{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,1,9]],"date-time":"2026-01-09T21:14:09Z","timestamp":1767993249411,"version":"3.49.0"},"reference-count":39,"publisher":"MDPI AG","issue":"3","license":[{"start":{"date-parts":[[2019,1,30]],"date-time":"2019-01-30T00:00:00Z","timestamp":1548806400000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"funder":[{"DOI":"10.13039\/501100003329","name":"Ministerio de Econom\u00eda y Competitividad","doi-asserted-by":"publisher","award":["TRA2016-80472-R"],"award-info":[{"award-number":["TRA2016-80472-R"]}],"id":[{"id":"10.13039\/501100003329","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100003329","name":"Ministerio de Econom\u00eda y Competitividad","doi-asserted-by":"publisher","award":["FIS2015-65998-C2-1"],"award-info":[{"award-number":["FIS2015-65998-C2-1"]}],"id":[{"id":"10.13039\/501100003329","id-type":"DOI","asserted-by":"publisher"}]},{"DOI":"10.13039\/501100003329","name":"Ministerio de Econom\u00eda y Competitividad","doi-asserted-by":"publisher","award":["FIS2015-65998-C2-2"],"award-info":[{"award-number":["FIS2015-65998-C2-2"]}],"id":[{"id":"10.13039\/501100003329","id-type":"DOI","asserted-by":"publisher"}]}],"content-domain":{"domain":[],"crossmark-restriction":false},"short-container-title":["Sensors"],"abstract":"<jats:p>Laser-generated ultrasound is a modern non-destructive testing technique. It has been investigated over recent years as an alternative to classical ultrasonic methods, mainly in industrial maintenance and quality control procedures. In this study, the detection and reconstruction of internal defects in a metallic sample is performed by means of a time-frequency analysis of ultrasonic waves generated by a laser-induced thermal mechanism. In the proposed methodology, we used wavelet transform due to its multi-resolution time frequency characteristics. In order to isolate and estimate the corresponding time of flight of eventual ultrasonic echoes related to internal defects, a density-based spatial clustering was applied to the resulting time frequency maps. Using the laser scan beam\u2019s position, the ultrasonic transducer\u2019s location and the echoes\u2019 arrival times were determined, the estimation of the defect\u2019s position was carried out afterwards. Finally, clustering algorithms were applied to the resulting geometric solutions from the set of the laser scan points which was proposed to obtain a two-dimensional projection of the defect outline over the scan plane. The study demonstrates that the proposed method of wavelet transform ultrasonic imaging can be effectively applied to detect and size internal defects without any reference information, which represents a valuable outcome for various applications in the industry.<\/jats:p>","DOI":"10.3390\/s19030573","type":"journal-article","created":{"date-parts":[[2019,1,30]],"date-time":"2019-01-30T10:58:27Z","timestamp":1548845907000},"page":"573","update-policy":"https:\/\/doi.org\/10.3390\/mdpi_crossmark_policy","source":"Crossref","is-referenced-by-count":23,"title":["Laser Ultrasound Inspection Based on Wavelet Transform and Data Clustering for Defect Estimation in Metallic Samples"],"prefix":"10.3390","volume":"19","author":[{"ORCID":"https:\/\/orcid.org\/0000-0003-2553-8205","authenticated-orcid":false,"given":"Hossam","family":"Selim","sequence":"first","affiliation":[{"name":"Physics Department, Universitat Polit\u00e8cnica de Catalunya, Rambla Sant Nebridi 22, 08222 Terrassa, Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0001-9282-838X","authenticated-orcid":false,"given":"Miguel","family":"Delgado Prieto","sequence":"additional","affiliation":[{"name":"Electronic Engineering Department, Universitat Polit\u00e8cnica de Catalunya, Rambla Sant Nebridi 22, 08222 Terrassa, Barcelona, Spain"}]},{"given":"Jos\u00e9","family":"Trull","sequence":"additional","affiliation":[{"name":"Physics Department, Universitat Polit\u00e8cnica de Catalunya, Rambla Sant Nebridi 22, 08222 Terrassa, Barcelona, Spain"}]},{"given":"Luis","family":"Romeral","sequence":"additional","affiliation":[{"name":"Electronic Engineering Department, Universitat Polit\u00e8cnica de Catalunya, Rambla Sant Nebridi 22, 08222 Terrassa, Barcelona, Spain"}]},{"ORCID":"https:\/\/orcid.org\/0000-0002-5244-8427","authenticated-orcid":false,"given":"Crina","family":"Cojocaru","sequence":"additional","affiliation":[{"name":"Physics Department, Universitat Polit\u00e8cnica de Catalunya, Rambla Sant Nebridi 22, 08222 Terrassa, Barcelona, Spain"}]}],"member":"1968","published-online":{"date-parts":[[2019,1,30]]},"reference":[{"key":"ref_1","doi-asserted-by":"crossref","unstructured":"Abbas, M., and Shafiee, M. 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