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Title: Acoustic metamaterials for medical ultrasound and non-destructive evaluation
Author: Laureti, Stefano
ISNI:       0000 0004 6423 5626
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 2016
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This thesis shows both the use of acoustic metamaterials and coded waveforms for Non-Destructive Testing (NDT) applications. The exotic features of the acoustic metamaterials have been exploited for imaging a sub-wavelength object at frequencies into the middle audible – low ultrasonic range, thus beating the so-called diffraction limit. This has been investigated by means of both Finite Element Modelling and a series of experiments. These demonstrate that acoustic metamaterials fabricated using additive manufacturing with a polymer substrate can be used successfully for imaging a subwavelength object within a frequency range that was not previously explored. The experimental setup made use of coded waveform excitation for characterising the performance of these metamaterials in the frequency domain. Such broadband excitations waveforms can be exploited together with advanced signal processing techniques such as Pulse Compression (PuC) to enhance the Signal-to-Noise Ratio (SNR). Hence, a first step toward the realization of an acoustic metamaterial device that can be used with coded waveforms and PuC has been investigated. Parallel research on the optimal use of coded signals with PuC techniques has been carried out. The main characteristics of several widely-used coded waveforms and advanced algorithms have been reported. Their features have been investigated numerically so as to provide a benchmark for choosing an optimal coded waveform and pulse compression algorithm for a given NDT application. In addition, the improvement in inspection capabilities given by these advanced signal processing techniques has been tested using real industrial NDT applications in highly scattering and attenuating samples. This has been done by programming a tailored post-processing/imaging algorithm for each specific application. Furthermore, a portable instrumentation system is described, which is capable of providing a performance comparable to standard bench-top PuC instruments. Finally, an innovative strategy for using coded signals and PuC in active thermography inspection has been investigated. This results in an enhanced defect discrimination in challenging materials with respect to the standard PuC thermography procedure.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: TK Electrical engineering. Electronics Nuclear engineering