Effects of anatomical characteristics of stimulus placements on the propagation and perception of distantly-presented bone-conducted ultrasound

Bone-conducted ultrasound (BCU) can be perceived even on distal body parts, such as the neck, chest, and upper limbs, making it promising for novel audio devices. However, the long and complex propagation paths of distantly-presented BCUs and unclear mechanisms of propagation and perception, along with potential anatomical effects, pose challenges. To investigate the effects of stimulus placement on the propagation and perception of distantly-presented BCU, vibration acceleration in the external auditory meatus and hearing thresholds were investigated for BCU stimuli presented at five points on the chest, five points on the back, and seven points on the arm. Results indicated that the back showed the most efficient in vibration propagation due to its simple structure and flat shape. Additionally, despite little changes in anatomical distance and propagation path to the head, elbow flexion significantly increased the vibration acceleration in the upper arm. These findings aid the application of distantly-presented BCU.