Excitation module for orthogonal fundamental mode fluxgate sensor

Abstract

A fluxgate is a device that has important applications in weak magnetic field measurements. Compared with the second harmonic mode, the orthogonal fundamental mode fluxgate exhibits a better performance in terms of lower noise and wider bandwidth, making it popular among researchers in this field. An amorphous wire is a vital part of any orthogonal fundamental mode fluxgate, and its excitation parameters determine the performance of the sensor (especially the noise level). For different structures and sizes of amorphous wires as probes, the optimal excitation parameters of orthogonal fundamental mode fluxgate are different. The conventional excitation module development scheme suffers from problems such as a complicated structure and low flexibility. To overcome these problems, a simple, compact, and effective excitation module is proposed, which is composed of a waveform generator, signal conditioning circuit, and voltage-controlled current source. Owing to the high flexibility, the frequency of the direct digital frequency synthesis is fully programmable. We tested the design performance indexes of key parameters, such as excitation signal waveform, amplitude, noise level, and bandwidth. The excitation current noise level is as low as 12.42 nA/sqrt (Hz) @ 20 kHz without Iac and 17.35 nA/sqrt (Hz) @ 20 kHz with Iac. The effective bandwidth of the alternating current output is 10–200 kHz. Moreover, a system test platform was developed, and this module was used to analyze the variation trend of the noise level of the fluxgate sensor under different excitation parameters (such as Iac, Idc, and excitation current frequency). It has been proved that the excitation module helps in effectively and quickly selecting the best excitation parameters to improve the performance of orthogonal fundamental mode fluxgates and shorten their development cycle.