Researchers at Delft University & Aix-Marseille University studied the use of ultrasound on glass to create a realistic illusion, where volunteers felt as if they were pressing a real mechanical button. This could potentially pave the way for higher quality haptic feedback systems in touchscreens.

The system used lights to optically track the movement of an approaching finger, then once connected, a piezo let out an ultrasound burst at 28.85kHz creating the illusion.

https://royalsocietypublishing.org/doi/10.1098/rsif.2022.0718