Acoustic streaming generated by ultrasonic transducers, measurements by means of 32 MHz Doppler

An approximate solution for the streaming velocity generated by flat and weakly focused transducers was derived by directly solving the Dirichlet boundary conditions for the Poisson equation. The theoretical calculations were verified using a purpose-designed 32 MHz pulsed Doppler unit. The applied average acoustic power was changed from l µW to 6 mW. The experiments were done on 4 mm diameter flat and focused transducers. The streaming velocity was measured along the ultrasonic beam from 0 to 20 mm. Streaming was induced in a solution of water and com starch. The experimental results showed that for a given acoustic power the streaming velocity was independent of the starch density in water changed from 0.3 grams to 40 grams of starch in 1 litre of distilled water. For applied acoustic powers, the streaming velocity changed Iinearly from 0.2 to 40 mm/s. Both, the theoretical solutions for pIane and focused waves, and the experimental results were in good agreement.