Research In Magnetohydrodynamic Based Microfluidics

With the advantages of miniaturization and integration, the planar electromagnets were designed in MHD micropump to improve the performance of conventional magnetohydrodynamic (MHD) micropump used in microfluidic systems. This paper present a novel MHD flow model with planar electromagnets, demonstrates the basic theoretical analysis of an AC MHD micropump and optimize the structure of MHD micropump by finite element analysis. Furthermore, the fabricated novel MHD micropump was integrated with impedance sensor, and realize the functions of pumping and impedance detection of biological samples. The influence of aspect ratio of channel, applied voltage on electrode, distribution of electric field and magnetic field, different coil and magnetic yoke materials, Joule heating, electroosmosis and slip condition on walls were investigated by software of COMSOL Multiphysics. By coupling of AC/DC module, laminar flow module and Joule heating flow in COMSOL Multiphysics, the model was built and computed. The results show that microchannel with aspect ratio of 1:1 was used in our simulation as the flow velocity decreased with the aspect ratio decreased. Flow velocity of 0.94 mL/min was observed in the paoposed MHD micropump. Flow velocity of 16.3 mm/s was achieved at the slip length of 10 ?m. The temperature was observed to decrease from 36.0? to 30.2? as the slip length value increased from 10 ?m to 90?m, respectively.As one important part of MHD micropump, the electromagnet was also simulated and fabricated. The effect of coil shape and magnetic yoke material on the performance of electromagnet was investigated by finite element method. The characterization of electromagnet was achieved by the controlling of magnetic beads under the magnetic field. The results indicate that a coil shape is better to generate a magnetic field, while a serpentine shape is prefer to generate a gradient of magnetic field. Magnetic yoke with higher permeability produce stronger magnetic field under the same applied voltage of coil. To produce the magnetic field along direction of Z axis, the magnetic yoke should have the property of perpendicular magnetic anisotropy (PMA). Co60Fe20E20 was used in this paper as magnetic yoke and have the ability of enhancement of magnetic field.The MHD micropump was successful fabricated by combining electromagnet and electrode. The fabrication process of MHD micropump was investigrated in this paper. The MHD micropump was characterized by polystyrene microspheres. The results show that the novel MHD micropump can pump microspheres successfully. It can further predit that the newly designed MHD micropump have the potential application in drug delivery system, chemical analysis, and enviromental detection areas when integrating with other sensing elements.The study of impedance sensor was independent researched in following chapters. The advantage of integration of MHD micropump and impedance sensor provides the ability of pretreat and detect of sample on one chip. Four structure types of electrodes were used to investigate the influence of electrode structure on impedance detection. The impedance detection of different concentrations of NaCl solution, different concentrations of polystyrene microspheres solutions, solutions containing different diameters of polystyrene microspheres and different concentrations of cell solutions were performed by Zennium electrochemical workstation in the frequency range of 1 Hz to 100 kHz. The results indicated that interdigitated electrodes with narrower width and narrower pitch have higher sensitivity.