High-precision voltammetry method for measuring the permeability of permalloy at ultra-low-frequency magnetic field

The permeability of permalloy at ultra-low-frequency magnetic field is a crucial and fundamental parameter for analyzing the low frequency shielding factor of magnetically shielded rooms. However, due to limitations in the accuracy of the existing magnetic flux signal measuring system, the permeability at ultra-low-frequency magnetic field is challenging to precisely determine. Therefore, a high-precision voltammetry method for measuring the permeability of permalloy at ultra-low-frequency magnetic field is proposed in this paper. First, the theory of the voltammetry method and the required level of induced voltage accuracy are derived and thoroughly analyzed. Then, the voltage acquisition module with ultra-low noise is designed by using four parallel instrumentation amplifiers, and the magnitude of the noise is quantified by establishing the noise analysis model for the voltage acquisition module. Finally, the system for measuring the permeability at ultra-low-frequency magnetic field is set up, and its feasibility is verified by comparing the measurement results of permeability at 10 Hz with the commercial soft magnetic instrument. The results show that the system is capable of measuring the permeability of permalloy at 0.01 Hz to 1 Hz, with repeatability error of less than 3%. The method can also be applied to measure the permeability of other soft magnetic materials.