Abstract:
A device implantable under skin is disclosed. The device includes a sealed housing containing electronics for at least stimulation or collection of data and at least one antenna for communicating with an external device, a magnet configured to hold said external device in proximity to the sealed housing. the sealed housing includes an upper cover being closest to the skin when the device is implanted, and a lower cover that is hermetically connected to the upper cover. The lower cover includes an elevated region, a recessed region, and at least one feedthrough element formed in the recessed region of the lower cover.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application is a Divisional of co-pending U.S. application Ser. No. 14/468,435, filed on Aug. 26, 2014, which claims priority under 35 U.S.C. §119(a) to application Ser. No. 13/186,153.6, filed in Europe on Sep. 26, 2013, all of which are hereby expressly incorporated by reference into the present application. 
     
    
     TECHNICAL FIELD 
       [0002]    The technical field relates to small connection ports, known in the art as feedthroughs, which may be used in subcutaneous active medical devices. A feedthrough element may include a conductor placed in a small opening in an electrically insulating material. 
       BACKGROUND 
       [0003]    Many implantable devices use feedthrough elements to connect a hermetically enclosed electronic board to an implanted device such as a measuring and/or a stimulating electrode and/or an electromechanical actuator. A feedthrough comprises an electrical connection between a hermetically closed enclosure and the outside surrounded by insulating material, which allows electrical signals to pass between the surroundings and the hermetical enclosure while maintaining the integrity of the hermetic enclosure. 
         [0004]    Implantable housings can be made from titanium. In the case of titanium housing, feedthroughs for the entire housing unit may be assembled into one main titanium body. The manufacturing of the titanium body thus requires a large number of welds, often at least one weld for each feedthrough. 
         [0005]    Sometimes, each feedthrough is directly brazed onto a titanium body and requires a complex machined titanium part. 
         [0006]    Sometimes the housing is made from alumina (aluminum oxide) which is a ceramic. Such a housing may have feedthroughs all around the outer perimeter of the ceramic. One of the technical difficulties with this design is the machining of very small holes (e.g., 0.4 mm diameter) all around the diameter of ceramic housing, which is made from a very hard material. Another issue is the cost of machining such small and precise holes, which have to be ground with diamond tools. 
       SUMMARY 
       [0007]    The disclosure describes an implantable device that may be used as a cochlear implant that overcomes the challenges noted above, providing ease of manufacturing and assembly and also a unique shape of the casing that facilitates routing of connecting electrodes to the feedthrough elements through a void created between the implanted device and the tissue of a user. 
         [0008]    In an embodiment, a device implantable under skin includes a sealed housing containing electronics for at least stimulation or collection of data and at least one antenna for communicating with an external device. The device also includes a magnet configured to hold the external device in proximity to the sealed housing. The sealed housing includes an upper cover being closest to the skin when the device is implanted and a lower cover that is hermetically connected to the upper cover, the lower cover including an elevated region, a recessed region, and at least one feedthrough element formed in the recessed region of the lower cover. 
         [0009]    In an embodiment, the at least one feedthrough element includes a plate shaped base with one or more holes, and the at least one feedthrough element is configured to connect an electrode, providing electric connection to the electronics housed within the sealed housing through conductive pins in the one or more holes. 
         [0010]    In an embodiment, the plate shaped base of the at least one feedthrough element is hermetically joined to the lower cover of the external housing. 
         [0011]    In an embodiment, the lower cover has a circular disc outer perimeter shape, and the lower cover includes an elevated part located radially adjacent to the at least one feedthrough element. 
         [0012]    In an embodiment, the elevated part is aligned radially with the at least one feedthrough element, and the elevated part is positioned farther away from a center of the lower cover. 
         [0013]    In an embodiment, the elevated region of the lower cover has a crescent shape spanning more than 50% of the lower cover, the at least one feedthrough element is surrounded on two sides by ends of the crescent shape. 
         [0014]    In an embodiment, the implantable device includes two feedthrough elements, each feedthrough element of the two feedthrough elements having a rectangular shape with rounded corners and having 14 connector pins. 
         [0015]    In an embodiment, the implantable device includes two feedthrough elements, each feedthrough element of the two feedthrough elements having a circular shape and having 4 connector pins. 
         [0016]    In an embodiment, the implantable device includes an electrically conducting lead connected to the at least one connector pin of the feedthrough element, and thereby electrically connected to the electronics in the sealed housing, a silicone overmolding surrounding the conducting lead, wherein the lead passes through a recessed region, to reach the outer circumference of the lower cover. Here the lead may connect or continue to a spirally coiled wire. 
         [0017]    In an embodiment, the upper cover has a hollow crown made of a biocompatible material and permeable to electromagnetic waves including magnetic fields. 
         [0018]    In an embodiment, the hollow crown includes an external wall forming an external radial periphery of the sealed housing, and an internal wall oriented towards a center of the sealed housing, and the external wall and the internal wall form an opening of an annular U-shaped groove. 
         [0019]    In an embodiment, the biocompatible material is aluminum oxide. It is well known that other ceramics such as zirconia toughened alumina, high purity alumina, or pure zirconia could be used for this purpose but aluminum oxide has been found to be preferable. 
         [0020]    In an embodiment, the lower cover is made of titanium. Titanium in this application denotes any titanium alloy or titanium like alloy suitable for implantation. That is any alloy which may be processed like titanium and inserted in the body without causing reaction or being degraded. 
         [0021]    In an embodiment, the sealed housing is a cochlear implant configured to be implanted under the skin of a human user and above the user&#39;s skull bone. 
         [0022]    The disclosure further describes a method of manufacturing an implantable device, whereby a number of manufacturing steps are performed:
       form a ceramic upper cover with a circumferential flange;   form a ceramic feedthrough element with a circumferential flange and a plurality of feedthrough pins;   braze a feedthrough titanium welding flange leak tight onto the circumferential flange of the ceramic feedthrough element and braze an upper cover titanium welding flange leak tight onto the circumferential flange of the ceramic upper cover;   form a titanium lower cover by stamping a titanium plate into a desired shape with a circumference an at least one opening with an edge;   weld the feedthrough titanium welding flange to the edge of the at least one opening of the titanium lower cover; and   weld the titanium lower cover onto the upper cover titanium welding flange to form a hermetically sealed enclosure with a plurality of insulated electric connections.
 
With this method a hermetic sealed enclosure may be made with very few steps and a high yield is ensured as especially the feedthrough element may be leak tested prior to the welding thereof onto the titanium lower cover. The welding between welding flanges and titanium lower cover may be performed by laser welding to minimize heat load on nearby elements such as the feedthrough pins and the electronics within the housing. The forming of the upper cover may comprise the formation of a hollow crown including an external wall forming an external radial periphery of the upper cover, and an internal wall oriented towards a center of the upper cover, and the external wall and the internal wall thus forming an opening of an annular U-shaped groove. In this case, the brazing of an upper cover titanium welding flange onto the circumferential flange of the ceramic upper cover comprises both of the brazing of one welding flange to the internal wall and the brazing of one further welding flange to an external wall. Also the welding of the upper cover titanium weld flanges to the titanium lower cover comprises welding of both internal and external upper cover weld flanges to the lower cover.
       
 
         [0029]    In an embodiment of the method, forming the titanium lower cover comprises stamping elevated parts and regions and providing a recessed region relative thereto and generating the at least one opening in a recessed region. As the elevated parts and regions are intended to abut the skull of the user in the implanted state, the opening in the recessed region will be spaced apart from the skull bone of the user. This allows for feedthrough pins to extend from the feedthrough element without interfering with the skull bone. 
         [0030]    An embodiment, the method comprise the further step of electrically connecting at least one electric lead to at least one of the metal pins outside of the hermetically sealed enclosure and cause the lead to extend in a recessed area from the pin to the outer circumference of the implantable device. At the outer circumference the leads may be joined in a spirally coiled multi-wire conductor. Thus leads may pass from the feedthrough pins to the outer regions of the housing without being subject to pressure in case the implanted housing inadvertently is pressed towards the skull bone. 
         [0031]    An embodiment of the method comprises the further step of connecting the pins inside the implantable device to a circuit board having a plurality of interconnected electronic components thereon. This processing step may be performed prior to the closing of the hermetically sealed enclosure. 
         [0032]    An embodiment of the method comprises the following additional steps:
       place the implantable device in a mould,   hold the leads in place in the recessed area,   inject hardenable fluid material into the mould in order to form an overmould which fixates the leads.
 
Preferably the hardenable fluid is a silicone, which will set into a flexible but resilient protective substance, which may absorb mechanical shocks as well as insulate the leads from the corrosive nature of body fluids.
       
 
         [0036]    An embodiment of the method comprises the following additional step: attach in a releasable manner a magnet to an exterior part of the exterior upper cover. Preferably the magnet is provided with a casing, which interfaces with a silicone intermediate part and this intermediate part ensures a connection with the hermetically sealed housing. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0037]      FIG. 1  illustrates a partial cross section view of an example of a cochlear implant housing with an external antenna related to the disclosure. 
           [0038]      FIG. 2A  illustrates a partial cross section view of an example of a cochlear implant housing according to an embodiment of the disclosure. 
           [0039]      FIG. 2B  illustrates a bottom view of an example of cochlear implant housing with a multipolar feedthrough element according to an embodiment of the disclosure. 
           [0040]      FIG. 2C  illustrates a bottom view of an example of a feedthrough element with  4  connection poles in a housing according to an embodiment of the disclosure. 
           [0041]      FIG. 2D  illustrates a detailed view of an example of a feedthrough element with  4  connection poles according to an embodiment of the disclosure. 
           [0042]      FIG. 2E  illustrates an example of construction details of a cochlear implant housing according to an embodiment of the disclosure. 
           [0043]      FIG. 3A  illustrates a cross section view of an example of a cochlear implant according to an embodiment of the disclosure. 
           [0044]      FIG. 3B  illustrates an enlarged portion of the cross section view of an example of a cochlear implant according to an embodiment of the disclosure. 
           [0045]      FIG. 3C  illustrates a cross section view of an example of a cochlear implant according to an embodiment of the disclosure. 
           [0046]      FIG. 3D  illustrates a cross sectional view corresponding to  FIG. 3B , but now with the a mold over silicone shealding. 
       
    
    
     DETAILED DESCRIPTION 
       [0047]    Neurostimulation implants can be used to stimulate and/or measure electrophysiological signals. An example of a neurostimulation implant is a cochlear implant as illustrated in  FIG. 1 . 
         [0048]    The cochlear implant includes an internal portion  100  which is surgically implanted in a patient (e.g., under the skin on the skull) and an external portion  120  which attaches externally above the implanted portion. In the example of  FIG. 1 , the cochlear implant includes an implantable hermetic housing  101  and an external antenna  108 . The implantable hermetic housing  101  includes electronics  102 , a receiving/transmitting antenna  103 , and a magnet  104  that holds the external portion  120  with the antenna  108  in position. The external antenna  108  can thus communicate with the electronics  102  in the implantable hermetic housing. The antennas  103 ,  108  may be coils, whereby magnetic energy and information may be transferred from the one coil to the other. 
         [0049]    The design of housing  101  is based on a main body  105  made from a ceramic, such as alumina, hermetically closed with a flat titanium cover  106 . The device can be implanted under a user&#39;s skin with the main body  105  oriented toward the skin (toward the outside of the user) and titanium cover oriented toward inside of the user. The titanium cover could be adjacent to the skull bone. 
         [0050]    The main body  105  includes a plurality of feedthroughs  107  and provides mechanical protection for electronics  102 , an air-tight and fluid-tight seal (hermetic seal) and electric insulation of the feedthroughs. As shown in  FIG. 1 , a feedthrough includes a pin made of conductive material  117  inserted into a small hole  118  formed in the main body  105 . The feedthroughs  107  are arranged radially around the outer circumference of main body  105 . 
         [0051]      FIGS. 2A and 2B  illustrate another example of a cochlear implant shown without the corresponding external device. In  FIG. 2A  the right hand side is a sectional view, whereas the left hand side is a side-view and in  FIG. 2B  the section line and side view are indicated. Thus the implant is shaped as an annular object with a central hole  218  or opening. This central hole  218  serves to receive a magnet  314  as shown in  FIG. 3C , which serves the same purpose as the prior art magnet  104 . The implant includes a subcutaneous hermetic housing  201 , which has a ceramic surface  202  on the side which faces the skin of the user, in order to allow receiving of energy by electromagnetic coupling of a coil of an external device (not shown). The implant also includes a U-shaped main body  203 , made of biocompatible ceramic. The U-shaped main body  203  has a U-shaped cross sectional profile, as shown in  FIG. 2A . This shape creates space within the main body to accommodate various components such as electronics board  208 . The U-shaped main body  203  can be manufactured with a Ceramic Injection Molding (CIM) process and offers a solid and strong shape against multiple external constrains such as pressure, impact and shock. According to  FIG. 2A , the U-shaped body is annularly shaped to circumvent the central hole  218 , wherein the magnet  314  is insertable, however the magnet  314  (see  FIG. 3C ) could well, in an alternative thereto, be placed to circumvent the U-shaped body, in which case no central hole would be provided. Also both a centrally placed and a circumferential magnetic means could be employed. 
         [0052]      FIG. 2B  shows a view from the bottom of the cochlear implant, and displays the bottom surface of stamped titanium cover  206 . The titanium cover  206  can be manufactured by stamping to obtain the desired shape. 
         [0053]    Apart from stamping from a rolled plate item, other ways of processing the disc like item are possible, such as shaping by machining out of a solid body or by metal powder techniques. A well known powder processing techniques comprises a first step of pressing a metal powder and a binder into a semi solid body which is later heat treated or sintered into a solid metal body of the desired shape. Possibly a final machining step is necessary to achieve desired tolerances. A further powder technique uses a laser beam which melts titanium power in a layer. By repetition of layers, the part is built (like fast prototyping with polymer). A step of high temperature sintering is needed to obtain the final density on the part 
         [0054]    As shown in  FIG. 2B , the stamped titanium cover  206  includes elevated parts  210  and an elevated region  211 . These elevations  210 ,  211  are elevated relative to the plane of the cover to abut a common plane indicated by dashed line  228  seen in  FIG. 3A , and thus create a recessed region  220 . When the cochlear implant is implanted in a user, between skin and bony tissue (such as on the skull of the user), the elevated parts  210  and elevated region  211  abuts against the bony tissue, while there remains a void between the bone tissue and the recessed region  220 . This void is useful for routing leads of electrodes from remote locations on the user&#39;s body to the implanted device. The leads can thus pass through the recessed region  220  and are protected from shock and impact by the cochlear implant supported on the elevated parts  210  and elevated region  211 . As seen in  FIG. 2A  connection pins  205  extend out of a plate  225  and into, but not beyond the region between plane  228  and the recessed region  220 . 
         [0055]    In an embodiment, elevated parts  210  may be left out of the stamped titanium cover  206 , but instead support on the skull bone may be created by the addition of a silicone distance mat, which is added on top of the recessed region of the stamped titanium cover  206 . In this case the stamped cover  206  would be flat in the entire recessed region without elevated parts. The protection of the leads would be created by the silicone mat being interposed between the leads and the recessed area in that particular region. Thus, the same functionality may be provided and create a secure path for electrodes without actually shaping elevated parts  210  in the titanium cover. 
         [0056]      FIG. 2B  illustrates an embodiment with two multipolar feedthrough elements  204 . In this embodiment each multipolar feedthrough element  204  includes 14 pins  205 , whereby each pin forms a connection pole. The feedthrough element  204  may comprise a base shaped as a plate  225 . The number of pins and the shape of the feedthrough elements are not limited to the illustrated embodiment. 
         [0057]    Each multipolar feedthrough element  204  may be made and the holes  227  created with the use of classic processing technique for implantable devices: a ceramic plate  225  with a first and a second flat side is initially made and provided with circular holes  227  directly connecting the first and the second sides, a platinum iridium pin  205  is inserted into each hole  227 , a feedthrough metal welding flange  216 B preferably made from titanium is added to a circumference flange of the ceramic plate  225 , and a gold brazing metal is used in a brazing process to fuse the inserted pins  205  and the titanium welding flange  216 B to the ceramics of the plate  225 . By this process an air and fluid tight electrically insulating plate  225  is provided with a multitude of electrical connections from the first to the second side. 
         [0058]    By creating feedthrough elements  204  separately from the stamped titanium cover  206 , it is possible to manufacture the titanium cover  206  through a stamping process and the multipolar feedthrough elements may be assembled onto the stamped titanium cover  206  by laser welding due to the feedthrough titanium welding flange  216 B on the feed-through ceramic plate  225 . This example of multipolar feedthrough elements  204  has a rectangle shape with rounded edges  207  which allows a continuous laser welding process in the assembly of the ceramic plate and the titanium cover  206 . In this way, feedthrough elements  204  and their connections to measuring and/or stimulation electrode leads are protected against direct constraints from the environment such as pressure, impact or shock. 
         [0059]    Assembly of multipolar feedthrough element  204  may well be achieved by a direct mounting process such as used in surface mounted devices (SMD) where there is already a well laid out and well established process road for manufacturing in both large and smaller numbers. In the above assembly process steps, it is the process steps up to and including the fusing of the ceramic plate with the pins and metal flange which are most error prone, however, each feedthrough element comprising ceramic plate  225  with the metal pins  205  and feedthroug welding flange  216 B may be tested prior to installment in the titanium cover  206 , and nonfunctional parts, such as parts not being leak proof may be discarded. This is opposed to the prior art feedthrough generation, where the holes  118  are generated along the circumference of the ceramic main body  105 , and in case one hole with inserted pin  117  comes out not leak proof, the entire main body has to be discarded, as an individual pin  117  is not exchangeable. This is at a time where a lot of processing hours and expensive material has been incorporated into the main body, and the result is poor yield. 
         [0060]      FIG. 2A  illustrates some internal components including electronics board  208 . 
         [0061]    Electronics board  208  is mounted by the pins  205  that enter into holes of electronics board  208  before they are soldered to gain contact with the circuitry embedded in the electronic board. These pins  205  pass also through the sealed holes  227  of the feedthrough elements  204 .  FIG. 2E  provides additional detail through an enlarged view of a cross section of the cochlear implant. 
         [0062]      FIG. 2E  illustrates an example of the construction of the implantable hermetic housing  201 . Inner and outer titanium welding flanges  216 A may be placed between the U-shaped main body  203  and the stamped titanium cover  206 . A titanium feedtrhough welding flange  216 B may be placed between the feedthrough element  204  and the stamped titanium cover  206 . The components may initially be brazed at brazing locations  217  in an oven to fuse the welding flanges  216 A,  216 B to the ceramic plate  225  and main body  203  respectively. The laser weld process finalizes the hermetically sealed hosing  201 . A laser weld  211  runs along the entire circumference of the main body  203  and has a weld intersection parallel to the common plane  228 . A laser weld  212  runs along the inner circumference of the main body  203  and has a weld intersection which is perpendicular to the common plane  228 , and lesser welds  215  runs along the perimeter of each ceramic plate  225  of every feedthrough element and also here the weld intersection is perpendicular to the common plane  228 . The advantages of the laser welds are that they are leak tight seams which may be generated without any production of fumes or gasses, and at the same time heat dissipation to brazed areas nearby or to the electronic components inside the housing  201  is manageable due to the short heating time and very limited metal melt zone. The laser welding may be performed in a controlled atmosphere to ensure that the atmosphere inside the housing  201 , which will be sealed off in an airtight manner by the welding process, has well known and pre-defined properties. Preferably the gas inside the hermetic chamber is a mix of argon and helium. The argon part provides for a protective atmosphere, where as the helium gas allows for leakage test. 
         [0063]      FIGS. 2C and 2D  illustrate an example of a multipolar feedthrough element that is a quad polar feedthrough element  209  having four pins  205 . The round shape of feedthrough element  209  facilitates laser welding of the feedthrough element to the stamped titanium cover  206 . 
         [0064]    An implantable connector (not shown) could be connected to the feedthrough pins  205  in order to connect leads for neuromodulation electrodes, cochlear electrode array, measuring electrodes for ECAP measures, an electromechanical actuator or antennas among others. 
         [0065]      FIGS. 3A-C  illustrates an example of additional details of components within the implantable hermetic housing  201 . As shown in  FIG. 3A , a voluminous area of the housing is formed between the inside of the U-shaped body  203  and the inside surface of the elevated region  211  of the stamped titanium cover  206 . Arrow  307  shows the height of this area, and as seen in  FIG. 3A  this height allows integration of components on both sides of board  208 , namely on the ceramic side  308  and on the lid side  309 . 
         [0066]    A tight area indicated by arrow  311  is defined between the ceramic plate  225  and the inside surface of the U-shaped body  203 . In this area, components can be integrated only on the ceramic side  308  as the lid side  309  is reserved for the feedthrough element. 
         [0067]    The ceramic side  308  may house an antenna  310  in order to be closest to the skin and the corresponding external antenna. The antenna  310  may be a coil. The lid side  309  can house the thickest components such as signal processors as it has the largest sectional depth  307 . The coil  310  couples wirelessly with a coil provided externally of the implanted housing, and energy as well as information is transmitted, through the magnetic coupling of the two coils, from the external part to the internal part, and an information signal may pass from the coil  310  of the implanted part to the external antenna. Possibly the implanted device comprises a rechargeable battery to facilitate the transmission of a wireless signal from the implanted part to an external receiver antenna and also to supplement the energy consumed by the electrodes in times of high demand. 
         [0068]    Alternatively or as a supplement to the antenna  310 , energy harvesting by movement may be implemented as known from mechanical wrist watches: a half-circle shaped disk rotates around its centre, caused by the unbalance and the movements of the watch by the arm. This rotation winds the clock spring. Such a system may be added into the implanted device, together with the housing. Here the rotation from the half-disk is used to drive a small generator, designed to produce power and able to charge a small rechargeable battery—designed to supply the cochlear implant. The energy harvester could be designed in many ways: another example is a magnet in a tube with a coil around it, able to move back and forth according to the movement of the head. This principle is known from the battery-free so-called shake flashlights. To facilitate the smaller size of the implant, the rotating system may be placed in a separate cabinet, implanted elsewhere in the head and connected to the cochlear implant through a wire. If the implant is placed right under the skin, a solar cell in the unit could add energy for charging during the day. However, the skilled person would appreciate that the energy harvester may also be placed at a different location in-vivo. 
         [0069]    As shown in  FIG. 3B , the recessed region  220  forms a space between the stamped titanium cover  206  and the skull bone tissue  302 . The wires or leads  303  which connect the pins in the feed-through to a device external to the housing  201 , such as to electrodes, sensors, antennas or transducers pass in this space wherein they are protected against shock and impact by a silicone overmolding  304  as seen in  FIG. 3C  and by the elevated parts and regions. 
         [0070]    As seen better in  FIG. 3C , the leads  303  pass out from the region of the housing and form a spiral  305  which is able to absorb forces that could be applied to the lead  303 . The spiral  305  is able to be stretched, folded and bend and can thus adapt to the individual surgery and the shape of the mastoidectomy as well as adapt to cranial growth and other changes which may take place after surgical implant of the device. The spiraled coil is wound around a pin, which is then drawn out to leave a void  310  at the center of the spiraled coil. Along the spiral, placed inside the void  310  left by the pin, or outside it such as along the ground electrode an antenna lead for FM communication may be placed. Also possibly any of the ground electrode, a measuring electrode, a stimulation electrode, or a lead passing over the top of the head to an implant at an opposed side of the head, may be used additionally as a radio antenna. Any inside or outside surface of the implanted housing or the circuitry board  208  may serve as a carrier for a radio frequency antenna such as a patch antenna or a rod antenna. Such antennas could allow the implanted part to communicate with external units by Bluetooth or similarly coded protocols, which could provide a wider band-width of the communication between external part and implanted part, than what is obtainable by means of the coil  310 . This requires an additional radio to be incorporated into the internal part. The higher frequencies used in usual RF transmission of information lead to a high degree of attenuation when transmitted through human tissue, however, the external antenna part and the implanted part are placed in very close proximity and are also located in well known positions with respect to each other, which allows for antenna designs with a high degree of directionality to be used, and also their closeness to each other situates the external and internal antennas within the near field of each other, and these two fact may ensure very good coupling between such two antennas, and this may overcome the problems of attenuation of the RF frequency signals transmitted through the tissues of the user. A similar argument goes for RF frequency transmission of signals between two implanted devices placed at each side of the head, whether the signals are transmitted directly from implanted part to implanted part, or signals are exchanged from one external part to the other, or from one external part to both of two implanted parts being placed at each side of the head of a user. One particular frequency band which would be open to such communication RF signals would be the band around 2.4 G Hz used for Bluetooth and Bluetooth low energy transmission. A patch antenna with a directional characteristic is disclosed in WO2007019855 and such an antenna could be used. 
         [0071]    The potential mix-up of the two BTE and antenna parts for the respective left and right ear can cause problems for users with an implant at each ear, because of differences in the two implants and/or stimulation schemes for the left and right ears. Also in school classes with many pupils carrying similar implant and external parts, such a mix-up may take place between pupils. An ID-chip, such as an RFID chip in each implanted part for identification is available and need only to communicate a short distance to the BTE (Behind The Ear) part or to the antenna part and to such a purpose only limited power and a small antenna is needed. A simple hand-shake procedure between external part and implant may be instigated prior to on-set of transmission of sound signals, to ensure that it is the correct external part, and not a part belonging to the other ear or a school friend. The identification hand shake may take place by means of the coil antennas in the external and internal parts, however here the communication is not so fast. In US2005/0255843A such an identification scheme is disclosed, which allows proprietary communication using magnetically coupled coils between two separate devices, such as a first and a second hearing aid sitting on each one of a users ears. This technique could also be implemented and used between an implanted part and an external part, provided the internal part has some energy storage capacity, eg a battery, which would allow it to transmit its own identification code to the external part when prompted. 
         [0072]      FIG. 3D  shows how the overmold with a hardenable substance such as silicone encapsulates the housing  201 . The silicone fills the void made under the housing by the recesses and elevated parts of the titanium cover  206  whereby all leads in the area are fixated and protected both against shock and tissue fluids of the body. Also al the pins of each feed-through are completely embedded in the silicone and thereby protected. 
         [0073]    While various aspects and embodiments have been disclosed herein, other aspects and embodiments will be apparent to those skilled in the art. The various aspects and embodiments disclosed herein are for purposes of illustration and are not intended to be limiting, with the true scope and spirit being indicated by the following claims. 
       LIST OF ELEMENTS 
       [0000]    
       
           100  internal portion 
           101  implantable hermetic housing 
           102  electronics 
           103  receiving antenna 
           104  magnet 
           105  main body from ceramic 
           106  flat titanium cover 
           107  feedthrough 
           108  external antenna 
           117  conductive material pin 
           118  small hole 
           120  external portion 
           201  subcutaneous hermetic housing 
           202  ceramic surface 
           203  u-shaped main body 
           204  multipolar feedthroughs 
           205  pin(s) 
           206  stamped titanium cover 
           207  rounded edge 
           208  electronics board 
           209  quad polar feedthrough 
           210  elevated part 
           211  elevated region 
           212  outer laser weld 
           213  inner laser weld 
           215  feed through laser welds 
           216 A upper cover titanium welding flange 
           216 B feedthrough titanium welding flange 
           217  brazing locations 
           218  central hole 
           220  recessed region 
           225  ceramic plate 
           227  hole 
           228  common plane 
           302  skull 
           303  wires 
           304  silicone overmolding 
           305  spiral 
           306  lead 
           307  voluminous area arrow 
           308  ceramic side 
           309  lid side 
           310  antenna 
           311  tight area arrow 
           314  exchangeable magnet