Publications
103 results found
Cegla F, Herdovics B, 2018, Coded excitation, motion and signal-to-noise ratio, IEEE International Symposium on Circuits and Systems (ISCAS), Publisher: IEEE, ISSN: 0271-4302
Previous work has shown that coded excitation can be used to considerably improve the signal-to-noise ratio (SNR) of signals received by transducers of poor sensitivity such as electromagnetic acoustic transducers (EMATs). EMATs are usually driven with signal powers of the order of kWs so that adequate SNR is achieved. With coded excitation these powers can be reduced to as low as 1-5W. A particular feature of the transmitted codes is that they are temporally long and contain intermittent intervals in which reception takes place. Because of the signal length there is concern that excessive movement of the probe or target can result in deterioration of the performance of such a system. Therefore, in this paper we investigate the effect that physical motion of the test piece can have on the acquired signals. Simulated results will be presented and discussed here.
Howard R, Cegla F, 2018, The Effect of Pits of Different Sizes on Ultrasonic Shear Wave Signals, 44th Annual Conference on Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, ISSN: 0094-243X
Zou F, Cegla F, 2018, On quantitative corrosion rate monitoring with ultrasound, Journal of Electroanalytical Chemistry, Vol: 812, Pages: 115-121, ISSN: 1572-6657
Wall-thickness loss rate (WTLR) is an important parameter that defines a corrosion process. The speed at which a WTLR can be determined is directly related to how quickly one can intervene in a process that is heading in the wrong direction. Ultrasonic testing has been widely used as a convenient and efficient technique for online corrosion monitoring. One of the key performance parameters of ultrasonic corrosion monitoring is detection speed. While WTLRs can be determined by fitting linear lines to wall-thickness loss (WTL) measurements, the presence of noise in the measurements makes it difficult to judge the confidence levels of the slopes that are calculated this way. In this paper, a statistics based approach for assessing the detection speeds that are achievable by ultrasonic corrosion monitoring systems is presented. Through the statistical analysis of experimental data, a state-of-the-art laboratory setup is shown to be able to detect both WTLRs and changes in WTLR that are of interest to industry (i.e. 0.1–0.2 mm/year) within 1–2 h.
Wang Y, Zou F, Cegla F, 2017, Acoustic waveguides: an attractive alternative for accurate and robust contact thermometry, Sensors and Actuators A: Physical, Vol: 270, Pages: 84-88, ISSN: 0924-4247
We report a robust and very precise method of measuring temperature using ultrasonic waves. Solid stainless steel waveguides are used to provide well-defined and stable ultrasonic wave propagation paths. Ultrasonic wave velocity is strongly temperature dependent. The arrival times of the ultrasonic wavepackets along a waveguide are used to infer the average temperature of the waveguide. Our ultrasonic temperature measurements exhibit a high precision (i.e. ±0.015 ⁰C) that is more than two times better than the quoted accuracy of 1/10 DIN resistance temperature detectors (RTDs). The responsiveness of the waveguides was also investigated. While ultrasonic measurements can be made at very high frequencies, the responsiveness is limited by the heat transfer into the active sensing area. The waveguides make it easy to customise the dimension of the active sensing area and a shorter response time than those of RTDs has been demonstrated. The technique presented in this paper is a robust and cost effective alternative to other contact temperature measurements.
Zou F, Cegla F, 2017, High Accuracy Ultrasonic Corrosion Rate Monitoring, Corrosion, Vol: 74, Pages: 2663-2679, ISSN: 0010-9312
Ultrasonic testing with permanently installed transducers is widely used for online corrosion monitoring in the field. In this paper, a carefully optimized ultrasonic corrosion monitoring technique for carrying out measurements in the laboratory is presented. It is shown that for thickness measurements of a 10 mm steel component, a repeatability of ~40 nm can be maintained over the period of a day. The technique has been applied to monitoring the wall losses of a steel sample during forced and unforced corrosion experiments. All ultrasonic wall loss measurements reported have been validated by optical surface profile scans and, where possible, by analytical predictions based on Faraday’s law. Further analysis of the results shows that wall loss rates in the order of 0.1 – 0.2 mm/year can be detected within 1 – 2 hours. This state-of-the-art laboratory technique is highly accurate and responsive, and possesses the potential for becoming a powerful alternative corrosion assessment tool that is convenient to use.
Zou F, Cegla, 2017, High accuracy ultrasonic monitoring of electrochemical processes, Electrochemistry Communications, Vol: 82, Pages: 134-138, ISSN: 1388-2481
Ultrasonic testing (UT) can be used for non-intrusive corrosion monitoring. In this paper, we firstly show that UT is not only capable of monitoring wall-thickness losses, but can also be exploited for tracking electrodeposition processes. All ultrasonic measurements reported are in agreement with analytical predictions and optical surface profile measurements. Since UT is highly sensitive to the coupling conditions and the relative acoustic properties of substrates and deposited materials, it can become an effective tool for studying the interface phenomena in which dissolution and deposition compete. Examples of these include passivation layer formation and scale deposition which are corrosion-inhibiting electrochemical processes.
Howard R, Cegla F, 2017, Detectability of corrosion damage with circumferential guided waves in reflection and transmission, NDT & E International, Vol: 91, Pages: 108-119, ISSN: 0963-8695
There is an increasing interest in high frequency short range guided waves to screen or monitor for corrosion. This contrasts with long range guided waves (LRGWs) which screen pipes for large patches of corrosion and have been successfully used in corrosion management for the past twenty years. The fundamental setup described in this paper uses circumferential guided waves, which are excited at a single location on a pipe and travel around the pipe wall and are detected at the same location. The study uses a finite element model assisted method to evaluate the detection capability of two short range circumferential guided wave setups which use both the reflected and transmitted signals. The setups themselves consist of either an axial array of transducers, for monitoring, or a single transducer which axially scans a pipe. Both setups have an array or scan pitch between either adjacent transducers or measurements. The detection capability of the fundamental Lamb wave modes (A0 and S0) in both reflection and transmission have been compared, as well as a hybrid shear horizontal wave setup, which uses the SH0 mode in reflection and the SH1 mode in transmission. A sensitivity analysis was conducted using two separate methods to determine the probability of detection (POD) for either the reflection or transmission signals. Both methods determine a POD for a specific defect, noise level, and array or scan pitch. Probability images are produced which map the POD for a range of defect sizes. For the parameters investigated in this study, it was found that in transmission large diameter defects have a higher detectability, whereas deep, narrow diameter defects are more detectable in reflection. A generalised overview of the sensitivity of short range guided waves is presented by combining both the reflection and transmission PODs. The data fused sensitivity of the S0 and SH hybrid modes are given as 0.6% and 0.75% cross sectional area (CSA) respectively, allowing for the comp
Isla J, Cegla FB, 2017, EMAT phased array: a feasibility study of surface crack detection, Ultrasonics, Vol: 78, Pages: 1-9, ISSN: 0041-624X
Electromagnetic-acoustic transducers (EMATs) consist of a magnet and a coil. They are advantageous in some non-destructive evaluation (NDE) applications because no direct contact with the specimen is needed to send and receive ultrasonic waves. However, EMATs commonly require excitation peak powers greater than 1 kW and therefore the driving electronics and the EMAT coils have to be bulky. This has hindered the development of EMAT phased arrays with characteristics similar to those of conventional piezoelectric phased arrays. Phased arrays are widely used in NDE because they offer superior defect characterization in comparison to single-element transducers. In this paper, we report a series of novel techniques and design elements that make it possible to construct an EMAT phased array that performs similarly to conventional piezoelectric arrays used in NDE. One of the key enabling features is the use of coded excitation to reduce the excitation peak power to less than 4.8 W (24 Vpp and 200 mA) so that racetrack coils with dimensions can be employed. Moreover, these racetrack coils are laid out along their shortest dimension so that 1/3 of their area is overlapped. This helps to reduce the crosstalk between the coils, i.e., the array elements, to less than −15 dB. We show that an 8-element EMAT phased array operating at a central frequency of 1 MHz can be used to detect defects which have a width and a depth of 0.2 and 0.8 mm respectively and are located on the surface opposite to the array.
Isla J, Cegla F, 2017, EMAT Phased Array Probe for Detecting Surface Cracks, Joint IEEE International Symposium on Applications of Ferroelectrics (ISAF) International Workshop on Acoustic Transduction Materials and Devices (IWATMD) / Piezoresponse Force Microscopy Workshop (PFM), Publisher: IEEE, Pages: 41-44
Isla J, Cegla FB, 2017, Coded excitation for pulse-echo systems, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 64, Pages: 736-748, ISSN: 0885-3010
Pulse compression has been used for decades in radar, sonar, medical, and industrial ultrasound. It consists in transmitting a modulated or coded excitation, which is then cross-correlated with the received signal such that received echoes are time compressed, thereby increasing their intensity and hence the system resolution and signal-to-noise ratio (SNR). A central problem in pulse-echo systems is that while longer coded excitations yield higher SNRs, the length of the coded excitation or sequence is limited by the distance between the closest reflector and the transmitter/receiver. In this paper, a new approach to coded excitation is presented whereby receive intervals or pauses are introduced within the excitation itself; reception takes place in these intervals. As a result, the code length is no longer limited by the distance to the closest reflector and a higher SNR increase can be realized. Moreover, the excitation can be coded in such a way that continuous transmission becomes possible, which reduces the overall duration of the system response to changes in the medium. The optimal distribution of the receive intervals within the excitation is discussed, and an example of its application in industrial ultrasound is presented. The example consists of an electromagnetic-acoustic transducer driven with 4.5 V, where a clear signal can be obtained in quasi-real-time (e.g., ~9-Hz refresh rate), while commercially available systems require 1200 V for a similar performance.
Benstock D, Cegla FB, 2017, Extreme value analysis (EVA) of inspection data and its uncertainties, NDT & E International, Vol: 87, Pages: 68-77, ISSN: 0963-8695
Extreme value analysis (EVA) is a statistical tool to estimate the likelihood of the occurrence of extreme values based on a few basic assumptions and observed/measured data. While output of this type of analysis cannot ever rival a full inspection, it can be a useful tool for partial coverage inspection (PCI), where access, cost or other limitations result in an incomplete dataset. In PCI, EVA can be used to estimate the largest defect that can be expected. Commonly the return level method is used to do this. However, the uncertainties associated with the return level are less commonly reported on. This paper presents an overview of how the return level and its 95% confidence intervals can be determined and how they vary based on different analysis parameters, such as the block size and extrapolation ratio. The analysis is then tested on simulated wall thickness data that has Gaussian and Exponential distributions. A curve that presents the confidence interval width as a percentage of the actual return level and as a function of the extrapolation ratio is presented. This is valid for the particular scale parameter (σ ) that was associated with the simulated data. And for this data it was concluded that, in general, extrapolations to an area the size of 500–1000 times the inspected area result in acceptable return level uncertainties (<20% at 95% confidence). When extrapolating to areas that are larger than 1000 times the inspected area the width of the confidence intervals can become larger than 30–50% of the actual return level. This was deemed unacceptable: for the example of wall thickness mapping that is used throughout this paper, these uncertainties can represent critical defects of nearly through wall extent. The curve that links the confidence interval width to the return value as a function of extrapolation ratio is valid only for a particular scale parameter value of the EVA model. However, it is imagineable that a few of such relati
Cegla FB, Herdovics B, 2016, Structural Health Monitoring (SHM) using torsional guided wave EMATs, Structural Health Monitoring: an international journal, Vol: 17, Pages: 24-38, ISSN: 1741-3168
Torsional guided wave inspection is widely used for pipeline inspection. Most commonly piezoelectric andmagnetostrictive transducers are used to generate torsional guided waves. These types of transducers require bondingor mechanical contact to the pipe which can result in changes over time which are undesirable for Structural HealthMonitoring. This paper presents a non-contact Lorentz force based Electromagnetic Acoustic Transducer for torsionalguided wave monitoring of pipelines. First, the excitation mechanism of the transducer is simulated by analyzing theeddy current and the static magnetic field using the finite element method. An EMAT transformer model is presentedwhich describes the eddy current generation transfer function and the ultrasound excitation. Independently simulatededdy current and magnetic fields are used to calculate the Lorentz force that an EMAT array induces on the surface ofa 3 inch schedule 40 pipe and an explicit finite element solver is then used to simulate the elastic wave propagationin the pipe. Then, the reception mechanism and the expected received signal levels are discussed. The constructionof an experimental transducer is described and measurement results from the transducer setup are presented. Themeasured and modeled performance agree well. Finally, a monitoring example is presented where an artificial defectwith 3% reflection coefficient is introduced and successfully detected with the designed sensor.
Howard R, Cegla F, 2016, On the probability of detecting wall thinning defects with dispersive circumferential guided waves, NDT & E International, Vol: 86, Pages: 73-82, ISSN: 0963-8695
Two ultrasonic techniques are well established for pipe inspection and monitoring: highly sensitive ultrasonic spot thickness measurements, which can be presented in C-scan form, or low frequency guided waves that rapidly screen large areas for big defects. Recently there has been a growing interest in pipe inspection and monitoring systems exploring the middle ground between these two techniques by using higher frequency guided waves over shorter distances. In this paper the use of an axial transducer array (more suitable for monitoring applications) or a single axially scanned transducer (more suitable for inspections) that sends and receives dispersive circumferential guided waves around a pipe has been studied. The presence of a defect is detected as a result of a change in the wave travel time around the pipe circumference as a result of the thickness reduction. Both measurement modalities have a pitch between adjacent transducers/measurements. By approximating the pipe to a plate, a finite element model assisted method to evaluate the detection capabilities (probability of detection-POD) of this short range guided wave technique as a function of scan or transducer pitch is presented. The performance of three guided wave modes (A0, S0, and SH1) are compared in a 10mm thick plate. The results help to optimize the pitch and defect sensitivity of the setup. For the parameters investigated in this study, it was found that the S0 mode, at 2MHz.mm, is the most suitable for detecting wide shallow defects. For the same detection capabilities a much wider pitch can be used for S0 mode transducers as compared to SH1 mode transducers. Whereas the SH1 mode, at 3MHz.mm, is better suited to detecting narrow and deep defects using a relatively small pitch. The S0 mode is much less sensitive to these defects. The A0 mode was excluded from the POD analysis because it had a much higher variability in average thickness measurements, at comparable SNRs, compared to the other two m
Cegla FB, Gajdacsi A, 2016, The effect of corrosion induced surface morphology changes on ultrasonically monitored corrosion rates, Smart Materials and Structures, Vol: 25, ISSN: 1361-665X
Corrosion rates obtained by very frequent (daily) measurements with permanently installed ultrasonic sensors have been shown to be highly inaccurate when changes in surface morphology lead to ultrasonic signal distortion. In this paper the accuracy of ultrasonically estimated corrosion rates (mean wall thickness loss) by means of standard signal processing methods (peak to peak—P2P, first arrival—FA, cross correlation—XC) was investigated and a novel thickness extraction algorithm (adaptive cross-correlation—AXC) is presented. All of the algorithms were tested on simulated ultrasonic data that was obtained by modelling the surface geometry evolution coupled with a fast ultrasonic signal simulator based on the distributed point source method. The performance of each algorithm could then be determined by comparing the actual known mean thickness losses of the simulated surfaces to the values that each algorithm returned. The results showed that AXC is the best of the investigated processing algorithms. For spatially random thickness loss 90% of AXC estimated thickness trends were within −10 to +25% of the actual mean loss rate (e.g. 0.75–1.1 mm year−1 would be measured for a 1 mm year−1 actual mean loss rate). The other algorithms (P2P, FA, XC) exhibited error distributions that were 5–10 times larger. All algorithms performed worse in scenarios where wall loss was not distributed randomly in space (spatially correlated thickness loss occured) and where the overall rms of the surface was either growing or declining. However, on these surfaces AXC also outperformed the other algorithms and showed almost an order of magnitude improvement compared to them.
Seher M, Challis R, Isla J, et al., 2016, The effect of metal load material and impedance matching on EMAT performance, INSIGHT, Vol: 58, Pages: 536-543, ISSN: 1354-2575
Isla J, Cegla F, 2016, Coded Excitation for Low SNR Pulse-Echo Systems: Enabling Quasi-Real-Time Low-Power EMATs, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, ISSN: 1948-5719
Isla J, Cegla FB, 2016, Optimization of the bias magnetic field of shear wave EMATs, IEEE Transactions on Ultrasonics, Ferroelectrics and Frequency Control, Vol: 63, Pages: 1148-1160, ISSN: 0885-3010
The main advantage of electromagnetic acoustic transducers (EMATs) over piezoelectric transducers is that no direct contact with the specimen under test is required. Therefore, EMATs can be used to test through coating layers. However, they produce weaker signals, and hence, their design has to be optimized. This paper focuses on the design of a Lorentz force shear wave EMAT and its application in thickness gaging; special emphasis is placed on the optimization of the design elements that correspond to the bias magnetic field of the EMAT. A configuration that consists of several magnets axisymmetrically arranged around a ferromagnetic core with like poles facing the core was found to give the best results. By using this configuration, magnetic flux densities in excess of 3 T were obtained in the surface of a specimen; the maximum value achieved by a single magnet under similar conditions is roughly 1.2 T. If the diameter of an EMAT ultrasonic aperture is 10 mm, the proposed configuration produces signals roughly 20 dB greater than a single magnet, while for a given overall EMAT volume, signals were greater than 3-6 dB. Linear and radial shear wave polarizations were also compared; a higher mode purity and signal intensity were obtained with the linear polarization.
Isla J, Cegla FB, 2016, The use of binary quantisation for the acquisition of low SNR ultrasonic signals: a study of the input dynamic range, IEEE Transactions on Ultrasonics Ferroelectrics and Frequency Control, Vol: 63, Pages: 1474-1482, ISSN: 1525-8955
Low-power excitation and/or low sensitivity transducers,such as electromagnetic acoustic transducers (EMATs),piezoelectric paints, air-coupled transducers, or small elementsof dense arrays may produce signals below the noise thresholdat the receiver. The information from those noisy signals canbe recovered after averaging or pulse-compression using binary(one-bit) quantisation only without experiencing significant losses.Hence, no analog-to-digital converter is required, which makesthe electronics faster, more compact and energy efficient. All thisis especially attractive for applications that require arrays withmany channels and high sampling rates, where the sampling ratecan be as high as the system clock. In this paper, the theory ofbinary quantisation is reviewed, mainly from previous work onwireless sensor networks, and the signal-to-noise ratio (SNR) ofthe input signals under which binary quantisation is of practicalinterest for ultrasound applications is investigated. The mainfindings are that in most practical cases binary quantisationcan be used with small errors when the input SNR is in theorder of 8 dB or less. Moreover, the maximum SNR after binaryquantisation and averaging can be estimated as 10 log10 N −2 dB,where N is the number of averages.
Isla J, Seher M, Challis R, et al., 2016, Optimal impedance on transmission of Lorentz force EMATs, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics, ISSN: 0094-243X
Electromagnetic-acoustic transducers (EMATs) are attractive for non-destructive inspections because direct contact with the specimen under test is not required. This advantage comes at a high cost in sensitivity and therefore it is important to optimise every aspect of an EMAT. The signal strength produced by EMATs is in part determined by the coil impedance regardless of the transduction mechanism (e.g. Lorentz force, magnetostriction, etc.). There is very little literature on how to select the coil impedance that maximises the wave intensity; this paper addresses that gap. A transformer circuit is used to model the interaction between the EMAT coil and the eddy currents that are generated beneath the coil in the conducting specimen. Expressions for the coil impedances that satisfy the maximum efficiency and maximum power transfer conditions on transmission are presented. To support this analysis, a tunable coil that consists of stacked identical thin layers independently accessed is used so that the coil inductance can be modified while leaving the radiation pattern of the EMAT unaffected.
Benstock D, Cegla F, 2016, Partial coverage inspection of corroded engineering components using extreme value analysis, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics, ISSN: 0094-243X
Ultrasonic thickness C-scans provide information about wall thickness of a component over the entire inspected area. They are performed to determine the condition of a component. However, this is time consuming, expensive and can be unfeasible where access to a component is restricted. The pressure to maximize inspection resources and minimize inspection costs has led to both the development of new sensing technologies and inspection strategies. Partial coverage inspection aims to tackle this challenge by using data from an ultrasonic thickness C-scan of a small fraction of a component’s area to extrapolate to the condition of the entire component. Extreme value analysis is a particular tool used in partial coverage inspection. Typical implementations of extreme value analysis partition a thickness map into a number of equally sized blocks and extract the minimum thickness from each block. Extreme value theory provides a limiting form for the probability distribution of this set of minimum thicknesses, from which the parameters of the limiting distribution can be extracted. This distribution provides a statistical model for the minimum thickness in a given area, which can be used for extrapolation. In this paper the basics of extreme value analysis and its assumptions are introduced. We discuss a new method for partitioning a thickness map, based on ensuring that there is evidence that the assumptions of extreme value theory are met by the inspection data. Examples of the implementation of this method are presented on both simulated and experimental data. Further it is shown that realistic predictions can be made from the statistical models developed using this methodology.
Howard R, Cegla F, 2016, Monitoring thicknesses along a line using SH guided waves, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: American Institute of Physics, ISSN: 0094-243X
Guided wave technology has been successfully implemented in the field of NDT as a defect screening technique for many years. The existing technique is able to detect large defects in pipes, albeit with limited sensitivity since the technique operates at low frequencies (10-70kHz). Ultrasonic wall thickness monitoring is also a well-established technique; using frequencies in the MHz range these spot measurements are able to measure precise wall thicknesses, but are very spatially selective. This project aims to explore the middle ground, using higher frequency guided waves to increase sensitivity whilst increasing the spatial area covered. SH guided waves (SH0 and SH1 modes) were sent between two transducers in a plate (simulating the propagation of a guided wave around the circumference of a pipe) and the time trace of the receiving transducer was analysed for changes in the group velocity as different defects were introduced into the plate. It is shown that the guided wave-defect interactions were too distorted for accurate thickness profiles to be extracted from line measurements. However, it is believed that this method can be a qualitative tool for defect screening.
Cegla F, Gajdacsi A, 2016, Mitigating the effects of surface morphology changes during ultrasonic wall thickness monitoring, 42nd Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AIP Publishing, ISSN: 0094-243X
Cegla FB, Benstock D, 2015, Sample selection for extreme value analysis of inspection data collected from corroded surfaces, Corrosion Science, Vol: 103, Pages: 206-214, ISSN: 0010-938X
Inspection of corroded engineering components is vital for ensuring safety throughout the lifetime of infrastructure. However, full inspection can be infeasible due to time constraints, budgetary limits or restricted access. Subsequently there is growing interest in partial coverage inspection (PCI) techniques which use data from the inspection of a limited area to assess the condition of larger areas of a component. Extreme value analysis (EVA) is a tool for PCI, it allows an inspector to build a statistical model of the smallest thicknesses across a component. Construction of extreme value models relies on the selection of the smallest thicknesses from the inspection data. Current methodologies rely on the judgement of the analyst to select sets of thickness minima and frequently the inspection data is not checked to ensure that the assumptions made by EVA are reasonable. Consequently, the resulting models can be subjective and can provide inadequate models for extrapolation. In this paper, a framework for building extreme value models of inspection data is introduced. The method selects a sample of thickness minima such that the data is compatible with the assumptions of EVA. It is shown that this framework can select a suitable set of minima for a large number of correlated exponential and Gaussian surfaces and the method is tested using real inspection data collected from an ultrasonic thickness C-scan of a rough surface.
Benstock D, Cegla F, 2015, The Effect of Surface Roughness on Extrapolation from Thickness C-scan Data using Extreme Value Theory, 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 1677-1687, ISSN: 0094-243X
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Gajdacsi A, Cegla F, 2015, Ultrasonic Wall Loss Monitoring of Rough Surfaces, 41st Annual Review of Progress in Quantitative Nondestructive Evaluation (QNDE), Publisher: AMER INST PHYSICS, Pages: 856-862, ISSN: 0094-243X
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Cegla F, Allin J, 2015, ULTRASONIC MONITORING OF PIPELINE WALL THICKNESS WITH AUTONOMOUS, WIRELESS SENSOR NETWORKS, OIL AND GAS PIPELINES: INTEGRITY AND SAFETY HANDBOOK, Editors: Revie, Publisher: JOHN WILEY & SONS INC, Pages: 571-586, ISBN: 978-1-118-21671-2
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Benstock D, Cegla F, Stone M, 2014, The influence of surface roughness on ultrasonic thickness measurements, Journal of the Acoustical Society of America, Vol: 136, Pages: 3028-3039, ISSN: 0001-4966
In corrosion assessment, ultrasonic wall-thickness measurements are often presented in the form ofa color map. However, this gives little quantitative information on the distribution of the thicknessmeasurements. The collected data can be used to form an empirical cumulative distribution function(ECDF), which provides information on the fraction of the surface with less than a certain thickness.It has been speculated that the ECDF could be used to draw conclusions about larger areas, frominspection data of smaller sub-sections. A detailed understanding of the errors introduced by suchan approach is required to be confident in its predictions. There are two major sources of error: theactual thickness variation due to the morphology of the surface and the interaction of the signalprocessing algorithm with the recorded ultrasonic signals. Parallel experimental and computationalstudies were performed using three surfaces, generated with Gaussian height distributions. Thesurfaces were machined onto mild steel plates and ultrasonic C-scans were performed, while the distributedpoint source method was used to perform equivalent simulations. ECDFs corresponding toeach of these surfaces (for both the experimental and computational data) are presented and theirvariation with changing surface roughness and different timing algorithms is discussed.
Gajdacsi A, Jarvis AJC, Huthwaite P, et al., 2014, Reconstruction of Temperature Distribution in a Steel Block Using an Ultrasonic Sensor Array, Journal of Nondestructive Evaluation, Vol: 33, Pages: 458-470, ISSN: 1573-4862
Permanently installed ultrasonic sensors have thecapability of measuring much smaller changes in the signalthan conventional sensors that are used for ultrasonic inspections.This is because uncertainties associated with couplingfluids and positional offsets are eliminated. Therefore it ispotentially possible to monitor the onset of material degradation.A particular degradation mechanism that we are keento monitor is high temperature hydrogen attack; where theamount of damage is linked to a drop in ultrasonic velocitywhich we hope can be monitored for with an ultrasonic array.The changes introduced in the ultrasonic propagation velocityare expected to be of the order of 1 % and in practice theyare observable only from a very limited field of view (i.e. fromthe outside of a pipe) and therefore the reconstruction is challengingto accomplish. In order to explore the feasibility ofthis, we are investigating the reconstruction of a non-uniformtemperature distribution which allows us to quickly evaluatethe sensitivity of our method to small spatial variations inultrasonic velocity of the material. Two reconstruction algorithmswere implemented and their performance comparedin simulated and real measurements. The results of the testswere encouraging: local temperature differences as low as10 ◦C could be detected, which corresponds to a local propagationvelocity change of 5 m/s (0.15 % relative velocitychange).
Jarvis AJC, Cegla FB, 2014, Scattering of Near Normal Incidence SH Waves by Sinusoidal and Rough Surfaces in 3-D: Comparison to the Scalar Wave Approximation, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Vol: 61, Pages: 1179-1190, ISSN: 0885-3010
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Attarian VA, Cegla FB, Cawley P, 2014, Long-term stability of guided wave structural health monitoring using distributed adhesively bonded piezoelectric transducers, STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, Vol: 13, Pages: 265-280, ISSN: 1475-9217
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- Citations: 28
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