Expanding Softness and Hardness Sensations in Mid-Air Ultrasonic Haptic Interfaces Combining Amplitude and Spatiotemporal Modulation

Abstract

Ultrasonic mid-air haptic interfaces have limited ability to simulate compliance and stiffness. In our previous research, we introduced spatiotemporal modulation (STM) of the ultrasonic focus to simulate the contact process between a finger and a virtual surface, extending the perceived softness range by varying the rate of contact area change and focal point speed. In this study, we combine STM with amplitude modulation (AM) to further explore the effects of the two aforementioned factors, along with output power variation, on perceived softness during the simulated contact between a palm and a virtual small sphere. Psychophysical experiments revealed that haptic stimuli with a higher contact area change rate, faster focal point speed, and lower output power amplitude were perceived as softer. By adjusting these parameters, we achieved a wide perceptual range, simulating objects perceived as up to 5.3 times softer and 4 times harder than the baseline modulus. Our findings contribute to advancing soft object simulation and enhance the rendering capabilities of ultrasonic haptic displays for VR and AR applications.

Keywords

• Mid-air haptics
• ultrasonic haptic displays
• softness perception
• softness rendering
• human-computer interaction