Tactile Perception Characteristics of Lips Stimulated by Airborne Ultrasound

Tactile presentation to faces is an unexplored field of study with significant potential. Considering the hygiene and the physical burden on users, non-contact tactile stimulation to faces is an effective method. Even though lips have a particularly high tactile sensitivity in the face, the tactile perception characteristics of lips in non-contact tactile presentation have hardly been investigated. This study is the first to investigate the tactile perception characteristics of lips in airborne ultrasound tactile presentation, which is a non-contact haptic technology that generates a force on a remote object by focusing ultrasound waves. From acoustic simulations and two subject experiments, it was confirmed that the lowest tactile thresholds of the lips were achieved at the valley-shaped area of the lips in terms of location, lateral modulation with periodic circular trajectories (LM
C
) in terms of modulation type, and 40 Hz in terms of modulation frequency. Furthermore, the tactile detection threshold of the lips could be lower by 3 dB than that of the palms with an appropriate presentation method. Although there are some limitations in the current devices, non-contact tactile presentation to lips using airborne ultrasound is potentially applicable to various fields, such as notifications, alerting, and virtual reality.