The principle of an optical method of photocathode processing control, which is one ofphotocathode processing monitoring techniques, is discussed. A designed monitoring apparatus is describedand has been applied to in...The principle of an optical method of photocathode processing control, which is one ofphotocathode processing monitoring techniques, is discussed. A designed monitoring apparatus is describedand has been applied to investigate the optical parameters of multialkali photoemitter during the process offabrication. Some actual schemes using the method to monitor the preparation of photocathodεs are sug-gested.展开更多
Many theoretical studies have been developed to study the spectral response of a fiber Bragg grating (FBG) under non-uniform strain distribution along the length of FBG in recent years. However, almost no experiments ...Many theoretical studies have been developed to study the spectral response of a fiber Bragg grating (FBG) under non-uniform strain distribution along the length of FBG in recent years. However, almost no experiments were designed to obtain the evolution of the spectrum when a FBG is subjected to non-uniform strain. In this paper, the spectral responses of a FBG under non-uniform strain distributions are given and a numerical simulation based on the Runge-Kutta method is introduced to investigate the responses of the FBG under some typical non-uniform transverse strain fields, including both linear strain gradient and quadratic strain field. Experiment is carried out by using loads applied at different locations near the FBG. Good agreements between experimental results and numerical simulations are obtained.展开更多
Partial discharge(PD)detection is considered one of the most crucial and effective methods for identifying defects in electrical equipment.Consequently,investigating advanced and efficient PD monitoring techniques is ...Partial discharge(PD)detection is considered one of the most crucial and effective methods for identifying defects in electrical equipment.Consequently,investigating advanced and efficient PD monitoring techniques is essential for the development of gas-insulated equipment(GIE)and the construction of ultra-high-voltage(UHV)networks.This paper first explores the causes and impact characteristics of various defects in GIE based on experimental results and simulation analysis.It then reviews current research on advanced PD measurement techniques,integrating acoustic,chemical and optical methods.The findings preliminarily demonstrate the unique advantages and applicability of the advanced methods for complex detection environments.Finally,this paper ad-dresses the technical challenges and potential breakthroughs associated with these detection techniques.In this regard,this study aims to provide technical insights and research directions for defect detection techniques in UHV GIE.展开更多
GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point...GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point optical monitoring method.展开更多
相较于传统沉船整体打捞工法,矩形曲线顶管底幕法具有施工周期短和对沉船损害小的优势.为了在沉船打捞过程中实时获取曲线顶管底幕法主要构件(顶梁、端板和管节)的位移,引入光频域反射计(optical frequency domain reflectometer,OFDR)...相较于传统沉船整体打捞工法,矩形曲线顶管底幕法具有施工周期短和对沉船损害小的优势.为了在沉船打捞过程中实时获取曲线顶管底幕法主要构件(顶梁、端板和管节)的位移,引入光频域反射计(optical frequency domain reflectometer,OFDR)光纤传感技术,推导了基于光纤监测应变的位移计算式.对顶梁、端板和管节分别布设光纤进行应变监测并计算其在施工过程中的位移.研究结果表明:在顶梁-端板框架沉放过程中,由于两侧顶梁受力不均,其沿竖向的变形模式有所差异,而端板所受影响较小,侧向位移最大值不超过0.3mm;在管节推进过程中,侧向位移和径向收敛位移趋势整体相似,均未超过1mm,端板和顶梁变形小于沉放阶段.该研究成果以期为光纤传感技术在地下工程结构物应变和位移监测的应用中提供技术基础和案例参考.展开更多
As a fiber sensor, optical time domain L reflectometer becomes more and more popular to measure parameters, such as strain and temperature in structural health monitoring （SHM） simultaneously. Since the accuracy of...As a fiber sensor, optical time domain L reflectometer becomes more and more popular to measure parameters, such as strain and temperature in structural health monitoring （SHM） simultaneously. Since the accuracy of range resolution in optical time domain reflectometer （OTDR） is determined by the pulse width of laser, the range resolution in order of centimeter is achieved by employing of picoseconds lasers which are not commercial. In this paper, to achieve this accuracy with conventional OTDR, Fourier wavelet regularized deconvolution （ForWaRD） method is employed to deconvolve and denoise the detected signal simultaneously. Simulations show that this method improves resolution of conventional OTDR system to the order of several centimeters.展开更多
Geotechnical engineering is characterized by many uncertainties,including soil material properties,environmental effects,and engineering design and construction,which bring a significant challenge to geotechnical moni...Geotechnical engineering is characterized by many uncertainties,including soil material properties,environmental effects,and engineering design and construction,which bring a significant challenge to geotechnical monitoring.However,conventional sensors with several inherent limitations,such as electromagnetic interference,signal loss in long-distance transmission,and low durability in harsh environments cannot fully meet current monitoring needs.Recently,fiber optic sensing technologies have been successfully applied in geotechnical monitoring due to the significant advantages of anti-electromagnetic interference,stable signal long-distance transmission,high durability,high sensitivity,and lightweight,which can be considered an ideal replacement for conventional sensors.In this paper,the working principle of different fiber optic sensing technologies,the development of fiber optic-based sensors,and the recent application status of these sensing technologies for geotechnical monitoring were comprehensively reviewed and discussed in detail.Finally,the challenges and countermeasures of the sensing technologies in geotechnical monitoring were also presented and discussed.展开更多
文摘The principle of an optical method of photocathode processing control, which is one ofphotocathode processing monitoring techniques, is discussed. A designed monitoring apparatus is describedand has been applied to investigate the optical parameters of multialkali photoemitter during the process offabrication. Some actual schemes using the method to monitor the preparation of photocathodεs are sug-gested.
基金supported by the National High Technology Research and Development Program of China (No.2007AA03Z117)the Key Program of National Natural Science Foundation of China (No.50830201)
文摘Many theoretical studies have been developed to study the spectral response of a fiber Bragg grating (FBG) under non-uniform strain distribution along the length of FBG in recent years. However, almost no experiments were designed to obtain the evolution of the spectrum when a FBG is subjected to non-uniform strain. In this paper, the spectral responses of a FBG under non-uniform strain distributions are given and a numerical simulation based on the Runge-Kutta method is introduced to investigate the responses of the FBG under some typical non-uniform transverse strain fields, including both linear strain gradient and quadratic strain field. Experiment is carried out by using loads applied at different locations near the FBG. Good agreements between experimental results and numerical simulations are obtained.
基金Natural Science Foundation of Beijing,Grant/Award Number:3244048National Natural Science Foundation of China,Grant/Award Number:52407175‘Chen Guang’project supported by the Shanghai Municipal Education Commission and the Shanghai Education Development Foundation,Grant/Award Number:21CGA63。
文摘Partial discharge(PD)detection is considered one of the most crucial and effective methods for identifying defects in electrical equipment.Consequently,investigating advanced and efficient PD monitoring techniques is essential for the development of gas-insulated equipment(GIE)and the construction of ultra-high-voltage(UHV)networks.This paper first explores the causes and impact characteristics of various defects in GIE based on experimental results and simulation analysis.It then reviews current research on advanced PD measurement techniques,integrating acoustic,chemical and optical methods.The findings preliminarily demonstrate the unique advantages and applicability of the advanced methods for complex detection environments.Finally,this paper ad-dresses the technical challenges and potential breakthroughs associated with these detection techniques.In this regard,this study aims to provide technical insights and research directions for defect detection techniques in UHV GIE.
文摘GFFs with less than 0.4 dB peak-to-peak error functions are routinely fabricated using commercially available coating machines by utilizing the natural error compensation mechanism of wavelength variable turning point optical monitoring method.
文摘相较于传统沉船整体打捞工法,矩形曲线顶管底幕法具有施工周期短和对沉船损害小的优势.为了在沉船打捞过程中实时获取曲线顶管底幕法主要构件(顶梁、端板和管节)的位移,引入光频域反射计(optical frequency domain reflectometer,OFDR)光纤传感技术,推导了基于光纤监测应变的位移计算式.对顶梁、端板和管节分别布设光纤进行应变监测并计算其在施工过程中的位移.研究结果表明:在顶梁-端板框架沉放过程中,由于两侧顶梁受力不均,其沿竖向的变形模式有所差异,而端板所受影响较小,侧向位移最大值不超过0.3mm;在管节推进过程中,侧向位移和径向收敛位移趋势整体相似,均未超过1mm,端板和顶梁变形小于沉放阶段.该研究成果以期为光纤传感技术在地下工程结构物应变和位移监测的应用中提供技术基础和案例参考.
文摘As a fiber sensor, optical time domain L reflectometer becomes more and more popular to measure parameters, such as strain and temperature in structural health monitoring （SHM） simultaneously. Since the accuracy of range resolution in optical time domain reflectometer （OTDR） is determined by the pulse width of laser, the range resolution in order of centimeter is achieved by employing of picoseconds lasers which are not commercial. In this paper, to achieve this accuracy with conventional OTDR, Fourier wavelet regularized deconvolution （ForWaRD） method is employed to deconvolve and denoise the detected signal simultaneously. Simulations show that this method improves resolution of conventional OTDR system to the order of several centimeters.
基金funded by the National Natural Science Foundation of China(grant no.52122805,52078103,42225702).
文摘Geotechnical engineering is characterized by many uncertainties,including soil material properties,environmental effects,and engineering design and construction,which bring a significant challenge to geotechnical monitoring.However,conventional sensors with several inherent limitations,such as electromagnetic interference,signal loss in long-distance transmission,and low durability in harsh environments cannot fully meet current monitoring needs.Recently,fiber optic sensing technologies have been successfully applied in geotechnical monitoring due to the significant advantages of anti-electromagnetic interference,stable signal long-distance transmission,high durability,high sensitivity,and lightweight,which can be considered an ideal replacement for conventional sensors.In this paper,the working principle of different fiber optic sensing technologies,the development of fiber optic-based sensors,and the recent application status of these sensing technologies for geotechnical monitoring were comprehensively reviewed and discussed in detail.Finally,the challenges and countermeasures of the sensing technologies in geotechnical monitoring were also presented and discussed.
