Demodulation Characteristics in Propagation Process of Amplitude-modulated Bone-conducted Ultrasound Presented to the Neck, Trunk and Arms
* Presenting author
Bone-conducted ultrasound (BCU) is can be heard clearly and can transmit speech information using amplitude-modulation (AM). Additionally, BCU is perceived even when presented to body parts distant from the head, like the neck, trunk, and arm. It is expected that demodulated low-frequency components appears by the nonlinearity existing in the human body when amplitude-modulated BCU (AM-BCU) were presented to such distal locations. First, to elucidate demodulation characteristics in the propagation process of such distantly-presented BCU, vibration at the external auditory meatus was measured when AM-BCU was presented to the neck, shoulder, upper limb, breastbone and backbone. The result showed spectrum peaks corresponding to the carrier frequency (30 kHz) and the modulation frequency. The level of the peak of the carrier tended to decrease depending on the distance between stimulation and measurement points, however, the peak of the modulator did not change by the distance. Second, vibrations around the cartilages of the auricle, tragus and articulations, that have strong nonlinearity, were measured. The demodulation components were larger for the auricle and tragus than the peripheral articulations. These result suggests the demodulation mainly occurs in the vicinity of the ear even when BCU is presented to distal body parts.