Low-power laser generated ultrasounds are lately gaining importance in the research world, thanks to the possibility of investigating a mechanical component structural integrity through a non-contact and Non-Destructive Testing (NDT) procedure. The ultrasounds are, however, very low in amplitude, making it necessary to use pre-processing and post-processing operations on the signals to detect them. The cross-correlation technique is used in this work, meaning that a random signal must be used as laser input. For this purpose, a highly random and simple-to-create code called T sequence, capable of enhancing the ultrasound detectability, is introduced (not previously available at the state of the art). Several important parameters which characterize the T sequence can influence the process: the number of pulses , the pulse duration δ and the distance between pulses . A Finite Element FE model of a 3 mm steel disk has been initially developed to analytically study the longitudinal ultrasound generation mechanism and the obtainable outputs. Later, experimental tests have shown that the T sequence is highly flexible for ultrasound detection purposes, making it optimal to use high and δ but low . In the end, apart from describing all phenomena that arise in the low-power laser generation process, the results of this study are also important for setting up an effective NDT procedure using this technology.
RANDOM SEQUENCE FOR OPTIMAL LOW-POWER LASER GENERATED ULTRASOUND / Dario Vangi, Antonio Virga, Michelangelo-Santo Gulino. - ELETTRONICO. - 882:(2017), pp. 1-14. (Intervento presentato al convegno XXIV A.I.VE.LA. Annual Meeting tenutosi a Brescia nel 27-28 Ottobre 2016) [10.1088/1742-6596/882/1/012013].
RANDOM SEQUENCE FOR OPTIMAL LOW-POWER LASER GENERATED ULTRASOUND
Dario Vangi;Antonio Virga;Michelangelo-Santo Gulino
2017
Abstract
Low-power laser generated ultrasounds are lately gaining importance in the research world, thanks to the possibility of investigating a mechanical component structural integrity through a non-contact and Non-Destructive Testing (NDT) procedure. The ultrasounds are, however, very low in amplitude, making it necessary to use pre-processing and post-processing operations on the signals to detect them. The cross-correlation technique is used in this work, meaning that a random signal must be used as laser input. For this purpose, a highly random and simple-to-create code called T sequence, capable of enhancing the ultrasound detectability, is introduced (not previously available at the state of the art). Several important parameters which characterize the T sequence can influence the process: the number of pulses , the pulse duration δ and the distance between pulses . A Finite Element FE model of a 3 mm steel disk has been initially developed to analytically study the longitudinal ultrasound generation mechanism and the obtainable outputs. Later, experimental tests have shown that the T sequence is highly flexible for ultrasound detection purposes, making it optimal to use high and δ but low . In the end, apart from describing all phenomena that arise in the low-power laser generation process, the results of this study are also important for setting up an effective NDT procedure using this technology.I documenti in FLORE sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.