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[(a)–(c)] Sample fabrication steps (features not to scale). (a) Permalloy disks and cavities are patterned on silicon surface. (b) Walls of microchannel are patterned from SPR-220 photoresist. (c) PDMS sealed to the photoresist contains fluid from above, and ports act as fluid reservoirs. (d) Magnetic fields are applied to micropump using five electromagnets while observations are made with optical microscope. (e) Real image of micropump with Py disks, cavities, and channel walls along with coordinate axes.
Calculated magnetic energy profiles for diameter sphere from diameter, 60 nm thick Py disk [(a)–(c)] and cavity [(d)–(f)]. Real images of trapped sphere are included as insets at top right of each figure. Calculations based on micromagnetic structures given by OOMMF simulations. Magnetic susceptibility of sphere is assumed as 0.5. (g) Scanning electron microscope image of submicron (500 nm diameter) magnetic particles (Spherotech CM-05-10) followed by three optical microscope images of a single particle (within dotted circle) being manipulated around the circumference of a magnetic disk by the rotating external fields and .
(a) Schematic of microrotor on lower section of channel and flow fields (dashed lines). The rectangular box indicates region where speed of the tracer particles was measured. (b) Illustrates cavity and microrotor at top of channel reverses flow for same direction of microsphere rotation as in (a). (c) Speed of tracer particles as a function of frequency of the applied rotating magnetic field for a single rotor and (d) number of rotating spheres in a different pumping channel.
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