The development and analysis of the performance of microfluidic components for lab-on-a-chip devices are becoming increasingly important because microfluidic applications are continuing to expand in the fields of biology, nanotechnology, and manufacturing. Therefore, the characterization of fluid behavior at the scales of microand nanometer levels is essential. A variety of microfluidic velocimetry techniques like micron-resolution Particle Image Velocimetry (lPIV), particle-tracking velocimetry (PTV), and others have been developed to characterize such microfluidic systems with spatial resolutions on the order of micrometers or less. This article discusses the fundamentals of established velocimetry techniques as well as the technical applications found in literature.

We demonstrate a rapid generation of twin opposing microvortices (TOMVs) induced by non-uniform alternating current (AC) electric fields together with a laser beam on a patterned pair of indium tin oxide (ITO) electrodes. A fast and strong jet flow region between twin microvortices is also generated. Its pattern and direction, such as whether it is symmetric or asymmetric, are controlled mainly by the location of a single laser spot relative to the ITO electrodes. With two laser beams, two separate flows are superposed to give a new one. In situ generation and control of the TOMV flow are tested in suspensions of fluorescent polystyrene particles, as well as in milk emulsions. This technique has great potential for dynamically manipulating micro-fluid flows, functioning as a micro-pump or mixer.

No abstract

This paper describes both qualitative and quantitative analysis of rapid microvortex flow generation and manipulation induced by opto-electrohydrodynamic technique. A flow named twin opposing microvortex (TOMV) is generated by infrared laser light under non-uniform alternating current (AC) electric fields. For the AC electric fields, frequency ranges from 3 kHz up to 2 MHz while the voltage is changed up to 10 Vp-p (peak-to-peak voltage). Simultaneously, the laser shines either of a pair of electrodes with a power of 0.5 W. Micron-resolution particle image velocimetry technique has been used to construct the velocity fields of the TOMV flow. The strength of the TOMV flow can be tuned by adjusting the AC voltage and frequency. The maximum measurable in-plane velocity of 54.7 µm s−1 outside electrode regions can be achieved with an AC signal of 9 Vp-p and 107 kHz and a laser beam of 0.5 W. This is achieved with indium tin oxide electrodes located on the top surface of a microchamber, in which the electrodes are 16 µm wide and 300 µm long with a spacing of 73 µm between them. This three-dimensional flow generation can be used for in situ micropump and mixing.