RANDOM SEQUENCE FOR OPTIMAL LOW-POWER LASER GENERATED ULTRASOUND

24th A.I.VE.LA. Annual Meeting

Vangi, D.^1 ; Virga, A.^1 ; Gulino, M.S.^1

Università degli Studi di Firenze, Department of Industrial Engineering, Italy^1

关键词: Cross correlation techniques;    Experimental test;    Mechanical components;    Non destructive testing;    Post processing;    State of the art;    Ultrasound detection;    Ultrasound generation;   

Others  :  https://iopscience.iop.org/article/10.1088/1742-6596/882/1/012013/pdf
DOI  :  10.1088/1742-6596/882/1/012013

来源: IOP

【 摘 要 】

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 Npulses, the pulse duration δ and the distance between pulses dpulses. 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 Npulsesand δ but low dpulses. 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.