Evaluation of the Performance of a Novel Piezo-Electric Actuator for Active Subcutaneous Bone Conduction Hearing Aid

Objectives: Evaluation of the transfer function efficiency of a newly-developed piezo-electric actuator for active subcutaneous bone conduction hearing aid, based on promontory and skull surface 3D motion.

Methods: Four Thiel embalmed whole head cadaver specimens were measured. A piezo-electric transduction actuator (PZTA), is implanted on three positions: 1) superior to the external auditory canal as close to the cochlea as possible, 2) 7cm, 3) 5cm posterior of the tragus in the temporal line. For each stimulation location two types of measurements were performed: 1) motions of the cochlear promontory were measured on the ipsilateral and contralateral side, at a single point using a 3-dimensional laser Doppler vibrometer (3D LDV) system, and measurements were repeated after mastoidectomy on the ipsilateral side; 2) three-dimensional motions of the bone surrounding the PZTA (70-90 points, covering an area of approximately 8×8 cm²) using the 3D LDV system.

Results: Stimulation at positions 1 and 2 induces higher promontory motion relative to position 3, with an average improvement of about 1 - 3 dB for 0.6-3 kHz and 5-7 dB at higher frequencies. The mastoidectomy affects negatively mostly the high frequencies. Surface wave patterns of the skull surface are qualitatively comparable for both the magnitude and phase of motion at low and mid frequencies. However, there are differences at high frequencies.

Conclusion: The sound transfer function efficacy of a novel subcutaneous bone conduction device have been quantified. The influence of stimulation position and the state of the mastoid have been analyzed.