Single-lockin detection of AC magnetic fields by fluxgate sensor

Abstract

We present a simple narrowband method to detect the amplitude of alternating magnetic fields by a fluxgate sensor using a single lock-in amplifier, improving the common method of using two phase sensitive demodulators (lock-in amplifiers). We eliminated the need for two phase-sensitivite demodulators by processing the reference signals of lock-in amplifier and of the fluxgate excitation unit. This setup can be used as a high-resolution, narrowband spectral analyzer of magnetic fields or as a system for measuring the AC response of magnetic markers. Two methods were introduced and tested; we achieved 2 kHz detecting noise spectral density of 80 pT/¥Hz in the laboratory environment. The method is directly usable for any fluxgate sensor or magnetometer, where the reference signals are available. Using a slow feedback compensatingloop further improves the dynamic range of the instrument.

High Sensitivity Fluxgate Sensor for Detection of AC Magnetic Field: Equipment for Characterization of Magnetic Material in Subsurface

“…Muftuler and Ider [5] have made measurements of AC magnetic field distribution using MRI. Janošek and Dado [6] proposed a simple method to narrow band detect the amplitude of the alternating magnetic fields by a fluxgate sensor using a single lock-in amplifier. Recently, Ando et.al [7] has using coupled-core fluxgate magnetometers for weak AC magnetic field detection.…”