This disclosure relates generally to microactuators (sometimes referred to as transducers). More particularly it relates to microactuators for use with fully implantable hearing aid systems.
Various different types of semi-implantable and fully-implantable hearing aids have been developed or proposed over the years. Cochlear implants utilize a direct electrical stimulation of the human cochlea in order to convey a perceivable signal to a human subject. Middle ear implants use mechanical stimulation of the ossicles or middle ear bones to convey a perceivable signal to a human subject. Air conduction hearing aids use a speaker element to create perceivable sound pressure signals in the air of the ear. Some implantable hearing aids have used a piezoelectric stack or pre-stressed piezoelectric materials to form a piezoelectric transducer having sufficient displacement to convey a perceivable signal to a human subject. See, for example, U.S. Pat. Nos. 5,772,575 (“Implantable Hearing Aid”) and 6,561,231 (“Method for filling acoustic Implantable Transducers”) and U.S. Patent Application Publication Documents US2002/0062875A1 (“Method for filling acoustic implantable transducers”) and US2003/0055311A1 (“Biocompatible Transducers”). What is needed is an improved fully implantable hearing aid microactuator.
A microactuator has a proximal end configured to receive an electrical signal and a distal end configured to be inserted into a fenestration of an otic bone to provide access through the lateral wall of the cochlea of a subject. The microactuator includes a piezoelectric transducer assembly having a piezoelectric transducer disposed on a membrane (the piezoelectric transducer having a smaller dimension than a corresponding dimension of the membrane), a hermetically sealed fluid cavity filled with a fluid sealed at a first end to a first side of the piezoelectric transducer assembly and at a second end to a diaphragm, a second cavity containing a vacuum or a gas sealed at a first end to a second side of the piezoelectric transducer assembly and at a second end to an end cap.
The accompanying drawings, which are incorporated into and constitute a part of this specification, illustrate one or more examples of embodiments and, together with the description of example embodiments, serve to explain the principles and implementations of the embodiments.
In the drawings:
Example embodiments are described herein in the context of a microactuator for use with a fully implantable hearing aid. Those of ordinary skill in the art will realize that the following description is illustrative only and is not intended to be in any way limiting. Other embodiments will readily suggest themselves to such skilled persons having the benefit of this disclosure. Reference will now be made in detail to implementations of the example embodiments as illustrated in the accompanying drawings. The same reference indicators will be used to the extent possible throughout the drawings and the following description to refer to the same or like items.
In the interest of clarity, not all of the routine features of the implementations described herein are shown and described. It will, of course, be appreciated that in the development of any such actual implementation, numerous implementation-specific decisions must be made in order to achieve the developer's specific goals, such as compliance with application- and business-related constraints, and that these specific goals will vary from one implementation to another and from one developer to another. Moreover, it will be appreciated that such a development effort might be complex and time-consuming, but would nevertheless be a routine undertaking of engineering for those of ordinary skill in the art having the benefit of this disclosure.
Turning to the figures,
Microactuator 10 further comprises a piezoelectric transducer membrane assembly 26 with a hot lead 28 coupled to a first electrical contact 30 and a ground lead 32 coupled to the case 34 of microactuator 10 and through that to a second electrical contact 36. First electrical contact 30 is insulated from case 34 of microactuator 10. Piezoelectric transducer membrane assembly 26 may comprise a cylindrical (circular axial cross-section) piezoelectric transducer 26a such as a lead zirconate titanate (PZT) crystal or stack of crystals (or other suitable piezoelectric material or materials) having a first diameter and a thin titanium membrane 26b of circular axial cross-section having a second, larger diameter to which piezoelectric transducer 26a is fixed. Making the piezoelectric transducer of smaller dimension than the membrane on which it is fixed provides an improved response by decoupling somewhat the piezoelectric transducer 26a from the case 34 through the flexible action of membrane 26b.
Placing the piezoelectric transducer membrane assembly 26 between the back cavity 60 and the fluid cavity 54 allows the piezoelectric transducer 26a to directly drive the relatively incompressible fluid body 54a contained in fluid cavity 54 to, in turn, drive distal diaphragm 46, the outside wall of which is in contact with the inside wall of the cochlea, to thereby impart the sensation of sound to the subject. Disposing a gas or vacuum in the back cavity 60 (on the opposite side of the piezoelectric transducer membrane assembly 26 from the fluid cavity 54) reduces resistance to the vibratory motion of the piezoelectric transducer membrane assembly 26 to improve performance and reduce power draw.
A sealant cavity 48 (initially open at the top) is defined at an outer periphery by the inside of feed-through flange 38 and is in one embodiment filled with a silicone sealant material (although those of ordinary skill in the art will now realize that other suitable sealant materials may be used instead). This sealant material protects first and second electrical contacts (30, 36), provides strain relief for microactuator lead wires 50 which couple microactuator 10 to other hearing aid component (not shown) and seals the proximal end 52 of microactuator 10 from moisture infiltration.
Fluid cavity 54 configured to contain fluid body 54a as discussed above is defined at an outer periphery by the inside wall of narrow portion 56 of microactuator 10, at a distal end by microactuator distal diaphragm 46 located at distal end 58 of microactuator 10, and at a proximal end by piezoelectric transducer membrane assembly 26. Fluid cavity 54 is filled with a fluid as described in more detail below in order to improve performance of the microactuator in conveying the impression of sound to the inner ear of a subject.
In one embodiment the piezoelectric transducer 26a has a thickness along a longitudinal axis in a range of from about 25 um to about 500 um with 100 um used in one example, the membrane 26b has a thickness in a range of from about 5 um to about 100 um with 25 um used in one example, and the diaphragm 46 has a thickness in a range of from about 5 um to about 100 um with 19 um+/−1 um used in one example. In one embodiment the piezoelectric transducer 26a is soldered to the membrane 26b.
Second (64), laser weld microactuator distal diaphragm 46 to the distal (narrow) end of microactuator flange 42 along the outside edge of diaphragm 46.
Third (66), attach (which may be accomplished with a laser weld) one end of hot lead (which may comprise gold such as gold wirebond) 28 to piezoelectric transducer membrane assembly 26 and a second end of hot lead 28 to first electrical contact 30 on microactuator end cap 40 which is nearest to piezoelectric transducer membrane assembly 26.
Fourth (68), assemble the sealed flange assembly (42, 46), the piezoelectric transducer membrane assembly 26 and the microactuator end cap 40 to form a partial microactuator assembly (42, 46, 26, 40). This step may be performed by sandwiching the piezoelectric transducer membrane assembly 26 with (on one side) the microactuator end cap 40 and (on the other side) the sealed flange assembly (42, 46) in a fixture to hold them together during a laser welding operation. This laser weld may be performed by rotating the fixture while welding along the intersection of the microactuator end cap 40, the piezoelectric transducer membrane assembly 26 and the sealed flange assembly (42, 46). This completes the back cavity which is a hermetically sealed cavity filled as described above and located between the piezoelectric transducer membrane assembly 26 and microactuator end cap 40. It also creates the fluid cavity 54. The back cavity may be evacuated, partially evacuated or filled with a selected gas or gasses at this time by conducting the operation in an environment which is evacuated or filled with the selected gas or gasses.
Fifth (70), mount the partial microactuator assembly (42, 46, 26, 40) and feed-through flange 38 into a fixture and perform a circumferential weld joining these two components. The feed-through flange 38 provides strain relief for the microactuator lead wires 50, defines the sealant cavity 48 and provides a retainer for the silicone sealant used to electrically isolate the connection between the microactuator lead wires 50 and microactuator end cap 40.
Sixth (72), fill the fluid cavity 54 with a fluid (which may in one embodiment be sterile water or sterile saline solution) using a vacuum process or other suitable method. In accordance with the vacuum process the microactuator assembly 10 is immersed in a container containing saline or another appropriate fluid. The container is then placed inside a vacuum chamber with one of the two ports 42d oriented facing upwardly (top port) and the other of the two ports 42d oriented facing downwardly (bottom port). When a vacuum is drawn on the vacuum chamber the air inside the microactuator fluid cavity exits from the top port and fluid enters the fluid cavity from the bottom port.
Seventh (74), seal the fluid cavity as follows. Plugs 44 are inserted into the ports 42d and laser welded to hermetically seal them. The laser welding forms a seal before the heat from the welding can appreciably heat the fluid in the fluid cavity 54. A single port 42d and corresponding plug 44 could be used as could more than two ports 42d and corresponding plugs 44 as will now be apparent to those of ordinary skill in the art having the benefit of this disclosure.
Eighth (76), attach the microactuator lead wires 50 to first and second electrical contacts (30, 36) at the outside of the microactuator. This may be performed by a laser weld.
Ninth (78), fill the sealant cavity 48 with silicone sealant material and cure it.
Tenth (80), place the silicone O-ring 20 on the narrow portion 56 of microactuator flange 42 so it is at the location where the outer diameter of the microactuator flange 42 changes from a smaller diameter to a larger diameter (as shown). O-ring 20 is configured to create a moisture-tight seal between the microactuator 10 and the sleeve 12 which holds it in place within the cochlea of the subject. This step may be performed at any time prior to installation.
While steps 1-10 above have been set forth in one order, those of ordinary skill in the art having the benefit of this disclosure will now realize that the steps could be broken down into sub-steps and that the steps and/or sub-steps may be performed in any convenient order in a production environment.
As described above, all surfaces in contact with the body of the subject may be of medical grade titanium except the medical grade silicone which may be used in the sealant cavity and Ethylene Tetrafluoroethylene (ETFE) which is a biocompatible material which may be used for insulating the microactuator lead wires 50.
While embodiments and applications have been shown and described, it would be apparent to those skilled in the art having the benefit of this disclosure that many more modifications than mentioned above are possible without departing from the inventive concepts disclosed herein. The invention, therefore, is not to be restricted except in the spirit of the appended claims.