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14 February 2011 Bidirectional magnetic microactuators for uTAS
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We present the design, fabrication and characterization of a novel bidirectional magnetic microactuator. The actuator has a planar structure and is easily fabricated using processes based on laser micromachining and soft lithography, allowing it to be readily integrated into microfluidic, microelectromechanical systems (MEMS) and lab-on-a-chip (LOC) designs. The new microactuator is a thin magnetic membrane with a central magnet feature. The membrane and magnet are both composed of a magnetic nanocomposite polymer (M-NCP) material that is fabricated by embedding magnetic powder in a polydimethysiloxane (PDMS) polymer matrix. The magnetic powder (MQP-12-5) has the chemical composition of (Nd0.7Ce0.3)10.5Fe83.9B5.6, and contains grains that are 5-6 microns in size. The powder is uniformly dispersed at a weight percentage of 75 wt-% in the PDMS matrix, and micropatterned using soft lithography micromolding to realize magnetic microstructures, which sit on a thinner magnetic PDMS membrane of the same material. The molds are fabricated by laser-etching into Poly (methyl methacrylate) (PMMA) using a Universal Laser System's VersaLASER© laser ablation system. The PDMS-based M-NCP is then poured and spun over the mold patterns, producing a thin polymer membrane to which the polymer micromagnets are attached, forming a one-piece actuator. The M-NCP is initially un-magnetized, but is then magnetized by placing it in a 2.5T magnetic field to produce permanent bidirectional magnetization that is polarized in the specified direction. To characterize the bidirectional actuators, a uniform magnetic field is established via a Helmholtz coil pair, and is characterized by applying varying currents. The magnetic field (and thus the actuator deflection) is controlled by regulating the current in the Helmholtz pair. Using this apparatus, deflection versus field characteristics are obtained, with maximum deflections varying as a function of actuator dimensions and the applied magnetic field. Permanent rare earth magnets are used to produce supplemental fields for higher magnetic fields and higher deflections. Deflections of 100 micrometers and more are observed for 3 to 8 mm square membranes with central magnetic features ranging from 0.8 to 3.6 mm squares, in magnetic fields ranging from 52 to 6.2 mT. In addition, smaller membranes (1 mm and 2 mm with 0.4 mm and 0.6 mm central magnets, respectively) also deflect 20 and 50 microns, respectively, under 72 mT fields.
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Daniel D. Hilbich, Ajit Khosla, Bonnie L. Gray, and Lesley Shannon "Bidirectional magnetic microactuators for uTAS", Proc. SPIE 7929, Microfluidics, BioMEMS, and Medical Microsystems IX, 79290H (14 February 2011);

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