Determining impedance of physical system

A system for determining an impedance of a physical system, comprising:

• an interface for receiving a measurement of a response of the physical system to a perturbation which is applied to the physical system, wherein the perturbation has a perturbation frequency, and wherein the measurement of the response is received in form of a response signal;
• a processor subsystem configured to determine an impedance of the physical system based on a ratio of the perturbation and the response, wherein the determining of the impedance comprises:
• converting the response signal into a frequency domain to identify a magnitude and phase of a first harmonic of the response signal and a magnitude and phase of a third harmonic of the response signal;
• expressing the magnitude and phase of the first harmonic as a first complex term and expressing the magnitude and phase of the third harmonic as a third complex term;
• and
• in determining the impedance, using as the response a sum of at least the first complex term and three times the third complex term.