Design and characterization of a multi-frequency bioimpedance measurement prototype

A multi-frequency bioimpedance measurement prototype is proposed, validated and characterized. It consists of an Improved Howland Current Source controlled by voltage, a load voltage sensing scheme through a discrete 3-opamp instrumentation amplifier, a phase and quadrature demodulation setup through analog multipliers, and digitization and processing of the signals using a digital benchtop multimeter. The electrical characterization of the measurement channel was done for resistive loads only, on four different circuits. Measurements were made on 10 frequencies, from 100 kHz to 1 MHz, with 10 load resistances, from 100 Omega to 1 k Omega, to obtain linearity, absolute error and frequency response. The best performance among the four circuits was a maximum absolute error of 5.55%, and -1.93% of load current variation at the worst case scenario.