Flow state of two parallel fluid streams within micro-channel. (a) Schematic diagram of microchannel and parallel fluid streams. The channel has two inlets and two outlets for two streams of fluids. The fluids exhibit laminar flow and a fully developed region is present over most of the channel, except regions near the inlets and outlets. An ultrasonic standing wave is set up across the channel width in the fully developed region. (b) Interface location between two fully developed parallel streams. When the two fluids have the same flow rate and viscosity, the interface lies at the center of the channel; the deviation is zero. When the flow rate or viscosity is changed, the fluid interface deviates from the center. For a given ratio of viscosities, the interface location can be controlled by the relative flow rate.
Acoustic field for different salt (NaCl) concentration. (a) Distribution of the acoustic radiation force for different NaCl concentrations at the cross-section 2000 μm downstream from the inlets. The calculated acoustic radiation force is normalized by the maximum magnitude in each case. DI water with input flow rate of 0.6 μl/min at the upper inlet and 2 mol/l NaCl solution with input flow rate of 2.4 μl/min at the lower inlet. Diffusion coefficient is D = 0.2 e-9 m2/s. The corresponding density, viscosity, and sound speed at different NaCl concentration are calculated according to Refs. 24 and 25. (b) Simulation results of the resonance frequencies for different NaCl concentrations at the cross-section 2000 μm downstream when different flow rate ratio were used. Total volume flow rate within the channel was set to be 3 μl/min. (c) Interface location for various flow rates and concentrations of NaCl. The interface is the location within the diffusion layer which has the mean NaCl concentration of the two fluids.
Sketch of the separation process of two species. Two different species were carried into the micro-channel through upper inlet. (a) Without acoustic field, all species (denoted as large and small dots) flow within the original suspension. (b) When the acoustic field is applied, the larger species that experienced a larger acoustic radiation force move faster than the smaller one towards the node. At the end of the channel, the larger species crossed the fluid interface into the destination fluid, while the smaller species did not cross the interface and remained within the original medium.
Acoustic micro-channel system. (a) Exploded view showing the various components in the system. (b) Top and front views of the microfluidic channel with piezoelectric transducer at the bottom.
Particle distributions in bi-fluid flow. (a) Captured image under UV light when no acoustic field applied, particles flow within its original solvent (DI water colored red). (b) Captured image under UV light when the acoustic field applied, particles are transported across the fluid interface. (c) Particle distribution and fluorescent density distribution along a cross section (2200 μm) downstream. Sample size: 100 (acoustic field applied) and 120 (no acoustic field applied).
Normalized color density and particle distribution for different NaCl concentrations in the destination fluid while the source fluid is kept as DI water. (a) 0.154 mol/l NaCl solution. (b) 0.615 mol/l NaCl solution. (c) 1.23 mol/l salt solution. (d) 3.075 mol/l salt solution.
Comparison of the diffusion layer and pressure node between experimental and simulation results. (a) The region of diffusion observed in experiments, given by the region where the dye intensity falls between 0.2 and 0.8, compares favorably with the numerical prediction for different concentration of NaCl. (b) The mean locations of the particles together with the minimum and maximum locations (shown in blue) are in good agreement with the location of the pressure node (predicted by numerical model and shown in red) for different concentration of NaCl.
Captured images of the polystyrene beads as they flow through the micro-channel. Upper fluid stream is a suspension of 3 μm and 10 μm beads in DI water with a flow rate of 50 μL/h. Lower fluid stream is clean DI water with a flow rate of 200 μL/h. (a) No ultrasound field was applied and all beads flow within the original suspension. (b) Ultrasound field applied at 20 Vpp and the larger beads are separated and transported to the lower fluid stream.
Relative separation efficiency of 10 and 3 μm polystyrene beads as well as C. parvum and G. lamblia.
Captured image of separation of G. lamblia and C. parvum in a microchannel under an ultrasound standing wave. The flow rate of the parasite solution was set to 50 μL/h and the flow rate of the parallel PBS buffer to 200 μL/h. The PZT transducer was driven by a sinusoidal waveform of 20 Vpp. The mobile G. lamblia were separated from C. parvum and re-diluted into the lower PBS buffer stream, demonstrating the separation and re-dilution process using the acoustic field.
Viability of parasites after being exposed to acoustic field at 20 Vpp at different exposure times.
Statistic results for water/water case.a
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