Imperial College London

DrFredericCegla

Faculty of EngineeringDepartment of Mechanical Engineering

Reader in Mechanical Engineering
 
 
 
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Contact

 

+44 (0)20 7594 8096f.cegla

 
 
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Location

 

567City and Guilds BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

102 results found

Chen Y, Yang Z, Bai X, Zou F, Cegla FBet al., 2023, High-precision in situ 3D ultrasonic imaging of localized corrosion-induced material morphological changes, NPJ MATERIALS DEGRADATION, Vol: 7

Journal article

Huang M, Cegla F, Lan B, 2023, Stiffness matrix method for modelling wave propagation in arbitrary multilayers, International Journal of Engineering Science, Vol: 190, ISSN: 0020-7225

Natural and engineered media usually involve combinations of solid, fluid and porous layers, and accurate and stable modelling of wave propagation in such complex multilayered media is fundamental to evaluating their properties with wave-based methods. Here we present a general stiffness matrix method for modelling waves in arbitrary multilayers. The method first formulates stiffness matrices for individual layers based on the governing wave equations for fluids and solids, and the Biot theory for porous materials. Then it utilises the boundary conditions considered at layer interfaces to assemble the layer matrices into a global system of equations, to obtain solutions for reflection and transmission coefficients at any incidence. Its advantage over existing methods is manifested by its unconditional computational stability, and its validity is proved by experimental validations on single solid sheets, porous layers, and porous-solid-porous battery electrodes. This establishes a powerful theoretical platform that allows us to develop advanced wave-based methods to quantitatively characterise properties of the layers, especially for layers of porous materials.

Journal article

Clarkson L, Zhang Y, Cegla F, 2023, A comparison of ultrasonic temperature monitoring using machine learning and physics-based methods for high-cycle thermal fatigue monitoring, STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, ISSN: 1475-9217

Journal article

Wei T, Fantetti A, Cegla F, Schwingshackl Cet al., 2023, An optical method to monitor transparent contact interfaces during high frequency shear vibration cycles, Wear, Vol: 524-525, Pages: 1-12, ISSN: 0043-1648

Contacting interfaces provide frictional damping in jointed structures subjected to high dynamic loads. Predicting this frictional damping during vibration cycles is highly important since it strongly affects the dynamic response of the assembly and hence the lifetime of parts. Since frictional damping is heavily influenced by the contact condition at the interface, the most direct and insightful approach is thereby to actively monitor the contact interface. Although several methods have already been proposed to monitor the contact interfaces quasi-statically or in pre-sliding, such as digital image correlation, X-Ray and ultrasound, only limited data is available of the frictional interface behaviour during high frequency vibration.To provide a better insight into the contact interface behaviour during high frequency cyclic motion, an optical method is here developed based on transparent friction specimens and total internal reflection, and applied to an existing friction test rig. The resulting measurements across the whole interface show a large variation in the real area of contact during each vibration cycle, which could be linked to the kinematics of the contact interface. This large variation is observed for the first time in high frequency oscillating contacts and is attributed to ageing effect and fracture of asperities. These two effects dominate the contact mechanism at different sliding velocities and induce variations in the real area of contact during each vibration cycle. These results suggest that the mechanisms behind high frequency contact behaviour are more complex than what commonly assumed in dynamics simulations.

Journal article

Zhang Y, Cegla F, 2023, Co-located dual-wave ultrasonics for component thickness and temperature distribution monitoring, Structural Health Monitoring, Vol: 22, Pages: 1090-1104, ISSN: 1475-9217

Permanently installed ultrasonic sensors have found increasing applications in the field of structural health monitoring (SHM), in particular with respect to thickness measurement and corrosion monitoring. As ultrasonic velocity is temperature dependent, the state and temperature distribution of a component contribute to much of the measurement uncertainties of an ultrasonic SHM system. On the other hand, the temperature dependency of ultrasonic velocity has also led to various temperature sensing methods for measuring temperature distributions within solid materials. While conventional ultrasound-based techniques can measure either a component’s thickness at a given temperature, or the internal temperature distributions at a given component thickness, measurement fluctuations and drifts can occur if both variables are set to change simultaneously. In this study, we propose a dual-wave approach to overcome the limitations of the existing methods. ‘Co-located’ shear and longitudinal pulse-echo measurements are used to simultaneously track the thickness change and through-thickness temperature variation of a steel plate in complex environmental conditions. Results of the verification experiments showed that, in the given conditions, the proposed dual-wave correction method could reduce thickness measurement uncertainties by approximately a factor of 5 and eliminate 90% of the drift in temperature predictions.

Journal article

Zhang Y, Dong H, Wang T, He G, Parkin IP, Cegla Fet al., 2023, Monitoring Dendrite Formation in Aqueous Zinc Batteries with SH0 Guided Waves, Editors: Rizzo, Milazzo, Publisher: SPRINGER-VERLAG SINGAPORE PTE LTD, Pages: 204-211, ISBN: 978-3-031-07321-2

Book chapter

Zhang Y, Cegla F, 2023, Simultaneous Monitoring of Component Thickness and Internal Temperature Gradient Using Ultrasound, Editors: Rizzo, Milazzo, Publisher: SPRINGER-VERLAG SINGAPORE PTE LTD, Pages: 790-798, ISBN: 978-3-031-07321-2

Book chapter

Zhang Y, Dong H, Wang T, He G, Parkin IP, Cegla Fet al., 2022, Ultrasonic guided wave monitoring of dendrite formation at electrode-electrolyte interface in aqueous zinc ion batteries, JOURNAL OF POWER SOURCES, Vol: 542, ISSN: 0378-7753

Journal article

Huang M, Kirkaldy N, Zhao Y, Patel Y, Cegla F, Lan Bet al., 2022, Quantitative characterisation of the layered structure within lithium-ion batteries using ultrasonic resonance, Journal of Energy Storage, Vol: 50, Pages: 1-14, ISSN: 2352-152X

Lithium-ion batteries (LIBs) are becoming an important energy storage solution to achieve carbon neutrality, but it remains challenging to characterise their internal states for the assurance of performance, durability and safety. This work reports a simple but powerful non-destructive characterisation technique, based on the formation of ultrasonic resonance from the repetitive layers within LIBs. A physical model is developed from the ground up, to interpret the results from standard experimental ultrasonic measurement setups. As output, the method delivers a range of critical pieces of information about the inner structure of LIBs, such as the number of layers, the average thicknesses of electrodes, the image of internal layers, and the states of charge variations across individual layers. This enables the quantitative tracking of internal cell properties, potentially providing new means of quality control during production processes, and tracking the states of health and charge during operation.

Journal article

Yung K, Garriga-Casanovas A, Khalili P, Cegla Fet al., 2022, Visually encoded contact inspection system for EMATs, Journal of Nondestructive Evaluation, Vol: 41, Pages: 1-9, ISSN: 0195-9298

Contact inspections are commonly performed in industry to check for defects and degradation, such as corrosion or cracks. Non-destructive evaluation (NDE) probes are being deployed with increasing frequency using autonomous robots, especially in harsh environments or in areas where access is restricted and difficult. Together with the NDE measurement, it is important to capture the 3D position of the probe so that the location where the data originated is known. This allows for the generation of 3D maps of the inspection, which ensure full scan coverage, and can be used for inspection reports and to generate digital twins of the structure for asset management. In this paper, a full inspection system integrating a robot mountable stereo camera system together with an electromagnetic acoustic transducer (EMAT) probe and a wireless NDE data acquisition system is presented. The system is capable of capturing and merging 3D positional data of the probe as it is scanned and NDE data. The system design in terms of hardware and software is described in this paper. A set of tests to evaluate its performance on relevant structural components are also presented, and the results are reported and discussed.

Journal article

Parra-Raad J, Cegla F, 2022, On the steerability of phased array EMATs: The dipole element, NDT & E INTERNATIONAL, Vol: 125, ISSN: 0963-8695

Journal article

Fantetti A, Mariani S, Pesaresi L, Nowell D, Cegla F, Schwingshackl Cet al., 2021, Ultrasonic monitoring of friction contacts during shear vibration cycles, Mechanical Systems and Signal Processing, Vol: 161, ISSN: 0888-3270

Complex high-value jointed structures such as aero-engines are carefully designed and optimized to prevent failure and maximise their life. In the design process, physically-based numerical models are employed to predict the nonlinear dynamic response of the structure. However, the reliability of these models is limited due to the lack of accurate validation data from metallic contact interfaces subjected to high-frequency vibration cycles. In this study, ultrasonic shear waves are used to characterise metallic contact interfaces during vibration cycles, hence providing new validation data for an understanding of the state of the friction contact. Supported by numerical simulations of wave propagation within the material, a novel experimental method is developed to simultaneously acquire ultrasonic measurements and friction hysteresis loops within the same test on a high-frequency friction rig. Large variability in the ultrasound reflection/transmission is observed within each hysteresis loop and is associated with stick/slip transitions. The measurement results reveal that the ultrasound technique can be used to detect stick and slip states in contact interfaces subjected to high-frequency shear vibration. This is the first observation of this type and paves the way towards real-time monitoring of vibrating contact interfaces in jointed structures, leading to a new physical understanding of the contact states and new validation data needed for improved nonlinear dynamic analyses.

Journal article

de Winton H, Cegla F, Hooper P, 2021, A method for objectively evaluating the defect detection performance of in-situ monitoring systems, Additive Manufacturing, Vol: 48, Pages: 1-13, ISSN: 2214-8604

In-situ monitoring systems have the potential to assess material quality in additive manufacturing processes on-the-fly, paving the way for accelerated component qualification using defect digital twins. However, current systems vary widely in sensor technology and data analysis methods, leading to a lack of consensus in how the performance of these systems should be measured and compared. This work proposes a methodology and set of metrics, specifically Receiver Operating Characteristic (ROC) and Probability of Detection (POD) curves, to allow objective comparison of performance between any system, regardless of its underlying technology. We demonstrate this approach by comparing the ability to detect increases in part-wide porosity using two of the most common co-axial monitoring techniques in laser powder bed fusion; photodiodes and high-speed cameras. Using ROC curves, we show that melt pool metrics extracted from the camera offer a better trade off between detection and false alarms compared to the photodiodebased system when discriminating between samples at a 0.5% porosity threshold. POD curves were used to characterise detection capability across all porosity levels. It was found that the camera-based system can detect 43% of compromised parts (0.5% porosity), while the photodiode system detects 20%. However, for significantly compromised parts (5% porosity), the camera based method reaches 100%, while the photodiode only achieves 85%. The developed methodology shows that while the camera-based system is measurably superior, further improvement is needed before commercial implementation can be realised. Ultimately, the ROC-POD methodology allows objective assessments of detection performance, enabling quantifiable progress in the development of defect detection systems based on in-situ monitoring.

Journal article

Huang J, Cegla F, Wickenden A, Coomber Met al., 2021, Simultaneous Measurements of Temperature and Viscosity for Viscous Fluids Using an Ultrasonic Waveguide, SENSORS, Vol: 21

Journal article

Parra-Raad J, Lan B, Cegla F, 2021, Orthogonally polarised shear waves for evaluating anisotropy and cracks in metals, Independent Nondestructive Testing and Evaluation (NDT and E) International, Vol: 121, ISSN: 0963-8695

The detection of crack-like defects using ultrasound is a problem widely studied by the non-destructive evaluation community. In this work, a technique of how to detect the presence of a crack-like defect and estimate its orientation in an anisotropic material by means of two orthogonal shear waves is presented. A detailed study of shear wave propagating and splitting at any incident angle, and its interaction with crack-like defects in anisotropic materials, is also presented. In this paper it is shown that by the use of two orthogonal shear waves with linear polarisation the authors could: 1) estimate the material level of anisotropy within approximately 0.5% of the measured value; 2) estimate the angular position of the principal shear directions of the material with respect to the orthogonal shear wave sources within ±5⁰ accuracy; 3) excite a shear wave purely polarised along one of the principal shear directions with two orthogonal shear waves placed at an arbitrary angular position; 4) detect the presence of a crack-like defect in an anisotropic material based on the back-wall echoes of two orthogonal shear waves, 5) estimate the orientation of a crack-like defect in an anisotropic material within ∼ ± 5⁰ of the theoretical value. The simulation and experimental results obtained show that the technique presented in this paper has potential to become an effective tool for crack-like defect detection and material characterisation.

Journal article

Khalili P, Cegla F, 2021, Excitation of Single-Mode Shear-Horizontal Guided Waves and Evaluation of Their Sensitivity to Very Shallow Crack-Like Defects, IEEE TRANSACTIONS ON ULTRASONICS FERROELECTRICS AND FREQUENCY CONTROL, Vol: 68, Pages: 818-828, ISSN: 0885-3010

Journal article

Hall T, Cegla F, van Arkel RJ, 2021, Simple smart implants: simultaneous monitoring of loosening and temperature in orthopaedics with an embedded ultrasound transducer, IEEE Transactions on Biomedical Circuits and Systems, Vol: 15, Pages: 102-110, ISSN: 1932-4545

Implant failure can have devastating consequences on patient outcomes following joint replacement. Time to diagnosis affects subsequent treatment success, but current diagnostics do not give early warning and lack accuracy. This research proposes an embedded ultrasound system to monitor implant fixation and temperature – a potential indicator of infection. Requiring only two implanted components: a piezoelectric transducer and a coil, pulse-echo responses are elicited via a three-coil inductive link. This passive system avoids the need for batteries, energy harvesters, and microprocessors, resulting in minimal changes to existing implant architecture. Proof-of-concept was demonstrated in vitro for a titanium plate cemented into synthetic bone, using a small embedded coil with 10 mm diameter. Gross loosening – simulated by completely debonding the implant-cement interface – was detectable with 95% confidence at up to 12 mm implantation depth. Temperature was calibrated with root mean square error of 0.19 °C at 5 mm, with measurements accurate to ±1 °C with 95% confidence up to 6 mm implantation depth. These data demonstrate that with only a transducer and coil implanted, it is possible to measure fixation and temperature simultaneously. This simple smart implant approach minimises the need to modify well-established implant designs, and hence could enable mass-market adoption.

Journal article

Garriga Casanovas A, Khalili P, Cegla F, 2020, Development of a new, wireless acquisition system for EMATs compatible with the robotics operating system, IEEE Sensors Journal, Vol: 20, Pages: 12783-12790, ISSN: 1530-437X

The deployment of transducers to perform in situ inspections of industrial components can be complicated, and in many cases is still performed manually by a team of operators, which involves significant costs and can be dangerous. Robots capable of deploying probes in difficult to access locations are becoming available. Electromagnetic acoustic transducers (EMAT) are well suited to be used with robots since they are noncontact transducers that do not require a coupling medium, and can easily perform scans. However, existing acquisition systems for EMATs are generally not suitable to be directly mounted on robots. In this paper, a new wireless acquisition system for EMATs is presented. The system is standalone, it transmits the inspection data over WiFi, and is compatible with the robotics operating system (ROS). In addition, it is designed to be modular, small and lightweight so that it can be easily mounted on robots. The system design in terms of hardware and software is described in thispaper. The resulting performance of the system is also reported.

Journal article

Zhang Y, Cegla F, Corcoran J, 2020, Ultrasonic monitoring of pipe wall interior surface temperature, STRUCTURAL HEALTH MONITORING-AN INTERNATIONAL JOURNAL, ISSN: 1475-9217

Journal article

Gu X, Cegla F, 2020, Modeling Surface Roughness-Related Uncertainties of Leaky Lamb Wave Clamp-on Ultrasonic Flowmeters, IEEE TRANSACTIONS ON INSTRUMENTATION AND MEASUREMENT, Vol: 69, Pages: 6843-6852, ISSN: 0018-9456

Journal article

Cegla F, 2020, Microwaves trigger thermo-acoustic ultrasound generation, ADVANCED PHOTONICS, Vol: 2

Journal article

Parra-Raad J, Khalili P, Cegla F, 2020, Shear waves with orthogonal polarisations for thickness measurement and crack detection using EMATs, NDT & E International, Vol: 111, Pages: 1-7, ISSN: 0963-8695

The use of polarised shear waves to detect the presence of crack-like defects seems to have received little or no attention in the past. The authors believe that the main reason for this appears to be the lack of a device with the capability to excite shear waves of different polarisations. In this paper, the authors, first, present the design of an EMAT that permits the excitation of two orthogonally polarised shear waves in metallic materials by means of two coils that are orthogonal with respect to each other. This is then followed by a 3D finite element analysis of the wavefield generated by the EMAT and its interactions with crack-like defects of different sizes, positions and orientations. Then a methodology of how this EMAT can be used to simultaneously measure material thickness and detect crack-like defects in pulse-echo mode is introduced. Good agreement between the finite element simulation and experimental results was observed which makes the presented technique a potential new method for simultaneous thickness measurements and crack detection.

Journal article

Herdovics B, Cegla F, 2020, Long-term stability of guided wave electromagnetic acoustic transducer systems, Structural Health Monitoring, Vol: 19, Pages: 3-11, ISSN: 1475-9217

This article evaluates the long-term stability of a Lorentz force guided wave electromagnetic acoustic transducer. The specific application of the investigated electromagnetic acoustic transducer is pipeline health monitoring using low-frequency (27 kHz) long-range torsional guided waves. There is a concern that repeated swings in the temperature of the structure can cause irreversible changes in the transduction mechanism and therefore pose a risk to the long-term stability of transducers. In this article we report on guided wave signals acquired on a custom-built transducer while it was exposed to more than 90 heating cycles. The highest temperature that was reached during cycling was 80°C and the measurements were acquired over a 14-month period. At the end of the 1-year period, the transducer phase had changed by 23.32° and its amplitude by 3.7%. However, this change was not gradual and most of the change occurred early on, before the highest temperature was first reached in the temperature cycling process. The observed change after this was 6.08° phase shift and 0.9% amplitude change. The possible sources of output changes were investigated, and it was found that the mechanical properties of the contact layer between the electromagnetic acoustic transducer and the pipe surface was very important. A soft silicone interlayer performed best and was able to reduce temperature-induced phase changes in the monitored signals from a maximum of 80 degrees phase change to about 20 degrees phase change, a fourfold reduction.

Journal article

Pesaresi L, Fantetti A, Cegla F, Salles L, Schwingshackl CWet al., 2020, On the use of ultrasound waves to monitor the local dynamics of friction joints, Experimental Mechanics, Vol: 60, Pages: 129-141, ISSN: 0014-4851

Friction joints are one of the fundamental means used for the assembly of structural components in engineering applications. The structural dynamics of these components becomes nonlinear, due to the nonlinear nature of the forces arising at the contact interface characterised by stick-slip phenomena and separation. Advanced numerical models have been proposed in the last decades which have shown some promising capabilities in capturing these local nonlinearities. However, despite the research efforts in producing more advanced models over the years, a lack of validation experiments made it difficult to have fully validated models. For this reason, experimental techniques which can provide insights into the local dynamics of joints can be of great interest for the refinement of such models and for the optimisation of the joint design and local wear predictions. In this paper, a preliminary study is presented where ultrasound waves are used to characterise the local dynamics of friction contacts by observing changes of the ultrasound reflection/transmission at the friction interface. The experimental technique is applied to a dynamic friction rig, where two steel specimens are rubbed against each other under a harmonic tangential excitation. Initial results show that, with a controlled experimental test procedure, this technique can identify microslip effects at the contact interface.

Journal article

Isla J, Cegla F, 2019, Simultaneous transmission and reception on all elements of an array: binary code excitation, Proceedings of the Royal Society A: Mathematical, Physical and Engineering Sciences, Vol: 475, Pages: 1-23, ISSN: 1364-5021

Pulse-echo arrays are used in radar, sonar, seismic, medical and non-destructive evaluation. There is a trend to produce arrays with an ever-increasing number of elements. This trend presents two major challenges: (i) often the size of the elements is reduced resulting in a lower signal-to-noise ratio (SNR) and (ii) the time required to record all of the signals that correspond to every transmit–receive path increases. Coded sequences with good autocorrelation properties can increase the SNR while orthogonal sets can be used to simultaneously acquire all of the signals that correspond to every transmit–receive path. However, a central problem of conventional coded sequences is that they cannot achieve good autocorrelation and orthogonality properties simultaneously due to their length being limited by the location of the closest reflectors. In this paper, a solution to this problem is presented by using coded sequences that have receive intervals. The proposed approach can be more than one order of magnitude faster than conventional methods. In addition, binary excitation and quantization can be employed, which reduces the data throughput by roughly an order of magnitude and allows for higher sampling rates. While this concept is generally applicable to any field, a 16-element system was built to experimentally demonstrate this principle for the first time using a conventional medical ultrasound probe.

Journal article

Herdovics B, Cegla F, 2019, Compensation of phase response changes in ultrasonic transducers caused by temperature variations, Structural Health Monitoring, Vol: 18, Pages: 508-523, ISSN: 1475-9217

One of the biggest challenges in structural health monitoring is the compensation of monitored data for environmental and operational conditions. In order to reliably estimate the changes in the structure, it is essential that the effects of environmental and operational conditions on the ultrasonic signal are compensated for before the signals are further analysed. The temperature-induced propagation speed change has the biggest effect on the ultrasonic signal and has been thoroughly investigated. This article investigates the subtler, yet also very important, changes in transducer output resulting from changes in the operating temperature. A compensation method is proposed which compensates for both the transducer phase response change and the wave’s propagation speed change. A key practical feature of the presented compensation method is that it uses only the ultrasonic signal itself for compensation estimation and can be used for any type of ultrasonic wave regardless of the type of transducer. For demonstration purposes, in this article, the results are shown for zero-order torsional guided waves, acquired by a purpose-built electromagnetic acoustic transducer. For signals with a 41.5°C temperature difference, the proposed compensation method was able to reduce the effect of environmental and operational conditions by 20 dB further (7 dB at the tail of the echo) compared to standard methods. This results in a much higher sensitivity to defects in areas where strong reflections are received. Furthermore, for the presented measurement setup, the precision to which the temperature-dependent change in wave propagation speed could be estimated was improved by 15%.

Journal article

Gu X, Cegla F, 2019, The effect of internal pipe wall roughness on the accuracy of clamp-on ultrasonic flow meters, IEEE Transactions on Instrumentation and Measurement, Vol: 68, Pages: 65-72, ISSN: 0018-9456

Clamp-on transit-time ultrasonic flowmeters (UFMs) suffer from poor accuracy compared with spool-piece UFMs due to uncertainties that result from the in-field installation process. One of the important sources of uncertainties is internal pipe wall roughness which affects the flow profile and also causes significant scattering of ultrasound. This paper purely focuses on the parametric study to quantify the uncertainties (related to internal pipe wall roughness) induced by scattering of ultrasound and it shows that these effects are large even without taking into account the associated flow disturbances. The flowmeter signals for a reference clamp-on flowmeter setup were simulated using 2-D finite element analysis including simplifying assumptions (to simulate the effect of flow) that were deemed appropriate. The validity of the simulations was indirectly verified by carrying out experiments with different separation distances between ultrasonic probes. The error predicted by the simulations and the experimentally observed errors were in good agreement. Then, this simulation method was applied on pipe walls with rough internal surfaces. For ultrasonic waves at 1 MHz, it was found that compared with smooth pipes, pipes with only a moderately rough internal surface (with 0.2-mm rms and 5-mm correlation length) can exhibit systematic errors of 2 in the flow velocity measurement. This demonstrates that pipe internal surface roughness is a very important factor that limits the accuracy of clamp on UFMs.

Journal article

Gu X, Cegla F, 2019, The uncertainties induced by internal pipe wall roughness on the measurements of clamp-on ultrasonic flow meters, IEEE International Ultrasonics Symposium (IUS), Publisher: IEEE, Pages: 1586-1589, ISSN: 1948-5719

Conference paper

Jarvis R, Farinha A, Kovac M, Cegla Fet al., 2018, NDE sensor delivery using unmanned aerial vehicles, Insight (Northampton): non-destructive testing and condition monitoring, Vol: 60, Pages: 463-467, ISSN: 1354-2575

The robotic deployment of NDE sensors has great cost-saving potential in cases where the measurement cost is high due to access restrictions or the need to temporarily decommission the test structure. Unmanned aerial vehicles (UAVs) are able to quickly reach inaccessible components to perform visual inspection and deploy NDE sensors. In this work, a mechanical sensor release mechanism is presented that has enabled electromagnetic acoustic transducers (EMATs) to be deployed onto a ferromagnetic pipe and a plate, after which the component wall thickness measurements can be transmitted wirelessly to a remote location. The reliability of the method and the most promising areas for future development are discussed.

Journal article

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.

Conference paper

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