THD, an EIS quality indicator

Total Harmonic Distortion quantifies the linearity of the response, Non Stationary Distortion indicates the effect of time-variance and transient regime.

Noise to Signal Ratio ensures the signal is large enough compared to the measurement noise.

Some results are given on electrical circuit as well on a discharging battery. Read more....

Electrochemical impedance spectroscopy (EIS) measurements at two different AC amplitudes (50 mA & 400 mA) are performed on the same Li-ion battery cell.

The non-linearity of the cell at low frequency is evident in the Nyquist plot to the right

After an equivalent circuit fit analysis, the charge transfer resistance is over-estimated by 8% with the 400 mA AC amplitude measurement.

The THD indicator can be used to detect this non-linearity and help optimize the stimulation amplitude