Patent ID: 8193804

Claim:
An apparatus to measure ac magnetization at mixture frequency, comprising: an ac generating unit to generate at least a first ac current with a frequency f 1 and a second ac current with a frequency f 2 ; a co-axial solenoid unit, driven by the first ac current and the second ac current to generate a first magnetic field and a second magnetic field; a pick-up solenoid, within the co-axial solenoid unit, wherein a sample is disposed in the pick-up solenoid for detecting an ac magnetization of the sample and multiple frequency-component signals corresponding to various frequency combinations of f 1 and f 2 are output; and a signal processing circuit, receiving the frequency-component signals, wherein the signal processing circuit processes the frequency-component signals and obtains the ac magnetization of the sample at a target frequency of (γ T f 1 +β T f 2 ), wherein γ T and β T are positive integers and the frequency f 1 and the frequency f 2 are two different frequencies.