Flextensional output actuators for surgically implantable hearing aids

DETAILED DESCRIPTION This invention relates to devices and methods relating to implantable hearing aids for placement within a middle ear or the inner ear.
In particular, the invention includes at least one output actuator comprising a piezo substrate typically having a first and a second substantially planar surfaces, a thickness, and a transverse size.
The substrate changes in thickness when a voltage is applied to the material.
The substrate may be, but is not limited to, a single crystal piezo (SCP).
Also, the substrate may be a single layer or may be a multi-layer composite.
Alternatively, the substrate may be dome-shaped.
Another variation of the invention includes a composite substrate comprising a plurality of substrate components.
The substrate components are aligned such that the composite substrate has a thickness, a first and a second substantially planar surfaces, and a composite transverse size.
The output actuator also has a first end cap mounted on a planar side of the substrate, the cap having an actuating surface.
The first end cap may be fixedly attached to a portion of the substrate in a manner such that a change in the transverse size of the substrate causes the actuating surface of the cap to move in a direction orthogonal to the surface of the substrate.
The output actuator is generally, but not necessarily encased within a biocompatible material.
The output actuator is also in mechanical communication with an auditory component of the middle ear such as an ossicle, or fluid of the inner ear.
The output actuator may also have a second end cap mounted on a planar side of the substrate opposite the first end cap.
This second end cap also has an actuating surface.
The second end cap may be fixedly attached to a portion of the substrate in a manner such that a change in the transverse size of the substrate causes the actuating surface of the cap to move in a direction orthogonal to the surface of the substrate.
The implantable hearing aid may also comprise output actuators which are stacked in a series