Time-domain based impedance measurement: strengths and drawbacks

While most applications of bio-impedance measurements for characterization of cells or tissue do not have any time requirements, newer developments like real time monitoring of moving cells or membrane recovery after high voltage application depend on fast measurement. This is not compatible with sweeping the frequency through the desired range while assessing magnitude and phase of the material under test (MUT). A high speed is only achievable by using broad-bandwidth excitation signals and monitoring the response in time-domain. Time-domain based methods can be distinguished by the excitation signals as well as by assessing the transmission or reflection behavior of the MUT. Although there is good agreement regarding the advantages of fast measurements, time-domain measurements are often rejected because of low precision and noise sensitivity. This paper points not only the advantages of impedance measurements in time domain but shows also drawbacks together with possible solutions.