Distributed Acoustic Sensing Based on Coherent Microwave Photonics Interferometry

Abstract

A microwave photonics method has been developed for measuring distributed acoustic signals. This method uses microwave-modulated low coherence light as a probe to interrogate distributed in-fiber interferometers, which are used to measure acoustic-induced strain. By sweeping the microwave frequency at a constant rate, the acoustic signals are encoded into the complex microwave spectrum. The microwave spectrum is transformed into the joint time–frequency domain and further processed to obtain the distributed acoustic signals. The method is first evaluated using an intrinsic Fabry Perot interferometer (IFPI). Acoustic signals of frequency up to 15.6 kHz were detected. The method was further demonstrated using an array of in-fiber weak reflectors and an external Michelson interferometer. Two piezoceramic cylinders (PCCs) driven at frequencies of 1700 Hz and 3430 Hz were used as acoustic sources. The experiment results show that the sensing system can locate multiple acoustic sources. The system resolves 20 nε when the spatial resolution is 5 cm. The recovered acoustic signals match the excitation signals in frequency, amplitude, and phase, indicating an excellent potential for distributed acoustic sensing (DAS).

Signal-to-Noise Ratio Improvement for Phase-Sensitive Optical Time-Domain Reflectometry Using a Genetic Least Mean Square Method

“…In recent years, a considerable number of valuable works has been conducted, and different schemes have been proposed to fulfill the distributed acoustic sensing, such as using phase-sensitive optical time-domain reflectometry (phase-sensitive OTDR) [11][12][13], Brillouin optical time-domain analysis (BOTDA), and optical frequency-domain reflectometry (OFDR) [14][15][16], and other methods [17]. Among them, OFDR is based on sweptwavelength homodyne interferometry.…”