Measurement of Hysteresis Loop on Soft Magnetic Materials Using Lock-In Amplifier

A new method is proposed to measure the magnetic hysteresis as a function of temperature. It is based on the spectral decomposition of magnetization and measurement of different harmonics using the harmonic-detection function of a lock-in amplifier. Applying this method, a measuring system of the BH loop was designed and fabricated. This system gives spectra of magnetic flux density B driven by an ac-magnetic field h. The BH loops are reconstructed from the spectra of the B. The spectra and BH loops were measured for a NiZn ferrite toroid at various temperatures. When the temperature increases from the room temperature, the higher harmonics of the spectra increase. Approaching the Curie temperature T C from below, magnetic loss and nonlinearity of the BH loops increase, and the loop shows the saturation just below T C .