INSTITUTE OF PHYSICS PUBLISHING JOURNAL OF MICROMECHANICS AND MICROENGINEERING J. Micromech. Microeng. 15 (2005) 861–866 doi:10.1088/0960-1317/15/4/026 A valveless micro impedance pump driven by electromagnetic actuation Derek Rinderknecht 1 , Anna Iwaniec Hickerson 1 and Morteza Gharib 2 1 Option of Bioengineering, California Institute of Technology, MC 205-45, 1200 E. California Blvd., Pasadena, CA 91125, USA 2 Hans W Liepmann Professor of Aeronautics and Bioengineering, California Institute of Technology, MC 205-45, 1200 E. California Blvd, Pasadena, CA 91125, USA E-mail: rinderkn@caltech.edu Received 25 October 2004, in final form 21 January 2005 Published 11 March 2005 Online at stacks.iop.org/JMM/15/861 Abstract Over the past two decades, a variety of micropumps have been explored for various applications in microfluidics such as control of pico- and nanoliter flows for drug delivery as well as chemical mixing and analysis. We present the fabrication and preliminary experimental studies of flow performance on the micro impedance pump, a previously unexplored method of pumping fluid on the microscale. The micro impedance pump was constructed of a simple thin-walled tube coupled at either end to glass capillary tubing and actuated electromagnetically. Through the cumulative effects of wave propagation and reflection originating from an excitation located asymmetrically along the length of the elastic tube, a pressure head can be established to drive flow. Flow rates were observed to be reversible and highly dependent on the profile of the excitation. Micro impedance pump flow studies were conducted in open and closed circuit flow configurations. Maximum flow rates of 16 ml min −1 have been achieved under closed loop flow conditions with an elastic tube diameter of 2 mm. Two size scales with channel diameters of 2 mm and 250 µm were also examined in open circuit flow, resulting in flow rates of 191 µl min −1 and 17 µl min −1 , respectively. 1. Introduction Recent interest in microfluidics and microfluidic devices has been predominately driven by the need for biomedical devices on the microscale as well as applications involving chemical control, mixing and analysis, which stem from the push toward lab-on-chip (LOC) methodologies. Micropumping is a necessary component of large integrated systems for sample control and mixing. A micropump requires a compact method of actuation and a mechanism to produce the flow. Commonly micropumps are driven by piezoelectric, electrostatic, electromagnetic, electrohydrodynamic or pneumatic actuators. Mechanisms of pumping vary greatly but can generally be grouped into two categories: displacement pumps and dynamic pumps [1]. These mechanisms can further be categorized in a variety of ways; one of which is the presence of valves. Conventional valves in microfluidics systems are subject to mechanical failure and, in the case of biological fluids, present further risk of malfunction due to clogging or to damage sensitive biomolecules. Current valveless pumping techniques mainly consist of peristaltic [2–5] and reciprocating diaphragm pumps relying on diffusers [6–10]. These systems are often fabricated on a substrate through the use of soft lithography on polymeric materials because they are flexible and allow the form and features of these devices to be created and remain functionally sound. Substrate-based systems, however, occupy much more volume than is actually required by the device. Here, we present a new valveless and substrate-free impedance-based technique for pumping fluid on the microscale. It should be noted that the phenomena resulting in impedance-defined flows has been known for quite some time [11–15]. However, this study is the first of its kind to demonstrate the feasibility of pumping with these phenomena on the microscale, under two different flow circuit configurations, and on two different size scales, 0960-1317/05/040861+06$30.00 © 2005 IOP Publishing Ltd Printed in the UK 861