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Title: Advances in EMAT measurements for NDE
Author: Ho, Kwok Shun
ISNI:       0000 0001 3579 3184
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2007
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This thesis describes a variety of experiments, many using advanced signal processing techniques, and electromagnetic acoustic transducers (EMATs). The first sections of this thesis describe the application of the pulse-compression signal processing technique with EMATs. This has been shown to improve the signal-to-noise ratio without the use of high levels of signal averaging, and thus potentially increases the speed of measurements. Ultrasonics thickness measurements and imaging were carried out to show that pulse-compression can be applied to the testing of the metals. The work was extended to demonstrate the successful measurement of fill level in drinks cans, and the detection of foreign bodies using fan-beam tomographic imaging in the drink cans. This thesis also describes the application of a continuous wavelet transform (CWT) to EMATs. The technique was applied to experimental EMAT data in thin metal plates, to identify propagation of s0, a0, a1, S1 and S2 modes in an aluminium plate from one waveform. To illustrate the usefulness of the approach, the extracted multiple modes were applied to tomographic reconstructions of artificial defects in plates. This thesis also describes metal texture measurements using EMATs and wavelet processing. The work described in this section focuses on the multi-scale discrete wavelet method where the analysis in time and in wavelet scale is discrete as opposed to the CWT. The use of discrete wavelet processing for signal analysis can improve the performance of EMATs data in highly noisy environments. Another section describes the use of the micro-stereolithography (MSL) process to fabricate EMATs, and this is followed by a description of the Synthetic Aperture Focussing Technique (SAFT) algorithm used to reconstruct images of data obtained from these EMATs. Finally, results are given, demonstrating that the EMA Ts can be used to perform NDE inspections. The thesis also contains conclusions and suggestions for further work.
Supervisor: Not available Sponsor: Crane Electronics Ltd ; Engineering and Physical Sciences Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TA Engineering (General). Civil engineering (General)