Patent Description:
Medical devices having one or more implantable components, generally referred to herein as implantable medical devices, have provided a wide range of therapeutic benefits to recipients over recent decades. In particular, partially or fully-implantable medical devices such as hearing prostheses (e.g., bone conduction devices, mechanical stimulators, cochlear implants, etc.), implantable pacemakers, defibrillators, functional electrical stimulation devices, and other implantable medical devices, have been successful in performing lifesaving and/or lifestyle enhancement functions and/or recipient monitoring for a number of years.

The types of implantable medical devices and the ranges of functions performed thereby have increased over the years. For example, many implantable medical devices now often include one or more instruments, apparatus, sensors, processors, controllers or other functional mechanical or electrical components that are permanently or temporarily implanted in a recipient. These functional devices are typically used to diagnose, prevent, monitor, treat, or manage a disease/injury or symptom thereof, or to investigate, replace or modify the anatomy or a physiological process. Many of these functional devices utilize power and/or data received from external devices that are part of, or operate in conjunction with, the implantable medical device. An example of an implantable auditory prosthesis is disclosed in <CIT>.

The invention provides an auditory prosthesis according to claim <NUM>.

The present disclosure provides also further examples, not falling under the scope of the claims but useful for better understanding of the invention.

Embodiments are described herein in conjunction with the accompanying drawings, in which:.

Certain embodiments described herein advantageously utilize a magnet of an external transmitter unit of an implantable medical device system, the external transmitter unit comprising at least one external inductive communication coil and a ferrite component configured to shield other components of the external transmitter unit from magnetic fields generated by the at least one external inductive communication coil. The implantable medical device system is advantageously compatible with magnetic resonance imaging (MRI), the magnet does not adversely affect (e.g., interfere with; degrade) operation of other components of the external transmitter unit, and the magnet is compatible with implanted devices comprising a diametrically magnetized implanted magnet. The magnet of certain such embodiments comprises a unitary (e.g., monolithic) body and has a plurality of portions, each portion having a corresponding magnetization (e.g., a magnetic dipole moment). The magnetizations are oriented relative to one another to provide a magnetic field that substantially perpendicularly intersects the ferrite component of the external transmitter unit.

The teachings detailed herein are applicable, in at least some embodiments, to any type of implantable medical device, for example, auditory prosthesis utilizing an implantable actuator assembly including but not limited to: electro-acoustic electrical/acoustic systems, cochlear implant devices, implantable hearing aid devices, middle ear implant devices, bone conduction devices (e.g., active bone conduction devices; passive bone conduction devices, percutaneous bone conduction devices; transcutaneous bone conduction devices), Direct Acoustic Cochlear Implant (DACI), middle ear transducer (MET), electro-acoustic implant devices, other types of auditory prosthesis devices, and/or combinations or variations thereof, or any other suitable hearing prosthesis system with or without one or more external components. Embodiments can include any type of medical device that can utilize the teachings detailed herein and/or variations thereof. In some embodiments, the teachings detailed herein and/or variations thereof can be utilized in other types of implantable medical devices beyond auditory prostheses. For example, the concepts described herein can be applied to any of a variety of implantable medical devices that utilize the transfer of power and/or data between an implanted component and an external component via inductive coupling (e.g., pacemakers; implantable EEG monitoring devices; visual prostheses).

<FIG> is a perspective view of an example cochlear implant auditory prosthesis <NUM> implanted in a recipient in accordance with certain embodiments described herein. The example auditory prosthesis <NUM> is shown in <FIG> as comprising an implanted stimulator unit <NUM> (e.g., an actuator) and an external microphone assembly <NUM> (e.g., a partially implantable cochlear implant). An example auditory prosthesis <NUM> (e.g., a totally implantable cochlear implant) in accordance with certain embodiments described herein can replace the external microphone assembly <NUM> shown in <FIG> with a subcutaneously implantable assembly comprising an acoustic transducer (e.g., microphone), as described more fully herein.

As shown in <FIG>, the recipient normally has an outer ear <NUM>, a middle ear <NUM>, and an inner ear <NUM>. In a fully functional ear, the outer ear <NUM> comprises an auricle <NUM> and an ear canal <NUM>. An acoustic pressure or sound wave <NUM> is collected by the auricle <NUM> and is channeled into and through the ear canal <NUM>. Disposed across the distal end of the ear canal <NUM> is a tympanic membrane <NUM> which vibrates in response to the sound wave <NUM>. This vibration is coupled to oval window or fenestra ovalis <NUM> through three bones of middle ear <NUM>, collectively referred to as the ossicles <NUM> and comprising the malleus <NUM>, the incus <NUM>, and the stapes <NUM>. The bones <NUM>, <NUM>, and <NUM> of the middle ear <NUM> serve to filter and amplify the sound wave <NUM>, causing the oval window <NUM> to articulate, or vibrate in response to vibration of the tympanic membrane <NUM>. This vibration sets up waves of fluid motion of the perilymph within the cochlea <NUM>. Such fluid motion, in turn, activates tiny hair cells (not shown) inside the cochlea <NUM>. Activation of the hair cells causes appropriate nerve impulses to be generated and transferred through the spiral ganglion cells (not shown) and auditory nerve <NUM> to the brain (also not shown) where they are perceived as sound.

As shown in <FIG>, the example auditory prosthesis <NUM> comprises one or more components which are temporarily or permanently implanted in the recipient. The example auditory prosthesis <NUM> is shown in <FIG> with an external component <NUM> which is directly or indirectly attached to the recipient's body, and an internal component <NUM> which is temporarily or permanently implanted in the recipient (e.g., positioned in a recess of the temporal bone adjacent auricle <NUM> of the recipient). The external component <NUM> typically comprises one or more input elements/devices for receiving input signals at a sound processing unit <NUM>. The one or more input elements/devices can include one or more sound input elements (e.g., one or more external microphones <NUM>) for detecting sound and/or one or more auxiliary input devices (not shown in <FIG>)(e.g., audio ports, such as a Direct Audio Input (DAI); data ports, such as a Universal Serial Bus (USB) port; cable ports, etc.). In the example of <FIG>, the sound processing unit <NUM> is a behind-the-ear (BTE) sound processing unit configured to be attached to, and worn adjacent to, the recipient's ear. However, in certain other embodiments, the sound processing unit <NUM> has other arrangements, such as by an OTE processing unit (e.g., a component having a generally cylindrical shape and which is configured to be magnetically coupled to the recipient's head), etc., a mini or micro-BTE unit, an in-the-canal unit that is configured to be located in the recipient's ear canal, a body-worn sound processing unit, etc..

The sound processing unit <NUM> of certain embodiments includes a power source (not shown in <FIG>)(e.g., battery), a processing module (not shown in <FIG>)(e.g., comprising one or more digital signal processors (DSPs), one or more microcontroller cores, one or more application-specific integrated circuits (ASICs), firmware, software, etc. arranged to perform signal processing operations), and an external transmitter unit <NUM>. In the illustrative embodiments of <FIG>, the external transmitter unit <NUM> comprises circuitry that includes at least one external inductive communication coil <NUM> (e.g., a wire antenna coil comprising multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire). The external transmitter unit <NUM> also generally comprises a magnet (not shown in <FIG>) secured directly or indirectly to the at least one external inductive communication coil <NUM>. The at least one external inductive communication coil <NUM> of the external transmitter unit <NUM> is part of an inductive radio frequency (RF) communication link with the internal component <NUM>. The sound processing unit <NUM> processes the signals from the input elements/devices (e.g., microphone <NUM> that is positioned externally to the recipient's body, in the depicted embodiment of <FIG>, by the recipient's auricle <NUM>). The sound processing unit <NUM> generates encoded signals, sometimes referred to herein as encoded data signals, which are provided to the external transmitter unit <NUM> (e.g., via a cable). As will be appreciated, the sound processing unit <NUM> can utilize digital processing techniques to provide frequency shaping, amplification, compression, and other signal conditioning, including conditioning based on recipient-specific fitting parameters.

The power source of the external component <NUM> is configured to provide power to the auditory prosthesis <NUM>, where the auditory prosthesis <NUM> includes a battery (e.g., located in the internal component <NUM>, or disposed in a separate implanted location) that is recharged by the power provided from the external component <NUM> (e.g., via a transcutaneous energy transfer link). The transcutaneous energy transfer link is used to transfer power and/or data to the internal component <NUM> of the auditory prosthesis <NUM>. Various types of energy transfer, such as infrared (IR), electromagnetic, capacitive, and inductive transfer, may be used to transfer the power and/or data from the external component <NUM> to the internal component <NUM>. During operation of the auditory prosthesis <NUM>, the power stored by the rechargeable battery is distributed to the various other implanted components as needed.

The internal component <NUM> comprises an internal receiver unit <NUM>, a stimulator unit <NUM>, and an elongate electrode assembly <NUM>. In some embodiments, the internal receiver unit <NUM> and the stimulator unit <NUM> are hermetically sealed within a biocompatible housing, sometimes collectively referred to as a stimulator/receiver unit. The internal receiver unit <NUM> comprises at least one internal inductive communication coil <NUM> (e.g., a wire antenna coil comprising multiple turns of electrically insulated single-strand or multi-strand platinum or gold wire), and generally, a magnet (not shown in <FIG>) fixed relative to the at least one internal inductive communication coil <NUM>. The at least one internal inductive communication coil <NUM> receives power and/or data signals from the at least one external inductive communication coil <NUM> via a transcutaneous energy transfer link (e.g., an inductive RF link). The stimulator unit <NUM> generates electrical stimulation signals based on the data signals, and the stimulation signals are delivered to the recipient via the elongate electrode assembly <NUM>.

The elongate electrode assembly <NUM> has a proximal end connected to the stimulator unit <NUM>, and a distal end implanted in the cochlea <NUM>. The electrode assembly <NUM> extends from the stimulator unit <NUM> to the cochlea <NUM> through the mastoid bone <NUM>. In some embodiments, the electrode assembly <NUM> can be implanted at least in the basal region <NUM>, and sometimes further. For example, the electrode assembly <NUM> can extend towards an apical end of the cochlea <NUM>, referred to as the cochlea apex <NUM>. In certain circumstances, the electrode assembly <NUM> can be inserted into the cochlea <NUM> via a cochleostomy <NUM>. In other circumstances, a cochleostomy can be formed through the round window <NUM>, the oval window <NUM>, the promontory <NUM>, or through an apical turn <NUM> of the cochlea <NUM>.

The elongate electrode assembly <NUM> comprises a longitudinally aligned and distally extending array <NUM> of electrodes or contacts <NUM>, sometimes referred to as electrode or contact array <NUM> herein, disposed along a length thereof. Although the electrode array <NUM> can be disposed on the electrode assembly <NUM>, in most practical applications, the electrode array <NUM> is integrated into the electrode assembly <NUM> (e.g., the electrode array <NUM> is disposed in the electrode assembly <NUM>). As noted, the stimulator unit <NUM> generates stimulation signals which are applied by the electrodes <NUM> to the cochlea <NUM>, thereby stimulating the auditory nerve <NUM>.

<FIG> schematically illustrate two perspective views of a first example configuration of an implanted magnet <NUM> (e.g., enclosed in an internal component <NUM> of an auditory prosthesis implanted beneath the recipient's skin <NUM>) and an external magnet <NUM> (e.g., enclosed in an external component <NUM> of the auditory prosthesis outside or on the recipient's skin <NUM>). The implanted magnet <NUM> has a magnetization comprising a single implanted magnetic dipole moment <NUM> and the external magnet <NUM> has a magnetization comprising a single external magnetic dipole moment <NUM> with a direction substantially parallel to and in the same direction as the single implanted magnetic dipole moment <NUM>. Each of the implanted magnet <NUM> and the external magnet <NUM> has a right circular cylindrical shape with a center axis and the respective magnetizations are substantially parallel to the respective center axes (e.g., the implanted magnet <NUM> and the external magnet <NUM> are axially magnetized) and the respective magnetizations are substantially perpendicular to the recipient's skin <NUM>. By having the respective axial magnetizations aligned with one another, the external magnet <NUM> provides sufficient retention to the implanted magnet <NUM> to keep the external component <NUM> in an operational position relative to the internal component <NUM>.

However, the orientation of the single implanted magnetic dipole moment <NUM> of the implanted magnet <NUM> (e.g., substantially perpendicular to the recipient's skin <NUM> as shown in the example configuration of <FIG>) has been described as being incompatible with magnetic-resonance imaging (MRI) since the magnetically-induced torque (τ = m × B) on the implanted magnet <NUM> due to the large MRI magnetic fields interacting with the single implanted magnetic dipole moment <NUM> is potentially detrimental (e.g., resulting in pain to the recipient and/or damage to the recipient and/or the auditory prosthesis).

<FIG> schematically illustrates a perspective view of a portion of the magnetic field <NUM> of the external magnet <NUM> of <FIG>. For example, the external magnet <NUM> can be a component of an external transmitter unit <NUM> comprising circuitry with at least one external inductive communication coil <NUM> (not shown in <FIG>) and a ferrite component <NUM> having a generally planar shape, positioned above and parallel to the at least one external inductive communication coil <NUM>, and configured to shield other components of the circuitry of the external transmitter unit <NUM> from magnetic fields generated by the at least one external inductive communication coil <NUM>. The magnetic field <NUM> of the external magnet <NUM> extends to and substantially perpendicularly intersects the ferrite component <NUM>, such that the magnetic field <NUM> does not saturate the ferrite component <NUM> (e.g., does not reduce the shielding provided by the ferrite component <NUM> of the other components of the circuitry of the external transmitter unit <NUM> from the magnetic fields generated by the at least one external inductive communication coil <NUM>).

<FIG> schematically illustrate two perspective views of a second example configuration of an implanted magnet <NUM> (e.g., enclosed in an internal component <NUM> of an auditory prosthesis implanted beneath the recipient's skin <NUM>) and an external magnet <NUM> (e.g., enclosed in an external component <NUM> of the auditory prosthesis outside or on the recipient's skin <NUM>). The implanted magnet <NUM> has a magnetization comprising a single implanted magnetic dipole moment <NUM> and the external magnet <NUM> has a magnetization comprising a single external magnetic dipole moment <NUM> with a direction substantially parallel to and in the opposite direction as the single implanted magnetic dipole moment <NUM>. Each of the implanted magnet <NUM> and the external magnet <NUM> has a right circular cylindrical shape with a center axis and the respective magnetizations are substantially perpendicular to the respective center axes (e.g., the implanted magnet <NUM> and the external magnet <NUM> are diametrically magnetized) and the respective magnetizations are substantially parallel to the recipient's skin <NUM>. By having the respective diametrical magnetizations aligned with one another, the external magnet <NUM> provides sufficient retention to the implanted magnet <NUM> to keep the external component <NUM> in an operational position relative to the internal component <NUM>.

In contrast to the example configuration of <FIG>, the orientation of the single implanted magnetic dipole moment <NUM> of the implanted magnet <NUM> (e.g., substantially parallel to the recipient's skin <NUM> as shown in the example configuration of <FIG>) has been described as being compatible with MRI since the magnetically-induced torque (τ = m × B) on the implanted magnet <NUM> due to the large MRI magnetic fields interacting with the single implanted magnetic dipole moment <NUM> has a lower magnitude than in <FIG>, and is less likely to be potentially detrimental (e.g., resulting in pain to the recipient and/or damage to the recipient and/or the auditory prosthesis). In addition, the orientation of the single external magnetic dipole moment <NUM> of the external magnet <NUM> (e.g., substantially parallel to the recipient's skin <NUM> as shown in the example configuration of <FIG>) is also compatible with MRI since the resulting magnetically-induced torque on the external magnet <NUM> is less likely to be potentially detrimental than in the example configuration of <FIG>.

<FIG> schematically illustrates a perspective view of a portion of the magnetic field <NUM> of the external magnet <NUM> of <FIG>. For example, the external magnet <NUM> can be a component of an external transmitter unit <NUM> comprising circuitry with at least one external inductive communication coil <NUM> (not shown in <FIG>) and the generally planar ferrite component <NUM> configured to shield other components of the circuitry of the external transmitter unit <NUM> from magnetic fields generated by the at least one external inductive communication coil <NUM>. The magnetic field <NUM> of the external magnet <NUM> extends to and is substantially parallel to the ferrite component <NUM>. As a result, the magnetic field <NUM> can saturate the ferrite component <NUM> (e.g., can reduce the shielding provided by the ferrite component <NUM> of the other components of the circuitry of the external transmitter unit <NUM> from the magnetic fields generated by the at least one external inductive communication coil <NUM>). In this way, the magnetic field <NUM> of the external magnet <NUM> in the example configuration of <FIG> can extend a significant distance away from the external magnet <NUM> and can interfere with other components of the circuitry of the external transmitter unit <NUM>, potentially adversely affecting operation of the circuitry (e.g., interfering with the inductive RF link to the internal component <NUM>). Such interference can result in various adverse effects, including but not limited to: reduction in the battery life of the auditory prosthesis <NUM> and/or sound processing unit <NUM> (e.g., by <NUM>%), increase in the RF link power consumption, increased RF tuning range, and reduced coil alignment tolerance for inductive charging.

Some previous systems have sought to address the unwanted magnetic fields of the external magnet by using a magnetic flux guide (e.g., cylindrical or can-shaped; comprising "mu-metal" or other materials with sufficiently high magnetic permittivity) between the external magnet and the circuitry of the external transmitter unit <NUM> to direct the magnetic field away from key components of the circuitry (see, e.g., <CIT>). However, such structures undesirably add mass and volume to the external transmitter unit <NUM>. Other previous systems have used an external magnet comprising a modified Halbach array to reduce unwanted magnetic fields (see, e.g., <CIT>). However, such structures can utilize undesirably larger diameters for the magnet assembly of the external transmitter unit <NUM>.

<FIG> schematically illustrates a cross-sectional view of an example apparatus <NUM> in accordance with certain embodiments described herein. The apparatus <NUM> comprises a housing <NUM> configured to be placed over a portion of skin <NUM> of a recipient. The portion of skin <NUM> overlays an implanted device <NUM>. The apparatus <NUM> further comprises circuitry <NUM> within the housing <NUM>, the circuitry <NUM> configured to wirelessly communicate with the implanted device <NUM>. The apparatus <NUM> further comprises a unitary magnet <NUM> (e.g., a monolithic magnet) in mechanical communication with the housing <NUM>. The magnet <NUM> comprises at least one first magnetic dipole moment <NUM> having a first magnitude and a first direction and at least one second magnetic dipole moment <NUM> having a second magnitude substantially equal to the first magnitude and a second direction substantially opposite to the first direction. In certain embodiments, the at least one first dipole magnetic moment <NUM> and the at least one second magnetic dipole moment <NUM> are configured to produce an external magnetic field configured to, when the housing <NUM> is placed over the portion of the skin <NUM>, attract the magnet <NUM> to the implanted device <NUM> while not adversely affecting operation of the circuitry <NUM>.

In certain embodiments, the apparatus <NUM> is an external component <NUM> of an implantable medical device (e.g., an auditory prosthesis system; a cochlear implant auditory prosthesis <NUM> as schematically illustrated by <FIG>), and the internal device <NUM> is an internal component <NUM> of the implantable medical device. For example, the apparatus <NUM> can be an external component <NUM> of an auditory prosthesis system selected from the group consisting of: a cochlear implant system, a Direct Acoustic Cochlear Implant (DACI) system, a middle ear implant system, a middle ear transducer (MET) system, an electro-acoustic implant system, another type of auditory prosthesis system, and/or combinations or variations thereof.

In certain embodiments, the external component <NUM> can comprise the housing <NUM> (e.g., comprising a polymer material and/or other material compatible for being placed in contact with the recipient's skin <NUM>), the circuitry <NUM> (e.g., comprising at least one microphone <NUM>, a sound processing unit <NUM>, a power source, an external transmitter unit <NUM>, and/or the at least one external inductive communication coil <NUM>, as schematically illustrated by <FIG>) within the housing <NUM>, and the magnet <NUM> which can be in mechanical communication with the housing <NUM>. For example, the magnet <NUM> can be contained within a cavity <NUM> of the housing <NUM> (e.g., as schematically illustrated by <FIG>), while in other examples, the magnet <NUM> can be affixed to an exterior portion of the housing <NUM> and/or can form part of an external surface of the housing <NUM>.

In certain embodiments, the magnet <NUM> comprises at least one ferromagnetic material selected from the group consisting of: iron, nickel, cobalt, and steel. The magnet <NUM> of certain embodiments comprises a permanent multipole magnet (e.g., a magnet having two or more portions with different magnetizations) having an external static magnetic field. The magnet <NUM> of certain embodiments is a non-separable unitary (e.g., monolithic) member (e.g., such that at least one first portion <NUM> comprising the at least one first magnetic dipole moment <NUM> and at least one second portion <NUM> comprising the at least one second magnetic dipole moment <NUM> cannot be easily separated from one another without damaging the magnet <NUM>). In certain other embodiments, the magnet <NUM> is a separable unitary (e.g., monolithic) member (e.g., configured to be separated into multiple portions at selected times without damaging the magnet <NUM>). For example, the separable unitary (e.g., monolithic) member can be separated into multiple portions when the magnet <NUM> is not mounted on or within the housing <NUM> and can be joined or rejoined together prior to being placed in mechanical communication with the other portions of the apparatus <NUM> (e.g., the first portion <NUM> and the second portion <NUM> are configured to be repeatedly and reversibly separated from one another and repeatedly and reversibly rejoined to one another without damaging the magnet <NUM>).

In certain embodiments, the magnet <NUM> has a first width that is substantially parallel to the portion of skin <NUM> upon (e.g., after) placement of the apparatus <NUM> over the portion of skin <NUM> (e.g., during operation of the circuitry <NUM>) and a first height that is substantially perpendicular to the portion of skin <NUM> upon (e.g., after) placement of the apparatus <NUM> over the portion of skin <NUM> (e.g., during operation of the circuitry <NUM>). In certain embodiments, the magnet <NUM> has a cylindrical shape with a cross-section (e.g., circular; elliptical; square; rectangular; polygonal; geometric; irregular; symmetric; non-symmetric) with straight, curved, or irregular sides. For example, the magnet <NUM> can have a right circular cylindrical shape in which the first width is a first diameter D<NUM>, the first height H<NUM> is substantially perpendicular to the first diameter, and having a first circumference C<NUM> (= πD<NUM>). The magnet <NUM> of certain embodiments has an orientation during operation of the apparatus <NUM> (e.g., during operation of the circuitry <NUM>) such that the first diameter D<NUM> is substantially parallel to the recipient's skin <NUM> and the first height H<NUM> is substantially perpendicular to the recipient's skin <NUM>. The first diameter D<NUM> of certain embodiments is in a range of <NUM> millimeters to <NUM> millimeters, and the first height H<NUM> of certain embodiments is in a range of <NUM> millimeter to <NUM> millimeters (e.g., selected to provide sufficient magnetic attractive force across the skin flap thickness of the recipient). In certain other embodiments, the magnet <NUM> has a rectangular prism or a hexagonal prism shape, and other shapes and/or sizes of the magnet <NUM> are also compatible with certain embodiments described herein. In certain embodiments, the magnet <NUM> has a non-symmetric shape such that the magnet <NUM> is configured to be contained within the housing <NUM> in a limited number of orientations (e.g., keyed to only one orientation).

In certain embodiments, the example internal component <NUM> can comprise an implantable housing <NUM> (e.g., comprising titanium and/or other biocompatible material compatible for being implanted beneath the recipient's skin <NUM>), circuitry <NUM>, and an internal magnet <NUM> having at least one third magnetic dipole moment <NUM>. The circuitry <NUM> of the implantable device <NUM> can comprise an implanted receiver unit <NUM>, a stimulator unit <NUM> (e.g., in operative communication with an elongate electrode assembly <NUM>), and/or the at least one internal inductive communication coil <NUM>, as schematically illustrated by <FIG>. For example, the internal magnet <NUM> and/or the circuitry <NUM> of the internal device <NUM> can be contained within one or more cavities <NUM> (e.g., hermetically sealed regions) of the implantable housing <NUM>.

As schematically illustrated by <FIG>, the at least one external inductive communication coil <NUM> can comprise a first planar inductor coil having a first plurality of turns and the first planar inductor coil can encircle the magnet <NUM> and/or can encircle a projection of the magnet <NUM> onto a plane defined by the first planar inductor coil. In addition, as schematically illustrated by <FIG>, the at least one internal inductive communication coil <NUM> can comprise a second planar inductor coil having a second plurality of turns and the second planar inductor coil can encircle the internal magnet <NUM> and/or can encircle a projection of the internal magnet <NUM> onto a plane defined by the second planar inductor coil.

In certain embodiments, the magnet <NUM> and the internal magnet <NUM> are configured to be magnetically attracted to one another with the recipient's skin <NUM> therebetween. The magnet <NUM> is positioned relative to the at least one external inductive communication coil <NUM> such that, when the apparatus <NUM> is placed in its operational position above the implanted device <NUM> (e.g., as schematically illustrated by <FIG>), the magnet <NUM> is attracted to the implanted magnet <NUM> and the magnet <NUM> is configured to position the apparatus <NUM> such that the at least one external inductive communication coil <NUM> is aligned with (e.g., centered over; concentric with and over) the at least one internal inductive communication coil <NUM>. As used herein, the term "concentric" refers to the relative positions of the centers of two or more components, and does not refer to any particular shapes of these components (e.g., the magnet <NUM> and the at least one external inductive communication coil <NUM> can be concentric with one another without either the magnet <NUM> or the at least one external inductive communication coil <NUM> having a circular shape).

In certain embodiments, when the apparatus <NUM> and the magnet <NUM> are placed in their operational positions, the magnet <NUM> is sufficiently close to the implanted magnet <NUM> such that the magnet <NUM> and the implanted magnet <NUM> are magnetically attracted to one another, and the at least one external inductive communication coil <NUM> within the housing <NUM> is configured to be in inductive communication with the at least one internal inductive communication coil <NUM> of the implanted device <NUM>. In certain such embodiments, the at least one external inductive communication coil <NUM> and the at least one internal inductive communication coil <NUM> form a transcutaneous inductive radio frequency (RF) communication link between the apparatus <NUM> and the implanted device <NUM> (e.g., the inductive communication coils <NUM>, <NUM> interact with one another via magnetic flux of one of the inductive communication coils <NUM>, <NUM> passing through the other one of the inductive communication coils <NUM>, <NUM>), across which the implanted device <NUM> receives power and/or data signals from the apparatus <NUM>. In certain embodiments, when the apparatus <NUM> and the magnet <NUM> are placed in their operational positions, the at least one external inductive communication coil is centered over the at least one internal inductive communication coil. For example, a center axis of the at least one external inductive communication coil <NUM> (e.g., coincident with an axis of symmetry of the shape of the magnet <NUM> and/or an axis of symmetry of a magnetic field produced by the magnet <NUM>) can be coincident with a center axis of the at least one internal inductive communication coil <NUM> (e.g., coincident with an axis of symmetry of the shape of the implanted magnet <NUM> and/or an axis of symmetry of a magnetic field produced by the implanted magnet <NUM>).

<FIG> schematically illustrate perspective views of an example external magnet <NUM> and an internal magnet <NUM> in accordance with certain embodiments described herein. The external magnet <NUM> and the internal magnet <NUM> are configured to be positioned with the recipient's skin <NUM> therebetween. The internal magnet <NUM> of <FIG> has a magnetization that comprises a single magnetic dipole moment <NUM> that is substantially parallel to the recipient's skin <NUM> and is oriented substantially perpendicular to a center axis <NUM> of the internal magnet <NUM> (e.g., the implanted magnet <NUM> is diametrically magnetized).

The external magnet <NUM> of <FIG> has a right circular cylindrical shape having a first diameter and a first height, and the external magnet <NUM> comprises a first magnetized portion <NUM> having a first magnetization comprising a first magnetic dipole moment <NUM> (e.g., the first portion <NUM> generating the first magnetic dipole moment <NUM>) and a second magnetized portion <NUM> having a second magnetization comprising a second magnetic dipole moment <NUM> different from the first magnetization (e.g., the second portion <NUM> generating the second magnetic dipole moment <NUM>). For example, in <FIG>, the first magnetized portion <NUM> comprises a first half of the external magnet <NUM>, the second magnetized portion <NUM> comprises a second half of the external magnet <NUM>, and the second magnetic dipole moment <NUM> has a magnitude substantially equal to the magnitude of the first magnetic dipole moment <NUM> and a second direction which is substantially parallel and opposite to a first direction of the first magnetic dipole moment <NUM>. The external magnet <NUM> of <FIG> is configured to be mounted to the housing <NUM> such that the first and second magnetic dipole moments <NUM>, <NUM> are substantially perpendicular to the portion of skin <NUM> during operation of the apparatus <NUM> (e.g., during operation of the circuitry <NUM>).

<FIG> schematically illustrates the magnetic field <NUM> of the external magnet <NUM> of <FIG> in relation to at least one planar ferrite component <NUM> in accordance with certain embodiments described herein. The at least one planar ferrite component <NUM> of <FIG> is positioned above and parallel to the at least one external inductive communication coil <NUM> (not shown in <FIG>), the at least one external inductive communication coil <NUM> configured to be in inductive communication with at least one internal inductive communication coil <NUM> of the implanted device <NUM>. The magnetic field <NUM> of the external magnet <NUM> extends to and substantially perpendicularly intersects the at least one planar ferrite component <NUM>. In certain such embodiments, the external magnet <NUM> is configured to interact with the implanted device <NUM> to provide sufficient magnetic force to retain the assembly <NUM> over the implanted device <NUM> while providing the same advantage of not saturating the at least one planar ferrite component <NUM> (e.g., does not reduce the shielding provided by the at least one planar ferrite component <NUM> of the other components of the circuitry of the external transmitter unit <NUM> from the magnetic fields generated by the at least one external inductive communication coil <NUM>; does not adversely affect, interfere with, degrade performance of the assembly <NUM>) as does the axially magnetized magnet <NUM> of <FIG>.

The external magnet <NUM> of certain embodiments comprises four poles: two "north" poles (labeled "N") and two "south" poles (labeled "S"). <FIG> schematically illustrate the external magnet <NUM> comprises two half portions each having one "north" pole and one "south" pole (e.g., each half portion having a corresponding magnetization comprising a magnetic dipole moment, with substantially equal magnitudes and substantially opposite directions). In <FIG>, the external magnet <NUM> is bisected by the first width (e.g., first diameter) between the first half portion and the second half portion such that the first half portion is a semicircular first portion <NUM> and the second half portion is a semicircular second portion <NUM>, with both the first and second magnetic dipole moments <NUM>, <NUM> oriented substantially parallel to a center axis <NUM> of the external magnet <NUM>. The external magnet <NUM> is mounted to the housing <NUM> such that first magnetic dipole moment <NUM> and the second magnetic dipole moment <NUM> of <FIG> are substantially perpendicular to the portion of skin <NUM> during operation of the circuitry <NUM>.

<FIG> schematically illustrate an alternative view of the external magnet <NUM> of <FIG> in accordance with certain embodiments described herein. As in <FIG>, the external magnet <NUM> comprises two portions each having one "north" pole and one "south" pole (e.g., each portion having a corresponding magnetization comprising a magnetic dipole moment, with substantially equal magnitudes and substantially opposite directions). However, in <FIG>, the first portion <NUM> has a right circular cylindrical shape having a second width (e.g., diameter) substantially equal to the first width (e.g., diameter) and the second portion <NUM> has a right circular cylindrical shape having a third width (e.g., diameter) substantially equal to the first width (e.g., diameter). In certain embodiments, as schematically illustrated by <FIG>, the first portion <NUM> has a second height substantially equal to one-half the first height, and the second portion <NUM> has a third height substantially equal to one-half the first height. In certain other embodiments, the second height is less than the third height. For example, the external magnet <NUM> of <FIG> can be a separable unitary member (e.g., in which the first portion <NUM> and the second portion <NUM> are configured to be repeatedly and reversibly separated from one another and repeatedly and reversibly rejoined to one another without damaging the magnet <NUM>), with the first portion <NUM> having a smaller height than does the second portion <NUM>. The external magnet <NUM> of <FIG> is configured to be mounted to the housing <NUM> such that the first magnetic dipole moment <NUM> and the second magnetic dipole moment <NUM> of <FIG> are substantially parallel to the portion of skin <NUM> during operation of the circuitry <NUM>.

In certain embodiments, the internal magnet <NUM> is also a unitary (e.g., monolithic) magnet comprising a plurality of magnetized portions with different magnetizations from one another (e.g., at least one first magnetic dipole moment having a first magnitude and a first direction and at least one second magnetic dipole moment having a second magnitude substantially equal to the first magnitude and a second direction substantially opposite to the first direction). The at least one first magnetic dipole moment of the internal magnet <NUM> and the at least one second magnetic dipole moment of the internal magnet <NUM> can be configured to produce a magnetic field configured to, when the external apparatus <NUM> is placed over the portion of skin <NUM>, attract the internal magnet <NUM> to the external apparatus <NUM> (e.g., to the external magnet <NUM>). As described herein with regard to the external magnet <NUM>, the internal magnet <NUM> of certain embodiments has a first width that is substantially parallel to the portion of skin <NUM> and a first height that is substantially perpendicular to the portion of skin upon implantation of the housing <NUM>. The internal magnet <NUM> of certain embodiments comprises a first portion generating the first magnetic dipole moment and a second portion generating the second magnetic dipole moment. In certain embodiments, the first portion comprises a first half of the internal magnet <NUM> and the second portion comprises a second half of the internal magnet <NUM>. For example, the first width can bisect the internal magnet <NUM> between the first half and the second half and the first direction and the second direction can be substantially perpendicular to the portion of skin <NUM> upon implantation of the housing <NUM>. For another example, the first portion can have a second width substantially equal to the first width and a second height substantially equal to one-half the first height, and the second portion can have a third width substantially equal to the first width and a third height substantially equal to one-half the first height, and the first direction and the second direction can be substantially parallel to the portion of skin <NUM> upon implantation of the housing <NUM>.

<FIG> schematically illustrate various example configurations of an external magnet <NUM> and an internal magnet <NUM> in accordance with certain embodiments described herein. In each of <FIG>, both the external magnet <NUM> and the internal magnet <NUM> is a multipole magnet (e.g., a magnet having two or more portions with different magnetizations). The magnetizations (e.g., magnetic dipole moments) of the various portions of the magnets are schematically shown by arrows. While the external magnet <NUM> and the internal magnet <NUM> of <FIG> are shown as having right circular cylindrical shapes, other shapes are also compatible with certain embodiments described herein.

In <FIG>, the external magnet <NUM> comprises two half portions <NUM>, <NUM> (e.g., semicircular half portions) having magnetizations <NUM>, <NUM> with substantially equal magnitudes and substantially opposite directions (e.g., substantially perpendicular to the portion of skin <NUM>), and the internal magnet <NUM> comprises two half portions <NUM>, <NUM> (e.g., semicircular half portions) having magnetizations <NUM>, <NUM> with substantially equal magnitudes and substantially opposite directions (e.g., substantially perpendicular to the portion of skin <NUM>).

In <FIG>, the external magnet <NUM> comprises first and second portions <NUM>, <NUM> having magnetizations <NUM>, <NUM> with substantially equal magnitudes and substantially opposite directions (e.g., substantially perpendicular to the portion of skin <NUM>) and a third portion <NUM> between the first portion <NUM> and the second portion <NUM>. The third portion <NUM> has a magnetization <NUM> that is substantially perpendicular to the magnetizations <NUM>, <NUM> of the first portion <NUM> and the second portion <NUM>. Similarly, the internal magnet <NUM> of <FIG> comprises first and second portions <NUM>, <NUM> having magnetizations <NUM>, <NUM> with substantially equal magnitudes and substantially opposite directions (e.g., substantially perpendicular to the portion of skin <NUM>) and a third portion <NUM> between the first portion <NUM> and the second portion <NUM>, the third portion <NUM> has a magnetization <NUM> that is substantially perpendicular to the magnetizations <NUM>, <NUM> of the first portion <NUM> and the second portion <NUM>. The magnetization <NUM> of the third portion <NUM> of the external magnet <NUM> is substantially equal and opposite to the magnetization <NUM> of the third portion <NUM> of the internal magnet <NUM>.

In <FIG>, the external magnet <NUM> comprises first and second portions <NUM>, <NUM> having magnetizations <NUM>, <NUM> with substantially equal magnitudes and substantially opposite directions (e.g., substantially perpendicular to the portion of skin <NUM>) and a third portion <NUM> between the first portion <NUM> and the second portion <NUM>, the third portion <NUM> having a magnetization <NUM> that is substantially perpendicular to the magnetizations <NUM>, <NUM> of the first portion <NUM> and the second portion <NUM>. The internal magnet <NUM> comprises two half portions <NUM>, <NUM> (e.g., semicircular half portions) having magnetizations <NUM>, <NUM> with substantially equal magnitudes and substantially opposite directions (e.g., substantially perpendicular to the portion of skin <NUM>).

In <FIG>, the external magnet <NUM> comprises a first portion <NUM> (e.g., a right circular cylindrical portion) and the second portion <NUM> surrounding a perimeter of the first portion <NUM> (e.g., a right circular cylindrical ring portion <NUM> concentric with the first portion <NUM>). In certain embodiments, the magnetizations <NUM>, <NUM> of the first and second portions <NUM>, <NUM> of the external magnet <NUM> have substantially equal magnitudes and are in substantially opposite directions. Similarly, the internal magnet <NUM> comprises a first portion <NUM> (e.g., a right circular cylindrical portion) and a second portion <NUM> surrounding a perimeter of the first portion <NUM> (e.g., a right circular cylindrical ring portion <NUM> concentric with the first portion <NUM>). In certain embodiments, the magnetizations <NUM>, <NUM> of the first and second portions <NUM>, <NUM> of the internal magnet <NUM> have substantially equal magnitudes and are in substantially opposite directions.

In <FIG>, the external magnet <NUM> comprises a first portion <NUM> (e.g., a right circular cylindrical portion) and a second portion <NUM> surrounding a perimeter of the first portion <NUM> (e.g., a right circular cylindrical ring portion <NUM> concentric with the first portion <NUM>), the first and second portions <NUM>, <NUM> having magnetizations substantially perpendicular to the portion of skin <NUM>, and a third portion <NUM> between the first portion <NUM> and the second portion <NUM>, the third portion <NUM> has a magnetization <NUM> that is substantially perpendicular to the magnetizations <NUM>, <NUM> of the first portion <NUM> and the second portion <NUM>. Similarly, the internal magnet <NUM> comprises a first portion <NUM> (e.g., a right circular cylindrical portion) and a second portion <NUM> surrounding a perimeter of the first portion <NUM> (e.g., a right circular cylindrical ring portion <NUM> concentric with the first portion <NUM>), the first and second portions <NUM>, <NUM> having magnetizations <NUM>, <NUM> substantially perpendicular to the portion of skin <NUM>, and a third portion <NUM> between the first portion <NUM> and the second portion <NUM>, the third portion <NUM> having a magnetization <NUM> that is substantially perpendicular to the magnetizations <NUM>, <NUM> of the first portion <NUM> and the second portion <NUM>. In certain embodiments, the magnetizations <NUM>, <NUM> of the first and second portions <NUM>, <NUM> of the external magnet <NUM> are substantially equal and opposite to one another, the magnetizations <NUM>, <NUM> of the first and second portions <NUM>, <NUM> of the internal magnet <NUM> are substantially equal and opposite to one another, and the magnetization <NUM> of the third portion <NUM> of the external magnet <NUM> and the magnetization <NUM> of the third portion <NUM> of the internal magnet <NUM> are substantially equal and opposite to one another.

In <FIG>, the external magnet <NUM> comprises a first portion <NUM> (e.g., a right circular cylindrical portion) and a second portion <NUM> surrounding a perimeter of the first portion <NUM> (e.g., a right circular cylindrical ring portion <NUM> concentric with the first portion <NUM>), the first and second portions <NUM>, <NUM> having magnetizations <NUM>, <NUM> substantially perpendicular to the portion of skin <NUM>, and a third portion <NUM> between the first portion <NUM> and the second portion <NUM>, the third portion <NUM> has a magnetization <NUM> that is substantially perpendicular to the magnetizations <NUM>, <NUM> of the first portion <NUM> and the second portion <NUM>. In certain embodiments, the magnetizations <NUM>, <NUM> of the first and second portions <NUM>, <NUM> of the external magnet <NUM> are substantially equal and opposite to one another. The internal magnet <NUM> comprises a first portion <NUM> (e.g., a right circular cylindrical portion) and a second portion <NUM> surrounding a perimeter of the first portion <NUM> (e.g., a right circular cylindrical ring portion <NUM> concentric with the first portion <NUM>). In certain embodiments, the magnetizations <NUM>, <NUM> of the first and second portions <NUM>, <NUM> of the internal magnet <NUM> have substantially equal magnitudes and are in substantially opposite directions.

In certain embodiments, the external magnet <NUM> and/or the internal magnet <NUM> provides increased retention force (e.g., for the same magnet size and weight) for a range of thicknesses of the portion of skin <NUM> (e.g., the skin flap thickness) between the external apparatus <NUM> and the implanted device <NUM>. Certain such embodiments advantageously provide a lighter external apparatus <NUM> and/or implanted device <NUM> for equivalent retention force. This effect is even more pronounced when both the external magnet <NUM> and the internal magnet <NUM> are multipole magnets.

<FIG> is a plot that compares the retention force provided by three external / internal magnet configurations. Each of the magnets had a right circular cylindrical shape with a diameter of <NUM> millimeters and a height of <NUM> millimeters. A first configuration of an axially polarized external magnet and an axially polarized internal magnet exhibited the largest retention forces for all magnet separation distances. For smaller magnet separation distances (e.g., less than about <NUM>-<NUM> millimeters), a second configuration of a multipole external magnet in accordance with certain embodiments described herein and a diametrically magnetized internal magnet had larger retention forces than did a third configuration of a diametrically magnetized external magnet and a diametrically magnetized internal magnet. For larger magnet separation distances (e.g., greater than about <NUM>-<NUM> millimeters), the third configuration had larger retention forces than did the second configuration. Therefore, for small skin flap thicknesses (e.g., less than <NUM> millimeters), in certain embodiments, a smaller multipole external magnet can provide a retention force equivalent to that of a larger diametrically magnetized external magnet. Thus, in certain embodiments, the multipole external magnet in conjunction with a diametrically magnetized internal magnet can provide superior retention forces than does an equivalently-sized diametrically magnetized external magnet in conjunction with the same diametrically magnetized internal magnet while also providing desirable MRI compatibility.

It is to be appreciated that the embodiments disclosed herein are not mutually exclusive and may be combined with one another in various arrangements.

Language of degree, as used herein, such as the terms "approximately," "about," "generally," and "substantially," represent a value, amount, or characteristic close to the stated value, amount, or characteristic that still performs a desired function or achieves a desired result. For example, the terms "approximately," "about," "generally," and "substantially" may refer to an amount that is within ± <NUM>% of, within ± <NUM>% of, within ± <NUM>% of, within ± <NUM> % of, or within ± <NUM> % of the stated amount. As another example, the terms "generally parallel" and "substantially parallel" refer to a value, amount, or characteristic that departs from exactly parallel by ± <NUM> degrees, by ± <NUM> degrees, by ± <NUM> degrees, by ± <NUM> degree, or by ± <NUM> degree, and the terms "generally perpendicular" and "substantially perpendicular" refer to a value, amount, or characteristic that departs from exactly perpendicular by ± <NUM> degrees, by ± <NUM> degrees, by ± <NUM> degrees, by ± <NUM> degree, or by ± <NUM> degree.

Claim 1:
An auditory prosthesis, comprising:
an external component (<NUM>) including an external magnet (<NUM>) and a housing (<NUM>) configured to be placed over a portion of skin (<NUM>) of a recipient;
an internal component (<NUM>, <NUM>), said internal component being implantable and configured to be overlaid by the portion of skin (<NUM>), including an internal magnet (<NUM>);
wherein the external magnet is configured to interact with the internal magnet to provide sufficient magnetic force to retain the external component over the internal component (<NUM>, <NUM>),
the external magnet (<NUM>) has only three magnetic dipole moments (<NUM>, <NUM>, <NUM>),
the internal magnet has only two magnetic dipole moments (<NUM>, <NUM>), and
the external component (<NUM>) includes an inductor communication coil (<NUM>) that encircles the
external magnet (<NUM>) and/or encircles a projection of the external magnet (<NUM>) onto a plane defined by the inductor coil (<NUM>),
wherein the external magnet (<NUM>) comprises first and second portions (<NUM>, <NUM>) having magnetizations (<NUM>, <NUM>) with substantially equal magnitudes and substantially opposite directions and a third portion (<NUM>) between the first portion (<NUM>) and the second portion (<NUM>), the third portion (<NUM>) having a magnetization (<NUM>) that is substantially perpendicular to the magnetizations (<NUM>, <NUM>) of the first portion (<NUM>) and the second portion (<NUM>).