Enhanced Bio-Impedance Demodulation Method Under Non-Integer Period Sampling Conditions

In this article, an enhanced bio-impedance demodulation method is proposed to accurately extract impedance from the time-domain signals, even under non-integer period sampling (NIPS) conditions. The conventional bio-impedance demodulation approach, which is based on the direct discrete Fourier transform (DFT) operation, is often limited by spectral leakage and fence effects due to its reliance on IPS. To overcome these limitations, a maximum amplitude spectral line (MASL) is used to replace the hidden spectral values, and an optimized bio-impedance demodulation formula is established taking into account the spectral leakage error. The method is evaluated through simulations and experiments on 2 resistors and 1 capacitor (2R-1C) circuits and ex vivo biological tissues. The experimental results of the real samples (pumpkin, carrot, and beef) show that the method provides highly accurate impedance demodulation, with a maximum relative error of impedance magnitude and a maximum absolute error of impedance phase less than 0.88% and 0.63°, respectively, from 10 kHz to 1 MHz. These results demonstrate the effectiveness of the proposed approach in accurately demodulating impedance at arbitrary frequencies and weakening the constraints imposed by IPS.