The Design of Mid-Air Ultrasonic Haptic Interfaces Based on the Perception of Lines

Mid-air ultrasonic feedback is a new form of haptic stimulation supporting mid-air, touch-free user interfaces. Functional implementation of ultrasonic haptic (UH) interfaces depend upon the ability to accurately distinguish between the intensity, shape, orientation, and movement of a signal. This user study (N = 15) investigates the ability to non-visually perceive two ultrasonic lines with varying lengths (3, 5, and 7 cm) and orientations (vertical and horizontal) using the palm of the hand. Key results showed that: (1) the orientation of the lines had no effect on a user’s accuracy when determining their relative lengths, (2) line length distinction significantly improved when the length difference was at least 4 cm, and (3) a clear learning curve was evident when evaluating a new user’s ability to perceive ultrasonic signals. The capabilities of UH technology identified and discussed within this study will help engineer user-friendly and functional mid-air haptic interfaces for future applications.