrap" in all grammatical forms is defined as partially or completely surrounding the distal end 76 of the medical device 28 with the distal end 84 of the sensor 82. The elongated section 86 is shown as being centrally disposed relative to the distal end 84 of the sensor 82. In some embodiments, the elongated section 86 can be disposed in an eccentric spatial relationship relative to the distal end 84 of the sensor 82.

[0061] Now refer to Figure 6 , which is set in Figure 3 The interchangeable head 64 of the medical device 28 may be Figure 5Schematic diagram of sensor 82. In some embodiments, sensor 82 may be provided on the distal end of any suitable medical instrument (even instruments without interchangeable heads) and / or on a distal end formed of any suitable material (such as metal or plastic). Sensor 82 may be provided on any suitable medical instrument, such as, but not limited to, any one or more of the following: a probe, an endoscope, and / or a surgical tool (such as an ENT tool, a suction tool, a minimally invasive device, or a razor) for insertion into a body part. Sensor 82 may be provided on the distal end of a tool having a rigid, or flexible, or bendable distal end. Sensor 82 is configured to detect the magnetic field radiator 26 ( Figure 2 ) at least a portion of the alternating magnetic field emitted by the . Additional orientation sensors (single-axis sensor, dual-axis sensor or tri-axis sensor) may be provided on the interchangeable head 64 and / or handle 62 ( Figure 3 and Figure 4 )superior.

[0062] The orientation sensor 82 is electrically isolated from the elongated shaft 74 and the cutting element 78 using, for example, an insulating layer of the sensor 82, as described with reference to FIG. Figure 7-9 Described in greater detail. In some embodiments where the sensor 82 includes a distal end 84 without the elongated section 86, a wire extending from the sensor 82 may be secured to the elongated shaft 74, for example, using self-adhesive tape (not shown).

[0063] Prior to inserting the elongated shafts 74 into the body part, at least some of the elongated shafts 74 can be disposed in a plastic biocompatible sleeve (not shown). In some embodiments, the sleeve can cover the elongated shafts 74 from the plastic proximal end 68 up to and including the distal end 84 of the head position sensor 82.

[0064] Now refer to Figure 7 , which is intercepted along line AA Figure 5 82. The sensor 82 includes a flexible printed circuit comprising alternating conductive layers 90 and dielectric layers 92. Figure 7 The illustrated sensor 82 includes six conductive layers 90 and six dielectric layers 92. The conductive layers 90 include at least one inner layer 94 that is patterned with traces to form a coil 96. The conductive layers 90 include a plurality of outer layers 100 that cover the inner layers 94 and are configured to connect to an electrical ground 102 to shield the coil 96 from electromagnetic interference.

[0065] exist Figure 7In the example shown, coil 96 is formed on four inner layers 94-1 through 94-4 connected by passages 104. In some embodiments, coil 96 may be formed from one, two, three, or any suitable number of layers 94. Bottom inner layer 94-1 includes a portion of coil 96 and electrical connector 98-1 to connect the portion of coil 96 disposed on inner layer 94-1 to a portion of coil 96 disposed near head 64 ( Figure 6 ) of the proximal end 68 ( Figure 6 ) electrical connector. The inner layer 94-2, above the inner layer 94-1, includes another portion of the coil 96 that is connected to a portion of the coil 96 of the inner layer 94-1 using the via 104-1. The inner layer 94-3, above the inner layer 94-2, includes another portion of the coil 96 that is connected to a portion of the coil 96 of the inner layer 94-2 using the via 104-2. The top inner layer 94-4, above the inner layer 94-3, includes another portion of the coil 96 that is connected to a portion of the coil 96 of the inner layer 94-3 using the via 104-3. The inner layer 94-4 also includes an electrical connector 98-2 to connect the coil 96 disposed on the inner layer 94-4 to an electrical connector (not shown) near the proximal end 68 of the head 64.

[0066] Each of the conductive inner layers 94 can be formed by selectively etching the conductive layer 90 of the conductive-dielectric layer pair 90, 92. The etched conductive-dielectric layer pair 90, 92 is appropriately connected and the via 104 is appropriately installed. Each of the conductive outer layers 100 can be formed by using an unetched or "raw" conductive-dielectric layer pair 90, 92. The conductive layer 90 can be formed from a flexible metal foil, such as, but not limited to, copper foil. The dielectric layer 92 can be formed from a flexible insulator, such as, but not limited to, a polymer. Each conductive outer layer 100 can have any suitable thickness, such as, but not limited to, within the range of 40 microns to 100 microns.

[0067] When the plurality of conductive outer layers 100 are connected and grounded, the layers 100 effectively act as one thick conductive layer that provides electromagnetic shielding. In some embodiments, the combined thickness of the conductive outer layers is in the range of 100 microns to 300 microns. In other embodiments, the combined thickness of the conductive outer layers may be less than 100 microns or greater than 300 microns. The penetrability of the outer layers 100 by electromagnetic signals varies with the frequency of the signal (for a conductor of a given thickness, the higher the frequency, the shorter the distance the signal can penetrate). The thickness and / or number of the outer layers 100 may be selected so as to configure the outer layers 100 as a low pass filter that filters out at least some of the electromagnetic interference while still allowing transmission of the electromagnetic interference emitted by the magnetic radiator 26 ( Figure 2) radiated by the coil 96 while allowing a significant amount of the 20 kHz signal to be detected by the coil 96. Additionally or alternatively, the thickness and / or number of outer conductive layers 100 may be selected to minimize electromagnetic interference while still maintaining sufficient flexibility of the flexible printed circuit to allow the flexible printed circuit to be wrapped around the medical device 28 ( Figure 6 ) around the distal end 76.

[0068] The electrical connections 98 from the coil 96 are also shielded from electromagnetic interference. The outer layer 100 includes the elongated section 86 ( Figure 5 ) corresponding elongated section 106 that covers the electrical connection 98 so as to shield the electrical connection 98 from electromagnetic interference.

[0069] Now refer to Figure 8 , which is Figure 5 A plan view of the inner layer 94-4 of the sensor 82. Figure 8 It is shown that when etching the conductive layer 90 ( Figure 7 ) to show the dielectric layer 92 beneath the conductive layer 90 surrounding the coil traces and connections 98-2, 108. The other inner layers 94 may be similarly formed.

[0070] Now refer to Figure 9 , which is Figure 5 Exploded view of sensor 82. Figure 9 1 and 2. A portion of a coil 96 formed on four dielectric layers 92 and connected by vias 104 is shown. For simplicity, Figure 9 Only a portion of the electrical connector 98 and the elongated section 106 are shown. Each conductive outer layer 100 is formed from a conductive-dielectric layer pair 90, 92 (as shown in inset 110). The coil 96 is typically shielded at the top by the outer layer 100. In some embodiments, the coil 96 includes a major surface that is at least 90% (e.g., 100%) shielded by the plurality of outer layers 100. Each outer layer 100 is typically covered with a conductor, such as a metal foil, for example, a copper foil. In some embodiments, each outer layer 100 includes a major surface that is at least 90% (e.g., 100%) covered by a metal foil, for example, a copper foil.

[0071] Now refer to Figure 10 , which is a flow chart 120 including steps in a method of manufacturing a medical device according to an embodiment of the present invention. Figure 6 and Figure 7 The method includes forming (block 122) the position sensor 82 from a flexible printed circuit comprising alternating conductive layers 90 and dielectric layers 92. The conductive layers 90 include at least one inner layer 94 patterned with traces to form a coil 96, and a plurality of outer layers 100 covering the at least one inner layer 94 and configured to connect to an electrical ground 102 to shield the coil 96 from electromagnetic interference. The step of block 122 includes a plurality of sub-steps described below with reference to blocks 124-130.

[0072] One of the sub-steps includes selecting (block 124) the thickness and / or number of outer layers 100 so as to configure the outer layers 100 as a low-pass filter that filters out at least some of the electromagnetic interference while still allowing transmission of signals at at least one frequency used by the position sensor 82 and / or minimizes electromagnetic interference while still maintaining sufficient flexibility of the flexible printed circuit to wrap the flexible printed circuit around the distal end 76. One of the sub-steps includes forming (block 126) the flexible printed circuit so that the plurality of outer layers 100 include an elongated portion 106 that covers the electrical connector 98 from the coil 96 to the proximal end 68 of the instrument 28 so as to shield the electrical connector 98 from electromagnetic interference. One of the sub-steps includes etching (block 128) the coil 96 and the electrical connector 98 from the respective conductive-dielectric layer pairs 90, 92. One of the sub-steps also includes connecting (block 130) the layer pairs 90, 92 together and installing the vias 104.

[0073] The method also includes wrapping (block 132 ) the position sensor 82 around the distal end 76 of the medical device 28 and adhering (block 134 ) the position sensor to the distal end.

[0074] For clarity, various features of the invention described in the context of separate embodiments may also be provided in combination in a single embodiment. Conversely, for simplicity, various features of the invention are described in the context of a single embodiment and may also be provided separately or in any suitable subcombination.

[0075] The above embodiments are cited by way of example, and the present invention is not limited by what has been specifically shown and described hereinabove. On the contrary, the scope of the present invention includes combinations and subcombinations of the various features described above, as well as variations and modifications thereof, which will occur to those skilled in the art upon reading the above description and which are not disclosed in the prior art.

Claims

1. A medical device comprising: an instrument comprising a distal end configured for insertion into a body part; and a position sensor comprising a flexible printed circuit comprising alternating conductive and dielectric layers and wrapped around the distal end of the instrument, the conductive layers comprising: at least one inner layer patterned with traces to form a coil; and A plurality of outer layers are positioned on top of the at least one inner layer and are configured to connect to an electrical ground to shield the coil from electromagnetic interference.

2. The device of claim 1, wherein the combined thickness of the outer layers is in the range of 100 microns to 300 microns.

3. The device of claim 1 , wherein the instrument includes a proximal end, the position sensor includes two electrical connectors electrically connecting the coil to the proximal end, and the plurality of outer layers include elongated sections covering the electrical connectors so as to shield the electrical connectors from the electromagnetic interference.

4. The apparatus of claim 1 , wherein the coil comprises a major surface, at least 90% of which is shielded by the plurality of outer layers.

5. The device of claim 1, wherein each outer layer of the plurality of outer layers comprises a major surface at least 90% of which is covered by the metal foil.

6. The device of claim 1, wherein each of the plurality of outer layers has a thickness in a range of 40 microns to 100 microns. The device of claim 1 , wherein the coil is formed of a plurality of layers connected by vias.

8. The device of claim 1, wherein the distal end of the instrument is formed as an elongated metal tool.

9. A method of manufacturing a medical device, the method comprising: A position sensor is formed from a flexible printed circuit comprising alternating conductive and dielectric layers, the conductive layers comprising: at least one inner layer patterned with traces to form a coil; and a plurality of outer layers positioned on top of the at least one inner layer and configured to connect to electrical ground so as to shield the coil from electromagnetic interference; wrapping the position sensor around a distal end of an instrument configured for insertion into a body part; and The position sensor is adhered to the distal end.

10. The method of claim 9, wherein the combined thickness of the outer layers is in the range of 100 microns to 300 microns.

11. The method of claim 9, further comprising forming the flexible printed circuit such that the plurality of outer layers include an elongated portion that covers electrical connections from the coil to the proximal end of the instrument to shield the electrical connections from the electromagnetic interference.

12. The method of claim 9, wherein the coil comprises a major surface, at least 90% of which is shielded by the plurality of outer layers.

13. The method of claim 9, wherein each outer layer of the plurality of outer layers comprises a major surface at least 90% of which is covered by metal foil.

14. The method of claim 9, wherein each of the plurality of outer layers has a thickness in a range of 40 microns to 100 microns.

15. The method of claim 9, wherein the coil is formed of a plurality of layers connected by vias.

16. The method of claim 9, wherein the distal end of the instrument is formed as an elongated metal tool.

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