**5. Conclusion**

Indeed, the acoustic emission phenomena have been utilized as a powerful tool with the purpose to either detect, locate or assess damage for a wide range of applications. Derived from its monitoring, one of the major challenges in analyzing the resulting wavelet or synchrosqueezing transform signal is to identify and extract each generated AE event. Typically, this event detection is carried out by a thresholding approach over the raw signal. In this regard, the wavelet algorithm has resulted in a very useful and successful technique in detecting the time of flight of the acoustic emission echoes generated by defects at their corresponding frequencies. The accuracy of the algorithm was investigated experimentally using metallic structure. This algorithm is more powerful than the conventional Fourier transform algorithm. Various mother wavelets have been used to compare the correlation between the mother wavelet and the acquired A-scan signals. A mother wavelet with higher correlation would provide more accurate results. Thus, it is important to select the mother wavelet carefully to avoid misleading results. In regard with the synchrosqueezing transform, although improved resolution capabilities, the error in regard with the time of flight determination is not reduced. The Morlet wavelet is revealed as the most suitable wavelet dealing with such acoustic emission waves generated by means of LASER excitation.

**109**

provided the original work is properly cited.

, Fernando Piñal Moctezuma2

, Luis Romeral Martínez<sup>2</sup>

\*Address all correspondence to: miguel.delgado@mcia.upc.edu

© 2019 The Author(s). Licensee IntechOpen. This chapter is distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/ by/3.0), which permits unrestricted use, distribution, and reproduction in any medium,

1 Physics Department, Technical University of Catalonia, Terrassa, Barcelona, Spain

2 Electronics Engineering Department, Technical University of Catalonia, Terrassa,

, Miguel Delgado Prieto2

and Crina Cojocaru1

\*,

*Wavelet Transform Applied to Internal Defect Detection by Means of Laser Ultrasound*

This work was supported in part by the CONACyT scholarship grant number 411711, Mexico, and the Ministry of Economy and Competitiveness under the

All authors declare that no conflict of interest exists at the time of manuscript

*DOI: http://dx.doi.org/10.5772/intechopen.84964*

TRA2016-80472-R Research Project, Spain.

**Acknowledgements**

**Conflict of interest**

submission.

**Author details**

Hossam Selim1

Barcelona, Spain

José Francisco Trull1

*Wavelet Transform Applied to Internal Defect Detection by Means of Laser Ultrasound DOI: http://dx.doi.org/10.5772/intechopen.84964*
