Propagation characteristics of amplitude-modulated bone-conducted ultrasound presented to the neck, trunk and arms

Bone-conducted ultrasound (BCU) is perceived even by the profoundly hearing impaired and a novel hearing aid has been developed. In the BCU hearing aid, the ultrasonic carrier is amplitude-modulated by speech signals and presented to the mastoid process of the temporal bone by a vibrator. However, BCU presented to parts of the body distant from the head can be perceived. In this study, vibration at the external auditory meatus was measured when amplitude-modulated BCU was presented to distal parts of the body. The results showed spectrum peaks corresponding to the carrier frequency (30 kHz) and the modulation frequency. The peak level of the carrier frequency tended to decrease depending on the distance between the external auditory meatus and the stimulation part basically. On the other hand, the peak level of the modulation frequency did not change with the distance between the external auditory meatus and the stimulation part, whereas the effect of modulation frequency was significant.