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

Abstract

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 (Hbias) and mechanical resonance frequency (fres). 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, fres 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 fres, 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 fres using an ultralow frequency (fac) magnetic field results in two modulation peaks with frequencies of fres ± fac. The frequency and resolution of the measured alternating current magnetic field can be obtained by varying fac and the modulation depth. A resolution around 1 nT for fac > 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 Hbias at fres because the ME sensor is still working at the quasi-working-point and helped by lock-in amplifier technology.

High-Resolution Magnetoelectric Sensor and Low-Frequency Measurement Using Frequency Up-Conversion Technique

“…In this method, another magnetic field, , with low frequency, , as a field to be measured is mixed with AC exciting field at resonance frequency, leading to two shoulder peaks located on the left and right sides of the main peak with frequency shift of . The intensity of and frequency can be tuned by varying the modulation depth (MD = ) and the frequency of the signal source [ 31 ]. The time base of the oscilloscope sampling is 40 ms, and the recording length is 100 k. Figure 6 a,b show the influence of the modulation frequency on the location of the shoulder peaks at an MD of 0.5%.…”

“…The frequency shifts from the main peak are , respectively, and the peak height is proportional to the measured magnetic field. After magnetic field calibration, the magnitude of the measured low-frequency weak magnetic field signal can be obtained by measuring the height of the shoulder peaks [ 31 , 32 , 33 , 34 ]. In general, the limit of detection (LOD) depends on the dimension of the ME sensor and the operating frequency, and the LOD under an AC field is smaller than that under a DC one.…”

High Resolution Magnetoelectric Sensor and Low-frequency Measurement using Frequency up-conversion Technique

“…In this method, another magnetic field with a low frequency , as a field to be measured, was mixed with the AC exciting field at resonance frequency, leading to two shoulder peaks located at the left and right sides of the main peak with a frequency shift of ± . The intensity of the and the frequency can be tuned by varying the modulation depth (MD= ⁄ ) and frequency of the signal source [30]. Figure 6a and 6b show the influence of the modulation frequency on location of the shoulder peaks at a MD of 0.5%.…”

“…The frequency shifts from the main peak are ± , respectively, and the peak height was proportional to the measured magnetic field. After magnetic field calibration, the magnitude of the measured low frequency weak magnetic field signal can be obtained via measuring the height of the shoulder peaks [30][31][32][33]. In general, the limit of detection (LOD) depends on the dimension of ME sensor and the operating frequency, and the LOD for the thin-film sensor is better than that of bulk one, and the LOD for AC field is smaller than that for DC one as well.…”

Self-biased Metglas/PVDF/Ni magnetoelectric laminate for AC magnetic sensors with a wide frequency range

“…Low-frequency AC magnetic signals less than 100 Hz must be detected in many fields, such as geomagnetic navigation [59], marine biosensors [60], and biological monitoring [61,62]. The signal-to-noise ratio at low frequency will decrease sharply due to the interference of noise; therefore, the magnetic sensing performance of the sample at low frequency, including the limit of detection (LOD) and resolutions, is studied by using modulation and demodulation technology [63,64].…”