Ultra-low frequency vibration detection based on long-arm time-accumulation interference scheme

Developing an ultra-low frequency acoustic sensor with high sensitivity is crucial for diverse applications, ranging from seismic monitoring, military operations, and pipeline surveillance. However, low-frequency system noise from distributed vibration-detection systems poses an ongoing challenge. Here, the scheme for the ultra-low frequency vibration detection based on long-arm time-accumulation (LATA) interference is proposed and demonstrated. The sensing system utilizes a double-pulse heterodyne coherent laser interferometric distributed acoustic wave detection signal method. The detected phase sinusoidal waveform signal is demodulated to obtain the measured low-frequency vibration signal. The low-frequency detection performance of both reflective and transmissive system architectures is verified. The experimental results show that the system detection frequency is as low as 0.05 Hz. Applying the symmetric structure effectively suppresses the common-mode noise (CMN) of the system and improves the detection performance. The proposed low-frequency vibration signaling method is expected to be applied in the field of large-scale monitoring, such as earthquake prediction, building health monitoring, geological exploration, and oil well survey.