System for transcutaneous energy transfer to an implantable medical device with mating elements

System for transcutaneous energy transfer to an implantable medical device adapted to be implanted under a cutaneous boundary having a housing having a first surface adapted to face the cutaneous boundary, the first surface of the housing of the implantable medical device having a first mating element, therapeutic componentry and a secondary coil operatively coupled to the therapeutic componentry. An external power source has housing having a first surface adapted to be placed closest to the cutaneous boundary, the first surface of the housing of the external power source having a second mating element and a primary coil capable of inductively energizing the secondary coil when externally placed in proximity of the secondary coil. The first mating element and the second mating element are configured to tactilely align the external power source with the implantable medical device.

FIELD

The present invention relates generally to transcutaneous energy transfer and, more particularly, to a system for transcutaneous energy transfer to an implantable medical device.

BACKGROUND

Implantable medical devices for producing a therapeutic result in a patient are well known. Examples of such implantable medical devices include implantable drug infusion pumps, implantable neurostimulators, implantable cardioverters, implantable cardiac pacemakers, implantable defibrillators and cochlear implants. Of course, it is recognized that other implantable medical devices are envisioned which utilize energy delivered or transferred from an external device.

A common element in all of these implantable medical devices is the need for electrical power in the implanted medical device. The implanted medical device requires electrical power to perform its therapeutic function whether it is driving an electrical infusion pump, providing an electrical neurostimulation pulse or providing an electrical cardiac stimulation pulse. This electrical power is derived from a power source.

Typically, a power source for an implantable medical device can take one of two forms. The first form utilizes an external power source that transcutaneously delivers energy via wires or radio frequency energy. Having electrical wires which perforate the skin is disadvantageous due, in part, to the risk of infection. Further, continuously coupling patients to an external power for therapy is, at least, a large inconvenience. The second form utilizes single cell batteries as the source of energy of the implantable medical device. This can be effective for low power applications, such as pacing devices. However, such single cell batteries usually do not supply the lasting power required to perform new therapies in newer implantable medical devices. In some cases, such as an implantable artificial heart, a single cell battery might last the patient only a few hours. In other, less extreme cases, a single cell unit might expel all or nearly all of its energy in less than a year. This is not desirable due to the need to explant and re-implant the implantable medical device or a portion of the device. One solution is for electrical power to be transcutaneously transferred through the use of inductive coupling. Such electrical power or energy can optionally be stored in a rechargeable battery. In this form, an internal power source, such as a battery, can be used for direct electrical power to the implanted medical device. When the battery has expended, or nearly expended, its capacity, the battery can be recharged transcutaneously, via inductive coupling from an external power source temporarily positioned on the surface of the skin.

U.S. Patent Application Publication US 2005/0075700A1 (U.S. patent application Ser. No. 10/837,506, Schommer et al, External Power Source For An Implantable Medical Device Having An Adjustable Magnetic core and System and Method Related Therefore, filed Apr. 30, 2004), discloses an external power source, and system and method using such external power source, for an implantable medical device having therapeutic componentry and a secondary coil operatively coupled to the therapeutic componentry. A primary coil is capable of inductively energizing the secondary coil when externally placed in proximity of the secondary coil. A repositionable magnetic core associated with the primary coil is capable of being repositioned by a user of the external power source. An indicator is capable of providing the user with information relative to coupling between the primary coil and the secondary coil as a function of repositioning of the repositionable magnetic core.

Transcutaneous energy transfer through the use of inductive coupling involves the placement of two coils positioned in close proximity to each other on opposite sides of the cutaneous boundary. The internal coil, or secondary coil, is part of or otherwise electrically associated with the implanted medical device. The external coil, or primary coil, is associated with the external power source or external charger, or recharger. The primary coil is driven with an alternating current. A current is induced in the secondary coil through inductive coupling. This current can then be used to power the implanted medical device or to charge, or recharge, an internal power source, or a combination of the two.

For implanted medical devices, the efficiency at which energy is transcutaneously transferred is crucial. First, the inductive coupling, while inductively inducing a current in the secondary coil, also has a tendency to heat surrounding components and tissue. The amount of heating of surrounding tissue, if excessive, can be deleterious. Since heating of surrounding tissue is limited, so also is the amount of energy transfer which can be accomplished per unit time. The higher the efficiency of energy transfer, the more energy can be transferred while at the same time limiting the heating of surrounding components and tissue. Second, it is desirable to limit the amount of time required to achieve a desired charge, or recharge, of an internal power source. While charging, or recharging, is occurring the patient necessarily has an external encumbrance attached to their body. This attachment may impair the patient's mobility and limit the patient's comfort. The higher the efficiency of the energy transfer system, the faster the desired charging, or recharging, can be accomplished limiting the inconvenience to the patient. Third, amount of charging, or recharging, can be limited by the amount of time required for charging, or recharging. Since the patient is typically inconvenienced during such charging, or recharging, there is a practical limit on the amount of time during which charging, or recharging, should occur. Hence, the size of the internal power source can be effectively limited by the amount of energy which can be transferred within the amount of charging time. The higher the efficiency of the energy transfer system, the greater amount of energy which can be transferred and, hence, the greater the practical size of the internal power source. This allows the use of implantable medical devices having higher power use requirements and providing greater therapeutic advantage to the patient and/or extends the time between charging effectively increasing patient comfort.

The efficiency of transcutaneous inductive energy transfer is directly related to the accuracy of positioning of the external, primary coil, to the internal, secondary coil. The two coils should be as close to each other as possible. Of course, since the position of the secondary coil is fixed following implantation, the closer that the primary coil can be positioned to the skin surface the better. The two coils should also be laterally aligned as close as possible. This alignment is typically accomplished by the patient by the attachment of the external power source/charger at the commencement of the charging process or when otherwise transferring power. It is often cumbersome and difficult for the patient, who typically is not a medical professional, to most accurately position the primary coil in the proper location. The lateral alignment is typically done tactilely by the patient. A typical implanted medical device is implanted close enough to the skin that the skin of the patient has a small protuberance at the site of implantation. This can be felt by the patient and can be used as a guide to position the external coil. However, this problem can be exacerbated because the lateral position of the secondary coil is not always laterally centered with the external protuberance providing the patient with tactile lateral location information.

Even if the primary coil is properly placed at the initiation of energy transfer or of the charging process, energy transfer and/or charging can continue over a signification period of time. During this time, it is usually impracticable for the patient to remain absolutely immobile. Charging can typically occur over several, perhaps many, hours. It is desirable for the patient to be able to continue With as many normal activities as possible. For example, since charging often is accomplished at night, it is desirable that the primary coil not move during normal sleep activities of the patient. As the patient may move during energy transfer or during charging, motions and activities of the patient may cause the primary coil to move with respect to the secondary coil. If this should happen, the efficiency of energy transfer is not optimum which limits the rate at which energy can be transferred and resulting in an increase in charging time, if the system utilizes charging, or a decrease in the amount of energy available to the implanted medical device, if direct energy transfer is utilized.

It also can be important to secure the primary coil in the proper location once the proper has been located by the patient. Without properly locating the external antenna with respect to the implantable medical device, efficient energy transfer may not be fully achieved.

Prior art implantable medical devices, external power sources, systems and methods have not always provided the best possible benefit leading to efficiency of energy transfer and patient comfort.

SUMMARY

It can be especially difficult to properly coaxially locate the primary coil of an external antenna with the secondary coil of an implantable medical device because it can be difficult to tactilely determine the location of the implantable medical device. Exacerbating the problem is that the secondary coil of the implantable medical device may not be centered on a face of the implantable medical device. In this case, even if the implantable medical device is properly located, the primary and secondary coils may still not be properly aligned.

In an embodiment, the present invention provides a system for transcutaneous energy transfer. An implantable medical device adapted to be implanted under a cutaneous boundary has a housing having a first surface adapted to face the cutaneous boundary, the first surface of the housing of the implantable medical device having a first mating element, therapeutic componentry and a secondary coil operatively coupled to the therapeutic componentry. An external power source has housing having a first surface adapted to be placed closest to the cutaneous boundary, the first surface of the housing of the external power source having a second mating element and a primary coil capable of inductively energizing the secondary coil when externally placed in proximity of the secondary coil. The first mating element and the second mating element are configured to tactilely align the external power source with the implantable medical device.

In an embodiment, the first mating element and the second mating element are configured to tactilely align the primary coil with the secondary coil.

In an embodiment, the first mating element is configured to be off-center of the first surface of the implantable medical device.

In an embodiment, a depression on the first surface of the external power source constitutes the second mating element and the first mating element of the implantable medical device is a projection.

In an embodiment, a depression on the first surface of the implantable medical device constitutes the first mating element and the second mating element of the external power surface is a projection.

In an embodiment, the first surface of the implantable medical device has a plurality of first mating elements and wherein the first surface of the external power source has a plurality of second mating elements and the plurality of first mating elements mate with respective ones of the plurality of second mating elements are collectively configured to tactilely coaxially align the primary coil with the secondary coil.

In an embodiment, the plurality of first mating elements and the plurality of second mating are asymmetrically arranged enabling tactile orientation of the external power source with respect to the implantable medical device.

In an embodiment, the first mating element is a ring and the second mating element is a ring mating with the ring of the first mating element.

In an embodiment, the ring of the first mating element and the ring of the second mating element are circular.

In an embodiment, the ring of the first mating element and the ring of the second mating element are oval.

In an embodiment, the present invention provides a method of transcutaneous energy transfer to a medical device implanted in a patient having a secondary charging coil using an external power source having a housing containing a primary coil, the housing having a first surface adapted to face the cutaneous boundary, the first surface of the housing of the implantable medical device having a first mating element; and having an external power source having a housing having a first surface adapted to be placed closest to the cutaneous boundary, the first surface of the housing of the external power source having a second mating element. The primary coil is positioned externally of the patient with respect to the secondary coil. The primary coil of the external power source is tactilely aligned with the secondary coil of the implantable medical device by moving the external power source with respect to the implantable medical device by aligning the second mating element of the external power source with the first mating element of the implantable medical device. Energy is transcutaneously transferred from the primary coil to the secondary coil.

In an embodiment, the tactilely aligning step uses a depression on the first surface of the external power source constituting the second mating element and the first mating element of the implantable medical device comprising a projection.

In an embodiment, the tactilely aligning step uses a depression on the first surface of the implantable medical device constituting the first mating element and the second mating element of the external power source comprising a projection.

In an embodiment, the tactilely aligning step utilizes a plurality of first mating elements and a plurality of second mating elements.

In an embodiment, the tactilely aligning step further orients the external power source with respect to the implantable medical device utilizing an asymmetrical arrangement of the plurality of first mating elements and the plurality of second mating elements.

In an embodiment, the first mating element is a ring mating with a ring of the first mating element.

In an embodiment, the rings are circular.

In an embodiment, the rings are oval.

DETAILED DESCRIPTION

The entire contents of U.S. patent application Ser. No. 11/414,151, Torgerson et al, Antenna for an External Power Source for an Implantable Medical Device, System and Method, filed Apr. 28, 2006, is hereby incorporated by reference.

FIG. 1illustrates a system10into which an improved external antenna32may be utilized. System10consists of implantable medical device12and external power supply14.

Implantable medical device12is situated under cutaneous boundary44. Implantable medical device12includes charging regulation module14, electronics module16and therapy module18. Charging regulation and therapy control is conventional. Implantable medical device12also has internal telemetry coil20configured in conventional manner to communicate through external telemetry coil22to an external programming device (not shown), charging unit23or other device in a conventional manner in order to both program and control implantable medical device and to externally obtain information from implantable medical device12once implantable medical device has been implanted. Internal telemetry coil20, rectangular in shape with dimensions of 1.85 inches (4.7 centimeters) by 1.89 inches (4.8 centimeters) constructed from 150 turns of 43 AWG wire, is sized to be larger than the diameter of secondary charging coil26.

Internal antenna25contains secondary coil26, constructed with 182 turns of 30 AWG wire with an inside diameter of 0.72 inches (1.83 centimeters) and an outside diameter of 1.43 inches (3.63 centimeters) with a height of 0.075 inches (0.19 centimeters). Magnetic shield28is positioned between secondary charging coil26and housing30and sized to cover the footprint of secondary charging coil26.

Internal telemetry coil20, having a larger diameter than secondary coil26, is not completely covered by magnetic shield28allowing implantable medical device12to communicate with the external programming device with internal telemetry coil20in spite of the presence of magnetic shield28.

Rechargeable power source24can be charged while implantable medical device12is in place in a patient through the use of charging regulation module14. In a preferred embodiment, charging regulation module14consists of charging unit23and external antenna32. Charging unit23contains the electronics necessary to drive primary coil34with an oscillating current in order to induce current in secondary coil26when primary coil34is placed in the proximity of secondary coil26. Charging unit23is operatively coupled to primary coil34by cable36. In an alternative embodiment, charging unit23and antenna32may be combined into a single unit. Antenna32may also optionally contain external telemetry coil22which may be operatively coupled to charging unit23if it is desired to communicate to or from implantable medical device12with charging regulation module14. Alternatively, antenna32may optionally contain external telemetry coil22which can be operatively coupled to an external programming device, either individually or together with external charging unit14.

As will be explained in more detail below, repositionable magnetic core38can help to focus electromagnetic energy from primary coil34to be more closely aligned with secondary coil26. Also as will be explained in more detail below, energy absorptive material40can help to absorb heat build-up in external antenna32which will also help allow for a lower temperature in implantable medical device12and/or help lower recharge times. Also as will be explained in more detail below, thermally conductive material42is positioned covering at least a portion of the surface of external antenna32which contacts cutaneous boundary44of the patient.

FIG. 2is a cross-sectional illustration of a close-up view of a variation of a portion of charging system10. Internal antenna25is shown having been implanted below cutaneous boundary44. Secondary coil26is positioned within internal antenna25above magnetic shield28.

External antenna38contains primary coil34and is positioned in transcutaneous superposition with respect to internal antenna25. Primary coil34is aligned with secondary coil26in order to facilitate transcutaneous energy transfer using electromagnetic coupling. Magnetic core38helps to focus electromagnetic energy generated by primary coil34transcutaneously toward secondary coil26. In this embodiment, magnetic core38extends between windings of primary coil34. External antenna32has a generally planar surface48intended to contact cutaneous boundary44. An edge of magnetic core38is coplanar with surface48to help promote electromagnetic fields to extend from primary coil34and be captured more readily by secondary coil26. Insulation46between magnetic core38and primary coil34, particularly on the side of external antenna32facing surface48, protects magnetic core38from collecting heat produced by primary coil34and increasing the surface of cutaneous boundary44.

FIG. 3illustrates an alternative embodiment of external antenna32used in charging system10. Again, external antenna38contains primary coil34and is positioned in transcutaneous superposition with respect to internal antenna25. Primary coil34is aligned with secondary coil26in order to facilitate transcutaneous energy transfer using electromagnetic coupling. Magnetic core38helps to focus electromagnetic energy generated by primary coil34transcutaneously toward secondary coil26. Central protrusion may be aligned with the axis of primary coil34.

However, external antenna32illustrated inFIG. 3extends magnetic core38further toward cutaneous boundary44and past surface48creating protrusion50. Central protrusion50extends beyond surface48creating a noticeable bump on surface48contacting cutaneous boundary44. In an embodiment, central protrusion50is circular in cross-section and has a conically shaped end intended to contact cutaneous boundary44. In an embodiment, central protrusion50is approximately 0.5 centimeters in diameter and extends approximately 0.5 centimeters beyond surface48. The outer diameter of central protrusion50may be not greater than, and perhaps less than, the inner diameter of primary coil34.

External antenna32may be pressed by the user against cutaneous boundary44as illustrated inFIG. 4. Central protrusion50pushes a portion of cutaneous boundary44away from its point of impact allowing external antenna32, in general, and magnetic core38, in particular, to come closer to secondary coil26.

Central protrusion50allows primary coil34to more efficiently electromagnetically couple with secondary coil26by allowing magnetic core38to be closer to internal antenna25and secondary coil26. Commonly, an external antenna32having a planar surface48may be able to come within1centimeter of secondary coil26of internal antenna25. However, central protrusion50is able to indent cutaneous boundary44and reduce the distance, commonly referred as the “air gap distance” between primary coil34and secondary coil26.

An alternative embodiment of external antenna32of charging system10can be seen by referring toFIG. 5andFIG. 6.FIG. 5is a cross-sectional view of external antenna32placed in the proximity of implantable medical device12and secondary coil26.FIG. 6is an underside perspective view of external antenna32unencumbered by implantable medical device12.

As inFIG. 3andFIG. 4, external antenna32ofFIG. 5andFIG. 6has central protrusion50enhancing electromagnetic coupling between primary coil34and secondary coil26as discussed above. In addition, external antenna32contains a plurality of peripheral protrusions52extending beyond surface48in a similar fashion to central protrusion50. Peripheral protrusions52may be sized and positioned to “fit” around the periphery of internal antenna25of implantable medical device12to further reduce the gap between primary coil34and secondary coil26. One or more peripheral protrusions52may be used. Peripheral protrusions may be circular in cross-section, conically shaped, square, rectangular or arcuate. Typically, peripheral protrusions52extend a similar distance beyond surface48as central protrusion50, however, peripheral protrusions52may extend farther or less far from surface48than central protrusion50. Peripheral protrusions52may extend approximately one-half of the distance that central protrusion50extends from surface48.

Peripheral protrusions52may be spaced from one another as illustrated inFIG. 6or may be more or less continuous around a periphery of external antenna32forming, to a large extent or entirely, a peripheral ring around external antenna32extending below surface48.

In an embodiment illustrated inFIG. 5, implantable medical device12, and, in particular, internal antenna25, has an indent54on the surface facing cutaneous boundary44aligned with central protrusion50. So configured, indent54of internal antenna25provides a locating feature allowing the user to tactilely determine the optimum positioning of external antenna32and will help hold external antenna32in proper position for electromagnetic energy transfer and will help ensure efficient energy transfer. Further, indent54may allow magnetic core38in protrusion50to get even closer to secondary coil26making energy transfer even more efficient.

In an embodiment illustrated inFIG. 5andFIG. 6, peripheral protrusions52may be sized and positioned to have a pattern, perhaps a circular pattern, slightly larger in diameter than internal antenna25allowing peripheral protrusions52to “fit” over the edge of internal antenna25enabling ease of tactile positioning of external antenna32with respect to internal antenna25. Further, peripheral protrusions52positioned in this manner may tend to push away skin of cutaneous boundary44and stretch cutaneous boundary44to be more thin over internal antenna25allowing external antenna32and, hence, primary coil34, to be closer to secondary coil26and increasing the efficiency of energy transfer.

FIG. 7illustrates an embodiment of external antenna32having screw56facilitating implementation of central protrusion50. Screw56may be turned clockwise or counter-clockwise to either increase the amount of protrusion or decrease the amount of protrusion of central protrusion50from surface48. Screw56may be turned by hand or by using a tool such as a screwdriver in a slot of the top surface of screw56. Screw56may extend through external antenna32as shown, facilitating tool manipulation, or may extend only partly through external antenna32allowing manipulation, for example, by hand turning central protrusion50. Screw56may be adjusted to create a greater or lesser extension of central protrusion50to account for patient comfort, varying implant locations and implant depths and type of skin or amount of fat tissue surrounding implantable medical device12.

FIG. 8illustrates an embodiment of external antenna32similar to the embodiment illustrated inFIG. 7. However, in the embodiment illustrated inFIG. 8, adjustable central protrusion50is designed to an adjustable plunger that ratchets within the body of external antenna32. The ratchet mechanism can allow central protrusion50to be adjusted relative to surface48.

FIG. 9illustrates an embodiment of external antenna32in which magnetic core38has a non-uniform cross-sectional area. Screw56is constructed of magnetic core38having a larger cross-section nearer the tip of central protrusion50and a smaller cross-section, farther away from the tip of central protrusion50. The greater amount of magnetic core38nearer the tip of central protrusion50increases the focusing effect of magnetic core38and increases the efficiency of energy transfer by keeping electromagnetic flux within magnetic core38farther toward secondary coil26. The remainder of screw56may be comprised of a non-magnetic protective material60such as an injection molded thermoplastic such as nylon 12, nylon PPA, polycarbonate or ABS. While the embodiment ofFIG. 8is illustrated with magnetic core38contained within screw56, it is to be recognized and understood that magnetic core38could also be contained within external antenna32and within central protrusion50without an adjustable screw56. That is, central protrusion50could be fixed and still contain magnetic core38on non-uniform cross-section.

While various embodiments of central protrusion50have been described, it is to be recognized and understood such embodiments and techniques could be used for one or more of peripheral protrusions52, either in addition to be used with central protrusion50or alternative to being used with central protrusion50.

While peripheral protrusions52have been illustrated and described as being used with central protrusion50, it is to be recognized and understood that peripheral protrusions52could be used to benefit in external antenna32without central protrusion50.

In an embodiment, a portion of insulating material46facing surface48could be formed of a low permeable material, such as bismuth graphite, to assist in forcing the electromagnetic field generated by primary coil34toward secondary coil26.

FIG. 10is a simplified view of the top surface80, i.e., the surface facing cutaneous boundary44, of implantable medical device12. Surface80of implantable medical device12contains mating element82. Mating element82provides a tactile element to surface80of implantable medical device12so that the location of secondary coil26may be tactilely located transcutaneously after implantable medical device12has been implanted into a patient. Mating element82provides a protrusion from or a depression in surface80of implantable medical device12. Although, the location of implantable medical device12typically may be identified following implantable due to the general shallowness of the implant location, determining the location of implantable medical device12does not necessarily translate to knowing the location of secondary coil26. As can be seen inFIG. 10, secondary coil26may be located off-center, i.e., not centered on surface80of implantable medical device.

FIG. 11provides a cross-sectional side view of implantable medical device12implanted under cutaneous boundary44. Mating element82, in this embodiment illustrated as a depression, is positioned in a predetermined relationship with secondary coil26. In this embodiment, mating element92is co-aligned with the axis of secondary coil26. External power source24has a complementary mating element84, in this embodiment illustrated as a projection, positioned in a predetermined relationship with primary coil34. In this embodiment, mating element84is co-aligned with the axis of primary coil34.

When transcutaneous energy transfer is desired to be initiated, such as for charging a rechargeable power source in implantable medical device12, external power source12, or typically an antenna associated with external power source12containing mating element84is placed on or near transcutaneous boundary44near the location of implantable medical device12. Such location can be generally determined by tactilely sensing a protrusion or bump that implantable medical device12makes in cutaneous boundary44due to the shallowness of the implant location.

However, merely placing external power source24in the vicinity of implantable medical device12does not necessarily mean that primary coil34and secondary coil26are aligned. Proper alignment of primary coil34and secondary coil26provides increased efficiency of energy transfer. As shown inFIG. 11, secondary coil26may not centered on surface80of implantable medical device. If primary coil34is centered on external power source24or if the corresponding off-centeredness does not match, the alignment of external power source24with implantable medical device12may actually lead to misalignment of primary coil34and secondary coil26.

The bump of mating element84on external power source24, however, may easily find the corresponding depression of mating element82on implantable medical device12automatically properly aligning primary coil34and secondary coil26due to the known predetermined relationship, e.g., co-axial relationship, of mating element84with primary coil34and the known, e.g., co-axial relationship, of mating element82with secondary coil26. An operator using external power source24, or an antenna of external power source24, may easily tactilely feel mating element84transcutaneously mate with mating element82of implantable medical device12. Once aligned, energy transfer may begin.

FIG. 12illustrates an alternative embodiment of mating elements82and84. In this embodiment, mating element82of implantable medical device12is a bump or projection and mating element84of external power source24is a depression. Nevertheless, mating elements82and84are complementary and operate in the same way to easily ensure proper alignment of primary coil34and secondary coil26as inFIG. 11.

FIGS. 13aand13billustrate an embodiment of transcutaneous energy transfer system10in which a plurality of mating elements82with implantable medical device12and a corresponding plurality of mating elements84with external power source24. In this embodiment, four (4) mating elements82and four (4) mating elements84are shown although other numbers of mating elements work as well. As inFIGS. 11 and 12, mating elements82may be either projections or depressions and, likewise, mating elements84may be either depressions or projections. Corresponding mating elements on each of implantable medical device12and external power source24should correspond, i.e., one could be a projection and the other a depression. Of course, not all mating elements82of implantable medical device need be all projections or depressions. Some of each could be utilized with corresponding mating elements84of external power source being complementary thereto. It is also to be recognized and understood that while, generally, mating elements (82and84) have been referred to as either projections or depressions, that combinations or more complex shapes could be utilized as well that may not strictly be either purely a projection or a depression. At least some of mating elements82should be complementary to and mate with corresponding ones of mating elements84of external power source24.

FIG. 14aand14billustrate another embodiment of transcutaneous energy transfer system10having a plurality of mating elements. In this embodiment, two mating elements82and two mating elements84similar to those illustrated with respect toFIGS. 13aand13B and an additional mating element86in the form of an elongated depression and an additional mating element88in the form of a complementary elongated projection, or bar, are utilized. This asymmetrical arrangement, or dissimilar shapes of mating elements, allows external power source24to be tactilely placed with respect to implantable medical device in a particular orientation, if that is desired.

FIGS. 15a,15b,15cand15dillustrate another embodiment of transcutaneous energy transfer system10having mating elements that form mating rings. Mating element90of implantable medical device12is an indented ring. Mating element92of external power source24is a complementary projecting ring. Although circular rings are illustrated, it is to be recognized and understood that other shapes, such as ovals, or even dual rings or incomplete rings could be utilized.

FIG. 16illustrates a side view of an alternative embodiment of the profile shape of a mating element, such as mating element80or mating element82. In this embodiment, mating elements94have a rounded, bump-like profile enabling easy engagement between corresponding complementary mating elements.

FIG. 17illustrates a side view of an alternative embodiment of the profile shape of a mating element, such as mating element80or mating element82. In this embodiment, mating elements96have a squared-off profile with a generally planar top. Such a shape may allow secure positioning of corresponding complementary mating elements.

FIG. 18illustrates a side view of an alternative embodiment of the profile shape of a mating element, such as mating element80or mating element82. In this embodiment, mating elements98a conical profile with a generally pointed end. Such a shape may allow precise positioning of corresponding complementary mating elements.

FIG. 19illustrates a side view of an alternative embodiment of the profile shape of a mating element, such as mating element80or mating element82. In this embodiment, mating elements96have truncated conical profile with a generally flat end. Such a shape may allow generally precise positioning of corresponding complementary mating elements perhaps with improved comfort.

It is to be recognized and understood that the invention is not limited by the shape of or the profile of mating elements. A wide variety of possible shapes and profiles are possible that have not been illustrated here.

Thus, embodiments of the invention are disclosed. One skilled in the art will appreciate that the present invention can be practiced with embodiments other than those disclosed. The disclosed embodiments are presented for purposes of illustration and not limitation, and the present invention is limited only by the claims that follow.