WO2013017172A1

WO2013017172A1 - Implantable hearing actuator with two membranes and an output coupler

Info

Publication number: WO2013017172A1
Application number: PCT/EP2011/063391
Authority: WO
Inventors: Renzo Magnin
Original assignee: Advanced Bionics Ag
Priority date: 2011-08-03
Filing date: 2011-08-03
Publication date: 2013-02-07

Abstract

The application relates to an implantable actuator for Stimulation of a component of the hearing of a user, comprising a hermetically sealed gas-filled Chamber formed by a rigid housing (64) having a first opening closed by a first membrane (66 ) and a second opening closed by a second membrane (67), wherein the first membrane is for supporting an Output coupling System ( 24, 86), wherein the Output coupling System is to be coupled to said hearing component and is to be driven by a transducer of the actuator comprising a mobile transducer assembly, wherein the first membrane and the second membrane are fixedly coupled via a membrane coupling means (24, 72, 86) and wherein the second membrane is designed with regard to membrane area and compliance in a manner so as to prevent displacement of the first membrane (66 ) and the mobile transducer assembly relative to the housing due to deviations of the atmospheric pressure from a reference value.

Description

IMPLANTABLE HEARING ACTUATOR WITH TWO MEMBRANES AND AN OUTPUT COUPLER

The present invention relates to an implantable actuator for stimulation of a component of the hearing of a user, comprising a hermetically sealed gas-filled chamber, and an output coupling element which is to be driven by a transducer of the actuator and which is to be coupled to the hearing component.

In case of a conductive or mixed hearing loss due to inefficient sound transmission through the external and/or middle and/or inner ear, one potential treatment method is direct acoustic cochlea stimulation (DACS) which involves the use of an implantable actuator for directly stimulating the inner ear fluid (perilymph) by simulating the operation of a normally functioning middle ear. In this way, a DACS actuator can compensate damages to the outer and/or middle and/or inner ear resulting in hearing loss. DACS actuators typically include a hermetically sealed gas-filled chamber contained within a biocompatible implantable housing. By hermetically sealing such chambers, contact of materials used in the actuator which are not biocompatible with tissue and body fluids is prevented. Typically, such hermetic seal is realized as a membrane made of biocompatible material which is laser- welded to the implantable housing. The gas pressure inside the chamber is typically equal to the barometric pressure which prevailed at the time of manufacturing, and this pressure will remain for the entire lifetime of the device (assuming constant temperature, since a change in temperature necessarily will result in a corresponding change in pressure). Since a DACS actuator is designed to simulate the operation of the middle ear, such devices necessarily are extremely finely balanced electromechanical systems. However, changes in atmospheric pressure will inherently result in a pressure difference between the interior of the gas-filled chamber and the exterior volume surrounding the chamber, which, in turn, will cause a deflection of the membrane and hence a change in compliance of the assembly5 composed of the membrane and mechanical and magnetic components attached to the membrane relative to mechanical and magnetic fixed parts of the actuator. In particular, while a DACS actuator, for example, may be optimized for operation at sea level and certain weather conditions, the user may find the performance of the actuator affected by variations in these conditions, resulting in degradation of the performance of the hearing instrument using 0 the actuator. An example of a DACS actuator is described in WO 2006/058368 Al, wherein an output coupling rod carrying an artificial incus is driven by an electromagnetic output transducer comprising a coil fixed to the housing and two axially spaced-apart magnetic elements fixed to the housing and provided for generating a magnetic biasing field, with a magnetically permeable armature being arranged between two opposed pole faces of the magnets in a manner defining a first and second working gap between the armature and the respective opposed pole faces. The armature is supported at one end by a high compliance spring element (aimed at centering the armature axis inside actuator body), and the other end is connected to the output coupling rod. One end of the cylindrical housing of the actuator is sealed by a titanium membrane which supports the output coupling rod which passes through the center of the membrane and is fixed at the membrane via a titanium ring to which it is welded. The titanium membrane acts as a spring (between mobile assembly and actuator cylindrical housing) featuring much lower compliance than above mentioned spring element (so that resulting spring stiffness is dominated by the titanium membrane). The other actuator cylindrical housing end is closed with a rigid mechanical part. Thereby a polarized reluctant system coupled to a mechanical resonant system is formed. The titanium membrane supporting the coupling rod forms an interface between the actuator external volume, which is partially filled with gas, and the external environment, with the external static pressure acting on the actuator internal gas pressure through the membrane, thereby preloading the membrane with a static force which results in a static bending of the membrane. Hence, when the membrane is not at its nominal static position, the spring characteristics changes and hence also the actuator transfer function changes.

WO 2010/116005 Al relates to a hearing assistance system comprising such implantable DACS actuator, wherein the system is provided with a barometric pressure sensor for sensing the presently prevailing atmospheric pressure and a correction signal unit for generating a correction signal as a predetermined function of the sensed atmospheric pressure. The correction signal is used by a pressure compensation element for adjusting the system gain in a manner so as to compensate for the impact of deviations of the atmospheric pressure from a reference value on the compliance of the gas-filled chamber. According to one example, the correction signal is applied to a mechanical pressure compensation element which is coupled to or forms part of the output transducer and which is adapted to mechanically displace an appropriate component of the output transducer. The pressure compensation element may be realized by a piston-like element or by a special membrane which is moved according to the correction signal by a correction actuator such as a piezoelement.

WO 2010/102342 Al relates to a hearing assistance system comprising an implantable DACS actuator, an external pressure sensor for measuring an external pressure outside the sealed housing of the actuator and a compensation module for determining a compensation factor for the actuator based on the external pressure. According to one embodiment, the physical operating characteristics of the actuator are modified based on the compensation factor to adjust the resonance behavior back to its original form by applying a DC signal and/or an asymmetrical AC signal to the signal coil of the actuator in accordance with the compensation factor.

WO 2009/152528 Al relates to an implantable sound sensor comprising hermetically sealed at one end by a membrane driven by a coupling mechanism, with the housing including a microphone which is driven by the membrane via a gas layer between the membrane and the diaphragm of the microphone.

US 2008/0132750 Al relates to an implantable hearing instrument comprising an implantable microphone; it is mentioned that changes in the environment, such as barometric pressure, may be compensated by providing for an adaptive filter.

US 2007/0027465 A 1 relates to an apparatus for reducing the sensitivity of the vestibular system to stimulation, wherein a control module including a sensing system for monitoring exogenous conditions, such as temperature and barometric pressure, is provided; passive pressure regulation can be provided via a pressure regulator. US 2007/0027405 Al relates to an apparatus for stimulating the vestibular system comprising an actuator including a control mechanism receiving control signals from a control module including a sensor system for monitoring exogenous conditions like barometric pressure. The control signals may be transmitted to the actuator via a wireless link. Also US 2004/0215236 A relates to a system for stimulating the vestibular system. WO 2005/099306 A2 relates to an implantable microphone having low acceleration sensitivity which utilizes a cancellation output from a cancellation surface indicative of acceleration acting on the microphone to counteract and/or cancel the effects of acceleration- induced pressures in the output of a microphone diaphragm. WO 2008/077943 A2 relates to an implantable hearing device comprising a vibration generator for applying vibrational stimulation to the inner ear fluid. According to one embodiment, the static pressure may be measured and compensated for.

It is an object of the invention to provide for an implantable hearing stimulation actuator comprising a hermetically sealed gas-filled chamber, wherein the performance of the actuator should remain constant as far as possible even when the system encounters changes in atmospheric pressure.

According to the invention, this object is achieved by an implantable actuator as defined in claims 1 and 5, respectively.

The invention is beneficial in that, by providing the housing with a second membrane, which second membrane is either fixedly coupled to the first membrane or is free to move relative to the first membrane and in this case has a compliance which is higher than the compliance of the first membrane times the area of the first membrane divided by the area of the second membrane, with the second membrane being designed with regard to its membrane area and its compliance in a manner so as to prevent displacement of the first membrane and the mobile transducer assembly relative to the housing due to deviations of the atmospheric pressure from a reference value, both axial displacement of the output coupling system and axial displacement of the mobile transducer assembly - both due to changes in atmospheric pressure - can be prevented, thereby preventing changes in the actuator performance as a function of the atmospheric pressure. Thus it is prevented that the output coupling system moves relative to the coupling site of the user's hearing as a function of the atmospheric pressure and that transducer performance changes as a function of the atmospheric pressure due to relative axial displacement of the mobile transducer portions relative to the fixed transducer assembly. The latter is particularly relevant in case that the transducer of an electromagnetic type where the properties of the transducer, such as the magnetic equivalent spring constant, may depend on the relative axial position of the mobile transducer assembly.

In the first case, the rigid coupling between the first and second membrane ensures that the external static pressure exerts oppositely equal forces on the first and second membrane and hence on the central axis of the actuator. According to one embodiment, a rod-like structure may be used for connecting the center of the first membrane and the center of the second membrane; according to an alternative embodiment, an incompressible liquid body extending between the first and second membrane and touching the first and second membrane may be used for achieving the rigid coupling between the first and second membrane.

In the second case (in which the second membrane is relatively softer than the first membrane and is free to move relative to the first membrane) the second membrane - due to its higher compliance - allows the gas content in the gas-filled chamber to expand or compress according to the changes in the atmospheric pressure, thereby allowing for internal actuator static pressure equalization with external environmental static pressure, thus reducing overall resulting static force on first membrane and preventing axial movement of the output coupling system .

Hereinafter, examples of the invention will be illustrated by reference to the attached drawings, wherein:

Fig. 1 is a schematic view of an example of an implanted hearing assistance system including an actuator according to the invention;

Fig. 2 is a schematic block diagram of an example of the system of Fig. 1 ;

Fig. 3 is a perspective view of the interior components of an example of an actuator according to the invention;

Fig. 4 is a longitudinal sectional view of the transducer of the actuator of Fig. 3 ;

Fig. 5 is a view like Fig. 4 wherein an alternative embodiment is shown;

Fig. 6 is a schematic view illustrating the principle of the embodiment of Fig. 4; and Fig. 7 is a schematic view illustrating the principle of the embodiment of Fig. 5.

Fig. 1 shows a cross-sectional view of the mastoid region, the middle ear and the inner ear of a patient after implantation of an actuator of an example of a hearing aid according to the invention, wherein the hearing aid is shown only schematically. The system comprises an external unit 10, which is worn outside the patient's body at the patient's head, and an implantable unit 12, which is implanted under the patient's skin 14, usually in an artificial bed created in the user's mastoid. The implantable unit 12 is connected via a cable assembly 18 to an actuator 20. While in Fig. 1 an electromechanical actuator coupled to an ossicle 22 via a coupling rod 24 is shown, the actuator 20 also may be an electromechanical actuator coupled directly to the cochlear wall, e.g. an artificial incus is coupled to a stapes prosthesis moving through the oval window.

The external unit 10 is fixed at the patient's skin 14 in a position opposite to the implantable unit 12, for example, by magnetic forces created between a magnetic fixation arrangement 26 provided in the external unit 10 and a cooperating magnetic fixation arrangement 28 provided in the implantable unit 12, respectively.

An example of a block diagram of the system of Fig. 1 is shown in Fig. 2. The external unit 10 includes a microphone arrangement 28, which typically comprises at least two spaced-apart microphones 30 and 32 for capturing audio signals from ambient sound, which audio signals are supplied to an audio signal processing unit 34, wherein they undergo, for example, acoustic beam forming. The processed audio signals are supplied to a transmission unit 36 connected to a transmission antenna 38 in order to enable transcutaneous transmission of the processed audio signals via an inductive link 40 to the implantable unit 12 which comprises a receiver antenna 42 connected to a receiver unit 44 for receiving the transmitted audio signals. The received audio signals are supplied to a driver unit 48 which drives the actuator 20.

The external unit 10 also comprises a power supply 50 which may be a replaceable or rechargeable battery, a power transmission unit 52 and a power transmission antenna 54 for transmitting power to the implantable unit 12 via a wireless power link 56. The implantable unit 12 comprises a power receiving antenna 58 and a power receiving unit 60 for powering the implanted electronic components with power received via the power link 56.

Preferably, the audio signal antennas 38, 42 are separated from the power antennas 54, 58 in order to optimize both the audio signal link 40 and the power link 56. However, if a particularly simple design is desired, the antennas 38 and 54 and the antennas 42 and 58 could be physically formed by a single antenna, respectively.

An example of the actuator 20 is shown in Figs. 3 and 4, wherein the actuator 20 comprises a hermetically sealed housing 64 which is closed on one end by a first titanium diaphragm membrane 66 which has a titanium ring 68 in its center and on the other end by a second titanium diaphragm membrane 67 having a titanium ring 69 in its center. The coupling rod 24 passes through the ring 68 which serves for fixing the coupling rod 24 at the first membrane 66; typically, the coupling rod 24 is welded to the ring 68. The membranes 66 and 67 serve to hermetically seal the interior of the housing 44, which is typically filled with air, so that the housing 64 forms a hermetically sealed gas-filled chamber. The membranes 66 and 67 may be laser welded to the housing 64.

The housing 64 surrounds an electromechanical output transducer 70 which is a electromagnetic motor comprising a central shaft 72, one end of which extends through the second membrane 67 and the ring 69 and is welded to the ring 69, thereby supporting the shaft 72, and the other end of which is connected to the coupling rod 24. The shaft 72 is made of a magnetically permeable material and comprises an armature 76 which is located between opposed pole faces of an upper magnet 78 and a lower magnet 79 which generate a magnetic biasing field between the pole faces. A first and a second working gap 81, 82 are defined between the armature 76 and the opposed pole faces of the magnets 78, 79. The magnets 78, 79 are supported by magnet supports 83, 84. The motor also includes a signal coil 80 which receives a driving signal from the output driver 48. The coupling rod 24 may comprises at its distal end an artificial incus 88 which is to be coupled to a stapes prosthesis. The general structure of the actuator 20, as far as the first membrane 66 and the electromagnetic motor concerned, is similar to that described in WO 2006/058368 Al. The electromechanical output transducer 70 serves to impart a reciprocating movement to the central shaft 72, thereby vibrating the coupling rod 24. Thus, by supplying a current/voltage to the coil 80 corresponding to the processed audio signals received from the external unit 10 the hearing of the patient can be stimulated according to the sound captured by the external unit 10. The membranes 66 and 67 along with magnetic forces generated by the magnets on the permeable armature serve to elastically support the coupling rod 24 and the shaft 72, thereby performing the function of a restoring spring.

The coil wires 85 are connected to laterally located feedthrough pins 86 (not shown in Fig. 3 but shown on Figs. 4 and 5). The coupling rod 24 and the shaft 72 including the armature 76 form a mobile assembly 86 which is driven by the coil 80 and the magnets 78, 79 which are fixed within the housing 64. In the embodiment shown in Figs. 3 and 4 the shaft 72 and the end of the coupling rod 24 connected to the shaft 72 form a rod-like structure which serves as a membrane coupling means for fixedly coupling the first membrane 66 and the second membrane 67 in order to prevent displacement of the center of the first membrane 66 and the center of the second membrane 67 relate to each other. After proper membranes individual dimensioning and due to such rigid coupling of the membranes 66, 67 they move in a push-pull manner and the external static pressure (which corresponds to or depends on the atmospheric pressure) exerts forces on the membranes 66, 67 which are equivalent and opposite with regard to the axis of the mobile assembly 86, so that changes in the atmospheric pressure do not result in an axial displacement of the centers of the membranes 66, 67 - and thus of the mobile assembly 86. The reciprocating movement of the rigidly coupled membranes 66, 67 induced in normal actuator operation due to the driving signal coming from the output driver 48 is illustrated in Fig. 6 (the upper part shows movement in one axial direction, and the lower part shows movement in the opposite axial direction).

As a result, the performance of the actuator 20 is essentially independent of the prevailing atmospheric pressure. Since the membranes 66, 67 are rigidly coupled, the system internal volume is kept constant when the membranes 66, 67 and the mobile assembly 86 move (when one of the membranes is moving outwardly, the other one is moving inwardly). The static pressure is the same on both membranes 66, 67 but creates opposite axial forces having the same magnitude but opposite directions, so that the impact of changes in the static pressure is essentially compensated. This requires that the compliance (spring constant) of the two membranes 66, 67 is essentially the same in the present example as the membranes surface areas are the same. In order to account for slight membrane area differences and to take mobile actuator assembly deformation due to static pressure into account, individual membranes compliances optimization may be required so as to achieve a constant mobile transducer assembly position between the transducer magnets poles irrespective of the static pressure. In the embodiments of Figs. 3 and 4, two mechanical springs formed by the membranes 66, 67 are added up in parallel but the air cushion spring effect (which is significantly smaller than the spring effect of the membranes 66, 67) is removed. Since thereby the overall spring force factor increases, compared to the construction of the actuator construction shown in WO 2006/058368 Al, this should be compensated for, e.g. by using thinner membranes and/or stronger force compensation magnets 78, 79.

Since both ends of the housing 64 are closed by the membranes 66, 67, a lateral positioning of the feed-through pins 86 is required. To this end, the cross-section of the housing 64 may be locally increased so as to have a cross-section of rather oval shape, wherein the shortest dimension should be selected such that the actuator housing 64 can still pass between critical nerves (facial nerve and chorda tympani) during surgery.

Rather than coupling the membranes 66, 67 via the rod-like mobile assembly 86, an incompressible liquid body fully filling the volume between first and second membranes 66, 67 could be used (not shown).

An alternative embodiment is shown in Fig. 5, wherein the second membrane 167 which serves to seal that end of the housing 64 which is opposite to the end sealed by the first membrane 66 does not act as a spring for supporting one end of the mobile assembly 86. Rather, in the embodiment of Fig. 5 the second membrane 167 is free to move relative to the first membrane 66 and is significantly softer than the first membrane 66, i.e. it has a compliance which is higher than the compliance of the first membrane 66, preferably by at least a factor of twice the ratio of the first membrane 66 area and the second membrane 167 area In the embodiment of Fig. 5, the end of the shaft 72 opposite to the end of the shaft connected to the coupling rod 24 is supported by a third centering membrane 90 which acts as a high compliance spring and which is gas-permeable, with that end of the shaft 72 passing through the center of the third membrane 90 and being fixed at the center of the third membrane 90.

The second membrane 167 preferably is made of titanium stamped foils with an accordeon or bellows-type ("zig-zag") shape.

The third membrane 90 primarily serves to center the shaft 72 with regard to the actuator axis and acts only with a very low force in the axial direction. Also in the embodiment of Fig. 5 the air cushion spring effect is removed (which is significantly lower than the spring effect of the titanium membranes). Since the overall spring force factor is lower in the embodiment of Fig. 5, compared for example to the embodiments of Figs. 3 and 4, this should be compensated for example by using a thicker spring membrane.

The second membrane 167 acts as an independent passive expansion membrane which is much softer than the first membrane 66, i.e. the actuator active mobile membrane (which acts as a spring element). Due to its softness, the second membrane 167 allows the actuator internal gas content to expand or compress according to the variation of the external static pressure, so that the first membrane 66 may keep a substantially constant shape irrespective of the presently prevailing external static pressure, thereby avoiding axial displacement of the mobile assembly 86 caused by variations of the external static pressure. This principle is illustrated in Fig. 7 (the upper part shows an expansion of the internal gas content due to lower static pressure, while the lower part shows a compression of the internal gas content due to higher static pressure).

While in the embodiments of Figs. 4 and 6 only one second membrane 67 is shown, there may be additional membranes, such as side by side on the same actuator side and coupled through mechanics (levers/rods) either located inside the housing or outside the housing. Also, there ma)' be more than one element serving to couple the various membranes as the membrane coupling means.

While in the embodiment of Fig. 5 only one second membrane 167 is shown, there may be additional membranes too.

Claims

1. An implantable actuator for stimulation of a component of the hearing of a user, comprising a hermetically sealed gas-filled chamber formed by a rigid housing (64) having a first opening closed by a first membrane (66) and a second opening closed by a second membrane (67), wherein the first membrane is for supporting an output coupling system (24, 86), wherein output coupling system is to be coupled to said hearing component and is to be driven by a transducer (70) of the actuator comprising a mobile transducer assembly (76), wherein the first membrane and the second membrane are fixedly coupled via a membrane coupling means (24, 72, 86) and wherein the second membrane is designed with regard to membrane area and compliance in a manner so as to prevent displacement of the first membrane (66) and the mobile transducer assembly relative to the housing due to deviations of the atmospheric pressure from a reference value.

2. The actuator of claim 1, wherein the membrane coupling means comprises a rod-like structure (24, 72, 86) connecting the center of the first membrane (66) and the center of the second membrane (67), respectively.

3. The actuator of claim 2, wherein the rod-like structure (24, 72, 86) has a first end connected to the center of the second membrane (67).

4. The actuator of claim 3, wherein the first end of the rod-like structure (24, 72, 86) is connected to the center of the second membrane (67) via a ring (69) which is fixed at the second membrane, with the first end of the rod-like element passing through the ring and being welded to the ring.

5. An implantable actuator for stimulation of a component of the hearing of a user, comprising a hermetically sealed gas-filled chamber formed by a rigid housing (64) having a first opening closed by a first membrane (66) and a second opening closed by a second membrane (167), wherein the first membrane is for supporting an output coupling system (24), wherein output coupling system is to be coupled to said hearing component and is to be driven by a transducer (70) of the actuator and which is to be coupled to said hearing component comprising a mobile transducer assembly (76), wherein the second membrane is free to move relative to all other actuator parts and wherein the second membrane has a compliance which is higher than the compliance of the first membrane times the area of the first membrane divided by the area of the second membrane, and wherein the second membrane is designed with regard to membrane area and compliance in a manner so as to prevent displacement of the first membrane and the mobile transducer assembly relative to the housing due to deviations of the atmospheric pressure from a reference value.

6. The actuator of claim 5, wherein the compliance of the second membrane (167) is higher than the compliance of the first membrane (66) at least by a factor of twice the surface area of the first membrane divided by the surface area of the second membrane.

7. The actuator of one of claims 5 and 6, wherein the output coupling element (24, 86) comprises or is connected to a rod-like structure (72) having a first end connected to the center of a third membrane (90) for centering the output coupling element.

8. The actuator of claim 7, wherein the third membrane (90) is gas-permeable.

9. The actuator of one of claims 5 to 8, wherein the second membrane (167) is made of stamped titanium foils with circular bellows-like shape.

10. The actuator of one of the preceding claims, wherein the first membrane (66) is made of titanium.

11. The actuator of one of claims 3 and 7, wherein the rod-like structure (24, 72, 86) comprises a shaft (72) which is fixed to an end of the output coupling element (24).

12. The actuator of one of the preceding claims, wherein the output coupling element (24) is connected to the center of the first membrane (66) via a ring (68) which is fixed at the first membrane, with an end of the output coupling element passing through the ring and being welded to the ring.

13. The actuator of one of the preceding claims, wherein the transducer (70) comprises a permanent magnet assembly (78, 79) fixed with regard to the housing (64) and wherein the mobile transducer assembly comprises a magnetically permeable armature (76) magnetically coupled to the permanent magnet assembly.

14. The actuator of claim 13, wherein the permanent magnet assembly (78, 79) comprises axially spaced first and second magnets (78, 79) defining an axially extending gap in- between, wherein the armature (76) is located within the gap.

15. The actuator of claim 14, wherein the transducer (70) comprises a coil (80) fixed within the housing (64), wherein the first and second magnets (78, 79) are for generating a biasing field region between opposed pole faces in said gap, and wherein the magnetically permeable armature (76) located in the biasing field region in a manner defining a first and second working gap (81, 82) between the armature and the respective opposed pole faces.

16. The actuator of claim 15 and one of claims 2 and 7, wherein the armature (76) forms part of the rod-like structure (24, 72, 86).

17. The actuator of one of claims 14 to 16, wherein the housing (64) comprises a cylindrical portion having an oval cross section, said portion comprising a lateral coil wire feedthrough interface (86).

18. The actuator of one of the preceding claims, wherein the output coupling rod (24) comprises an artificial incus (88).