Abstract:
In bone conduction auditory prostheses, a suspension of the electronic components relative to the vibrating mass is beneficial for a number of reasons. The suspension systems depicted also function as a seal, so as to prevent infiltration of direct, water, or other contaminants into the housing. The present technology utilizes a combination suspension and sealing system that seals the housing of an auditory prosthesis while still providing sufficient suspension functionality.

Description:
BACKGROUND 
       [0001]    Hearing loss, which can be due to many different causes, is generally of two types: conductive and sensorineural. Sensorineural hearing loss is due to the absence or destruction of the hair cells in the cochlea that transduce sound signals into nerve impulses. Various hearing prostheses are commercially available to provide individuals suffering from sensorineural hearing loss with the ability to perceive sound. For example, cochlear implants use an electrode array implanted in the cochlea of a recipient (i.e., the inner ear of the recipient) to bypass the mechanisms of the middle and outer ear. More specifically, an electrical stimulus is provided via the electrode array to the auditory nerve, thereby causing a hearing percept. 
         [0002]    Conductive hearing loss occurs when the normal mechanical pathways that provide sound to hair cells in the cochlea are impeded, for example, by damage to the ossicular chain or the ear canal. Individuals suffering from conductive hearing loss can retain some form of residual hearing because some or all of the hair cells in the cochlea function normally. 
         [0003]    Individuals suffering from conductive hearing loss often receive a conventional hearing aid. Such hearing aids rely on principles of air conduction to transmit acoustic signals to the cochlea. In particular, a hearing aid typically uses an arrangement positioned in the recipient&#39;s ear canal or on the outer ear to amplify a sound received by the outer ear of the recipient. This amplified sound reaches the cochlea causing motion of the perilymph and stimulation of the auditory nerve. 
         [0004]    In contrast to conventional hearing aids, which rely primarily on the principles of air conduction, certain types of hearing prostheses commonly referred to as bone conduction devices, convert a received sound into vibrations. The vibrations are transferred through the skull to the cochlea causing motion of the perilymph and stimulation of the auditory nerve, which results in the perception of the received sound. Bone conduction devices are suitable to treat a variety of types of hearing loss and can be suitable for individuals who cannot derive sufficient benefit from conventional hearing aids. 
       SUMMARY 
       [0005]    In bone conduction auditory prostheses, a suspension of the electronic components relative to the vibrating mass is beneficial for a number of reasons. For example, if vibrations are isolated from the microphones, feedback can be reduced or eliminated. In another example, minimization of the vibrating coupling mass helps to maximize the transmission of vibrations through the skin. Utilizing a suspension system with a seal, so as to prevent infiltration of dirt, water, or other contaminants into the housing is desirable. However, creating too stiff of a suspension in an effort to maintain sealing capability can adversely affect the benefits attendant with a suspension system. The present technology utilizes a combination suspension and sealing system that seals the housing of an auditory prosthesis while still providing sufficient suspension functionality. 
         [0006]    This summary is provided to introduce a selection of concepts in a simplified form that are further described below in the Detailed Description. This summary is not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used to limit the scope of the claimed subject matter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0007]      FIG. 1A  depicts a partial perspective view of a percutaneous bone conduction device worn on a recipient. 
           [0008]      FIG. 1B  is a schematic diagram of a percutaneous bone conduction device. 
           [0009]      FIG. 2  depicts a cross-sectional schematic view of a transcutaneous bone conduction device worn on a recipient. 
           [0010]      FIGS. 3A and 3B  depict partial cross-sectional schematic views of external portions of transcutaneous bone conduction devices and percutaneous bone conduction devices, respectively. 
           [0011]      FIG. 4  depicts a partial cross-sectional schematic view of an external portion of a transcutaneous bone conduction device. 
           [0012]      FIG. 5A  depicts a partial cross-sectional schematic view of a bone conduction device utilizing an aspect of a sealing and suspension system. 
           [0013]      FIG. 5B  depicts an enlarged partial cross-sectional schematic view of the bone conduction device of  FIG. 5A . 
           [0014]      FIG. 6A  depicts a partial cross-sectional schematic view of a bone conduction device utilizing another embodiment of a sealing and suspension system. 
           [0015]      FIG. 6B  depicts an enlarged partial cross-sectional schematic view of the bone conduction device of  FIG. 6A . 
           [0016]      FIGS. 7A-7D  depict enlarged partial cross-sectional schematic views of bone conduction devices utilizing alternative aspects of sealing and suspension systems. 
           [0017]      FIGS. 8A-8C  depict enlarged partial cross-sectional schematic views of bone conduction devices utilizing alternative aspects of sealing and suspension systems. 
           [0018]      FIGS. 9A-9C  depict enlarged partial cross-sectional schematic views of bone conduction devices utilizing alternative aspects of sealing and suspension systems. 
           [0019]      FIG. 10  depicts a relationship between frequency and damping, for a sealing and suspension system that utilizes two materials. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The sealing and suspension technologies described herein can typically be utilized with bone conduction devices. Such devices include transcutaneous bone conduction devices that transmit vibrations through the skin of a recipient to the recipient&#39;s skull, as well as percutaneous bone conduction devices that anchor directly to a recipient&#39;s skull. Transcutaneous bone conduction devices can be biased toward the recipient&#39;s skull by a magnetic force, an adhesive, a hard or soft headband or anatomical features (such as the pinna). In percutaneous bone conduction devices, an external portion thereof is secured to a bone anchor with, e.g., a snap connection. By utilizing the sealing and suspension technologies described herein, the external portion of the bone conduction device can be sealed against intrusion of water, sweat, dirt, and so on, while still providing sufficient damping of vibration so as to reduce feedback. 
         [0021]    The technologies described herein contemplate sealing and suspension systems utilized in an external portion of a bone conduction device that can be utilized in both percutaneous and transcutaneous applications. Such devices can include a housing containing sound processing components, microphones, and a vibration element. When used in a transcutaneous application, a vibration transmission element is attached to the vibration element and held on the skin (typically via magnetic components). When used in a percutaneous application, the vibration element can be connected to the anchor that penetrates the skin, e.g., by a post or shaft having a removable snap coupling apparatus that connects to the anchor. 
         [0022]      FIG. 1A  depicts a partial perspective view of a percutaneous bone conduction device  100  positioned behind outer ear  101  of the recipient and comprises a sound input element  126  to receive sound signals  107 . The sound input element  126  can be a microphone, telecoil or similar. In the present example, sound input element  126  can be located, for example, on or in bone conduction device  100 , or on a cable extending from bone conduction device  100 . Also, bone conduction device  100  comprises a digital sound processor (not shown), a vibrating electromagnetic actuator and/or various other operational components. 
         [0023]    More particularly, sound input device  126  converts received sound signals into electrical signals. These electrical signals are processed by the sound processor. The sound processor generates control signals that cause the actuator to vibrate. In other words, the actuator converts the electrical signals into mechanical force to impart vibrations to skull bone  136  of the recipient. 
         [0024]    Bone conduction device  100  further includes transmission element  140  to transfers vibrations from the bone conduction device to the recipient. The illustrated transmission element  140  includes a coupling apparatus to attach bone conduction device  100  to the recipient. In the example of  FIG. 1A , the coupling apparatus of transmission element  140  is attached to an anchor system (not shown) implanted in the recipient. An exemplary anchor system (also referred to as a fixation system) can include a percutaneous abutment fixed to the recipient&#39;s skull bone  136 . The abutment extends from skull bone  136  through muscle  134 , fat  128  and skin  132  so that transmission element  140  can be attached thereto. Such a percutaneous abutment provides an attachment location for coupling apparatus that facilitates efficient transmission of mechanical force. 
         [0025]    It is noted that sound input element  126  can comprise devices other than a microphone, such as, for example, a telecoil, etc. In another aspect, sound input element  126  can be located remote from the bone conduction device  100  and can take the form of a microphone or the like located on a so-called behind-the-ear (BTE) device that hangs from the recipient&#39;s ear or forms part of a body worn component, such as a wireless accessory. Alternatively, sound input element  126  can be subcutaneously implanted in the recipient, or positioned in the recipient&#39;s ear canal or positioned within the pinna. Sound input element  126  can also be a component that receives an electronic signal indicative of sound, such as, from an external audio device. For example, sound input element  126  can receive a sound signal in the form of an electrical signal from an MP3 player or a smartphone electronically connected to sound input element  126  via a wired or wireless connection. 
         [0026]    The sound processing unit of the bone conduction device  100  processes the output of the sound input element  126 , which is typically in the form of an electrical signal. The processing unit generates control signals that cause an associated actuator to vibrate. In other words, the actuator converts the electrical signals into mechanical vibrations for delivery to the recipient&#39;s skull. These mechanical vibrations are delivered by an external portion of the auditory prosthesis  100 , as described below. 
         [0027]      FIG. 1B  is a schematic diagram of a percutaneous bone conduction device  100 . Sound  107  is received by sound input element  152 . In some arrangements, sound input element  152  is a microphone configured to receive sound  107 , and to convert sound  107  into electrical signal  154 . Alternatively, sound  107  is received by sound input element  152  as an electrical signal. As shown in  FIG. 1B , electrical signal  154  is output by sound input element  152  to electronics module  156 . Electronics module  156  is configured to convert electrical signal  154  into adjusted electrical signal  158 . As described below in more detail, electronics module  156  can include a sound processor, control electronics, transducer drive components, and a variety of other elements. 
         [0028]    As shown in  FIG. 1B , transducer or vibration element  160  receives adjusted electrical signal  158  and generates a mechanical output force in the form of vibrations that are delivered to the skull of the recipient via a transmission element  140 , as described above. The transmission element  140  connects to the anchor system  162 , so as to couple the anchor system  162  to bone conduction device  100 . Delivery of this output force causes motion or vibration of the recipient&#39;s skull, thereby activating the hair cells in the recipient&#39;s cochlea (not shown) via cochlea fluid motion. 
         [0029]      FIG. 1B  also illustrates power module  170 . Power module  170  provides electrical power to one or more components of bone conduction device  100 . For ease of illustration, power module  170  has been shown connected only to user interface module  168  and electronics module  156 . However, it should be appreciated that power module  170  can be used to supply power to any electrically powered circuits/components of bone conduction device  100 . 
         [0030]    User interface module  168 , which is included in bone conduction device  100 , allows the recipient to interact with bone conduction device  100 . For example, user interface module  168  can allow the recipient to adjust the volume, alter the speech processing strategies, power on/off the device, etc. In the example of  FIG. 1B , user interface module  168  communicates with electronics module  156  via signal line  164 . 
         [0031]    Bone conduction device  100  can further include external interface module that can be used to connect electronics module  156  to an external device, such as a fitting system. Using external interface module  166 , the external device, can obtain information from the bone conduction device  100  (e.g., the current parameters, data, alarms, etc.) and/or modify the parameters of the bone conduction device  100  used in processing received sounds and/or performing other functions. 
         [0032]    In the example of  FIG. 1B , sound input element  152 , electronics module  156 , vibration element  160 , power module  170 , user interface module  168 , and external interface module have been shown as integrated in a single housing, referred to as housing  150 . However, it should be appreciated that in certain examples, one or more of the illustrated components can be housed in separate or different housings. For example, the sound input element  152  and electronics module  156  can be disposed in a BTE device that is physically isolated from the actuator. Similarly, it should also be appreciated that in such aspects, direct connections between the various modules and devices are not necessary and that the components can communicate, for example, via wireless connections. 
         [0033]      FIG. 2  depicts an exemplary aspect of a transcutaneous bone conduction device  200  that includes an external portion  204  and an implantable portion  206 . The transcutaneous bone conduction device  200  of  FIG. 2  is a passive transcutaneous bone conduction device in that a transducer or vibration element  208  is located in the external portion  204 . In general, the external portion  204  can include the control and sound processing components depicted above in  FIG. 1B . For clarity however, these components are generally not depicted; instead, structural elements particular to a transcutaneous bone conduction device  200  are shown. 
         [0034]    Vibration element  208  is located in housing  210  of the external component, and is coupled via a transmission element  211  to the plate  212 , which can be discrete from the housing  210  as depicted, or disposed within the housing  210 . Plate  212  can be in the form of a permanent magnet and/or in another form that generates and/or is reactive to a magnetic field, or otherwise permits the establishment of magnetic attraction between the external portion  204  and the implantable portion  206  sufficient to hold the external portion  204  against the skin of the recipient. In other examples, magnets or magnetic materials can be discrete from plate  212 . Magnetic attraction can be further enhanced by utilization of a magnetic implantable plate  216 . In alternative aspects, multiple magnets in both the external portion  204  and implantable portion  206  can be utilized. 
         [0035]    In an exemplary aspect, the vibration element  208  is a device that delivers vibration stimulus to the skull of a recipient. In operation, sound input element  126  converts sound into electrical signals. Specifically, the transcutaneous bone conduction device  200  provides these electrical signals to vibration element  208 , or to a sound processor (not shown) that processes the electrical signals, and then provides those processed signals to vibration element  208 . The vibration element  208  converts the electrical signals (processed or unprocessed) into vibrations. Because vibration element  208  is mechanically coupled to plate  212 , the vibrations are transferred from the vibration element  208  to plate  212  via transmission element  211 . Implantable plate assembly  214  is part of the implantable portion  206 , and can be made of a ferromagnetic material that can be in the form of a permanent magnet, that generates and/or is reactive to a magnetic field, or otherwise permits the establishment of a magnetic attraction between the external portion  204  and the implantable portion  206  sufficient to hold the external portion  204  against the skin  132  of the recipient. Accordingly, vibrations produced by the vibration element  208  of the external portion  204  are transferred from plate  212  across the skin  132  to implantable plate  216  of implantable plate assembly  214 . This can be accomplished as a result of mechanical conduction of the vibrations through the skin  132 , resulting from the external portion  204  being in direct contact with the skin  132  and/or from the magnetic field between the two plates  212 ,  216 . These vibrations are transferred without a component penetrating the skin  132 , fat  128 , or muscular  134  layers on the head. 
         [0036]    As can be seen, the implantable plate assembly  214  is substantially rigidly attached to bone fixture  218  in this aspect. Implantable plate assembly  214  includes through hole  220  that is contoured to the outer contours of the bone fixture  218 , in this case, a bone screw that is secured to the bone  136  of the skull. This through hole  220  thus forms a bone fixture interface section that is contoured to the exposed section of the bone fixture  218 . In an exemplary aspect, the sections are sized and dimensioned such that at least a slip fit or an interference fit exists with respect to the sections. Plate screw  222  is used to secure implantable plate assembly  214  to bone fixture  218 . As can be seen in  FIG. 2 , the head of the plate screw  222  is larger than the hole through the implantable plate assembly  214 , and thus the plate screw  222  positively retains the implantable plate assembly  214  to the bone fixture  218 . In certain aspect, a silicon layer  224  is located between the implantable plate  216  and bone  136  of the skull. 
         [0037]    The external portion of a bone conduction auditory prosthesis can be utilized in both the percutaneous application of  FIGS. 1A and 1B , and the transcutaneous application of  FIG. 2 . For example, a bone conduction auditory prosthesis can include a housing containing, e.g., the various modules and elements depicted in  FIG. 1B . Those elements include vibration element  160  ( FIG. 1B ), which is equivalent to vibration element  208  ( FIG. 2 ). The vibration element can be connected to a transmission element  140  ( FIG. 1B ) or  211  ( FIG. 2 ). Such a transmission element can be connected to an anchor system  162  ( FIG. 1B ) in a percutaneous bone conduction application or a plate in a transcutaneous bone conduction application. Alternatively, the transmission element can include a plate or other generally flat component or element  212  ( FIG. 2 ) to be utilized in a transcutaneous application. This increases manufacturing efficiencies by allowing the same bone conduction device to be used in either configuration. Such devices are described in further detail below. 
         [0038]      FIGS. 3A-3B  depict partial cross-sectional schematic views of external portions  300   a - b  of transcutaneous bone conduction devices and percutaneous bone conduction devices, respectively. Common elements are described generally together. Each of the depicted aspects includes a housing  301   a - b  that surrounds a number of components. These components include, but are not limited to a vibration element  304   a - b , sound processing electronics  324   a - b , batteries  326   a - b , and so on. Not all elements utilized in transcutaneous or percutaneous bone conduction devices are depicted in the figures, but are described elsewhere herein and known to a person of skill in the art. A microphone or other sound input element  305   a - b  is disposed on the housing  301   a - b  and is connected to the sound processor component  324   a - b . A transmission element  306   a - b  extending through the housing  301   a - b  is connected to the vibration element  304   a - b . A sealing and suspension system  303   a - b  is disposed between the housing  301   a - b  and the transmission element  306   a - b . Examples of sealing and suspension systems  303   a - b  are described in more detail below. The transmission element  306   a  is connected to an enlarged element  308   a  in the form of a plate  316   a  in the case of the transcutaneous bone conduction device  300   a.    
         [0039]    In the transcutaneous bone conduction device  300   a  depicted in  FIG. 3A , an underside  318   a  of the plate  316   a  is adapted to contact the skin of a recipient. A magnet housing  302   a  contains one or more masses  310   a , which can be a magnet or other magnetic material. Either or both of the housing  302   a  and the masses  310   a  can be connected to the plate  316   a  with one or more resilient elements  312   a  that can further dampen unwanted vibration. Different types of resilient elements  312   a , such as coil springs, leaf springs, torsion springs, shape-memory elements, wave springs, and elastomeric elements, can be utilized in the external portions described herein. Technologies related to the suspension of magnets or masses in bone conduction devices are described in U.S. Patent Application Ser. No. 62/043,013, filed Aug. 28, 2014, the disclosure of which is hereby incorporated by reference herein in its entirety. Turning to the percutaneous bone conduction device of  FIG. 3B , the transmission element  306   b  can be connected to a bone anchor system  308   b  in the form of a screw. The bone anchor system  308   b  is secured directly to the skull S of a recipient. 
         [0040]      FIG. 4  depicts a partial cross-sectional schematic view of another aspect of an external portion  400  of a transcutaneous bone conduction device. The external portion  400  includes a housing  402  in which is disposed a vibration element  404 . The vibration element  404  is connected to a transmission element  408  that is seated within an opening in the housing  402 . Thus, the external portion  400  of  FIG. 4  is utilized in a dedicated transcutaneous bone conduction application, unlike certain of the previous examples that can be interchanged between transcutaneous and percutaneous applications. In the depicted aspect, the transmission element  408  includes a shaft  414  connected to or integral with a plate  416 . As in the previous examples, the plate  416  has a lower surface  418  adapted to contact the skin of a recipient, as well as an upper surface  420 . Additionally, a sealing and suspension system  419  is disposed between the housing  402  and the transmission element  408  (e.g., at the outer perimeter of the plate  416 ). Resilient members  412  flexibly connect the upper surface  420  to one or more masses  410 . The external portion  400  also includes a number of additional components  424  required for the functionality of the external portion  400 . These are described generally above and can include a battery, electronics, wireless communication devices, and so on. A sound input element such as a microphone  428  is disposed on the housing  402  and in communication with the sound processor component  424 . To further reduce feedback, the components  424  can be connected to the masses  410  at interfaces  426 . 
         [0041]      FIG. 5A  depicts a partial cross-sectional schematic view of a bone conduction device  500  utilizing an aspect of a sealing and suspension system  502 .  FIG. 5B  depicts an enlarged partial cross-sectional schematic view of the bone conduction device  500  of  FIG. 5A , and is described simultaneously therewith. The depicted bone conduction device  500  is a transcutaneous bone conduction device, due to the utilization of a transmission element  504  in the form of an enlarged plate that delivers vibrations through the skin of a recipient. The sealing and suspension system  502  described in conjunction therewith can also be utilized with percutaneous bone conduction devices, where the transmission element is connected to an anchor extending from the skull of the recipient. The transmission element  504  defines an actuation axis A, along which the transmission element  504  reciprocally vibrates during actuation. A housing  506  contains components (not depicted, but described elsewhere herein) required for operation of the device  500 . The housing  506  is generally rigid and includes an interface surface  508  that defines an opening  510  through which the transmission element  504  extends. In the depicted aspect, the interface surface  508  is pitched relative to the actuation axis A. In that regard, the opening  510  defines a maximum dimension or extent D MAX  and a minimum dimension or extent D MIN . The dimension, in certain examples, can be a diameter, for example, in aspects where the transmission element  504  is substantially round. Positioned generally in opposition to the interface surface  508  is an outer surface  512  of the transmission element  504 . In the depicted aspect, the outer surface  512  is also pitched relative to the actuation axis A. The interface surface  508  and the outer surface  512  have approximately the same pitch in  FIGS. 5A and 5B . A substantially annular elastic element  514  is disposed between the interface surface  508  and the outer surface  512 , so as to form the sealing and suspension system  502 . 
         [0042]    Like the interface surface  508  and the outer surface  512 , the elastic element  514  is also pitched relative to the actuation axis A. In certain aspects, the elastic element  514  can be pitched at an angle of about 70° to the actuation axis A. In other examples, the elastic element can be at an angle between about 90° (unpitched) to about 60° to the actuation axis A. In other examples, the elastic element can be at an angle between about 90° (unpitched) to about 45° to the actuation axis A. In other examples, the elastic element can be at an angle between about 60° to about 45° to the actuation axis A. More specifically, the elastic element  514  includes an outer periphery  516  disposed proximate the interface surface  508  and an inner periphery  518  disposed proximate the outer surface  512 . The elastic element  514  defines an element axis A E  that is substantially parallel to, and in some examples coaxial with, the actuation axis A. However, the elastic element  514  also defines a material axis A M  that, in certain examples, can be parallel to, orthogonal to, or disposed at an angle to the actuation axis A. In certain examples, the material axis A M  is defined by a cross-section of the elastic element  514 . For example, the material axis A M  can be substantially parallel to, and disposed substantially equidistant from, both of the outer periphery  516  and the inner periphery  518 . The periphery of the elastic element  514  can also be defined by an upper periphery  520  and a lower periphery  522 , and the material axis A M  can be disposed substantially orthogonal to the upper periphery  520  and the lower periphery  522 . The elastic element  514  has a total material volume that is banded and defined by the outer periphery  516 , inner periphery  518 , upper periphery  520 , and lower periphery  522 . 
         [0043]    In order to ensure proper sealing of the opening  510  and support of the transmission element  504 , the elastic element  514  is configured so as to be disposed within the maximum extent D MAX  of the opening  510 . That is, if the opening  510  defines a circular cross section of a cylinder having an axis coaxial with actuation axis A and having walls  524  parallel to the actuation axis A, the outer periphery  516  of the elastic element  514  is entirely disposed within that cylinder defined by the maximum extent D MAX . Such a configuration allows a significant amount of the total material volume of the elastic element  514  to be subject to (and therefore dampen) vibrations between the interface surface  508  and the outer surface  512 , which provides for the most efficient use of the greatest quantity of material available in the elastic element  514 . In the depicted aspect, substantially all of the total material volume of the elastic element  514  is bounded by the interface surface  508  and the outer surface  512 , as depicted by lines  526 . 
         [0044]      FIG. 6A  depicts a partial cross-sectional schematic view of a bone conduction device  600  utilizing an aspect of a sealing and suspension system  602 .  FIG. 6B  depicts an enlarged partial cross-sectional schematic view of the bone conduction device  600  of  FIG. 6A , and is described simultaneously therewith. Many of the components depicted in  FIGS. 6A and 6B  are also depicted and described with regard to  FIGS. 5A and 5B . These components utilize similar reference numbers, beginning with  600 , and are not necessarily described further. Notable differences between the bone conduction device  500  and bone conduction device  600  are described in more detail below. 
         [0045]    In  FIGS. 6A and 6B , an interface surface  608  includes a profile  650  that can include a pattern or texture. Serrated, toothed, and crenellated profiles are also contemplated. A similar profile  652  can be formed on an outer surface  612  of a transmission element  604 . These profiles,  650 ,  652  form a plurality of discrete contact surfaces  654  or points along both an outer periphery  616  and an inner periphery  618  of the elastic element  614 . Thus, adjacent contact surfaces  654  are separated by gaps  656  between the elastic element  614  and the interface surface  608  and the outer surface  612 . These gaps  656  and contact surfaces  654  help reduce axial stiffness of the elastic element  614  as it is deflected during actuation of the transmission element  604 , while still maintaining a robust seal. 
         [0046]      FIGS. 7A-7D  depict enlarged partial cross-sectional schematic views of bone conduction devices  700   a - d  utilizing alternative aspects of sealing and suspension systems  702   a - d . Each of  FIGS. 7A-7D  depict an interface surface  704   a - d  and an outer surface  706   a - d , which correspond generally to those surfaces as described elsewhere herein. An elastic element  708   a - d  is disposed between the interface surface  704   a - d  and the outer surface  706   a - d . In  FIG. 7A , only the interface surface  704   a  includes a profile  710   a  that includes a plurality of teeth  712   a  that act as contact surfaces. Between adjacent teeth  712   a  are gaps  714   a  that help reduce axial stiffness of the elastic element  708   a . In certain examples, these gaps  714   a  can be filled with an adhesive or other component to improve retention. In such examples, it can be advantageous that the adhesive displays very high flexibility so as to not reduce the overall flexibility attendant with utilization of the gaps. In  FIG. 7B , both the interface surface  704   b  and the outer surface  706   b  include a profile  710   b . In  FIGS. 7C and 7D , neither the interface  704   c - d  nor the outer surface  706   c - d  include a profile. However, the elastic element  708   c - d  includes one or more surfaces having a profile  710   c - d . In these cases, the profiles  710   c - d  include teeth  712   c - d  that form gaps  714   c - d  therebetween. Thus, in this configuration, axial stiffness of the elastic element  708   c - d  is also reduced. 
         [0047]    It has been discovered that maintaining discrete contact surfaces (e.g., contact areas separated by non-contacting areas or gaps) between the interface surface and the elastic element and/or between the outer surface and the elastic element helps reduce axial stiffness of the elastic element. This is because that deflection caused by movement of transmission element only deforms and distorts areas of the elastic element proximate the discrete contact surfaces. During vibrations, portions of the elastic element are therefore able to deform into the gaps disposed between the discrete contact surfaces. By deforming a smaller volume of the elastic element proximate the interface and/or outer surfaces, the elastic element applies less return resistive force (e.g., stiffness) against the vibration transmission element. This improved performance is also present when the gaps are present between teeth formed on the elastic element. 
         [0048]      FIGS. 8A-8C  depict enlarged partial cross-sectional schematic views of bone conduction devices  800   a - c  utilizing further alternative aspects of sealing and suspension systems  802   a - c . Each of  FIGS. 8A-8C  depict an interface surface  804   a - d  and an outer surface  806   a - c , which correspond generally to those surfaces as described elsewhere herein. An elastic element  808   a - c  is disposed between the interface surface  804   a - c  and the outer surface  806   a - c.    
         [0049]    In  FIG. 8A , a transmission element  810   a  defines an actuation axis A, along which the transmission element  810   a  reciprocally vibrates during actuation. A housing  812   a  is generally rigid and includes the interface surface  804   a  that defines an opening  814   a  through which the transmission element  810   a  extends. Since the interface surface  804  is substantially parallel to the actuation axis A, the opening  814   a  defines a single maximum dimension or extent D MAX . The elastic element  808   a  is annular, and includes an outer periphery  816   a  disposed proximate the interface surface  804   a  and an inner periphery  818   a  disposed proximate the outer surface  806   a . The elastic element  808   a , therefore, defines a material axis A M  that, in certain examples, is defined by a periphery of a cross-section of the elastic element  808   a . Here, the material axis A M  is substantially parallel to, and disposed substantially equidistant from, both of the outer periphery  816   a  and the inner periphery  818   a , and is also substantially parallel to the actuation axis A. As depicted in previous examples, the elastic element  808   a  is configured so as to be disposed within the maximum extent D MAX  of the opening  814   a . Moreover, to optimize the total volume of elastic element  808   a  available to dampen vibrations, substantially all of the total material volume is disposed between the interface surface  804   a  and the outer surface  806   a , as depicted by lines  820   a.    
         [0050]    Turning to  FIG. 8B , a transmission element  810   b  defines an actuation axis A, along which the transmission element  810   b  reciprocally vibrates during actuation. A housing  812   b  is generally rigid and includes the interface surface  804   b  that defines an opening  814   b  through which the transmission element  810   b  extends. Here, the interface surface  804   b  and the outer surface  806   b  each define one or more recesses  830   b . The elastic element  808   b  includes an outer periphery  816   b  disposed proximate the interface surface  804   b  and an inner periphery  818   b  disposed proximate the outer surface  806   b . The outer periphery  816   b  and an inner periphery  818   b  are formed to mate with the recesses  830   b . This mating contact can help improve retention of the transmission element  810   b  in the housing  812   b  during vibration. Additionally, the interface surface  804   b  can also be textured or patterned, as described above. The elastic element  808   b  defines a material axis A M  that, in certain examples, is defined by a periphery of a cross-section of the elastic element  808   b . When split on the material axis A M  the outer periphery  816   b  and the inner periphery  818   b  have cross sections that are substantially mirror images of each other. As depicted in previous aspects, to optimize the total volume of elastic element  808   b  available to dampen vibrations, the substantially all of the total material volume is disposed between the interface surface  804   b  and the outer surface  806   b , as depicted by lines  820   b . The sealing and suspension system  814   c  of  FIG. 8C  is substantially similar to that depicted in  FIG. 8B , but includes a mechanical stop  840   c  to protect the sealing and suspension system  814   c  from excessive mechanical forces, which can occur, for example, if the bone conduction devices  800   c  is dropped. 
         [0051]    Other configurations of sealing and suspension systems can be utilized to provide damping functionality for a wide range of frequencies. For example,  FIGS. 9A-9C  depict enlarged partial cross-sectional schematic views of bone conduction devices  900   a - c  utilizing alternative aspects of sealing and suspension systems  902   a - c . A housing  904   a - c  and a transmission element  906   a - c  are depicted. In  FIG. 9A , an elastomer element  908   a  includes a plurality of air cells  910   a , which reduces stiffness of the elastomer element  908   a . In  FIG. 9B , an elastomer element  908   b  has an hour-glass or tapered shape. This allows for different parts of the elastomer element  908   b  to dominate in different frequency ranges. For example, in the depicted aspect, the thinner central portion  912   b  part is active at higher frequencies (e.g., lower displacements), while the whole elastomer element  908   b  is active at lower frequencies (e.g., larger displacements).  FIG. 9C  an elastomer element  908   c  is manufactured from two materials  914   c ,  916   c . Utilizing two materials  914   c ,  916   c  in series, as depicted, provides damping in wider frequency range. 
         [0052]    For example,  FIG. 10  depicts a relationship between frequency and damping, for a sealing and suspension system that utilizes two viscoelastic materials. In general, damping as a function of frequency through a viscoelastic material can be defined by a bell-shaped curve (as indicated by the curves associated with Material  1  and Material  2 , individually). By combining two materials with different maximum damping frequencies in series (e.g., as depicted in  FIG. 9C ), a wider range of frequencies of vibrations through the two-material-layer can be dampened effectively, as compared to only using one material. 
         [0053]    This disclosure described some aspects of the present technology with reference to the accompanying drawings, in which only some of the possible aspects were shown. Other aspects, however, can be embodied in many different forms and should not be construed as limited to the examples set forth herein. Rather, these examples were provided so that this disclosure was thorough and complete and fully conveyed the scope of the possible examples to those skilled in the art. 
         [0054]    Although specific aspects were described herein, the scope of the technology is not limited to those specific aspects. One skilled in the art will recognize other aspects or improvements that are within the scope of the present technology. Therefore, the specific structure, acts, or media are disclosed only as illustrative examples. The scope of the technology is defined by the following claims and any equivalents therein.