Lock-in amplifiers as a platform for weak signal measurements: Development and applications

The accuracy of modern scientific research and technological advancement is highly reliant on the ability to accurately measure weak signals. The lock-in amplifier (LIA) represents an indispensable instrument, skillfully extracting these faint signals from a backdrop of noise. As the pursuit of accuracy intensifies, LIA technology has been continuously adapted and optimized. This review offers a comprehensive analysis of the evolution and applications of LIAs in weak signal measurements. It presents a structured introduction to the historical development of LIAs and evaluates their diverse applications across various domains, including impedance, optical, electrochemical, thermal, and biosensing methods. By examining specific examples in each field, it showcases the significant impact of LIAs on enhancing measurement precision. The review concludes by highlighting persistent challenges encountered by LIAs in practical settings and explores potential avenues for their future advancement. Future research aims to address practical challenges, including further noise reduction, improved system stability, and ease of use, ensuring LIAs continue to play a pivotal role in scientific and technological progress.