Q-Factor Determination Apparatus and Method for Wireless Power Transfer System

A method includes applying an excitation including a voltage step to a resonant tank comprising a first coil and a capacitor, comparing a damped sinusoidal waveform having a resonant attenuation envelope with a predetermined threshold voltage and detecting a last time instant at which a value of the damped sinusoidal waveform is equal to the predetermined threshold voltage, calculating a quality factor of the resonant tank based on a plurality of parameters derived from the last time instant, and determining whether a foreign object is magnetically coupled to the first coil based on the quality factor.