A microcontroller based 100 kHz - 1 MHz multi-frequency bio-impedance measurement device

Abstract

Complex impedance measurement of biological systems is gaining wide popularity in determining the pathological and physiological status of biological tissues in research applications such as; skin hydration, dental decay, body fat content, tissue ischemia, food freshness, blood freshness and etc. The device presented in this study is a four-probe, multi frequency, portable bio-impedance measurement device based on the principles of magnitude-ratio and phase-di erence detection. The system is built with a DDS frequency generator, a voltage controlled current source, two high frequency instrumentation ampli ers, a phase-gain detector and a microcontroller unit. The software for the microcontroller is written and compiled on CodeVisionAVR C Compiler and the microcontroller is programmed on AVRStudio 4. The accuracy and precision of the prototype device are checked against the HP 4284A LCR meter using di erent RC test loads. The results show that the overall percentage error averages of the real and imaginary parts of the complex impedance are 0.80 % and 1.78 % respectively. The Cole-Cole diagrams are generated to obtain the Cole parameters, R0, R1, fc and ® that give valuable information about the physiological status of biological tissues. Those parameters are also checked against the LCR meter. The percentage errors of ® are found to be high due to relatively high phase-di erence detection errors.|Keywords: bioimpedance, magnitude-ratio and phase-difference detection, direct digital synthesis (DDS), Cole-Cole plot, Cole-Cole parameters.