In a demonstrator haptic smartphone display dubbed the Hap2Phone, the company uses a series of thin-film piezoelectric actuators lined up along two parallel edges of the display to modulate the friction coefficient of the glass’ surface by activating precise vibrational modes in the material, creating distinct variations in touch sensations.
“The friction of flat screens can be globally modulated by the application of ultrasonic vibration with varying amplitude to create the illusion of a texture” reads an academic paper co-authored by the company’s CEO Cédrick Chappaz. “We can describe this as ultrasonic lubrication, the discontinued contact due to the vibrational modes leads to a friction reduction” Chappaz explained eeNews Europe when interviewed about the technology.
According to the company’s CEO, by modulating the friction coefficient at various touch-points, these haptics can deliver touch sensations ranging from intense to soft clicks, springs, buttons or gliders, even giving a feel for elasticity and all kinds of high-to-low elevation points and textures. It is the changes in friction detected by the nerve endings in the user’s fingertips that are interpreted by the brain as different textures.
Of course, different materials behave differently when excited by the piezo actuators at tens of kilohertz, and Hap2U has developed the hardware and software know-how to be able to simulate and anticipate both the vibrational and acoustical behaviours of a full mechanical stack. The company’s engineers can then design the optimum piezoelectric layout to get the best mechanical coupling for a given geometry.