Methods and apparatus for
digital demodulation of signals obtained in the measurement of electrical bioimpedance or bioadmittance of an object. One example comprises: generating an
excitation signal of known frequency content; applying the
excitation signal to the object; sensing a response
signal of the object; sampling and digitizing the response
signal to acquire a digitized response
signal representing the response signal with respect to frequency content, amplitude and phase; correlating, for each frequency fAC of the
excitation signal applied, digitized samples of the response signal, with discrete values representing the excitation signal; calculating, using the correlated signals for each frequency fAC of the excitation signal applied, complex values for the bioimpedance Z(fAC); providing, over time, a set of digital bioimpedance waveforms Z(fAC,t)); separating the base bioimpedance Z0(fAC), from the waveforms; and separating the changes of bioimpedance ΔZ(fAC,t), from the waveforms.