Adjusting single-axis acoustic levitators in real time using rainbow schlieren deflectometry.

Acoustic levitation uses focused high-intensity airborne ultrasound to hold particles in mid-air. It is becoming an important tool for experiments in spectrometry, lab-on-a-droplet, and display technologies. Nowadays, arrays of multiple small transducers can be used to build acoustic levitators; however, their performance depends on the optimal alignment. This work describes a simple method capable of visualizing a 2D projection of the acoustic field in real time using rainbow schlieren deflectometry. Good agreement was found between the images obtained with this technique and simulations of the acoustic pressure. It was also found that the maximum amplitudes of the field were obtained with the levitator aligned so that the power consumption was minimum, showing another simple and affordable way to adjust the levitators. As a result of the alignment optimization, it was possible for the first time to levitate steel and mercury in a levitator constructed with off-the-shelf components. The schlieren technique was applied to the TinyLev acoustic levitation system, but it can be applied to visualize the acoustic potential produced by different types of levitation systems.