Application of digital signal processing to vibrating sample magnetometry

Digital signal processing is presented as an alternative to the use of a lock-in amplifier in vibrating sample magnetometry. The operation of the conventional analog lock-in amplifier is reviewed prior to describing the digital process. The latter uses a programmable wave-form digitizer to capture the signal and reference voltages and then transmits them to a computer where the operations of the analog phase sensitive detector are carried out in software. The digital filtering process is contrasted with the analog low-pass filter and is shown to be superior from the points of view of speed and flexibility. Incorporation of this digital scheme into a conventional vibrating sample magnetometer is described and data taken in both digital and analog fashion are compared. Signal averaging methods unique to the digital system are described and the results are discussed for a sample having a moment of 3 × 10^-5emu.