Multiplexed dynamic strain sensing system based on a fiber ring laser using a non-tunable fiber Fabry-Perot filter.

In this paper, a non-tunable fiber Fabry-Perot filter (FFPF) is configured to demodulate dynamic strain signals in a multiplexed dynamic sensing system based on a fiber ring laser. A semiconductor optical amplifier (SOA) contained in the fiber ring laser cavity enables this system to implement multiplex operation because of the inhomogeneous broadening of the SOA source. The shift of the reflective spectrum of the fiber Bragg grating caused by external dynamic strain is demodulated by the FFPF in the laser cavity, which ultimately generates an amplified output. In the experiment, the sensing system can respond to dynamic strains at ultra-high frequencies up to megahertz, and an example for detection of ultrasonic signals in water has been successfully demonstrated. A dual-channel system for multiplexing demodulation is also discussed. This system presented here has a simple structure and a low cost, which makes it attractive for dynamic strain detection in structural health monitoring.

Detection of dynamic signals from multiplexed SOA-based fiber-ring laser sensors.

A simple matched filter demodulation configuration for detecting dynamic signals from multiplexed semiconductor optical amplifier (SOA)-based fiber-ring laser sensors is investigated theoretically and experimentally. It is feasible for multiple points fiber Bragg grating sensing because the inhomogeneous broadening of the SOA source makes it possible to produce multimode lasing without mode competition. The best operating points for matched filter demodulation and the wavelength demodulation range are investigated. In the experiment, the simultaneous dual-channel detection of dynamic strains at high frequencies is presented by using piezoelectric transducers. An example application for simultaneous two-channel ultrasonic detection has been successfully demonstrated. The detection system design is simple, low cost, and high precision, making it attractive for applications in structure health monitoring.

Analysis of land subsidence caused by hydrodynamic force in Loess Hilly and gully region based on SBAS-InSAR.

After large-scale land consolidation in hilly loess region of the Loess Plateau in China, land subsidence has a wide affecting area and considerable difficulty of prevention. Hence, large-scale, stabilized, and continuous deformation monitoring is urgently needed for slopes. In this study, land consolidation zone in the loess platform area of Weinan, China, was selected as the object, and the 30-scene Sentinel-1A data in Jan, 2018 to Dec, 2019 were analyzed. The mean annual velocity of ground deformation was from -6.19 mm∙a-1 to 3.86 mm∙a-1, and Accumulated deformation velocity was within -8.49 mm∙a-1 to 7.24 mm∙a-1. Accumulated deformation of land consolidation changed with the seasons changing. The interrelationship between the spatiotemporal variations in ground subsidence and the precipitation, ground water, loess engineering properties was also discussed. Accumulated deformation of land consolidation changed with the seasons changing. The precipitation accelerated the subsidence by unexpected strong precipitation reflects that the infiltration of rainwater can lead to compacted loess deformation which caused by moistening effect. Under varying ground water environment, external loads may lead to soil collapse, resulting in non-uniform land subsidence. Co-compression deformation of original loess and compacted loess is main influencing factors of subsidence. These findings have important implications and significant positive effects on the prevention of potential hazard such as subsidence and side slope slip.