Background Ultrasonic tactile representation utilizes focused ultrasound to create tactile sensations on the bare skin of a user's hand that is not in contact with a device. This study is a preliminary investigation on whether different ultrasonic haptic rendering methods have an impact on the perceptual threshold. Methods This study conducted experiments with the adaptive step method to obtain participants' perceptual thresholds. We examine (1) whether different parts on the palm of the hand have different perceptual thresholds; (2) whether the perceptual threshold is different when the ultrasonic focus point is stationary and when it moves in different trajectories; (3) whether different moving speeds of the ultrasonic focus point have an influence on the perceptual threshold; and (4) whether the addition of a DC offset to the modulating wave has an impact on the perceptual threshold. Results The results show that the center of the palm is more sensitive to ultrasonic haptics than the fingertip; compared with a fast-moving focus point, the palm is more sensitive to a stationary and slow-moving focus point. When the modulating wave has a DC offset, the palm is sensitive to a much smaller modulation amplitude. Conclusion For the future ultrasonic tactile representation systems, dynamic adjustment of intensity is required to compensate the difference in perceptual thresholds under different rendering methods to achieve more realistic ultrasonic haptics.

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