Noise Characterization of Coil Detection Type Magnetic Field Sensor Utilizing Pulse Excitation Amorphous Wire Magneto-Impedance Element

摘要

In this experiment, we investigated noise characteristics of a pulse magneto-impedance sensor which is based on an amorphous magnetic wire with a pickup coil. For a helical static magnetization, the ac current i passing the wire induces a coil voltage V_c in the coil around the wire. The pulsed excitation, combining both high and low frequency harmonic, produces the voltage V_c with dc current biasing. We describe improvements of pulse excitation conditions for an amorphous magnetic wire to reduce magnetic noises. The relation between the time interval of a current pulse train T and magnetic noises was investigated. The magnetic noise is suppressed clearly when T is smaller than 1.5 μs for pulse width 10 ns. Under the optimal conditions, the rms noise of 1-cm-long an amorphous wire magneto-impedance sensor with 600 turns of the pickup was estimated as 1 pT/Hz~(1/2) at 20 Hz～500 Hz.