The success of any perimeter intrusion detection system depends on three important performance parameters： the probability of detection （POD）, the nuisance alarm rate （NAR）, and the false alarm rate （FAR）. The ...The success of any perimeter intrusion detection system depends on three important performance parameters： the probability of detection （POD）, the nuisance alarm rate （NAR）, and the false alarm rate （FAR）. The most fundamental parameter, POD, is normally related to a number of factors such as the event of interest, the sensitivity of the sensor, the installation quality of the system, and the reliability of the sensing equipment. The suppression of nuisance alarms without degrading sensitivity in fiber optic intrusion detection systems is key to maintaining acceptable performance. Signal processing algorithms that maintain the POD and eliminate nuisance alarms are crucial for achieving this. In this paper, a robust event classification system using supervised neural networks together with a level crossings （LCs） based feature extraction algorithm is presented for the detection and recognition of intrusion and non-intrusion events in a fence-based fiber-optic intrusion detection system. A level crossings algorithm is also used with a dynamic threshold to suppress torrential rain-induced nuisance alarms in a fence system. Results show that rain-induced nuisance alarms can be suppressed for rainfall rates in excess of 100mm/hr with the simultaneous detection of intrusion events. The use of a level crossing based detection and novel classification algorithm is also presented for a buried pipeline fiber optic intrusion detection system for the suppression of nuisance events and discrimination of intrusion events. The sensor employed for both types of systems is a distributed bidirectional fiber-optic Mach-Zehnder （MZ） interferometer.展开更多
Fiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspec...Fiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. The recent progress of FOH is introduced from five aspects, including large-scale FOH array, very-low-frequency detection, fiber-optic vector hydrophone (FOVH), towed linear array, and deep-sea and long-haul transmission. The above five aspects indicate the future development trends in the FOH research field, and they also provide a guideline for the practical applications of FOH as well as its array.展开更多
Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points alo...Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points along the length of a single fiber.Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of' crack locations,Labora- tory experiments on plain concrete beams and post-tensioned FRP tendons were pcrlormed to evaluate the crack detection capability of the sensor system.The acoustic emission sensor was able to detect initiation,growth and location of the cracks in concrete as well as in the FRP tendons.The AE system is potentially suitable lot applications involving health monitoring of structures following an earthquake.展开更多
In this paper, we review our researches on the topics of the structural health monitoring （SHM） with the fiber-optic distributed strain sensor. Highly-dense information on strains in a structure can be useful to ide...In this paper, we review our researches on the topics of the structural health monitoring （SHM） with the fiber-optic distributed strain sensor. Highly-dense information on strains in a structure can be useful to identify some kind of existing damages or applied loads in implementation of SHM. The fiber-optic distributed sensors developed by the authors have been applied to the damage detection of a single-lap joint and load identification of a beam simply supported. We confirmed that the applicability of the distributed sensor to SHM could be improved as making the spatial resolution higher. In addition, we showed that the simulation technique considering both structural and optical effects seamlessly in strain measurement could be powerful tools to evaluate the performance of a sensing system and design it for SHM. Finally, the technique for simultaneous distributed strain and temperature measurement using the PANDA-fiber Bragg grating （FBG） is shown in this paper, because problems caused by the cross-sensitivity toward strain and temperature would be always inevitable in strain measurement for SHM.展开更多
Railroad condition monitoring is paramount due to frequent passage through densely populated regions.This significance arises from the potential consequences of accidents such as train derailments,hazardous materials ...Railroad condition monitoring is paramount due to frequent passage through densely populated regions.This significance arises from the potential consequences of accidents such as train derailments,hazardous materials leaks,or collisions which may have far-reaching impacts on communities and the surrounding areas.As a solution to this issue,the use of distributed acoustic sensing(DAS)-fiber optic cables along railroads provides a feasible tool for monitoring the health of these extended infrastructures.Nevertheless,analyzing DAS data to assess railroad health or detect potential damage is a challenging task.Due to the large amount of data generated by DAS,as well as the unstructured patterns and substantial noise present,traditional analysis methods are ineffective in interpreting this data.This paper introduces a novel approach that harnesses the power of deep learning through a combination of CNNs and LSTMs,augmented by sliding window techniques(CNN-LSTM-SW),to advance the state-of-the-art in the railroad condition monitoring system.As well as it presents the potential for DAS and fiber optic sensing technologies to revolutionize the proposed CNN-LSTM-SW model to detect conditions along the rail track networks.Extracting insights from the data of High tonnage load(HTL)-a 4.16 km fiber optic and DAS setup,we were able to distinguish train position,normal condition,and abnormal conditions along the railroad.Notably,our investigation demonstrated that the proposed approaches could serve as efficient techniques for processing DAS signals and detecting the condition of railroad infrastructures at any remote distance with DAS-Fiber optic cable setup.Moreover,in terms of pinpointing the train's position,the CNN-LSTM architecture showcased an impressive 97%detection rate.Applying a sliding window,the CNN-LSTM labeled data,the remaining 3%of misclassified labels have been improved dramatically by predicting the exact locations of each type of condition.Altogether,these proposed models exhibit promising potential for accu展开更多
In the realm of acoustic signal detection,the identification of weak signals,particularly in the presence of negative signal-to-noise ratios,poses a significant challenge.This challenge is further heightened when sign...In the realm of acoustic signal detection,the identification of weak signals,particularly in the presence of negative signal-to-noise ratios,poses a significant challenge.This challenge is further heightened when signals are acquired through fiber-optic hydrophones,as these signals often lack physical significance and resist clear systematic modeling.Conventional processing methods,e.g.,low-pass filter(LPF),require a thorough understanding of the effective signal bandwidth for noise reduction,and may introduce undesirable time lags.This paper introduces an innovative feedback control method with dual Kalman filters for the demodulation of phase signals with noises in fiber-optic hydrophones.A mathematical model of the closed-loop system is established to guide the design of the feedback control,aiming to achieve a balance with the input phase signal.The dual Kalman filters are instrumental in mitigating the effects of signal noise,observation noise,and control execution noise,thereby enabling precise estimation for the input phase signals.The effectiveness of this feedback control method is demonstrated through examples,showcasing the restoration of low-noise signals,negative signal-to-noise ratio signals,and multi-frequency signals.This research contributes to the technical advancement of high-performance devices,including fiber-optic hydrophones and phase-locked amplifiers.展开更多
The spatial resolution of conventional distributed fiber optic sensors is 1 m at best, which is inadequate to locate the damage precisely. We adopt an improved sensing technique based on the Brillouin optical time-dom...The spatial resolution of conventional distributed fiber optic sensors is 1 m at best, which is inadequate to locate the damage precisely. We adopt an improved sensing technique based on the Brillouin optical time-domain analysis （BOTDA）. The stepped pump light is input to stimulate the phonon so that the spatial resolution can be increased to centimeter order and the strain accuracy of 25 micro-strains is obtained. The feasibility of this sensing technique is demonstrated through strain measurement of three concrete box-girders in bending. Experimental results show that the improved BOTDA measurement can provide a comprehensive description on the strain distribution of steel rebar or concrete. Compared with the conventional strain gauges, the improved BOTDA measurement is more stable. By virtue of higher spatial resolution and better measurement accuracy, it has become possible to perform crack detection and localization for concrete structures.展开更多
In view of the poor scale factor stability of the interferometric fiber optic gyroscope(IFOG),it is a creative method to use laser to drive the IFOG for its better frequency stabilization characteristics instead of th...In view of the poor scale factor stability of the interferometric fiber optic gyroscope(IFOG),it is a creative method to use laser to drive the IFOG for its better frequency stabilization characteristics instead of the broadband light source.As the linewidth of laser is narrow,the errors of coherent backscattering,polarization coupling,and Kerr effect are reintroduced which cause more noise and drift.This paper studies laser spectrum broadening based on external phase modulation of Gaussian white noise(GWN).The theoretical analysis and test results indicate that this method has a good effect on spectrum broadening and can be used to improve the performance of the laser-driven IFOG.In the established closed-loop IFOG,a four-state modulation(FSM)is adopted to avoid temperature instability of the multifunction integrated-optic chip(MIOC)and drift caused by the electronic circuit in demodulation.The experimental results show that the IFOG driven by broadened laser has the angular random walk noise of 0.0038°/√h and the drift of 0.017°/h,which are 62%and 66%better than those without modulation respectively,of which the drift has reached the level of the broadband light source.Although the noise still needs further reduction,its scale factor stability is 0.38 ppm,which has an overwhelming advantage compared with the traditional IFOG.展开更多
Based on the transverse electro-optic effect of lithium niobate crystal,combined with polarizers and Faraday rotator,this paper presents a collinear closed-loop fiber optic current transformer with spatial non-recipro...Based on the transverse electro-optic effect of lithium niobate crystal,combined with polarizers and Faraday rotator,this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method,and the feasibility of the scheme is verified by both the theoretical and experimental evidences.The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency,improves the sensitivity and stability of the system,and reduces the volume and cost of fiber optic current transformer.The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect,which enhances the signal to noise ratio and simplifies demodulation mode.The experimental results show that the current ratio errors measured at room temperature range from 1%to 120%of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S.The temperature stability of the current transformer is also tested,and the ratio error measured at the rated current does not exceed±0.2%in the range of-30℃to 50℃.展开更多
The micro-cantilever beam with a twin long period optic fiber grating sensitive to the strain and the vibration is designed to use as the sensor head.The micro-displacement of wavelength caused by strain or vibration ...The micro-cantilever beam with a twin long period optic fiber grating sensitive to the strain and the vibration is designed to use as the sensor head.The micro-displacement of wavelength caused by strain or vibration is amplified in the system.Special cladding material is used to eliminate the interference brougth about the temperature.The designing structure is enabled to detect the micro-information.展开更多
文摘The success of any perimeter intrusion detection system depends on three important performance parameters： the probability of detection （POD）, the nuisance alarm rate （NAR）, and the false alarm rate （FAR）. The most fundamental parameter, POD, is normally related to a number of factors such as the event of interest, the sensitivity of the sensor, the installation quality of the system, and the reliability of the sensing equipment. The suppression of nuisance alarms without degrading sensitivity in fiber optic intrusion detection systems is key to maintaining acceptable performance. Signal processing algorithms that maintain the POD and eliminate nuisance alarms are crucial for achieving this. In this paper, a robust event classification system using supervised neural networks together with a level crossings （LCs） based feature extraction algorithm is presented for the detection and recognition of intrusion and non-intrusion events in a fence-based fiber-optic intrusion detection system. A level crossings algorithm is also used with a dynamic threshold to suppress torrential rain-induced nuisance alarms in a fence system. Results show that rain-induced nuisance alarms can be suppressed for rainfall rates in excess of 100mm/hr with the simultaneous detection of intrusion events. The use of a level crossing based detection and novel classification algorithm is also presented for a buried pipeline fiber optic intrusion detection system for the suppression of nuisance events and discrimination of intrusion events. The sensor employed for both types of systems is a distributed bidirectional fiber-optic Mach-Zehnder （MZ） interferometer.
基金The authors would like to acknowledge the support of the National Natural Science Foundation of China(Grant Nos.61775238,61705263,and 61705262).
文摘Fiber-optic hydrophone (FOH) is a significant type of acoustic sensor, which can be used in both military and civilian fields such as underwater target detection, oil and natural gas prospecting, and earthquake inspection. The recent progress of FOH is introduced from five aspects, including large-scale FOH array, very-low-frequency detection, fiber-optic vector hydrophone (FOVH), towed linear array, and deep-sea and long-haul transmission. The above five aspects indicate the future development trends in the FOH research field, and they also provide a guideline for the practical applications of FOH as well as its array.
基金National Science Foundation,Grant number CMS-9900338
文摘Development and testing of a serially multiplexed fiber optic sensor system is described.The sensor differs from conventional fiber optic acoustic systems,as it is capable of sensing AE emissions at several points along the length of a single fiber.Multiplexing provides for single channel detection of cracks and their locations in large structural systems. An algorithm was developed for signal recognition and tagging of the AE waveforms for detection of' crack locations,Labora- tory experiments on plain concrete beams and post-tensioned FRP tendons were pcrlormed to evaluate the crack detection capability of the sensor system.The acoustic emission sensor was able to detect initiation,growth and location of the cracks in concrete as well as in the FRP tendons.The AE system is potentially suitable lot applications involving health monitoring of structures following an earthquake.
文摘In this paper, we review our researches on the topics of the structural health monitoring （SHM） with the fiber-optic distributed strain sensor. Highly-dense information on strains in a structure can be useful to identify some kind of existing damages or applied loads in implementation of SHM. The fiber-optic distributed sensors developed by the authors have been applied to the damage detection of a single-lap joint and load identification of a beam simply supported. We confirmed that the applicability of the distributed sensor to SHM could be improved as making the spatial resolution higher. In addition, we showed that the simulation technique considering both structural and optical effects seamlessly in strain measurement could be powerful tools to evaluate the performance of a sensing system and design it for SHM. Finally, the technique for simultaneous distributed strain and temperature measurement using the PANDA-fiber Bragg grating （FBG） is shown in this paper, because problems caused by the cross-sensitivity toward strain and temperature would be always inevitable in strain measurement for SHM.
基金supported by funding from The Association of American Railroads(AAR)-MxV Rail(Award number:21-0825-007538)Impact Area Accelerator Award Grant 2023 from Georgia Southern University's Office of Research.
文摘Railroad condition monitoring is paramount due to frequent passage through densely populated regions.This significance arises from the potential consequences of accidents such as train derailments,hazardous materials leaks,or collisions which may have far-reaching impacts on communities and the surrounding areas.As a solution to this issue,the use of distributed acoustic sensing(DAS)-fiber optic cables along railroads provides a feasible tool for monitoring the health of these extended infrastructures.Nevertheless,analyzing DAS data to assess railroad health or detect potential damage is a challenging task.Due to the large amount of data generated by DAS,as well as the unstructured patterns and substantial noise present,traditional analysis methods are ineffective in interpreting this data.This paper introduces a novel approach that harnesses the power of deep learning through a combination of CNNs and LSTMs,augmented by sliding window techniques(CNN-LSTM-SW),to advance the state-of-the-art in the railroad condition monitoring system.As well as it presents the potential for DAS and fiber optic sensing technologies to revolutionize the proposed CNN-LSTM-SW model to detect conditions along the rail track networks.Extracting insights from the data of High tonnage load(HTL)-a 4.16 km fiber optic and DAS setup,we were able to distinguish train position,normal condition,and abnormal conditions along the railroad.Notably,our investigation demonstrated that the proposed approaches could serve as efficient techniques for processing DAS signals and detecting the condition of railroad infrastructures at any remote distance with DAS-Fiber optic cable setup.Moreover,in terms of pinpointing the train's position,the CNN-LSTM architecture showcased an impressive 97%detection rate.Applying a sliding window,the CNN-LSTM labeled data,the remaining 3%of misclassified labels have been improved dramatically by predicting the exact locations of each type of condition.Altogether,these proposed models exhibit promising potential for accu
基金Project supported by the National Key Research and Development Program of China(No.2022YFB3203600)the National Natural Science Foundation of China(Nos.12172323,12132013+1 种基金12332003)the Zhejiang Provincial Natural Science Foundation of China(No.LZ22A020003)。
文摘In the realm of acoustic signal detection,the identification of weak signals,particularly in the presence of negative signal-to-noise ratios,poses a significant challenge.This challenge is further heightened when signals are acquired through fiber-optic hydrophones,as these signals often lack physical significance and resist clear systematic modeling.Conventional processing methods,e.g.,low-pass filter(LPF),require a thorough understanding of the effective signal bandwidth for noise reduction,and may introduce undesirable time lags.This paper introduces an innovative feedback control method with dual Kalman filters for the demodulation of phase signals with noises in fiber-optic hydrophones.A mathematical model of the closed-loop system is established to guide the design of the feedback control,aiming to achieve a balance with the input phase signal.The dual Kalman filters are instrumental in mitigating the effects of signal noise,observation noise,and control execution noise,thereby enabling precise estimation for the input phase signals.The effectiveness of this feedback control method is demonstrated through examples,showcasing the restoration of low-noise signals,negative signal-to-noise ratio signals,and multi-frequency signals.This research contributes to the technical advancement of high-performance devices,including fiber-optic hydrophones and phase-locked amplifiers.
基金supported by the National Natural Science Foundation of China (Nos.50725828 and 50608017)the Sustentation Fund for Young Teachers of Southeast University
文摘The spatial resolution of conventional distributed fiber optic sensors is 1 m at best, which is inadequate to locate the damage precisely. We adopt an improved sensing technique based on the Brillouin optical time-domain analysis （BOTDA）. The stepped pump light is input to stimulate the phonon so that the spatial resolution can be increased to centimeter order and the strain accuracy of 25 micro-strains is obtained. The feasibility of this sensing technique is demonstrated through strain measurement of three concrete box-girders in bending. Experimental results show that the improved BOTDA measurement can provide a comprehensive description on the strain distribution of steel rebar or concrete. Compared with the conventional strain gauges, the improved BOTDA measurement is more stable. By virtue of higher spatial resolution and better measurement accuracy, it has become possible to perform crack detection and localization for concrete structures.
文摘In view of the poor scale factor stability of the interferometric fiber optic gyroscope(IFOG),it is a creative method to use laser to drive the IFOG for its better frequency stabilization characteristics instead of the broadband light source.As the linewidth of laser is narrow,the errors of coherent backscattering,polarization coupling,and Kerr effect are reintroduced which cause more noise and drift.This paper studies laser spectrum broadening based on external phase modulation of Gaussian white noise(GWN).The theoretical analysis and test results indicate that this method has a good effect on spectrum broadening and can be used to improve the performance of the laser-driven IFOG.In the established closed-loop IFOG,a four-state modulation(FSM)is adopted to avoid temperature instability of the multifunction integrated-optic chip(MIOC)and drift caused by the electronic circuit in demodulation.The experimental results show that the IFOG driven by broadened laser has the angular random walk noise of 0.0038°/√h and the drift of 0.017°/h,which are 62%and 66%better than those without modulation respectively,of which the drift has reached the level of the broadband light source.Although the noise still needs further reduction,its scale factor stability is 0.38 ppm,which has an overwhelming advantage compared with the traditional IFOG.
基金This work was supported by the National Natural Science Foundation of China(Grant No.61735011)the Science and the Key Research and Development Program of Hebei Province(Grant No.19251703D)the Local Science and Technology Development Projects of the Central Committee(Grant No.19941708G).
文摘Based on the transverse electro-optic effect of lithium niobate crystal,combined with polarizers and Faraday rotator,this paper presents a collinear closed-loop fiber optic current transformer with spatial non-reciprocity modulation method,and the feasibility of the scheme is verified by both the theoretical and experimental evidences.The detection scheme avoids the limitation of the transition time of the sensing fiber coil on the phase modulation frequency,improves the sensitivity and stability of the system,and reduces the volume and cost of fiber optic current transformer.The sawtooth wave modulation scheme is adopted to realize phase bias modulation and feedback modulation through phase shift of sawtooth wave to achieve closed-loop detection effect,which enhances the signal to noise ratio and simplifies demodulation mode.The experimental results show that the current ratio errors measured at room temperature range from 1%to 120%of rated current meet the requirements of national standard GB/T 20840.8-2007 and reach the accuracy level of 0.2S.The temperature stability of the current transformer is also tested,and the ratio error measured at the rated current does not exceed±0.2%in the range of-30℃to 50℃.
文摘The micro-cantilever beam with a twin long period optic fiber grating sensitive to the strain and the vibration is designed to use as the sensor head.The micro-displacement of wavelength caused by strain or vibration is amplified in the system.Special cladding material is used to eliminate the interference brougth about the temperature.The designing structure is enabled to detect the micro-information.
