Developing an electrical bioimpedance system using lock-in amplifier principles

This work presents the development of a system for measuring electrical bioimpedance using lock-in amplifier principles. The system is comprised of two parts: hardware and software. It was validated with three Cole-Cole electrical models reported in the literature replicating biological responses. These models include the TBC Circuit, which corresponds to body composition; the RR Circuit, which corresponds to respiratory rate; and the LC Circuit, which corresponds to lung composition. The system was measured in two frequency ranges: low frequencies from 5 Hz to 10
³
Hz and high frequencies from 10
³
Hz to 10
⁵
Hz. The device performs well in precisely measuring low voltages related to low impedances in the impedance under test, where electrical noise can impact accuracy. The developed system presents absolute errors lower than 20 Ω in the Impedance Magnitude.