Application of Lock-in Amplifier to Weak Magnetic Field Detection

Abstract—A lock-in amplifier (LIA) is designed and optimized to recover weak magnetic signals from noise. The proposed LIA is based on phase-sensitive detection technique (PSD), obtain needed signal at the specific reference frequency and reject noise signals at other frequencies. A measurement system applies this LIA to operate at a particular reference frequency which avoids interferences. The application of the LIA is the weak magnetic signal detection in a high noise level environment. The desired signal is in voice frequency. In this system the LIA acts as a detector and programmable low pass filter combined. Experiments are performed to verify the feasibility of the LIA. The result of the test shows that very small signals can be detected in the presence of large amounts of uncorrelated noise when the frequency and phase of the desired signal are known.