Circuit Architecture for Electrical Impedance Spectroscopy Instrumentation to Address Electrode Impedance Mismatch in Clinical Devices

A mismatch in electrode impedance is a common and significant source of artefact in electrical impedance spectroscopy systems. We have analysed these artefacts, identifying key parameters in the optimisation of both current and voltage excited electrical impedance spectroscopy systems. We have used this information to develop a new clinical system for investigating muscle impedance anisotropy in human limbs, with the aim of developing biomarkers for various muscle pathologies. This new instrumentation integrates buffering at the front-end, which isolates the electrodes from both multiplexing and wiring parasitics. Modelling of the front-end instrumentation demonstrates an input impedance of over 1
$\text{G}\Omega $
in parallel with 0.4 pF. The clinical system currently has 16 electrodes, with the capability for more, and operates over a physiologically relevant frequency range of 76 Hz to 625 kHz. Results presented in this paper show that the new system operates with reduced levels of artefact, even in the presence of a significant mismatch in electrode impedances.