Patent Publication Number: US-11653160-B2

Title: Dynamic fitting for device worn on recipient&#39;s body

Description:
CLAIM OF PRIORITY 
     The present application is a continuation of U.S. patent application Ser. No. 17/257,815 filed Jan. 4, 2021 which is a U.S. national stage filing of PCT Appl. No. PCT/IB2019/056505 filed Jul. 30, 2019 which claims the benefit of priority to U.S. Provisional Appl. No. 62/715,185 filed Aug. 6, 2018, each of which is incorporated in its entirety by reference herein. 
    
    
     BACKGROUND 
     Field 
     The present application relates generally to bone conduction auditory prostheses, and more specifically systems and methods for pressing external actuators of such auditory prostheses against the head of the recipient. 
     Description of the Related Art 
     Hearing loss, which may be due to many different causes, is generally of two types, conductive and/or sensorineural. Conductive hearing loss occurs when the normal mechanical pathways of the outer and/or middle ear are impeded, for example, by damage to the ossicular chain or ear canal. Sensorineural hearing loss occurs when there is damage to the inner ear, or to the nerve pathways from the inner ear to the brain. 
     Individuals who suffer from conductive hearing loss typically have some form of residual hearing because the hair cells in the cochlea are undamaged. As a result, individuals suffering from conductive hearing loss might receive an auditory prosthesis that generates mechanical motion of the cochlea fluid instead of a hearing aid based on the type of conductive loss, amount of hearing loss and customer preference. Such prostheses include, for example, bone conduction devices and direct acoustic stimulators. 
     Bone conduction devices mechanically transmit sound information to a recipient&#39;s cochlea by transferring vibrations to a person&#39;s skull, enabling the hearing prosthesis to be effective regardless of whether there is disease or damage in the middle ear. Traditionally, bone conduction devices transfer vibrations from an external actuator (e.g., vibrator) to the skull, e.g., through a percutaneous bone conduction implant that penetrates the skin and is physically attached to both the actuator and the skull. Typically, the external actuator is connected to the percutaneous bone conduction implant located behind the outer ear facilitating the efficient transfer of sound via the skull to the cochlea. The bone conduction implant connecting the actuator to the skull generally comprises two components: a bone attachment piece (e.g., bone fixture/fixture) that is attached or implanted directly to the skull, and a skin-penetrating piece attached to the bone attachment piece, commonly referred to as an abutment. 
     SUMMARY 
     In one aspect disclosed herein, an apparatus is provided. The apparatus comprises a support configured to be worn on a head of a recipient and to hold at least one bone conduction device next to the recipient&#39;s skull. The at least one bone conduction device provides auditory stimulation to the recipient. The support is configured to generate a force that presses against the head and to actively adjust the force while the support is worn by the recipient. 
     In another aspect disclosed herein, an apparatus is provided. The apparatus comprises a structure configured to be worn on a head of a recipient and to press at least one bone conduction actuator against the head such that vibrations generated by the at least one bone conduction actuator are transmitted through skin of the recipient at a location where the skin covers a temporal bone of the recipient. The structure comprises at least one adjustment mechanism configured to adjust at least one of a length and a shape of the structure without mechanical manipulation of the at least one adjustment mechanism. 
     In another aspect disclosed herein, a method is provided. The method comprises providing at least one vibration generator configured to be worn on a head of a recipient and to transmit vibrations indicative of auditory information. The method further comprises, in response to control signals, while the at least one vibration generator is worn by the recipient, modifying a static component of a force applied by the at least one vibration generator to the head. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments are described herein in conjunction with the accompanying drawings, in which: 
         FIG.  1 A  is a perspective view of an example bone conduction auditory prosthesis in accordance with certain embodiments described herein; 
         FIG.  1 B  is a functional block diagram of an example bone conduction auditory prosthesis in accordance with certain embodiments described herein; 
         FIG.  1 C  schematically illustrates an operationally removable component of an example bone conduction auditory prosthesis in accordance with certain embodiments described herein; 
         FIGS.  2 A- 2 E  schematically illustrate various views of an example apparatus in accordance with certain embodiments described herein; 
         FIG.  3    schematically illustrates another example apparatus comprising an elastic portion in accordance with certain embodiments described herein; 
         FIGS.  4 A- 4 D  schematically illustrate an example apparatus comprising two adjustment mechanisms in accordance with certain embodiments described herein; 
         FIGS.  5 A and  5 B  schematically illustrate two example apparatuses comprising at least one adjustment mechanism comprising at least one piezoelectric bending mechanism in accordance with certain embodiments described herein; 
         FIGS.  5 C and  5 D  schematically illustrate two example piezoelectric bending mechanisms in accordance with certain embodiments described herein; 
         FIG.  6    schematically illustrates another example adjustment mechanism in accordance with certain embodiments described herein; 
         FIG.  7    is a plot showing voltage applied to at least one adjustment mechanism as a function of time to provide both the static component of the force and the vibrational component of the force in accordance with certain embodiments described herein; and 
         FIGS.  8 A and  8 B  are flow diagrams of two examples of a method in accordance with certain embodiments described herein. 
     
    
    
     DETAILED DESCRIPTION 
     For non-invasive or non-surgical bone conduction auditory prostheses, the transmission of auditory stimulation from the bone conduction auditory prosthesis to the recipient via the recipient&#39;s skin is dependent at least in part on the force with which the auditory prosthesis is pressed against the recipient&#39;s skin. While larger forces are generally conducive to better sound quality (e.g., better transmission of the auditory stimulation), the higher forces can be less comfortable to the recipient, and, when applied for excessively long periods of time, can result in injury to the recipient&#39;s skin. Certain embodiments described herein actively (e.g., dynamically) adjust the force while the auditory prosthesis is worn by the recipient in a “hands-free” manner. The active adjustment of the force is in response at least in part to detected operational conditions, including but not limited to the categories of auditory information being provided to the recipient via the auditory stimulation (e.g., speech, music, noise, the recipient&#39;s name, etc.), to increase the force during some operational conditions warranting better sound quality and to decrease the force during other operational conditions that do not warrant better sound quality. 
       FIG.  1 A  is a perspective view of an example bone conduction auditory prosthesis  100  in accordance with certain embodiments described herein.  FIG.  1 B  is a functional block diagram of an example bone conduction auditory prosthesis  100  in accordance with certain embodiments described herein.  FIG.  1 C  schematically illustrates an operationally removable component  300  of an example bone conduction auditory prosthesis  100  in accordance with certain embodiments described herein. 
     As shown in  FIG.  1 A , the recipient has an outer ear  101 , a middle ear  102 , and an inner ear  103 . Elements of the outer ear  101 , the middle ear  102 , and the inner ear  103  are described below, followed by a description of the auditory prosthesis  100 . In a fully functional human hearing anatomy, the outer ear  101  comprises an auricle  105  and an ear canal  106 . A sound wave or acoustic pressure  107  is collected by the auricle  105  and channeled into and through the ear canal  106 . Disposed across the distal end of the ear canal  106  is a tympanic membrane  104  which vibrates in response to the acoustic wave  107 . This vibration is coupled to the oval window or fenestra ovalis  110  through three bones of the middle ear  102 , collectively referred to as the ossicles  111  and comprising the malleus  112 , the incus  113 , and the stapes  114 . The ossicles  111  of the middle ear  102  serve to filter and amplify the acoustic wave  107 , causing the oval window  110  to vibrate. Such vibrations set up waves of fluid motion within the cochlea  139 . Such fluid motion, in turn, activates hair cells (not shown) that line the inside of the cochlea  139 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells and the auditory nerve  116  to the brain (not shown), where they are perceived as sound. 
       FIG.  1 A  also illustrates an example positioning of the auditory prosthesis  100  relative to the outer ear  101 , the middle ear  102 , and the inner ear  103  of a recipient of the auditory prosthesis  100 . As shown in  FIG.  1 A , the auditory prosthesis  100  is positioned behind the outer ear  101  of the recipient and comprises a sound input element  126  to receive sound signals. The sound input element  126  can comprise, for example, a microphone, telecoil, etc. and can be located, for example, on or in the auditory prosthesis  100 , or on a cable extending from the auditory prosthesis  100 . 
     In certain embodiments, the auditory prosthesis  100  comprises an operationally removable component  300 , as schematically illustrated by  FIGS.  1 B and  1 C . By operationally removable, it is meant that the component  300  is releasably coupled to the recipient&#39;s head and/or any support holding the component  300  in such a manner that the recipient can relatively easily connect the operationally removable component  300  to the recipient&#39;s head and/or the support and can relatively easily remove the operationally removable component  300  from the recipient&#39;s head and/or the support during normal use of the auditory prosthesis  100 , repeatedly if desired. The operationally removable component  300  of the auditory prosthesis  100  further includes a coupling apparatus  140  (e.g., having a longitudinal axis  150 ). In certain embodiments, the coupling apparatus  140  is configured to be pressed directly against the recipient&#39;s head and to transmit acoustic vibrations to the recipient&#39;s head, while in certain other embodiments, the coupling apparatus  140  is configured to mate with a corresponding mating apparatus of the support and to transmit acoustic vibrations to the recipient&#39;s head (e.g., via the support). 
     The operationally removable component  300  includes the sound input element  126 , a sound processor (e.g., an electronics module  204  as shown in  FIG.  1 B ), and an actuator  206  (e.g., a transducer module, as shown in  FIG.  1 B ) configured to generate acoustic vibrations. The actuator  206  can comprise a vibrator (e.g., a vibrating electromagnetic actuator; a vibrating piezoelectric actuator; other type of vibrating actuator), and the operationally removable component  300  is sometimes referred to herein as a vibrator unit. More particularly, the sound input element  126  (e.g., a microphone) converts received sound signals  107  into electrical signals  222 . Alternatively, sound signals  107  are received by the sound input element  126  as electrical signals (e.g., via a cable or wireless connection, such as from an audiovisual device). The electrical signals  222  from the sound input element  126  are processed by the electronics module  204 , which can include a sound processing circuit, control electronics, transducer drive components, and a variety of other elements. 
     The electronics module  204  is configured to respond to the electrical signals  222  by generating control signals  224  which cause the actuator  206  to vibrate, generating a mechanical output force in the form of acoustic vibrations that are delivered to the skull of the recipient through the skin (e.g., via the coupling apparatus  140 ). In other words, the operationally removable component  300  converts the received sound signals  107  into mechanical motion using the actuator  206  to impart vibrations to the recipient&#39;s skull (e.g., via the recipient&#39;s skin). 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  139  via cochlea fluid motion. 
     As shown in  FIG.  1 B , the operationally removable component  300  can further comprise a power module  210  configured to provide electrical power to one or more components of the auditory prosthesis  100 . For ease of illustration, the power module  210  has been shown connected only to user interface module  212  and the electronics module  204 . However, it should be appreciated that the power module  210  can be used to supply power to any electrically powered circuits/components of the auditory prosthesis  100 . The user interface module  212  is configured to allow the recipient to interact with the auditory prosthesis  100 . For example, the user interface module  212  can allow the recipient to adjust the volume, alter the speech processing strategies, power on/off the device, etc. In the example of  FIG.  1 B , the user interface module  212  communicates with the electronics module  204  via the signal line  228 . The auditory prosthesis  100  of certain embodiments further includes an external interface module  214  configured to connect the electronics module  204  to an external device, such as a fitting system. Using the external interface module  214 , the operationally removable component  300  can obtain information from the auditory prosthesis  100  (e.g., the current parameters, data, alarms, etc.) and/or modify the parameters of the auditory prosthesis  100  used in processing received sounds and/or performing other functions. 
     In the example of  FIG.  1 B , the sound input element  126 , the electronics module  204 , the actuator  206  (e.g., transducer module), the power module  210 , the user interface module  212 , and the external interface module  214  have been shown as integrated in a single housing  225 . 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, in some embodiments, the actuator  206  and the sound input element  126  are housed in separate housings to eliminate a potential pathway for feedback. The sound input element  126 , the electronics module  204 , the power module  210 , the user interface module  212 , and the external interface module  214  can be housed in a behind-the-ear (BTE) component that is suspended from the pinna (e.g., by an ear hook). Similarly, it should also be appreciated that in certain such embodiments, direct connections between the various modules and devices are not necessary and that the components can communicate, for example, via wireless connections. 
       FIG.  1 C  depicts a side view of an operationally removable component  300  of an example bone conduction auditory prosthesis  100  in accordance with certain embodiments described herein. The example operationally removable component  300  of  FIG.  1 C  comprises the actuator  206  and the coupling apparatus  140  with a longitudinal axis  150  (e.g., an axis along a length of the coupling apparatus  140 ; an axis about which the coupling apparatus  140  is at least partially symmetric). The coupling apparatus  140  is mechanically coupled, via the mechanical coupling shaft  143 , to the actuator  206  within the component  300 . The coupling apparatus  140  is configured to be mated to a corresponding mating structure of the support (not shown) by pressing the coupling apparatus  140  against the mating structure in a direction along the longitudinal axis  150  (e.g., snap-coupled). In certain embodiments, the operationally removable component  300  is directly vibrationally connected to and removably coupled to the recipient&#39;s skull via the coupling apparatus  140 , while in certain other embodiments, the operationally removable component  300  is directly vibrationally connected to and removably coupled to the support via the coupling apparatus  140 , and the support is directly vibrationally connected to and removably coupled to the recipient&#39;s skull. 
     Acoustic vibrations from the actuator  206  are transferred from the actuator  206  to the coupling apparatus  140  and then to the recipient (e.g., via the support). More particularly, the actuator  206  of the operationally removable component  300  is in vibrational communication with the coupling apparatus  140  such that vibrations generated by the actuator  206 , in response to a sound captured by the sound input element  126 , are transmitted to the coupling apparatus  140  and then to the recipient (e.g., via the support) in a manner that at least effectively evokes hearing percept. By “effectively evokes a hearing percept,” it is meant that the vibrations are such that a typical human between 18 years old and 40 years old having a fully functioning cochlea receiving such vibrations, where the vibrations communicate speech, would be able to understand the speech communicated by those vibrations in a manner sufficient to carry on a conversation provided that those adult humans are fluent in the language forming the basis of the speech. In certain embodiments, the vibrational communication effectively evokes a hearing percept, if not a functionally utilitarian hearing percept. 
     In certain embodiments, the coupling apparatus  140  comprises a male component and the mating structure of the support comprises a female component configured to mate with the male component of the coupling apparatus  140 . In certain embodiments, this configuration can be reversed, with the coupling apparatus  140  comprises a female component and the mating structure of the support comprises a male component configured to mate with the female component of the coupling apparatus  140 . While  FIG.  1 C  illustrates one example component  300  in accordance with certain embodiments described herein, other components  300  (e.g., comprising a coupling apparatus  140  configured to contact the recipient&#39;s skin, or any other coupling apparatus  140  of any type, size/having any geometry) are also compatible with certain embodiments described herein. 
       FIGS.  2 A- 2 E  schematically illustrate various views of an example apparatus  400  in accordance with certain embodiments described herein.  FIGS.  3 ,  4 A- 4 D,  5 A- 5 D, and  6    schematically illustrate other example apparatuses  400  in accordance with certain embodiments described herein. The apparatus  400  comprises a support  410  configured to be worn on a head of a recipient and to hold at least one bone conduction device  420  next to the recipient&#39;s skull. The at least one bone conduction device  420  provides auditory stimulation to the recipient. The support  410  is configured to generate a force that presses against the head and to actively (e.g., dynamically) adjust the force while the support  410  is worn by the recipient. 
     In certain embodiments, the apparatus  400  is configured to be used in conjunction with a bone conduction auditory prosthesis system comprising at least one bone conduction device  420  (e.g., at least one bone conduction actuator; at least one operationally removable component  300 ; at least one sound processor device; at least one vibration generator) configured to provide auditory stimulation to the recipient by generating acoustic vibrations and applying the acoustic vibrations to the recipient&#39;s skull via the recipient&#39;s skin. The at least one bone conduction device  420  of certain embodiments is wholly external to the recipient and is configured to be used non-invasively or non-surgically (e.g., without the use of surgically implanted portions such as a fixture and an abutment as utilized in percutaneous bone conduction auditory prostheses). 
     For non-invasive or non-surgical bone conduction auditory prostheses, the transmission of auditory stimulation from the at least one bone conduction device  420  to the recipient via the recipient&#39;s skin is dependent at least in part on the force with which the at least one bone conduction device  420  is pressed against the recipient&#39;s skin. While larger forces are generally conducive to better sound quality (e.g., better transmission of the auditory stimulation), the higher forces can be less comfortable to the recipient, and, when applied for excessively long periods of time, can result in injury to the recipient&#39;s skin. In certain embodiments, the apparatus  400  is configured to actively adjust the force applied to the recipient&#39;s skin between at least two values including but not limited to: a first value corresponding to a force sufficient to hold the support  410  on the recipient&#39;s head (e.g., a retention value; a lower bound value; a “loose” fit value) and a second value larger than the first value, the second value corresponding to a force beyond which the recipient would not be expected to perceive any improvement of the sound quality from the auditory prosthesis (e.g., a saturation value; an upper bound value; a “tight” fit value). Examples of the second value of the force include but are not limited to: 3 newtons per square centimeter multiplied by the area of contact with the recipient&#39;s skin; force level obtained from “International Organization for Standardization No. 389-3  “Acoustics—Reference zero for the calibration of audiometric equipment—Part  3 : Reference equivalent threshold vibratory force levels for pure tones and bone vibrators,”  2016). 
     In certain embodiments, the support  410  and the at least one bone conduction device  420  are integral with one another. In certain other embodiments, the support  410  and the at least one bone conduction device  420  are modular (e.g., can be relatively easily attached to one another and relatively easily detached from one another during normal use, repeatedly if desired). While  FIGS.  2 A- 2 C  schematically illustrate an embodiment in which the support  410  is configured to be used in conjunction with a single bone conduction device  420  at one side of the recipient&#39;s head (e.g., generating and providing acoustic vibrations to one of the recipient&#39;s middle ears  102 ), in certain other embodiments, the support  410  is configured to be used in conjunction with two single bone conduction devices  420  at opposite sides of the recipient&#39;s head (e.g., each generating and providing acoustic vibrations to a corresponding one of the recipient&#39;s two middle ears  102 ). 
     In certain embodiments, the support  410  (e.g., structure; frame; elongate body) comprises one or more materials and has sufficient mechanical rigidity to support the at least one bone conduction device  420  when the support  410  is worn by the recipient. For example, the support  410  can comprise one or more flexible portions  430  configured to generate the force pressing against the head upon the one or more flexible portions  430  being elastically deformed (e.g., upon the support  410  being worn on the head of the recipient). Examples of the one or more materials include but are not limited to: metals (e.g., aluminum), metal matrix composites, polymers (e.g., polyether ether ketone (“PEEK”), polyoxymethylene (“POM”), polyphenylsulfone (“PPSU”)), plastics, reinforced plastics, silicone, silicone-based materials, ceramics, ceramic matrix composites, fiberglass-containing materials, and resin-based materials. For another example, as schematically illustrated in  FIG.  3   , the support  410  can comprise at least one elastic portion  510  (e.g., elastic band) configured to encircle at least a portion of the recipient&#39;s skull and at least one inelastic portion  520  (e.g., clasp) configured to provide manual adjustment of the amount of tension in the elastic portion  510  while the support  410  is being worn by the recipient. 
     The support  410  of certain embodiments is configured to contact the recipient&#39;s skin in one or more locations along the recipient&#39;s skull when the support  410  is worn by the recipient. For example, as schematically illustrated in  FIGS.  2 A- 2 C , the one or more flexible portions  430  can comprise first and second elongate portions  430   a ,  430   b  that extend around a portion of the recipient&#39;s head (e.g., the rear portion), and as schematically illustrated in  FIGS.  4 A- 4 D , a single flexible portion  430  can extend around the portion of the recipient&#39;s head. The support  410  can further comprise two end portions  440   a ,  440   b  at opposite ends of the one or more flexible portions  430  and that contact the recipient&#39;s skin at two locations  442   a ,  442   b  on opposite sides of the recipient&#39;s skull (e.g., at locations of the skin covering the left and right temporal bones; at locations of the skin covering the left and right mastoid bones; at locations above the left and right ears). While the first end portion  440   a  is configured to press against a first side of the head at the first location  442   a  and the second end portion  440   b  is configured to press against a second side of the heat at the second location  442   b , the support  410  of certain embodiments can also contact the recipient&#39;s skin and/or hair at other locations on the recipient&#39;s head (e.g., a portion of one or both of the auricles  105 , which can provide a stabilizing force to the support  410 ). In certain embodiments, the portions of the support  410  that are configured to contact the recipient&#39;s skin (e.g., end portions  440   a ,  440   b ) comprises a first material (e.g., metal) selected to provide a predetermined structural rigidity and a second material (e.g., silicone) covering (e.g., coating) the first material. The second material can be selected to provide a predetermined comfort level to the recipient when in contact with the recipient&#39;s skin. 
     In certain embodiments, the at least one bone conduction device  420  is configured to mate with a corresponding mating apparatus (not shown) of the support  410  and to provide auditory stimulation to the recipient (e.g., to transmit acoustic vibrations to the recipient&#39;s head) via the support  410 . For example, as schematically illustrated in  FIGS.  2 A- 2 C , a portion of the at least one bone conduction device  420  (e.g., a coupling apparatus  140  of a component  300  comprising an actuator  206 ) is mechanically coupled to at least one of the end portions  440   a ,  440   b  of the support  410 . The force generated by the support  410  is directly applied by the support  410  to the recipient&#39;s skin, and the acoustic vibrations generated by the at least one bone conduction device  420  are transmitted to the recipient&#39;s head through the support  410 . In certain other embodiments, the force generated by the support  410  presses the at least one bone conduction device  420  directly against the recipient&#39;s head such that the at least one bone conduction device  420  directly provides auditory stimulation to the recipient (e.g., the acoustic vibrations are directly transmitted to the recipient&#39;s head without the acoustic vibrations being transmitted through the support  410 ). For example, the bone conduction device  420  can comprise a pad attached to the coupling apparatus  140  and configured to comfortably contact the recipient&#39;s skin, and the bone conduction device  420  can be held by the support  410  such that the pad presses directly against the recipient&#39;s head. 
     In certain embodiments, the support  410  is configured to actively adjust the force pressing against the head while the support  410  is worn by the recipient. For example, as described herein, the support  410  can comprise at least one adjustment mechanism  450  configured to adjust at least one of a length and a shape of the support  410 , without mechanical manipulation of the at least one adjustment mechanism  450  (e.g., in a “hands-free” manner; without handling the support  410 ; without adjusting a hand-operated mechanism such as a ratcheting mechanism). In certain embodiments, the at least one adjustment mechanism  450  comprises an internal power source (e.g., battery) configured to provide power for operation of the at least one adjustment mechanism  450 , while in certain other embodiments, the at least one adjustment mechanism  450  is configured to receive power from the bone conduction device  420  for operation of the at least one adjustment mechanism  450 . In certain embodiments, the at least one adjustment mechanism  450  comprises an internal controller (e.g., microprocessor) configured to generate control signals for controlling operation of the at least one adjustment mechanism  450 , while in certain other embodiments, the at least one adjustment mechanism  450  is configured to receive control signals from the bone conduction device  420  (e.g., via wired communication; via wireless communication) for controlling operation of the at least one adjustment mechanism  450 . 
     In certain embodiments in which the support  410  comprises one or more flexible portions  430 , the adjustment of the length and/or shape of the support  410  while the support  410  is worn by the recipient modifies an elastic deformation of the one or more flexible portions  430 . The at least one adjustment mechanism  450  of certain such embodiments is positioned along the support  410  between the first end portion  440   a  and the second end portion  440   b  (e.g., equidistantly between the first and second end portions  440   a ,  440   b ; at a location offset from a center of the one or more flexible portions  430 ). For another example, as schematically illustrated in  FIG.  3   , the support  410  can comprise at least one adjustment mechanism  450  configured to adjust a tension force of the elastic portion  510 . 
     In certain embodiments, the at least one adjustment mechanism  450  comprises at least one actuator  452  (e.g., configured to expand or contract in response to one or more control signals). The at least one actuator  452  can include one or more actuators selected from the group consisting of: at least one piezoelectric element, at least one hydraulic element, at least one pneumatic element, and at least one motor (e.g., screw-drive motor; stepper motor; ultrasonic motor; inchworm motor). For example, as schematically illustrated in  FIGS.  2 A- 2 E , the at least one adjustment mechanism  450  further comprises at least one hinge  454  mechanically coupled to the at least one actuator  452 , and the at least one hinge  454  is configured to open or close (e.g., by bending; by pivoting) in response to the at least one actuator  452  expanding or contracting. By controllably opening and closing the at least one hinge  454 , the at least one adjustment mechanism  450  modifies an orientation between the flexible portions  430  of the support  410 , thereby modifying a shape of the support  410  and the amount of force applied by the support  410  to the recipient&#39;s skin. While the at least one adjustment mechanism  450  of the example apparatus  400  of  FIGS.  2 A- 2 E  comprises a single actuator  452  and hinge  454 , in certain other embodiments, the apparatus  400  comprises multiple actuators  452  and hinges  454  (e.g., a first actuator  452  and hinge  454  on a first side of the support  410  and a second actuator  452  and hinge  454  on a second side of the support  410 ). 
     For another example, as schematically illustrated in  FIG.  3   , the at least one actuator  452  is between and mechanically coupled to two portions  456  of the support  410  configured to move relative to one another (e.g., two portions of the elastic portion  510 ; two portions of the inelastic portion  520 ; a portion of the elastic portion  510  and a portion of the inelastic portion  520 ). By controllably expanding and contracting the at least one actuator  452 , the at least one adjustment mechanism  450  modifies a length of the support  410  (e.g., the length between the two portions  456 ) and the amount of force applied by the elastic portion  510  of the support  410  to the recipient&#39;s skin. In certain embodiments, the at least one adjustment mechanism  450  can comprise a first adjustment mechanism configured to provide coarse adjustments (e.g., adjustments with large increments) and a second adjustment mechanism configured to provide fine adjustments (e.g., adjustments with small increments). 
       FIGS.  4 A- 4 D  schematically illustrate an example apparatus  400  comprising two adjustment mechanisms  450   a ,  450   b  in accordance with certain embodiments described herein. A first adjustment mechanism  450   a  is part of the first end portion  440   a  and a second adjustment mechanism  450   b  is part of the second end portion  440   b . The first adjustment mechanism  450   a  comprises a first actuator  452   a  (e.g., piston) and the second adjustment mechanism  450   b  comprises a second actuator  452   b  (e.g., piston). By expanding the first and second actuators  452   a ,  452   b  (e.g., see  FIG.  4 C ) while the support  410  is worn on the recipient&#39;s head, the force applied by the first and second end portions  440   a ,  440   b  to the recipient&#39;s skin is increased. Conversely, by contracting the first and second actuators  452   a ,  452   b  (e.g., see  FIG.  4 D ) while the support  410  is worn on the recipient&#39;s head, the force applied by the first and second end portions  440   a ,  440   b  to the recipient&#39;s skin is decreased. In certain other embodiments, only one of the first and second end portions  440   a ,  440   b  comprises an actuator which is configured to expand and contract. 
       FIGS.  5 A and  5 B  schematically illustrate two example apparatuses  400  comprising at least one adjustment mechanism  450  comprising at least one piezoelectric bending mechanism  460  in accordance with certain embodiments described herein.  FIG.  5 A  schematically illustrates one piezoelectric bending mechanism  460  positioned between (e.g., equidistantly) the first and second end portions  440   a ,  440   b .  FIG.  5 B  schematically illustrates two piezoelectric bending mechanisms  460   a ,  460   b  positioned along the support  410  (e.g., on portions of the elongate portion  430  positioned at opposite sides of the recipient&#39;s head). The piezoelectric bending mechanism  460  is mechanically coupled to the flexible portions  430 , and is configured to bend (e.g., either towards the head or away from the head) in response to control signals, thereby modifying an orientation between the flexible portions  430  of the support  410 , a shape of the support  410 , and the amount of force applied by the support  410  to the recipient&#39;s skin 
       FIGS.  5 C and  5 D  schematically illustrate two example piezoelectric bending mechanisms  460  in accordance with certain embodiments described herein. The piezoelectric bending mechanism  460  of  FIG.  5 C  comprises a single piezoelectric element  462  alongside a non-piezoelectric portion  464  of the bending mechanism  460  (e.g., a unilayer configuration), the piezoelectric element  462  configured to expand and contract in response to control signals, thereby bending the bending mechanism  460  and modifying the force applied by the first and second end portions  440   a ,  440   b  while the support  410  is worn by the recipient. The piezoelectric bending mechanism  460  of  FIG.  5 D  comprises a pair of piezoelectric elements  462   a ,  462   b  positioned alongside one another (e.g., a dual layer configuration). For example, one piezoelectric element  462   a  can be on a first side of the support  410  (e.g., a side closest to the recipient&#39;s head) and the other piezoelectric element  462   b  can be on a second side of the support  410  (e.g., a side farthest from the recipient&#39;s head). The piezoelectric elements  462   a ,  462   b  are configured to expand and contract in response to control signals such that when one piezoelectric element  462   a  expands, the other piezoelectric element  462   b  contracts and vice versa, thereby bending the bending mechanism  460  and modifying the force applied by the first and second end portions  440   a ,  440   b  while the support  410  is worn by the recipient. 
       FIG.  6    schematically illustrates another example adjustment mechanism  450  in accordance with certain embodiments described herein. The example adjustment mechanism  450  is configured to modify a pressure applied to the recipient&#39;s skin in response to the modified force applied to the recipient&#39;s skin. The adjustment mechanism  450  comprises an actuator  452  that comprises an interface surface  610  that is configured to contact the recipient&#39;s skin. For example, the actuator  452  can comprise a soft, adaptive material (e.g., foam; incompressible fluid) contained in a reservoir or bladder that defines a shape of the interface surface  610 . As shown on the left side of  FIG.  6   , when the applied force is at a first force value (e.g., 1 newton), the interface surface  610  pressing against the recipient&#39;s skin has a first shape, resulting in the contact area between the interface surface  610  and the recipient&#39;s skin having a first area value (e.g., 1 cm 2 ), and a first pressure (e.g., 1 newton/cm 2 ) applied to the recipient&#39;s skin. As shown on the right side of  FIG.  6   , when the applied force is at a second force value (e.g., 5 newtons) that is larger than the first force value, the interface surface  610  pressing against the recipient&#39;s skin has a second shape (e.g., flatter, less convex than the first shape), resulting in the contact area between the interface surface  610  and the recipient&#39;s skin having a second area value (e.g., 4 cm 2 ) that is larger than the first area value, and a second pressure (e.g., 1.25 newton/cm 2 ) applied to the recipient&#39; skin. While the second pressure is higher than the first pressure, the ratio of the second pressure to the first pressure (e.g., 1.25:1) is less than the ratio of the second force value to the first force value (e.g., 5:1). Thus, certain embodiments described herein advantageously provide an increased force applied to the recipient&#39;s skin while the pressure applied to the recipient&#39;s skin is increased by a lesser degree. In certain other embodiments, the pressure applied can remain unchanged or reduced upon application of a higher force value. 
     In certain embodiments, the support  410  is configured to actively adjust the force pressing against the head in response at least in part to operational conditions detected while the support  410  is worn by the recipient. For example, the at least one adjustment mechanism  450  can be configured to adjust the at least one of a length and a shape of the support  410  in response to control signals generated while the support  410  is worn by the recipient, and the control signals can be generated in response to the detected operational conditions. In certain embodiments, the at least one adjustment mechanism  450  is in operative communication (e.g., wired communication; wireless communication) with the at least one bone conduction device  420  and at least some of the control signals are generated by the at least one bone conduction device  420  and received by the at least one adjustment mechanism  450 . In certain other embodiments, the at least one adjustment mechanism  450  comprises one or more sensors (e.g., accelerometers) and at least some of the control signals are generated by the at least one adjustment mechanism  450 . 
     In certain embodiments, the operational conditions include but are not limited to one or more of the following: motion of the recipient&#39;s head; location of the recipient; time of day; category of auditory information being provided to the recipient via the auditory stimulation (e.g., transmitted by the vibrations); and input received from the recipient. For example, the motion of the recipient&#39;s head can be monitored by one or more sensors (e.g., accelerometers) in the at least one bone conduction device  420  and/or the at least one adjustment mechanism  450 . Control signals configured to instruct the at least one adjustment mechanism  450  to increase the force can be generated in response to the one or more sensors detecting accelerations larger than a predetermined threshold (e.g., due to rough housing, falls, and/or other activities by the recipient) that could adversely affect the retention of the support  410  on the recipient&#39;s head and/or the transmission of the auditory stimulation (e.g., vibrations) from the at least one bone conduction device  420  to the recipient. 
     For another example, the location of the recipient can be monitored by one or more sensors (e.g., global positioning system sensors) in the at least one bone conduction device  420  and/or the at least one adjustment mechanism  450 . Control signals configured to instruct the at least one adjustment mechanism  450  to increase the force can be generated in response to the one or more sensors detecting that the recipient is at a location (e.g., selected by the recipient) at which better sound quality is warranted (e.g., in a lecture hall; at a concert or theater venue). 
     For another example, the time of day can be monitored by one or more clocks in the at least one bone conduction device  420  and/or the at least one adjustment mechanism  450 . Control signals configured to instruct the at least one adjustment mechanism  450  to adjust the force can be generated in response to the one or more clocks detecting that the time of day is within one or more predetermined time periods (e.g., selected by the recipient). The force can be increased in time periods during which better sound quality is warranted (e.g., during daytime) and/or can be decreased in time periods during which better sound quality is not warranted (e.g., during bedtime). 
     For another example, the time period during which a force is above a predetermined force threshold can be monitored by one or more clocks, timers, or counters in the at least one bone conduction device  420  and/or the at least one adjustment mechanism  450 . Control signals configured to instruct the at least one adjustment mechanism  450  to decrease the force can be generated in response to the one or more clocks detecting that the force has been above the predetermined force threshold for a time period longer than one or more predetermined time periods (e.g., selected by the recipient). By decreasing the force (e.g., intermittently) in this manner, certain embodiments can help prevent larger forces from being applied for excessively long periods of time which could otherwise result in injury to the recipient&#39;s skin. By monitoring the time period during which the force is above a predetermined force threshold, certain embodiments described herein can provide an estimate of the time period of active use of the bone conduction device  420  which can be provided to a pre-approved third party (e.g., a parent of a child recipient; a clinician; a cost reimbursement provider). In certain embodiments in which the recipient is allowed to temporarily override the predetermined force threshold (e.g., a force threshold corresponding to safe long-term usage), such monitoring can advantageously be used to determine whether the recipient is overusing the override option or to prevent the recipient from overusing the override option. 
     For another example, the category of the auditory information can be monitored by the at least one bone conduction device  420  and/or the at least one adjustment mechanism  450 . Control signals configured to instruct the at least one adjustment mechanism  450  to increase the force can be generated in response to detecting that the auditory information is in one or more of the following categories: speech; music; information from streaming content (e.g., television), a telephone, and/or a telecoil (e.g., by detecting that the source of the auditory information is from a source different from a microphone of the bone conduction device  420 ); sounds indicative of dangerous conditions (e.g., sound of oncoming vehicle); and the recipient&#39;s name. Control signals configured to instruct the at least one adjustment mechanism  450  to decrease the force can be generated in response to detecting that the auditory information is in one or more of the following categories: noise (e.g., excessive noise above a predetermined threshold; wind sounds) and quiet (e.g., sound below a predetermined threshold). For example, the control signals can be generated by an environmental classifier that uses the output from one or more microphones to categorize the recipient&#39;s sound environment (e.g., speech in noise, speech in quiet, music, wind noise). The classifier can comprise a classification algorithm (e.g., a trained neural network) that is executed by a processor that is part of the at least one adjustment mechanism  450 , the at least one bone conduction device  420  or another device (e.g., a mobile phone in wireless communication with the at least one adjustment mechanism  450 ). Each classifier category can be assigned a force that correlates with the perceived listening effort/listening difficultly expected in the corresponding environment. For example, a relatively high force can be applied when the classifier output corresponds to “speech in noise,” whereas a relatively low force can be applied when the classifier output corresponds to “wind noise.” 
     The specific operational conditions and/or their threshold parameters triggering the active adjustment of the force can be selected and/or adjusted in response to input received from the recipient, for example, from the recipient&#39;s mobile device (e.g., smartphone; tablet) running a corresponding software application and in wireless communication with the support  410  and/or the at least one bone conduction device  420 . In certain embodiments, the operational conditions and/or their triggering threshold parameters can be overridden (e.g., temporarily) by the recipient. For example, the input received from the recipient can increase and/or decrease the force regardless of the detected operational conditions. 
     In certain embodiments, the at least one adjustment mechanism  450  is configured to modify (e.g., actively adjust) a static component of a force applied by the at least one adjustment mechanism  450  in response to the control signals and to generate and apply vibrations indicative of auditory information to the recipient&#39;s skin. As used herein, the phrase “static component” refers to a component (e.g., a portion of a force; a portion of a voltage) which changes more slowly than does a component corresponding to the vibrations indicative of auditory information. In certain embodiments, the at least one adjustment mechanism  450  comprises at least one actuator  452  (e.g., piezoelectric element) which expands and contracts in response to a voltage applied to the at least one actuator  452 . As schematically illustrated in  FIG.  7   , a static component of the force can be modified in response to control signals  710  (e.g., generated in response at least in part to operational conditions detected while the support  410  is worn by the recipient) by modifying a static component  720  of a voltage applied to the at least one actuator  452 . In addition, the at least one actuator  452  can be driven by a non-static component  730  of the voltage applied to the at least one actuator  452  to generate the vibrations indicative of auditory information. That is, in some embodiments, the at least one adjustment mechanism  450  is configured to superimpose a dynamic signal (e.g., a signal representative of audio content with frequencies within the audible range) with a static signal (e.g., having no frequency component or a frequency component that is outside the audible frequency range) to generate an instantaneous drive signal for at least one actuator  452 . In certain such embodiments, the at least one actuator  452  is configured to generate a composite force, representative of the instantaneous drive signal, that comprises audio content (e.g., the dynamic signal) and a transmission force (e.g., the static signal) that influences the transmission of the dynamic force to the skull of the recipient. As shown in  FIG.  7   , the instantaneous signal (and corresponding composite force) comprise distinct components. By utilizing the at least one adjustment mechanism  450  to provide both the static component of the force and the vibrational component of the force, certain such embodiments can advantageously utilize the stiffness of the support  410  to generate the vibrations indicative of auditory information while avoiding use of a separate actuator (e.g., a vibration generator comprising a counter-mass). 
     Certain embodiments comprise a non-surgical bone conduction device comprising at least one actuator and a signal processor, wherein the signal processor is configured to produce a drive signal for the at least one actuator. The drive signal comprises: (i) a first signal component that fluctuates at frequencies within the audible range, and (ii) a second signal component that does not fluctuate or fluctuates at frequencies outside the audible range. In certain embodiments, the actuator is configured to provide a compressive force to retain the bone conduction device of the head of a recipient and/or transmit vibrations to the recipient&#39;s skull to evoke a hearing percept. In certain such embodiments, the actuator can be configured to modulate substantially all of the compressive force applied by the bone conduction device to the recipient&#39;s skull (e.g., the bone conduction device can be configured to not apply any force in the absence of a static clamping force generated by the actuator). In certain embodiments, the bone conduction device comprises a resilient frame that retains the bone conduction device on the skull of a recipient, but applies insufficient force to transit vibrations (e.g., the frame does not facilitate transmission of vibrations), in the absence of a clamping force from the actuator. 
       FIGS.  8 A and  8 B  are flow diagrams of two examples of a method  800  in accordance with certain embodiments described herein. In an operational block  810 , the method  800  comprises providing at least one vibration generator (e.g., at least one bone conduction device  420 ) configured to be worn on a head of a recipient and to transmit vibrations indicative of auditory information. In an operational block  820 , the method  800  further comprises modifying a static component of a force applied by the at least one vibration generator to the head in response to control signals while the at least one vibration generator is worn by the recipient. 
     In certain embodiments, the method  800  further comprises detecting one or more conditions of operation of the at least one vibration generator and generating the control signals at least in part in response to the detected one or more conditions of operation. The detected one or more conditions of operation comprise one or more of the following: motion of the head; the auditory information being in at least one category (e.g., at least one of: speech; music; information from streaming content, a telephone, and/or a telecoil; noise; sounds indicative of dangerous conditions; the recipient&#39;s name). Modifying the static component of the force in certain embodiments comprises increasing the static component in response to control signals indicative of a first set of the one or more conditions of operation (e.g., a set of conditions of operation warranting better sound quality) and decreasing the static component in response to control signals indicative of a second set of the one or more conditions of operation (e.g., a set of conditions of operation not warranting better sound quality). 
     In certain embodiments (see, e.g.,  FIG.  8 B ), the method  800  further comprises generating the control signals at least in part in response to input received from the recipient in an operational block  830 , monitoring a duration of time during which the static component of the force is over a predetermined threshold in an operational block  840 , and overriding the input received from the recipient when the duration is greater than a predetermined value in an operational block  850 . 
     While the example apparatus  400  has been described herein with regard to non-invasive or non-surgical bone conduction devices, other types of auditory prostheses may be used in conjunction with certain embodiments described herein. For example, for an cochlear implant auditory prosthesis comprising an external sound processor having a communication coil, the support  410  of certain embodiments described herein can be used to provide the retention force holding the external sound processor device and its communication coil in proximity to an implanted communication coil of the cochlear implant auditory prosthesis to provide sufficient coupling between the external and internal communication coils regardless of changes of the skin flap thickness of the skin overlaying the internal communication coil. Certain such embodiments advantageously avoid using magnets to supply the retention force and changing the magnet within the external sound processor device to account for changes of the skin flap thickness. 
     It is to be appreciated that the embodiments disclosed herein are not mutually exclusive and may be combined with one another in various arrangements. 
     The invention described and claimed herein is not to be limited in scope by the specific example embodiments herein disclosed, since these embodiments are intended as illustrations, and not limitations, of several aspects of the invention. Any equivalent embodiments are intended to be within the scope of this invention. Indeed, various modifications of the invention in form and detail, in addition to those shown and described herein, will become apparent to those skilled in the art from the foregoing description. Such modifications are also intended to fall within the scope of the claims. The breadth and scope of the invention should not be limited by any of the example embodiments disclosed herein, but should be defined only in accordance with the claims and their equivalents.