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21606 Systematic Approach for Correction of Design Deficiencies in Particle Detection Electronics Jacqueline Bulaclac Mentor: John LaRue & Richard Nelson The Coulter Counter is used to count small biological particles in solution. The original concept was based on the increase in the electrical resistance of an orifice as the presence of a biological particle altered the electrical conduction path. We have worked to adapt this type of device to MEMS devices. The detection of a particle is proportional to resistance change and the amplitude of the excitation. The Coulter Counter is currently used for sizing DNA fragments and sorting of biological cells or cell fragments. While the Coulter Counter traditionally utilizes DC excitation, our research group’s Summer 2003 research extended this by implementing an amplitude modulation and demodulation approach for detecting biological particles. The results of the Summer 2003 research identified a number of design problems that become potentially significant as the channel dimensions were reduced to the low micron or submicron range. We propose to find solutions to these problems to support the next generation of devices to be fabricated by this research group. The identified problems are as follows: (1) Parasitic capacitances in the current source circuit construction and the effects of the channel’s high resistances, (2) The current demodulation approach utilizes a fourquadrant multiplier and an active four pole low pass Butterworth filter whose input DC level can exceed the allowable input voltage, and (3) The parasitic capacitances or the frequency-dependent input impedance of the instrumentation amplifier.