Physical Analysis and Derivation of Design Constants for the Operation of an Ultrasonic Focused Hearing Aid

In this paper, we investigated the potential of a focused ultrasound receiver that can overcome the high-frequency sensitivity limitations of conventional electromagnetic hearing aid receivers and the acoustic distortion caused by multiple reflections and resonances in the ear canal by focusing and delivering an ultrasound beam directly to the eardrum. Based on the structure of a focused ultrasound beam incident on the eardrum in the confined environment of the ear canal, we presented the acoustic and physical structure and performed mathematical analysis. Based on these results, we calculated the constants required for the experimental design. A multi-layer PZT structure was considered as the radiator of the focused ultrasound receiver inserted into the ear canal. Through frequency-dependent acoustic analysis, we designed a compact radiator that can radiate the focused parametric acoustic signal to the center of the eardrum. For the proposed focused ultrasound receiver structure comprised of the multi-layer PZT radiator, transient response and total harmonic distortion were measured using a parametric SR-AM modulator, a laser vibrometer, and a tubular microphone. Experimental results show that the proposed ultrasonic focused receiver has improved performance in transient response compared to an electromagnetic receiver.