Calibration of acoustic trapping forces by fluid drag forces

A transverse acoustic trapping was experimentally demonstrated in a similar manner to optical tweezers. With its relatively simple scheme and low intensity, a single beam ultrasound was used to laterally manipulate lipid droplets underneath a thin mylar membrane. The droplets were directed towards the beam focus, within the range of hundreds of micrometers. Acoustic trapping forces acted on the droplets were also calibrated to viscous drag forces in a fluid flow, and its magnitudes were found in the order of tens of nanonewtons. This device, hence, may be capable of quantifying mechanical properties of large biological particles.