External charger for wirelessly powering implantable medical devices (IMDs)

Abstract

An external charger for wirelessly supplying power to an implantable medical device (IMD) is disclosed, comprising a charging coil and one or more sensing coils preferably housed in a charging coil assembly coupled to an electronic module via a cable. The charging coil is preferably a wire winding, while the sensing coils are preferably formed in one or more traces on a circuit board. One or more voltages induced on the one or more sensing coils can be used to determine the phase angle between the voltage and a drive signal for the charging coil. The determined phase angle can then be used to determine the position of the charging coil relative to the IMD. Additionally, more than one parameter (phase angle, amplitude, resonant frequency) that can be determined using the voltage can be used to determine the position, which includes the radial offset and depth of the charging coil relative to the IMD.

Description

[0001] This application is a divisional application of patent application No. 201780037621.9, filed on June 9, 2017, entitled "External Charger for an Implantable Medical Device that Determines Position Using a Phase Angle or Multiple Parameters Determined from at Least One Sensing Coil". Technical Field

[0002] This invention relates to a wireless external charger for implantable medical device systems. Background Technology

[0003] Implantable stimulation devices are those that generate and deliver electrical stimulation to the body's nerves and tissues for the treatment of various biological disorders, such as pacemakers for treating arrhythmias; defibrillators for treating cardiac fibrillation; cochlear stimulators for treating deafness; retinal stimulators for treating blindness; muscle stimulators for generating coordinated limb movements; spinal cord stimulators for treating chronic pain; cortical and deep brain stimulators (DBS) for treating motor and psychological disorders; and other neurostimulators for treating urinary incontinence, sleep apnea, shoulder subluxation, etc. The following description will focus primarily on the use of the invention within spinal cord stimulation (SCS) systems, such as those disclosed in U.S. Patent 6,516,227. However, the invention can be found to be applicable in any implantable medical device system, including deep brain stimulation (DBS) systems.

[0004] As shown in Figures 1A-1C, an SCS system typically includes an implantable pulse generator (IPG) 10 (more generally, an implantable medical device (IMD) 10), which includes a biocompatible device housing 12 formed of a conductive material, such as, for example, titanium. The housing 12 typically houses the circuitry and battery 14 required for the IMD 10 to function (Figure 1C), but the IMD can also be powered by external RF energy without a battery. The IMD 10 is coupled to electrodes 16 via one or more electrode leads 18, such that the electrodes 16 form an electrode array 20. The electrodes 16 are carried on a flexible body 22, which also houses individual signal lines 24 coupled to each electrode. In the illustrated embodiment, there are eight electrodes (Ex) on each lead 18, but the number of leads and electrodes is specific and can therefore vary. The leads 18 are coupled to the IMD 10 using lead connectors 26, which are secured in a non-conductive head material 28, which may include, for example, epoxy resin.

[0005] As shown in the cross-section of Figure 1C, the IMD 10 typically includes a printed circuit board (PCB) 30, and various electronic components 32 mounted to the PCB 30, some of which will be discussed later. Two coils (more generally, antennas) are shown in the IMD 10: a telemetry coil 34 for sending / receiving data to / from an external controller (not shown); and a charging coil 36 for charging or recharging the IMD's battery 14 using an external charger, which will be discussed in detail later.

[0006] Figure 2 illustrates the IMD 10 communicating with an external charger 50 for wirelessly transmitting power to the IMD 10, which can then be used to recharge the IMD's battery 14. Power transmission from the external charger 50 is achieved via a primary charging coil 52. Like the IMD 10, the external charger 50 also includes a PCB 54 on which electronic components 56 are housed. Again, some of these electronic components 56 will be discussed later. A user interface 58, including touch-sensitive buttons and possibly a display and speaker, allows a patient or clinician to operate the external charger 50. A battery 60, which itself may be rechargeable, provides power to the external charger 50. The external charger 50 can also receive AC power from a wall socket. A handheld housing 62, sized to fit in the user's hand, contains all components.

[0007] Power transfer from the external charger 50 to the IMD 10 occurs wirelessly and percutaneously via inductive coupling through the patient's tissue 25. Figure 3 shows details of the circuitry used to achieve this functionality. The primary charging coil 52 in the external charger 50 is energized with an AC current Icharge via a charging circuit 64 to create an AC magnetic charging field 66. This magnetic field 66 induces a current in the secondary charging coil 36 within the IMD 10, thereby providing a voltage across the coil 36 that is rectified (38) to a DC level and used to recharge the battery 14, possibly provided via a battery charging and protection circuit 40, as shown. The frequency of the magnetic field 66 may be around 80 kHz. When charging the battery 14 in this manner, typically the housing 62 of the external charger 50 comes into contact with the patient's tissue 25 using a charger holding device or the patient's clothing, but this is not strictly necessary.

[0008] IMD 10 can also use reflected impedance modulation to transmit data back to external charger 50 during charging, which is sometimes referred to in the art as Load Shift Keying (LSK). This involves modulating the impedance of charging coil 36 with data bits (“LSK data”) provided by control circuitry 42 of IMD 10 to transmit serially from IMD 10 to external charger 50. For example, and depending on the logic state of the bits to be transmitted, the ends of coil 36 can be selectively short-circuited to ground by transistor 44, or transistor 46 connected in series with coil 36 can be selectively open-circuited to modulate the impedance of coil 36. At external charger 50, LSK demodulator 68 determines whether a logic “0” or “1” has been transmitted by evaluating the amplitude of AC voltage Vcoil, which is generated on coil 52 of external charger in response to charging current Icharge and the transmitted data, and then reports this data to control circuitry 72 of external charger for analysis. This post-telemetry from IMD 10 can provide useful data about the charging of external charger 50, such as the capacity of IMD's battery 14, or whether charging of battery 14 is complete, and whether the operation of external charger 50 and the generation of magnetic field 66 can be stopped. LSK communication is further described, for example, in U.S. Patent Application Publication 2013 / 0096652.

[0009] The external charger 50 may also include one or more thermistors 71, which can be used to report the temperature of the external charger 50 (expressed as voltage Vtherm) to its control circuitry 72, which can then control the generation of the magnetic field 66 to keep the temperature within safe limits. See, for example, USP 8,321,029, which describes temperature control in an external charging device.

[0010] The Vcoil across the charging coil 52 of the external charger can also be evaluated by the alignment circuit 70 to determine how well the external charger 50 is aligned with respect to the IMD 10. This is important because if the external charger 50 is not well aligned with the IMD 10, the magnetic field 66 generated by the charging coil 52 will not be efficiently received by the charging coil 36 in the IMD 10. The efficiency of power transfer can be quantified as the "coupling" (k, which ranges between 0 and 1) between the transmitting coil 52 and the receiving coil 36, and generally includes the extent to which the power consumed at the transmitting coil 52 in the external charger 50 is received at the receiving coil 36 in the IMD 10. It is generally desirable that the coupling between the coils 52 and 36 be as high as possible: higher coupling results in faster charging of the IMD battery 14 and minimal consumption of the power of the external charger 50. Poor coupling is disadvantageous because it will require high power consumption (e.g., high Icharge) in the external charger 50 to fully charge the IMD battery 14. The use of high power depletes the battery 60 in the external charger 50, and more importantly can cause the external charger 50 to heat up and potentially burn or harm the patient.

[0011] Generally, if the external charger 50 is well aligned with the IMD 10, as the charging circuit 64 supplies the charging current Icharge to the charging coil 52, Vcoil will drop. Thus, the alignment circuit 70 can compare Vcoil with an alignment threshold Vt, preferably after it has been rectified 76 to a DC voltage. If Vcoil < Vt, the external charger 50 considers itself to be well aligned with the underlying IMD 10. If Vcoil > Vt, the external charger 50 will consider itself misaligned and can indicate this fact to the patient, such that the patient can attempt to move the charger 50 to a better alignment. For example, the user interface 58 of the charger 50 can include an alignment indicator 74. The alignment indicator 74 can include a speaker (not shown), which can "beep" at the patient when misalignment is detected. The alignment indicator 74 can also or alternatively include one or more light emitting diodes (one or more LEDs; not shown), which can similarly indicate misalignment.

[0012] The charger-to-IMD coupling depends on many variables, such as the permeability of the materials used in the external charger 50 and the IMD 10, and the materials inherent in the environment. The coupling is also affected by the relative positions of the external charger 50 and the IMD 10, as Figures 4A-4CAs shown. For optimal coupling (higher k value), preferably, the axes (52' and 36') around which coils 52 and 36 are wound are parallel and collinear, with coils 52 and 36 as close to each other as possible (d1), as... Figure 4A As shown. Distance d1 indicates the depth between the external charger 50 and the IMD 10, and it is generally constant, assuming the external charger is typically placed on the patient's tissue 25 and the IMD 10 has been implanted at a specific depth. Deviations from these ideals generally reduce coupling, such as Figure 4B-4C As shown. For example, in Figure 4B In the middle, coil axes 52' and 36' are not collinear, but rather laterally offset (x). Figure 4C In the IMD, coil axes 52' and 36' are parallel and collinear, but IMD 10 is relatively deep (d2). In any of these non-ideal conditions, coupling will be reduced, meaning that the battery 14 of the IMD will not charge quickly, or the external charger 50 must output more power (e.g., Icharge must be higher) to affect the same charging rate of the battery 14 of the IPG.

[0013] refer to Figure 4C It should be noted that the depth d2 of the IMD 10 cannot typically be changed, as this parameter is determined by how the IMD 10 is implanted in the patient. As a result, the external charger 50 can be aligned with the IMD 10 even if the coupling between the external charger 50 and the IMD 10 is relatively poor (and therefore Vcoil is relatively high). In this case, adjusting the alignment threshold Vt used by the alignment circuit 70 (i.e., upward) may be useful so that the external charger 50 does not unreasonably indicate misalignment to the patient when the patient is unable to improve the alignment. USP 9,227,075 describes a technique for adjusting Vt according to the implantation depth to resolve misalignment, although this technique is not described here. Summary of the Invention

[0014] In a first example, an external charger for wirelessly supplying power to an implantable medical device (IMD) is disclosed, comprising: a charging coil configured to generate a magnetic field when excited by a drive signal to wirelessly supply power to the IMD; a sensing coil configured to induce a sensing signal by the magnetic field, the sensing signal being affected by the position of the charging coil relative to the IMD; and a control circuit configured to determine a phase angle between the sensing signal and the drive signal, and to use the phase angle to determine the position of the charging coil relative to the IMD.

[0015] The sensing coil can be concentric with the charging coil. The control circuit can be configured to generate a drive signal.

[0016] The external charger may also include an electronic module and a charging coil assembly coupled to the electronic module via a cable, wherein the charging coil and the sensing coil are within the charging coil assembly, and wherein control circuitry is within the electronic module. The external charger may also include a circuit board, wherein the sensing coil is formed in one or more traces on the circuit board. The charging coil may include a wire winding placed on one side of the circuit board, or the circuit board may be placed within the wire winding of the charging coil.

[0017] The control circuit can be configured to determine whether the charging coil is aligned or centered relative to the IMD based on a phase angle, wherein alignment includes a case where the coupling between the charging coil and the IMD is higher than a first coupling value, and alignment includes a case where the coupling between the charging coil and the IMD is higher than a second coupling value lower than the first coupling value. The control circuit may also include a threshold, wherein the control circuit is configured to determine whether the charging coil is aligned or centered relative to the IMD by comparing the phase angle with the threshold. The control circuit can also be configured to determine whether the charging coil is aligned relative to the IMD and whether the charging coil is centered relative to the IMD based on the phase angle. In this case, the control circuit may further include a first threshold and a second threshold, wherein the control circuit is configured to determine whether the charging coil is centered by comparing the phase angle with the first threshold and whether the charging coil is aligned by comparing the phase angle with the second threshold.

[0018] The sensing signal may include voltage. The external charger may also include a user interface configured to indicate to the user the determined position of the charging coil relative to the IMD. The charging coil may include a first radius, and the sensing coil may include a second radius smaller than the first radius.

[0019] The sensing coil may include a circle or two circles of different radii, wherein the two circles may be connected such that the current flowing through the two circles will flow in different directions in the two circles.

[0020] In a second example, an external charger for wirelessly supplying power to an implantable medical device (IMD) includes: a charging coil configured to generate a magnetic field when excited by a driving signal to wirelessly supply power to the IMD as a coupling system; a sensing coil configured to induce a sensing signal by the magnetic field, the sensing signal being affected by the position of the charging coil relative to the IMD; and control circuitry configured to determine the position of the charging coil relative to the IMD based on a plurality of parameters, each of which can be determined using the sensing signal.

[0021] The sensing coil may be concentric with the charging coil. The external charger may also include a user interface configured to indicate the determined location to the user. Multiple parameters may include a complex number, including at least one of the following: the amplitude of the sensed signal, the phase angle between the sensed signal and the drive signal, and the resonant frequency of the coupling system.

[0022] The control circuit can be configured to determine, based on a plurality of parameters, whether the charging coil is aligned, centered, or aligned and centered relative to the IMD, wherein centeredness includes a case where the coupling between the charging coil and the IMD is higher than a first coupling value, and wherein alignment includes a case where the coupling between the charging coil and the IMD is higher than a second coupling value lower than the first coupling value.

[0023] The external charger may also include an electronic module and a charging coil assembly coupled to the electronic module via a cable, wherein the charging coil and the sensing coil are within the charging coil assembly, and wherein control circuitry is within the electronic module. The external charger may also include a circuit board, wherein the sensing coil is formed in one or more traces in the circuit board. The charging coil may include a wire winding placed on one side of the circuit board, or the circuit board may be placed within the wire winding of the charging coil.

[0024] The control circuit may further include a database or have access to a database, wherein the database includes multiple thresholds, and the control circuit is configured to compare each of the multiple parameters with one of the thresholds to determine the position of the charging coil relative to the IMD. The control circuit may be configured to determine the radius of the lateral offset of the charging coil relative to the IMD, and also to determine the depth between the charging coil and the IMD. The control circuit may further include a database or have access to a database, wherein the database includes values ​​of the multiple parameters at different radial offsets and depths between the charging coil and the IMD, and the control circuit is configured to compare the multiple parameters with the values ​​to determine the position of the charging coil relative to the IMD. The determined position may include the radius and depth between the charging coil and the IMD.

[0025] The sensing coil may include a circle or two circles of different radii, wherein the two circles may be connected such that the current flowing through the two circles will flow in different directions in the two circles. Attached Figure Description

[0026] Figures 1A-1C show different views of an implantable pulse generator (an implantable medical device (IMD)) according to the prior art.

[0027] Figure 2 shows an external charger for charging the battery in the IMD according to the prior art, while Figure 3 shows the circuitry of both according to the prior art.

[0028] Figures 4A-4CVarious locations between the external charger and the IMD, according to existing technology, are shown that can affect their coupling.

[0029] Figures 5A-5E An improved charging system with a charging coil assembly and an electronic module according to an example of the present invention is shown, wherein... Figure 5B-5E An example according to the invention is shown using a charging coil in a charging coil assembly with one or more sensing coils.

[0030] Figures 6A-6C An example according to the invention is shown using a first alignment sensing coil of constant radius in a charging coil assembly, and circuitry for detecting and indicating misalignment between the charging coil and the IMD.

[0031] Figures 7A-7C An example of the invention is shown using a second alignment sensing coil with edge detection capability in a charging coil assembly, and circuitry for detecting and indicating misalignment between the charging coil and the IMD.

[0032] Figure 8A and 8B An example of the use of a third alignment sensing coil arrangement comprising two or more separate alignment sensing coils in a charging coil assembly according to the invention is shown, as well as circuitry for detecting and indicating misalignment between the charging coil and the IMD.

[0033] Figures 9A-9C An example of the use of a centering sensing coil in a charging coil assembly according to the invention is shown, as well as circuitry for detecting and indicating misalignment between the charging coil and the IMD.

[0034] Figure 10A and 10B An example of the use of an alignment sensing coil and a centering sensing coil in a charging coil assembly according to the present invention is shown, as well as circuitry for detecting and indicating misalignment and / or misalignment between the charging coil and the IMD.

[0035] Figure 11A and 11B An example of the invention is shown using a single alignment / centering sensing coil in a charging coil assembly, and circuitry for detecting and indicating misalignment and / or misalignment between the charging coil and the IMD.

[0036] Figure 12A An algorithm operable in a charging system according to an example of the invention is shown for determining alignment and centering and for controlling the magnetic field generated by the charging coil, while Figure 12B A magnetic field generated by an algorithm according to an example of the present invention is shown.

[0037] Figure 13A A modified positioning circuit for a charger system according to an example of the invention is shown, which is capable of determining the positioning of the IMD to the charger using one or more sensing coil parameters, including amplitude, phase angle, and resonant frequency. Figure 13B-13D The circuits and methods for determining or measuring these parameters according to an example of the present invention are shown.

[0038] Figure 14A and 14B The diagram illustrates an equipotential contour of experimentally determined data according to an example of the invention, which correlates the amplitude, phase angle, and resonant frequency of the sensing coil with the radius and depth from the charger to the IMD, as shown in... Figure 13A All of the modified position circuits are used.

[0039] Figure 15A An example of a power circuit for a charger system according to the present invention is shown, which can adjust the magnetic field power using one or more sensing coil parameters, including amplitude, phase angle, and resonant frequency. Figure 15B The experiment demonstrates how the location of the charger to the IMD, according to an example of the invention, affects the power received at the IMD.

[0040] Figure 16 An example of an integrated external charger according to the present invention is shown, wherein the electronics, charging coil and one or more sensing coils are housed in a single housing.

[0041] Figures 17A-17E An example according to the invention is shown using an additional sensing coil arranged in such a way that it provides information about one or more directions through which the charging coil 126 is misaligned or out of alignment with respect to the IMD.

[0042] Figure 18 An example according to the invention is shown how one or more sensing coils in a charging system can be actively driven to determine the charger's position to the IMD and / or how to adjust the magnetic field power.

[0043] Figure 19 An example according to the invention is shown how to assist the charger to the IMD in positioning and / or magnetic field power adjustment by providing hardware that enables the IMD to telemetryally transmit coupling parameters to the charging system. Detailed Implementation

[0044] An improved charging system 100 for IMD 10 Figure 5AAs shown in the diagram, the charging system 100 includes two main parts: an electronic module 104 and a charging coil assembly 102 including a charging coil 126. The electronic module 104 and the charging coil assembly 102 are connected by a cable 106. The cable 106 can be detached from both the electronic module 104 and the charging coil assembly 102 via a port / connector arrangement, but as shown, the cable 106 is permanently attached to the charging coil assembly 102. The other end of the cable 106 includes a connector 108, which can be attached to and detached from port 122 of the electronic module 104.

[0045] Electronic module 104 preferably includes a battery 110 and active circuitry 112, some of which are described below, within its housing 105. Electronic module 104 may also include a port 114 (e.g., a USB port) to allow its battery 110 to be recharged in a conventional manner, and / or to allow data to be read from or programmed into the electronic module (such as new operating software). Housing 105 may also carry a user interface, as shown in the side view of FIG5B, which may include an on / off switch for starting / stopping the generation of magnetic field 66, and one or more LEDs 118a and 118b. In one example, LED 118a is used to indicate the power status of electronic module 104. For example, LED 118a may illuminate while its battery 110 is charging and may flash to indicate that the battery 110 needs charging. LED 118b may operate as explained further below. More sophisticated user interfaces, such as those incorporating speakers and displays, may also be used. User interface elements may be included on other sides of the housing 105 of the electronic module and may be positioned such that they are easily observable for use in therapeutic applications at hand (e.g., SCS, DBS). Electronics are integrated within the housing 105 of the electronic module 104 via circuit board 120.

[0046] The charging coil assembly 102 preferably comprises only passive electronic components that are stimulated or read by the active circuitry 112 within the electronic module 104. Such components include the previously mentioned primary charging coil 126, as shown, which includes copper wire windings and is powered by the charging circuitry 64 within the electronic module 104. Figure 6AThe charging coil assembly 102 is excited to create a magnetic charging field 66 that provides power to the IMD 10, such as for recharging the battery 14 of the IMD 10. One or more sensing coils are also included within the charging coil assembly 102. As explained in detail later, the one or more sensing coils are measured in various ways to perform different functions in the charging system 100. For example, sensing coil measurements can be used to determine the position of the charging coil 126 (charging coil assembly 102) relative to the IMD 10 being charged, and more specifically to determine whether the charging coil 126 is aligned and / or centered relative to the IMD 10 being charged. Sensing coil measurements can also be used to adjust the power of the magnetic field 66 provided by the charging coil 126.

[0047] like Figure 5B As shown in the cross-section, one or more sensing coils are preferably formed using one or more traces in a circuit board 124, which also serves to integrate electronic components within the charging coil assembly 102. The circuit board 124 is... Figure 5C Shown separately. While it is preferred that the charging coil 126 includes a wire winding and one or more sensing coils include traces within the circuit board 124, this is not strictly necessary: ​​the charging coil 126 may also be formed from traces in the circuit board 124, and one or more sensing coils may include wire windings. Note that the charging coil 126 and one or more sensing coils (and are concentric) are also formed in parallel planes, and may also be formed in the same plane, as shown below regarding Figure 5D Further discussion.

[0048] Preferably, other passive components included within the charging coil assembly 102 include one or more tuning capacitors 131. As shown in the circuit diagram later (e.g., Figure 6A As shown, capacitor 131 is coupled to charging coil 126 to tune the resonant frequency of the LC circuit (e.g., up to 80 kHz). Those skilled in the art will understand that the value of capacitor 131 (C) connected to charging coil 126 will depend on the inductance (L) of the coil, selected according to the equation f(res) = 1 / sqrt(2πLC). Each of one or more sensing coils may also be coupled to tuning capacitor 131, but this is not necessary and is not shown in other circuit diagrams. Tuning capacitor 131 may be placed in series or parallel with its associated coil, but a series configuration is shown in subsequent figures.

[0049] The charging coil assembly 102 may also include one or more temperature sensors, such as a thermistor 136, which can be used to report the temperature of the charging coil assembly 102 to the electronic module 104. Figure 6A(Vtherm). This temperature data can then control the generation of the magnetic field 66, keeping the temperature within safe limits. See, for example, USP 8,321,029, which describes temperature control in an external charging device.

[0050] The electronic components within the charging coil assembly 102 can be integrated separately. Figure 5B and 5C In this configuration, a single circuit board 124 is used, wherein a charging coil 126 is mounted on the patient-facing side of the circuit board 124, and wherein a wire 134 in the cable 106 is preferably coupled to the circuit board 124. However, as... Figure 5D As shown, two circuit boards 124a and 124b are used. Circuit board 124b is located outside the area of ​​charging coil 126 and includes capacitor 131. Circuit board 124a is located within the area of ​​charging coil 126 and includes one or more sensing coils and a thermistor 136. Figure 5D In the arrangement of the two circuit boards 124a and 124b, it is noteworthy in cross-section that the charging coil 126 and the circuit boards 124a and 124b can typically be located in the same plane, which allows for a thinner structure of the charging coil assembly 102. Figure 5D In this configuration, wires 134 within cable 106 can be connected to both circuit boards 124a and 124b to allow communication between components and electronic module 104. The two circuit boards 124a and 124b may also have a connection between them (not shown).

[0051] Components in the charging coil assembly 102 are integrated within a housing 125, which can be formed in various ways. In one example, the housing 125 may include a top and bottom formed of rigid plastic, which may be spiral-jointed, snap-fitted, ultrasonically welded, or solvent-bonded together. Alternatively, the housing 125 may include one or more plastic materials molded onto the electronic components. One side of the housing 125 may include indentation 132 to accommodate the thickness of a material (not shown), which may be used to attach the charging coil assembly 102 to a patient, the patient's clothing, or a holding device such as a charging belt or shoulder strap. See, for example, U.S. Patent Application Publication 2016 / 0301239, which discloses a belt for holding a charging coil assembly and control module that can be used with the charging system 100. This material may include, for example, Velcro or double-sided tape.

[0052] Figure 5EAnother example of the charging coil assembly 102 is shown. This example shows one or more thermistors 136 on top of a PCB 124, along with the charging coil 126 and other components such as one or more tuning capacitors 131. To aid in temperature detection, a heat diffuser 123 is included, as disclosed in U.S. Provisional Patent Application Serial No. 62 / 514,304, filed June 2, 2017. The heat diffuser 123 is shown inside and in contact with the charging coil 126, but may cover the charging coil 126 or may appear outside the charging coil 126. As the name suggests, the heat diffuser 123 helps conduct the heat generated by the excitation of the charging coil 126 and the generation of the magnetic charging field 66, and thus provides a more uniform temperature to each of the one or more thermistors 136. In one example, the heat diffuser 123 includes a deformable layer with a viscous side that can be pressed onto the PCB 124 and the one or more thermistors 136 (such as a thermally conductive acrylic interface pad, part number 5590H, manufactured by 3M Company). In a preferred example, four thermistors 136 are present, each thermistor 136 being placed equally at 90 degrees on the PCB 124 within the charging coil 126. Figure 5E In the example, the underside of PCB 124 is typically flat and lacks any components or other structures. As a result, this underside can directly contact the inner surface of the bottom of housing 125. Note that the relative lack of components in charging coil assembly 102 means that the top or bottom of charging coil assembly 102 can face the patient during charging of the patient's IMD 10.

[0053] Before discussing the operation of one or more sensing coils, it is understandable that... Figure 6A Other aspects of the charging system 100 shown. Similar to the external charger 50 described earlier (FIG. 3), the electronic module 104 may include (as part of the circuit 112); Figure 5A Control circuit 72 controls charging circuit 64 to generate charging current Icharge. This current passes through connector / port 108 / 122 and wires 134 in cable 106 to excite charging coil 126, generating magnetic field 66. The voltage Vcoil across charging coil 126, generated, can be monitored via LSK communication from IMD 10, possibly using a voltage divider to reduce the voltage. Furthermore, one or more temperature indications (Vtherm) can be reported from one or more thermistors 136 in charging coil assembly 102 to allow control circuit 72 to control the generation of magnetic field 66, as previously mentioned. Such conventional aspects can be used in all examples of charging system 100 and are not discussed or illustrated in the following examples.

[0054] While it is preferable to house the control circuitry 72 and other circuitry 112 within the electronics module 104, this is not strictly necessary, and instead, these components may reside within the charging coil assembly 102, for example, on its circuit board 124. Thus, the electronics module 104 may contain only the battery 110 and the user interface. The control circuitry 72 may include a firmware-programmable microcontroller, such as any STM32F4 ARM series microcontroller supplied by STMicroeletronics, Inc., as described at http: / / www.st.com / content / st_com / en / products / microstrollers / stm32-32-bit-arm-cortex-mcus / stm32f4-series.html?querycriteria=productId=SS1577. The control circuitry 72 may also include an FPGA, DSP, or other similar digital logic device, or may at least partially include analog circuitry, as explained further below. The control circuit 72 may also include a firmware-programmable memory that is accessible to the microcontroller or other digital logic device if the logic device does not contain suitable on-chip memory.

[0055] exist Figures 6A-6C In the first example shown, the charging system 100 includes circuitry 140 to determine the position of the charging coil 126 in the charging coil assembly 102 relative to the lower IMD 10 being charged. The position circuitry 140 in this example includes portions of control circuitry 72 and can therefore be operated digitally as programmed firmware; however, the position circuitry 140 may also include analog components as further explained below.

[0056] As explained further below, the positioning of the charger to the IMD can determine, for example, whether the charging coil 126 and the IMD 10 are "aligned" or "centered". The boundary between alignment and misalignment refers to whether the positioning between the charging coil 126 (more generally, the charging coil assembly 102) and the IMD 10 is significantly poor, such that the charging coil 126 will no longer adequately charge the battery 14 of the IMD. For example, if the coupling value k between the charging coil 126 and the IMD 10 is greater than 0.35, then the charging coil 126 can be said to be aligned with the IMD 10; if k is less than or equal to 0.35, then it can be said to be misaligned, although this value will be specific and may vary. The alignment of the charger to the IMD was discussed before discussing charger-to-IMD centering.

[0057] Alignment is determined using measurements obtained from sensing coil 128, where sensing coil 128 is located... Figures 6A-6CThere is only one example. The sensing coil 128 is referred to herein as an "alignment" sensing coil, consistent with its function of determining alignment. However, as discussed further below, other sensing coils may be used in the charging coil assembly 102 for different purposes.

[0058] like Figure 6B As shown, the single alignment sensing coil 128 is preferably circular and includes a radius ra measured from the center 150 of the charging coil 126. The charging coil 126 is also preferably circular and, in the example shown, has a radius rp from the center 150, such that the charging coil and the alignment sensing coil are concentric. The radius rp can include the inner, outer, or average radius of the charging coil 126. Figure 6B For simplicity, the following figures are depicted as a single circle. Preferably, the radius ra is smaller than rp (e.g., ra is between 50% and 100% of rp), as this is useful for identifying misalignment, as explained later. However, this is not strictly necessary. The radius ra can also be equal to or even greater than rp. Furthermore, the charging coil and sensing coil can take shapes other than circles (e.g., squares, rectangles, or other shapes), but a circular coil is described for simplicity. Note that even non-circular coils can share the same center and are therefore concentric.

[0059] Radius ra and rp are also preferably set according to the dimensions of IMD 10 (of which battery 14 is being charged). In this respect, it can be said that IMD 10 has a radius ri. Radius ri can be an estimated or average distance from the center 160 of IMD 10. The center 160 can include the center or centroid of the charging coil 36 (FIGs 1B and 1C) in IMD 10, and can include the point that provides maximum coupling and therefore the fastest charging of battery 14 of IMD when it is perfectly aligned with the center 150 of charging coil 126 (charging coil assembly 102). Radius ri can also include the average distance between the center 160 and a significant boundary of IMD 10, such as its charging coil 36 or its housing 12 or the centroid of such a boundary. The radii ra and rp are preferably larger than the radius ri of IMD 10, because this will allow the charging coil 126 to vary laterally in position from IMD 10 while still keeping IMD 10 completely defined within the area of ​​the charging coil 126. For example, preferably the radii ra and / or rp are at least twice the radius ri.

[0060] When the charging coil 126 generates a magnetic field 66, a certain amount of magnetic field 66 will couple to the alignment sensing coil 128, the degree of coupling being influenced by the position of the underlying IMD 10. This coupling causes a voltage Va to form across the alignment sensing coil 128, which will be smaller when the IMD 10 is typically defined by the area of ​​the alignment sensing coil 128. This is in Figure 6B The graph shows the voltage Va as a function of radius r, where r includes the radial offset between charging coil 126 and IMD 10, i.e., the distance between their centers 150 and 160. Like magnetic field 66 and Vcoil, voltage Va is essentially AC and will have a frequency equal to the frequency of magnetic field 66 coupled to it.

[0061] Va can be discussed and Figure 6B The maximum amplitude Va+ (such as its root mean square, zero-to-peak, or peak-to-peak values) is represented by a curve. As the radius r increases from the perfectly aligned state (r = 0), the amplitude Va+ increases slowly because IMD 10 is still generally defined by the alignment sensing coil 128. When the radius r increases to the point that IMD 10 breaches the alignment sensing coil 128, the amplitude Va+ begins to increase significantly more. For simplicity, in Figure 6B This increase is illustrated linearly, but other cases may exist. As the radius r increases further, IMD 10 will eventually lie completely outside the alignment sensing coil 128, at which point the amplitude Va+ will be maximized and again constant, because IMD 10 has almost no effect on the coupling to the alignment sensing coil 128. Note that later in... Figure 14A The figure shows a more accurate curve of the magnitude Va+ obtained from the experimental results.

[0062] The amplitude Va+ can be customized through proper design of the alignment sensing coil 128. In this regard, it is worth noting that Vcoil can be in the range of approximately + / - 50V. Conversely, Va is preferably varied within a range that can be handled by the sensing electronics in the electronics module 104, as will be explained further below. For example, Va can preferably be set to vary between + / - 1V. Setting the amplitude Va+ can be achieved by changing the proximity of the alignment sensing coil 128 to the charging coil 126, for example, by changing ra relative to rp. The amplitude Va+ can also be set by designing the conductive traces in the circuit board 124 (to which the alignment sensing coil 128 is constructed). For example, the thickness and / or width of the traces of the alignment sensing coil 128 can be varied, as can the number of turns forming the alignment sensing coil 128. The amplitude Va+ will typically scale with the number of turns. Note that although the circular sensing coil 128 appears to consist of only a single trace (which is shown in the figure as a single turn for simplicity), it may actually be something else entirely, and instead, multiple turns of the circular sensing coil 128 may be formed in a single-stage or multi-stage trace circuit board.

[0063] The magnitude alignment threshold Va+(th) can be selected from the relationship between Va+ and radius r. (Discussed later) Figure 6B The different thresholds Vp+(th) are shown. In the example shown, Va+(th) can be determined as the point where r = ra (i.e., when the center 160 of IMD 10 is located at sensing coil 128). At this time, as Figure 6C As shown, IMD 10 is roughly half inside and half outside of the sensing coil 128 (and charging coil 126). However, this is just an example and experiments and simulations can specify Va+(th) to be selected in different ways. For example, as a practical problem, Figure 6C Misalignment between the charging coil 126 and the IMD 10 may cause the charging coil 36 of the IMD to receive too little magnetic field 66. If so, a lower value of Va+(th) can be selected, which will indicate misalignment when the radius r is less than ra.

[0064] Once a suitable amplitude alignment threshold Va+(th) is determined, the position circuit 140 can use it to determine and indicate alignment and / or misalignment with the patient. Figure 6A As shown, the AC signal Va formed at both ends of the alignment sensing coil 128 is transmitted to the electronic module 104 via cable 106. In this example, Va is digitized via analog-to-digital converter 142 and presented to position circuit 140. In position circuit 140, the amplitude Va+ can be determined, and later... Figures 13A-13DExplain how this occurs. In any case, the position circuit 140 can digitally compare the amplitude Va+ with an amplitude alignment threshold Va+(th) stored in or accessible by the position circuit 140. Analog circuitry can also be used, but it is not shown. For example, an analog amplitude Va+ generated, for example, by a rectifier circuit (not shown), can be compared with an analog amplitude alignment threshold Va+(th) at a comparator.

[0065] Regardless of how Va+ is sensed and compared to Va+(th), position circuit 140 can issue an alignment indicator 74. For example, if Va+ > Va+(th), position circuit 140 can issue an misalignment indicator 74, which may include emitting an sound (“beep”) from a speaker, issuing a notification on a display (if the electronics module 104 has one), or illuminating one of the LEDs (e.g., 118b). As discussed in detail later, Va+ can be compared to Va+(th) periodically, and the Va+ measurement results can be averaged to smooth out noise in the data. The alignment indicator 74 can stop if the patient is able to move the charging coil housing 102 to achieve better alignment between the charging coil 126 and the IMD 10. Note that the alignment indicator 74 can alert the patient to alignment, misalignment, or both.

[0066] An IMD 10 of moderate depth d in the patient's tissue, and therefore a moderate distance between the charging coil 126 and the IMD 10, can be assumed to select the amplitude alignment threshold Va+(th). However, in actual use, the patient's IMD 10 can be shallower or deeper than assumed, in which case Va+ will decrease or increase respectively, as... Figure 6B As shown by the dashed lines in the diagram. The single, constant amplitude alignment threshold Va+(th) used in the position circuit 140 is sufficient to determine alignment at these different depths. On the other hand, the single Va+(th) can also be counter-indicated because it does not intersect with the curve where Va increases at all depths, or may not intersect with a curve close enough to the desired radius (e.g., r = ra) to accurately establish the boundary between alignment and misalignment. Therefore, Va+(th) can be adjustable to increase Va+(th) for patients with deep implants and decrease Va+(th) for patients with shallow implants, thereby appropriately indicating misalignment in both cases. For example, the amplitude alignment threshold Va+(th) can be adjusted using the tuning process described in USP 9,227,075, discussed in the background art.

[0067] The voltage Va induced across the alignment sensing coil 128 will vary not only according to the depth of the IMD 10, but also according to the power of the magnetic field 66 generated by the charging coil 126. It is important to recognize this because the power of the charging coil 126 and therefore the magnetic field 66 can be controlled and varied in the charging system 102 for various reasons, some of which will be discussed later. This control will also affect Va, which can make it difficult to compare the amplitude Va+ with a set amplitude alignment threshold Va+(th). Therefore, it is necessary for the position circuit 140 to normalize the Va+ measurement relative to the power of the magnetic field 66 before comparing it with the amplitude alignment threshold Va+(th). This normalization of the Va+ measurement may include, for example, dividing Va+ by any number of parameters that will indicate the magnetic field strength. This can include the magnitude of the voltage across the charging coil 126 (Vcoil+), the magnitude of the current through the charging coil 126 (Icharge+), or inputs to the charging circuit 64, such as the duty cycle by which the charging circuit 64 drives the charging coil 126, as explained later. Instead of normalizing the sensing coil measurement Va+, the threshold Va+(th) can also be normalized (e.g., by multiplying it by a parameter indicating the magnetic field strength).

[0068] However, normalization of the sensing coil measurements is not strictly necessary. For example, the charging coil 126 can be controlled to generate a test or default magnetic field 66 with a known constant power at the time when the sensing coil measurements are obtained to determine alignment, as discussed further below. Therefore, the amplitude Va+ will not change due to variations in the magnetic field power at those times, thus allowing for the selection and more reliable application of the amplitude alignment threshold Va+(th).

[0069] Figures 7A-7C Another example is shown where a single sensing coil can be used to determine alignment. In this example, the alignment sensing coil 128' includes an edge detector coil, so named because coil 128' is shaped to detect the presence of IMD 10 when IMD 10 typically breaches the region (A) defined by two circular concentric parts (the inner part with a smaller diameter ra1 and the outer part with a larger diameter ra2) relative to the center 150. Alignment sensing coil 128' is circular and again concentric with charging coil 126. The inner and outer parts are connected such that current flowing through alignment sensing coil 128' will flow in different directions in the two parts. For example, and as... Figure 7AAs indicated by the arrows, the current flowing clockwise in the smaller diameter component (ra1) will flow counterclockwise in the larger diameter component (ra2). Ignoring IMD 10 for now, note that the magnetic field 66 passing through the component aligning the sensing coil 128' will induce currents in the two components that are opposite each other due to the way they are connected. Then, in effect, the total current flowing in the alignment sensing coil 128' and the resulting voltage Va across it will be proportional to the difference between the regions between the outer and inner components (i.e., the region A defined between them).

[0070] picture Figures 6A-6C Like the first single alignment sensing coil 128, the radii of the inner (ra1) and outer (ra2) components are approximately close to, but preferably smaller than, the radius rp of the charging coil 126. Furthermore, the values ​​of radii ra1 and ra2 are preferably close (e.g., ra1 is between 50% and 95% of ra2) to define a narrow region A. For simplicity, the average radius of the two components and therefore the alignment sensing coil 128' can generally be referred to as a single radius ra. As with the alignment sensing coil 128 described earlier, each of the inner and outer components of the alignment sensing coil 128' can be customized according to their thickness, length, and number of turns, but this is not shown. Furthermore, modifying these variables is useful for adjusting the range of Va. The alignment sensing coil 128' is again preferably formed in traces on the circuit board 124, but this is not strictly necessary.

[0071] When the charging coil 126 is fully aligned with the IMD 10 (i.e., when r = 0 and centers 150 and 160 coincide), the IMD 10 will not eclipse region A of the alignment sensing coil 128'. Therefore, the IMD 10 has a limited effect on the coupling of the magnetic field 66 with the alignment sensing coil 128', and the amplitude Va+ will approach its maximum value, as... Figure 7A As shown, as the radius r increases, IMD 10 will begin to encroach on region A of the alignment sensing coil 128', and Va+ will begin to decrease, eventually reaching a minimum when IMD 10 approximately obscures the alignment sensing coil 128' to its maximum extent (i.e., when r = ra). As r increases further, IMD 10 will eventually begin to move outside region A, and Va+ will increase, eventually reaching a maximum when IMD 10 no longer affects the coupling with the alignment sensing coil 128'. Note that the amplitude Va+ at its maximum value (high values ​​of r) will be higher (Δ) than Va+ at low values ​​(e.g., r = 0), simply because at low values ​​IMD 10 will have some small coupling with the alignment sensing coil 128'.

[0072] The minimum value of the amplitude Va+ helps in selecting the amplitude alignment threshold Va+(th) that can be used by the position circuitry 140 when using the alignment sensing coil 128'. While the amplitude alignment threshold Va+(th) can be set to the minimum value of Va+, Va+(th) can also be set to a value slightly higher than that minimum to ensure it is not "missed" by the position circuitry 140. Therefore, and as before, the amplitude Va+ of the alignment sensing coil 128' can be sensed and used to indicate misalignment by comparing it with the alignment threshold Va+(th).

[0073] Position circuit 140 can be modified to take into account misalignment when it is determined. Figure 7A The difference in shape of Va+ relative to the radius curve. For example, position circuit 140 can determine whether Va+ has decreased (e.g., to Va(th)) and subsequently begins to increase, and at that time issue a misalignment indicator 74. In this regard, it is worth noting that position circuit 140 can store previous Va+ measurements as a function of time.

[0074] The use of the edge detection alignment sensing coil 128' and the shape of its Va+ curve relative to the radius allows for the selection of the amplitude alignment threshold Va+(th), which can accurately establish the boundary between alignment and misalignment, regardless of the IMD 10 depth. Figure 7A Two Va+ curves are shown for deep and shallow implants. A single Va+(th) above the minimum Va+ value can be selected for both extreme cases, thus allowing Va+ to be used to determine alignment regardless of implant depth, and potentially eliminating the need to adjust Va(th) for different IMD depths. That said, according to USP 9,227,075 discussed earlier, Va+(th) can be adjusted for different IMD depths as before. Furthermore, as discussed earlier, Va+ or Va+(th) can be normalized to account for the power of magnetic field 66.

[0075] Figure 8A and 8B Another alignment sensing coil arrangement 128” is presented, which is functionally similar to Figures 7A-7CThe edge detection alignment sensing coil 128' is used, but concentric inner and outer alignment sensing coils 128_1 and 128_2 are used without connection. As in the alignment sensing coil 128', the inner and outer alignment sensing coils 128_1 and 128_2 have radii ra1 and ra2 that are preferably close in value. However, because the alignment sensing coils 128_1 and 128_2 are not connected, they will each sense separate voltages Va1 and Va2 transmitted to the electronics module 104 via cable 106. As before, each of the alignment sensing coils 128_1 and 128_2 can be customized according to their geometry and number of turns to achieve Va1 and Va2 values ​​suitable for the electronics module 104.

[0076] At electronic module 104, voltages Va1 and Va2 can be subtracted (or added if the voltages have opposite polarities), and are approximately equal to Figures 7A-7C The edge detection aligns with the odd-numbered voltage Va of the sensing coil 128'. Therefore, the amplitude Va+ curve again undergoes the same process as... Figure 8A The minimum value is shown, where the alignment threshold Va+(th) is established as already discussed. The processing of the sensed voltages Va1 and Va2 can occur in the position circuit as before, where A / D converters 142_1 and 142_2 are used to digitize these voltages, and where their subtraction occurs in the position circuit 140. Alternatively, both voltages Va2 and Va1 can be presented to the differential amplifier 144, which can perform the subtraction before digitization and presentation to the position circuit 140, as shown by the dashed lines. Otherwise, the position circuit 140 for the alignment sense coil arrangement 128 (hereinafter also simply referred to as alignment sense coil 128), even if it includes two sense coils 128_1 and 128_2, can be used as before to determine and indicate misalignment. Furthermore, the amplitude alignment threshold Va+(th) usable by the position circuit 140 can be adjustable based on the implantation depth, and / or the position circuit 140 can apply normalization to account for the power of the magnetic field 66, as previously explained.

[0077] Although the alignment sensing coil 128 shown includes two alignment sensing coils 128_1 and 128_2, it is noted that even more alignment sensing coils 128_x can be used, such as, for example, three or more. Including even more alignment sensing coils 128_x will provide additional information and allow the position circuit 140 to determine alignment with further precision.

[0078] Alignment sensing coils 128, 128', and 128' have been described to determine misalignment between charging coil 126 (more generally, charging coil assembly 102) and IMD 10, i.e., when the alignment is so poor that charging coil 126 and IMD's charging coil 36 are not well coupled, and therefore charging coil 126 cannot adequately charge IMD's battery 14 in its current position. However, in the following example, charging system 100 uses one or more sensing coils to determine whether charging coil 126 is "centered" relative to IMD 10. As explained below, charging coil 126 is "centered" relative to IMD 10 when it is well aligned with IMD 10 (i.e., when charging coil 126 and IMD's charging coil 36 are very well coupled, and therefore charging coil 126 can quickly charge IMD's battery 14). For example, if the coupling value between charging coil 126 and IMD 10 is greater than 0.65, then charging coil 126 can be said to be "centered" relative to IMD 10. 10 is aligned, but if k is less than or equal to 0.65, it is not aligned, although again this value is specific. Therefore, charging coil 126 can be aligned (not misaligned) with IMD 10, even if it is not aligned, for example, if 0.35 <k≤0.65。

[0079] To detect when the charging coil assembly 102 is aligned with the IMD 10, the circuit board 124 may include one or more alignment sensing coils 129, firstly in Figures 9A-9C As shown in the example, the centering sensing coil 129 is circular, similar to... Figures 6A-6C The alignment sensing coil 128, but the sensing coil 129 may also include an edge detector centering sensing coil (129'), which is geometrically similar to the earlier alignment sensing coil. Figures 7A-7C The edge detector alignment sensing coil 128' shown is similar. Sensing coil 129 may also include one or more separate centering sensing coils (129_1 and 129_2; collectively 129”), which are geometrically similar to those shown earlier. Figure 8A and 8B The alignment sensing coil 128” shown is similar. For simplicity, the alignment sensing coil is then indicated by element 129, although alternative geometries 129' or 129”, not shown, can also be used.

[0080] Similar to the alignment sensing coil, the alignment sensing coil 129 induces a voltage Vc (or Vc1 and Vc2, if two or more separate alignment sensing coils are used according to 129"). Like Va, the maximum amplitude Vc+ of Vc is a function of the coupling with the primary charging coil 126 and the coupling related to the proximity of the IMD 10. Therefore, the amplitude Vc+ will decrease as the IMD 10 approaches the area surrounded by the alignment sensing coil 129. Again, the alignment sensing coil 129 can be formed in conductive traces on the circuit board 124, but may also include wire windings, and the geometry of the sensing coil 129 can be customized to obtain the values ​​of Vc (or Vc1 and Vc2), which can be processed by the electronics module 104.

[0081] Similar to the alignment sensing coil 128, the centering sensing coil 129 is preferably centered around the center 150 and includes a radius rc (or radii rc1 and rc2, or an average radius of rc if 129' or 129" is used). In one example, the radius rc can be approximately equal to the radius ri of IMD 10. As shown in the graph of amplitude Vc+ versus radius r (which illustrates the relationship with earlier...),... Figure 6B Similar to the single sensing coil (Vc+), when the charging coil 126 (charging coil assembly 102) is perfectly aligned with the underlying IMD 10 (i.e., when centers 150 and 160 coincide and r = 0), Vc+ will be at its minimum. As the radius r increases, the IMD 10 will almost immediately begin to break through the range of the centering sensing coil 129, and therefore Vc+ will begin to increase, eventually reaching its maximum when the IMD 10 is no longer coupled to the centering sensing coil 129. From this graph, the amplitude alignment threshold Vc+(th) can be selected. As with the amplitude alignment threshold Va+(th) discussed earlier, Vc+(th) can be selected in a different way. In the example shown, Vc+(th) is selected to establish that the charging coil 126 is aligned relative to the IMD 10 if the radius r between the charging coil 126 and the IMD 10 is less than 1 / 2rc. Therefore, as long as the center 160 of IMD 10 is located within the small region A' relative to the center 150 of charging coil 126, charging coil assembly 102 will be considered aligned with IMD 10, such as Figure 9B As shown.

[0082] Then, the position circuit 140 can compare the measured amplitude Vc+ with Vc+(th) and issue a centering indication 75. For example, if the charging coil 126 is not centered, i.e., if Vc > Vc(th), then the centering indicator 75 can be issued, which, like the alignment indicator 74, can include using a speaker, LED, etc. The centering indicator 75 can warn the patient about the centered condition, the uncentered condition, or both. It should also be noted that the sensing circuit for Vc (e.g., the A / D converter 142) can also be the same or similar to the circuit for sensing Va.

[0083] Similar to the amplitude alignment threshold Va+(th), as described above, the centering threshold Vc+(th) can also be adjusted for each patient based on the specific depth of the IMD 10 of each patient, and / or the position circuit 140 can apply normalization to account for the power of the magnetic field 66.

[0084] Regarding this, the alignment of the charging coil 126 with the IMD 10 has been discussed separately ( Figure 6A-8B ). However, when the two techniques are used together, there are additional advantages to IMD 10 charging, as Figure 10A-11B shown. In particular, using the two techniques together allows the charging system 100 to determine and / or indicate three possible positions of the charging coil 126 relative to the IMD 10: centered (e.g., r < 1 / 2rc or k > 0.65), misaligned (e.g., r > ra or k ≤ 0.35), and an intermediate position of intermediate coupling where the charging coil 126 is not centered but also not misaligned with the IMD (1 / 2rc < r < ra or 0.35 < k ≤ 0.65).

[0085] Starting with Figure 10A and 10B , in addition to the charging coil 126, the charging coil assembly 102 also includes both an alignment sensing coil 128 and a centering sensing coil 129, which can be constructed in any of the various forms described earlier. For simplicity, single coils 128 and 129 of radii ra and rc are shown (see Figure 6B and 9A ).

[0086] The position circuit 140 is programmed with an alignment and centering algorithm 180, which will be referenced Figure 12A and 12BFurther discussion. Algorithm 180 receives, as digitized, Va and Vc, and compares the amplitudes Va+ and Vc+ with thresholds Va+(th) and Vc+(th) as before to determine whether the charging coil 126 is centered, misaligned, or misaligned but not misaligned. Either or both of alignment indicator 74 and / or alignment indicator 75 may be issued accordingly. Those skilled in the art will appreciate that algorithm 180 can be stored on any non-transitory computer-readable medium, including solid-state memory within control circuitry 72.

[0087] One advantage of using a single alignment 128 and centering 129 sensing coil, or two different concentric coils, more generally relates to the normalization of sensing coil measurements. Va and Vc will vary with the power of the magnetic field 66 generated by the charging coil 126, and as discussed above, such measurements can be normalized to remove the magnetic field power as a variable, and comparisons with thresholds Va+(th) and Vc+(th) are more reliable. However, when using two or more sensing coils, other measurements can be used to normalize the measurements of one sensing coil, because these other measurements will generally indicate the magnetic field strength (even if affected by IMD coupling). For example, before comparing the amplitude Va+ with the amplitude alignment threshold Va+(th), the amplitude Va+ can be divided by the amplitude Vc+, and before comparing Vc+ with the centering threshold Vc+(th), Vc+ can be divided by Va+.

[0088] In practice, an additional sensing coil can be included in the charging coil assembly 102 and measured solely for normalization purposes. For example, in Figure 10B In this configuration, the sensing coil 128 and its measured voltage Va need not be used for alignment determination. Instead, centering and / or alignment can be determined by the sensing coil 129 and its voltage Vc (as per [reference to...]). Figure 11A and 11B (To be further explained), Va+ is used only to normalize Vc+ (e.g., Vc+ / Va+) before being compared with the relevant thresholds (Va+(th) and / or Vc+(th)).

[0089] A single sensing coil can also be used to detect alignment and centering. For example, in Figure 11A and 11B In this example, a single alignment / centering sensing coil 130 is used. In the example shown, the alignment / centering sensing coil 130 is circular, but it can include an edge detector sensing coil (130') or separate centering sensing coils (130_1 and 130_2; collectively 130”), which is similar to... Figures 7A-8BThose shown in. For simplicity, the alignment / centering sensing coil is subsequently referred to by element 130, even though alternative geometries 130' or 130'' that are not shown may also be used.

[0090] The radius rx of the alignment / centering sensing coil 130 is preferably between the radii ra and rc of the respective alignment coils and centering coils 128 and 129 described earlier. The magnitude Vx+ of the voltage Vx induced across the coil 130 can be compared to separate magnitude thresholds Va+(th) and Vc+(th) in the alignment and centering algorithms 180 of the position circuit 140. Such thresholds can be selected to establish boundaries for the centering situation (within region A') and misalignment situation (outside region A'') of the charging coil 126 relative to the IMD 10. Such boundaries can be consistent with or established based on the radii of the respective alignment coils and centering coils 128 and 129 presented earlier. For example, the alignment magnitude threshold Va+(th) can establish the radius ra outside of which the IMD 10 is considered misaligned (i.e., when Vx+ > Va+(th)), while the centering magnitude threshold Vc+(th) can establish the radius 1 / 2Vc within which the IMD is considered centered (when Vx+ < Vc+(th)). Additionally, alignment indicators and centering indicators 74 and 75 can be used to indicate centering, misalignment, and / or alignment but not centered situations.

[0091] Before a detailed explanation regarding Figure 12A and 12B A brief summary of an example of the alignment and centering algorithm 180 is presented. Algorithm 180 requires that at the start of an IMD charging session, the patient first center the charging coil 126 (charging coil assembly 102) with the underlying IMD 10 (e.g., r < 1 / 2rc). Thereafter and during charging, the charging coil 126 can move and even move from an uncentered position (e.g., r > 1 / 2rc), as long as the charging coil 126 remains aligned with the IMD 10 (e.g., r < ra). However, if the charging coil 126 moves to the extent that it is no longer aligned with the IMD 10 (e.g., r > ra), then before charging will seriously start again, the patient will be required to re-center the charging coil assembly 102 (e.g., r < 1 / 2rc).

[0092] This operation of the alignment and centering algorithm 180 is beneficial because it ensures that the charging coil 126 is centered with the IMD 10 initially and after misalignment, and thus the two are very well coupled. Requiring such centered positioning means that the charging coil 126 is less likely to quickly move out of alignment with the IMD 10 because it would have to move a perceivable distance (from 1 / 2rc to ra) to do so.

[0093] This is an improvement over previous alignment techniques where charger-to-IMD positioning was evaluated only by a simple aligned / unaligned determination. Consider, for example, FIG. 3 where alignment (70) is determined solely by comparing the Vcoil of the primary coil 52 to an alignment threshold Vt. Assume that at the start of a charging session the external charger 50 is relatively poorly aligned with the IMD 10, perhaps because as Figure 4B shown it is significantly offset (x). Also assume that the external charger 50 is still technically aligned, because Vcoil < Vt (even though Vcoil is also very close to Vt). The external charger 50 may easily lose alignment (Vcoil > Vt) quickly when the patient moves. This provides a frustrating usage model for the patient who believes his external charger 50 is aligned, only to later find, perhaps seconds later, that alignment demands his attention. Even thereafter, if the patient moves the external charger 50 back into alignment with the IMD 10 (Vcoil < Vt), the charger may quickly become misaligned with the IMD again (if it is again on the verge of being misaligned).

[0094] The alignment and centering algorithm 180 solves this problem because charging cannot begin if the charging coil assembly 102 is only marginally aligned with the IMD 10. Instead, the charging coil assembly 102 must then be centered with the IMD 10, which in effect requires very good alignment with the IMD 10 provided by the centering.

[0095] Figure 12A The alignment and centering algorithm 180 is shown in the form of a flowchart, while Figure 12B the magnetic field generated at the charging coil 126 as a result of the algorithm is shown. First, the patient turns on the charger system 100 (190), for example by pressing the on / off button 116 on the housing 105 of the electronic module 104 ( Figure 5B ). A test or default magnetic field can then be generated from the charging coil 126 (192). As earlier mentioned, this test magnetic field 66 can be of a known constant power, and the power can be lower than the power of the true magnetic field 66 that will later be used to operably charge the battery 14 of the IMD during the process. The use of a low-power magnetic field is preferred to ensure that the IMD 10 is not over-powered before the charging system 100 can determine whether the charging coil 126 is centered. The constant power test magnetic field is performed using the charging circuit 64 by using a set duty cycle, as described in detail later.

[0096] Algorithm 180 can be used as a first step to infer the presence of IMD 10 (193)—whether the charging system 100 detects the presence of IMD 10, so that position and charging can begin to be evaluated. Detection of the presence of IMD 10 can occur in any number of ways. For example, the amplitude Vcoil+ of the voltage formed across the charging coil 126 can be evaluated during the generation of the test magnetic field and compared with the IMD presence amplitude threshold Vp+(th).

[0097] Alternatively, the charging system 100 may use measurements obtained from any of the sensing coils shown earlier to determine the presence of the IMD, and later use those measurements during algorithm 180 to determine charger-to-IMD alignment and / or centering. For example, Figure 12A The bottom shows the alignment of the sensing coil 128 (see...). Figure 6B A graph of the amplitude Va+ measured at () is shown. In addition to evaluating the alignment amplitude threshold Va+(th) discussed earlier, Va+ can be compared to the IMD presence threshold Vp+(th) (which can be set just below the maximum value of Va+). If Va+ > Vp+(th), the charging system 100 (e.g., position circuit 140) can determine that IMD 10 is not yet within the detectable range of the charging coil 126 (charging coil assembly 102). Although not shown, the presence or absence of the detected IMD 10 can be indicated to the user by an alarm (e.g., one or more of LEDs 118a or 118b) issued by the user interface of the charging system. Therefore, it should be noted that the charging system 100 can determine, in addition to aligning and misaligning, and / or centering and misaligning (the cases where IMD 10 is present relative to the charging coil 126), that IMD 10 is not present relative to the charging coil 126.

[0098] At step 193, other techniques can be used to determine the presence of IMD 10 relative to charging coil 126. For example, the technique of USP 9,186,520 can be used, which can also be used to automatically turn on the charging system when the presence of IMD 10 is detected.

[0099] Once it is determined that the IMD is present and the test magnetic field 66 is generated, one or more voltages are sensed to determine whether the charging coil 126 is aligned with the IMD 10 (194). For example, the magnitude Vc+ of the alignment sensing coil 129 or Vx+ of the alignment / centering sensing coil 130 (possibly normalized in various ways as earlier described) can be compared with the centering threshold Vc+(th). Initially, it can be expected that the charging coil 126 is not well aligned, especially if the patient is in the process of placing the charging coil assembly 102 close to the IMD 10. In such a case, the patient will be warned (centering indication 75) that the charging coil 126 is not aligned (196) so that he can attempt to move the charging coil assembly 102 to a better position relative to the IMD 10. Such an alert can be in various forms as previously described. In a particular example, such an alert can include illuminating an LED (e.g., 118b) on the electronic module 104 in a color indicating the alignment / centering state. For example, the LED 118b may initially be lit red until the charging coil 126 is aligned.

[0100] The assessment of alignment (194) can be repeated at sensible intervals (such as about every 1.0 second). Once alignment is achieved - for example, when Vc+ or Vx+ < Vc(th) and thus the radius r between the charging coil 126 and the IMD 10 is less than 1 / 2rc as discussed in the previous example - the previously issued misalignment alert can be stopped (198). For example, the LED 118b can now be lit green to indicate that the charging coil 126 is aligned. Additionally, the charging coil 126 can now generate a real magnetic field 66 operable to charge the battery 14 of the IMD 10 (200). The power of such a real magnetic field 66 may be higher than that of the test magnetic field and can also vary according to normal charging coil 126 operation and control, as Figure 12B shown by the arrow in, and as further discussed subsequently. The real magnetic field 66 can continue to be generated for a reasonable period of time (t1) (such as about 30 seconds).

[0101] Thereafter, the alignment and centering algorithm 180 will measure the alignment of the charging coil assembly 102 relative to the IMD 10 (202). This measurement can again involve using a constant low - power test magnetic field. Preferably, the alignment measurement occurs quickly, for example, within a period of time (t2) of 1.0 second and thus does not significantly interrupt the charging of the IMD 10 by the real magnetic field. Misalignment can be determined by evaluating the magnitude Va+ of the sensing coil 128 or the magnitude Vx+ of the alignment / centering sensing coil 130 (possibly normalized in various ways as earlier described).

[0102] If the charging coil 126 is not misaligned (204) - for example, if Va+ or Vx+ < Va+(th) and thus the radius r is less than ra, as discussed in the previous example - then charging can continue (200) where the charging coil 126 generates a real magnetic field again within another period t1. Note that in this example, at this time the charging coil 126 may no longer be centered with the IMD 10. That is, the radius r can be greater than 1 / 2rc but less than ra. However, in this example, this is not important: as long as there is no more significant misalignment and thus the IMD 10 is still reasonably coupled to the charging coil 126 and is sufficiently charged by it, charging via the real magnetic field can continue.

[0103] If the charging coil 126 is misaligned (206) - for example, if Va+ or Vx+ > Va+(th) and thus the radius r is greater than ra - then the patient is warned again (alignment indicator 74), such as by lighting the LED 118b red again. Then the algorithm 180 essentially returns to its start: a test magnetic field is generated from the charging coil (192), and before the real magnetic field starts again (200), the patient must move the charging coil assembly 102 again to center it with the IMD 10 (e.g., r < 1 / 2rc) (194 - 198).

[0104] As just discussed, it may be immaterial to the alignment and charging algorithm 180 that: the charging coil 126 eventually becomes misaligned with the IMD 10, as long as it also remains aligned (202 - 206). Normal charging of the IMD 10 can continue. However, the optional steps in the algorithm 180 shown in dashed lines can also be used to inform the user of the misaligned but aligned situation, even if it does not affect charging. If the charging coil 126 is not misaligned (204), the algorithm 180 can still check whether it is still aligned (208), similar to what initially occurred in step 194. If the still - aligned charging coil 126 is still aligned (210), charging can continue. In this case, the LED 118b can remain green (or can turn green if previously lit amber, as just explained). However, if the still - aligned charging coil 126 is not aligned (212), the fact can also be warned to the user, even if charging will continue and even if the patient is not required to move the charging coil 102 now. For example, in this case, the LED 118b may be lit amber. In fact, these optional steps in the algorithm 180 measure three different situations of the charging system and issue three different alerts: aligned situation (green), misaligned but not misaligned situation (amber), and misaligned situation (red).

[0105] It should be noted that the steps 202 and 208 for evaluating alignment and centering do not need to occur in the order shown and can be evaluated simultaneously. For example, it may be wise to evaluate alignment (202) only when the charging coil 126 has become misaligned (208).

[0106] While it is not strictly necessary to use potentially different “test” and “real” magnetic fields 66 to describe the alignment and centering algorithm 180, the charging coil 126 can generate a single real magnetic field 66 by operating the entire algorithm 180 in a manner that meaningfully supplies power to the IMD 10. In this case, normalization of the sensing coil measurements may become more important to account for possible variations in the power of the magnetic field 66, as discussed earlier.

[0107] In this disclosure, the position of the charger to the IMD has been determined with reference to the maximum amplitude of the voltage induced on the sensing coil (e.g., alignment and / or centering). However, the inventors recognize that other sensing coil parameters can be used to determine the charger-to-IMD positioning, particularly the phase angle (θ) of the induced voltage relative to the signal used to drive the charging coil 126, and the resonant frequency (f(res)) of the charger / IMD system. The inventors also recognize that the use of two or more sensing coil parameters (e.g., two or more of amplitude, phase angle (θ), and resonant frequency f(res)) can be used to improve positioning determination, particularly by allowing the depth (d) of the charger to the IMD and the radius (r) of the charger to the IMD to be determined. Before discussing these concepts in detail, refer to Figures 13A-13C Further details of the circuitry in the charger system 100 will be discussed.

[0108] Figure 13A Further details regarding the charging circuit 64 for energizing the charging coil 126 with AC current Icharge are shown. A digital drive signal D is formed by a square wave generator 65, which may include a portion of the control circuitry 72. The drive signal D comprises a pulse width modulation (PWM) signal with a periodic repetition of high (logic '1') for time portion 'a' and low for time portion 'b'. Therefore, the drive signal D has a duty cycle DC equal to a / (a+b). Furthermore, the drive signal D has a frequency f equal to 1 / (a+b). The frequency f of the drive signal is approximately set to or close to the resonant frequency of the LC circuit of capacitor 131 / charging coil 126 (e.g., approximately 80 kHz), but the frequency of the drive signal can also be adjusted, as explained later.

[0109] The charging circuit 64 may include a well-known H-bridge configuration, comprising two N-channel transistors coupled to a supply voltage Vcc and two P-channel transistors coupled to a reference potential such as ground (GND). The transistors are turned on and off by a drive signal D and its logic complement D*. In doing so, the supply voltage Vcc and ground are alternated at a frequency f across the LC circuit, thereby generating a magnetic charging field 66 at that frequency. The supply voltage Vcc may include a battery 110 in the electronic module 104. Figure 5A The voltage of the drive signal D can be adjusted from that voltage. As is well known, the duty cycle DC of the drive signal D can be increased from 0 to 50% to increase Icharge, thereby setting the power of the charging coil 126 to be excited and thus setting the power of the generated magnetic field 66.

[0110] The AC voltage Vy induced across the sensing coil 178 (e.g., any of the previously described 128, 128', 128”, 129, 129', 129”, 130, 130', or 130”) will also have a frequency equal to f, but may be offset by a phase angle (θ) relative to the drive signal D (and therefore relative to the voltage Vcoil across the charging coil 126 and the magnetic field 66). This is in Figure 13B As shown, the phase angle θ is measured as the difference between the center (top 'a') of the drive signal D and when Vy = 0. However, this is arbitrary, and the phase angle θ of the sensing coil voltage Vy can be determined with respect to different reference points, or with respect to Vcoil or the magnetic field 66.

[0111] As mentioned earlier, the sensing coil voltage Vy is digitized at A / D 142 and sampled at a frequency Fs. As shown, the digitized samples are provided to the Vy amplitude and phase angle determination module 170, which can more generally operate as firmware within the position circuit 140 and control circuit 72. Module 170 is capable of simultaneously determining the amplitude (Vy+) and phase angle (θ) of Vy by evaluating N digitized samples of Vy. Figure 13C The mathematics involved is explained. Basically, each sample (Vy) N Multiply by orthogonal trigonometric functions (sin(ωx t)) N ) or cos(ωx t N The values ​​are summed together and normalized using the sample size (1 / N) to represent the values ​​I and R. The amplitude (Vy+) and phase angle (θ) of Vy are then determined as functions of I and R, as shown in the equation on the right. Note that the amplitude Vy+ determined in this way includes the zero to peak value of Vy. Figure 13B As shown.

[0112] As those skilled in the art will understand, the amplitude Vy+ and phase angle θ can also be determined in different ways, and they do not need to be determined simultaneously in the same module or circuit. For example, the amplitude Vy+ can be determined by rectifying Vy to a DC voltage (e.g., using a full-wave rectifier). The phase angle θ can also be determined using analog components. Figure 13D For example, it is shown that the phase angle between Vy and the drive signal D can be determined using a phase comparator 182. As is known, the phase comparator 182 outputs a voltage (Vcntr) representing the phase angle θ. If needed, the sensed voltage Vy can be clipped and level-shifted to a digital signal that is more easily compared with the digital drive signal D at the phase detector 182.

[0113] It should be noted that the number of samples (N) of Vy and the frequency (Fs) at which such samples are obtained can vary depending on the desired accuracy of Vy+ and θ, as well as how long the measurement should take.

[0114] Another sensing coil parameter that can be evaluated to determine the charger-IMD positioning is the resonant frequency f(res) of the charger-IMD system. The resonant frequency f(res) can be determined by the resonant frequency determination module 172 within the position circuit 140. Figure 13A As determined in module 170, it can also be operated as firmware. Module 172 can use the phase angle θ determined in module 170 to help determine the resonant frequency f(res). Specifically, module 172 can change the frequency f of the drive signal D until the phase angle θ received from module 170 is equal to 0, thereby establishing f(res) at that frequency f. This frequency change can be an iterative process and may require several adjustments to the frequency of the drive signal D. How the frequency is adjusted may involve consideration of the polarity of the phase angle θ. For example, if the phase angle is positive, module 172 can decrease the frequency f, and if the phase angle is negative, it can increase the frequency f.

[0115] Frequency adjustment of the drive signal D to determine the resonant frequency f(res) can be achieved by changing one or both of the time portions 'a' and 'b' at the square wave generator 65. In one example, the two time portions 'a' and 'b' can be scaled equally to keep the duty cycle DC of the drive signal D constant, and thus keep the power of the charging coil 126 and the magnetic field 66 constant. However, this is not strictly necessary, because the changes in duty cycle and power caused by small frequency adjustments can be negligible or permissible. Therefore, only portion 'a' or 'b' can be varied.

[0116] Analog circuits can also be used to measure f(res) of the charger-IMD system. (See again...) Figure 13DThe determined phase angle (denoted as Vcntr) can be compared with the reference voltage (Vref) at comparator 186. When the phase angle is zero degrees, Vref can be set to equal Vcntr, and thus the comparator can output a digital signal to square wave generator 65 to indicate whether the phase angle is higher ('1') or lower ('0') than zero degrees. Therefore, square wave generator 65 can then increase or decrease the frequency of the drive signal D, which is provided back to phase comparator 182 via feedback loop 190, until Vcntr = Vref and the phase angle θ is equal to zero, at which point f(res) is determined as the frequency f to which the drive signal D has been adjusted. Other analog feedback circuits, such as phase-locked loops or delay-locked loops, can also be used.

[0117] Figure 14A Experimental results show how the parameters of amplitude Vy+ (top left), phase angle θ (top right), and resonant frequency f(res) (bottom left), measured from sensing coil 178, vary with radial offset r and depth d between the centers 150 and 160 of charging coil 126 and IMD 10, respectively. Figure 14B The same data is shown, but plotted for each sensing coil parameter at a constant depth (d = 10 mm), which represents the typical depth at which the charging coil assembly 102 and the IMD 10 would separate when the IMD 10 is implanted in the patient. In this experiment, the radius rp of the charging coil 126 is approximately 30 mm, and the radius of the sensing coil 178 (circular in this example; see example) Figure 11B It is approximately 15-20mm.

[0118] Figure 14B It was verified that any one of the sensing coil parameters—amplitude Vy+, phase angle θ, or resonant frequency f(res)—can be individually measured and evaluated to determine the charger-to-IMD positioning—such as alignment or centering as discussed earlier. For example, and as referenced, for instance... Figure 6B As discussed earlier, the amplitude threshold Vy+(th) can be stored in conjunction with the position circuit 140 ( Figure 13A) in the associated database 200 and compared with the measured amplitude Vy+ (module 170) to determine the positioning of the charging coil 126. As the data shows, the amplitude threshold Vy+(th) = 0.18 V establishes a charger-to-IMD radius r of approximately 27 mm at the indicated depth (d = 10 mm), which is close to the radius of the charging coil 126 (approximately 30 mm). Thus, this threshold will serve as a good determiner of charger-to-IMD alignment such that if Vy+ < Vy+(th), the charging coil 126 will be considered aligned with the IMD 10, and if Vy+ ≥ Vy+(th), it is misaligned. Different thresholds can also be stored and applied to determine a more stringent centering position, such as Vy+(th') = 0.14 V, which defines the charging coil 126 as centered when the charging coil 126 is at or below a tighter 20 mm radius relative to the IMD 10. Depending on the comparison with one or more amplitude thresholds, the IMD position circuit 140 can indicate (74,75) the determined position to the user, such as whether the charging coil 126 is centered, misaligned but aligned, or misaligned, as earlier explained. As earlier discussed ( Figure 10A and 10B ), more than one sensing coil 178 concentric with the charging coil 126 can also be used.

[0119] The measured resonant frequency f(res) can also be used alone to determine charger-to-IMD positioning. As Figure 14B shown, the resonant frequency threshold f(res)(th) = 81.2 kHz establishes a charger-to-IMD radius r of approximately 27.5 mm at the indicated depth (d = 10 mm), which can again be used as a good determiner of charger-to-IMD alignment: if f(res) > f(res)(th), the charging coil 126 will be considered aligned with the IMD 10, and if f(res) ≤ f(res)(th), it is misaligned. Different thresholds can again be applied to determine a more stringent centering position, such as f(res)(th') = 81.4 kHz, which defines a tighter 20 mm centering radius, but Figure 14B [[ID=!1]]this additional threshold is not shown. Additionally, the resonant frequency f(res) measured from more than one sensing coil 178 can also be used.

[0120] The measured phase angle θ can also be used alone to determine charger-to-IMD positioning. From Figure 14BThe data shows that when r = 0, the phase angle θ measured from sensing coil 178 significantly lags behind the drive signal D (10°) and decreases at higher radii, eventually approaching zero degrees, which is closer to the radius (30 mm) of charging coil 126. A phase angle threshold θ(th) of approximately 0.8 degrees is again used as a suitable alignment threshold for the geometry of the charging coil 126 under discussion and the indicated depth. Furthermore, although not shown, additional phase angle thresholds can be used to determine alignment, and the phase angle can be measured from more than one sensing coil 178.

[0121] Refer again Figure 13A The various thresholds (Vy+(th), θ(th), and f(res)(th)) just described can be stored in database 200 and compared with measured values, which can be Figure 14A The data represents three dimensions (Vy(r,d)), θ(r,d), and f(res)(r,d)). Additionally, the depth d between the charging coil 126 and the IMD 10 can be stored, which can also vary between patients. Prior knowledge of the depth d allows for the determination of sensing coil parameter thresholds with higher precision. This can be important because, as... Figure 14A As shown by the equipotential lines, the measured parameters can vary depending on the IMD 10 depth d, meaning that a single threshold may not be suitable for determining the position (alignment and centering) at all depths.

[0122] If it exists Figure 14A Given the three-dimensional data and the known depth d, the appropriate threshold for each sensing coil parameter can be determined (e.g., looked up) from database 200. For example, if the charger depth to IMD is known to be 15 mm, and misalignment should be indicated when the radius r exceeds 31 mm, then the appropriate resonant frequency threshold f(res)(th) would be approximately 80.9 kHz, as indicated by... Figure 14A The dashed line in the resonant frequency data is shown. The charger can also be calculated or learned to the IMD depth d and then stored in database 200 to allow for the selection of an appropriate threshold using techniques such as those described in USP 9,227,075, which are not described here.

[0123] Although the measured sensing coil parameters vary with depth, using the phase angle θ to determine the positioning of the charger relative to the IMD is particularly promising because of its relative insensitivity to depth d. Referring again to FIG. 14A, note that the isoclines of the previously selected threshold θ(th) = 0.8 are relatively vertical, especially at lower depths (d ≤ 15 mm). This means that this phase angle threshold θ(th) will work well for determining alignment at large depths (i.e., from 0 < d < 15 mm). In this depth range, the error e in the established misalignment radius only varies slightly from about 25 - 28 mm, which is tolerable.

[0124] The consideration by the IMD position circuit 140 of more than one measured sensing coil parameter can also allow determination of both the radius r and the depth d between the charging coil 126 and the IMD 10 (especially if the database 200 includes the three - dimensional data of FIG. 14A). For example, assume that the module 170 determines the magnitudes of Vy and Vy+ to be 0.14 V. As Figure 14A the isoclines in [reference] show, it is not possible to know whether the charging coil 126 is, for example, at position X1 or X2 based solely on Vy+. However, if the module 170 also determines that the phase angle θ is 4.0°, then the position module 140 can determine (using Vy+(r, d) and θ(r, d)) that the charging coil 126 must be at position X1, that is, at approximately r = 17 mm and d = 10 mm relative to the IMD 10 (measured relative to their centers 160 and 150).

[0125] In another example, assume that the module 170 determines Vy+ to be 0.30 V. As Figure 14A the isoclines in [reference] show, it is not possible to know whether the charging coil 126 is, for example, at position Y1 or Y2. However, if the module 172 also determines that the resonant frequency is 80.9 kHz, then the position module 140 can determine (using Vy+(r, d) and θ(r, d)) that the charging coil 126 must be at position Y1, that is, at approximately r = 28 and d = 18 mm relative to the IMD. The consideration of a third measured sensing coil parameter (phase angle) can improve the position determination accuracy or verify the determined position result.

[0126] Since the depth d should remain relatively constant for the patient, calculating the depth may not always be strictly necessary for the charging system, especially considering that the disclosed techniques can be used to learn the depth. For example, the consideration of more than one sensing coil parameter can be done at different time points (t2) during the charging session; Figure 12BAlternatively, the radius r and depth d can be determined when the patient uses the charging system 100 at different times. The depth at each of these measurement points can be stored in the database 200 and should generally not vary. Therefore, the determined depth can eventually be averaged from these various measurements and then simply stored in the database 200 for use without having to determine it every time a sensing coil measurement is performed.

[0127] It is known that the position of the charging coil 126 relative to the IMD 10 in both radius r and depth d is useful. As discussed earlier, the depth d is typically determined by the depth at which the IMD 10 is implanted in the patient, since the charging coil assembly 102 is usually pressed against the patient. Therefore, the patient may not be able to do anything to adjust the depth. Conversely, the radius between the charging coil 126 and the IMD 10 is adjustable by the patient by laterally (radially) adjusting the position of the charging coil assembly 102 relative to the IMD 10. Therefore, the IMD position circuit 140 preferably adjusts one or more thresholds for each IMD depth. For example, and referring to Figure 14A For the equipotential line of f(res), if the alignment radius is defined as r = 32 mm, then if the depth is d = 5 mm, the alignment threshold f(res)(th) of the resonant frequency will be set to approximately 81.4 kHz; if the depth is d = 10 mm, it will be 81.1 kHz; if the depth is d = 15 mm, it will be 80.9 kHz, and so on. When the measured f(res) is below the appropriate depth threshold, then the position indicator (e.g., 74) will only indicate the position (in this case, misalignment). Similar adjustments can be made to the position thresholds for the amplitude Vy+ and phase angle θ based on the depth.

[0128] Position determination and indication can also occur by evaluating more than one sensing coil parameter and comparing more than one threshold. For example, and again referencing Figure 14A An equipotential line can indicate misalignment if f(res) < 81.1 kHz at a depth d = 10 mm and if Vy+ > 0.23 V, at an alignment radius r = 32 mm as indicated by Z. A phase angle can also be measured and considered, where misalignment is indicated or confirmed if θ < θ(th) = 0.1°.

[0129] Although about Figure 12A and 12BThe alignment and centering algorithm 180 described earlier focuses on using the amplitude (Vy+) of the voltage of the sensing coil, but it should be noted that algorithm 180 is equally effective for sensing coil parameters that also use the phase angle θ or the resonant frequency f(res). Therefore, any of these other sensing coil parameters can be measured and compared to an appropriate threshold (steps 194, 202, 208 of algorithm 180) to determine whether the charging coil 126 is aligned, aligned but not aligned, or misaligned. Furthermore, these same steps can also measure and evaluate more than one of the sensing coil parameters Vy+, θ, and f(res), as explained above, which can improve the accuracy of charger-to-IMD position determination.

[0130] The sensing coil parameters, namely the phase angle θ and the resonant frequency f(res), are less affected by the power of the magnetic field 66 provided by the charging coil 126 during the measurement (unlike the voltage amplitude Vy+, which will vary with the magnetic field power). Therefore, normalization of these measurements may be unnecessary, and consequently, a constant, low-power test magnetic field may not be required during these measurements. In other words, if θ and f(res) are used as the measured sensing coil parameters in algorithm 180, a real (potentially varying) magnetic field can be used during the measurement (e.g., during t2), and the test magnetic field can be omitted.

[0131] One or more of the sensing coil parameters Vy+, θ, and f(res) can also be used to adjust the power of the magnetic field 66 delivered to the IMD 10. This is useful because the non-ideal coupling between the charging coil 126 and the IMD 10 caused by imperfect charger-to-IMD positioning can be remedied by increasing the power of the magnetic field 66 supplied to the IMD 10. In other words, if low coupling is caused by charger-to-IMD positioning, the power of the magnetic field is increased to ensure that the IMD 10 receives the same amount of power (regardless of coupling).

[0132] about Figure 15A Let's discuss power control further. Figure 15A Further details regarding the power circuit 145 that can be used in the charging system are shown. Similar to the position circuit 140 described earlier, the power circuit 145 can operate as firmware including control circuitry 72, but this is not strictly necessary, as analog circuitry can also be used in some aspects. Control circuitry 72 may again include the Vy amplitude and phase angle determination module 170, the resonant frequency determination module 172, and the database 200, and... Figure 15A In this case, those modules have been moved out of the position circuit 140 and replaced by a common component (providing data to) both the position circuit 140 and the power circuit 145.

[0133] In one example, data regarding the position of the charging coil 126 relative to the IMD 10 (at least the radius r, and preferably also the depth d) is provided to the power circuit 145. As explained earlier ( Figure 14A Both r and d can be determined by evaluating two or more sensing coil parameters in Vy+, θ, and f(res). However, and also as explained earlier, the depth d can be programmed into the control circuit 72 and / or learned.

[0134] The power circuit 145 can evaluate the radius r and depth d to determine the appropriate power for the magnetic field 66. As explained earlier, the magnetic field power can be set by adjusting the duty cycle DC of the drive signal D, because increasing the duty cycle DC will increase the Icharge flowing through the charging coil 126. However, increasing the duty cycle of the drive signal is only one way to increase the magnetic field power, and other methods can also be used, depending on the charging circuit 64 used to excite the charging coil 126.

[0135] Lookup table 146 can be stored within or in a memory accessible to power circuit 145, used to set the duty cycle DC of square wave generator 65 and charging circuit 64 depending on the radius and depth of charging coil 126 relative to IMD 10. For example, if both radius and depth are relatively small (r1, d1), charging coil 126 and IMD 10 will be relatively well coupled. Therefore, more magnetic field 66 generated at charging coil 126 will reach IMD 10, and thus the duty cycle for that location can be relatively small (DC1). Conversely, if one or both of the radius and depth are large (e.g., r2, d2), the coupling will be poorer. Therefore, power circuit 145 will instruct square wave generator 65 to increase the duty cycle (e.g., to DC3) to ensure that IMD 10 is receiving a sufficient amount of power. As noted above, it is preferable that IMD 10 receives a constant amount of power regardless of the charger's positioning relative to the IMD.

[0136] The amount of power received by IMD 10 can be determined experimentally in various ways by measuring various parameters in IMD 10. In one example, the received power can be evaluated as the amount of charging current Ibat received by battery 14 of IMD 10. Figure 15A The technician will understand that when coupling decreases (i.e., when r or d increases), Ibat will also decrease if the magnetic field power is not adjusted. This is in Figure 15B The diagram illustrates that when the charging coil 126 generates a magnetic field 66 with constant power (i.e., when Icharge and the duty cycle DC are constant), the IMD 10 receives power (Ibat) according to its radius and depth. Specifically, Figure 15BVarious regions of Ibat, as derived from experiments, are shown. As illustrated, lower values ​​of Ibat (e.g., between Ibat1 and Ibat2) are associated with poorer coupling and location regions with higher radius r and / or depth d values. To compensate, this location region is provided with a high duty cycle (DC5) in lookup table 146, and therefore with higher magnetic field power. Conversely, higher Ibat values ​​(e.g., >Ibat5) are associated with high coupling and location regions with lower radius r and / or depth d values. To compensate, this location region is provided with a low duty cycle (DC1) and therefore with lower magnetic field power in lookup table 146. Preferably, the duty cycle associated with each location region will cause Ibat in IMD 10 to be relatively constant, and therefore independent of the charger-to-IMD location. Alternatively, the selected duty cycle (power) may not result in a constant Ibat for all possible positions of the charging coil 126 relative to the IMD 10, but will at least ensure that the value of Ibat does not drop below a minimum, thus ensuring that the IMD 10 receives sufficient power regardless of the charger's position relative to the IMD.

[0137] While it is preferable that the power circuit 145 determines the appropriate adjustment of the power to the magnetic field 66 using knowledge of the radius and depth (e.g., using sensing coil parameters Vy+, θ, and / or f(res)), this is not strictly necessary. Instead, the power circuit 145 may alternatively receive the sensing coil parameters Vy+, θ, and / or f(res) themselves and adjust the power without determining the radius and depth as an intermediate step.

[0138] In one example, such as earlier binding Figure 12B The power of the magnetic field 66 is adjusted using sensing coil measurements obtained during the emission of a test or default magnetic field from the charging coil 126. In this example, one or more of the sensing coil parameters Vy+, θ, and / or f(res) are periodically measured during the test magnetic field (e.g., during time t1) and using the calculated power (e.g., duty cycle DC) used during the subsequent actual magnetic field period (t2). In this way, using the example of t1 and t2 provided earlier, the magnetic field power is adjusted approximately every 30 seconds, which reasonably adapts to the timescale expected to move the charging coil assembly 102. Of course, this is not strictly necessary. Furthermore, although not in Figure 12B As shown, additional sensing coil parameter measurements can be taken (during time period t2) specifically for magnetic field power adjustment purposes. Therefore, different time periods can exist during which sensing coil parameter measurements are taken to determine the charger's location to the IMD and for magnetic field power adjustment purposes.

[0139] Similar to earlier combination Figure 12B The sensor coil parameter measurements discussed for magnetic field power adjustment do not require the use of a low-power test magnetic field; instead, the actual magnetic field used to charge the IMD 10 can be used. As discussed earlier, this may make it more important to normalize the measurement results to the current power of the magnetic field (especially the voltage amplitude Vy+ measurement results), but less important for the phase angle θ and resonant frequency f(res) measurement results.

[0140] The power adjustment of the magnetic field using power circuit 145 can also occur based on the determined position of the charger relative to the IMD. For example, if position circuit 140 determines that charging coil 126 is aligned with IMD 10, then power circuit 145 may only be able to adjust the power. In this respect, and as... Figure 15A As shown, the position circuit 140 can transmit the alignment status to the power circuit 145 via signal 147.

[0141] The inventors also recognize that it is advantageous to provide a true magnetic field 66 optimized at the resonant frequency of the charger / IMD system (i.e., a magnetic field optimized at the frequency given the mutual inductance provided by the coupled charger / IMD system) during power supply to the IMD 10. Providing power at the resonant frequency means that more power of the magnetic field 66 will reach the IMD 10 and thus be used to charge the battery 14 of the IMD 10. Furthermore, providing power at the resonant frequency increases the signal induced on the sensing coil (Vy), thus making it easier to derive the amplitude Vy+, phase angle θ, and resonant frequency f(res). Note that this use of the resonant frequency differs from the purpose described earlier: while f(res) can be measured during the test cycle (t2) and used to determine charger-to-IMD positioning and / or how to adjust the magnetic field power (e.g., by duty cycle adjustment), here we refer to the frequency at which the magnetic field 66 is adjusted during the provision of the true magnetic field.

[0142] Fortunately, providing power during a real magnetic field can be achieved using the same circuit described earlier to measure f(res), which is useful for location determination and power adjustment. For example, during the measurement period (t2; see Figure 12B During this period, it can be determined that the resonant frequency of the charger / IMD system is f(res). As previously described, this f(res) measurement result can be used to determine and indicate the (74,75)IMD to the charger position and adjust the power of the subsequent real magnetic field (t1), for example, by changing the duty cycle DC of the drive signal D applied to the charging circuit 64.

[0143] Furthermore, within the subsequent actual magnetic field cycle (t1), the frequency of the drive signal can be independently set to f(res) (or allowed to remain there) to ensure efficient power delivery to IMD 10. Note that this adjustment of the frequency of the magnetic field 66 can be independent of its power adjustment. As previously stated, the drive signal D has a duty cycle (power) equal to a / a+b, while its frequency is 1 / a+b. Therefore, although f(res) is governed by a+b, 'a' can still be independently varied within the drive signal cycle to set the duty cycle DC.

[0144] Similar to power adjustment, it might be reasonable to measure f(res) during the test cycle (t2) and set f = f(res) during the subsequent real magnetic field cycle (t2). In this way, the frequency is adjusted approximately every 30 seconds to match the resonance of the charger / IMD system. However, the frequency of the drive signal D, and therefore the frequency of the magnetic field, can also be adjusted at different time scales, or pseudo-continuously adjusted by continuously sampling the sensing coil voltage and determining f(res) during the generation of the real magnetic field.

[0145] Although it has a separate electronic module 104 and charging coil assembly 102 (see Figure 5A and 5B The disclosed IMD position and power adjustment technology is described in the context of a charger system 100, but this is not mandatory. Instead, the described technology can also be implemented in an integrated external charger (where electronics, charging coils, and one or more sensing coils are housed together). For example, Figure 16 An integrated external charger 50' is shown, in which all components are housed in a single housing 62, which is generally similar to that described earlier in Figure 2. The charger 50' includes a circuit board 54 carrying the windings of a primary charging coil 52. The traces of the circuit board 54 may include one or more sensing coils 178 formed in any of the various ways described. The control circuitry 72' can be programmed with a position circuitry 140, a power circuitry 145, and other supporting circuitry and programs, all of which are explained in detail above. Therefore, for the purposes of the disclosed technology, it is not important whether the charging / sensing coils are separate from the electronics or whether they are housed in separate housings.

[0146] The disclosed sensing coil can infer the charger's position to the IMD (e.g., centering and / or alignment), but lacks the ability to infer the direction in which the charging coil assembly 102 might be misaligned or misaligned. Nevertheless, the sensing coil in the charging system 100 can be modified to provide the patient with an indication of the direction of misalignment or misalignment.

[0147] For example, Figure 17A It includes two alignment sensing coils 178a and 178b, which can induce voltages Vya and Vyb across their terminals. In the example shown, the alignment sensing coils 178a and 178b include earlier information regarding... Figures 7A-7C The disclosed type of edge detection coil is acceptable, but it is not strictly necessary. Furthermore, the two coils 178a and 178b shown can also serve as centering sensing coils (like...). Figures 9A-9C Coil 129), or as a combination of alignment / centering sensing coils (like... Figure 11A and 11B It is operated using coil 130. Alternatively, a pair of alignment sensing coils and a pair of centering sensing coils can be used, similar to... Figure 10A and 10B As shown in the diagram. For simplicity, these alternatives are not shown.

[0148] Figure 17A As can be seen, sensing coils 178a and 178b each cover approximately half a circumference of PCB 124, as shown in areas A and B. If the charging coil assembly 102 (charging coil 126) shifts such that IMD 10 (not shown) blocks area A of sensing coil 178a, then the amplitude Vya+ will decrease. Therefore, the control circuitry 72 in the electronics module 104 will understand that the charging coil assembly 102 should move downwards to better align (or better center) with IMD 10. Similarly, if IMD 10 blocks area B of sensing coil 178b, then the amplitude Vyb+ will decrease, indicating that the charging coil assembly 102 should move upwards. The direction of misalignment or miscentering can be indicated via the electronics module user interface, or more preferably, the direction of movement required for alignment or centering can be fixed, and USP 8,473,066 discusses various indicating devices, including LEDs that can be illuminated on the housing 105 to indicate the direction. The sensor coil parameters, including the phase angle θ and resonant frequency f(res), can also be measured from each of the sensing coils 178a and 178b to help determine the orientation of the charger to IMD positioning and magnetic field power adjustment.

[0149] Figure 17B Similar to Figure 17AHowever, regions A and B are added, surrounded by alignment (or sensing) coils 178a and 178b, where each coil essentially covers a semicircle. In this example, both induced voltages Vya and Vyb can be used to determine the direction of misalignment or miscentering. For example, if Vya+ drops a relatively large value from its maximum value, while Vyb+ drops only a small amount, it indicates that IMD 10 largely obscures region A, but only to a very small extent obscures region B. Therefore, in this example, charging system 100 can instruct the charging coil assembly to move upwards to better align or center the assembly with the IMD. Furthermore, it is also possible to... Figure 14B Each of the sensing coils 178a and 178b measures the phase angle θ and the resonant frequency f(res), which is then used for magnetic field power adjustment. Note that due to the non-arc nature of the regions A and B enclosed by the sensing coils 178a and 178b, and unlike earlier examples of sensing coils, the sensing coils 178a and 178b are not concentric with the charging coil 126.

[0150] Figure 17C Similar to Figure 17B However, connecting two sensing coils together to form a single differential sensing coil 178 is sometimes called a butterfly coil. In this case, the direction of misalignment or misalignment will be indicated by the relative polarity of the induced voltage Vy. If Vy is significantly negative, IMD 10 will largely block region A, while if Vy is significantly positive, it will largely block region B. If Vy = 0, this indicates that the charging coil 126 and IMD 10 are perfectly aligned. The phase angle θ and the resonant frequency f(res) can also be measured from the sensing coil 178 in Figure 17C, where the phase angle is particularly useful in determining the polarity of Vy. The sensing coil 178 is also not concentric with the charging coil 126.

[0151] Figure 17D Including with Figure 17A The sensing coils in this circuit are similar to sensing coils 178a-d, but there are more than two sensing coils, each covering approximately one-quarter of the circumference of the circuit board 124, as shown in area AD. This provides directional information along the orthogonal axes (along the X and Y directions), thus allowing the charging system to determine not only whether the charging coil 126 is misaligned or misaligned in the up / down direction, but also whether it is misaligned or misaligned in the left / right direction.

[0152] Figure 17E Another example is shown where a sensing coil can be used in charging system 100 to infer the direction of misalignment or misalignment. Figure 17EIn this configuration, the charging coil 126 is typically elongated (more specifically, a rectangular shape as shown) and has a long dimension X that is significantly longer than its other orthogonal dimension Y. Also included within the charging coil 128 (e.g., within the PCB 124) are sensing coils 178a and 178b, which also have a long X dimension and a significantly shorter Y dimension. Two sensing coils are shown, but there can be three or more. Dimension X is preferably significantly larger than IMD 10. As a result, alignment between the charging coil 126 and IMD 10 in the X direction is generally not a concern, as it is expected that IMD 10 will fit well within the X dimension. However, alignment in the smaller Y direction may still be of concern, and therefore sensing coils 178a and 178b are used to determine misalignment in the Y direction, which can be done by monitoring Vya and Vyb as explained above. Furthermore, any one or more of amplitude, phase angle, and / or resonant frequency can be collected from Vya and / or Vyb to help determine alignment in the Y direction. Although sensing coils 178a and 178b are as Figure 17B They can be separated as described above, but they can also be connected together to form a single sensing coil (if needed), such as... Figure 17C As shown. Note that, Figure 17E The charging coil 126 and sensing coil 178, as shown in the diagram, can be used in generally linear charging systems, such as when used with or within a charging band, as previously mentioned. With such a charging band, the patient will generally not need to worry about the alignment of the band around their waist (X; in SCS applications), but will instead only need to worry about adjusting the band higher or lower around their waist (Y).

[0153] In this regard, voltage (e.g., Va, Vc, Vx, Vy) has been evaluated from various publicly available sensing coils. However, sensing coil current can also be evaluated, where current amplitude, phase, or resonance is used in the disclosed alignment and power adjustment techniques.

[0154] Other modifications to the charging system 100 are possible. Figure 18For example, one or more sensing coils 178 in the charging coil assembly 102 are shown to not only require passive devices for sensing magnetic fields, but can also be actively excited to generate their own magnetic fields to aid in alignment and / or power adjustment. As shown, a sensing coil drive circuit 65 has been added to the electronics module 104, which in this example generates an AC current Isense driven to the sensing coil 178. Any sensing coil disclosed earlier can be used in this example. The frequency of Isense can be equal to the resonant frequency at which the charging coil 126 is driven, but this is not strictly necessary. The frequency of Isense can be tuned according to the capacitor 131 coupled to the sensing coil. The capacitor 131 is shown in parallel with the sensing coil, but it can also be placed in series.

[0155] During the period when the charging coil 126 is also being driven by Icharge, one or more sensing coils 178 can be driven by Isense, but preferably they will be driven during the short test period (t2) when the charging coil 126 is not energized (t1) (see Figure 12B When the sensing coil is driven, a magnetic field 67 is formed. A voltage Vsense will be established across the sensing coil 178, which, as before, will be affected by the coupling between the charging coil 126 and the position of the IMD 10 relative to the sensing coil. As before, Vsense will be smaller if the IMD 10 is defined by the sensing coil 178, and larger if the IMD is not defined by the sensing coil. Therefore, Vsense can again be compared with one or more thresholds to determine the alignment, centering, and / or presence of the IMD 10, and can also be used to adjust the power of the magnetic field 66 generated by the charging coil 126, consistent with the principles explained earlier.

[0156] Figure 19 Another variation of the charging system 100 is shown, in which telemetry feedback from the IMD 10 is used to assist in charger positioning to the IMD and / or magnetic field power adjustment. In this example, parameters indicating the coupling between the primary charging coil 126 in the charging coil assembly 102 and the secondary charging coil 36 in the IMD 10 are telemetrically transmitted to the charging system 100. In one example, the coupling parameters include the current Ibat flowing into the battery during charging, which can typically be scaled as the secondary charging coil 36 receives the magnetic field 66 of the primary charging coil 126. However, this coupling parameter is only an example, and other parameters in the IMD 10, such as the DC voltage generated by the rectifier 38, can also be used.

[0157] The battery charging current Ibat can be measured in a conventional manner via circuit 41 in IMD 10. For example, although not shown, Ibat can flow through a small sensing resistor (e.g., R = 1 ohm), and the voltage (V) across that resistor can be measured by a differential amplifier, allowing the current (Ibat = V / R) to be derived. Ibat (or more generally, the coupling parameter) is received at control circuit 42 of IMD 10, and can then be telemetryally transmitted to charging system 100. This telemetry technique can occur in several ways. For example, the coupling parameter can be modulated into LSK data, where it affects Vcoil generated by charging coil 126. Vcoil (68) can then be demodulated as explained earlier, thereby informing control circuit 72 of charging system 100 of the value of the telemetry-transmitted coupling parameter.

[0158] Alternatively, the coupling parameters can be telemetry transmitted via another communication link established between antenna 45 in IMD 10 and antenna 127 in charging coil assembly 102. Antenna 45 may include an additional antenna in IMD 10 for communicating with external devices, such as handheld external controllers or clinician programmers, which are further explained in detail in U.S. Patent Application Publication 2015 / 0360038. Antennas 45 and 127 may include coils that communicate via near-field magnetic induction using a suitable modulation scheme, such as frequency shift keying (FSK). Antennas 45 and 127 may also include short-range RF antennas that communicate via far-field electromagnetic waves according to communication standards, such as Bluetooth, WiFi, MICS, Zibgee, or others. When the discrete antenna 127 is used in charging coil assembly 102 to receive the coupling parameters, the received data (represented as voltage Vtelem) can be reported to control circuitry 72 in electronics module 104 via cable 106, which can then demodulate the data. The demodulation circuitry for antenna 127 can also be located in charging coil assembly 102.

[0159] The combination of the coupling parameter (Vtelem) at control circuit 72 with the reception of data (Vsense) reported from one or more sensing coils can improve the disclosed charger-to-IMD position determination and / or magnetic field power adjustment. For example, Vy can indicate that charging coil 126 is misaligned with IMD 10 (because Vy > Vy(th)). However, if the coupling parameter indicates that the battery 14 in IMD 10 receives a sufficient amount of current (Ibat), the position circuit 140 can ultimately determine that alignment is appropriate. Furthermore, if Ibat is sufficient, the power circuit 145 can decide not to increase the power of magnetic field 66 (e.g., the duty cycle (DC) described earlier), or can increase the power to a lesser extent than otherwise indicated by lookup table 146. Figure 15A ).

[0160] While the disclosed techniques are described in the context of a charger system 100 for charging the battery 14 in the IMD 10, this is not strictly necessary. The charger system 100 can also be used to provide continuous magnetic field 66 power to an IMD lacking a battery. In this case, charger-to-IMD positioning and power adjustment are also important, and perhaps even more so, because an IMD lacking a battery may cease operation if it does not receive sufficient power from a poorly located or unpower-optimized external charger.

[0161] The term "a" in the appended claims should be interpreted as covering one or more structures, not just a single structure.

Claims

1. An external charger for wirelessly supplying power to an implantable medical device (IMD), comprising: A charging coil configured to generate a magnetic field when excited by a driving signal to wirelessly provide energy to the IMD as a coupling system; A sensing coil, wherein the sensing coil is configured to induce a sensing signal by the magnetic field, the sensing signal being affected by the position of the charging coil relative to the IMD; as well as A control circuit configured to determine a plurality of parameters using the sensing signal, wherein the control circuit is further configured to determine the position of the charging coil relative to the IMD using the plurality of parameters. The plurality of parameters includes at least two of the following: The amplitude of the sensed signal, The phase angle between the sensing signal and the driving signal, and The resonant frequency of the coupling system.

2. The external charger according to claim 1, wherein the sensing coil is concentric with the charging coil.

3. The external charger of claim 1 further includes a user interface configured to indicate the determined location to a user.

4. The external charger according to claim 1, in, The control circuit is configured to determine, based on the plurality of parameters, whether the charging coil is aligned or centered relative to the IMD. The pair includes cases where the coupling between the charging coil and the IMD is higher than a first coupling value, and The alignment includes a case where the coupling between the charging coil and the IMD is higher than a second coupling value, where the second coupling value is lower than the first coupling value.

5. The external charger of claim 1 further includes an electronic module and a charging coil assembly coupled to the electronic module via a cable. The charging coil and the sensing coil are located within the charging coil assembly, and The control circuit is located within the electronic module.

6. The external charger of claim 1 further includes a circuit board, wherein the sensing coil is formed in one or more traces in the circuit board.

7. The external charger of claim 6, wherein the charging coil comprises a wire winding placed on one side of the circuit board.

8. The external charger of claim 6, wherein the charging coil includes a wire winding, and wherein the circuit board is placed within the wire winding of the charging coil.

9. The external charger according to claim 1, in, The control circuit also includes a database or has access to a database, wherein the database includes a plurality of thresholds, and wherein the control circuit is configured to compare each of the plurality of parameters with one of the thresholds to determine the position of the charging coil relative to the IMD.

10. The external charger of claim 1, wherein the control circuitry is configured to determine the radius of the lateral offset of the charging coil relative to the IMD.

11. The external charger of claim 10, wherein the control circuitry is further configured to determine the depth between the charging coil and the IMD.

12. The external charger of claim 1, wherein the control circuitry further includes a database or has access to a database, wherein the database includes values ​​for the plurality of parameters at different radial offsets and depths between the charging coil and the IMD, wherein the control circuitry is configured to compare the plurality of parameters with the values ​​to determine the position of the charging coil relative to the IMD.

13. The external charger of claim 1, wherein the determined location includes the radius and depth between the charging coil and the IMD.

14. The external charger of claim 1, wherein the sensing coil comprises a circle.

15. The external charger of claim 1, wherein the sensing coil comprises two circles of different radii.

16. The external charger of claim 15, wherein the two circles are connected such that the current flowing through the two circles will flow in different directions in the two circles.

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