Fiber Optic Acoustic Emission Research Articles

AE-IRMamba: Low-Complexity Inverted Residual Mamba for Identification of Piezoelectric Ceramic and Optical Fiber Acoustic Emission Sensors Signals

AE-IRMamba: Low-Complexity Inverted Residual Mamba for Identification of Piezoelectric Ceramic and Optical Fiber Acoustic Emission Sensors Signals

A Hybrid GAN-Inception Deep Learning Approach for Enhanced Coordinate-Based Acoustic Emission Source Localization

In this paper, we propose a novel approach to coordinate-based acoustic emission (AE) source localization to address the challenges of limited and imbalanced datasets from fiber-optic AE sensors used for structural health monitoring (SHM). We have developed a hybrid deep learning model combining four generative adversarial network (GAN) variants for data augmentation with an adapted inception neural network for regression-based prediction. The experimental setup features a single fiber-optic AE sensor based on a tightly coiled fiber-optic Fabry-Perot interferometer formed by two identical fiber Bragg gratings. AE signals were generated using the Hsu-Nielsen pencil lead break test on a grid-marked thin aluminum plate with 35 distinct locations, simulating real-world structural monitoring conditions in bounded isotropic plate-like structures. It is demonstrated that the single-sensor configuration can achieve precise localization, avoiding the need for a multiple sensor array. The GAN-based signal augmentation expanded the dataset from 900 to 4500 samples, with the Wasserstein distance between the original and synthetic datasets decreasing by 83% after 2000 training epochs, demonstrating the high fidelity of the synthetic data. Among the GAN variants, the standard GAN architecture proved the most effective, outperforming other variants in this specific application. The hybrid model exhibits superior performance compared to non-augmented deep learning approaches, with the median error distribution comparisons revealing a significant 50% reduction in prediction errors, accompanied by substantially improved consistency across various AE source locations. Overall, this developed hybrid approach offers a promising solution for enhancing AE-based SHM in complex infrastructures, improving damage detection accuracy and reliability for more efficient predictive maintenance strategies.

Acoustic emission and multiscale computation-guided tensile damage identification in woven composite laminates at cryogenic temperatures as low as 20 K

For laminated composite structures as key components of storage tanks serving at cryogenic temperature, it is crucial to identify the damage mechanisms for evaluating their mechanical properties and guiding structural design. In this work, the cryogenic tensile damage behavior of a thin-walled woven composite laminate was investigated through the acoustic emission (AE) monitoring and multiscale finite element (FE) computation at typical low temperatures of 153 K, 77 K and 20 K. We first established temperature-dependent constitutive laws for the microscale and mesoscale constituents of such composites based on experimental data, followed by the development of a hierarchical computational framework for modeling multiscale damage characteristics at different low temperatures. A fiber-optic acoustic emission measurement system was constructed to provide online monitoring of tensile damage of the woven composite laminates at cryogenic temperatures as low as 20 K. The comparations were made between the predicted cryogenic damage characteristics and in-situ AE signal analysis, assisted by scanning electron microscope (SEM) observations. The computed cryogenic damage evolution closely matched the AE signal identification results. The results indicate that fiber breakage and matrix cracking are the dominant cryogenic damage modes, and that the different low temperatures exert significant effects on the properties of the epoxy matrix, yarns and composite laminates. The combination of the AE monitoring system and the computational scheme provides a valuable tool for evaluating structural integrity and guiding the microstructural design of composite laminates used in cryogenic environments.

Cryogenic damage behavior of carbon fiber reinforced polymer composite laminates via fiber-optic acoustic emission

Cryogenic temperatures cause significant changes in the mechanical response and microscopic failure mechanisms of carbon fiber reinforced polymer (CFRP) composites. However, the mechanisms by which cryogenic temperatures affect composites are not yet fully understood due to a lack of adequate in-situ characterization techniques. Herein, the cryogenic damage evolution process of CFRP composites was investigated by constructed fiber-optic acoustic emission (AE) detection system. Tensile damage behavior of woven CFRP composites at 300 K, 153 K and 77 K was evaluated by AE characteristic response and cluster analysis combined with scanning electron microscopy. According to the results, increased damage activity within the composites at cryogenic condition promoted the release of mechanical energy, as well as an increase in the contribution of fiber damage to overall damage, which are the dominant micro-strengthening mechanisms of composite laminates under cryogenic conditions. This study provides a novel explanation for understanding the cryogenic damage behavior of composites.

Identification of Corrosion-Induced Optical Fiber Acoustic Emission Sensor Signals on the Bottom Plate of Oil Storage Tank Based on Multichannel Attention Mechanism (CBAM)

Identification of Corrosion-Induced Optical Fiber Acoustic Emission Sensor Signals on the Bottom Plate of Oil Storage Tank Based on Multichannel Attention Mechanism (CBAM)

Monitoring the fluidized bed reactor for polyethylene polymerization based on fibre optic acoustic emission sensor

AbstractThis paper presents applications of a new class of fibre optic acoustic emission (FOAE) sensor to monitor the operation of fluidized bed reactors used in polyethylene production. Specifically, the sensor was implemented to detect undesired, abnormal phenomena related to particle agglomeration, wall sheeting, fine overflow, and variations in the superficial gas velocity. The experiments were executed using a fluidized bed cold model setup for polyethylene powders with average particle sizes of 250, 1000, and 2000 μm. The results demonstrated that the presence of agglomerated particles in the fluidized bed reactor increases the kurtosis of the acoustic emission (AE) signal. Furthermore, the overflow of small particles can be detected by mounting the FOAE sensor below the gas distributor plate and monitoring an increase in the root mean square (RMS) of the AE signal. The AE signal RMS increased with the rising superficial gas velocity. Besides, forming a sheet layer on the reactor wall decreased the AE signal RMS. The proposed sensor's main benefits are its simple design, rapid response to abnormal conditions in the fluidized bed reactor, immunity against electromagnetic noise, high‐temperature resistance, and safety in hazardous areas.

Research on high precision optical fiber acoustic emission system for weak damage location on concrete

• Concrete weak AE location requires high detection accuracy of the system. • Random fiber laser enables the system to pick up weak AE waves on concrete. • Simulation and tests verify that the system can detect concrete AE wave reliably. • Random fiber laser and adaptive search strategy ensure a high location accuracy. • Accurate time difference of arrival can be used for a high precision AE location. A high precision optical fiber acoustic emission (AE) locating system with designed random fiber lasers (RFLs) and a proposed adaptive time of arrival extraction strategy for weak damage source location on concrete is proposed. The low frequency-noise and narrow linewidth of RFLs enable the system to obtain a high signal detection resolution of 8.32 × 10 −7 m/s within 500 kHz. Meanwhile, an adaptive threshold search strategy to optimize the onset time of the AE wave, thus maintaining small location errors from the perspective of improving the time difference of arrival (TDOA). Then, AE source localization is transformed into a genetic algorithm optimization process with TDOA as a parameter. The reliability of the RFL sensor in detecting weak pseudo-damage source signals from concrete is verified by simulation and experiment on a concrete slab with dimensions of 0.9 m × 0.9 m × 0.1 m. A total of 64 pseudo damage source location tests are performed at 16 random points on a concrete slab surface. The maximum axial location error of the system is 2.78%. The root mean square errors and standard deviations of the absolute errors are 2.8 cm and 9 mm, respectively. The accuracy and robustness of location are analyzed. Finally, the proposed system is used to locate the plane mapping points of concrete specimens cracked by crack water frost heaving, and the locating accuracy is 93.4%.

High-Sensitivity Demodulation of Fiber-Optic Acoustic Emission Sensor Using Self-Injection Locked Diode Laser

We demonstrate the use of a self-injection locked distributed feedback (DFB) diode laser for high-sensitivity detection of acoustic emission (AE) using a fiber-coil Fabry-Perot interferometer (FPI) sensor. The FPI AE sensor is formed by two weak fiber Bragg gratings on the ends of a long span of coiled fiber, resulting in dense sinusoidal fringes in its reflection spectrum that allows the use of a modified phase-generated carrier demodulation method. The demodulation method does not require agile tuning capability of the laser, which makes the self-injection locked laser particularly attractive for the application. Experimental results indicate that the self-injection locked laser increases the signal-to-noise ratio by ∼33 dB compared with the free-running DFB laser. We studied the mode-hopping and laser instability of the self-injection locked laser and their effect on the demodulated signal and found that a mode hopping event causes an abrupt change in the laser intensity after the resonator inside the feedback loop. It manifests itself as a short transient signal in the output of the AE sensor system. With the identification of the mode-hopping events, the associated spurious signal can be identified and discarded in the signal processing without causing significant disruption to the sensor system. Experiment shows that the frequency of locked lasers could oscillate during unstable operations. The fundamental frequency is determined by the time delay of the feedback light and is typically much larger than the AE frequency. Therefore, the laser frequency oscillations have no negative effect on the performance of the sensor system. Finally, we show that the frequency of mode-hopping occurrence is related to the length of the feedback loop and reducing the loop length can effectively reduce the frequency of mode-hopping occurrence.

DFB Fiber Laser Based on External Optical Feedback Theory Applied in Long-Distance Power Transformer Partial Discharge Detection

Active fiber optic acoustic emission (AE) sensors cause external optical feedback (EOF) in engineering applications, resulting in performance loss when used for long-distance partial discharge detection in power transformers. This work employs a distributed feedback fiber laser (DFB-FL) as a sensor to construct a partial discharge detection system. Furthermore, two schemes that improve the long-distance detection performance of DFB-FL are proposed by Suppressing EOF (S-EOF) and Introducing EOF (I-EOF). Then, partial discharge tests in an 80 kVA power transformer validate that both schemes can implement long-distance partial discharge detection. Experimental results indicate that the S-EOF system has a significant signal-to-noise ratio, which is 6.01 dB higher than the piezoelectric transducer (PZT). The S-EOF scheme is suitable for long-term online partial discharge monitoring. The I-EOF system has a high sensitivity for partial discharge detection, and its detectable discharge magnitude is lower than 65.8 pC. The I-EOF scheme is applicable for short-term systemic sampling and daily inspections.

DFB-FL Applied in the Liquid-Solid Composite Dielectric for Ultra-High Sensitive Partial Discharge Acoustic Emission Detection

The traditional fiber optic acoustic emission (AE) sensor, used to detect the partial discharge (PD) in the liquid-solid composite dielectric such as oil-immersed transformers, is not satisfactory in engineering applications due to the limitation of sensitivity and sensor size. This work proposes that the distributed feedback fiber laser (DFB-FL), benefiting from its tiny size and ultra-high sensitivity, is a better choice for PD AE detection. We build the PD AE detection system using erbium-ytterbium co-doped (Er-Yb-co-doped) DFB-FL, with suitable photoelectric components to design the demodulation system and intensity noise of DFB-FL as an index. Noise analysis shows that the average noise amplitude of the system is reduced by 91.67% after digital filtering technology and pump laser power regulation technology. We also use an 80 kVA oil-immersed transformer winding structure to construct a liquid-solid composite dielectric PD AE detection platform. Moreover, experiment results in different pump power show that the DFB-FL PD AE detection system can effectively detect the PD AE signal in the environment with sizeable acoustic impedance. The peak-to-peak value of its response is 31.36 times larger than the background noise and 637% higher than piezoelectric transducer sensors (PZT).

Intelligent Monitoring System Based on Optical Fiber Acoustic Emission Sensor and Its Application in Partial Discharge Diagnosis of Gas-insulated Switchgear

Intelligent Monitoring System Based on Optical Fiber Acoustic Emission Sensor and Its Application in Partial Discharge Diagnosis of Gas-insulated Switchgear

Research on High Precision Optical Fiber Acoustic Emission System for Weak Damage Location on Concrete

Research on High Precision Optical Fiber Acoustic Emission System for Weak Damage Location on Concrete

Practical results and prospects of using fiber optical sensors of acoustic emission for diagnosting the technical condition of aircraft units

Peripheral sensors for measuring aircraft parameters are an integral part of any system for diagnostics and forecasting of technical condition. Their principle of operation in relation to operation at aviation complexes is to convert mechanical, electromagnetic or light quantities into electrical ones for their subsequent processing. The process of radiation of disturbances propagating in the material caused by the dynamic local rearrangement of the structure of materials under the action of internal stresses leading to a change in the crystal lattice or the movement of micro- and / or macrodefects is called acoustic emission. So, the analysis of differences in the form of acoustic waves allows the classification of the type of deformation: crack or plastic deformation, which allows you to more accurately determine the current state of the airframe or diagnosed nodes. The principle of operation of such sensors is based on the effect of converting the linear dimensions of a Bragg cell, made on an optical fiber, into a change in the reflected wavelength. A necessary condition for obtaining correct results of measurements of stress states is the need for temperature compensation of the Bragg cells, which is achieved by introducing additional cells that are mechanically decoupled from the material being diagnosed and react only to the temperature component. The advantage of this method is the absence of the need for additional adjustment of the cells and their alignment, as well as the independence of measurements from the effects of electromagnetic radiation; the sensors are lightweight, vibration-resistant, and insensitive to electromagnetic fields. The article presents the practical results of using fiber-optic acoustic emission sensors for diagnosing the technical condition of critical components and assemblies of aircraft, as well as outlines the prospects for their deepest integration into a unified information and analytical system for diagnosing and predicting the technical state of aviation complexes. The developed technical solutions aimed at simplifying the methods of processing broadband acoustic emission signals, which make it possible to design acoustic emission sensors based on optical fiber, are structurally simpler and cheaper, with an increased signal-to-noise ratio, due to one conversion of an acoustic-optical signal into an electrical one.

Stabilization of high sensitivity optical fiber AE sensing for long-term detection

The optical fiber acoustic emission (AE) sensing system with high sensitivity is stabilized for long-term detection in this paper. The high linear slope window of the phase-shifted fiber Bragg grating (PS-FBG) spectrum is tracked by the tunable laser source (TLS) to maintain high AE detection sensitivity. The experimental results show that the proposed method successfully solves the problem of PS-FBG spectrum shift caused by cross sensitivity of temperature and strain. In the high linear slope window of the spectrum, the stabilized sensing system can guarantee the AE strain sensitivity of 0.63nε/Hz1/2 at 200 kHz under the DC voltage of 10 mV. The stability of the AE sensing system is verified by stretching a carbon fibre reinforced plastic (CFRP) sample. The practical application demonstrates that the stabilized system can accurately capture the lowest order modes in the plate wave during long-term AE detection.

Structural Health Monitoring Using Fibre Optic Acoustic Emission Sensors.

Acoustic emission (AE) is widely used for condition monitoring of critical components and structures. Conventional AE techniques employ wideband or resonant piezoelectric sensors to detect elastic stress waves propagating through various types of structural materials, including composites during damage evolution. Recent developments in fibre optic acoustic emission sensors (FOAES) have enabled new ways of detecting and monitoring damage evolution using AE. An optical fibre consists of a core with a high refractive index and a surrounding cladding. The buffer layer and outer jacket both act as protective polymer layers. Glass optical fibres can be used for manufacturing AE sensors of sufficiently small size to enable their embedding into fibre-reinforced polymer composite materials. The embedding process protects the FOAES against environmental stresses prolonging operational lifetime. The immunity of FOAES to electromagnetic interference makes this type of sensor attractive for condition monitoring purposes across a wide range of challenging operational environments. This paper provides an exhaustive review of recent developments on FOAES including their fundamental operational principles and key industrial applications.

Research of Acoustic Emission Health Monitoring Test of Plane Welding Joint

The welding joint is the key area of Aircraft bearing structure, which is not only subjected to alternating fatigue force, but also to the impact force during takeoff and landing. In this paper, the formation model of fatigue crack is studied, and the health monitoring of aircraft welds based on optical fiber acoustic emission technology is proposed in combination with the principle of acoustic emission detection. The sensor arrangement scheme and test conclusion are given through the actual acoustic emission test of simulated damage of welding joint, which provides the basis for the health monitoring of welding joint of aircraft in service.

High-resolution random fiber laser acoustic emission sensor.

A high resolution fiber-optic acoustic emission (AE) sensor using a random fiber laser (RFL) is proposed. The AE probe is undertaken by a random-gratings-based erbium-doped RFL. A narrow linewidth π-FBG is used as a wavelength locking and sensing element in the RFL. The random distributed feedback in RFL significantly extends the effective cavity length of the laser, thus reduces the thermal frequency noise of the laser and improves the resolution of AE signal. A narrow lasing operation with a 20 dB linewidth of ∼10.41 kHz and a frequency noise of ∼10 Hz/√Hz above 1 kHz is realized. The 3×3 coupler interrogation technique is used for signal demodulation. A high AE signal resolution of ∼280 fɛ/√Hz @ 1 kHz is obtained. To the best of our knowledge, this is the first time that RFL is used in the 3×3 coupler based AE demodulation scheme to improve the system resolution.

Sensitivity Analysis of Adaptive Holographic Fiber-Optic Acoustic Emission Sensors during the Registration of Acoustic Waves In a Plate

Paper presents the results of studying the features of recording acoustic emission waves by fiber-optic sensors. Fiber-optic sensors are used as an elastic medium that receives acoustic emission waves. Optical fibers were built between the layers of the polymer composite material during the manufacturing process. The measuring system is constructed on the basis of an adaptive interferometer. Optical fibers are part of the interferometer optical scheme. The elastic wave acting on an optical fiber changes its optical density, changing the interference pattern of the optical beam. The work of the holographic interferometer based on the fact that the interference pattern, formed by the object and reference light beams, is a dynamic hologram that is constantly recorded in the photorefractive crystal during the elastic action on the fiber. Sensitivity of fiber-optic sensors based on an adaptive interferometer allows recording acoustic emission waves. The acoustic emission waves were generated by the Hsu-Nielsen source. A significant difference in the speed of sound is explained by the anisotropy of the properties of the composite material. The structure and density of the material’s fibers in different directions are different. The wavelet transformation was used to form the signal front.

Fiber-Optic Interferometric Sensor Based on the Self-Interference Pulse Interrogation Approach for Acoustic Emission Sensing in the Graphite/Epoxy Composite

Fiber-optic acoustic emission sensors are highly attractive for non-destructive testing applications in composites due to their small size, galvanic isolation, and immunity to electromagnetic interference (EMI). The significant part of such sensors is based on the Fabry-Perot interferometers (FPIs) because of their small size, high sensitivity, and their ease of embedding into a composite structure. However, linear demodulation techniques of their signals suffer from the limited dynamic range and require an additional operating point control. In this paper, we propose the novel self-interference interrogation approach for the fiber-optic FPI-based acoustic emission sensor, which allows the FPI to be interrogated as a two-beamlike interferometer with current-induced frequency modulation of the light source. Then, with using of a PGC-ATAN demodulation algorithm or similar, phase signals can be measured independently of the interferometer operating point with the extended dynamic range. The sensor is based on the fiber-optic FPI that consists of the optical fiber segment bounded by two TiO2 mirrors: the semitransparent one (20%-25% reflecting and -1.6-dB loss) in the fiber and the external one (99.9% reflecting) at the fiber tip. The mirrors are spaced 7 mm apart. Two FPI sensors were fabricated and experimentally investigated. One sensor was mounted on the surface of the graphite/epoxy composite plate, and another one was embedded into its structure. The experimental investigation results of two considered interferometric acoustic emission sensors in comparison with the reference piezoelectric transducer GT301 are presented. Obtained results confirmed the efficiency of the proposed interrogation approach in terms of FPI usage as a two-beamlike interferometer for acoustic emission signals detection and might be used for the implementation in existing and new FPI-based acoustic emission sensing systems.

On-Line Registration of Damages in Composite Materials with Fiber-Optic Acoustic Emission Sensors

This paper presents the results of the analysis of acoustic emission signals registered by using fiber-optic sensors during the propagation of ultrasonic waves in a polymer composite material. Fiber-optical sensors for acoustic emission were constructed according to the scheme of an adaptive holographic interferometer. Unlike piezoelectric sensors, fiber-optic sensors are distributed type sensors. This imposes certain features on the detection of signals in plates in which fiber-optic sensors are embedded. It is established that the difference of the spectrum of acoustic emission signals is registered in different directions of wave propagation. The local maximums of the spectrum are determined by the mode of wave propagation in the plate in different directions and the location of fiber-optic sensors.