Laser Doppler Vibrometry and FEM Simulations of Ultrasonic Mid-Air Haptics

Ultrasonic phased arrays are used to deliver midair haptic feedback in both research and commercial applications and strongly rely on the Acoustic Radiation Pressure (ARP) that arises at the air-skin interface. The ARP generated by ultrasonic mid-air haptic feedback technology today is orders of magnitude lower than most forces involved in traditional contact haptic devices, however can be leveraged to produce a rich plethora of perceptible tactile sensations. Therefore, how a viscoelastic structure such as the human skin responds to the ARP is an important research topic that merits further investigation. To that end, we detail herein a methodology to investigate the mechanical response of viscoelastic materials to this type of stimulation. Our research is divided into a laser doppler vibrometry experimental study and a Finite Element Model (FEM) computer simulation of a skin-mimicking phantom slab. Through comparison of experimental and simulation results under different ultrasound stimulation schemes we observe good qualitative and quantitative agreement, thus successfully advancing towards the development of a numerical tool for optimising ultrasonic mid-air haptic stimuli.