In the past two decades Brillouin-based sensors have emerged as a newly-developed optical fiber sensing technology for distributed temperature and strain measurements. Among these, the Brillouin optical time domain reflectometer (BOTDR) has attracted more and more research attention, because of its exclusive advantages, including single-end access, simple system architecture, easy implementation and widespread field applications. It is realized mainly by injecting optical pulses into the fiber and detecting the Brillouin frequency shift (BFS), which is linearly related to the change of ambient temperature and axial strain of the sensing fiber. In this paper, the authors provide a review of new progress on performance improvement and applications of BOTDR in the last decade. Firstly, the recent advances in improving the performance of BOTDRs are summarized, such as spatial resolution, signal-to-noise ratio and measurement accuracy, measurement speed, cross sensitivity and other properties. Moreover, novel-type optical fibers bring new characteristics to optic fiber sensors, hence we introduce the different Brillouin sensing features of special fibers, mainly covering the plastic optical fiber, photonic crystal fiber, few-mode fiber and other special fibers. Additionally, we present a brief overview of BOTDR application scenarios in many industrial fields and intelligent perception, including structural health monitoring of large-range infrastructure, geological disaster prewarning and other applications. To conclude, we discuss several challenges and prospects in the future development of BOTDRs.

No abstract

No abstract

Disturbance rejection performance for rolling hydraulic position control system has always been a knotty issue. To guarantee the transient performance and improve disturbance rejection performance of the rolling hydraulic position control system, a compound controller, composed of a feedforward controller part based on proportional integral laws and a compensation part based on disturbance observer, is designed and investigated. In this article, a detailed analysis and design principles of the composite controller are provided. Additionally, stability analysis of the controller is proved using Lyapunov function adapted to the system. Finally, a rigorous analysis of the disturbance rejection performance is given with consideration of both instantaneous disturbances and low-frequency disturbances. For single pulse disturbance, the maximum error is reduced from 3.5% to 0.6%. Furthermore, for more complicated disturbance, sinusoidal disturbance is lower than 50 Hz, disturbance rejection performance decreases with increasing frequency and maximum error is reduced from 5.4% to 1.6%. The test results demonstrate that for single pulse disturbance, the maximum error is reduced from 4.12% to 0.64%. Furthermore, for more complicated disturbance, sinusoidal disturbance is lower than 50 Hz, disturbance rejection performance decreases with increasing frequency and maximum error is reduced from 2.71% to 0.70%. Both simulation and experiment results demonstrate that the proposed method possesses a better disturbance rejection performance than the proportional integral method.

No abstract