Sampling Strategy for Ultrasonic Mid-Air Haptics

Mid-air tactile stimulation using ultrasonics has been used in a variety of human computer interfaces in the form of prototypes as well as products. When generating these tactile patterns with mid-air tactile ultrasonic displays, the common approach has been to sample the patterns using the hardware update rate capabilities to their full extent. In the current study we show that the hardware update rate can impact perception, but unexpectedly we find that higher update rates do not improve pattern perception. In a first user study, we highlight the effect of update rate on the perceived strength of a pattern, especially for patterns rendered at slow rate of less than 10 Hz. In a second user study, we identify the evolution of the optimal update rate according to variations in pattern size. Our main results show that update rate should be designated as additional parameter for tactile patterns. We also discuss how the relationships we defined in the current study can be implemented into designer tools so that designers remain oblivious to this additional complexity.