Here, we use a calibrated high gradient laser trap to directly measure the total time-averaged 3D force on a dielectric silica parti- cle in the regime of an ultrasonic standing wave. Acoustic radiation and acoustic streaming apply forces on an optically trapped particle within an acoustofluidic device. From measuring the induced displacements from the laser trap center in three dimen- sions the acoustic forces (0.2-50pN) can be calculated in dependence of the particle position and excitation frequency. Thus, the real pressure distributions within acoustofluidic devices can be mapped out. The three dimensional direct measurement, as pre- sented here, opens up the possibility to quantify so far inaccessible small scale phenomena such as the effects of: a.) local and global acoustic streaming, and b.) boundaries or close-by objects.
Lamprecht, A., Lakämper, S., Schaap, I. A. T., & Dual, J. (2015). Measurement of 3D-forces on a micro particle in acoustofluidic devices using an optical trap. In Physics Procedia (Vol. 70, pp. 89–93). Elsevier. https://doi.org/10.1016/j.phpro.2015.08.049