Evaluation of Propagation Characteristics of Bone- conducted Ultrasound Presented to the Neck, Trunk and Arms.
* Presenting author
High-frequency sound above 20 kHz can be heard clearly via bone conduction (Bone-conducted ultrasound: BCU). Additionally, BCU is perceived even when presented to body parts distant from the head, like neck, trunk, and arm, and is expected to be applied for novel devices that transmit sound selectively to persons who touch a vibrator by the arm or so. First, to elucidate propagation characteristics of such distantly-presented BCU, vibration in the ear canal was measured using an acceleration sensor when a 30-kHz tone was presented to the neck, arm, and trunk. A prominent spectrum peak corresponding to the stimulus frequency was obtained. Further, the vibration tended to attenuate when the stimulus points were moved away from the head, whereas some exceptions existed.Second, vibrations of the upper limb were measured at 9 surface points lined up straight from the forearm to shoulder when BCU was presented to nearby the wrist. The vibration tended to attenuate depending on the distance from the vibrator basically, however, some points with swollen upper-arm muscles showed larger amplitudes.These results suggest that efficiency of the propagation varies depending on the stimulus points, and the upper-arm muscles are suitable also for stimulus location of BCU.