Preliminary assessment of remote photoelectric excitation of an actuator for a hearing implant.

Sound modulated infrared (IR) light, as an alternative signal (and energy) transmission method, was evaluated for remote powering of a hearing implant via an implanted photodiode receiver. One human cadaveric temporal bone was used to test this concept by locating an IR source (LED) in the ear canal 4 mm away from the eardrum and a photodiode in the middle ear cavity. The photodiode output was directly used to drive a piezo-ceramic disc actuator which was located externally for facilitating the test. The displacement frequency response of the actuator was measured by a laser vibrometer. It was found that, at a LED current of 8.6 mA, the actuator displacement was about 22.4 nm, equivalent to a stapes displacement from about 91 dB sound-pressure-level (SPL) stimulation at the eardrum. The IR light transmittance through the eardrum (compared to through an air path) was about 67%. The LED optical power was 0.77 mW (its maximal irradiance was about 3.95 mW/cm2) which is a safe to the human body. Current consumption can be reduced by a factor of 3-5 by using a more efficient LED and photodiode.