Patent Publication Number: US-6707920-B2

Title: Implantable hearing aid microphone

Description:
FIELD OF THE INVENTION 
     The present invention related to the field of implantable hearing aid devices, and in particular, to implantable hearing aid microphones employable in fully- and semi-implantable hearing aid systems. 
     BACKGROUND OF THE INVENTION 
     Traditional hearing aids are placed in a user&#39;s ear canal. The devices function to receive and amplify acoustic signals within the ear canal to yield enhanced hearing. In some devices, “behind-the-ear” units have been utilized which comprise a microphone to transduce the acoustic input into an electrical signal, some type of signal processing circuitry to modify the signal appropriate to the individual hearing loss, an output transducer (commonly referred to in the field as a “receiver”) to transduce the processed electrical signal back into acoustic energy, and a battery to supply power to the electrical components. 
     More recently, a number of different types of fully- or semi-implantable hearing aid devices have been proposed. By way of primary example, implantable devices include those which employ implanted electromechanical transducers for stimulation of the ossicular chain and/or oval window (see e.g., U.S. Pat. No. 5,702,342), and those which utilize implanted exciter coils to electromagnetically stimulate magnets fixed within the middle ear (see e.g., U.S. Pat. No. 5,897,486). In these as well as other implanted devices, acoustic signals are received by an implantable microphone, wherein the acoustic signal is converted to an electrical signal that is employed to drive an actuator that stimulates the ossicular chain and/or oval window. 
     As may be appreciated, such implantable hearing aid microphones must necessarily be positioned at a location that facilitates the receipt of acoustic signals and effective signal conversion/transmission to an implanted actuator. For such purposes, implantable hearing aid microphones are most typically positioned in a surgical procedure between a patient&#39;s skull and skin, at a location rearward and upward of a patient&#39;s ear (e.g., in the mastoid region). 
     Given such positioning, the size and ease of installation of implantable hearing aid microphones are primary considerations in the further development and acceptance of implantable hearing aid systems. Further, due to the subcutaneous location of implantable hearing aid microphones, it is important that effective and efficient amplification be provided to yield a high fidelity signal. Relatedly, the componentry cost of providing such amplification is of importance to achieving widespread use of implantable system. Finally, it is important that the overall design of implantable microphones mitigate servicing/replacement needs. 
     SUMMARY OF THE INVENTION 
     In view of the foregoing, a primary objective of the present invention is to provide an implantable hearing aid microphone having a relatively small profile, particularly in the lateral extent. 
     Another objective of the present invention is to provide an implantable hearing aid microphone that reduces the extent of exposed surfaces for tissue attachment/infiltration, thereby reducing the potential need/periodicity of microphone servicing/replacement. 
     An additional objective of the present invention is to provide an implantable hearing aid microphone that is reliable and cost effective. 
     Yet further objectives of the present invention are to provide an implantable hearing aid microphone that is relatively robust and that provides for effective and efficient acoustic signal conversion to yield a high fidelity signal for middle ear stimulation. 
     One or more of the above objectives and additional advantages are realized in the implantable hearing aid microphone apparatus comprising the present invention. Such apparatus includes a housing having an internal chamber with an aperture thereto defined by a peripheral rim surrounding the aperture. A first diaphragm is sealably positioned across the aperture. Additionally, a microphone having a second diaphragm is disposed within the internal chamber to define an enclosed volume between the first and second diaphragms for mechanically amplifying acoustic signals received by the first diaphragm. 
     In one aspect of the present invention, the first diaphragm is recessed relative to the peripheral rim surrounding the aperture. More particularly, the first diaphragm may be preferably recessed between about 0.5 mm and 1.0 mm relative to the peripheral rim of the housing and across the lateral extent of the first diaphragm. Further, the outer edge of the peripheral rim may be disposed in a first plane and at least an outer face of the first diaphragm may be flat and disposed in parallel relation to the first plane. 
     In another aspect of the present invention, the internal chamber may be defined to comprise at least a first portion having a first cross-sectional area adjacent to the first diaphragm, and a second portion extending away from the first portion about an axis transfer to the aperture and/or first diaphragm and having a second cross-sectional area adjacent to the second diaphragm. Preferably, the first cross-sectional area is greater than the second-sectional area. Relatedly, it is preferable that the first diaphragm having an effective cross-sectional area (i.e., the area exposed for receipt of acoustic signals) that is at least about 100 times greater than the effective cross-sectional area of the second diaphragm. 
     The second portion of the internal chamber may adjoin the first portion internal chamber at a reduced opening therebetween, wherein the opening is smaller than and is positioned in opposing relation to the aperture. Further, the aperture and the opening may be coaxially aligned and may each be of circular configuration. 
     In one arrangement, the second portion of the internal chamber may be of an L-shaped configuration, wherein an opening between the first and second portions of the internal chamber is located at an end of a first leg of the second portion. In turn, the second diaphragm is positioned in a second leg of the second portion. Preferably, both the first and second legs of the second internal chamber portion, as well as the first internal chamber portion may, each be of a cylindrical configuration. Further, the first and second legs of the L-shaped second internal chamber portion may adjoin an internally rounded elbow. 
     In yet another aspect of the present invention, the first diaphragm may comprise a biocompatible material. By way of primary example, the first diaphragm may comprise a material selected from a group consisting of titanium and titanium-alloys. Further, it is preferable that the maximum cross-width of the first diaphragm (i.e., as measured across the area exposed for receipt of acoustic signals) established between about 8 and 15 millimeters, and most preferably between about 10-12 millimeters. Further, it is preferable that the first diaphragm thickness be established at between about 10 and 20 microns across the lateral extent thereof, and most preferably between about 12 and 15 microns. 
     By virtue of the above-noted features, an implantable microphone may be provided to reduce exposed surfaces for tissue infiltration. Further, a microphone may be constructed to reduce lateral space requirements upon surgical installation. Additionally, a microphone may be readily fabricated and assembled in a cost effective manner, while also yielding effective, high-quality signal amplification capabilities. 
     Additional aspects and advantages of the present invention will be apparent to those skilled in the art upon review of the further description that follows. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is isometric, cross-sectional view of one embodiment of the present invention. 
     FIGS. 2A and 2B are cross-sectional and top views, respectively, of the embodiment shown in FIG.  1 . 
     FIGS. 3A and 3B are cross-sectional and top views, respectively, of an alternate embodiment of the present invention. 
    
    
     DETAILED DESCRIPTION 
     FIGS. 1,  2 A and  2 B illustrate one embodiment of an implantable hearing aid microphone comprising the present invention. The microphone embodiment  10  comprises a housing  20  that defines an internal chamber  30 . The chamber  30  has an aperture  42  across which a first diaphragm  52  is sealably disposed. In the illustrated embodiment, housing  20  includes a base member  22  and a peripheral member  24  defining the aperture  42 . The peripheral edge of the first diaphragm  52  is fixedly interconnected between the base member  22  and peripheral member  24  of the housing  20  (e.g., via laser welding). 
     As best shown by FIG. 2A, the first diaphragm  52  is recessed relative to the outer peripheral member  24 . In this regard, it is preferable that the first diaphragm  52  be recessed a distance t relative to the outer rim of peripheral member  24 , wherein preferably 0.5 mm&lt;t&lt;1.0 mm. Further, it is preferable that the outer, peripheral rim of the peripheral member  24  lie substantially within a first plane, and that at least an outer surface of the first diaphragm  52  be configured (i.e., flat) and positioned in a substantial parallel relationship to the first plane. 
     As illustrated in FIGS. 1 and 2A, internal chamber  30  may be provided to include a first portion  32  and a second portion  34 . The first portion  32  is disposed adjacent to the first diaphragm  52 . The second portion  34  adjoins and extends away from the first portion  32  at an opening  44  therebetween and about an axis that is transverse to the first diaphragm  52  and aperture  42 . As shown, opening  44  may be of a reduced cross-sectional area relative to aperture  42 . 
     In the microphone embodiment  10 , the second internal chamber portion  34  may be of L-shaped configuration, wherein the second portion  34  comprises a first leg  34   a  that extends away from the first internal chamber portion  32  about an axis that is substantially perpendicular to a center plane of the first diaphragm  52 . The second internal chamber portion  34  further includes a second leg  34   b  interconnected to the first leg  34   a  at a rounded elbow  34   c.    
     Aperture  42  and opening  44  may each be of a circular configuration and may each be aligned about a common center axis. Correspondingly, such common center axis may be aligned with a center axis for first diaphragm  52  which may also be of a circular shape. Further, the first internal chamber portion  32  and first leg  34   a  of the second internal chamber portion  34  may each be of a cylindrical configuration, and may each be aligned on the same center axis as aperture  42  and opening  44 . The second leg  34   b  of the second portion  34  of chamber  32  may be disposed to extend substantially perpendicularly from the first leg  34   a  of the second portion  34 . As such, it can be seen that the second leg  34   b  may share a wall portion  36  with the first portion  32  of the internal chamber  30 . 
     As shown in FIGS. 1 and 2A, the above-noted second diaphragm  54  is disposed at the interface between the first leg  34   a  and second leg  34   b  of the second chamber portion  34 . More particularly, the second diaphragm  54  may be provided at a port of a conventional hearing aid microphone  60  which is disposed within the second leg  34   b  of the second chamber portion  34 . In this regard, conventional hearing aid microphone  60  may comprise an electret condenser microphone. By way of example, conventional hearing aid microphone  60  may comprise a microphone unit offered under the name Model FG, offered by Knowles Electronics of Itasca, Ill. In this regard, the second diaphragm  54  may be provided as part of the conventional hearing aid microphone  60 . As may be appreciated, hearing aid microphone  60  may be provided with electrical power and control signals and may provide an electrical output signal, each of which signals are carried by corresponding signal lines  70   a ,  70   b  or  70   c.    
     In use, the microphone embodiment  10  may be surgically implanted in the mastoid region of a patient, wherein the aperture  42  and the first diaphragm  52  are positioned immediately adjacent to and facing the skin of the patient. Upon receipt of an acoustic signal the first diaphragm  52  will vibrate to act upon the enclosed volume within chamber  30  and thereby mechanically amplify the acoustic signal as received by the second diaphragm  54 . In this regard, it has been found that the effective cross-sectional area (i.e., the area exposed to the receipt of acoustic signals) of the first diaphragm  52  should be at least about 100 times greater than the effective cross-sectional area of the second diaphragm  54 . Such one hundred-fold size differential provides for about 100 times amplification of acoustic signals (40 dB), thereby compensating for the attenuation associated with acoustic signal passage through a patient&#39;s skin tissue. 
     Upon receipt of the acoustic signals at the second diaphragm  54 , the conventionally microphone device  60  will convert the mechanical acoustic signal into an electrical signal for output via one of the signal lines  70   a ,  70   b  or  70   c . In turn, such output signal may be further conditioned and/or directly transmitted to an internal hearing aid actuator device that stimulates the ossicular chain and/or tympanic membrane. In one approach, the output signal may be provided to an electromechanical transducer having a probe positioned to mechanically stimulate the incus. 
     The housing  20  and first diaphragm  52  are preferably constructed from biocompatible materials. In particular, titanium and/or biocompatible titanium-containing alloys may be utilized for the construction of such components. With particular respect to the first diaphragm  52  it is preferable that the material utilized and thickness thereof be established to yield resonant frequency above about 8 kHz when mechanically loaded by tissue, wherein the resonance preferably has no greater than about a 20 dB excursion. Further, attenuation effects of the first diaphragm  52  are preferably no more than 10 dB from about 250 Hz to 5.5 kHz. By way of example, first diaphragm  52  may comprise titanium, and may be of a flat, disk-shaped configuration having a thickness of between about 10 and 20 microns, and most preferably between about 12 and 15 microns. 
     Referring again now to FIG. 1 as well as FIGS. 3A and 3B, optional features that may be employed in conjunction with the present invention are illustrated. In particular, FIG. 1 illustrates in phantom lines the inclusion of a support member  80  that is located within the first portion  32  of the internal chamber  30  of housing  20 . As illustrated, the support member  80  may include a cylindrical, peripheral flange  82  as well as a support plate  84 . The peripheral flange  82  may be interconnected to the internal cylindrical surface of the base member  22  (e.g., via laser welding). 
     The support plate  84  is positioned to be spaced a predetermined distance r away from a back surface of a first diaphragm  52 . In this regard, the opposing surface of plate member  84  and first diaphragm may each be substantially flat and disposed in parallel relation. Preferably, distance r is between about 1.0 and 5.0 microns. In order to provide for the passage of acoustic signals therethrough, the support plate  84  may comprise a number of apertures  86 , including a central aperture coaxially aligned with aperture  42  and opening  44 . In use, the support member  80  provides a mechanism to limit over-deflection of the first diaphragm  52 . 
     The embodiments described above are for exemplary purposes only and are not intended to limit the scope of the present invention. Various adaptations, modifications and extensions will be apparent to one skilled in the art and are intended to be within the scope of the invention as defined by claims which follow.