Advanced methods in measurement of the noise of fluxgate sensors

Metrological Instrumentation

Fluxgate-sensors still are the best peforming room-temperature vectorial magnetic sensors in the nT-mT range. Multiple applications (i.e. medical imaging and scanning, space instrumentiation), require the knowledge of the noise properties of the respective sensor, or generally of the whole magnetometer. As other magnetic sensors do, fluxgates exhibit 1/f noise behaviour, which is well documented in the common range of 0.1-10 Hz and they reach a PSD of units of pT(rms) @ 1 Hz. The origin of the overall noise figures is not very clear to the comunity, as several approaches to explain the noise by Barkhausen noise, magnetostriction, eddy-currents and thermal effects did not reach the levels commonly measured. In addition, for extremely low and high frequencies of operation (<< 100 mHz and >> 1 kHz), only few reliable results were published, as the contribution from the excitation and detection electronics starts to be indistungishable from the influence of the sensor itself.

In his PhD thesis, Mr. Janosek focuses on a low-noise, compact gradiometer for space application, which requires lowest sensor noise as possible, mainly on frequencies << 100 mHz. This requires first to identify the limits of the excitation and signal processing of the fluxgate sensor output voltage and further try to minimize the noise sources. In the first step, which will be done at the IGSM of TU Braunschweig, he will focus on isolating the noise contribution of the sensor itself. There are advanced methods published in the literature, which however are not widely repeated by other authors (such as correlation techniques available on modern spectrum analyzers). He will also try a novel approach of thermally modulating the output of the fluxgate sensor during noise measurements, which could, together with proper signal processing methods, allow to isolate the noise contribution of the sensor and its core.

TU Braunschweig
Ph.D. student: