A working-point perturbation method for the magnetoelectric sensor to measure DC to ultralow-frequency-AC weak magnetic fields simultaneously

摘要

Magnetoelectric (ME) sensors for the weak magnetic field measurement have attracted a lot of attention because of their high sensitivity and easy integration. However, the ME sensor performs well only at its working-point under a direct current (DC) bias field ( H bias ) and mechanical resonance frequency ( f res ). The measurement of DC to ultralow frequency (0–100?Hz) weak magnetic fields has increasing demands, such as in geomagnetic anomaly fields, geological and mineral exploration, magnetocardiography, and magnetoencephalography. Unfortunately, f res of ME sensors is on the order of several tens of kilohertz, which is far higher than the ultralow frequency desired. Moreover, if the operation frequency deviates from f res , the sensitivity will deteriorate rapidly. In this study, a working-point perturbation method was used to measure the weak magnetic fields at 0–100?Hz with a high magnetic field resolution. (1) The perturbation of f res using an ultralow frequency ( f ac ) magnetic field results in two modulation peaks with frequencies of f res ± f ac . The frequency and resolution of the measured alternating current magnetic field can be obtained by varying f ac and the modulation depth. A resolution around 1 nT for f ac 10?Hz and a lowest operation frequency of 0.1?Hz were achieved using our measurement system. (2) A high field resolution of 3 nT (better than the frequency perturbation method with a resolution of 16 nT at 0.1?Hz) can be achieved by the perturbation of H bias at f res because the ME sensor is still working at the quasi-working-point and helped by lock-in amplifier technology.