Local Control of Eckart Streaming Near Focus of Concave Ultrasound Source with Two Coaxially Arranged Transducers

概要

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The control of acoustic streaming is expected to provide a promising method in microfluidic technologies. However, there are few research reports on such acoustic systems to control streaming velocity. To confirm whether velocity is affected by sound field distribution, we carried out some experiments using a focusing ultrasound transducer that consists of two coaxially arranged concentric piezoelectric elements: i.e., one is an inner disc element and the other an outer ring element. Both the elements can be driven by electric signals at the same frequency of 3.45 MHz but different phase angles. The spheroidal beam equation (SBE) for describing finite-amplitude ultrasound beams in a viscous fluid is successfully used to predict focused sound pressure distribution. The external driving force acting on the fluid is readily calculated on the basis of sound pressure, and then streaming velocity can be theoretically predicted using the continuity equation and Navier-Stokes equation with the term of force. The profiles of speed along and across the beam axis are measured by laser Doppler velocimetry. It has been confirmed that experimental data and theoretical predictions are in good agreement. The feasibility of controlling streaming is discussed by changing the phase difference between the two signals.
Published by the Japan Society of Applied Physics through the Institute of Pure and Applied Physicsの論文
2006-05-30