Abstract:
An implantable medical device, such as an implantable cochlear stimulator (ICS) system, utilizes laminated, sectionalized or particle-ized permanent magnets and/or keepers in both the implant portion and external (non-implanted) portion so as to reduce the electrical energy absorbed by both the implant device and the external device when in use. In one embodiment, the implant device employs a sectionalized, laminated or particle-based “keeper”, while the external device employs a sectionalized, laminated or particle-ized magnet, making the implant device immune to being damaged by MRI (magnetic resonance imaging). The combination of the sectionalized/laminated/particle magnets and the sectionalized/laminated/particle keepers creates a very high electrical resistance path across the boundaries of the laminations, sections, or particles, thereby reducing the magnitude of eddy currents that would otherwise flow transversely through the keeper in the presence of a magnetic flux passing through the keeper or magnet. The reduction of eddy currents, in turn, reduces energy loss.

Description:
This application claims the benefit of U.S. Provisional Patent Application Ser. No. 60/094,300, filed Jul. 27, 1998. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to implantable devices, and more particularly to implantable medical devices having a permanent magnet therein that aligns an external (non-implanted) coupling device with the implantable device so that an electromagnetic signal may be optimally coupled between the two devices. 
     It is known in the art for an implantable medical device, e.g., implantable cochlear stimulator (ICS), to have a permanent magnet placed therein. An external (non-implanted) device, e.g., a headpiece of an ICS system, also has a permanent magnet placed therein. Both the external device and the implantable device may have coils mounted therein to allow power and information to be electromagnetically coupled, e.g., inductively coupled, between the two devices. Optimum signal and power coupling occurs when the implanted coil in the implantable device and the external coil in the external device are properly aligned. The magnetic attraction between the two permanent magnets, one located in the implantable device (typically in the center of the implant coil) and the other located in the external device (also typically located in the center of the external coil), magnetically hold the external device in a proper position so that the needed alignment between the two devices is maintained. See, e.g., U.S. Pat. Nos. 4,352,960 (Dormer et al.) and 4,726,378 (Kaplan), both of which patents are incorporated herein by reference. 
     It is also known in the art to replace one of the magnets, e.g., the magnet in the implant device, with a “keeper”. A keeper is generally made from a material which is not magnetic, per se, i.e., is not magnetized, but which provides a low reluctance magnetic path for magnetic flux. The use of a keeper advantageously improves the resistance of the implant system to MRI magnetic fields, in the event such MRI fields should be applied to the patient. That is, should MRI (magnetic resonance imaging) be conducted on the patient having the implant, the magnet in the implant becomes demagnetized and distorts the MRI image. A keeper, if used in place of the implant magnet, is not damaged by the MRI and distorts the MRI image less. 
     Disadvantageously, when power and signals must be electromagnetically transferred between the implant device and the external device, placing a magnet or keeper within the coils used for the power and signal transmission absorbs power and reduces the efficiency of the system. Here, system efficiency is defined as the ratio of input power delivered to a transmission coil input to output power recoverable at a receiving coil. What is needed, therefore, is a system that allows magnetic attraction to maintain a proper alignment between an implantable device and an external device without having the magnetic elements absorb large amounts of power, thereby making the system more efficient. What is further needed is such a system that is compatible with MRI, i.e., that allows MRI to be conducted when necessary without harming the implant device and without significantly distorting the MRI image. 
     SUMMARY OF THE INVENTION 
     The present invention addresses the above and other needs by laminating and/or sectionalizing the magnet and/or keeper used in both the implant device and external device so as to reduce the electrical energy absorbed by both the implant device and the external device. In order to avoid being damaged by MRI, it is preferred that the implant device employ a sectionalized or laminated “keeper”, while the external device employ a laminated or sectionalized magnet, or a magnet comprising small electrically-isolated magnetic particles. The use of such laminated, sectionalized or particle-ized components advantageously creates a very high electrical resistance path across the boundaries of the laminations, sections, or paticles, thereby reducing the magnitude of eddy currents that would otherwise flow transversely through the keeper in the presence of a magnetic flux passing through the keeper or magnet. The reduction of eddy currents, in turn, reduces energy loss. 
     In accordance with one aspect of the invention, an implantable medical device includes a receiving coil adapted to be electromagnetically coupled with a transmitting coil of an external device, and a magnetic element responsive to a magnetic field. The magnetic element holds the implantable medical device in a desired position that aligns the receiving coil with the transmitting coil for efficient power and signal transfer between the receiving and transmitting coils. Also included are means for reducing energy loss within the magnetic element as power and signal transfers occur between the receiving and transmitting coils. Thus, the implantable medical device operates with less loss relative to the amount of energy coupled into the receiving coil. 
     In accordance with another aspect of the invention, a medical device system is provided that includes an implantable part and an external (non-implanted) part. The implantable part and the external part each have a coil therein through which power may be inductively coupled from the external part to the implantable part when the respective coils are aligned. The system includes a first magnetic element in the external part, and a second magnetic element in the implanted part adapted to be magnetically attracted to the magnetic element in the external part. This magnetic attraction aligns the respective coils for efficient power and signal transfer. Moreover, as a key element of the system, at least the second magnetic element has electrical resistance blocking means therein for minimizing the formation and/or flow of eddy currents in the second magnetic element when in the presence of a magnetic field. Thus, with eddy currents minimized or eliminated, the transfer of power into the implantable part may be made more efficient. 
     In accordance with yet a further aspect of the invention, there is provided a method for reducing power losses associated with the transfer of energy into an implantable medical device from an external device via inductive coupling. For such method, it is understood that the implantable medical device has a first magnetic element therein adapted to be magnetically attracted to a second (non-implanted) magnetic element. The method includes the steps of: (1) positioning the first magnetic element relative to an implanted coil within the implantable medical device so that when the first magnetic element is maximally magnetically attracted to the second magnetic element, the implanted coil is aligned with an external coil for efficient inductive coupling; and (2) configuring the first (implanted) magnetic element so as to minimize the formation of eddy currents therein when the second magnetic element is in the presence of a magnetic field. 
     It is thus an object of the present invention to provide an ICS system that efficiently transfers signals and power between an external portion and an implanted portion. 
     It is another object of the present invention to provide an implant device that reduces the amount of energy lost to the magnet or keeper, thereby increasing the efficiency of the implant device. 
     It is a further object of the invention to provide an implantable cochlear stimulator (ICS) system having sectionalized, laminated, or particle-ized magnets and/or keepers in an external portion and in an implantable portion, which magnets and/or keepers are used to hold the external portion in proper alignment with the implant portion when the ICS system is in use, and wherein the sectionalized or laminated magnets and/or keepers, or other magnetic elements made from small electrically-isolated magnetic particles, reduce the amount of energy lost in the magnets or keepers, thereby making energy transfer between the two components more efficient. 
    
    
     BRIEF DESCRIPTION OF THE 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 diagram of an implantable medical system, such as an implantable cochlear stimulation (ICS) system; 
     FIG. 2 illustrates the proper alignment between two coils in order to achieve optimum inductive coupling between the coils when one of the coils is spaced apart from the other; 
     FIG. 3A schematically illustrates all implanted coil aligned with an external coil in order to achieve optimum power transfer between the two coils; 
     FIG. 3B schematically illustrates the implanted and external coils of FIG.  3 A and further shows the use of a permanent magnet and/or keeper in order to hold the two coils a proper aligned relationship, and further illustrates other components that are typically used within an implanted device and an external device; 
     FIG. 4 is a perspective view of a circuit board on which a coil and magnet are mounted, along with other circuit components, for use within an ICS; 
     FIG. 5A shows a front view of a rectangular-shaped sectionalized magnet; 
     FIG. 5B shows a side view of the sectionalized magnet of FIG. 5A; 
     FIG. 6A illustrates one embodiment of a sectionalized cylindrical magnet; 
     FIG. 6B is a side view of the sectionalized cylindrical magnet of FIG. 6A; 
     FIG. 7 shows a perspective view of another embodiment of a rectangular magnet that may be used within an ICS; 
     FIG. 8 depicts a perspective view of a rectangular-shaped laminated keeper that may be used within an ICS in accordance with a preferred embodiment of the invention; 
     FIG. 9A illustrates another embodiment of a particle-based magnet which is sintered with a dielectric; and 
     FIG. 9B shows an enlarged view of a portion of the magnet of FIG. 9A, and illustrates the particles and dielectric. 
     Corresponding reference characters indicate corresponding components throughout the several views of the drawings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     The following description is of the best mode presently contemplated for carrying out the invention. This description 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 FIG. 1, there is shown a simplified block diagram of an implantable medical system  10 . As seen in FIG. 1, the system  10  includes an implant device  12  and an external device  14 . The implant device  12  is implanted, i.e., located subcutaneous, or underneath the skin  16  of a patient. The external device  14  is located external to the patient, i.e., is not implanted within the patient, although typically the external device  14  will be located adjacent the skin  16  of the patient, and may be worn next to the skin  16  of the patient on a continual or part-time basis. 
     The external device  14  is also typically coupled electrically to a controller/processor  18 , which controller/processor  18  may also be worn or carried by the patient. One or more sensors  20  is typically connected to the controller/processor  18  in order to provide the controller/processor  18  with sensed information that determines, in part, the type of control signals that the controller/processor  18  sends to the external device  14  for communication to the implant device  12 . A suitable power source  21 , e.g., a battery, provides operating power for the entire system  10 . 
     The external device  14  is electrically coupled to the implant device  12  through the use of an external coil  22  (located within the external device  14 ) and an implant coil  24  (located within the implant device  12 ). It should be noted that the implant coil  24  may also be referred to as a receiving coil  24 , and the external coil  22  may be referred to as the transmission coil  22 , inasmuch as the coil  22  transmits power and/or control information (represented by the wavy arrow  30  in FIG. 1) that are received by the coil  24 . For simplicity, FIG. 1 shows power/signals  30  being sent only from the external device  14  to the implant device  12 . However, it is to be understood that signals may also be sent (transmitted) from the implant device  12  to the external device  14 . 
     The medical system  10  shown in FIG. 1 is intended to generically apply to many different types of medical systems, e.g., tissue or nerve stimulators, implantable sensors or monitors, and the like. 
     A preferred medical system  10  for purposes of the present invention is an implantable cochlear stimulator (ICS) system. In such ICS system, the implant device comprises an ICS ( 12 ), and includes an electrode array (not shown) that is intended to be implanted within the cochlea of the patient. The implant coil  24 , and related electrical circuitry, and then implanted in a convenient location, e.g., behind the ear of the patient. Further in such system, the external device comprises a headpiece ( 14 ) intended to be magnetically attracted to and held in position on the outside of the patient&#39;s skin, adjacent the ICS. The headpiece ( 14 ) is then connected to a speech processor ( 18 ) , and the speech processor in turn is coupled to a microphone ( 20 ). 
     In operation, the microphone ( 20 ) senses audible sounds, which are conveyed to the speech processor ( 18 ). Note, in some embodiments, the processor ( 18 ) and microphone ( 20 ) may be included within the same housing as the headpiece ( 14 ). The speech processor ( 18 ) then processes the sensed sounds, and sends appropriate electrical control signals to the headpiece ( 14 ) for transmission as control/power signals ( 30 ) to the receiving coil ( 24 ) of the ICS ( 12 ). The ICS ( 12 ) derives its operating power from the signals ( 30 ) thus received, and further receives control information from the signals ( 30 ) thus received. This control information indicates which electrodes of its electrode array should provide an electrical stimulus to the cochlea, and the amplitude of such stimulus. In this manner, then, the nerves in the cochlea of a deaf patient are provided with a pattern of electrical stimuli representative of sounds sensed through the microphone ( 20 ), thus affording the patient the sensation of “hearing”. 
     As explained more fully below, in order to achieve an optimum signal and power transfer between the implant coil  24  and the external coil  22 , it is necessary that the coils  22  and  24  be properly aligned with each other. Such alignment has typically been achieved by including a first magnet  26  in the external device and a second magnet  28  in the implant device. In some instances, the second magnet  28  may be replaced with a magnetic element, i.e., a magnet keeper, or an element that is not a magnet, but rather is an element that creates a low reluctance path for magnetic flux, and which is thereby strongly attracted to the first magnet  26 . The use of a magnetic keeper may be desirable, for example, if the patient perceives that there may someday be a need to be subjected to magnetic resonance imaging (MRI). MRI and implanted magnets are not compatible with each other inasmuch as the presence of the implanted magnet could interfere with the MRI process. Moreover, the strong magnetic fields associated with MRI could damage an implanted magnet. 
     Regardless of whether the implanted magnetic element  28  is a magnet or a magnetic keeper, the magnetic attraction between the two magnetic elements  26  and  28 , represented in FIG. 1 by the arrow  32 , not only serves to properly align the two coils  22  and  24  so that optimum signal/power transfer can occur, but also provides a holding force that maintains the external device  14  in its desired position adjacent the skin  16  of the patient. In the case of an ICS system, for example, the magnetic attraction serves to hold the headpiece ( 14 ) behind the ear of the patient, in proper alignment with the implanted ICS ( 12 ). 
     The presence of the magnet elements  26  and  28 , in close proximity to the coils  22  and  24 , which close proximity is required in order to maintain the desired alignment between the coils, disadvantageously also degrades the transfer of power to the implant device. This is because some of the power transmitted from the external device is lost within the magnet elements  26  and  28 , as explained more fully below. The present invention is directed to particular designs and configurations for the magnetic elements  26  and  28  that minimize the power losses that occur in such elements. By minimizing such losses, the operating efficiency of the system  10  may advantageously be improved, thereby allowing, e.g., a longer operating time between battery recharges, or a smaller battery (power source  21 ) to be used. 
     To better understand and appreciate why losses occur with the magnetic elements  26  and  28  when in the presence of a magnetic field, reference is made to FIGS. 2 and 3. FIG. 2 illustrates the proper alignment between two coils  22 ′ and  24 ′ in order to achieve optimum coupling between the coils when one of the coils, e.g., coil  24 ′, is spaced apart from the other coil  22 ′, by at least the thickness of the skin  16 . It is a well known principle of physics that when an electrical current I 1  flows within a coil  22 ′, a magnetic field B, represented by the arrow  34  in FIG. 2, is created. By convention, the magnetic field B has a magnitude and direction associated with it, with the arrow  34  pointing in the direction of the north pole associated with the magnetic field B. It is helpful to think of a magnetic field B as having magnetic flux associated therewith, which magnetic flux flows out from the magnet in the direction of the magnetic&#39;s north pole, spreads out and returns to the magnet at the magnet&#39;s south pole. 
     If the magnetic flux created by the current I 1  in coil  22 ′ varies as a function of time, i.e., if the current I 1  is an ac current as opposed to a dc current, it also induces a current I 2  in a coil  24 ′ that is aligned with the coil  22 ′. The magnitude of the current I 2  induced in coil  24 ′ by the varying magnetic flux created by current I 1  is a function of how much of the magnetic flux created by current I 1  flowing in coil  22 ′ passes through coil  24 ′. A maximum current I 2  is induced in coil  24 ′ when a maximum amount of varying magnetic flux passes through coil  24 ′. Such maximum current I 2  occurs when the coil  24 ′ is properly aligned with the coil  22 ′. The best alignment between two coils occurs when the distance separating the coils is minimized, and the centers of the coils are coaxial. 
     When two coils are aligned such that an ac signal (electrical current I 1 ) applied to one induces an ac signal (electrical current I 2 ) in the other, the coils are said to be “inductively coupled” with each other. It is noted that inductive coupling is the principle upon which many electromagnetic components operate, e.g., transformers. That is, as is known in the art, a transformer is used to transfer power from one circuit, connected to one of the coils, to another circuit, connected to the other coil, without a direct electrical connection between the coils or circuits. Through proper design control, e.g., selecting the number of turns in the coils, spacing between coils, etc., it is possible to achieve a desired signal transformation as the signal is transferred from one circuit to the other. 
     Inductive coupling is typically the principle used to transfer power from an external device  14  to an implant device  12 , e.g., an ICS. That is, a carrier signal having a selected frequency F 1 , is applied to coil  22 ′, so as to cause an ac current I 1  to flow through the windings of the coil  22 ′. The flow of current I 1  causes a corresponding alternating magnetic field to be created, which alternating magnetic field also passes through coil  24 ′ and induces an ac current I 2  in the coil  24 ′. The frequency of the current I 2  is the same as the frequency of the current I 1 . 
     Through appropriate electrical circuitry, e.g., a rectifier circuit, the power associated with the current I 2  may be recovered and used to power the implant device  12 . Control signals may also be transferred from the external device  14  to the implant device  12  by modulating the amplitude of the current I 1  with a modulated control signal at a frequency F 2 , where F 2  is typically much less than the frequency F 1 . Such modulated signal may then be recovered from the current I 2 , induced on the implant coil  24 ′, using conventional demodulation techniques. 
     FIG. 3A schematically illustrates the desired alignment between the implanted coil  24 ′ and the external coil  22 ′. Each coil is shown in cross section with a dot within a circle, i.e., the symbol “⊙”, signifying an electrical current that is flowing out of the plane of the paper, and with an “x” within a circle, i.e., the symbol “{circle around (x)}”, signifying an electrical current that is flowing into the plane of the paper. Such are conventional symbols used in the electrical arts. Thus, as shown in FIG. 3A, the current I 1  and the current I 2 , at a given instant of time, are flowing out of the plane of the paper at the top of the coil, and are flowing into the plane of the paper at the bottom of the coil. The current I 1  flowing in this direction creates the magnetic field B having the polarity (direction) shown, which in turn induces the current I 2  flowing in the direction shown. These directions change or alternate, as the direction of flow of current I 1  changes. 
     The proper alignment between coils  22 ′ and  24 ′ is achieved when as much of the magnetic flux as possible associated with the magnetic field B (created in the external coil  22 ′) passes through the implanted coil  24 ′. Where there is a non-zero lateral separation distance “d” between the two coils, it is not possible for all of the magnetic flux created in coil  22 ′ to pass through coil  24 ′. However, by aligning the centers of the coils so that each is co-axial with the other, and by keeping the distance “d” as small as possible, it is possible for much of the magnetic flux created in coil  22 ′ to also pass through coil  241 , thereby providing efficient inductive coupling between the two coils. 
     For illustrative purposes only, the implanted coil  24 ′ is depicted in FIG. 3A as having just two turns, while the external coil  22 ′ is depicted as having three turns. The number of turns used in each of the implanted and external coils will vary, of course, depending upon the particular application and design. 
     FIG. 3B schematically illustrates a preferred way for packaging an implant device  12  and external device  14 . The implant device  12  includes an implanted coil  24 ′ (represented as having 4 turns) mounted within an implant housing  38 . The external device similarly has an external coil  22 ′ (represented as having 8 turns) mounted within an external housing  40 . The implant coil  24 ′ of the implant device  12  is mounted on a suitable printed circuit (pc) board  42 , or other substrate, held within the housing  38 . The magnetic element  28  is also mounted on the pc board  42 , centered within the coil  24 ′. Other circuit elements, e.g., an integrated circuit (IC) processor  46 , and electrical components  50 , such as capacitors, resistors, and the like, are also mounted on the pc board. Similarly, the external coil  22 ′ of the external device  14  is mounted on a suitable pc board  44 , or other substrate, held within the external housing  40 . The magnetic element  26  is also mounted on the pc board  44 , centered within the coil  22 ′. Other circuit elements, e.g., an IC processor/controller  48 , and electrical components  50 , such as capacitors, resistors, and the like, are also mounted on the pc board. The magnetic field created by the current I 1  flowing through the coils  22 ′ is represented by the dotted lines  34 . 
     The implant housing  38  must be made from a suitable biocompatible material, e.g., glass or ceramic or other material that allows a magnetic field to readily pass therethrough (so that inductive coupling is not hampered). The external housing  40  may be made from any suitable material, e.g., plastic, that does not interfere with inductive coupling. A suitable housing for use with the implant device  12  is described in U.S. Pat. No. 4,991,582, incorporated herein by reference. 
     FIG. 4 shows a perspective view of a circuit board  52  on which an implant coil  24 ′ and magnet  28  are mounted, along with other circuit components  50  for use within an ICS. The assembly shown in FIG. 4 also includes a smaller transmit coil  54  for allowing signals to be transmitted from the implant device  12  to an external device  14 . The assembly shown in FIG. 4 is adapted to be inserted into a housing of the type described in the referenced &#39;582 U.S. patent. 
     As should be evident from the foregoing, the typical implant medical device  12  employs a magnet, or magnetic element  28 , positioned near or within an implant coil  24 ′. Magnetic flux, which represents the medium or vehicle by which power is transferred into the implant device, passes through the magnetic element  28 . 
     As is known from physics, every electrical current has a magnetic field associated therewith. Similarly, every varying magnetic field, or varying magnetic flux, induces a current or voltage when a conductive medium is present. For purposes of the present invention, a desired current is inducted in the implant coil  22 ′. However, the magnetic element  28  also represents a conductive medium within the magnetic field in which an undesired current is induced. The undesired current induced in the magnetic element  28 , for purposes of this application, is referred to as an “eddy” current, and such eddy current flows in a direction that is transverse to the direction of the magnetic flux. Such eddy current is dissipated in the resistance associated with the conductive medium. The power represented by the current dissipated in the resistance may be expressed as [I(e)] 2 R, where I(e) is the magnitude of the eddy current and R is the resistance of the conductive medium in which the eddy current is dissipated. The power thus dissipated is manifest as heat, and represents an energy loss. 
     In order to make the transfer of energy into the implant device more efficient, it is thus an object of the present invention to minimize the lost energy associated with the formation of eddy currents. This may be done by decreasing the resistance of the conductive medium wherein the eddy currents flow, and/or by minimizing the amplitude of the eddy currents formed. Of these two energy-loss-reduction techniques, decreasing the amplitude of the eddy currents is the most effective because the energy dissipated varies as the square of the eddy current amplitude. 
     In accordance with the present invention, the amplitude of the eddy currents formed in the conductive medium used for the implant magnetic element  28 , and/or the external magnetic element  26 , is achieved by creating high resistance barriers to eddy current flow, thereby minimizing the amplitude of any eddy currents that are formed. Such high resistance barriers, in turn, are created by sectionalizing or laminating the magnets or magnetic elements which are used. 
     For example, with reference to FIG. 5A, there is shown a front view of a rectangular-shaped sectionalized magnet  28 ′ made in accordance with the teachings of the present invention. FIG. 5B shows a side view of the sectionalized magnet  28 ′ of FIG.  5 A. As seen in FIGS. 5A and 5B, the sectionalized magnet is made from individual magnetic elements  60 , having a rectangular or square cross section, and having one side polarized as a north pole and one sized polarized as a south pole. A multiplicity of such elements  60  are bonded together, using a suitable dielectric bonding agent, such as epoxy, so as to create a rectangular-shaped magnet  28 ′, one face of which is a south pole, and the other face of which is a north pole. Thus, a dielectric boundary layer  62  is created between each of the sections  60 . This dielectric boundary layer  62  represents a high resistance barrier to any eddy currents which might otherwise flow within the magnetic elements in the direction of the arrow  64  (FIG.  5 B). 
     FIG. 6A illustrates one embodiment of a sectionalized cylindrical magnet  26 ′, which is the preferred shape of the magnet within the external device  14 . It is to be noted, however, that a rectangular shaped magnet could also be used within the external device  14 , if desired. The shape of the magnet is not important. What is important is that the magnet be sectionalized in a way so that a high resistance barrier is created which minimizes the amplitude of any eddy currents within the magnetic material. 
     FIG. 6B is a side view of the sectionalized cylindrical magnet of FIG.  6 A. Note from these figures that the cylindrical magnet is sectionalized into thin slices  66 . Wedge-shaped openings  68  may optionally be made in each slice at desired locations in each slice. Although shown in FIG. 6B as being wedge-shaped, such openings may in practice comprise a narrow slot. These wedge- or other-shaped openings are filled with a suitable dielectric (insulative) material, thereby providing a high resistance barrier to any eddy currents that might tend to flow around or near the periphery of the slice. The dielectric material also serves as a bonding agent or cement that glues the slices together to form the sectionalized magnet. 
     It is noted that the wedge-shaped openings are optional and need not always be employed. That is, for many applications, simply using stacked layers, slices or segments to form the cylindrical magnet will be sufficient to keep eddy current losses at a minimum. Further, it is also possible to utilize a coiled (spiraling) lamination for the cylindrical magnet so long as the ends of the coil or spiral are not electrically connected to each other. 
     FIG. 7 shows a perspective view of another embodiment of a rectangular magnet that is preferably used within an implantable cochlear stimulator (ICS) ( 12 ) or within a headpiece ( 14 ) used with the ICS. Such sectionalized magnet is made up of five individual magnetic elements or sections  60 ′, each of which is bonded to an adjoining section by way of a suitable bonding agent or cement that forms a dielectric layer  62 ′. The dielectric layer  62 ′ provides a very high resistance barrier that minimizes eddy current formation. Each section  60 ′ has approximate dimensions of 0.070 by 0.070 by 0.350 inches, which means the assembled sectionalized magnet has approximate dimensions of 0.070 by 0.350 by 0.352 inches, where the additional 0.002 inches represents the approximate combined thickness of the dielectric bonding agent. Any suitable dielectric cement or epoxy may be used to bond the magnetic sections together. A representative epoxy is “MD20”, available from Master Bond, Inc., of Hackensack, N.J. 
     A five-piece sectionalized magnet as shown in FIG. 7, when used in an ICS system, results in a significant energy loss reduction. For example, tests conducted to date with the five-piece magnet shown in FIG. 7, have increased coil Q (quality factor) from 22 to 30 at 200 KHz. Although these results (obtained using the five-piece magnet shown in FIG. 7) are somewhat dependant upon the load connected to the inductive coupled coils, the tests conducted indicate that the overall power transfer losses are reduced by approximately 20%. 
     FIG. 8 depicts a perspective view of a rectangular-shaped laminated magnetic keeper  70  that may be used within an ICS in accordance with a preferred embodiment of the invention. A magnetic keeper provides a low reluctance path for the magnetic flux, but is not itself a magnet, and resists being permanently magnetized. Thus, the magnetic keeper  70  provides an ideal element  28 ″ for use within an implant device  12  where MRI may someday be needed. The particular magnetic keeper embodiment illustrated in FIG. 8 is intended for use within an ICS. As seen in FIG. 8, the keeper  70  utilizes thirty-five individual layers  72  that are laminated together using a suitable insulative bonding agent or cement. While the overall dimensions of the magnetic keeper  70  may be suited for a particular application, for an exemplary ICS application, the dimensions maybe, e.g., 0.350 by 0.355 by 0.070 inches. Thus, each individual segment or layer has dimensions that are approximately 0.350 inches long by 0.070 inches high by 0.010 inches thick. 
     The individual laminated layers of the keeper  70  may be made from any suitable material. Preferred materials include silicon steel or Hiperco Alloy 50. Silicon steel is a common material that is commercially available from numerous sources. Hiperco Alloy 50 may be obtained from Carpenter Technology Corporation, a Division of Carpenter Steel Company, of Auburn, Calif. 
     FIG. 9A illustrates another embodiment of a particle-based magnet that may be used with the invention. The particle-based magnet  80  is made from many magnetic particles  82  which are electrically-isolated from each other. The particles  82  are typically sintered and shaped, as desired, and immersed or embedded within a dielectric  84 . FIG. 9B shows an enlarged view of a portion of the magnet  80  of FIG. 9A, and schematically illustrates the particles  82  and dielectric  84 . During the sintering process, the individual magnetic particles  82  are subjected to a external magnetic field in order to align such particles in a desired polarity. Further details associated with such a particle-based magnet may be found in U.S. Pat. No. 5,594,186, entitled “High Density Metal Components Manufactured by Powder Metallurgy”, incorporated herein by reference. Commercially, such a particle-based magnet  70  may be made from a material known as “Accucore”, available from Magnetics International, Inc., of Burns Harbor, Ind. 
     As described above, it is thus seen that the present invention provides an implant system that efficiently transfers signals and power between an external portion and an implanted portion. That is, it is seen that the invention provides an implant device that reduces the amount of energy lost to the magnet or keeper, thereby increasing the efficiency of the implant device. 
     As further described above, it is seen that the invention provides an implantable cochlear stimulator (ICS) system having sectionalized or laminated magnets and/or keepers in an external portion and in an implantable portion, wherein such magnets and/or keepers are used to hold the external portion in proper alignment with the implant portion when the ICS system is in use, and wherein the sectionalized or laminated magnets and/or keepers reduce the amount of energy lost in the magnets or keepers, thereby making energy transfer between the two components more efficient. 
     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.