U.S. patent application number 13/933490 was filed with the patent office on 2016-07-07 for magnet arrangement for bone conduction hearing implant.
The applicant listed for this patent is Vibrant Med-El Hearing Technology GmbH. Invention is credited to Thomas Lechleitner, Markus Nagl.
Application Number | 20160198270 13/933490 |
Document ID | / |
Family ID | 48874513 |
Filed Date | 2016-07-07 |
United States Patent
Application |
20160198270 |
Kind Code |
A9 |
Nagl; Markus ; et
al. |
July 7, 2016 |
MAGNET ARRANGEMENT FOR BONE CONDUCTION HEARING IMPLANT
Abstract
An implantable magnetic transducer arrangement is described for
a hearing implant in a recipient patient. An implant housing
hermetically encapsulates an interior housing volume and is fixedly
attached to skull bone beneath the skin of the patient. A magnetic
transducer is located within the housing volume and includes
multiple permanent magnets wherein adjacent magnets have opposite
magnetic polarities, and one or more suspension elements that
resiliently couple adjacent magnets to allow their relative
movement. The magnetic transducer forms a coupled oscillating
system with an external magnetic drive component above the skin of
the patient to develop a mechanical stimulation signal to the
implant housing for delivery by bone conduction of the skull bone
as an audio signal to the cochlea of the patient.
Inventors: |
Nagl; Markus; (Volders,
AT) ; Lechleitner; Thomas; (Polling, AT) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Vibrant Med-El Hearing Technology GmbH |
Innsbruck |
|
AT |
|
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140012070 A1 |
January 9, 2014 |
|
|
Family ID: |
48874513 |
Appl. No.: |
13/933490 |
Filed: |
July 2, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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13780193 |
Feb 28, 2013 |
|
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13933490 |
|
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61669161 |
Jul 9, 2012 |
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Current U.S.
Class: |
600/25 |
Current CPC
Class: |
A61N 1/3718 20130101;
A61N 1/36036 20170801; H04R 11/02 20130101; H04R 25/60 20130101;
H04R 25/606 20130101; H04R 25/556 20130101; A61N 1/37518
20170801 |
International
Class: |
H04R 25/00 20060101
H04R025/00 |
Claims
1. An implantable magnetic transducer arrangement for a hearing
implant in a recipient patient, the arrangement comprising: an
implant housing hermetically encapsulating an interior housing
volume and fixedly attached to skull bone beneath the skin of the
patient; a magnetic transducer within the housing volume having: i.
a plurality of permanent magnets wherein adjacent magnets have
opposite magnetic polarities; and ii. one or more suspension
elements resiliently coupling adjacent magnets to allow their
relative movement; wherein the magnetic transducer forms a coupled
oscillating system with an external magnetic drive component above
the skin of the patient to develop a mechanical stimulation signal
to the implant housing for delivery by bone conduction of the skull
bone as an audio signal to the cochlea of the patient.
2. A transducer arrangement according to claim 1, wherein the
magnets include: an inner cylindrical magnet, and at least one ring
magnet concentrically outside the inner cylindrical magnet.
3. A transducer arrangement according to claim 2, wherein a
plurality of ring magnets are concentrically arranged outside the
inner cylindrical magnet.
4. A transducer arrangement according to claim 1, wherein the
suspension elements include a spring membrane coupled to the
cylindrical magnet on one side and coupled to the at least one ring
magnet on the opposite side.
5. A transducer arrangement according to claim 1, wherein the
suspension elements include a pair of spring membranes lying in
parallel planes with the cylindrical magnet coupled to one of the
spring membranes and the at least one ring magnet coupled to the
other spring membrane.
6. A transducer arrangement according to claim 1, wherein the
magnets are pie-shaped segments connected by suspension elements to
form a cylindrical disk.
7. A transducer arrangement according to claim 6, wherein each
magnet has the same size and shape.
8. A transducer arrangement according to claim 6, wherein the
magnets have a plurality of different sizes and shapes.
9. A transducer arrangement according to claim 1, wherein at least
one of the magnets interacts with an external holding magnet to
affix the external drive coil in position on the skin of the
patient.
10. A hearing implant system having an implantable magnetic
transducer arrangement according to any of claims 1-9.
Description
[0001] This application claims priority from U.S. Provisional
Patent Application 61/669,161, filed Jul. 9, 2012, and from U.S.
patent application Ser. No. 13/780,193, filed Feb. 28, 2013, which
are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to medical implants, and more
specifically to a novel transcutaneous auditory prosthetic implant
system.
BACKGROUND ART
[0003] A normal ear transmits sounds as shown in FIG. 1 through the
outer ear 101 to the tympanic membrane (eardrum) 102, which moves
the ossicles of the middle ear 103 (malleus, incus, and stapes)
that vibrate the oval window 106 and round window 107 membranes of
the cochlea 104. The cochlea 104 is a long narrow duct wound
spirally about its axis for approximately two and a half turns. It
includes an upper channel known as the scala vestibuli and a lower
channel known as the scala tympani, which are connected by the
cochlear duct. The cochlea 104 forms an upright spiraling cone with
a center called the modiolar where the spiral ganglion cells of the
cochlear nerve 105 reside. In response to received sounds
transmitted by the middle ear 103, the fluid-filled cochlea 104
functions as a transducer to generate electric pulses which are
transmitted to the cochlear nerve 105, and ultimately to the
brain.
[0004] Hearing is impaired when there are problems in the ability
to transduce external sounds into meaningful action potentials
along the neural substrate of the cochlea 104. To improve impaired
hearing, auditory prostheses have been developed. For example, when
the impairment is related to operation of the middle ear 103, a
conventional hearing aid or middle ear implant may be used to
provide acoustic-mechanical stimulation to the auditory system in
the form of amplified sound. Or when the impairment is associated
with the cochlea 104, a cochlear implant with an implanted
stimulation electrode can electrically stimulate auditory nerve
tissue with small currents delivered by multiple electrode contacts
distributed along the electrode.
[0005] Middle ear implants employ electromagnetic transducers to
convert sounds into mechanical vibration of the middle ear 103. A
transducer housing comprising a magnet assembly and a coil winding
is attached to the ossicle bones within the middle ear 103 and
microphone signal current is delivered to the coil winding to
generate an electromagnetic field. The magnet vibrates in response
to the interaction of the magnetic fields, causing vibration of the
ossicle bones of the middle ear 103. See U.S. Pat. No. 6,190,305,
which is incorporated herein by reference.
[0006] U.S. Patent Publication 20070191673 (incorporated herein by
reference) described another type of implantable hearing prosthesis
system which uses bone conduction to deliver an audio signal to the
cochlea for sound perception in persons with conductive or mixed
conductive/sensorineural hearing loss. An implanted floating mass
transducer (FMT) is affixed to the temporal bone. In response to an
externally generated electrical audio signal, the FMT couples a
mechanical stimulation signal to the temporal bone for delivery by
bone conduction to the cochlea for perception as a sound signal. A
certain amount of electronic circuitry must also be implanted with
the FMT to provide power to the implanted device and at least some
signal processing which is needed for converting the external
electrical signal into the mechanical stimulation signal and
mechanically driving the FMT.
[0007] One problem with implantable hearing prosthesis systems
arises when the patient undergoes Magnetic Resonance Imaging (MRI)
examination. Interactions occur between the implant magnet and the
applied external magnetic field for the MRI. The external magnetic
field from the MRI may create a torque on the implant magnet, which
may displace the magnet or the whole implant housing out of proper
position and/or may damage the adjacent tissue in the patient. The
implant magnet may also cause imaging artifacts in the MRI image,
there may be induced voltages in the receiving coil, and hearing
artifacts due to the interaction of the external magnetic field of
the MRI with the implanted device.
[0008] Thus, for existing implant systems with magnet arrangements,
it is common to either not permit MRI or at most limit use of MRI
to lower field strengths. Other existing solutions include use of a
surgically removable magnets, spherical implant magnets (e.g. U.S.
Pat. No. 7,566,296), and various ring magnet designs (e.g., U.S.
Provisional Patent 61/227,632, filed Jul. 22, 2009). Among those
solutions that do not require surgery to remove the magnet, the
spherical magnet design may be the most convenient and safest
option for MRI investigations even at very high field strengths.
But the spherical magnet arrangement requires a relatively large
magnet much larger than the thickness of the other components of
the implant, thereby increasing the volume occupied by the implant.
This in turn can create its own problems. For example, some
systems, such as cochlear implants, are implanted between the skin
and underlying bone. The "spherical bump" of the magnet housing
therefore requires preparing a recess into the underlying bone.
This is an additional step during implantation in such applications
which can be very challenging or even impossible in case of very
young children.
[0009] U.S. Patent Publication 20120029267 (incorporated herein by
reference) describes an implantable hearing prosthesis having two
planar implant magnets connected by a flexible connector member
which is fixable to underlying skull bone. Each of the implant
magnets is in the specific form of a center disk having magnetic
polarity in one axial direction. Around the disk magnet is another
ring magnet having an opposite magnetic polarity in a different
direction. This ring/disk magnet arrangement has less magnetic
interaction with an external magnetic field such as an MRI
field.
SUMMARY
[0010] Embodiments of the present invention are directed to an
implantable magnetic transducer arrangement for a hearing implant
in a recipient patient. An implant housing hermetically
encapsulates an interior housing volume and is fixedly attached to
skull bone beneath the skin of the patient. A magnetic transducer
is located within the housing volume and includes multiple
permanent magnets wherein adjacent magnets have opposite magnetic
polarities, and one or more suspension elements that resiliently
couple adjacent magnets to allow their relative movement. The
magnetic transducer forms a coupled oscillating system with an
external magnetic drive component above the skin of the patient to
develop a mechanical stimulation signal to the implant housing for
delivery by bone conduction of the skull bone as an audio signal to
the cochlea of the patient.
[0011] The magnets may include an inner cylindrical magnet, and at
least one ring magnet concentrically outside the inner cylindrical
magnet; and in some embodiments, there may be multiple ring magnets
concentrically arranged outside the inner cylindrical magnet. In
specific such embodiments, the suspension elements may include a
spring membrane coupled to the cylindrical magnet on one side and
coupled to the at least one ring magnet on the opposite side. Or
the suspension elements may include a pair of spring membranes
lying in parallel planes with the cylindrical magnet coupled to one
of the spring membranes and the at least one ring magnet coupled to
the other spring membrane.
[0012] Or the magnets may be pie-shaped segments connected by
suspension elements to form a cylindrical disk. In specific such
embodiments, each magnet may have the same size and shape, or the
magnets may have different sizes and shapes.
[0013] Embodiments of the present invention also include a hearing
implant system having an implantable magnetic transducer
arrangement according to any of the foregoing.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 shows anatomical structures of a typical human
ear.
[0015] FIG. 2 A-B shows a top plant view and side cross-sectional
view respectively of a magnetic arrangement for a hearing implant
according to one specific embodiment of the present invention.
[0016] FIG. 3 shows the magnetic field from an external signal
drive coil interacting with a magnet arrangement as shown in FIG.
2.
[0017] FIG. 4 A-D shows a magnetic transducer using a magnet
arrangement according to an embodiment of the present
invention.
[0018] FIG. 5 is a graph of frequency vs. output force that shows
that properly designing a spring system can achieve a frequency
range optimal for speech understanding.
[0019] FIG. 6 shows an embodiment of the present invention together
with the elastic spring functioning of the skin.
[0020] FIG. 7 shows an embodiment having multiple concentric ring
magnets of alternating magnetic polarities.
[0021] FIG. 8 shows an embodiment with two parallel spring
membranes.
[0022] FIG. 9 shows an embodiment with multiple pie shaped sections
connected by resilient suspension elements.
DETAILED DESCRIPTION
[0023] Embodiments of the present invention are directed to an
implantable MRI-compatible magnetic arrangement for a simple cheap
and small-size mechanical transducer such as for a bone conduction
hearing implant. The magnetic arrangement includes multiple
permanent magnets wherein adjacent magnets have opposite magnetic
polarities. One or more suspension elements (e.g. silicone,
membrane, etc.) resiliently couple adjacent magnets to allow their
relative movement. The resulting magnetic transducer thus forms a
coupled oscillating system with an external magnetic drive
component above the skin of the patient to develop a mechanical
stimulation signal to the implant housing surrounding the magnets
for delivery by bone conduction of the skull bone as an audio
signal to the cochlea of the patient.
[0024] FIG. 2 A shows a top plant view and FIG. 2B shows a side
cross-sectional view of a magnetic arrangement 200 for a hearing
implant according to one specific embodiment. An inner cylindrical
magnet 201 has a magnetic field polarity with the south magnetic
pole on top and the north magnetic pole on the bottom. An outer
ring magnet 202 fits concentrically outside around the inner
cylindrical magnet 201 and has an opposite magnetic field polarity
with the north magnetic pole on top and the south magnetic pole on
the bottom. Spring membrane 203 (e.g., silicone material) acts as a
suspension element that resiliently couples the inner cylindrical
magnet 201 and the outer ring magnet 202 to allow their relative
movement. The magnetic arrangement 200 is stable as soon as the
magnets 201 and 202 are assembled and the restoring forces
contribute to the forces from the spring membrane 203.
[0025] As shown in FIG. 3, the magnetic field from an external
signal drive coil 301 causes the inner cylindrical magnet 201 and
the outer ring magnet 202 to be displaced relative to each other in
opposite directions. Geometric and volumetric construction
characteristics of the magnets 201 and 202 affect the magnetic
dipole moment to reduce/minimize torque on the arrangement caused
by external magnetic field (e.g. MRI) such that:
m=V.sub.1H.sub.1-V.sub.2H.sub.2=0
where m is the magnetic dipole moment, V is the volume of each
magnet, and H is magnetic field strength of each magnet.
[0026] Such a magnetic arrangement also possesses a tunable
frequency characteristic as a function of the elastic properties of
the spring element 203 and the mass of the magnet arrangement 200.
The suspension element spring membrane 203 critically contributes
to the spring stiffness--e.g., soft silicone promotes a softer
spring, harder silicone promotes a stiffer spring.
[0027] FIG. 4 A-D shows the above magnetic arrangement implemented
as an implantable bone conduction transducer 400 enclosed within a
hermetic housing 401. In such a transducer 400, the inner cylinder
magnet 201, housing spacer 402, hermetic housing 401 and the
patient skull act as one common mass. The outer ring magnet 202
vibrates suspended by the spring membrane 203 within the air gap
403 between the outer surface of the ring magnet 202 and the
hermetic housing 401 in a push-pull configuration that is driven by
the external magnetic field of the external signal drive coil 301.
(Such operation is not limited to the specific form of external
signal drive coil 301 as shown in FIG. 3). The external signal
drive coil 301 excites a magnetic field such that the magnetic
poles of the external coil arrangement that are opposite to the
inner cylinder magnet 201 and outer ring magnet 202 each have
opposing magnetic polarities. In another specific embodiment, the
external signal drive coil 301 may include two or more coil
assemblies. The bone conduction transducer 400 will equivalently
work with the outer ring magnet 202, housing spacer 402 and
hermetic housing 401 acting as a single common mass where the inner
cylinder magnet 201 vibrates suspended by the spring membrane 203
within the outer ring magnet 202 as shown in FIG. 4C-D. The spring
membrane 203 may be made of any elastic material (e.g., silicone)
and may fill only a part or the entire gap between inner cylinder
magnet 201 and outer ring magnet 202 as shown in FIG. 4A and 4C. It
may be useful if only one part is fixed at one end at a bevel on
the inner cylinder magnet 201 by an o-ring suspension
element/spring membrane 203. This may ease the manufacturing
process and allow for easy alignment (i.e. centering) during
assembly. The hermetic housing 401 does not require an electric or
any other feed-through which is an advantage compared to
conventional actively driven bone conduction devices.
[0028] In addition to its function as being a part of the magnetic
driving system the inner cylinder magnet 201 also acts as the
holding magnet for the external device. Ideally, the diameter of
the outer device coincides with the diameter of the inner cylinder
magnet 201 such that the external device is affected as little as
possible by the vibrating outer ring magnet 202. But with regards
to an external magnetic far field such as that from an MRI
apparatus, the magnetic polarities of the internal magnets 201 and
202 oppose and are intended to cancel each other out. This net
minimizing of the magnetic fields of the implant magnets reduces
their magnetic interactions with the external MRI field to minimize
adverse effects such as torque forces and imaging artifacts.
[0029] Such an implantable bone conduction transducer differs from
the prior art in some important aspects. The implantable transducer
has only passive implantable components and all the transducer
functionality is in the implantable device itself; no prior art
device takes advantage of this combination. Prior art transducers
having only passive implantable components also utilize the skin
acting as the spring element, with all the obvious disadvantages
because the skin has poor elastic damping properties and if the
magnetic forces are too strong, the skin may be traumatized or
damaged.
[0030] Other prior art devices that do not rely on a separated
attachment and transducer section (such as the Xomed Audiant) are
likely to fail because the external device oscillates with such a
large amplitude. Embodiments of the present invention provide
considerably reduced oscillation amplitude of the external portion.
This allows (but does not require) the attachment and transducer
functionality to be located in the same component, but at the same
time overcomes the shortcomings of the Audiant device.
[0031] Embodiments of the present invention form a coupled
oscillating system. One oscillator is the implantable arrangement
of ring and disk magnet described above, and another oscillator
includes a conventional external magnet, the skin and the
implantable magnet arrangement as in the prior art. The first
spring-mass system resonance frequency of the first implantable
oscillator is determined by the mass of the vibrating magnet and
the spring constant of the spring membrane 203. The second
spring-mass system resonance frequency is determined by the mass of
the vibrating magnet 201 or 202, the external portion and the skin
acting as spring and damping element. One disadvantage of the prior
art is, that the elastic properties of the skin cannot be exactly
determined and also change somewhat over time, and the output force
of the magnetic transducer arrangement 200 may become insufficient
over the full frequency range for speech understanding. This is for
example shown in FIG. 5. The output force of the bone conduction
transducer drops quickly with frequencies that deviate only
slightly from the resonance frequency. The coupled oscillator
system allows the desired frequency range of resonance to be
broadened by superimposing the resonance behavior of the two
spring-mass systems. FIG. 5 shows a graph of output force over
frequency showing that appropriate design of the spring systems
enables achievement of a frequency range that is optimal for speech
understanding.
[0032] FIG. 6 shows another embodiment of the present invention
along with symbolic elements for the spring and dampening functions
of the patient's skin. Specifically, an implantable magnetic
transducer arrangement 600 includes an implantable transducer
housing 604 which is fixedly attached to the skull bone 609 beneath
the skin 608 of an implanted patient. Within the transducer housing
604 is a spring membrane 603 that coupled on one side to a
cylindrical magnet 601 and coupled on the other side to at least
one ring magnet 602. In an alternative embodiment, both magnets 601
and 602 may be attached on the same side of the spring membrane
603. An external portion 605 is attached on the patient skin 608
over the transducer housing 604 by an attachment magnet 606 that is
held in place by magnetic attraction to the implanted cylindrical
magnet 601. A communication signal is sent through the external
coil 607 that forms a dynamically changing coil magnetic field
creating a coupled oscillator system 610 between the external
portion 605, the magnet arrangement within the transducer housing
604, the skin spring function 611, and the skin damping function
612. The dynamic magnetic field of the external coil 607
alternately attracts and repels the cylinder magnet 601 that is
coupled to the transducer housing 604 as vibration that acts as a
mechanical stimulation signal to the skull bone 605 for bone
conduction to the cochlea for perception as sound.
[0033] Further embodiments may be implemented based on using a
higher number of spring elements, which can lead to a further
enlarged resonant frequency range. FIG. 7 one possible embodiment
featuring an inner central cylinder magnet 701 and multiple
concentric outer ring magnets 702 of alternating magnetic field
polarities which are mounted on a connecting membrane spring
suspension element 703 in a hermetic housing attached to the skull.
The magnets 701 and 702 are deflected by a dynamic magnetic field
signal from an external device. In such an arrangement, the
individual suspension elements 703 between adjacent magnets may
have different spring constants, which can allow for multiple
different oscillation modes.
[0034] FIG. 8 shows another embodiment of an implantable magnetic
transducer 800 having multiple suspension elements in the specific
form of a pair of spring membranes 803 lying in parallel planes
with the inner cylindrical magnet 801 coupled to one of the spring
membranes 803 and an outer ring magnet 802 coupled to the other
spring membrane 803. Again, the two different spring membranes 803
can be chosen to have different spring constants; for example, they
may be made of different materials such as silicone, platinum,
etc.
[0035] FIG. 9 shows another possible embodiment featuring a
cylindrical magnet 900 divided into multiple individual pie shaped
magnets 901 mounted on connecting suspension elements 902. Each
pie-shaped magnet 901 may have the same size and shape, or they may
have multiple different sizes and shapes. To control torque and
provide tunable frequency characteristics the properties of the
suspension elements 902 can be controlled (e.g. hard/soft silicone,
etc.). Adjacent suspension elements 902 may be alternatingly soft
and hard, thereby forming groups of pie-shaped magnets 901 between
e.g. hard suspension elements 902 and having differing resonance
frequencies. Adjacent pie shaped magnets 901 may have magnetic
polarities in different directions, for example in opposite axial
directions as shown in FIG. 9.
[0036] Although various exemplary embodiments of the invention have
been disclosed, it should be apparent to those skilled in the art
that various changes and modifications can be made which will
achieve some of the advantages of the invention without departing
from the true scope of the invention.
* * * * *