For smooth touch-interfaces like smartphone displays, an illusion of texture can be created by varying the force of the friction exerted on the user's finger. Most of today's texture-generating systems depend on tiny motors placed under the display surface to create a diffuse overall vibration. Researchers at List came up with an improved system that can provide a much more accurate perception of texture, letting users feel a different texture with each finger. The research won Best Paper Award at IEEE World Haptics 2017.

The researchers decided that, rather than increasing the friction coefficient over the entire surface, they would reduce the coefficient using ultrasound to generate a sort of "air cushion" around the finger. "What is new is that we were able to generate the air cushion very locally, providing a much more precise sensation of touch." Piezoelectric switches were placed under the display's surface, where they vibrate at select frequencies so as not to propagate the vibrations over the entire surface.

The system, patented by List, creates an illusion of texture on surfaces that can be touched by several fingers at the same time. Ultimately, transparent piezoelectric materials could be deposited directly on surfaces using deposition techniques developed by Leti.