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

Abstract

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.

Gold-implanted plasmonic quartz plate as a launch pad for laser-driven photoacoustic microfluidic pumps

“…This implication clearly contradicts our observation that the fluid remains motionless there despite it being in direct contact with the vibrating quartz surface. The same argument of single pulse jet formation can be applied to acoustophoresis, photophoresis, and other phenomena by which tracing microspheres should be pushed forward first and then will drag fluid along (6, 7, 32–36). Since neither the microspheres nor the fluid near the windows exhibit any obvious movement, those theories do not hold true.…”

“…This pump is a semitransparent plasmonic quartz window; it is based on our recently discovered principle of photoacoustic laser streaming: an ultrasound wave generated by a resonant laser pulse drives fluid through acoustic streaming (5–9). Because the whole surface of the quartz window is covered with a plasmonic layer, an ultrasound wave can be generated from any point on the window, making it a micropump launch pad.…”

“…Because the whole surface of the quartz window is covered with a plasmonic layer, an ultrasound wave can be generated from any point on the window, making it a micropump launch pad. This photoacoustic window overcomes major shortcomings of previous photoacoustic cavities which had to be created individually by the same laser beam (5); it has allowed us to verify the underlying pumping mechanism and to explore the interaction of fluids with laser and ultrasound in an unprecedented time–space regime (5–11).…”

Introduction of measurement techniques in ultrasonic electronics: Basic principles and recent trends

“…Force sensors [279][280][281][282][283][284][285] Object detection [286][287][288] Acceleration [289][290][291][292][293] Gyro sensors [294][295][296][297][298][299] Bio sensors 234,256,257,[300][301][302] Gas=chemical sensors 186,233,240,243,[246][247][248]250,251,253,254,261,303,304) Application of piezoelectric thin films 214,215,218,305) Microfluidic control 306) Continued on next page:…”

“…For example, piezoelectric thin films are used for microspectroscopy with high precision and as filters of very high frequencies. 214,215,218,305) Piezoelectric transducers are also used for microfluidic control, 306) in which acoustic streaming in a small area can be controlled by acoustic transducers.…”