Patent Publication Number: US-2023156416-A1

Title: Bone conduction magnetic retention system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a Continuation application of U.S. patent application Ser. No. 17/387,551, filed Jul. 28, 2021, which is a Continuation application of U.S. patent application Ser. No. 16/148,146, filed Oct. 1, 2018, now U.S. Pat. No. 11,082,783, which is a Continuation application of U.S. patent application Ser. No. 14/811,138, filed Jul. 28, 2015, now U.S. Pat. No. 10,091,594, which claims priority to Provisional U.S. Patent Application No. 62/030,319, entitled BONE CONDUCTION MAGNETIC RETENTION SYSTEM, filed on Jul. 29, 2014, naming Johan GUSTAFSSON of Mölnlycke, Sweden, as an inventor, the entire contents of that application being incorporated herein by reference in its entirety. 
    
    
     BACKGROUND 
     Hearing loss, which may 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 to bypass the mechanisms of the ear. More specifically, an electrical stimulus is provided via the electrode array to the auditory nerve, thereby causing a hearing percept. 
     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 may retain some form of residual hearing because the hair cells in the cochlea may remain undamaged. 
     Individuals suffering from conductive hearing loss typically receive an acoustic hearing aid. 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. 
     In contrast to 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 generation of nerve impulses, which result in the perception of the received sound. Bone conduction devices are suitable to treat a variety of types of hearing loss and may be suitable for individuals who cannot derive sufficient benefit from acoustic hearing aids, cochlear implants, etc., or for individuals who suffer from stuttering problems. 
     SUMMARY 
     In accordance with one aspect, there is an external component of a medical device, comprising a transducer including a static magnetic flux circuit that interacts with a dynamic magnetic flux circuit and a magnetic retention system configured to retain the external component to a recipient via interaction with a ferromagnetic component attached to a recipient, the magnetic retention system including a magnetic flux circuit that encircles the static magnetic flux path of the transducer. 
     In accordance with another aspect, there is an external component of a bone conduction system, comprising an actuator, and a permanent magnet separate from the actuator, wherein the permanent magnet generates a permanent magnetic field having substantial components located outside the actuator on substantially opposite sides of the actuator for removably attaching the external component to a recipient via interaction of the permanent magnetic field with ferromagnetic material of an implanted component. 
     In accordance with yet another aspect, there is a removable component of a bone conduction system, comprising a recipient interface component, an actuator coupled to the recipient interface component, the actuator including a seismic mass, wherein actuation of the actuator moves the seismic mass relative to the recipient interface component, and a plurality of retention magnets separate from the seismic mass. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Some embodiments are described below with reference to the attached drawings, in which: 
         FIG.  1 A  is a perspective view of an exemplary bone conduction device in which at least some embodiments can be implemented; 
         FIG.  1 B  is a perspective view of an alternate exemplary bone conduction device in which at least some embodiments can be implemented; 
         FIG.  2    is a schematic diagram conceptually illustrating a removable component of a percutaneous bone conduction device in accordance with at least some exemplary embodiments; 
         FIG.  3    is a schematic diagram conceptually illustrating a passive transcutaneous bone conduction device in accordance with at least some exemplary embodiments; 
         FIG.  4 A  is a schematic diagram of an exemplary embodiment of a bone conduction device; 
         FIG.  4 B  is a schematic diagram of another exemplary embodiment of a bone conduction device; 
         FIG.  5    is a schematic diagram of an exemplary electromagnetic actuator assembly according to an exemplary embodiment; 
         FIG.  6    is a schematic diagram of an exemplary magnetic flux circuit of a retention system according to an exemplary embodiment; 
         FIG.  7    is a schematic diagram of a portion of another exemplary magnetic flux circuit of a retention system according to an exemplary embodiment; 
         FIG.  8    is a schematic diagram of a portion of another exemplary magnetic flux circuit of a retention system according to an exemplary embodiment; 
         FIG.  9    is a schematic diagram of exemplary magnetic flux circuits of an actuator according to an exemplary embodiment; 
         FIG.  10    is a schematic diagram depicting an exemplary magnetic flux circuit of an exemplary retention system combined with an exemplary magnetic flux circuit of an actuator according to an exemplary embodiment; 
         FIG.  11    is another schematic diagram depicting an exemplary magnetic flux circuit of an exemplary retention system combined with an exemplary magnetic flux circuit of an actuator according to an exemplary embodiment; 
         FIG.  12    depicts a height dimension of the external component of  FIG.  4 A ; and 
         FIG.  13    depicts an alternate embodiment of an external component. 
     
    
    
     DETAILED DESCRIPTION 
       FIG.  1 A  is a perspective view of a bone conduction device  100 A in which embodiments may be implemented. As shown, the recipient has an outer ear  101 , a middle ear  102  and an inner ear  103 . Elements of outer ear  101 , middle ear  102  and inner ear  103  are described below, followed by a description of bone conduction device  100 . 
     In a fully functional human hearing anatomy, outer ear  101  comprises an auricle  105  and an ear canal  106 . A sound wave or acoustic pressure  107  is collected by auricle  105  and channeled into and through ear canal  106 . Disposed across the distal end of ear canal  106  is a tympanic membrane  104  which vibrates in response to acoustic wave  107 . This vibration is coupled to oval window or fenestra ovalis  210  through three bones of 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 middle ear  102  serve to filter and amplify acoustic wave  107 , causing oval window  210  to vibrate. Such vibration sets up waves of fluid motion within cochlea  139 . Such fluid motion, in turn, activates hair cells (not shown) that line the inside of cochlea  139 . Activation of the hair cells causes appropriate nerve impulses to be transferred through the spiral ganglion cells and auditory nerve  116  to the brain (not shown), where they are perceived as sound. 
       FIG.  1 A  also illustrates the positioning of bone conduction device  100 A relative to outer ear  101 , middle ear  102  and inner ear  103  of a recipient of device  100 . As shown, bone conduction device  100  is positioned behind outer ear  101  of the recipient and comprises a sound input element  126 A to receive sound signals. The sound input element may comprise, for example, a microphone, telecoil, etc. In an exemplary embodiment, sound input element  126 A may be located, for example, on or in bone conduction device  100 A, or on a cable extending from bone conduction device  100 A. 
     In an exemplary embodiment, bone conduction device  100 A comprises an operationally removable component and a bone conduction implant. The operationally removable component is operationally releasably coupled to the bone conduction implant. By operationally releasably coupled, it is meant that it is releasable in such a manner that the recipient can relatively easily attach and remove the operationally removable component during normal use of the bone conduction device  100 A. Such releasable coupling is accomplished via a coupling assembly of the operationally removable component and a corresponding mating apparatus of the bone conduction implant, as will be detailed below. This as contrasted with how the bone conduction implant is attached to the skull, as will also be detailed below. The operationally removable component includes a sound processor (not shown), a vibrating electromagnetic actuator and/or a vibrating piezoelectric actuator and/or other type of actuator (not shown—which are sometimes referred to herein as a species of the genus vibrator) and/or various other operational components, such as sound input device  126 A. In this regard, the operationally removable component is sometimes referred to herein as a vibrator unit. More particularly, sound input device  126 A (e.g., a microphone) converts received sound signals into electrical signals. These electrical signals are processed by the sound processor. The sound processor generates control signals which cause the actuator to vibrate. In other words, the actuator converts the electrical signals into mechanical motion to impart vibrations to the recipient&#39;s skull. 
     As illustrated, the operationally removable component of the bone conduction device  100 A further includes a coupling assembly  240  configured to operationally removably attach the operationally removable component to a bone conduction implant (also referred to as an anchor system and/or a fixation system) which is implanted in the recipient. In the embodiment of  FIG.  1   , coupling assembly  240  is coupled to the bone conduction implant (not shown) implanted in the recipient in a manner that is further detailed below with respect to exemplary embodiments of the bone conduction implant. Briefly, an exemplary bone conduction implant may include a percutaneous abutment attached to a bone fixture via a screw, the bone fixture being fixed to the recipient&#39;s skull bone  136 . The abutment extends from the bone fixture which is screwed into bone  136 , through muscle  134 , fat  128  and skin  232  so that the coupling assembly may be attached thereto. Such a percutaneous abutment provides an attachment location for the coupling assembly that facilitates efficient transmission of mechanical force. 
     It is noted that while many of the details of the embodiments presented herein are described with respect to a percutaneous bone conduction device, some or all of the teachings disclosed herein may be utilized in transcutaneous bone conduction devices and/or other devices that utilize a vibrating electromagnetic actuator. For example, embodiments also include passive transcutaneous bone conduction systems where no active component (e.g., the actuator) is implanted beneath the skin (it is instead located in an external component), and the implantable part is, for instance, a ferromagnetic plate. Some embodiments of the passive transcutaneous bone conduction systems are configured for use where the vibrator (located in an external component) containing the actuator is held in place by pressing the vibrator against the skin of the recipient. In the embodiments detailed herein, the external component is held against the skin via a magnetic coupling (magnetic material and/or magnets being implanted in the recipient and the vibrator having a magnet and/or magnetic material to complete the magnetic circuit, thereby coupling the vibrator to the recipient). 
     More specifically,  FIG.  1 B  is a perspective view of a transcutaneous bone conduction device  100 B in which embodiments can be implemented. 
       FIG.  1 B  also illustrates the positioning of bone conduction device  100 B relative to outer ear  101 , middle ear  102  and inner ear  103  of a recipient of device  100 . As shown, bone conduction device  100  is positioned behind outer ear  101  of the recipient. Bone conduction device  100 B comprises an external component  140 B and implantable component  150 . The bone conduction device  100 B includes a sound input element  126 B to receive sound signals. As with sound input element  126 A, sound input element  126 B may comprise, for example, a microphone, telecoil, etc. In an exemplary embodiment, sound input element  126 B may be located, for example, on or in bone conduction device  100 B, on a cable or tube extending from bone conduction device  100 B, etc. Alternatively, sound input element  126 B may be subcutaneously implanted in the recipient, or positioned in the recipient&#39;s ear. Sound input element  126 B may also be a component that receives an electronic signal indicative of sound, such as, for example, from an external audio device. For example, sound input element  126 B may receive a sound signal in the form of an electrical signal from an MP3 player electronically connected to sound input element  126 B. 
     Bone conduction device  100 B comprises a sound processor (not shown), an actuator (also not shown) and/or various other operational components. In operation, sound input device  126 B converts received sounds into electrical signals. These electrical signals are utilized by the sound processor to generate control signals that cause the actuator to vibrate. In other words, the actuator converts the electrical signals into mechanical vibrations for delivery to the recipient&#39;s skull. 
     In accordance with some embodiments, a fixation system  162  may be used to secure implantable component  150  to skull  136 . As described below, fixation system  162  may be a bone screw fixed to skull  136 , and also attached to implantable component  150 . 
     In one arrangement of  FIG.  1 B , bone conduction device  100 B can be a passive transcutaneous bone conduction device. That is, no active components, such as the actuator, are implanted beneath the recipient&#39;s skin  132 . In such an arrangement, the active actuator is located in external component  140 B, and implantable component  150  includes a magnetic plate, as will be discussed in greater detail below. The magnetic plate of the implantable component  150  vibrates in response to vibrations transmitted through the skin, mechanically and/or via a magnetic field, that are generated by an external magnetic plate. 
       FIG.  2    is an embodiment of a removable component (external component)  200  of a bone conduction device in accordance with an embodiment corresponding to that of  FIG.  1 A , illustrating use of a percutaneous bone conduction device. Removable component  200 , corresponding to, for example, the external component of bone conduction device  100 A of  FIG.  1 A , includes a housing  242 , a vibrating electromagnetic actuator  250 , and a coupling assembly  240  that extends from housing  242  and is mechanically linked to vibrating electromagnetic actuator  250 . Collectively, vibrating electromagnetic actuator  250  and coupling assembly  240  form a vibrating electromagnetic actuator-coupling assembly  280 . Vibrating electromagnetic actuator-coupling assembly  280  is suspended in housing  242  by spring  244 . In an exemplary embodiment, spring  244  is connected to coupling assembly  240 , and vibrating electromagnetic actuator  250  is supported by coupling assembly  240 . It is noted that while embodiments are detailed herein that utilize a spring, alternate embodiments can utilize other types of resilient elements. Accordingly, unless otherwise noted, disclosure of a spring herein also includes disclosure of any other type of resilient element that can be utilized to practice the respective embodiment and/or variations thereof. 
       FIG.  3    depicts an exemplary embodiment of a transcutaneous bone conduction device  300  according to an embodiment that includes an external device  340  (corresponding to, for example, element  140 B of  FIG.  1 B ) and an implantable component  350  (corresponding to, for example, element  150  of  FIG.  1 B ). The transcutaneous bone conduction device  300  of  FIG.  3    is a passive transcutaneous bone conduction device in that a vibrating electromagnetic actuator  342  is located in the external device  340 . Vibrating electromagnetic actuator  342  is located in housing  344  of the external component and is coupled to a support assembly in the form of a plate  346 . Plate  346  may 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 device  340  and the implantable component  350  sufficient to hold the external device  340  against the skin of the recipient. 
     In an exemplary embodiment, the vibrating electromagnetic actuator  342  is a device that converts electrical signals into vibration. In operation, sound input element  126  converts sound into electrical signals. Specifically, the transcutaneous bone conduction device  300  provides these electrical signals to vibrating actuator  342 , or to a sound processor (not shown) that processes the electrical signals, and then provides those processed signals to vibrating electromagnetic actuator  342 . The vibrating electromagnetic actuator  342  converts the electrical signals (processed or unprocessed) into vibrations. Because vibrating electromagnetic actuator  342  is mechanically coupled to plate  346 , the vibrations are transferred from the vibrating actuator  342  to plate  346 . Implanted plate assembly  352  is part of the implantable component  350 , and is made of a ferromagnetic material that may 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 device  340  and the implantable component  350  sufficient to hold the external device  340  against the skin of the recipient, as will be detailed further below. Accordingly, vibrations produced by the vibrating electromagnetic actuator  342  of the external device  340  are transferred from plate  346  across the skin to plate  355  of implanted plate assembly  352 . This can be accomplished as a result of mechanical conduction of the vibrations through the skin, resulting from the external device  340  being in direct contact with the skin and/or from the magnetic field between the two plates. These vibrations are transferred without penetrating the skin with a solid object, such as an abutment, as detailed herein with respect to a percutaneous bone conduction device. 
     As may be seen, the implanted plate assembly  352  is substantially rigidly attached to a bone fixture  341  in this embodiment. Plate screw  356  is used to secure plate assembly  352  to bone fixture  341 . The portions of plate screw  356  that interface with the bone fixture  341  substantially correspond to an abutment screw discussed in some additional detail below, thus permitting plate screw  356  to readily fit into an existing bone fixture used in a percutaneous bone conduction device. In an exemplary embodiment, plate screw  356  is configured so that the same tools and procedures that are used to install and/or remove an abutment screw (described below) from bone fixture  341  can be used to install and/or remove plate screw  356  from the bone fixture  341  (and thus the plate assembly  352 ). 
     As will be detailed below, the teachings detailed herein and/or variations thereof can be applicable to the various embodiments of  FIGS.  2 - 3    and/or variations thereof. In an exemplary embodiment, the various teachings detailed herein and/or variations thereof can be applied to the various embodiments of  FIGS.  2 - 3    to obtain a hearing prosthesis where a vibrating actuator of an external component (element  200  of  FIG.  2   , element  340  of  FIG.  3   ) is removably attached to a recipient such that the actuator is in vibrational communication with a recipient such that vibrations generated by the vibrating electromagnetic actuator in response to a sound captured by sound capture devices of the various embodiments are ultimately transmitted to bone of a recipient 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 that receives 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. That said, it is noted that embodiments can also effectively evoke a hearing percept in humans younger than 18 years old and older than 40 years old and/or in humans without a fully functioning cochlea and/or in humans that are not completely fluent in the language forming the basis of the speech. In other words, the aforementioned population of 18 to 40 year olds is provided by way of example and not by way of limitation. 
     Some exemplary features of a magnetic retention system for retaining the removable external device of a bone conduction device to a recipient will now be described in terms of a passive transcutaneous bone conduction device of  FIG.  1 B , followed by an example of use for a percutaneous bone conduction device of  FIG.  1 A . It is noted that any and/or all of these features and/or variations thereof may be utilized in other types of prostheses and/or medical devices and/or other devices. It is further noted that while embodiments detailed herein are often referred to in terms of the electromagnetic transducer being an actuator, it is to be understood that any of these teachings, unless otherwise specifically noted, are equally applicable to electromagnetic transducers that receive vibration and output a signal resulting from the received vibrations. It is further noted that other types of actuators, such as by way of example only and not by way of limitation, piezoelectric actuators, can be utilized in some embodiments. That is, any disclosure detailed herein of an electromagnetic actuator/transducer corresponds to a disclosure of a piezoelectric actuator/transducer. 
     More specifically, referring now to  FIG.  4 A , which depicts a schematic of an exemplary bone conduction device  400 A, the exemplary bone conduction device  400 A utilizing permanent magnets to retain external device  440 A corresponding to external device  340  of  FIG.  3   .  FIG.  4 A  further depicts an implantable component  450 A corresponding to implantable component  350  of  FIG.  3   . 
     In an exemplary embodiment, external device  440 A has the functionality of a transducer/actuator, irrespective of whether it is used with implantable component  450 A. That is, in some exemplary embodiments, external device  440 A will vibrate whether or not the implantable component  450 A is present (e.g., whether or not the static magnetic field extends to the implantable component  450 A, as will be detailed below). 
     The external device  440 A includes a vibrating electromagnetic actuator enclosed in a housing, hereinafter referred to as an actuator assembly, represented by black box  480 . Additional details of the vibrating electromagnetic actuator are provided below. Again it is noted that in an alternate embodiment, black box  480  is an actuator assembly that is a piezoelectric actuator. 
     External device  440 A further includes element  458 A, which is a permanent magnet having a North-South alignment in a first direction relative to a longitudinal axis  490  of the electromagnetic actuator (the vertical direction of  FIG.  4 A , which is parallel to the direction of movement of components of the actuator during actuation thereof, indicated by arrow  499 , as will be detailed below). Element  458 B is a permanent magnet having a North-South alignment in a second direction relative to a longitudinal axis of the electromagnetic actuator, the second direction being opposite the first direction. In an exemplary embodiment, the permanent magnets are bar magnets (having a longitudinal direction extending normal to the plane of FIG.  4 A). In some embodiments, the bar magnets have hogged-out sections in the center to accommodate the actuator assembly  480 . In some embodiments, the magnets can be “C” shaped magnets, with the tips of the “C” facing the opposite “C.” In some embodiments, the magnets can be crescent moon magnets. In alternative embodiments, other configurations of the magnets can be utilized. It is noted that in some embodiments, the shapes of the permanent magnets of the implantable components may drive the shapes of the magnets of the external component. For example, if magnets of the implantable component are half-moon shaped (collectively forming a circular shape), the permanent magnets of the external component can be semi-circular shaped and/or half-circular shaped (all shapes with respect to the cross-section lying on a plane normal to the longitudinal axis of the bone conduction device). Any configuration of permanent magnet(s) that can enable the teachings detailed herein and/or variations thereof to be practiced can be utilized in at least some embodiments. 
       FIG.  4 A  also shows that external device  440 A includes a support assembly  446 A, which corresponds to plate  346  of  FIG.  3    as described above. It is through support assembly  446 A that vibrations generated by the actuator of actuator assembly  480  of the external device  440 A are transferred from the external component  440 A to the skin of the recipient to evoke a hearing percept. In an exemplary embodiment, support assembly  446 A is made at least partially of a non-ferromagnetic material that is compatible with the skin of the recipient (or at least is coated with a material that is compatible with the skin of the recipient). In at least some exemplary embodiments, the support assembly  446 A is free of any permanent magnet components. In this regard, in at least some exemplary embodiments, the support assembly  446 A is configured to substantially avoid influencing the magnetic flux generated by the permanent magnets  458 A and  458 B. 
     It is noted that in an exemplary embodiment, the external device  440 A can be located within a housing. In an exemplary embodiment, the housing can be a housing that is connected to the components depicted in  FIG.  4 A  by a spring. Alternatively, the housing can be rigidly mounted to the components depicted in  FIG.  4 A . 
     Continuing with reference to  FIG.  4 A , the device  400 A further includes an implantable component  450 A, corresponding to implantable component  350  of  FIG.  3   . In some embodiments, implantable component  450 A includes at least two permanent magnets  458 C and  458 D. Permanent magnet  458 C has a North-South alignment in a first direction relative to a longitudinal axis of the electromagnetic actuator (the vertical direction of  FIG.  4 A ). Permanent magnet  458 D has a North-South alignment in a second direction relative to a longitudinal axis of the electromagnetic actuator, the second direction being opposite the first direction. In an exemplary embodiment, the permanent magnets are bar magnets (having a longitudinal direction extending normal to the plane of  FIG.  4 A ). In at least some exemplary embodiments, during operational use of the bone conduction device  400 A, the external device  440 A is aligned with the implantable component  450 A such that the poles of the permanent magnets  458 A and  458 C have a North-South alignment in the same direction and the poles of the permanent magnets  458 B and  458 D have a North-South alignment in the same direction (but opposite of that of magnets  458 A and  458 C). In at least some exemplary embodiments, permanent magnets  458 C and  458 D are bar magnets connected to one another via chassis  459  of the implantable component  450 A. In an exemplary embodiment, the chassis  459  is a nonmagnetic material (e.g., titanium). In alternative embodiments, other configurations of the magnets can be utilized, some of which will be described below. Any configuration of permanent magnet(s) that can enable the teachings detailed herein and/or variations thereof to be practiced can be utilized in at least some embodiments. 
     That said, in an alternative embodiment, it is noted that the implantable component  450 A does not include permanent magnets. In at least some embodiments, elements  458 C and  458 D are replaced with other types of ferromagnetic material (e.g. soft iron (albeit encapsulated in titanium, etc.)). Also, elements  458 C and  458 D can be replaced with a single, monolithic component. Any configuration of ferromagnetic material of the implantable component  450 A that will enable the permanent magnets of the external device  440 A to establish a magnetic coupling with the implantable component  450 A that will enable the external device  440 A to be retained on the surface of the skin as detailed herein can be utilized in at least some embodiments. 
     In operation, sound input element  126  ( FIG.  3   ) converts sound into electrical signals. As noted above, the bone conduction device provides these electrical signals to a sound processor which processes the signals and provides the processed signals to the vibrating electromagnetic actuator of external device  440 A, which then converts the electrical signals (processed or unprocessed) into vibrations. Because the vibrating electromagnetic actuator of external device  440 A is mechanically coupled to support assembly  446 A, which can include a plate having a surface configured to abut skin of the recipient, the vibrations are transferred from the vibrating electromagnetic actuator to support assembly  446 A and then to the recipient via the support assembly  446 A, to evoke a hearing percept, all while the external device  440 A is retained on the recipient via the magnetic coupling between the permanent magnets of the external device  440 A and the ferromagnetic material (e.g., permanent magnets) of the implantable component  450 A. 
     As noted above, in some embodiments some of the teachings detailed herein are applicable to percutaneous bone conduction devices.  FIG.  4 B  depicts a schematic of an exemplary bone conduction device  400 B corresponding to the removable external component of the bone conduction device  200  of  FIG.  2    plus an implantable component  450 B, the exemplary bone conduction device  400 B having the aforementioned static magnetic flux features. 
     In an exemplary embodiment, external device  440 B has the functionality of a transducer/actuator, irrespective of whether it is used with implantable component  450 B. The external device  440 B includes an actuator assembly, again represented by black box  480 . External device  440 B further includes the permanent magnets and the yoke (the latter being optional) of  FIG.  4 A . 
     The external device  440 B further includes a support assembly  446 B. When the actuator of the actuator assembly  480  is actuated, a counterweight assembly of the actuator (also referred to as seismic mass, discussed in greater detail below) moves relative to the support assembly, as will be further detailed below, and thus generates vibrations, which are transmitted through the support assembly  446 B. 
     Support assembly  446 B is configured to interface with a cap  462  of implantable component  450 B, and thus support assembly  446 B is a recipient interface component. Specifically, support assembly  446 B includes a recess configured to receive cap  462 . In the embodiment of  FIG.  4 B , the external device  440 B (the removable component) is held to the implantable component  450 B in general, or to the cap  462  in particular, via magnetic attraction due to the permanent magnets  458 A and  458 B, as cap  460  includes a ferromagnetic component (e.g., soft iron and/or permanent magnets), as will be described below. First, however, additional details of the implantable component  450 B will now be described. 
     Specifically, implantable component  450 B of  FIG.  4 B  is in the form of bone conduction implant which includes a percutaneous abutment attached to a bone fixture via a screw, the bone fixture being fixed to the recipient&#39;s skull bone  136 . The abutment extends from the bone fixture which is screwed into bone  136 , through muscle  134 , fat  128  and skin  132  so that the coupling apparatus can be attached thereto. Such a percutaneous abutment provides an attachment location for the coupling apparatus of the removable component of the percutaneous bone conduction device that facilitates efficient transmission of mechanical force from the removable component  440 B to the implantable component  450 B. More specifically, the implantable component  450 B includes a bone fixture  410  configured to screw into the skull bone  136 , a skin-penetrating abutment  420  and an abutment screw  430  that is in the form of an elongate coupling shaft. As may be seen, the abutment screw  430  connects and holds the abutment  420  to the fixture  410 , thereby rigidly attaching abutment  420  to bone fixture  410 . The rigid attachment is such that the abutment is vibrationally connected to the fixture  410  such that at least some of the vibrational energy transmitted to the abutment is transmitted to the fixture in a sufficient manner to effectively evoke a hearing percept. 
     As noted above, bone conduction implant  450 B further includes a cap  462 , which is or includes a ferromagnetic component, although in alternate embodiments, a ferromagnetic component is part of the abutment  420  (in which case the cap may or may not be present). The cap  462  is directly attached to the abutment  420  via a snap-couple, although in other embodiments, it can be connected in another manner (e.g., screwed onto the abutment screw  430 , welded or otherwise adhered to the abutment, etc.). Any device, system or method that will enable the implantable component  450 B to serve as a component that will enable the removable component  440 B to be magnetically coupled thereto can be used in some embodiments. 
     While the configuration depicted in  FIG.  4 B  depicts the implantable component  450 B having a male configuration that is received in the female configuration of the removable external component  440 B, the reverse can be the case in some embodiments. Any configuration that will enable the removable external component  440 B to be magnetically held to the implantable component  450 B can be used in some embodiments providing that the teachings detailed herein and/or variations thereof can be practiced. 
     Prior to describing some specifics of the performance of the magnetic retention system according to some embodiments, some high-level principles of operation of an exemplary electromagnetic actuator of the actuator assembly  480  will now be described. It is noted that these are but exemplary features of an exemplary electromagnetic actuator, and other actuators can be used in alternate embodiments. For example, the actuator described below is a “balanced actuator.” Conversely, an unbalanced actuator can be used. Further, as noted above, a piezoelectric actuator can be used. The following provides a frame of reference to describe the circuit of the magnetic flux of the retention system relative to the magnetic flux circuits of the of the electromagnetic actuator of the actuator assembly  480  (in embodiments that so use an electromagnetic actuator). 
       FIG.  5    is a cross-sectional view of the actuator assembly  480  used in the embodiments of  FIGS.  4 A and  4 B . The actuator assembly  480  includes a housing  501  that encloses a vibrating electromagnetic actuator-coupling assembly  580 . The vibrating electromagnetic actuator-coupling assembly  580  includes a vibrating electromagnetic transducer  550  in the form of an actuator and a vibration transfer component  540 . Vibration transfer component  540  is rigidly connected to vibrating electromagnetic transducer  550  and transfers vibrational energy therefrom to the housing  501  (although in other embodiments, vibration transfer component  540  is configured to conduct the vibrations through the housing  501 ) and thus to the support apparatuses of the various devices ( 446 A,  446 B) so that it can be transferred to the recipient to evoke a hearing percept. 
     As illustrated in  FIG.  5   , vibrating electromagnetic actuator  550  includes a bobbin assembly  554  and a counterweight assembly  555  (also referred to as a seismic mass). As illustrated, bobbin assembly  554  includes a bobbin  554 A and a coil  554 B that is wrapped around a core  554 C of bobbin  554 A. In the illustrated embodiment, bobbin assembly  554  is radially symmetrical. It is noted that unless otherwise specified, the electromagnetic transducers detailed herein are radially symmetrical. 
     Counterweight assembly  555  includes springs  556  and  557 , permanent magnets  558 A and  558 B, yokes  560 A,  560 B and  560 C, spacers  562 , and counterweight mass  570 . Spacers  562  provide a connective support between spring  556  and the other elements of counterweight assembly  555  just detailed, although it is noted that in some embodiments these spacers are not present and the spring is connected only to the counterweight mass  570 , while in other embodiments the spring is only connected to the spacers. Springs  556  and  557  connect bobbin assembly  554  via spacers  522  and  524  to the rest of counterweight assembly  555  and permit counterweight assembly  555  to move relative to bobbin assembly  554  upon interaction of a dynamic magnetic flux produced by coil  554 B. The static magnetic flux is produced by permanent magnets  558 A and  558 B of counterweight assembly  555 . In this regard, counterweight assembly  555  is a static magnetic field generator where the permanent magnets  558 A and  558 B are arranged such that their respective south poles face each other and their respective north poles face away from each other. It is noted that in other embodiments, the respective south poles may face away from each other and the respective north poles may face each other. 
     Coil  554 B, in particular, may be energized with an alternating current to create the dynamic magnetic flux about coil  554 B. In an exemplary embodiment, bobbin  554 A is made of a soft iron. The iron of bobbin  554 A is conducive to the establishment of a magnetic conduction path for the dynamic magnetic flux. In an exemplary embodiment, the yokes of the counterweight assembly  555  are made of soft iron also conducive to the establishment of a magnetic conduction path for the static magnetic flux. 
     The soft iron of the bobbin and yokes may be of a type that increases the magnetic coupling of the respective magnetic fields, thereby providing a magnetic conduction path for the respective magnetic fields. As will be further detailed below, in other embodiments, other types of material, at least for the bobbin, can be utilized in at least some embodiments. 
     As may be seen, vibrating electromagnetic actuator  550  includes two axial air gaps  570 A and  570 B that are located between bobbin assembly  554  and counterweight assembly  555 . With respect to a radially symmetrical bobbin assembly  554  and counterweight assembly  555 , such as that detailed in  FIG.  5   , air gaps  570 A and  570 B extend in the direction of the primary relative movement between bobbin assembly  554  and counterweight assembly  555 , indicated by arrow  500 A (the primary relative movement is discussed in greater detail below). 
     Further, as may be seen in  FIG.  5   , the vibrating electromagnetic actuator  550  includes two radial air gaps  572 A and  572 B that are located between bobbin assembly  554  and counterweight assembly  555 . With respect to a radially symmetrical bobbin assembly  554  and counterweight assembly  555 , the air gap extends about the direction of relative movement between bobbin assembly  554  and counterweight assembly  555 . As may be seen in  FIG.  5   , the permanent magnets  558 A and  558 B are arranged such that their respective south poles face each other and their respective north poles face away from each other. 
     In the electromagnetic actuator of  FIG.  5   , the radial air gaps  572 A and  572 B close static magnetic flux between the bobbin  554 A and the yokes  560 B and  560 C, respectively. Further, axial air gaps  570 A and  570 B close the static and dynamic magnetic flux between the bobbin  554 A and the yoke  560 A. Accordingly, in the radially symmetrical device of  FIG.  5   , there are a total of four (4) air gaps. In an exemplary embodiment, the air gaps are gaps in which little to no material having substantial magnetic aspects is located in the air gap. They are areas of relatively high reluctance but magnetic flux still flows therethrough. Accordingly, an air gap is not limited to a gap that is filled by air. In this vein, additional gaps that do not close a magnetic field may be present, but they are not air gaps. 
     Is further noted that while the exemplary embodiments depicted in the figures correspond to a balance electromagnetic actuator (transducer) alternate embodiments can utilize unbalanced electromagnetic actuators. Any type of actuator (transducer) that can be utilized to implement the teachings detailed herein and are variations thereof can utilize in at least some embodiments. 
     As can be seen from  FIG.  5   , the vibrating electromagnetic actuator  550  includes a passage passing all the way therethrough. (In order to better convey the concepts of the teachings herein, the “background lines” of the cross-sectional views are not depicted in the figures.) It is to be understood that in at least the case of a radially symmetric transducer according to the embodiment of  FIG.  5   , components such as springs  556  and  557 , the bobbin  664 , etc., extend about the longitudinal axis of the transducer. (It was determined that depicting such background lines would distract from the concepts of the teachings herein.) More particularly, the bobbin  554 A includes space therein, in the form of bore  554 D that passes all the way therethough, including through bobbin extension  554 E. 
     The arrangement of the permanent magnets  458 A and  458 B relative to the actuator of actuator assembly  480  can have some exemplary utilitarian value as will be partially described below. With respect to the arrangement, in view of the above, it can be seen that in some embodiments, there is a removable component of a bone conduction system, such as by way of example and not by way of limitation, external components  440 A and  440 B of bone conduction devices  400 A and  400 B as detailed in  FIGS.  4 A and  4 B , where the removable components  440 A and  400 B can comprise a recipient interface component, such as by way of example only and not by way of limitation, support assembly  446 A and  446 B as detailed above. The removable component further includes an actuator coupled to the recipient interface component, the actuator including a seismic mass. Accordingly, in an exemplary embodiment, the actuator can correspond to the actuator of the actuator assembly  480  detailed above. In this exemplary embodiment, actuation of the actuator moves the seismic mass relative to the recipient interface component. In an exemplary embodiment, this is achieved by rigidly fastening the actuator assembly  480  to the recipient interface/support assembly  446 A or  446 B. The removable component further includes a plurality of retention magnets  458 A and  458 B separate from the seismic mass. 
     The arrangement of  FIGS.  4 A and  4 B  in view of  FIG.  5    can be described as an external component  440 A that is configured such that actuation of the actuator of the actuator assembly  480  moves a seismic mass (counterweight assembly  555 ) along a first direction (e.g., as represented by arrows  499  of  FIG.  4 A and  500 A  of  FIG.  5   ) normal to a surface of skin of a recipient of the device. The magnetic retention system of the external component includes at least one permanent magnet (one or both of permanent magnets  458 A and  458 B). The actuator of the external component includes at least one permanent magnet  558 A and/or  558 B. A plane normal to the first direction (represented by plane  691  of  FIG.  6   , discussed below) bisects at least one permanent magnet of the actuator ( 558 A and/or  558 B) and the at least one permanent magnet of the magnetic retention system ( 458 A and/or  458 B). 
     As can be seen from the embodiments of  FIGS.  4 A and  4 B , which are symmetric about the plane normal to the view thereof, the actuator (e.g., actuator  550 , located within housing  501  of the actuator assembly  480 ) is located between the permanent magnets  458 A and  458 B. In an exemplary embodiment, this enables the removable component to have an overall height that is less than that which would be the case if the permanent magnets were located between the actuator and the implantable component ( 450 A or  450 B). 
     It is noted that during operation of the bone conduction devices detailed herein, there will be some movement of the overall removable component  440 A or  440 B. By way of example only and not by way of limitation, with respect to the passive transcutaneous bone conduction system, where the skin supports the removable component  440 A, actuation of the actuator thereof will cause the entire removable component  440 A to move back and forth towards and away from the underlying bone, owing to the flexibility of the overlying skin. However, a magnitude of movement of the seismic mass of the actuator is greater than that of any movement of the retention magnets  458 A and  458 B, relative to bone of the recipient adjacent to the external component and/or relative to the recipient interface component  446 A. With regard to the latter, in a perfect system, the retention magnets  458 A and  458 B will not move relative to the support assembly  446 A. Because all systems are not perfect, there will be some movement. However, the magnitude of that movement will be much lower than that of the seismic mass. 
       FIG.  6    depicts an exemplary static magnetic flux generated by the permanent magnets  458 A and  458 B, along with the permanent magnets  458 C and  458 D, used to retain the external component  440 A to the recipient ( FIG.  6    corresponds to the embodiment of  FIG.  4 A , with some components of the bone conduction device are removed for clarity). Again it is noted that in some embodiments, a different implantable component arrangement can be used (having different permanent magnets that that depicted, or none, as will be detailed below). As can be seen from  FIG.  6   , the static magnetic flux  680  travels in a circuit  681  that crosses the outer surfaces of the skin  132  (represented by dashed line  10 ), fat  128  and muscle  134  layers of the recipient. The distance between the permanent magnets  458 A and  458 B and the implantable component constituting an air gap  679  (providing that no magnetically conductive components/components having magnetic attributes are located therebetween—if so, the air gap distance would be different). The static magnetic flux circuit  681  also crosses the outer surface of bone  136  (represented by dashed line  20 ). Accordingly, the plurality of retention magnets  448 A and  448 B generate a magnetic field having a single (i.e., only one) magnetic retention circuit  681 . That said, there may be multiple circuits, but the circuits will be aligned relative to a frame of reference of  FIG.  6    (there can be more circuits “in front of” and/or “behind” that depicted in  FIG.  6    (e.g., due to the use of multiple bar magnets in front of and/or behind that depicted in  FIG.  6   )). It is noted that the retention magnets can generate a flux having another circuit, but if that circuit is not a retention circuit (i.e., used to retain the removable component to the recipient), there is still only one retention circuit. 
     Also as can be seen from  FIG.  6   , the static magnetic flux is asymmetrical. In an exemplary embodiment, the static magnetic flux  680  flows in one direction in one circuit (circuit  681 ), and there is not another static magnetic flux circuit that flows in an opposite direction, or at least not a direction that would render the static magnetic flux (overall static magnetic flux of the bone conduction device) to be symmetrical. Further, as can be seen from  FIG.  6   , the external component  440 A is configured such that the static magnetic flux flows in a circuit (circuit  681 ) that flows through the two permanent magnets  458 A and  458 B and at least one yoke (yoke  460 ) that is a part of the external component. A substantial portion of the static magnetic flux  680  that flows in the circuit  681  flows through at least one of an implantable permanent magnet ( 458 C and/or  458 D) or a second yoke (where permanent magnets  458 C and  458 D of the figures is replaced with a ferromagnetic material such as soft iron etc., as noted above) that is implantable. 
     That said,  FIG.  7    depicts an alternate embodiment of an implantable component, implantable component  750 A, which includes a yoke  759  to which the permanent magnets  458 C and  458 D are attached.  FIG.  7    depicts a portion of a flux circuit  781 , which is identical to that of flux circuit  681  of  FIG.  6   , except that the flux travelling between magnet  458 C and  458 D is channeled through yoke  759 . In an exemplary embodiment, yoke  759  is a soft iron component. 
     Further,  FIG.  8    depicts another alternate embodiment of an implantable component, implantable component  850 A, which utilizes a magnet arrangement (a single bar magnet  858 , although multiple magnets can be used) where the North-South pole axis is parallel to the surface of the skull/perpendicular to the longitudinal axis of the bone conduction device. As can be seen, the implantable component  850 A includes yokes  859 A and  859 B, while in some embodiments, a single yoke is used (the yoke surrounds the bar magnet  858 ) or no yoke(s) are used.  FIG.  8    depicts a portion of a flux circuit  881 , which is identical to that of flux  681  of  FIG.  6   , except as to how the flux is channeled through the implantable component of  FIG.  8    as shown. In an exemplary embodiment, yokes  859 A and  859 B are made of soft iron (which can be encapsulated in another material). Thus, in an exemplary embodiment, the exemplary passive transcutaneous bone conduction device includes an implantable component having a permanent magnet having a North-South pole axis, wherein the implantable component is configured such that the North-South pole axis is parallel to bone of the recipient when the implantable component is implanted and attached to bone of a recipient. 
     It is noted that in an exemplary embodiment, the implantable component can be configured such that the permanent magnets thereof and/or the yoke(s) are contained in a housing. In an exemplary embodiment, the housing can be a hermetically sealed housing that hermetically isolates the permanent magnets and/or yoke(s) from body fluid of the recipient. 
     An exemplary embodiment is directed towards how the magnetic flux used to retain the external components  440 A and  440 B to the recipient via the implantable component ( 450 A and  450 B, respectively) interacts (or again, does not interact) with the magnetic fluxes of the actuator. For example, in an exemplary embodiment, there is an external component of a medical device (e.g., external component  440 A or  440 B) comprising an actuator  480  including a static magnetic flux path that reacts with a dynamic magnetic flux path to actuate the actuator. The external component further includes a magnetic retention system (e.g., utilizing magnets  458 A and  458 B) configured to retain the external components  440 A and  440 B to a recipient via interaction with a ferromagnetic component attached to a recipient (e.g., the permanent magnets and/or soft iron components of the implantable components  450 A and  450 B), and the magnetic retention system including a magnetic flux path circuit (e.g., flux path  681  of  FIG.  6    or as modified in view of  FIG.  7  or  8   ) that encircles the static magnetic flux path circuit(s) of the actuator. In an exemplary embodiment, the circuit of the retention system encapsulates the flux path circuits of the actuator. 
     The arrangement of  FIGS.  4 A and  4 B  in view of  FIG.  5    can further be described as a bone conduction device including an external component ( 440 A,  440 B) thereof, including an actuator (the actuator of actuator assembly  480 ), which includes permanent magnets ( 558 A and  558 B) and a permanent magnet ( 448 A and/or  448 B) separate from the actuator. The permanent magnet generates a permanent magnetic field ( 681 ) having a component (e.g., the component flowing through one of the permanent magnets  458 A and  458 B) located outside the actuator on substantially opposite sides of the actuator. This permanent magnetic field enables the removable attachment of the external component ( 440 A,  440 B) to a recipient via interaction of the permanent magnetic field  681  with ferromagnetic material of an implanted component ( 450 A,  450 B). 
     Additional details of this exemplary embodiment will be described below, but first, magnetic flux path circuits of an exemplary actuator will be detailed so as to put this embodiment into perspective. Specifically,  FIG.  9    details an exemplary static and magnetic flux path of an exemplary transducer  950  having a principle of operation corresponding to that of transducer  550  detailed above, and used in the actuator assembly  480 . More specifically,  FIG.  9    depicts a portion of an electromagnetic transducer  950 . The electromagnetic transducer  950  is identical to electromagnetic transducer  550  detailed above, with the exception that there is no bobbin extension  554 E, and the components in proximity thereto are adjusted accordingly (e.g., the spacer and the bottom spring are extended). In other embodiments, electromagnetic transducer  950  can correspond exactly to any of the electromagnetic transducers detailed herein and/or variations thereof. In this regard, the teachings below can be applicable, in at least some embodiments, to any of the electromagnetic transducers detailed herein and/or variations thereof unless otherwise specified, as is the case in the broader context that any of the specific teachings detailed herein and/or variations thereof can be applicable to any of the embodiments detailed herein and/or variations thereof unless otherwise specified. 
     As with bobbin assembly  554 , bobbin assembly  954  is configured to generate a dynamic magnetic flux when energized by an electric current. In this exemplary embodiment, bobbin  954 A is made of a material that is conducive to the establishment of a magnetic conduction path for the dynamic magnetic flux. Additional aspects of this feature are described in greater detail below. 
       FIG.  9    depicts the respective static magnetic flux  980  and static magnetic flux  984  of permanent magnets  558 A and  558 B (like components of  FIG.  5    not being labeled for clarity), and dynamic magnetic flux  982  of the coil in the electromagnetic transducer  950  when the coil is energized according to a first current direction and when bobbin assembly  954  and counterweight assembly  955  are at a balance point with respect to magnetically induced relative movement between the two (hereinafter, the “balance point”). (When the current is reversed, the direction of the dynamic magnetic flux  982  is reversed.) That is, while it is to be understood that the counterweight assembly  955  moves in an oscillatory manner relative to the bobbin assembly  954  when the coil is energized, there is an equilibrium point at the fixed location corresponding to the balance point at which the counterweight assembly  954  returns to relative to the bobbin assembly  954  when the coil is not energized. It is noted that when the current direction is reversed, the direction of the dynamic magnetic flux is reversed from that depicted in  FIG.  9     
     It is noted that as with all the figures depicting magnetic fluxes,  FIG.  9    does not depict the magnitude/scale of the magnetic fluxes. In this regard, it is noted that in some embodiments, at the moment that the coil is energized and when bobbin assembly  954  and counterweight assembly  955  are at the balance point, relatively little, if any, static magnetic flux flows through the core of the bobbin  954 A/the hole of the coil formed as a result of the coil being wound about the core of the bobbin  954 A. Accordingly,  FIG.  9    depicts this fact. However, in some embodiments, it is noted that during operation, the amount of static magnetic flux that flows through these components increases as the bobbin assembly  954  travels away from the balance point (both downward and upward away from the balance point) and/or decreases as the bobbin assembly  954  travels towards the balance point (both downward and upward towards the balance point). 
     It is noted that the directions and paths of the static magnetic fluxes and dynamic magnetic fluxes are representative of some exemplary embodiments, and, in other embodiments, the directions and/or paths of the fluxes can vary from those depicted. 
     Still referring to  FIG.  9   , it can be seen that the dynamic magnetic flux  982  travels through the bobbin core  954 C about which coils  954 B extend. In the embodiment of  FIG.  9   , because bobbin  954 A is made of a magnetically permeable material (e.g., a highly permeable material), the bobbin core  954 C is a magnetic core. In this regard, effectively all, if not all, of the dynamic magnetic flux  982  travels through the material of the bobbin  954 A. That is, essentially no dynamic magnetic flux travels through the space  954 D in the bobbin. In this regard, the electromagnetic transducer  550  is configured such that the effective dynamic magnetic flux travels through the material of bobbin  954 A. 
       FIG.  10    depicts the magnetic flux path  681  generated by the permanent magnets  458 A- 458 D of the magnetic retention system of  FIG.  6    along with the static magnetic flux path  980  and static magnetic flux path  984  of permanent magnets  558 A and  558 B and the dynamic magnetic flux path  982  of the coil of the actuator used in the actuator assembly  480 , collectively identified as actuator flux  997 . As can be seen, the magnetic flux of the retention system encircles/goes around the magnetic fluxes of the actuator (the actuator flux  997 ). 
     Accordingly, as can be seen, the external component  440 A according to some embodiments is configured to channel the magnetic flux of the magnetic retention system in a circuit around the actuator assembly  448 , and thus the actuator thereof. Further, as can be seen from  FIGS.  4 A,  6  and  10   , embodiments include an implantable component  450 A of a passive transcutaneous bone conduction device comprising ferromagnetic material (whether it be a permanent magnet or soft iron or a combination thereof or other materials/components) configured to be totally implanted underneath skin of the recipient and attached to bone of the recipient. The passive transcutaneous bone conduction device is configured such that the magnetic flux circuit  681  of the magnetic retention system extends through skin of the recipient to the ferromagnetic material (e.g., permanent magnets  458 C and  458 D, etc.) of the implantable component  450 A resulting in magnetic attraction between the external component  440 A and the implantable component  450 A, thereby removably retaining the external component  440 A to the recipient. 
     Accordingly, an exemplary embodiment includes a magnetic retention flux path circuit that extends as will now be detailed, where the following is described in terms of an external component that includes yoke  460 , although in an alternate embodiment, the yoke  460  is not present—that is, in some embodiments, there may or may not be a ferromagnetic component (yoke  460 ) extending from a first lateral location of the removable component proximate a first of the retention magnets  458 B to a second lateral location of the removable component proximate a second of the retention magnets  458 B. In an exemplary embodiment, there is a magnetic flux path circuit that is established by a plurality of retention magnets  458 A and  458 B, where the circuit extends from a first of the retention magnets ( 458 B) to the ferromagnetic component  460 , through the ferromagnetic component  460 , from the ferromagnetic component  460  to the second of the retention magnets  458 A, and from the second of the retention magnet  458 A out of removable component beyond the recipient interface component (support assembly  466 A or  466 B) and then back into the removable component and then to the first retention magnet  458 B. 
     In view of  FIG.  10   , an exemplary embodiment can be described as an external component  440 A that is configured such that actuation of the actuator of the actuator assembly  480  moves a seismic mass (counterweight assembly  555 ) along a first direction (e.g., as represented by arrows  399  of  FIG.  4 A and  500 A  of  FIG.  5   ) normal to a surface of a skin of a recipient of the device. The magnetic retention system of the external component includes a static magnetic flux circuit  681 . The actuator of the external component includes one or more static magnetic fluxes and/or one or more dynamic magnetic fluxes. A plane normal to the first direction (represented by plane  691  of  FIG.  10   ) bisects the flux circuit  681  of the retention system and the magnetic fluxes  997  of the actuator. In an exemplary embodiment, a plane normal to the first direction (represented by plane  1091  of  FIG.  10   ) bisects the flux circuit  681  of the retention system and divides the magnetic fluxes  997  of the actuator in half. That is, the plane  1091  is located such that the fluxes of the actuator are located evenly above and below the plane, and the retention flux is bisected by the plane. 
       FIG.  11    depicts an exemplary static magnetic flux path of an exemplary magnetic retention system for the percutaneous bone conduction device  400 B of  FIG.  4 B , along with the magnetic flux paths of the actuator, where the implantable component  450 B is functionally represented in black-box format. Specifically, as can be seen, the magnetic flux path  1181  encircles the flux paths of the actuator (paths  997 ). While there are similarities between the flux path  1181  of the percutaneous bone conduction device  400 B and the flux path of the magnetic retention system of the transcutaneous bone conduction device  400 A, it can be seen that in an exemplary embodiment, flux path  1181  does not extend into the recipient/does not extend beneath the outer surface of the skin of the recipient. Moreover, in an exemplary embodiment, the support assembly  466 B includes a component configured to channel the magnetic flux path  1181  to the implantable component  450 B. More specifically, the support assembly  446 B includes components  466 B′ (although in other embodiments,  466 B′ can be a single component) made of soft iron or other magnetic material that channels the magnetic flux path  1181  from the permanent magnet  458 A to the implantable component  450 B, which includes ferromagnetic material (e.g., a permanent magnet). From the implantable component  450 B, the magnetic flux path  1181  is channeled through  466 B′ to the permanent magnet  458 B. 
     As can be seen from  FIG.  11   , support assembly  446 B includes element  466 B″. This is a component that is not conducive to channeling the magnetic flux  1181 , thus “forcing” the magnetic flux path  1181  to travel to the implantable component  450 B, or at least presenting a path that is less conducive to the conduction of the static flux path  1181  therethrough. That said, in an alternate embodiment,  466 B″ can instead also be soft iron or the like, the relative thinness of that section as compared to those of  466 B′ encouraging the magnetic flux path  1181  to travel to the implantable component  450 B. 
     It is noted that in at least some embodiments, not all of the magnetic flux of the retention system of the percutaneous bone conduction device is channeled to the implantable component  450 B (just as in at least some embodiments not all of the magnetic fluxes retention system of the passive transcutaneous bone conduction device  400 A travels to the implantable component). Some of this flux can bypass the implantable component  450 B. Still, sufficient magnetic attraction between the removable component  440 B and the implantable component  450 B exists to removably retain the removable component  440 B to the implantable component  450 B. 
     Accordingly, in view of  FIGS.  4 B and  11   , an exemplary embodiment includes a percutaneous bone conduction device, comprising an external component  440 B and a percutaneous implant  450 B of the percutaneous bone conduction device including ferromagnetic material configured to be connected to bone of a recipient and to extend through skin of the recipient. The percutaneous bone conduction device  400 B is configured such that the magnetic flux  1181  of the magnetic retention system extends to the ferromagnetic material of the percutaneous implant, resulting in magnetic attraction between the external component  440 B and the percutaneous implant, thereby removably retaining the external component  440 B to the recipient. 
     Further, as can be seen, the percutaneous bone conduction device  400 B includes a permanent magnetic field (flux  1181 ) that travels in a circuit that passes through at least one permanent magnet ( 458 A and/or  458 B) and the ferromagnetic material of the implantable component  450 B and encircles the actuator of actuator assembly  480 , thereby removably attaching the external component  440 B to the recipient. Thus, an exemplary embodiment includes an external component including a plurality of retention magnets that generate a magnetic field having a circuit  681  that retains the external component to the recipient. The actuator of that external component, being an electromagnetic actuator having a static magnetic field circuit that interacts with a dynamic magnetic field circuit to actuate the actuator, is arranged (or, more accurately, the external component is arranged) such that the static magnetic field circuit and the circuit that retains the external component to the recipient have completely separate paths. That is, no parts of the paths overlap one another. That said, in such an embodiment, the fluxes can interact, providing that the circuits to not cross one another (in the embodiments depicted herein, one circuit encircles the other). 
     As noted above, an exemplary embodiment is such that the magnetic flux of the permanent magnets of the magnetic retention system of the bone conduction devices encircles the actuator of the actuator assembly  480  (or other transducer used in a medical device other than a bone conduction device). In an exemplary embodiment, there is no interaction between the magnetic field of the retention system and the magnetic fields of the actuator. By no interaction, it is meant that at most, only trace amounts of the magnetic flux of the retention system interacts with the fluxes of the actuator. This is as a result of trace amounts of the flux of the retention system entering the actuator and/or trace amounts of the fluxes of the actuator escaping the actuator. That said, in an exemplary embodiment, effectively no interaction between the flux of the retention system and the fluxes of the actuator interact with one another. In this regard, more than trace amounts of the fluxes can interact with each other, providing that the interaction enables the bone conduction device to effectively evoke a hearing percept while being held to the recipient via the magnetic retention system. In an exemplary embodiment, the path of the magnetic field of the retention system follows a path where the strongest field strength of that path is present where the maximum field strength of the fluxes of the actuator is only 30%, 25%, 20%, 15%, 10%, 5% or 0% or any value or range of values therebetween in 1% increments of the maximum field strength of the static magnetic field(s) when the coil of the actuator is not energized. 
     In an exemplary embodiment, the permanent magnets of the retention system are such that the seismic mass of the actuator is moved no more than about 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29 or 30 micrometers from the equilibrium point (i.e., the location where the seismic mass is stationary in the absence of a dynamic magnetic flux), which could be the balance point of a balanced actuator, in the presence of the permanent magnets of the retention system of the external component relative to that which would be the case in the absence of the permanent magnets of the retention system of the external component. That is, for example, placement of the permanent magnets in the external component (e.g., magnets  458 A and  458 B) can result in a magnetic field that moves the seismic mass no more than about 5 micrometers from its equilibrium point. 
     In an exemplary embodiment, at least about 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95% or about 100%, or any value or range of values therebetween in about 1% increments, of the magnetic flux of the retention system occupies space where at most, only trace amounts, if any, of the static magnetic fluxes of the actuator are present. 
     In an exemplary embodiment, the removable external components are such that a magnetic saturation level of functional components of the actuator is at least approximately on the same level in the presence of the retention system as that which would be the case in the absence of the retention system (i.e., the removal of the permanent magnets  448 A and  448 B). 
     In view of the above, an exemplary embodiment is such that substantially all of the magnetic flux of the magnetic retention system is separated from the static magnetic flux path of the actuator. In an exemplary embodiment, the dynamic magnetic flux of the actuator is such that the dynamic magnetic flux is effectively isolated from interaction with the magnetic field of the retention system. 
     Further, in view of the above, an exemplary embodiment includes an external component for a bone conduction system comprising an actuator including a static magnetic flux path that reacts with a dynamic magnetic flux path to actuate the actuator and a magnetic retention system configured to retain the external component to a recipient via interaction with a ferromagnetic component attached to a recipient, the magnetic retention system including a magnetic flux path that encapsulates the static magnetic flux path of the actuator. 
     Embodiments of at least some of the teachings detailed herein and/or variations thereof can have utility in that it provides a compact external device. More specifically, referring to  FIG.  12   , external component  440 A is again depicted.  FIG.  12    depicts the overall height H 1  of the external component  440 A, as dimensioned from a first surface of external component configured to contact skin of the recipient (e.g., the recipient interface component corresponding to the bottom of support assembly  446 A) to the top of the external component (which can correspond to the top of the yoke  460  or a portion of the housing of the external component that covers the yoke  460  (if present) or otherwise houses the permanent magnet(s) of the retention system and the actuator assembly  480 ). In an exemplary embodiment, the height H 1  is no more than about 7 mm, 8 mm, 9 mm, 10 mm, 11 mm, 12 mm, 13 mm, 14 mm or about 15 mm. 
     Accordingly, an exemplary embodiment includes an external component that includes a first surface configured to contact skin of the recipient (e.g., the bottom surface of support assembly  460 A) through which vibrations generated by the actuator are conducted into skin of the recipient. A height of the external component as dimensioned from the first surface is no more than about fifteen millimeters. 
     In at least some embodiments, the distance between the aforementioned first surface configured to contact skin of the recipient to the center of mass/center of gravity of the external component  740 A is no more than about 3 mm, 4 mm, 5 mm, 6 mm, 7 mm, 8 mm, 9 mm or about 10 mm. 
     In at least some exemplary embodiments, the aforementioned height values alone and/or in combination with the reduced overall weight of the external component can have utility in that the lever effect can be reduced relative to that which might otherwise be the case without the aforementioned features without decreasing performance, again relative to that which might otherwise be the case without the aforementioned features. By way of example only, and not by way limitation, by reducing the lever effect, the peak pressures at the bottom portions of the pressure plate relative to the direction of gravity can be reduced (e.g., because the moment about the external component resulting from the mass thereof and/or the distance of the center of gravity/center of mass thereof from the skin is reduced relative to that which would otherwise be the case). In an exemplary embodiment, this can reduce the chances of necrosis, or the like, and/or reduce the sensation of pinching, or the like, relative to that which would be the case for the aforementioned alternate configuration. 
     It is noted that in at least some embodiments, the magnetic field of the retention systems are channeled about electronic circuitry of the removable components to limit interaction therewith. That is, the magnetic field of the retention systems can interfere with the electronic circuitry of the medical devices (e.g., a sound processor of a bone conduction device, the recording apparatus of a telemetry device of a medical device, etc.). Accordingly, in an exemplary embodiment, the external components are configured such that the circuit in which the magnetic flux of the magnetic retention system flows is isolated from the electronic circuitry of the removable component, even when the circuitry is located between magnet  458 A and  458 B (e.g., where actuator assembly  448  is located). 
     Referring now to  FIG.  13   , it is seen that there is an exemplary external component  440 X which is a quasi-black box functional depiction of an external component usable with a passive transcutaneous bone conduction system and a percutaneous bone conduction system, depending on the recipient interface arrangement as will be detailed below. External component  440 X includes permanent magnets  458 A and  458 B as detailed above with respect to  440 A and  440 B. The configuration of external component  440 X is such that it is left-right compatible with little or no modification. That is, external component  440 X can be placed on the left side of the recipient or the right side of the recipient (providing that the implantable component is present). In an exemplary embodiment, this is achieved by simply flipping over the external component  440 X. That is, in an exemplary embodiment, side “A” is utilized for the recipient interface if the implant is located on the left side of the recipient, and side “B” is utilized for the recipient interface if the implant is located on the right side of the recipient. Accordingly, an exemplary embodiment, the external component  440 X includes two recipient interfaces  446 X. As can be seen, the actuator assembly  480  is placed into vibrational communication with the recipient interfaces  446 X via components  1313 . 
     In an exemplary embodiment, the external component  440 X is configured such that it is structurally substantially symmetric about the plane normal to the longitudinal axis. That said, as will be detailed below, in an alternative embodiment, the external component  440 X is not structurally substantially symmetric. 
     In an exemplary embodiment, this can be achieved because the magnetic flux circuit of the permanent magnets  458 A and  458 B encircle the actuator  480 . More particularly, the component of the magnetic flux circuit that passes through side “A” can be substantially identical to that which passes through side “B,” (albeit the direction of the magnetic flux is reversed) at least when the external component  440 X is located away from any other magnetic components. Accordingly, in an exemplary embodiment, there is no yoke  460  of magnetically conductive material to channel the magnetic flux from one of the permanent magnets of the other permanent magnet. Instead, both recipient interfaces  446 X are made at least in part of magnetically nonconductive material such that the magnetic fluxes are not influenced thereby, or at least such that the magnetic fluxes can be utilized to achieve the left-right compatibility. Indeed, with respect to the latter, the recipient interfaces  446 X can have magnetically conductive material extending from the permanent magnets towards the center of the recipient interfaces that can to the arrangement of the support assembly  446 B of external component  446 B. Accordingly, as noted above, in an exemplary embodiment, the external component  440 X is substantially structurally symmetric about the plane normal to the longitudinal axis. Of course, there may be components that are located on one side a plane that are not located on the other, such as by way of example only and not by way of limitation, the sound processor, a microphone, etc. Still these are relatively minor components with respect to the overall weight of the external component  440 X. Thus, the external component  440 X is still substantially structurally symmetric about the aforementioned plane. 
     That said, in an alternate embodiment, a variation of the external component  440 X can be configured such that includes a yoke  460  that is movable from side “B” to side “A” and visa-versa. In an exemplary embodiment, the yoke  460  can be located over the recipient interface of a given side. Alternatively, the recipient interface of one side can be replaced by the yoke, and the yoke can be replaced by a recipient interface. Any device, system and/or method that can enable the left-right compatibility can be utilized in at least some embodiments. 
     It is noted that any disclosure of an apparatus or system herein corresponds to a method of utilizing that device and/or system. By way of example only and not by way of limitation, with respect to the just detailed external component  440 X, a method can include placing a bone conduction device  440 X onto a recipient on a first side of the recipient and evoking a hearing percept, and then placing the bone conduction device  440 X onto that same recipient on a second side the recipient opposite the first side the recipient and also evoking a hearing percept. In an exemplary embodiment, this method is performed without modifying the external component  440 X. in an alternate embodiment, this method is performed by a rearranging components of the external component  440 X that are removably attached to the other components of the external component  440 X (e.g., the yoke  460 ). 
     It is further noted that any method of manufacture described herein constitutes a disclosure of the resulting product, and any description of how a device is made constitutes a disclosure of the corresponding method of manufacture. Also, it is noted that any method detailed herein constitutes a disclosure of a device to practice the method, and any functionality of a device detailed herein constitutes a method of use including that functionality. 
     While various embodiments of the present invention have been described above, it should be understood that they have been presented by way of example only and not limitation. It will be apparent to persons skilled in the relevant art that various changes in form and detail can be made therein without departing from the spirit and scope of the invention. Thus, the breadth and scope of the present invention should not be limited by any of the above-described exemplary embodiments, but should be defined only in accordance with the following claims and their equivalents.