The most critical step in a line-structured light three-dimensional scan modeling system is to extract the centerline of the light stripe, but the interference of various environmental factors makes this extraction difficult. Several problems exists in a line-structured light streak image issues such as light spot interference, uneven distribution of light intensity, large differences in the width of the light bars, and complex background. This paper proposed a solution to overcome these problems. First, the structured light image is binarized using the Otsu method. Then, the improved density-based spatial clustering of applications with nose (DBSCAN) algorithm is used to retain the core points and remove the boundary and noise points. Finally, the core points are used as inputs to construct the graph data structure, and the shortest path search algorithm that fits the line-structured light streak image is used to obtain the center-line of the light streak. The experimental results show that the algorithm of this paper runs within 150 ms and the error is within 0.2 pixels. Moreover, this algorithm is applicable to various complex environments, meeting the requirements of real-time calculations, accuracy, and stability.

The probability of power transformer failure is extremely low, which leads to a great impact on further in-depth analysis results due to unbalanced data when processing transformer fault data. To solve these problems, this study processes and judges the unbalanced data using an confrontation neural network combined with an artificial neural network, uses the distributed acoustic wave sensing technology based on ultraweak fiber Bragg gratings to collect and analyze the data of the simulation site of the transformer built in a laboratory, and achieves good results on the collected transformer fault simulation data. This method has an important referential significance for developing the small sample fault identification system of the on-load transformer using confrontation generation network.

This paper proposes an artificial neural network-based fault detection and prediction model for on-load transformers using distributed fiber optic sensing technology. By artificially simulating the fault and normal operating states of transformers and using the k-means synthetic minority oversampling technique data expansion method, a small number of fault datasets can be limitedly expanded so that the amount of fault data can be consistent with that of normal data. Therefore, the expanded fault data and normal operation data can be input into the convolutional neural networks long short term memory identification model. Finally, the fault recognition rate can be increased to 100%, which has significant implications for the development of fault recognition systems for on-load transformers based on distributed fiber optic sensing technology.

Optical fiber microseismic monitoring technology is used to monitor and alert the microvibration events generated during production activities through observation and analysis with passivity and high reliability. Herein, the sensors are vertically installed on the side bolts along the roadway, and the monitoring substation is installed in the chamber. The sensors and the monitoring substation constitute a monitoring network through the laid optical cables. Besides, the simplex method is used to locate the seismic source. This method is free from divergence problems in the location calculation and is highly stable. Moreover, in this method, the solution of the partial derivative and inverse matrix is not required, which reduces the calculation amount and improves the calculation efficiency. Additionally, each sensor can use different wave velocities during the calculation based on the actual situation. The optical fiber microseismic monitoring system was installed in Shanxi Wuyang Coal Mine for preliminary monitoring and application, and the monitoring results were analyzed. The results show that the system can monitor mine activities and warn early, thereby playing a positive role in safe production.

Aiming to resolve the deficiencies of low accuracy and poor anti-interference ability of traditional thermal pipeline-leakage detection methods,an distributed optical-fiber temperature-measurement system combined with the pipeline-leakage model is adopted herein to measure the temperature field along the thermal pipeline.When the leakage occurs, hot water or steam in the pipeline will flow out and change the temperature field around the leakage point, and the system can rapidly catch the temperature change and locate the leakage. The experimental results show that the temperature accuracy,which is the error between the measuring temperature value and the true value, is within ±1 ℃ and the spatial resolution is no more than 2 m.The system has been successfully applied to the thermal pipeline of the Jining Canal Power Plant, accurately measured the temperature variation along a 15 km thermal pipeline and precisely alerted a leakage, indicating that the distributed optical-fiber temperature-measurement system has a broad application prospect in the field of thermal pipeline-leakage monitoring.

To meet the application requirements of real-time carbon dioxide (CO₂)-gas online monitoring, this paper proposes an online detection system for the CO₂ gas based on tunable diode laser absorption spectroscopy according to the theory of Beer-Lambert law. The selected absorption spectrum wavelength of the system is 1 609.583 nm. Futher, two reference optical paths are built to eliminate the signal fluctuation of the light source and automatically detect the absorption peak to improve the stability and accuracy of the detection system. The calibration of the system shows that the relative measurement error of the system is less than 0.8%, the system repeatability is less than 0.06%, and the response time is less than or equal to 18 s. Continuous monitoring of CO₂ in the air for 4 h shows that the fluctuation range of the volume fraction measurement is 360×10^-6 to 400×10^-6. The system has good stability and reliability and can meet the application requirements of real-time CO₂ gas online monitoring.

A double fiber Bragg grating (FBG) flow-velocity sensor is designed for measuring the flow velocity. The sensor mainly comprises shell, FBG measuring module, and fixture. The sensitivity and dynamic range are tested, and the influence of different temperature and pressure on the performance of the sensor is analyzed. The sensitivity of the fiber-optic flow sensor is 76 mm/s, and the flow velocity is measured in the range of 0 to 1.2 m/s. The sensor is insensitive to temperature and ambient pressure and can meet the needs of flow-velocity measurement in the fields of the exploitation and transportation of oil and gas as well as the oceans and rivers.

To improve the energy conversion efficiency of electromagnetic acoustic transducers (EMATs), the coil backplane of the EMAT is optimized. First, the influence of the coil backplane thickness on ultrasonic signals is evaluated via experimental research. Then, the carbonyl iron powder plate is selected as the coil backplane and its influence on the magnetic field of the sensor working area is analyzed via finite element simulation. Finally, the performance of EMATs before and after optimization is compared using experiments. Results show that the optimal thickness of the coil backplane is 1.5~2.0 mm. Moreover, the use of the carbonyl iron powder plate with the same size as the coil working area of the coil backplane can improve the transduction efficiency of EMATs. Compared with the sensors that use nonmagnetic materials as coil backplanes, the SNR of the optimized sensors doubled and the working lift-off distance increased 1 mm, respectively.

In this study, a method for maintaining polarization- output of a distributed feedback fiber laser (DFB-FL) via polarization coupling method is proposed. DFB-FL is a type of narrow-line-width light source produced via phase shift grating etched on an active optical fiber. The grating formation process based on side exposure will induce the tangential index distribution polarization of the fiber, ensuring that the narrow-line-width laser exhibits single linear polarization characteristics. The output fiber of DFB-FL can be replaced with a polarization-maintaining fiber using the polarization-maintaining welding machine. During this process, the angle between the laser polarization direction and the slow axis of the polarization-maintaining fiber of DFB-FL can be adjusted by rotating the fiber. Moreover, the change in the laser power and polarization extinction ratio can be measured using a power meter and extinction ratio tester. When both the laser power and polarization extinction ratio are maximum, polarization coupling can be achieved between DFB-FL and the polarization-maintaining fiber. Results show that the polarization extinction ratio of the DFB-FL is greater than 30 dB and the polarization state is linearly polarized. Compared with the single-mode output fiber laser, the laser efficiency, line width, and noise of the polarization-maintaining output fiber laser show no significant changes.