Abstract:
A headpiece for a cochlear implant system includes a transcutaneous transmission coil that transfers power and/or data to an implantable device implanted under a user&#39;s skin. The headpiece includes a magnet for holding the transmission coil in close proximity to the receiver coil in the implanted device, which also contains a magnet, and provides the desired alignment between the coils so that inductive coupling may efficiently occur. The headpiece has a bottom surface for skin contact that includes a plurality of flexible bumps configured to distribute pressure over a large surface area while allowing blood flow throughout the area. This also provides friction contact with the skin to help secure the headpiece, reducing movement due to lateral loading, while reducing skin irritation and erosion.

Description:
RELATED APPLICATIONS 
     The present application claims the benefit under 35 U.S.C. §119(e) to U.S. Provisional Patent Application No. 61/041,338, filed on Apr. 1, 2008, which is herein incorporated by reference in its entirety. 
    
    
     BACKGROUND OF INVENTION 
     The present invention relates to the transfer of electromagnetic energy between coils, and more particularly, to an external device secured to the skin of a patient, having a coil for transmitting power and/or data to an implanted device and/or to a replenishable power source associated with the implanted device. 
     The present invention will be described in the context of a cochlear implant system; however, it should be understood that it is also useful for other medical devices such as neuromuscular stimulators, implantable pumps, and other implantable devices that are designed to be surgically inserted within a patient&#39;s body to carry out a medically related function for an extended period of time. Indeed, the present invention can be used in any device having an implantable portion including an implanted coil and an external portion containing an external coil for placement on the skin of the patient in alignment with the implanted coil. In a cochlear implant system, the portion of the system containing the external coil is placed on the head and is referred to as the “headpiece”. The term “headpiece” will be used herein to refer to the portion of the system containing the external coil, regardless of where it is used on the body. 
     A common way of achieving alignment between an external coil and an implanted coil is to employ a magnet in both the headpiece and the implanted device. The magnetic attractive force associated with such magnets holds the external coil in close proximity to the implanted coil and provides the desired alignment between the coils for efficient electromagnetic coupling, which may be RF, inductance, optical, or the like. 
     However, a known problem is that the pressure of the headpiece against the skin may cause skin irritation and/or tissue damage due to blood flow restriction. The issue is further compounded by variable skin curvatures resulting, in part, from the shape of the implanted device and variable skin thicknesses among patients. Because of this, force may be applied over a small area of the skin flap, resulting in very high local pressures, which can lead to irritation, soreness, redness, and even necrosis of the skin flap tissue or extrusion of the implanted device. Reducing magnetic forces to address the pressure issues has the undesirable effect of poor headpiece retention. 
     Attempts have been made to improve headpiece comfort and retention by providing a textured elastomeric material at the periphery on the skin side surface of the headpiece, or providing a ring or disk of textured rubber having adhesive on one side to stick to the skin side surface of the headpiece. U.S. patent application Ser. No. 10/741,411, filed Dec. 19, 2003, which is incorporated herein by reference, discloses a shell for covering a headpiece in which portions of the shell that come into contact with skin are covered with or made of a material that is comfortable against the skin; a material such as fabric or foam or other material with similar qualities may be used to maintain a comfortable feel against the skin in moist environments, such as when a user sweats. Other headpiece designs have used an open antenna coil design having a ring of rigid plastic bumps at the perimeter on the skin side surface. 
     In view of the above, what is needed is a headpiece that can transmit power and/or data transcutaneously to an implanted device, wherein such headpiece is readily attachable to the skin in close proximity to the implanted device, easily and reliably retained in proper alignment with the implanted device, and does not promote skin erosion, irritation, or discomfort, even with minor changes of the skin that commonly occur. 
     SUMMARY OF INVENTION 
     The present invention solves the above and other needs by providing a magnet- and coil-containing headpiece with bottom surface having a plurality of flexible bumps that define multiple low- and zero-pressure channels. This allows blood to flow in nearly every part of the skin and tissue underneath the headpiece. Because the bumps can resiliently deform and flex independently, the headpiece conforms to the contour of the skin, thus more evenly distributing headpiece forces over a larger skin area, further improving comfort and blood flow. Additionally, the resiliency of the bumps allows for the headpiece to dynamically conform to the skin with minor changes of the skin. Such changes can occur as the surgical wound heals, with swelling that can last one or two months following surgery. Changes to skin flap thickness can also occur with pregnancy, water retention, weight gain or loss, age, hair growth, and movement with chewing or talking. This ability to conform to the contour of the skin allows the headpiece to adjust naturally to small changes, being relatively insensitive to magnet strength, such that the magnet strength does not need to be adjusted as often by adding, subtracting, or replacing magnets in the headpiece. While major changes may require such adjustment, minor changes will be accommodated by the flexible bumps. 
     The bump configuration, shape, surface finish, and material can be used to provide a high-friction interface to reduce movement of the headpiece under lateral loading, thereby improving retention of the headpiece. 
     In some embodiments of the invention, a rigid bottom surface may be used to provide support for the bumps, allowing use of the softest possible materials for the bumps themselves, further improving comfort and reducing pressure without compromising retention. 
    
    
     
       BRIEF DESCRIPTION OF ACCOMPANYING DRAWINGS 
       The above and other aspects, features and advantages of the present invention will be more apparent from the following more particular description thereof, presented in conjunction with the following drawings wherein: 
         FIG. 1  is a block/schematic view, and  FIGS. 1A-1E  are perspective and side views, of an embodiment of the present invention; 
         FIGS. 2 and 2A  are side views of two embodiments of the present invention; 
         FIGS. 3 and 3A  are side cross sectional views of two embodiments of the present invention; 
         FIGS. 4 and 4A  are bottom (skin-side) views of two embodiments of the present invention; 
         FIGS. 5-11  are cross sectional side views, each with a bottom view of a single bump, of various embodiments of the bottom portion of the present invention; 
         FIGS. 12-15  illustrate steps for manufacturing a headpiece according to one embodiment of the present invention; 
         FIGS. 16-19  illustrate steps for manufacturing a headpiece according to an alternative embodiment of the present invention; 
         FIG. 20  is a perspective view of the inside bottom cover of the headpiece according to one embodiment of the present invention; 
         FIG. 21  is a side cross sectional view of the completed bottom portion of the headpiece including the bottom cover shown in  FIG. 20 ; 
         FIG. 22  is a bottom view of the completed headpiece including the bottom portion shown in  FIG. 21 ; 
         FIG. 23  is a side cross sectional view of a subassembly of one embodiment of the present invention; 
         FIG. 24  is a side cross sectional view of a subassembly of an alternative embodiment of the present invention; 
         FIG. 25  is a side cross sectional view of a subassembly of another alternative embodiment of the present invention; 
         FIG. 26  is a side cross sectional view of another alternative embodiment of the present invention; and 
         FIG. 27  is a side cross sectional view of another alternative embodiment of the present invention. 
     
    
    
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF INVENTION 
     The following description of the presently contemplated best mode of practicing the invention is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. The scope of the invention should be determined with reference to the claims. 
     Referring first to  FIGS. 1 and 1A , there are shown a schematic diagram and perspective illustration of a cochlear implant system  1000  having external componentry  10  and implanted componentry  60 . The implanted componentry  60  may comprise a single implanted device or may comprise two or more separate devices that can be detachably attached to each other; for example, a lead may be permanently integrated with an implantable cochlear stimulator (ICS), or a battery may be sealed within the housing of the ICS, or the lead and/or battery may be detachably attachable to the ICS, or the ICS may otherwise be modular. As used herein, the terms “implanted device” and “cochlear implant” refer to the implanted componentry, whether it is a single device or separate devices working together as part of the implanted portion of the system. Implanted device  60  comprises a coil  65  and a magnet  202  positioned in a portion  200  of implanted device  60  such that when implanted, coil  65  and magnet  202  are located proximate the skin  50 . 
     Just as the implanted componentry may comprise a single implanted device or multiple components, external componentry  10  may comprise a single integrated device, such as described in U.S. patent application Ser. No. 12/398,058 entitled “Integrated Cochlear Implant Headpiece,” or a modular device, such as described in U.S. patent application Ser. No. 12/397,982 entitled “Modular Speech Processor Headpiece,” which are incorporated herein by reference in their entirety. Alternatively, external componentry  10  may comprise separate external components that work together and can be individually selected and individually replaced, such as the battery  35  of the behind the ear processor shown in  FIG. 1B . External componentry  10  comprises headpiece  100 , which includes a coil  30  for transmitting power and/or data through the skin  50  to implanted device  60  via an RF or other electromagnetic link that couples power from external coil  30  to internal coil  65 . So long as a suitable link, e.g., an inductive link, is established between these two coils, power and/or data can be continuously supplied to the implanted device  60  from the external device  10 . 
     The efficiency with which electromagnetic power may be transcutaneously transferred between a transmission coil and a receiving coil is a function of the alignment and distance between the coils. It is thus desirable to position the external device  10  as close as possible to the implanted device  60 . In use, headpiece  100  is located as close as possible to implanted device  60  so as to provide the strongest signal coupling between coils  30  and  65 . Headpiece  100  includes a magnet  102  to magnetically couple to internal magnet  202  of implanted device  60  to retain headpiece  100  against the skin. The magnetic attractive force holds external coil  30  in close proximity to internal coil  65  and provides the desired alignment between the coils so that inductive coupling may efficiently occur. Either or both of magnets  102  and  202  may be fixed or detachable. For example, it may be advantageous to be able to temporarily take away the internal magnet  202  in order to use magnetic resonance imaging (MRI). It also may be advantageous to be able to take out external magnet  102  to install one or more magnets of various strengths in headpiece  100 . 
     Optionally, headpiece  100  may be constructed of flexible non-rigid materials in order to conform to the contour of the portion of the user&#39;s skin  50  to which the headpiece  100  is attached and can be made in a variety of shapes and colors, such as various skin tones or designer colors or patterns. The headpiece is preferably thin and lightweight. 
     In addition to external coil  30  and magnet  102 , external componentry  10  includes a power source  35  and control circuitry  40 . The power source  35  and control circuitry  40  may be located on a person&#39;s belt or pocket or behind the ear (BTE), and attached to external coil  30  via a cable. See, e.g., U.S. Pat. No. 5,603,726, which is incorporated herein by reference. Alternatively, power source  35  and/or control circuitry  40  may be included within headpiece  100  housing coil  30 . See, e.g., U.S. Pat. No. 5,948,006 and U.S. patent application Ser. Nos. 12/398,058 and 12/397,982, which are incorporated herein by reference. In either case, most or all of electronic circuitry  40  may be embodied in one or more integrated circuits (IC). 
     Headpiece  100  transmits a modulated signal  75  from external transmission coil  30 , through skin  50 , to internal receiving coil  65  of implanted device  60 . Modulated signal  75  is controlled by electronic circuitry  40  powered by a battery or other power source  35  (e.g., a supercapacitor, ultracapacitor, or other energy-storage device). Circuitry  80  within implanted device  60  demodulates the signal to obtain data, and/or rectifies the signal to obtain power, as is known in the art. The recovered data may be used to control the operation of implanted device  60 . Hence, headpiece  100  is able to selectively control and/or power implanted device  60 . 
     Some implantable devices, such as neural or auditory stimulators, do not require internal batteries as a power source, but rather receive power directly via transcutaneous coupling. See, e.g., U.S. Pat. No. 5,603,726, which describes an implantable cochlear stimulator powered by an external wearable system and is incorporated herein by reference. 
     Other implantable devices contain an optional battery or other power source  70 , e.g., an ultracapacitor. The optional power source  70  is preferably of the secondary type, which can be recharged by transcutaneously coupling power from external power source  35  via external coil  30  and internal coil  65 . Headpiece  100  is used to supply power for recharging optional power source  70  with power derived from modulated signal  75 . For example, U.S. Pat. No. 4,082,097, which is incorporated herein by reference, discloses a system for charging a rechargeable battery in an implanted human tissue stimulator by means on an external power source. 
     In addition to transmitting information and data from the external coil to the implanted device, some implantable devices may also transmit information and data back to an external device relating to the status of the device and the signals it senses in the patient&#39;s body. Such backtelemetry data may include, e.g., an indication of the voltage level obtained by rectifying and filtering the inductively-coupled carrier signal received from external coil  30 . Such voltage will be at a peak (maximum) value when the implant coil  65  and external coil  30  are properly aligned. Thus, such signal may be used as a feedback signal to trigger circuitry within the headpiece whenever proper alignment and/or improper alignment exists. See U.S. Pat. Nos. 5,324,316; 5,312,439; and 5,358,514; which describe a small implantable microstimulator and are incorporated herein by reference. Therefore, while the invention is described herein with the “transmission” coil, or primary coil, in the external portion and the “receiver” coil, or secondary coil, in the implanted portion, it should be understood that for some applications, data (or even power) could be transmitted from the implanted coil to the external coil, as described above. 
       FIGS. 1C-1E  show detail of the headpiece  100  of  FIG. 1B .  FIG. 1C  is a top perspective view of headpiece  100  showing a top cover  110  having a top face  11 .  FIG. 1D  is a bottom perspective view of headpiece  100  showing a bottom cover  120  having a bottom (skin-side) face  12  having a surface  13  from which protrude flexible bumps  14 .  FIG. 1E  is a side view of headpiece  100  showing the side of both top cover  110  and bottom cover  120  with flexible bumps  14  protruding from surface  13 . 
       FIGS. 2 and 2A  show side views of two embodiments of the headpiece  100  having a top face  11  and a bottom (or skin-side) face  12  having a surface  13  from which protrude flexible bumps  14 .  FIGS. 3 and 3A  are side cross sectional views of the embodiments of headpiece  100  shown in  FIGS. 2 and 2A , respectively, showing external coil  30  and external magnet  102 . The top cover  110  and bottom cover  120  of the headpiece  100  may comprise, for example, a blend of polycarbonate and acrylonitrile butadiene styrene (ABS). Surface  13  may comprise a rubber or other elastomeric coating, molding, or other covering on bottom cover  120  of headpiece  100 . Alternatively, surface  13  may be formed by the housing of headpiece  100 , with flexible bumps  14  adhered directly to surface  13  or formed by injecting rubber through holes in the housing to form flexible bumps  14  protruding from surface  13 , as will be described in more detail below. Flexible bumps  14  may be molded from the same material as the surrounding surface  13 , or may comprise different material. Flexible bumps  14  may comprise, for example, a thermoplastic elastomer (TPE) such as SANTOPRENE TPE or VERSOLLAN TPE, or a silicone rubber such as SILASTIC silicone elastomer. The flexible bumps  14  preferably comprise material having a durometer of between 20 and 70 Shore A, preferably between 30 and 70 Shore A, and more preferably between 30 and 60 Shore A, and most preferably about 50 Shore A. 
     While flexible bumps  14  may be permanently attached to headpiece  100 , such as by permanently adhering to the bottom of the housing or by being formed integral with a covering that may be molded or bonded or the like to at least the bottom face of the housing of headpiece  100 , flexible bumps  14  may alternatively be supplied as part of a removable or detachable pad or envelope. As used herein with respect to the inventive flexible bumps, detachable means designed to be removed from the headpiece without damaging either the headpiece or the detachable piece; removable means designed to be removed from the headpiece without damaging the headpiece. A pad may be adhesively applied to the bottom of headpiece  100 ; alternatively, the pad may engage with the headpiece  100  using a fastener or one or more engaging features. The pad may form a cap  28  that fits over the bottom of the headpiece  100  and extends partway up the sides, as illustrated in  FIG. 27 . The amount that it extends is not limited, but greater extension provides for more secure attachment. To install the cap  28 , the cap is placed over the bottom of the headpiece  100 , and air is then pushed out through a hole in the bottom of the cap (not shown) or burped out from between the cap and headpiece by peeling back an edge of the cap and pressing the cap against the headpiece, creating a suction effect, which helps hold the cap in place. The cap remains in place on the headpiece due to the suction effect and frictional engagement with the headpiece. Alternatively, the headpiece may be placed within an envelope having flexible rubber bumps on at least one surface such that the bumps are facing the skin when the headpiece is in use. The envelope may be similar to the pouch described in U.S. Pat. No. 5,948,006, incorporated herein by reference. The envelope may completely cover the headpiece, and may provide water resistance; alternatively, portions of the headpiece may be exposed instead of covered by the envelope, such as to avoid attenuation in the region of a microphone. A cap or envelope configuration would generally be considered detachable since the headpiece could be removed from the cap or envelope without damaging either the headpiece or cap or envelope. The pad having adhesive may be detachable, but may alternatively be considered removable because, although removing the pad would not damage the headpiece, the adhesive may allow only limited or no reuse of the pad. Having the bumps permanently attached to the headpiece will generally allow for a thinner profile; on the other hand, detachability or removability may be advantageous for cleaning, replacing, or providing different thicknesses, colors, or the like. Providing various pad or envelope thicknesses or different heights of bumps provides adjustability of the attraction force between the implanted and external magnet by varying their distance. 
     Flexible bumps  14  may be of any shape and size, but are preferably of a size and shape that aids in retaining headpiece  100  against the skin while allowing blood to flow in regions of skin adjacent the bumps. The length of each bump as measured from surrounding surface  13  is preferably between 0.010 and 0.040 inches, and more preferably 0.020 to 0.040 inches. The bumps preferably have a maximum width of between 0.010 and 0.040 inches and more preferably between 0.020 and 0.040 inches, and most preferably between 0.020 and 0.035 inches. For bumps that are circular in cross section, such as those shown in  FIGS. 2-8 , this width is the diameter. For bumps having other cross-sectional shapes, such as square or rectangular, this width is the largest width dimension. The tips of the bumps may be convex, flat, concave, or any other shape. Bumps with concave tips, such as shown in  FIG. 7 , may provide additional adhesion to the skin by acting as suction cups. 
     The bottom face  12  of the headpiece  100  is preferably generally concave, as illustrated in  FIGS. 2 ,  2 A,  3 , and  3 A, but may be flat or of any shape. The lengths of the bumps may be the same as each other, as in the embodiment shown in  FIG. 2A , or may vary, as in the embodiment shown in  FIG. 2 . For example, the face  12 , whether flat or concave, may have longer bumps on one or more outer concentric rings and shorter bumps on inner rings, which may create a similar effect as having the surrounding surface  13  of a concave shape. As another alternative, adjacent bumps can be different sizes, differing in both length and width. Longer bumps may be thinner and shorter bumps fatter, for example. By having different sizes, as the longer bumps deflect, the shorter bumps are recruited to take more of the load. As yet another embodiment, illustrated in  FIG. 26 , the bottom face  12  may be concave, but the lengths of the bumps may vary such that the bumps at the periphery are shorter and therefore stiffer than the bumps in the center, which are longer and therefore more flexible. As seen in its relaxed condition, the tips of the bumps line up to form a flat surface, as shown by the dashed line  26 , even though the bottom face  12  is concave. However, when positioned on the skin, the flexible bumps follow the natural curvature of the head, with those bumps in the center deforming under the load of magnetic attraction because of their relative flexibility. Although the bumps are illustrated in the figures as lying in a direction parallel to the axis of the headpiece, the bumps may alternatively extend perpendicularly from the surface  13  or at any other angle. 
       FIGS. 4 and 4A  show bottom (skin-side) views of the headpiece  100  showing an array of flexible bumps  14 . As shown in  FIG. 4A , at least some of the bumps may be arranged in one ring or more rings, which may be concentric. However, their arrangement is not limited. It should be understood that any configuration of a plurality of bumps is possible. Advantageously, maximizing the surface area covered by bumps minimizes the pressure against the skin. For example, for a circular headpiece, it may be preferable to have bumps covering a substantial area of the circle instead of just in a ring at the perimeter. Furthermore, the bumps may be substantially uniformly distributed across the circle, or there may be more bumps in the middle or more at the periphery. The key is to minimize pressure against the skin while allowing adequate blood flow. 
       FIGS. 5-11  are cross sectional side views and a bottom view of a single bump of various embodiments of the bottom surface of headpiece  100 . These views are meant only as examples; the shape is not limited to these shapes. As used herein, the “base” of the bump is that portion extending from the bottom surface, and the “tip” of the bump is that portion that will contact the skin.  FIG. 5  shows bumps having a right cylindrical base and a hemispherical tip, which has the advantage of being one of the easier shapes to manufacture.  FIG. 6  shows frustoconical bumps having a conical base and flat tip.  FIG. 7  shows bumps having a conical base and concave tip.  FIG. 8  shows bumps having a right cylindrical base and a conical tip.  FIG. 9  shows bumps having a regular pyramidal base extending to a pointed tip.  FIG. 10  shows bumps having a tapered rectangular base that is truncated to form a flat rectangular tip.  FIG. 11  shows bumps having a rectangular base tapering to a wedge-shaped tip. 
       FIGS. 12-15  illustrate steps for manufacturing a headpiece according to one embodiment of the present invention. In  FIG. 12 , a bottom cover  120  is provided, having an inside face  17 , a bottom face  12 , and holes  15  therethrough. In  FIG. 13 , an elastomeric material  22  is added to the bottom cover  120 , such as from the inside face  17 , flowing through holes  15 , and forming flexible bumps  14  protruding from surface  13  of the bottom face  12 , and forming magnet and antenna coil locating features  20  on a portion of the elastomeric material inside the bottom cover. The step illustrated in  FIG. 13  can be accomplished in a number of ways, such as by insert molding with liquid silicone rubber, transfer molding, or compression molding, or casting. Note that the elastomeric material  22  is continuous from the inside to the outside of the headpiece, forming a strong, permanent mechanical lock of the elastomeric material. In  FIG. 14 , a magnet  102  and an antenna coil  30  are placed within the bottom cover  120 , taking advantage of the locating features  20  formed in the elastomeric material  22 . Note that some of the locating features  20  may be formed by the bottom cover  120  itself, as will be illustrated later. In  FIG. 15 , a top cover  110  is joined to the bottom cover  120 , sealing the magnet  102  and coil  30  within the headpiece  100 . 
       FIGS. 16-19  illustrate steps for manufacturing a headpiece according to an alternative embodiment of the present invention, which may have a detachable or removable pad containing the flexible bumps  14 . As shown in  FIG. 16 , in this embodiment, a bottom cover  120  is provided, but without through holes. The bottom cover  120  has magnet- and coil-locating features  20 , which may be molded into the bottom cover material itself or may be added by an elastomeric or other material molded or cast into the bottom cover or provided as a separate part and glued or otherwise attached to the inside surface  17  of the bottom cover. In  FIG. 17 , the magnet  102  and antenna coil  30  are placed within the bottom cover  120 , using the locating features  20 . In  FIG. 18 , a top cover  110  is joined to the bottom cover  120 , sealing the magnet  102  and coil  30  within. In  FIG. 19 , an elastomeric pad  24  having a plurality of flexible bumps  14  is adhered to the bottom face  12  either by molding it directly to the bottom face  12  of the bottom cover  120  or by forming the elastomeric pad with bumps first and then adhering it with an adhesive, engagement features, or other method, to the bottom face  12 . 
     As can be seen by directly comparing  FIGS. 15 and 19 , the embodiment of  FIG. 15  provides an advantage of not requiring the additional thickness of the pad, which could be about 1 mm. It has the added advantage of supporting the flexible bumps  14  with the bottom cover  120 , which may be relatively rigid, allowing the bumps to be made of the most flexible material possible. It also provides an advantage of more securely fixing the bumps to the bottom cover  120 . For example, the edge  25  of the pad  24  of  FIG. 19  might have a tendency to peel off of the bottom face  12  whereas there is no edge in the embodiment of  FIG. 15  to peel off. On the other hand, the embodiment of  FIG. 19  may be preferred when removability or detachability of bumps is desired, such as to change pad thickness or to another geometry or for cleaning. 
       FIG. 20  is a perspective view of the inside of the bottom cover  120  of a headpiece according to one embodiment of the present invention, showing the holes  15 . This embodiment has a large open area  21  in the center portion such that surface  13  of the completed headpiece will be formed by the hard plastic bottom cover  120  on the outer portion, and the inner portion will be formed by the molded elastomer. This provides rigidity in the outer region and conformity in the center region. 
       FIG. 21  is a side cross sectional view of the completed bottom portion of the headpiece, showing flexible bumps  14  extending through holes  15  in the hard bottom cover  120  of  FIG. 20 , and showing an elastomeric surface  23  formed during the molding process in the center portion. Various features  20  can be seen molded into the hard bottom cover  120  and the elastomer  22  for locating the magnet and antenna coil. 
       FIG. 22  is a bottom view of the completed headpiece  100  of  FIGS. 20 and 21 , showing flexible bumps  14  protruding from surface  13  of bottom face  12 . Surface  13  is formed by the bottom cover  120  on the periphery and by the elastomer  22  in the center portion. 
       FIG. 23  is a side cross sectional view of one embodiment of a portion of the present invention, showing detail of  FIG. 13 . Since the flexible bumps  14  extend from the hard bottom cover  120  they are more supported and constrained than in the embodiment of  FIG. 24 , in which a pad  24  is adhered to the bottom cover  120 . This provides more positional control of the individual flexible bumps  14 , which in turn provides more overall stability to the headpiece. 
       FIG. 24  is a side cross sectional view of an alternative embodiment of a portion of the present invention, showing detail of the housing and rubber pad  24  of  FIG. 19 . Since the rubber pad  24  is flexible, the overall structure will tend to move more than the embodiment of  FIG. 23 . 
       FIG. 25  is a side cross sectional view of another alternative embodiment of a portion of the present invention, similar to that shown in  FIG. 24 , but with fillets formed at the junction  16  of the surface  13  and the flexible bumps  14  to provide support to the flexible bumps  14 . This helps maintain positional control of the bumps, providing more overall stability to the headpiece. 
     From the above, it is thus seen that the present invention provides a device including a transmission coil that is compatible with many types of implanted devices. The headpiece is skin-adhering and coil-aligning via a magnet paired with a magnet of an implanted device, easy to apply and remove, atraumatic, and available in a variety of colors or shapes. The flexible bumps also improve impact resistance, protecting both the headpiece and the underlying implanted coil, by dissipating the energy. 
     While the invention herein disclosed has been described by means of specific embodiments and applications thereof, numerous modifications and variations could be made thereto by those skilled in the art without departing from the scope of the invention set forth in the claims. For example, invention may take the form of an elastomeric pad having the flexible bumps, wherein the pad comprises a sealed membrane filled with air, liquid, and/or gel to further distribute the forces. While the invention has been described specifically with respect to a “headpiece” for use with a cochlear implant, the headpiece may be for use anywhere on the body aligned with any implanted device, which may comprise a tissue stimulator, sensor, pump, or any other implantable device that requires an electromagnetic link to be established therewith.