Effects of laser light and AC signals on opto-electrohydrodynamic flow with twin microvortices: I. non-uniform AC electric fields

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.

Influence of laser power and beam path under nonuniform AC electric fields on 3D microvortex flow

“…Some optical tweezers have been combined with other measurement techniques for obtaining chemical information (e.g., Raman spectroscopy), applying forces and measuring displacement (e.g., force spectroscopy), visualizing the motion of particles and fluids (e.g., epifluorescence or confocal microscopy) [6,13,[20][21][22][23]. With Raman microscopy, optical tweezers have been used to measure the physical and chemical properties of trapped particles.…”

“…Epifluorescence microscopy provides a clear visualization of tracer particles so that precise control of particle manipulation is achieved. Thus, velocity fields are accurately calculated through the micronresolution particle image velocimetry (μPIV) technique [23,24]. Besides these measurement combinations, external forces from electric fields or plasmons are added into an optical trapping system.…”

“…The OEHD flow, termed twin opposing microvortex (TOMV) flow, mainly combines electrical forces from non-uniform electric fields with optical forces from a moderately focused laser beam. The TOMV flow is generated from a simple microfluidic device (also termed a TOMV device) consisting of a pair of coplanar indium tin oxide (ITO) electrodes (figure 1) [14,23]. This opto-EHD flow generation relies on laser light (e.g., power and beam path) and electric fields (e.g., electrode arrangement and shape as well as AC voltage and frequency) [14,23,[29][30][31].…”

“…The TOMV flow is generated from a simple microfluidic device (also termed a TOMV device) consisting of a pair of coplanar indium tin oxide (ITO) electrodes (figure 1) [14,23]. This opto-EHD flow generation relies on laser light (e.g., power and beam path) and electric fields (e.g., electrode arrangement and shape as well as AC voltage and frequency) [14,23,[29][30][31]. Microvortex flows similar to four-roll-mill flows have been created in a device in which a pair of coplanar metal electrodes creates non-uniform AC electric fields and a highly focused laser beam passes through the region between the electrodes in the direction perpendicular to the electrodes [29,32,33].…”

“…Unfortunately, most of the work in this area lacks quantitative analysis of fluid motion since their motion is a 3D and strong microvortex flow, and great attention has been paid to only particle manipulation and patterning. Recently, however, the effect of AC electric fields on OEHD fluid motions has been quantitatively investigated to illuminate the details of the OEHD flows [23]. Nevertheless, the effect of laser light on these flows has not been thoroughly studied.…”