Ultra high sensitive magnetic measurement system based on Lock-in amplifier technique and giant magnetoresistance sensor

Abstract

The signal processing circuit utilising the Lock-in technique has been developed for a magnetic field measurement device, enabling the processing of signals from sensors with amplitudes significantly smaller than noise levels. This circuit is integrated with a giant magnetoresistance (GMR) sensor to measure weak magnetic field sources. The proposed device was validated through experiments measuring alternating magnetic fields in the range of 0-0.04 G. The magnetic field source was generated by a Helmholtz coil pair fabricated using 3D printing technology, capable of producing a uniform magnetic field with adjustable intensity, frequency, and direction. Experimental results showed that the device has a limit of detection (LOD) of 3.81 nT, corresponding to a change of 6.5 µV at the sensor output. The signal processing circuit achieves an experimental gain factor of 1386, with a linear operating range from 0-7 mV input, corresponding to an output range of 0-10 V, with the circuit’s input LOD being approximately 631 nV. In the low-signal range, the proposed device demonstrates a better ability to detect magnetic field and voltage signals than commercial measurement devices. This magnetic field measurement system can detect the magnetism of superparamagnetic nanoparticles (SPMNPs) associated with molecular biological targets, supporting the development of biomedical analysis devices.