Vol 17 No 12, December 2008 c  2008 Chin. Phys. Soc. 1674-1056/2008/17(12)/4541-06 Chinese Physics B and IOP Publishing Ltd Electrohydromechanical analysis based on conductivity gradient in microchannel ∗ Jiang Hong-Yuan(姜洪源) a) , Ren Yu-Kun(任玉坤) a) † , Ao Hong-Rui(敖宏瑞) a) , and Antonio Ramos b) a) School of Mechatronics Engineering, Harbin Institute of Technology, Harbin 150001, China b) Department Electronica y Electromagnetismo, Universidad de Sevilla, Avda Reina Mercedes s/n, Sevilla 41012, Spain (Received 3 March 2008; revised manuscript received 4 April 2008) Fluid manipulation is very important in any lab-on-a-chip system. This paper analyses phenomena which use the alternating current (AC) electric field to deflect and manipulate coflowing streams of two different electrolytes (with conductivity gradient) within a microfluidic channel. The basic theory of the electrohydrodynamics and simulation of the analytical model are used to explain the phenomena. The velocity induced for different voltages and conductivity gradient are computed. The results show that when the AC electrical signal is applied on the electrodes, the fluid with higher conductivity occupies a larger region of the channel and the interface of the two fluids is deflected. It will provide some basic reference for people who want to do more study in the control of different fluids with conductivity gradient in a microfluidic channel. Keywords: electrohydrodynamics, conductivity gradient, theoretical analysis, numerical simulation PACC: 4700, 4762 1. Introduction The lab-on-a-chip (LOC) is a new technology in the micro-electromechanical system (MEMS). [1] In the system of LOC, we have much work to study. [2] Dy- namic control of fluids is important in LOC technol- ogy, and MEMS devices are often used for this. [3] How- ever, these devices are often complicated to construct and cannot be integrated into LOC easily. Now, the AC electric field-induced flow can be used to move fluids and analyse or produce mixing. [4−7] These tech- niques include micromechanical methods, direct cur- rent (DC) electro-osmosis, electro-wetting, thermo- capillary pumping, and AC electro-osmosis. [8] Recently, a new phenomenon to control two fluids with conductivity gradient was found. [9] The simply experimental model is shown in Fig.1. The device is made of interdigitated electrodes which occupies the width of the channel, and the two fluids are potassium chloride with conductivity gradient (σ 2 >σ 1 ). The fluids are laminar flow, which is shown in Fig.2(a). Figure 2(b) shows that when the AC electrical sig- nal(voltage) is applied on the electrodes, the fluid with higher conductivity occupies a larger region of the channel and the interface of the two fluids is de- flected. The phenomena are interesting and we try to do some studies about the basic theory and simulation Fig.1. The model of microchannel. Fig.2. The phenomenon of the experiment. * Project supported by the 111 Project (Grant No B07018). † E-mail: xiaoyu2002-2001@163.com http://www.iop.org/journals/cpb http://cpb.iphy.ac.cn