Patent Publication Number: US-2012029267-A1

Title: Electromagnetic Bone Conduction Hearing Device

Description:
This application claims priority from U.S. Provisional Patent 61/356,717, filed Jun. 21, 2010, which is incorporated herein by reference. 
    
    
     FIELD OF THE INVENTION 
     The present invention relates to medical implants, and more specifically to a novel transcutaneous auditory prosthetic implant system. 
     BACKGROUND ART 
     A normal ear transmits sounds as shown in  FIG. 1  through the outer ear  101  to the tympanic membrane (eardrum)  102 , which moves the ossicles of the middle ear  103  (malleus, incus, and stapes) that vibrate the oval window  106  and round window  107  membranes of the cochlea  104 . The cochlea  104  is a long narrow duct wound spirally about its axis for approximately two and a half turns. It includes an upper channel known as the scala vestibuli and a lower channel known as the scala tympani, which are connected by the cochlear duct. The cochlea  104  forms an upright spiraling cone with a center called the modiolar where the spiral ganglion cells of the cochlear nerve  105  reside. In response to received sounds transmitted by the middle ear  103 , the fluid-filled cochlea  104  functions as a transducer to generate electric pulses which are transmitted to the cochlear nerve  105 , and ultimately to the brain. 
     Hearing is impaired when there are problems in the ability to transduce external sounds into meaningful action potentials along the neural substrate of the cochlea  104 . To improve impaired hearing, auditory prostheses have been developed. For example, when the impairment is related to operation of the middle ear  103 , a conventional hearing aid or middle ear implant may be used to provide acoustic-mechanical stimulation to the auditory system in the form of amplified sound. Or when the impairment is associated with the cochlea  104 , a cochlear implant with an implanted stimulation electrode can electrically stimulate auditory nerve tissue with small currents delivered by multiple electrode contacts distributed along the electrode. 
     Middle ear implants employ electromagnetic transducers to convert sounds into mechanical vibration of the middle ear  103 . A coil winding is held stationary by attachment to a non-vibrating structure within the middle ear  103  and microphone signal current is delivered to the coil winding to generate an electromagnetic field. A magnet is attached to an ossicle within the middle ear  103  so that the magnetic field of the magnet interacts with the magnetic field of the coil. The magnet vibrates in response to the interaction of the magnetic fields, causing vibration of the bones of the middle ear  103 . See U.S. Pat. No. 6,190,305, which is incorporated herein by reference. 
     U.S. Patent Publication 20070191673 (incorporated herein by reference) describes another type of implantable hearing prosthesis system which uses bone conduction to deliver an audio signal to the cochlea for sound perception in persons with conductive or mixed conductive/sensorineural hearing loss. An implanted floating mass transducer (FMT) is affixed to the temporal bone. In response to an externally generated electrical audio signal, the FMT couples a mechanical stimulation signal to the temporal bone for delivery by bone conduction to the cochlea for perception as a sound signal. A certain amount of electronic circuitry must also be implanted with the FMT to provide power to the implanted device and at least some signal processing which is needed for converting the external electrical signal into the mechanical stimulation signal and mechanically driving the FMT. 
     SUMMARY OF THE INVENTION 
     Embodiments of the present invention are directed to an implantable hearing prosthesis for a recipient patient. An implantable attachment magnet is fixable beneath the skin of the patient to underlying skull bone and is adapted to magnetically connect with an external attachment magnet over the skin. An implantable signal transducer also is fixable beneath the skin of the patient to underlying skull bone and is adapted to transform a magnetic audio signal from an external signal drive coil into a corresponding mechanical stimulation signal for delivery by bone conduction of the skull bone as an audio signal to the cochlea. A connector member flexibly connects and positions the attachment magnet a fixed distance from the signal transducer. 
     The attachment magnet and/or the signal transducer may include an outer ring magnet having a first magnetization direction and inner core magnet having an opposite second magnetization direction. The signal transducer may be adapted for fixed attachment to the skull bone by a pair of radially opposed bone screws, and/or into a recessed transducer well in the skull bone. The signal transducer may be hermetically enclosed, or enclosed by a biocompatible membrane. 
     Embodiments of the present invention also include an external component for an implantable hearing prosthesis of a recipient patient. An external attachment magnet is fixable on the skin and is adapted to magnetically connect with an implanted attachment magnet beneath the skin. An external signal drive coil provides a magnetic audio signal to a cooperating implant signal transducer beneath the skin. A connector member flexibly connects and positions the external attachment magnet a fixed distance from the signal drive coil. 
     Such embodiments may also include a processor housing containing the external attachment magnet, and a signal processor within the processor housing for generating an electrical audio signal output for development by the signal drive coil as the magnetic audio signal. There may be at least one sensing microphone for developing an audio input signal to the signal processor. And an external ring magnet may surround the signal drive coil and cooperate with a corresponding ring magnet in the implant signal transducer. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows anatomical structures of a typical human ear. 
         FIG. 2  shows a cross-sectional view of an implantable hearing prosthesis arrangement according to an embodiment of the present invention. 
         FIG. 3  A-B shows top plan views of the outside and internal structures of an external component for an embodiment of the invention. 
         FIG. 4  shows a top plan view of the implant portion of an embodiment of the invention. 
     
    
    
     DETAILED DESCRIPTION OF SPECIFIC EMBODIMENTS 
     Various embodiments of the present invention are directed to an implantable hearing prosthesis for a recipient patient. An implant component and an external signal drive component each have two main lobes characterized by a distinctive magnet arrangement and a flexible connector member that maintains a constant distance between the two main lobes. One of the external main lobes contains a sensing microphone, an audio signal processor, and an attachment magnet which magnetically connects with a corresponding implant attachment magnet that forms one of the implant main lobes. The other external main lobe contains a ring drive magnet surrounding an electromagnetic signal drive coil that generates a magnetic drive signal from the signal processor which is representative of sound detected by the sensing microphone. The other implant main lobe is a ring magnet arrangement that is fixed to the skull bone to magnetically couple the magnetic drive signal to the skull bone which delivers the signal to the cochlea by bone conduction where it is sensed as sound by the patient. 
       FIG. 2  shows a cross-sectional view of one exemplary embodiment of the present invention including an implantable attachment magnet  202  which is fixable beneath the skin  205  of the patient to underlying skull bone  218 . The implantable attachment magnet  202  magnetically connects with a corresponding external attachment magnet  208  over the skin  205 . An implantable signal transducer  203  magnetically cooperates with corresponding external signal drive coil  204  that provides an externally generated magnetic audio signal to couple a corresponding mechanical stimulation signal to the skull bone  218  for delivery by bone conduction as an audio signal to the cochlea. An implant connector member  216  flexibly connects and positions the attachment magnet  202  a fixed distance from the signal transducer  203 . A corresponding external component  201  includes an external attachment magnet  208  that is fixable on the skin  205  to magnetically connect with the implant attachment magnet  202  beneath the skin  205 . An external signal drive coil  204  provides the magnetic audio signal to the implant signal transducer  203  beneath the skin  205 . An external connector member  217  flexibly connects and positions the external attachment magnet  208  a fixed distance from the signal drive coil  204 . 
     In the embodiment shown in  FIG. 2 , the implant attachment magnet  202  is specifically implemented as an outer ring magnet  210  having a first magnetization direction and inner core magnet  209  having an opposite second magnetization direction. Likewise, the signal transducer  203  also includes an outer ring magnet  214  having a first magnetization direction and inner core magnet  213  having an opposite second magnetization direction. Such ring magnet arrangements minimize problems that can arise from strong external magnetic fields such as with magnetic resonance imaging. This subject is explored more fully in U.S. Provisional Patent Application 61/227,632, filed Jul. 22, 2009; which is incorporated herein by reference. In the embodiment shown in  FIG. 2 , the external attachment magnet  208  is a typical disk-shaped magnet sized adapted to magnetically connect with the inner core magnet  209  of the implant attachment magnet  202 . In other embodiments, the external attachment magnet  208  may be like the implant attachment magnet  202  in having an inner core magnet that is surrounded by an outer ring magnet, both of which are sized and adapted to optimize the magnetic connection with the implant attachment magnet  202 . Similarly, the external signal drive coil  204  shown in the embodiment in  FIG. 2  includes an outer ring magnet  212  sized and magnetically adapted to optimize the cooperation with the outer ring magnet  214  of the implanted signal transducer  203 . The inner core  211  of the signal drive coil  204  includes an electromagnetic coil (with or without a core) that produces the magnetic audio signal which is coupled across the skin to the implanted signal transducer  203 . 
       FIG. 3  A-B shows top plan views providing further detail regarding the outside and internal structures of the external component  201 . The external attachment magnet  208  is contained within a processor housing  301  made of an impact resistant material such as plastic. A battery compartment  302  contains a battery power supply  304  that provides electrical power to the external component  201 . The processor housing  301  also contains openings for one or more sensing microphones  207  that sense the nearby acoustic environment and generate a representative microphone signal output. A signal processor  305  within the processor housing  301  receives the microphone signal and generates a corresponding electrical stimulation signal output. Signal leads  303  in the flexible member  217  couple the electrical stimulation signal from the signal processor  305  to the signal drive coil  204  for output to the implant. 
       FIG. 4  shows a top plan view providing further detail regarding the implant portion used in  FIG. 2 . The implant signal transducer  203  may be adapted for fixed attachment to the skull bone  218  by one or more bone screws  215  through corresponding flange openings  401  distributed around the outer circumference of the implant signal transducer  203 . Alternatively or in addition, some embodiments may be adapted for fixation of the signal transducer  203  in a prepared recessed transducer well in the skull bone  218 . The lobe of the signal transducer  203  and/or the lobe of the implant attachment magnet  202  may be hermetically enclosed such as with a biocompatible membrane. 
     One advantage embodiments of the present invention possess which is lacking in earlier arrangements such as FMT-based systems is that there is no requirement that the implanted components include electronic circuits and associated power circuitry. The prior art has to convert a received electrical signal and therefore must have some necessary functional overhead including electrical power and signal conversion circuitry. But with embodiments of the present invention there is simply no requirement for any subcutaneous electronic circuitry. 
     Although various exemplary embodiments of the invention have been disclosed, it should be apparent to those skilled in the art that various changes and modifications can be made which will achieve some of the advantages of the invention without departing from the true scope of the invention.