Ultrasonic Guided Waves Research Articles

Split-spectrum processing technique for SNR enhancement of ultrasonic guided wave

Ultrasonic guided wave (UGW) systems are broadly used in several branches of industry where the structural integrity is of concern. In those systems, signal interpretation can often be challenging due to the multi-modal and dispersive propagation of UGWs. This results in degradation of the signals in terms of signal-to-noise ratio (SNR) and spatial resolution. This paper employs the split-spectrum processing (SSP) technique in order to enhance the SNR and spatial resolution of UGW signals using the optimized filter bank parameters in real time scenario for pipe inspection. SSP technique has already been developed for other applications such as conventional ultrasonic testing for SNR enhancement. In this work, an investigation is provided to clarify the sensitivity of SSP performance to the filter bank parameter values for UGWs such as processing bandwidth, filter bandwidth, filter separation and a number of filters. As a result, the optimum values are estimated to significantly improve the SNR and spatial resolution of UGWs. The proposed method is synthetically and experimentally compared with conventional approaches employing different SSP recombination algorithms. The Polarity Thresholding (PT) and PT with Minimization (PTM) algorithms were found to be the best recombination algorithms. They substantially improved the SNR up to 36.9dB and 38.9dB respectively. The outcome of the work presented in this paper paves the way to enhance the reliability of UGW inspections.

Influence of the Spatial Dimensions of Ultrasonic Transducers on the Frequency Spectrum of Guided Waves.

Ultrasonic guided wave (UGW)-based condition monitoring has shown great promise in detecting, localizing, and characterizing damage in complex systems. However, the application of guided waves for damage detection is challenging due to the existence of multiple modes and dispersion. This results in distorted wave packets with limited resolution and the interference of multiple reflected modes. To develop reliable inspection systems, either the transducers have to be optimized to generate a desired single mode of guided waves with known dispersive properties, or the frequency responses of all modes present in the structure must be known to predict wave interaction. Currently, there is a lack of methods to predict the response spectrum of guided wave modes, especially in cases when multiple modes are being excited simultaneously. Such methods are of vital importance for further understanding wave propagation within the structures as well as wave-damage interaction. In this study, a novel method to predict the response spectrum of guided wave modes was proposed based on Fourier analysis of the particle velocity distribution on the excitation area. The method proposed in this study estimates an excitability function based on the spatial dimensions of the transducer, type of vibration, and dispersive properties of the medium. As a result, the response amplitude as a function of frequency for each guided wave mode present in the structure can be separately obtained. The method was validated with numerical simulations on the aluminum and glass fiber composite samples. The key findings showed that it can be applied to estimate the response spectrum of a guided wave mode on any type of material (either isotropic structures, or multi layered anisotropic composites) and under any type of excitation if the phase velocity dispersion curve and the particle velocity distribution of the wave source was known initially. Thus, the proposed method may be a beneficial tool to explain and predict the response spectrum of guided waves throughout the development of any structural health monitoring system.

Propagation characteristics of ultrasonic guided waves in continuously welded rail

Rail defects cause numerous railway accidents. Trains are derailed and serious consequences often occur. Compared to traditional bulk wave testing, ultrasonic guided waves (UGWs) can provide larger monitoring ranges and complete coverage of the waveguide cross-section. These advantages are of significant importance for the non-destructive testing (NDT) of the continuously welded rail, and the technique is therefore widely used in high-speed railways. UGWs in continuous welded rail (CWR) and their propagation characteristics have been discussed in this paper. Finite element methods (FEMs) were used to accomplish a vibration modal analysis, which is extended by a subsequent dispersion analysis. Wave structure features were illustrated by displacement profiles. It was concluded that guided waves have the ability to detect defects in the rail via choice of proper mode and frequency. Additionally, thermal conduction that is caused by temperature variation in the rail is added into modeling and simulation. The results indicated that unbalanced thermal distribution may lead to the attenuation of UGWs in the rail.

Detection of minor damage in structures with guided wave signals and nonlinear oscillator

Ultrasonic Guided Wave (UGW)-based method is a very promising nondestructive testing (NDT) technique for detecting defects in elongated structures, such as pipelines, railway tracks and elongated bars. Minor damage in structures only introduce weak reflections of UGW, which limits the detection range of the method and make it ineffective to use guided wave signals for reliable detections of minor structural damages. In this paper, a novel technique based on analyzing the responses of a nonlinear oscillator with the recorded UGW signal as an added input is proposed for the detection of minor structural damage. The theoretical background is that tiny differences in the input function of a nonlinear system can lead to large differences in the solution of the system. To detect the minor damage, the weak UGW signal is treated as the driving force of the nonlinear system. Minor defect in structures can be detected by analyzing the responses of the nonlinear oscillator. To verify the feasibility of the proposed approach, experimental studies on pipe specimens with several damage scenarios are carried out. Lyapunov exponents are used to identify the echo signal of the weak UGW. For locating the minor defect, Lyapunov exponents with a moving window are used to determine the arriving time of the echo signal. The results demonstrate the effectiveness of the proposed approach for detecting the minor damage in pipe structures even when the noise effect is significant. The proposed approach increases the sensitivity and applicability of UGW-based methods to detect the minor damage in structures with weak guided wave signals.

Novel Remote NDE Technique for Pipes Combining HTS-SQUID and Ultrasonic Guided Wave

This paper describes basic research of a novel remote nondestructive evaluation (NDE) technique for pipes combining high-sensitive high-temperature superconductor superconducting quantum interference device (HTS-SQUID) and ultrasonic guided waves. Measurements of magnetic signals due to acoustic emission (AE) and ultrasonic-guided waves on a steel pipe were demonstrated using an HTS-SQUID gradiometer. To convert the guided waves into magnetic signals, the inverse magnetostrictive effect of a magnetized nickel thin plate glued around the pipe's circumference was utilized. An AE sensor and alternative magnetized nickel thin plate with wound coil were used as AE and ultrasonic-guided wave transmitters. Magnetic signals due to AE and ultrasonic guided waves were successfully measured by the HTS-SQUID gradiometer, which was set above the nickel film with a lift-off of about 2 mm.

Preventing microbial biofilms on catheter tubes using ultrasonic guided waves

Biofilms on indwelling tubes and medical prosthetic devices are among the leading causes of antibiotic-resistant bacterial infections. In this work, a new anti-biofilm catheter prototype was proposed. By combining an endotracheal tube (ET) with a group of ultrasonic guided wave (UGW) transducers, the general idea was to prevent bacteria aggregation with UGW vibrations. Based on quantitative analysis of UGW propagation, detailed approach was achieved through (a) selection of ultrasonic frequency, wave modes and vibration amplitude; and (b) adoption of wave coupling and 45° wave incidence technique. Performance of the proposed UGW-ET prototype was demonstrated via in vitro experiments, during which it deterred deposition of Pseudomonas aeruginosa (P. aeruginosa) biofilms successfully. With current configuration, UGW amplitudes ranged from 0.05–5 nm could be optimal to achieve biofilm prevention. This work sheds a light in the underlying mechanism of ultrasound-mediated biofilm prevention, and will inspire the development of new catheters of better antibacterial capability.

A comparative convergence and accuracy study of composite guided-ultrasonic wave solution methods: Comparing the unified analytic method, SAFE method and DISPERSE

Multiple approaches and programs are available to the public to predict ultrasonic guided-wave propagation dispersion curves in a material. Each approach and program will have its own advantage and disadvantage making it suitable for a specific end use and less suitable for others. This manuscript aims to compare three different guided-ultrasonic wave dispersion curves retrieval methods for multiple cases. First a single layer of isotropic, unidirectional, orthotropic and monoclinic material is examined, followed by a multi-layer case (consisting of 10 layers of the aforementioned materials) and finally four different laminates and one sandwich laminate are evaluated. The goal of this manuscript is to give a concise overview of the advantages and limitations of each approach to assist the end user in choosing the right program to use.

Applications of a nanocomposite-inspired in-situ broadband ultrasonic sensor to acousto-ultrasonics-based passive and active structural health monitoring

A novel nanocomposite-inspired in-situ broadband ultrasonic sensor previously developed, with carbon black as the nanofiller and polyvinylidene fluoride as the matrix, was networked for acousto-ultrasonic wave-based passive and active structural health monitoring (SHM). Being lightweight and small, this kind of sensor was proven to be capable of perceiving strain perturbation in virtue of the tunneling effect in the formed nanofiller conductive network when acousto-ultrasonic waves traverse the sensor. Proof-of-concept validation was implemented, to examine the sensor performance in responding to acousto-ultrasonic waves in a broad frequency regime: from acoustic emission (AE) of lower frequencies to guided ultrasonic waves (GUWs) of higher frequencies. Results have demonstrated the high fidelity, ultrafast response and high sensitivity of the sensor to acousto-ultrasonic waves up to 400kHz yet with an ultra-low magnitude (of the order of micro-strain). The sensor is proven to possess sensitivity and accuracy comparable with commercial piezoelectric ultrasonic transducers, whereas with greater flexibility in accommodating curved structural surfaces. Application paradigms of using the sensor for damage evaluation have spotlighted the capability of the sensor in compromising “sensing cost” with “sensing effectiveness” for passive AE- or active GUW-based SHM.

Toward Robotic Inspection of Dry Storage Casks for Spent Nuclear Fuel

Extended dry storage of spent nuclear fuel makes it desirable to assess the structural integrity of the storage canisters. Stress corrosion cracking of the stainless steel canister is a potential degradation mode especially in marine environments. Sensing technologies are being developed with the aim of detecting the presence of chloride-bearing salts on the surface of the canister as well as whether cracks exist. Laser-induced breakdown spectroscopy (LIBS) methods for the detection of Chlorine are presented. In addition, ultrasonic-guided wave detection of crack-like notches oriented either parallel or perpendicular to the shear horizontal wave vector is demonstrated using the pulse-echo mode, which greatly simplifies the robotic delivery of the noncontact electromagnetic acoustic transducers (EMATs). Robotic delivery of both EMATs and the LIBS system is necessary due to the high temperature and radiation environment inside the cask where the measurements need to be made. Furthermore, the space to make the measurements is very constrained and maneuverability is confined by the geometry of the storage cask. In fact, a large portion of the canister surface is inaccessible due to the presence of guide channels on the inside of the cask's overpack, which is strong motivation for using guided waves for crack detection. Among the design requirements for the robotic system are to localize and track where sensor measurements are made to enable return to those locations, to avoid wedging or jamming of the robot, and to tolerate high temperatures and radiation levels.

Ultrasonic imaging algorithm for the health monitoring of pipes

This paper presents a numerical study where guided ultrasonic waves (GUWs) are processed using a new imaging algorithm for the health monitoring of pipes. The numerical model mimics the generation and detection of guided waves from the transducers of two annular arrays located inside a pipe. The fastest mode of the detected signals is processed using the continuous wavelet transform and the Hilbert transform to extract two damage-sensitive features. The estimation of the features for the healthy condition is formulated in terms of an optimization problem solved with a competitive optimization algorithm. Finally, a probabilistic approach is used to create an image of the pipe to reveal the presence of possible structural anomalies. With respect to most GUW-based imaging methods, the proposed approach is baseline-free which means that data from pristine pipes are not necessary. A commercial finite element code is utilized to mimic the operation of the two arrays each made of four ultrasonic transducers in contact with the interior wall of a pipe. While one of the transducers acts as transmitter, the other seven act as sensors, and this is repeated for all the elements of the rings. The time waveforms associated with all the possible actuator–sensor pairs are processed using the algorithm proposed here. To demonstrate the advantages of the proposed approach, the findings are compared to the results obtained using a conventional pitch-catch approach. The results are promising and future studies should focus on the experimental validation of the methodology.

A method of recognition and elimination to the pseudo defect signals by ultrasonic guided wave NDT for pipes

The detected signals using ultrasonic guided wave non-destructive testing (NDT) for pipes with the method of excited and received to one end of pipe, which run with come-and-go many times of reflection and transmission between the two ends of pipe and the defect location in pipe until its energy dissipation over. The multiple reflection and transmission process lead to the appearance of the pseudo defect signals which seriously affect the judgement of the defect numbers and its locations in pipes. Aiming at the difficulty problem of the pseudo defect signal identification, the sketch map of the propagation path of ultrasonic guided wave in pipeline is drawn. The position characteristic of the pseudo defect signal is summarized. Namely: the pseudo defect signal does not appear in the first reflection cycle of the detected signals or its amplitude of the signal is negligible; meanwhile, the larger amplitude of the pseudo defect signal appear from the the second reflection cycle of the detected signals, and which is symmetric with the real defect signal about the time domain midpoint of the signal period in the second reflection cycle. The correctness of this characteristic law is verified by using numerical simulation and experimental results. According to the characteristic law of the pseudo defect signal, the defect wave packet signals in the ultrasonic guided wave detected signals were identified and extracted, and the matching pursuit method and the numerical comparison assignment method were used to eliminate the pseudo defect signal. The conclusion are shown that the proposed method of the pseudo defect signal recognition and elimination in the ultrasonic guided wave NDT for pipes is practical and effective, which achieves the goal of discarding the false and retain the true detected signals, and solve the the detected signals recognition difficulty problem in ultrasonic guided wave NDT for pipes, and also greatly promotes the application of the ultrasonic guided wave NDT technology.

Finite Element Analysis of Crack Growth for Structural Health Monitoring of Mooring Chains using Ultrasonic Guided Waves and Acoustic Emission

As offshore oil and gas exploration and production goes further afield and into deeper waters, more offshore operations, are conducted from floating platforms, which are moored to the seabed by chains, polyester tether lines, or combinations of both. Moreover, the forecasted large scale deployment of offshore renewable energy systems in deep water will rely upon similar mooring systems. Mooring lines are safety-critical systems on offshore floating and semi-submersible platforms. The lines are usually subject to immense environmental and structural forces such as currents, oceans waves, and hurricanes. Other forces include impact with the seabed, abrasion, increased drag due to accumulation of marine organisms and salt water corrosion. Failure of one or more of mooring lines can result in disastrous consequences for safety, the environment and production.Mooring chain life can be significantly reduced, leading to unacceptable risk of catastrophic failure, if early damage is not detected. Chain mounted equipment is available to monitor chain tension and bending, but detection of damage caused by stress concentrations, fatigue, corrosion and fretting or combinations of these is not currently possible. The Ultrasonic Guided Waves (UGW) and Acoustic Emission (AE) techniques are capable of detecting cracks in mooring chains and fatigue damage. This paper describes a methodology of Finite Element Analysis (FEA) for crack initiation and crack growth simulation for Structural Health Monitoring (SHM) applying UGW and AE.

Dispersion and Sensitivity Analysis of Quasi-Scholte Wave Liquid Sensing by Analytical Methods

Ultrasonic-guided wave sensing relies on perturbation of wave propagation by changing physical properties of the target media. Solid waveguides, through which guided waves can be transduced between the transducer and the target media, are frequently employed for liquid sensing and several other applications. In this manuscript, liquid sensing sensitivity of dispersive quasi-Scholte waves, which are guided interface waves that travel at the solid-liquid boundary, is investigated. Dispersion analysis of quasi-Scholte waves is done and sensitivities of quasi-Scholte waves to changes in fluid density and speed of sound in a dipstick configuration are analyzed. An experimentally verified analytical model based on a global matrix approach is employed in a nondimensional manner to generate representative dispersion and sensitivity surfaces. Optimum configurations with respect to the material properties of the liquid and of the waveguide are illustrated, which would enable optimal quasi-Scholte liquid sensing.

Ultrasonic guided waves for reinforced plastics safety

The application of ultrasonic guided waves (UGW) to the field of preventive maintenance of composite structures is in continuous increase. Today, UGW is taking an important economical place, especially in the fields of transport and nuclear technology, where the safety of individuals is of higher importance than financial cost.

Ultrasonic Guided Wave Propagation through Welded Lap Joints

The objective of the research presented here is the investigation of ultrasonic guided wave (UGW) propagation through the lap joint welded plates used in the construction of a storage tank floors. The investigations have been performed using numerical simulation by finite element method (FEM) and tested by measurement of the transmission losses of the guided waves transmitted through the welded lap joints. Propagation of the symmetric S0 mode in the welded stainless steel plates in the cases of different lap joint overlap width, operation frequency, and additional plate bonding caused by corrosion were investigated. It was shown that the transmission losses of the S0 mode can vary in the range of 2 dB to 8 dB depending on the ratio between lap joint width and wavelength. It was also demonstrated that additional bonding in the overlap zone caused by corrosion can essentially reduce transmission losses.

Nonlinear Damage Localization in Structures Using Nonlinear Vibration Modulation of Ultrasonic-Guided Waves

This paper proposes a method for nonlinear damage localization in the beam and plate structures with nonlinear vibration modulation of ultrasonic-guided waves. In the proposed technique, the damaged metal beam and plate are designed to form a cantilever structure. A magnetic system is also involved in the model to control the dynamics of this cantilever structure. The oscillation model exhibits nonlinear vibration that is used to modulate the ultrasonic-guided waves. By utilizing a synchronous phase-locked demodulation technique, the nonlinear reflection profile from the nonlinear scatterer is extracted and employed for localizing the nonlinear damage. The proposed technique has the merits of being perceptive to nonlinear scattering sources, without requiring a damage-free signal, and with enhanced performance at a wide range of frequencies. These merits have been experimentally validated by localizing fatigue crack in a metal beam and imaging simulated contact defect in a metal plate. The proposed technique is suitable in the structural health monitoring (SHM) for nonlinear damage localization in the absence of a baseline signal by ultrasonic-guided waves.

High precision ultrasonic guided wave technique for inspection of power transmission line

Due to the merits of high inspection speed and long detecting distance, Ultrasonic Guided Wave(UGW) method has been commonly applied to the on-line maintenance of power transmission line. However, the guided wave propagation in this structure is very complicated, leading to the unfavorable defect localization accuracy. Aiming at this situation, a high precision UGW technique for inspection of local surface defect in power transmission line is proposed. The technique is realized by adopting a novel segmental piezoelectric ring transducer and transducer mounting scheme, combining with the comprehensive characterization of wave propagation and circumferential defect positioning with multiple piezoelectric elements. Firstly, the propagation path of guided waves in the multi-wires of transmission line under the proposed technique condition is investigated experimentally. Next, the wave velocities are calculated by dispersion curves and experiment test respectively, and from comparing of the two results, the guided wave mode propagated in transmission line is confirmed to be F(1,1) mode. Finally, the axial and circumferential positioning of local defective wires in transmission line are both achieved, by using multiple piezoelectric elements to surround the stands and send elastic waves into every single wire. The proposed research can play a role of guiding the development of highly effective UGW method and detecting system for multi-wire transmission line.

A Laser-Based Fiber Bragg Grating Ultrasonic Sensing System for Structural Health Monitoring

Fiber Bragg gratings (FBGs) have being seen for a growing application in the field of structural health monitoring (SHM) because of their lightweight features. This letter introduces an adaptive SHM sensing system based on the ultrasonic guided wave (UGW) and FBG sensor technology. First, the capability of the proposed SHM sensing system used to detect UGW is demonstrated by the frequency detection of Rayleigh wave that is generated by the piezoelectric transducers with a function generator. Furthermore, a nanosecond pulse laser is utilized to generate Lamb wave on an aluminum plate, while the SHM sensing system is employed to detect the wave in a long distance. Finally, the SHM sensing system is used to locate the source of Rayleigh wave that is created by a pulsed laser. The experiment results show the proposed SHM sensing system is capable of localizing and monitoring the UGW by using four FBG cascaded on a loaded aluminum plate.

A unified formulation for predictive modeling of guided-ultrasonic wave dispersion curves in metallic and composite materials

To predict dispersion curves it is common to use different solution approaches depending on the material type, isotropic or composite, of the medium in which the wave propagates. The two different solution methods are defined in different domains, frequency–wavespeed domain for isotropic materials, and wavenumber–wavespeed domain for composites which can lead to difficulties, and unsatisfying results when predicting the dispersion curves for hybrid laminates which contain both isotropic and composite materials. This article, therefore, proposes a unified formulation defined in the wavenumber–wavespeed domain for both isotropic and composite materials. The unified formulation, simple, and mathematically straightforward formulation, utilizes Christoffel’s equation for a lamina to obtain the eigenvalues and eigenvectors. The eigenvalues and eigenvectors are then used to set up the field matrix from which the dispersion curves could be retrieved. Once the dispersion curves were obtained the waves are grouped using a modeshape analysis. A spline algorithm is applied to obtain a continuous solution from a rough domain which was used to reduce computational time. In addition, this article highlights the challenges faced in the numerical process, and provides a discussions of the methods used to overcome these obstacles.

Observation of ultrasonic guided wave propagation behaviours in pre-stressed multi-wire structures

Ultrasonic guided wave (UGW) is a promising technique for nondestructive testing of pre-stressed multi-wire structures, such as steel strand and wire rope. The understanding of the propagation behaviours of UGW in these structures is a priority to applications. In the present study, first the properties of the UGW missing frequency band in the pre-stressed seven-wire steel strand is experimentally examined. The high correlation between the observed results and the previously published findings proves the feasibility of the magnetostrictive sensor (MsS) based testing method. The evolution of missing frequency band of UGW in slightly tensioned steel strand is discussed. Two calibration equations representing the relationship between the missing band parameters and the tensile force are given to derive a new tensile force measurement method, which is capable of measuring an incremental of stress of approximately 3MPa. Second, the effects of tensile force on the UGW propagation behaviours in three types of complicated steel wire ropes are alternatively investigated based on the short time Fourier transform (STFT) results of the received direct transmission wave (DTW) signals. The observed inherent missing frequency band of the longitudinal mode UGW in the pre-stressed steel wire rope and its shifting to a higher frequency range as the increases of the applied tensile force are reported for the first time. The influence of applied tensile force on the amplitude of the DTW signal and the unique UGW energy jump behaviour observed in a wire rope of 16.0mm, 6×Fi(29)+IWRC are also investigated, despite the fact that they cannot yet be explained.