Positive phase error from parallel conductance in tetrapolar bio-impedance measurements and its compensation

Bioimpedance measurements are of great use and can provide considerable insight into biological processes. However, there are a number of possible sources of measurement error that must be considered. The most dominant source of error is found in bipolar measurements where electrode polarisation effects are superimposed on the true impedance of the sample. Even with the tetrapolar approach that is commonly used to circumvent this issue, other errors can persist. Here we characterise the positive phase and rise in impedance magnitude with frequency that can result from the presence of any parallel conductive pathways in the measurement set-up. It is shown that fitting experimental data to an equivalent electrical circuit model allows for more accurate determination of the true sample impedance as validated through finite element modelling (FEM) of the measurement chamber. Finally, the equivalent circuit model is used to extract dispersion information from cell cultures to characterise their growth.