Pulsed Schlieren Imaging of Ultrasonic Haptics and Levitation using Phased Arrays
This work addresses the need for better visualization tools in ultrasonic haptics and levitation research, though it is incremental as it builds on existing schlieren methods.
The researchers tackled the problem of visualizing ultrasonic acoustic fields used for haptic effects and particle levitation by applying both traditional and background-oriented schlieren imaging techniques, achieving the first demonstration of background-oriented schlieren for ultrasonic fields in air with improved algorithms and synchronized LED pulsing.
Ultrasonic acoustic fields have recently been used to generate haptic effects on the human skin as well as to levitate small sub-wavelength size particles. Schlieren imaging and background-oriented schlieren techniques can be used for acoustic wave pattern and beam shape visualization. These techniques exploit variations in the refractive index of a propagation medium by applying refractive optics or cross-correlation algorithms of photographs of illuminated background patterns. Here both background-oriented and traditional schlieren systems are used to visualize the regions of the acoustic power involved in creating dynamic haptic sensations and dynamic levitation traps. We demonstrate for the first time the application of back-ground-oriented schlieren for imaging ultrasonic fields in air. We detail our imaging apparatus and present improved algorithms used to visualize these phenomena that we have produced using multiple phased arrays. Moreover, to improve imaging, we leverage an electronically controlled, high-output LED which is pulsed in synchrony with the ultrasonic carrier frequency.