Low-frequency noise characterization of a magnetic field monitoring system using an anisotropic magnetoresistance

• Noise measurements based on an AMR with dedicated noise reduction techniques have achieved values of 5 nT Hz−1/2 at 0.1 mHz.
• AMR is a suitable technology for low-frequency space applications like eLISA, a space-based gravitational wave detector.
• The results for chip-scale sensors show similar noise at 0.1 mHz than the fluxgate magnetometers used in LISA Pathfinder, the eLISA technology demonstrator.

A detailed study about magnetic sensing techniques based on anisotropic magnetoresistive sensors shows that the technology is suitable for low-frequency space applications like the eLISA mission. Low noise magnetic measurements at the sub-millihertz frequencies were taken by using different electronic noise reduction techniques in the signal conditioning circuit. We found that conventional modulation techniques reversing the sensor bridge excitation do not reduce the potential 1/f noise of the magnetoresistors, so alternative methods such as flipping and electro-magnetic feedback are necessary. In addition, a low-frequency noise analysis of the signal conditioning circuits has been performed in order to identify and minimize the different main contributions from the overall noise. The results for chip-scale magnetoresistances exhibit similar noise along the eLISA bandwidth (0.1 mHz − 1 Hz) to the noise measured by means of the voluminous fluxgate magnetometers used in its precursor mission, known as LISA Pathfinder.