High-Spatial-Resolution Distributed Acoustic Sensor Utilizing a Positive- and Negative-Swept Pulse

A distributed acoustic sensor (DAS) with a one- centimeter spatial resolution is proposed and demonstrated using pulse-compression phase-sensitive optical time-domain reflectometry (Φ-OTDR). A positive- and negative- swept pulse was used to expand the frequency modulation range of a heterodyne DAS system to achieve a high spatial resolution. A Rayleigh-enhanced single-mode fiber (eSMF) was used to magnify the backscattering signal and suppress the fading noise. The combination of pulse compression and eSMF allows the system to fully quantify perturbations with a high spatial resolution of 1.2 cm and a strain resolution of 1.46 nϵ/√Hz. In addition, the detection and positioning of multiple acoustic emission (AE) sources at frequencies of 120 ∼ 130 kHz is also demonstrated. Hence, the high-spatial-resolution DAS system proposed in this work could potentially be used for structural health monitoring for large equipment, such as spacecrafts, hypersonic vehicles, and deep-sea submersibles.