Mid-Air Thermo-Tactile Feedback using Ultrasound Haptic Display

This paper presents a mid-air thermo-tactile feedback system using an ultrasound haptic display. We design a proof-of-concept thermo-tactile feedback system with an open-top chamber, heat modules, and an ultrasound display. Our approach is to provide heated airflow along the path to the focused pressure point created from the ultrasound display to generate thermal and vibrotactile cues in mid-air simultaneously. We confirm that our system can generate the thermo-tactile stimuli up to 54.2°C with 3.43 mN when the ultrasonic haptic signal was set to 100 Hz with a 12 mm radius of the cue size. We also confirm that our system can provide a stable temperature (mean error=0.25%). We measure the warm detection threshold (WDT) and the heat-pain detection threshold (HPDT). The results show that the mean WDT was 32.8°C (SD=1.12), and the mean HPDT was 44.6°C (SD=1.64), which are consistent with the contact-based thermal thresholds. We also found that the accuracy of haptic pattern identification is similar for non-thermal (98.1%) and thermal conditions (97.2%), showing a non-significant effect of high temperature. We finally confirmed that thermo-tactile feedback further enhances the user experiences.