UC Irvine

Most sensors that serve important purposes in the medical industry are impedance based. This has created the need for impedance sampling systems in the medical industry. Most of these systems are rather large, difficult to use, and can only sample one item at a time. In this paper we explore the design of an impedance sampling system that can take input from 100 sensors simultaneously. The system communicates and is powered through a micro-USB connection. The front end can provide an excitation voltage of 200mV, 400mV, 1V, and 2V peak-to-peak and frequency of 0.1Hz – 100kHz. There are two modes of operation: frequency sweep and live plot. The frequency sweep mode is used to test an unknown impedance to see what voltage and frequency it responds best to. The data collected is then used to setup the live plot. Conversions are done by providing the excitation signal to an unknown impedance and measuring the current through the impedance to back calculate the impedance via a propriety discrete Fourier transform (DFT) algorithm. To maximize dynamic range and performance, a multiplexer is used at the transimpedance amplifier to provide variable gain based on the maximum input range and selected peak-to-peak excitation voltage. The impedance range measurable by the system is 1Ω - 1MΩ. Due to the complexity and low-noise nature of the device, calibration is an extremely important step to getting the best performance out of the system. To facilitate easier calibration, a multiplexer is tied to the input that connects known, accurate, and low drift impedances so that users can call for autocalibration of the device. Software is provided so that users can adjust start/end frequency, number of steps, excitation voltage, and excitation frequency depending on which mode they are using the device in. Users can also recalibrate a device for a specific voltage through the software by the click of the button. Plots are provided for both modes and can be exported through the software along with raw data.