Systems and methods for wireless power transfer systems with improved coupling

Abstract

A wireless power transfer system is provided. The system includes a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator including a receive coil element, and a transmit resonator including a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient and the receive coil element and the transmit coil element are oriented substantially parallel to one another.

Description

SYSTEMS AND METHODS FOR WIRELESS POWER TRANSFER SYSTEMSWITH IMPROVED COUPLINGCROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 614,720 filed on December 26, 2023, which is incorporated by reference herein in its entirety.BACKGROUND OF THE DISCLOSURE a. Field of the Disclosure

[0002] The present disclosure relates generally to wireless power transfer systems and implantable medical devices, and more specifically, relates to wireless power systems with improved coupling between a transmit resonator and an implantable receive resonator. b. Background

[0003] There are various types of implantable medical devices, including pacemakers and heart pumps, that require pow er from an external power source to operate. For example, a transcutaneous energy transfer system (TETS) may be used to provide power to an implanted ventricular assist device target for long-term support. At least some known mechanical circulatory support (MCS) devices use a power cable (i.e., driveline) that is connected to the implanted pump and extends out past the tissue and skin layer of the patient to the outside of the body in order to be connected to a power source. In this configuration, patients are able to be supported and can survive many years, however there is a risk of developing an infection at the exit site where the driveline exits the body. The infection risk generally prevents patients from participating in certain activities that may compromise the site, such as bathing, swimming, or activities that may cause trauma to the exit site (e.g. pulling on the driveline). While the patient’s heart failure condition improves and they are able to achieve an improved quality of life, the risk of infection may prevent the device and system from being truly forgettable, as the patient must always be vigilant in caring for and protecting the exit site from infection. In contrast, an MCS device with aviable TETS platform that wirelessly transfers power to the implanted device eliminates the driveline and associated infection risk, as an exit site no longer exists.

[0004] TETS technology is currently available in other implantable devices (e.g., neuromodulation devices) where the power demands are relatively low; implant depth is relatively shallow, and risk of thermal damage to surrounding tissues is relatively low. There have been numerous attempts to develop a TETS platform for MCS over the past few decades, however the relatively high power demands and thermal challenges have made the solution challenging. At least some of these approaches have also required relatively large coils where a transmit coil is external and connected to a power source, and must transmit power to an implanted receive coil. However, separation distance between the transmit and receive coils in at least some known systems results in relatively poor power transfer efficiency. Further, challenges also exists with keeping the coils in a fixed orientation relative to one another.

[0005] At least one known system involves placing a transmit coil around the chest of the patient so that it is co-planar with an implanted receive coil that is placed around a lung in the thoracic space of the patient. This may result in higher power transfer efficiency, but generally requires a more difficult implant procedures. Depending upon implementation and the coil sizes, this approach may be more capable of maintaining stable operation during relative movement between the coils.

[0006] Therefore, a need exists to achieve a TETS platform that can reduce separation distance between coils, achieve relatively high power transfer efficiency (reducing thermal effects), and lower the risk to the surrounding tissue.SUMMARY OF THE DISCLOSURE

[0007] In one aspect, a wireless power transfer system is provided. The system includes a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator including a receive coil element, and a transmit resonator including a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient andthe receive coil element and the transmit coil element are oriented substantially parallel to one another.

[0008] In another aspect, a wireless power transfer system is provided. The wireless power transfer system includes a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator including a receive coil element, a transmit resonator including a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient and the receive coil element and the transmit coil element are oriented substantially parallel to one another, and a garment configured to secure a position of the transmit resonator relative to the receive resonator.

[0009] In yet another aspect, a method of operating a wireless power transfer system is provided. The method includes at least partially inserting a transmit coil of a transmit resonator into a receive coil of a receive resonator while the transmit coil and the receive coil are oriented substantially parallel to one another, wherein the receive resonator is implanted subcutaneously within a patient, and wherein the transmit resonator is external to the patient, and transmitting power wirelessly from the transmit resonator to the receive resonator.BRIEF DESCRIPTION OF THE DRAWINGS

[0010] FIG. 1 is a simplified electrical circuit diagram of one embodiment of a wireless power transfer system.

[0011] FIG. 2 is an illustration of the wireless power transfer system of FIG. 1 being used to supply power to a ventricular assist device (VAD).

[0012] FIG. 3 is a perspective view of one embodiment of a wireless power transfer system.

[0013] FIGS. 4A and 4B are perspective views of the transmit resonator being inserted into the receive resonator of the wireless power transfer system show n in FIG. 3.

[0014] FIG. 5 is a cross-sectional view of the wireless power transfer sy stem shown in FIG. 3.

[0015] FIG. 6 is a schematic diagram of an alternative wireless power transfer system.DETAILED DESCRIPTION OF THE DISCLOSURE

[0016] The present disclosure is directed to systems and methods for wireless power transfer. A wireless power transfer system includes a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator including a receive coil element, and a transmit resonator including a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient and the receive coil element and the transmit coil element are oriented substantially parallel to one another.

[0017] Referring now to the drawings, FIG. l is a simplified circuit of an example wireless power transfer system 100. The system 100 includes an external transmit resonator 102 and an implantable receive resonator 104. In the system shown in FIG. 1, a power source Vs is electrically connected with the transmit resonator 102, providing power to the transmit resonator 102. The receive resonator 104 is connected to a load 106 (e.g., an implantable medical device). The receive resonator 104 and the load 106 may be electrically connected with a switching or rectifying device (not shown).

[0018] In the example embodiment, the transmit resonator 102 includes a coil Lx connected to the power source Vs by a capacitor Cx. Further, the receive resonator 104 includes a coil Ly connected to the load 106 by a capacitor Cy. Inductors Lx and Ly are coupled by a coupling coefficient k. Mxyis the mutual inductance between the two coils. The mutual inductance, Mxy, is related to the coupling coefficient k as shown in the below Equation (1).

[0019] In operation, the transmit resonator 102 transmits wireless power received from the power source Vs. The receive resonator 104 receives the power wirelessly transmitted by the transmit resonator 102, and transmits the received power to the load 106.

[0020] FIG. 2 illustrates one embodiment of a patient 200 using an external coil 202 (such as the transmit resonator 102 shown in FIG. 1) to wirelessly transmit power to an implanted coil 204 (such as the receive resonator 104 shown in FIG. 1). The implanted coil 204 uses the received power to power an implanted device 206. For example, the implanted device 206 may include a pacemaker or heart pump (e.g., a left ventricular assist device (LVAD)). In some embodiments, the implanted coil 204 and / or the implanted device 206 may include or be coupled to a controller or a battery. For example, in some embodiments, a controller and / or a battery may be coupled between the implanted coil 204 and the implanted device 206.

[0021] In one embodiment, the external coil 202 is communicatively coupled to a computing device 210, for example, via wired or wireless connection, such that the external coil 202 may receive signals from and transmit signals to the computing device 210. In some embodiments, the computing device 210 is a power source for the external coil 202. In other embodiments, the external coil 202 is coupled to an alternative power supply (not shown). The computing device 210 includes a processor 212 in communication with a memory 214. In some embodiments, executable instructions are stored in the memory 214.

[0022] The computing device 210 further includes a user interface (UI) 216. The UI 216 presents information to a user (e.g., the patient 200). For example, the UI 216 may include a display adapter (not shown) that may be coupled to a display device, such as a cathode ray tube (CRT), a liquid crystal display (LCD), an organic LED (OLED) display, and / or an 'electronic ink” display. UI 216 may also include one or more user interfaces that a user may interact with (e.g., buttons, membrane switches, touch screen, etc.). In some embodiments, the UI 216 includes one or more display devices. Further, in some embodiments, presentation interface may not generate visual content, but may be limited to generating audible and / or computer-generated spoken-word content. In the example embodiment, the UI 216 displays one or more representations designed to aid the patient 200 in placing the external coil 202 such that the coupling betw een the external coil 202and the implanted coil 204 is optimal. In some embodiments, the computing device 210 may be a wearable device. For example, in one embodiment, the computing device 210 is a wrist watch, and the UI 216 is displayed on the wrist watch.

[0023] The systems and methods disclosed herein provide a transcutaneous energy transfer system (TETS) that enables a substantially co-planar arrangement between transmit and receive coils that is different from at least some known systems. The coils are closely coupled with a relatively minimal separation distance, thereby achieving relatively high power transfer efficiency and acceptable thermal performance with relatively small coils. As described herein, a receive coil is implanted in a sub-cutaneous region under a relatively thin layer of tissue / skin. This allows an external transmit coil to be effectively inserted into the receive coil without breaching or penetrating the tissue / skin.

[0024] FIG. 3 is a perspective view of one embodiment of a wireless power transfer system 300. The wireless power transfer system 300 includes a transmit resonator 302 (e g., such as the transmit resonator 102 shown in FIG. 1 or the external coil 202 shown in FIG. 2) and a receive resonator 304 (e.g., such as the receive resonator 104 shown in FIG. 1 or the implanted coil 204 shown in FIG. 2).

[0025] As described further below, the receive resonator 304 is implanted (e g., subcutaneously) within a patient (e.g., patient 200 shown in FIG. 2), while the transmit resonator 302 is external to the patient. Accordingly, the patient’s skin (omitted for clarity in FIG. 3) is positioned between the transmit resonator 302 and the receive resonator 304. The receive resonator 304 may be anchored, for example, within a muscle layer of the abdominal are of the patient. An implantation procedure of the receive resonator 304 may be performed to form a depression or indent within a center of the receive resonator 304.

[0026] In this embodiment, the receive resonator 304 has a generally toroidal shape, and defines an aperture 306 extending through the receive resonator 304. Alternatively, as described further below the receive resonator 304 has a generally toroidal shape, but with a cap-shaped portion extending across one side of the toroidal shape (such that the receive resonator 304 defines a recess instead of an aperture). A first cable 308 extends from the transmit resonator 302 (e.g., to a power source for the transmit resonator302), and a second cable 310 extends from the receive resonator 304 (e g., to an implanted medical device).

[0027] As shown in FIG. 3, the transmit resonator 302 is at least partially insertable into the aperture 306 (or recess) in the receive resonator 304 (with the understanding that the patient’s skin and tissue would still be positioned between the transmit resonator 302 and the receive resonator 304). With the transmit resonator 302 at least partially inserted, coil elements (not shown in FIG. 3) in the transmit resonator 302 and the receive resonator 304 are oriented substantially parallel to one another and are coplanar (or nearly co-planar) with one another. This results in a relatively strong coupling (and relatively high wireless power transfer efficiency) between the transmit resonator 302 and the receive resonator 304.

[0028] Notably, the transmit resonator 302 and the receive resonator 304 are relatively small devices and are positioned closely to one another. For example, the transmit resonator 302 may have an outer diameter in a range of approximately 25 to 40 millimeters (mm) and a height in a range of approximately 5 to 10 mm. The receive resonator 204 may have an outer diameter in a range of 55 to 70 mm, and a height in a range of approximately 10 to 20 mm. Further, a thickness of the skin between the transmit resonator 302 and the receive resonator 304 may be in a range of 1 to 10 mm. Alternatively, the transmit and receive resonators 302 and 304 may have any suitable dimensions.

[0029] In some embodiments, the transmit resonator 302 is connected to the first cable 308 using a right-angle connector to ensure the transmit resonator 302 and the first cable 308 have a relatively low profile.

[0030] To maintain coupling between the transmit resonator 302 and the receive resonator 304, in some embodiments, a suitable garment (e.g., a belt, harness, strap, vest, or the like) that secures a position of the transmit resonator 302 relative to the receive resonator 304 may be worn by the patient. The garment may include, for example, a pouch that holds the transmit resonator 302. Further, in some embodiments, the garment mayinclude one or more cooling devices (e.g., a fan) to dissipate thermal energy generated by the transmit resonator 302.

[0031] Further, in some embodiments, one or more permanent magnets may be included in the transmit resonator 302 and the receive resonator 304 such that the permanent magnet(s) in the transmit resonator 302 are attracted to the permanent magnet(s) in the receive resonator 304. The permanent magnets may be configured to achieve proper alignment and spacing between the transmit resonator 302 and the receive resonator, 304 while also ensuring that pressure on the skin 322 and tissue is kept to a minimum so as not to overly compress the skin 322 and tissue (e.g.. to facilitate preventing tissue necrosis).

[0032] Notably, while the transmit resonator 302 is transmitting power to the receive resonator 304, the magnetic field generated by operation of the transmit resonator 302 will actually gently pull the transmit resonator 302 towards the receive resonator 304.

[0033] FIGS. 4A and 4B are perspective views of the transmit resonator 302 being inserted into the receive resonator 304. In the views shown in FIGS. 4A and 4B, the skin 320 of the patient is shown, so the receive resonator 304 is not visible (as the receive resonator 304 is located below the skin 320). FIG. 4A shows the transmit resonator 302 prior to insertion, and FIG. 4B shows the transmit resonator 302 inserted into the receive resonator 304.

[0034] As shown in FIGS. 4A and 4B. in this embodiment, an indented region 322 is formed in the skin 320 of the patient. The indented region 322 corresponds to the aperture 306 (or recess) defined by the receive resonator 304. Accordingly, when the transmit resonator 302 is at least partially inserted into the indented region 322, the transmit resonator 302 is also at least partially inserted into the aperture 306 (or recess) defined by the receive resonator 304.

[0035] FIG. 5 is a cross-sectional view of the wireless power transfer system 300, with the transmit resonator 302, the receive resonator 304, and the skin 320 all shown.

[0036] In this embodiment, the transmit resonator 302 includes a transmit coil element 330 surrounding a core 332. The receive resonator 304 includes a receive coil element 334. The core 332 in the transmit resonator 302 is formed of a magnetic material, and may, for example, be formed of a ferrite material, such as nickel-based or manganese- based ferrites. Nickel-based ferrites generally have lower electrical conductivity and reduced losses, while manganese-based ferrites have a higher magnetic permeability (while still having acceptable losses), facilitating containing magnetic field lines, and reducing fringing fields entering nearby conductors (e.g., a titanium enclosure or copper in a nearby PCB) to prevent losses. In other embodiments, other ty pes of ferrite materials may be used. For example, in some embodiments, a magnesium-based ferrite (e.g., MgCuZn, which may outperform nickel-based and manganese-based ferrites in a frequency range around 1 Megahertz (MHz)) may be used.

[0037] Each of the transmit resonator 302 and the receive resonator 304 may be, for example, a Litz wire resonator or a stacked plate resonator. In a Litz wire resonator, the coil element 330 or 334 includes a plurality of loops of Litz wire. In a stacked plate resonator, the coil element 330 or 334 includes a plurality' of stacked plates that may include a plurality' of alternating dielectric layers and conductive layers arranged in a stack. The dielectric layers may be formed of, for example, ceramic, plastic, glass, and / or mica.

[0038] As shown in FIG. 5, the transmit coil element 330 is oriented substantially parallel to the receive coil element 334. That is. a first longitudinal axis 340 that passes through a center of the transmit coil element 330 (and is thus perpendicular to a plane in which the transmit coil element 300 lies) is substantially parallel to a second longitudinal axis 342 that passes through a center of the receive coil element 334 (and is thus perpendicular to a plane in which the receive coil element 334 lies). In FIG. 5, the first longitudinal axis 340 is coincident with the second longitudinal axis 342. However, those of skill in the art will appreciate that, in some embodiments, the first longitudinal axis 340 may be slightly offset with respect to the second longitudinal axis 342.

[0039] As used herein, the transmit coil element 330 being oriented substantially parallel to the receive coil element 334 means that the first longitudinal axis 340 and the second longitudinal axis 342 are within 10° or less of being parallel to one another, moreparticularly within 5° or less of being parallel to one another, or even more particularly within 1° or less of being parallel to one another.

[0040] As shown in FIG. 5, the transmit resonator 302 is inserted into the receive resonator 304 such that at least a portion of the transmit coil element 330 is positioned inside of the receive coil element 334. In some embodiments, the entire transmit coil element 330 may be positioned within the receive coil element 334 (such that the transmit coil element 330 and the receive coil element 334 are co-planar). In other embodiments (e.g., the embodiment shown in FIG. 4), not all of the transmit coil element 330 is positioned within the receive coil element 334. That is. the transmit coil element 330 is slightly offset from the receive coil element 334 along at least one of the first longitudinal axis 340 and the second longitudinal axis 342. This may be referred to as the transmit coil element 330 being nearly co-planar with the receive coil element 334. Notably, using the systems and methods disclosed herein, the transmit resonator 302 and the receive resonator 304 may be aligned such that a wireless power transfer efficiency of 90% or greater is achievable.

[0041] In the embodiment shown in FIG. 5, the receive resonator 304 includes a receive resonator housing 350 that encloses the receive coil element 334 and one or more electronics components 352 (e g., a printed circuit board). The receive resonator housing 350 includes a first annular tapered wall 354 that at least partially defines the aperture 306 (or recess).

[0042] The transmit resonator 302 includes a transmit resonator housing 360 that encloses the transmit coil element 330 and the core 332. The transmit resonator housing 360 includes a second annular tapered wall 362. Notably, as shown in FIG. 5, the first annular tapered wall 354 and the second annular tapered wall 362 are complementary. This facilitates shaping the skin 320 around the transmit resonator 302 and the receive resonator 304 to enable at least a portion of the transmit coil element 330 to be positioned inside of the receive coil element 334. Further, the complementary surfaces of the first annular tapered wall 354 and the second annular tapered wall 362 facilitate reducing high contact forces to reduce tissue trauma or erosion.

[0043] FIG. 6 is a schematic diagram of an alternative wireless power transfer system 600. Similar to the wireless power transfer system 300 (shown in FIGS. 3-5), the wireless power transfer system 600 includes a transmit resonator 602 and a receive resonator 604 (with the skin 320 of the patient between the transmit resonator 602 and the receive resonator 604. A first cable 608 extends from the transmit resonator 602 (e.g., to a power source for the transmit resonator 602), and a second cable 610 extends from the receive resonator 604 (e.g., to an implanted medical device).

[0044] In this embodiment, however, the receive resonator 604 has a different shape than the receive resonator 304. Specifically, a first portion 670 of the receive resonator 604 has a generally toroidal shape, but the receive resonator 604 also includes second, cap-shaped portion 672 positioned on one side of the first, toroidal-shaped portion 670. This results in the receive resonator 604 defining a recess 606, instead of an aperture. In one embodiment, the first portion 670 is made of ceramic and at least some of the second portion 672 is made of titanium. Alternatively, the transmit and receive resonators described herein may be made of any suitable material.

[0045] Similar to the apertures 306 of the wireless power transfer system 300, the recess 606 of the wireless power transfer system 600 is configured to receive at least a portion of the transmit resonator 602. That is, the transmit resonator 602 is configured to be at least partially inserted into the receive resonator 602 such that a transmit coil element 630 is oriented substantially parallel to a receive coil element 634, with at least a portion of the transmit coil element 630 positioned inside of the receive coil element 634. Thus, the coupling between the transmit resonator 602 and the receive resonator 604 operates substantially similarly to the coupling between the transmit resonator 302 and the receive resonator 304.

[0046] Here, how ever, the second portion 672 of the receive resonator 604 enables including one or more additional electrical components 680 within the receive resonator 604. The electrical components 680 may include, for example, a communications module (e.g., a Bluetooth low energy communication module) that enables the receive resonator 604 to wirelessly communicate with one or more external devices (e g., the transmit resonator 602 and / or another external device). Locating thecommunications module in the receive resonator 604 (i.e., in a relatively shallow subcutaneous region) facilitates reliable communications. In some embodiments, the electrical components 680 may include a controller for controlling operation of the implanted medical device. The second portion 672 also provides additional space to accommodate a connector 682 that couples the receive resonator 604 to the second cable 610.

[0047] In at least some embodiments, the receive resonator 604 and / or the implanted device (e.g., a controller of the implanted device) is capable of communicating with one or more devices outside of the patient. For example, as noted above, the receive resonator 604 may include a communications module. For example, a charging status of the implanted device, a batten- status, wireless power transfer efficiency, operating parameters of the implanted device, etc. may be communicated. In one embodiment, one or more operational parameters of the receive resonator 604 are monitored (e g., by monitoring power wirelessly received by the receive resonator 604). If the operational parameter(s) exceed or fall below a certain threshold, an alert may be generated and wirelessly communicated to an external device. For example, if the transmit resonator 602 becomes partially or wholly uncoupled from the receive resonator 604, that uncoupling may be detected from the monitoring and communicated to an external device, prompting the patient to verily the positioning of the transmit resonator 602 to the receive resonator 604.

[0048] In another embodiment, instead of transmitting an alert via wireless communications, the receiver resonator 604 may generate an audible or haptic alert based on monitored operational parameters of the receive resonator 604. For example the receive resonator may include a speaker or vibratory device that alerts the patient when the transmit resonator 602 becomes partially or wholly uncoupled from the receive resonator 604.

[0049] Although in the embodiments shown, the transmit resonator inserts into the receive resonator, alternatively, the transmit resonator and the receive resonator may be configured such that the receive resonator inserts into the transmit resonator. In such embodiments, the implanted receive resonator (instead of the transmit resonator) includes acore within the receive coil. Further, the implanted receive resonator forms a protrusion (instead of an indentation) in the patient's skin, and that protrusion is received within an aperture or recess defined by the transmit resonator to couple the transmit resonator to the receive resonator. Notably, this results in the receive resonator being smaller than the transmit resonator, which may increase the thermal energy' generated by the receve resonator (relative to the embodiments discussed above). Including the core in the implanted receive resonator instead of the external transmit resonator may also increase thermal energy generation of the receive resonator.

[0050] Although the embodiments described herein are discussed in the context of a wireless power transfer system for a heart pump, those of skill in the art will appreciate that the features described herein may be implemented for a variety of implantable medical devices.

[0051] The embodiments described herein are directed to wireless power transfer systems and methods. A wireless power transfer system includes a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator including a receive coil element, and a transmit resonator including a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient and the receive coil element and the transmit coil element are oriented substantially parallel to one another.

[0052] Although the embodiments and examples disclosed herein have been described with reference to particular embodiments, it is to be understood that these embodiments and examples are merely illustrative of the principles and applications of the present disclosure. It is therefore to be understood that numerous modifications can be made to the illustrative embodiments and examples and that other arrangements can be devised without departing from the spirit and scope of the present disclosure as defined by the claims. Thus, it is intended that the present application cover the modifications and variations of these embodiments and their equivalents.

[0053] This written description uses examples to disclose the disclosure, including the best mode, and also to enable any person skilled in the art to practice the disclosure, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the disclosure is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.

Claims

WHAT IS CLAIMED IS:1 . A wireless power transfer system comprising: a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator comprising a receive coil element: and a transmit resonator comprising a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient and the receive coil element and the transmit coil element are oriented substantially parallel to one another.

2. The wireless power transfer system of claim 1. wherein the receive resonator defines an aperture extending through the receive resonator, and wherein the transmit coil element is configured to be at least partially inserted into the aperture.

3. The wireless power transfer system of claim 1, wherein the receive resonator defines a recess, and wherein the transmit coil element is configured to be at least partially inserted into the recess.

4. The wireless powder transfer system of claim 1 , wherein at least one of the receive coil element and the transmit coil element comprises a plurality of loops of Litz wire.

5. The wireless power transfer system of claim 1. wherein at least one of the receive coil element and the transmit coil element comprises a plurality of alternating dielectric layers and conductive layers arranged in a stack.

6. The wireless power transfer system of claim 1, wherein the receive resonator comprises a receive resonator housing, the receive resonator housing comprising a first annular tapered wall.

7. The wireless pow er transfer system of claim 6, wherein the transmit resonator comprises a transmit resonator housing, the transmit resonator housing comprising a second annular tapered w all that is complementary' to the first annular tapered wall.

8. The wireless powder transfer system of claim 1 , wherein the transmit resonator and the receive resonator each comprise at least one permanent magnet to facilitate securing a position of the receive resonator with respect to the transmit resonator.

9. The wireless power transfer system of claim 1. wherein the receive resonator comprises a communications module configured to communicate with at least one external device.

10. The wireless power transfer system of claim 9, wherein the communications module is configured to transmit an alert to the at least one external device when the transmit resonator becomes at least partially uncoupled from the receive resonator.

11. The wireless power transfer system of claim 1, wherein the receive resonator comprises a device that generates an audible or haptic alert when the transmit resonator becomes at least partially uncoupled from the receive resonator.

12. The wireless power transfer system of claim 1. wherein the transmit resonator has an outer diameter in a range of approximately 25 to 40 millimeters.

13. A wireless power transfer system comprising: a receive resonator configured to be implanted subcutaneously within a patient, the receive resonator comprising a receive coil element: a transmit resonator comprising a transmit coil element, the transmit coil element configured to be inserted at least partially inside of the receive coil element while the transmit resonator is external to the patient and the receive coil element and the transmit coil element are oriented substantially parallel to one another; and a garment configured to secure a position of the transmit resonator relative to the receive resonator.

14. The wireless pow er transfer system of claim 13, wherein the garment comprises at least one of a belt, a vest, a harness, and a strap.

15. The wireless power transfer system of claim 13, wherein the receive resonator defines an aperture extending through the receive resonator, and wherein the transmit coil element is configured to be at least partially inserted into the aperture.

16. The wireless power transfer system of claim 13, wherein the receive resonator defines a recess, and wherein the transmit coil element is configured to be at least partially inserted into the recess.

17. A method of operating a wireless power transfer system, the method comprising: at least partially inserting a transmit coil of a transmit resonator into a receive coil of a receive resonator while the transmit coil and the receive coil are oriented substantiallyparallel to one another, wherein the receive resonator is implanted subcutaneously within a patient, and wherein the transmit resonator is external to the patient; and transmitting power wirelessly from the transmit resonator to the receive resonator.

18. The method of claim 17, wherein at least partially inserting the transmit coil comprises at least partially inserting the transmit coil into an aperture extending through the receive resonator.

19. The method of claim 17, wherein at least partially inserting the transmit coil comprises at least partially inserting the transmit coil into a recess defined in the receive resonator.

20. The method of claim 17, further comprising communicating an alert from the receive resonator when the transmit resonator becomes at least partially uncoupled from the receive resonator.

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