Abstract:
The invention is directed to an implanted microphone having reduced sensitivity to vibration. In this regard, the microphone differentiates between the desirable and undesirable vibration by utilizing at least one motion sensor to produce a motion signal when an implanted microphone is in motion. This motion signal is used to yield a microphone output signal that is less vibration sensitive. In a first arrangement, the motion signal may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. In another arrangement, the motion signal may be utilized to actuate at least one actuator. Such an actuator may be capable of applying a force to move the implantable microphone or an implant capsule so as to reduce movement of a microphone diaphragm relative to the skin of a patient which covers the microphone diaphragm.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS  
       [0001]     This application claims priority under 35 U.S.C.  119  to U.S. Provisional Application No. 60/518,537 entitled: “Active Vibration Attenuation for Implantable Microphone,” having a filing date of Nov. 7, 2003; the contents of which are incorporated herein as if set forth in full. 
     
    
     FIELD OF THE INVENTION  
       [0002]     The present invention relates to implanted microphone assemblies, e.g., as employed in implantable hearing instruments, and more particularly, to implanted microphone assemblies having reduced sensitivity to vibration.  
       BACKGROUND OF THE INVENTION  
       [0003]     In the class of hearing aid systems generally referred to as implantable hearing instruments, some or all of various hearing augmentation componentry is positioned subcutaneously on, within, or proximate to a patient&#39;s skull, typically at locations proximate the mastoid process. In this regard, implantable hearing instruments may be generally divided into two sub-classes, namely semi-implantable and fully implantable. In a semi-implantable hearing instrument, one or more components such as a microphone, signal processor, and transmitter may be externally located to receive, process, and inductively transmit an audio signal to implanted components such as a transducer. In a fully implantable hearing instrument, typically all of the components, e.g., the microphone, signal processor, and transducer, are located subcutaneously. In either arrangement, an implantable transducer is utilized to stimulate a component of the patient&#39;s auditory system (e.g., ossicles and/or the cochlea).  
         [0004]     By way of example, one type of implantable transducer includes an electromechanical transducer having a magnetic coil that drives a vibratory actuator. The actuator is positioned to interface with and stimulate the ossicular chain of the patient via physical engagement. (See e.g., U.S. Pat. No. 5,702,342). In this regard, one or more bones of the ossicular chain are made to mechanically vibrate, which causes the ossicular chain to stimulate the cochlea through its natural input, the so-called oval window.  
         [0005]     As may be appreciated, hearing instruments that propose utilizing an implanted microphone will require that the microphone be positioned at a location that facilitates the receipt of acoustic signals. For such purposes, an implantable microphone may be positioned (e.g., in a surgical procedure) between a patient&#39;s skull and skin, for example, at a location rearward and upward of a patient&#39;s ear (e.g., in the mastoid region).  
         [0006]     For a wearer a hearing instrument including an implanted microphone (e.g., middle ear transducer or cochlear implant stimulation systems), the skin and tissue covering the microphone diaphragm may increase the vibration sensitivity of the instrument to the point where body sounds and the wearer&#39;s own voice, conveyed via bone conduction, may saturate internal amplifier stages and thus lead to distortion. Also, in systems employing a middle ear stimulation transducer, the system may produce feedback by picking up and amplifying vibration caused by the stimulation transducer.  
         [0007]     Certain proposed methods intended to mitigate vibration sensitivity may potentially also have an undesired effect on sensitivity to airborne sound as conducted through the skin. It is therefore desirable to have a means of reducing system response to vibration, without affecting sound sensitivity. This is the goal of the present invention.  
       SUMMARY OF THE INVENTION  
       [0008]     In order to achieve this goal, it is necessary to differentiate between the desirable case, caused by outside sound, of the skin moving relative to an (stationary) implant housing, and the undesirable case, caused by bone vibration, of an implant housing moving relative to the (stationary) skin, which will result in the inertia of the skin exerting a force on the microphone diaphragm.  
         [0009]     According to a primary aspect of the invention, differentiation between the desirable and undesirable cases is achieved by utilizing at least one motion sensor to produce a signal when an implanted microphone is in motion (e.g., relative to an intertial mass). Such a sensor may be, without limitation, an acceleration sensor and/or a velocity sensor. In any case, the signal is indicative movement of the implanted microphone diaphragm. In turn, this signal is used to yield a microphone output signal that is less vibration sensitive.  
         [0010]     The motion sensor(s) may be interconnected to an implantable support member for co-movement therewith. For example, such support member may be a part of an implantable microphone or part of an implantable capsule to which the implantable microphone is mounted.  
         [0011]     In the first arrangement, the implantable microphone may comprise a microphone housing, an external diaphragm disposed across an aperture of the housing, and a microphone transducer interconnected to the microphone housing and operable to provide an output signal responsive to movement of the diaphragm. Such output signal may be supplied to an implantable stimulation transducer for middle ear, inner ear and/or cochlear implant stimulation. In this arrangement, the motion sensor(s) may be interconnected to the microphone housing and/or the microphone transducer for co-movement therewith. An example of a middle ear stimulation transducer arrangement is described in U.S. Pat. No. 6,491,622, hereby incorporated by reference.  
         [0012]     In the second arrangement, the implanted microphone may be supportably interconnected within an opening of an implant capsule, wherein the external diaphragm is located to receive incident acoustic waves and a microphone transducer is hermetically sealed within the implant capsule. In this arrangement, the motion sensor(s) may be interconnected to the implant capsule for co-movement therewith. Such implant capsule may also hermetically house other componentry (e.g., processor and/or circuit componentry, a rechargeable energy source and storage device, etc.) and may provide one or more signal terminal(s) for electrical interconnection (e.g., via one or more cables) with an implantable stimulation transducer for middle ear or cochlear implant stimulation.  
         [0013]     In either arrangement, the motion sensor(s) may be positioned such that an axis of sensitivity of the sensor is aligned with a principal direction of movement of the microphone diaphragm. Such a principal direction of movement may be substantially normal to a surface (e.g., a planar surface) defined by the diaphragm. Such alignment of the motion sensor may allow for enhanced detection of undesired movement between the diaphragm and overlying tissue (e.g., skin). More preferably, such an axis of sensitivity may extend through the center of mass of the microphone. This may allow for more accurately identifying movement of the microphone as an assembly. Accordingly, the center of mass of the microphone assembly and motion sensor(s) may be located on a common axis that may also be directed normal to the principal direction of movement of the microphone diaphragm. In an arrangement where a plurality of motion sensor(s) are employed, the sensors may be positioned so that their centroid or combinative center of mass is located on such a common axis.  
         [0014]     In another aspect utilizing a motion sensor to yield a microphone output signal that is less vibration sensitive, the output of the motion sensor may be processed with an output of the implantable microphone transducer to provide an audio signal that is less vibration-sensitive than the microphone output alone. For example, the motion sensor output may be appropriately scaled, phase shifted and/or frequency-shaped to match a difference in frequency response between the motion sensor output and the microphone transducer output, then subtracted from the microphone transducer output to yield a net, improved audio signal employable for driving a middle ear transducer, an inner ear transducer and/or a cochlear implant stimulation system.  
         [0015]     In a yet further aspect of the invention, the motion sensor output may be utilized by a controller to provide a control output to at least one actuator. Such an actuator may be capable of moving an implantable microphone assembly housing or an implant capsule (e.g., relative to a vibrational source), so as to substantially reduce movement of the microphone diaphragm relative to the skin of a patient which covers the microphone diaphragm. By way of example only, a piezo-electric, electromagnetic, or acoustic actuator(s) may be employed.  
         [0016]     As noted, in certain arrangements the motion sensor(s) may be interconnected to a part of an implantable microphone for co-movement therewith. In such arrangements, the actuator(s) may be interconnected to an implant capsule and actuatable to apply forces to the microphone (e.g., the microphone housing) so as to reduce undesired movement of the external diaphragm. In such arrangements, a compliant member may be interposed between the microphone assembly and that portion of the implant capsule to which the actuator(s) is interconnected. As further noted above, in certain arrangements the motion sensor(s) may be interconnected to an implant capsule. In turn the motion sensor(s) may be interconnected to a proof mass, i.e., a reference mass for the motion sensor(s). In such arrangements, the actuator(s) may be interconnected to the microphone (e.g., the microphone housing) and actuatable to apply forces against the implant capsule and/or the motion sensor (e.g., a proof mass of the sensor) to reduce undesired movement of the external diaphragm. Further, a compliant member may be interposed between the implant capsule and a patient&#39;s skull or other anatomical structure upon implantation, allowing forces of the actuator to move the implant capsule relative to the skull or other anatomical structure.  
         [0017]     Preferably, in each of the noted arrangements utilizing an actuator(s), the actuator(s) may be desirably positioned to apply a force directed along an axis extending through the center of mass of the microphone. More preferably, this axis passing through the center of mass of the microphone may also be aligned with a principal direction of movement of the microphone diaphragm. Further, the motion sensor(s) and actuator(s) may be located on a common axis that may pass through the center of mass of the microphone and/or be aligned with the principal direction of movement of the diaphragm. Further, where a plurality of actuators are employed, the actuators may be desirably positioned so that the centroid or combinative center of mass of such actuators is located on such a common axis.  
         [0018]     In a related aspect, a method for attenuating undesired movement of an implantable microphone is provided. The method includes generating a motion signal that is indicative of movement of an implantable support member associated with an implantable microphone diaphragm. Preferably, the implantable support member is substantially isolated from outside sound such that the motion of the member is primarily caused by undesirable sources of vibration. In response to the motion signal, a force is applied at least in part to the support member to reduce relative movement between the microphone diaphragm and tissue overlying the microphone diaphragm. In this regard, the microphone diaphragm may be moved in response to the undesired motion to reduce or attenuate relative movement between the microphone diaphragm and overlying tissue. As will be appreciated, such relative movement may result in the application of forces to the diaphragm, which may be represented as undesired sound (e.g., noise). By reducing this relative movement, the output of an implanted microphone may be enhanced for hearing purposes.  
         [0019]     In order to reduce the relative movement between the microphone diaphragm and the overlying tissue, it may be desirable to monitor the motion of the support member in a direction most likely to result in undesired relative movement. For instance, a planar diaphragm may have a primary direction of movement in a direction that is substantially normal to its planar surface. Accordingly, undesired movement in this direction may be more likely to result in undesired forced being applied to the diaphragm that may in turn be represented as undesirable sound. In this regard, a sensor operative to generate a motion signal in this direction may be utilized.  
         [0020]     Further, to reduce relative movement, it may be desirable to apply a force aligned with the primary direction of movement of the microphone diaphragm. That is, by moving the microphone diaphragm primarily in the direction that is most likely to result in undesirable sound, more relative movement may be attenuated. Accordingly, more undesirable sound may be removed from an output of the microphone. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0021]      FIG. 1  illustrates a fully implantable hearing instrument as implanted in a wearer&#39;s skull;  
         [0022]      FIG. 2  is a schematic, cross-sectional illustration of one embodiment of the present invention.  
         [0023]      FIG. 3  is a schematic, cross-sectional illustration of another embodiment of the present invention.  
         [0024]      FIG. 4  is a schematic, cross-sectional illustration of yet another embodiment of the present invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0025]     Reference will now be made to the accompanying drawings, which at least assist in illustrating the various pertinent features of the present invention. In this regard, the following description of a hearing instrument is presented for purposes of illustration and description. Furthermore, the description is not intended to limit the invention to the form disclosed herein. Consequently, variations and modifications commensurate with the following teachings, and skill and knowledge of the relevant art, are within the scope of the present invention. The embodiments described herein are further intended to explain the best modes known of practicing the invention and to enable others skilled in the art to utilize the invention in such, or other embodiments and with various modifications required by the particular application(s) or use(s) of the present invention.  
         [0000]     Hearing Instrument System:  
         [0026]      FIG. 1  illustrates one application of the present invention. As illustrated, the application comprises a fully implantable hearing instrument system. As will be appreciated, certain aspects of the present invention may be employed in conjunction with semi-implantable hearing instruments as well as fully implantable hearing instruments, and therefore the illustrated application is for purposes of illustration and not limitation.  
         [0027]     In the illustrated system, a biocompatible implant capsule  100  is located subcutaneously on a patient&#39;s skull. The implant capsule  100  includes a signal receiver  118  (e.g., comprising a coil element) and a microphone diaphragm  12  that is positioned to receive acoustic signals through overlying tissue. The implant housing  100  may further be utilized to house a number of components of the fully implantable hearing instrument. For instance, the implant capsule  100  may house an energy storage device, a microphone transducer, and a signal processor. Various additional processing logic and/or circuitry components may also be included in the implant capsule  100  as a matter of design choice. Typically, a signal processor within the implant capsule  100  is electrically interconnected via wire  106  to a transducer  108 .  
         [0028]     The transducer  108  is supportably connected to a positioning system  110 , which in turn, is connected to a bone anchor  116  mounted within the patient&#39;s mastoid process (e.g., via a hole drilled through the skull). The transducer  108  includes a connection apparatus  112  for connecting the transducer  108  to the ossicles  120  of the patient. In a connected state, the connection apparatus  112  provides a communication path for acoustic stimulation of the ossicles  120 , e.g., through transmission of vibrations to the incus  122 .  
         [0029]     During normal operation, acoustic signals are received subcutaneously at the microphone diaphragm  12 . Upon receipt of the acoustic signals, a signal processor within the implant capsule  100  processes the signals to provide a processed audio drive signal via wire  106  to the transducer  108 . As will be appreciated, the signal processor may utilize digital processing techniques to provide frequency shaping, amplification, compression, and other signal conditioning, including conditioning based on patient-specific fitting parameters. The audio drive signal causes the transducer  108  to transmit vibrations at acoustic frequencies to the connection apparatus  112  to effect the desired sound sensation via mechanical stimulation of the incus  122  of the patient.  
         [0030]     To power the fully implantable hearing instrument system of  FIG. 1 , an external charger (not shown) may be utilized to transcutaneously re-charge an energy storage device within the implant capsule  100 . In this regard, the external charger may be configured for disposition behind the ear of the implant wearer in alignment with the implant capsule  100 . The external charger and the implant capsule  100  may each include one or more magnets to facilitate retentive juxtaposed positioning. Such an external charger may include a power source and a transmitter that is operative to transcutaneously transmit, for example, RF signals to the signal receiver  118 . In this regard, the signal receiver  118  may also include, for example, rectifying circuitry to convert a received signal into an electrical signal for use in charging the energy storage device. In addition to being operative to recharge the on-board energy storage device, such an external charger may also provide program instructions to the processor of the fully implantable hearing instrument system.  
         [0000]     Vibration Attenuation:  
         [0031]      FIGS. 2, 3  and  4  show alternate embodiments of the present invention. In each embodiment a microphone assembly  10  is mounted within an opening of an implant capsule  100 . The microphone assembly  10  includes an external diaphragm  12  (e.g., a titanium membrane) and a housing having a surrounding support member  14  and fixedly interconnected support members  15 ,  16 , which combinatively define a chamber  17  behind the diaphragm  12 . The microphone assembly  10  may further include a microphone transducer  18  that is supportably interconnected to support member  15  and interfaces with chamber  17 , wherein the microphone transducer  18  provides an electrical output responsive to vibrations of the diaphragm  12 . The microphone transducer  18  may be defined by any of a wide variety of electroacoustic transducers, including for example, capacitor arrangements (e.g., electret microphones) and electrodynamic arrangements.  
         [0032]     One or more processor(s) and/or circuit component(s)  60  and an on-board energy storage device (not shown) may be supportably mounted to a circuit board  64  disposed within implant capsule  100 . In the embodiment of  FIG. 2 , the circuit board is supportably interconnected via support(s)  66  to the implant capsule  100 . In the embodiments of  FIGS. 3 and 4  the circuit board  64  is supportably interconnected via support(s)  66  to the support member  15  of the microphone assembly  10 . The processor(s) and/or circuit component(s)  60  may process the output signal of microphone transducer  18  to provide a drive signal to an implanted transducer. The processor(s) and/or circuit component(s)  60  may be electrically interconnected with an implanted, inductive coil assembly (not shown), wherein an external coil assembly (i.e., selectively locatable outside a patient body) may be inductively coupled with the inductive coil assembly to recharge the on-board energy storage device, to provide program instructions to the processor(s)  60 , etc.  
         [0033]     As may be appreciated, in the embodiments shown in  FIGS. 2, 3  and  4 , vibrations transmitted through a patient&#39;s skull will cause vibration of the implant capsule  100  and microphone assembly  10  relative to the skin that overlies the given embodiment. In this regard, the movement of the diaphragm  12  relative to the overlying skin may result in the exertion of a force on the diaphragm  12 . The exerted force may cause undesired vibration of the diaphragm  12 , which may be included in the electrical output of the transducer  18  as received sound. Forces aligned with the principal direction of movement of the diaphragm  12  are of particular interest for purposes of reducing undesired vibration. That is, forces exerted in this direction tend to result in a majority of undesired relative movement between the diaphragm  12  and overlying skin. As shown in  FIGS. 2, 3  and  4 , the diaphragm&#39;s principal direction of movement is substantially normal to the surface of the diaphragm  12 . Therefore, in the embodiments of  FIGS. 2, 3  and  4  vibrations transmitted through the patient&#39;s skull that cause movement in a direction normal to the surface of the diaphragm  12  are of primary concern.  
         [0034]     To actively address such transmitted vibration and, hence, undesired vibration of the diaphragm  12 , each of the embodiments includes a motion sensor  70  that provides an output signal proportional to the vibrational movement of the support member to which it is attached. In the  FIG. 2  and  FIG. 3  embodiments, the motion sensor  70  is supportably interconnected to the support member  15  of microphone assembly  10  via interconnect member(s)  19 . In the  FIG. 4  embodiment, the accelerometer  70  is directly mounted to a base portion of the implant capsule  100  and a proof mass  72  is interconnected thereto. As will be appreciated, motion sensor may include one or more directions or “axes” of motion sensitivity. In this regard, motion sensor may monitor motion in a single axis or in multiple axes (e.g., three axes).  
         [0035]     In each of the arrangements, the motion sensor  70  may be located such that at least one axis of sensitivity of the motion sensor  70  is aligned with the principle direction of movement of the diaphragm  12 . That is, at least one axis of sensitivity of the accelerometer  70  may be located such that it is sensitive to movement normal to the surface of the diaphragm  12 . More preferably, this axis of sensitivity may also pass through a center of mass of the microphone assembly  10 . In this regard, the movement of the microphone assembly  10  in the direction most likely to result in undesired vibration within the diaphragm  12  may be more accurately monitored. As may be appreciated, multiple motion sensor may be employed in the embodiments with corresponding analogous mounting arrangements to that shown for the motion sensor  70  in the given embodiment.  
         [0036]     With particular respect to the embodiment of  FIG. 2 , the motion sensor output signal is provided to the processor(s) and/or circuit component(s)  60  for processing together with the output signal from microphone transducer  18 . More particularly, the processor(s) and/or circuit component(s)  60  may scale and frequency-shape the motion sensor output of, for example, an accelerometer output signal to match a difference in the frequency response between such signal and the output signal of the microphone transducer  18 . In turn, the scaled, frequency-shaped accelerometer output signal may be subtracted from the microphone transducer output signal to produce a net audio signal. Such net audio signal may then be further processed and output to an implanted stimulation transducer for stimulation of a middle ear component or cochlear implant. As may be appreciated, by virtue of the arrangement of the  FIG. 2  embodiment, the net audio signal will reflect reduced vibration sensitivity.  
         [0037]     Referring now to  FIG. 3 , the motion sensor output signal may be provided to a controller  80 . In turn the controller  80  may provide a control signal to an actuator  90  (e.g., a piezo-electric actuator), wherein an actuator member  92  of the actuator  90  is provided to selectively impart forces against the support member  15  of microphone assembly so as to reduce the movement of the external diaphragm  12 , relative to the skin of a patient that covers the external diaphragm  12 . Further in this regard, the embodiment of  FIG. 2  includes a compliant member  96  (e.g., comprising an elastomer material) interposed between the microphone assembly  10  and that portion of implant capsule  100  to which actuator  90  is interconnected. The compliant member  96  facilitates reduced vibration of the microphone assembly  10  in response to forces applied thereto by actuator member  92  while providing enhanced ability of the actuator to move that portion of the microphone including the diaphragm. As shown, the compliant member  96  surrounds the microphone assembly  10  and is interconnected at its inner and outer periphery to implant capsule  100 . Numerous other arrangements are also possible, e.g., the compliant member may be interconnected between the support member  14  and implant capsule  100 .  
         [0038]     Referring now to  FIG. 4 , the motion sensor output signal may be provided to a controller  80  which in turn may provide a control signal to an actuator  90  (e.g., a piezo-electric actuator) that is interconnected to support member  15  of microphone assembly  10  via interconnect member(s)  19 . The actuator  90  includes an actuator member  92  disposed to actively impart forces against the proof mass  72  interconnected to the motion sensor  70  so as to reduce movement of the implant capsule  100 . In turn, movement of the microphone assembly  10 , including external diaphragm  12 , relative to the skin of the patient is reduced. In this embodiment, a compliant member  102  may be interposed between implant capsule  100  and the skull of a patient.  
         [0039]     In each of the  FIG. 3  and  FIG. 4  arrangements, the controller  80  may be provided so that the actuator  90  selectively reduces undesired vibrations within a predetermined frequency range of concern (e.g., 100 Hz to 10 kHz). To enhance performance, the actuator  90  may be located to exert a force that is directed in the principle direction of movement of the diaphragm  12  (e.g., normal to the surface of the diaphragm  12 ). Furthermore, it may be desirable that the actuator exerts such a force along an axis that passes through the center of mass of the microphone assembly  10 . As will be appreciated, by exerting a force aligned with an axis that passes substantially through the center of mass of the microphone assembly  10 , movement of the microphone assembly  10  along that axis may be achieved while minimizing or eliminating rotation of the assembly about one or more orthogonal axes. Further, both the motion sensor  70  and actuator  90  may be located on a common axis that passes though the center of mass of the microphone assembly  10 . Additionally, the various components mounted on circuit board  64  may be arranged so that their collective center of mass is substantially located on such a common axis passing through the center of mass of the of microphone assembly  10 . Finally, multiple actuators may be employed in the embodiments of  FIG. 3  and  FIG. 4  with corresponding analogous mounting arrangements to that shown for actuator  90  in the given embodiment.  
         [0040]     In the  FIG. 3  and  FIG. 4  embodiments, by virtue of the reduced movement of microphone assembly  10  relative to the overlying skin of a patient, the audio output signal provided by the processor(s) and/or circuit component(s)  60  (e.g., to an implanted transducer) will reflect reduced vibration sensitivity. In turn, stimulation of a middle ear transducer or cochlear implant may be enhanced.  
         [0041]     As shown in  FIGS. 3 and 4 , the motion sensor  70  and/or controller  80  may also provide output signal(s) to the processor and/or circuit component(s)  60  for generation of an enhanced audio output signal in the manner described with reference to  FIG. 2 . That is, the  FIG. 2  embodiment may be employed in combination with either of the  FIG. 3  or  FIG. 4  embodiments.  
         [0042]     Those skilled in the art will appreciate variations of the above-described embodiments that fall within the scope of the invention. As a result, the invention is not limited to the specific examples and illustrations discussed above, but only by the following claims and their equivalents.