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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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