A DSP-enhanced AC susceptometer for characterisation of superconductors

This paper explains the design and implementation of a low-cost susceptometer. Much emphasis is laid on the implementation of a software-based lock-in amplifier as an alternative for an analogue based lock-in amplifier for the susceptomer´s signal processing. The lock-in amplifier acts as a discriminating voltmeter measuring the inphase and the out-of-phase susceptibilities at a reference frequency, from a noisy environment, of high temperature superconducting samples. From susceptibility measurements, important parameters such as critical temperature and critical current were determined.