Study on the most influential parameters in low-power laser generated ultrasound

Vangi, Dario; Virga, Antonio; Gulino, Michelangelo-Santo

doi:10.5937/fmet1703323v

Cited by 7 publications

(7 citation statements)

References 13 publications

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“…Because of the sequences randomness which is necessary to obtain only one and easily characterizable peak in the cross-correlation [15], represents a mean distance between pulses. Considering = 2000 and = 800 , the trend of SNR is shown in figure 13.…”

Section: Distance Between Pulsesmentioning

confidence: 99%

“…PN codes (e.g. Golay codes and M sequences [10,14]) have a precise order in ON/OFF lengths too, so that the only sequences' parameters that can be modified are the length in terms of point and the length in terms of time [15].…”

Section: T Sequencementioning

confidence: 99%

“…Its application can be effective only if highly random signals are used as laser inputs [15]: the most widely used sequences for this application are PN codes [10][11][12][13][14]. PN codes are extremely random but the thermo-elastic effect is not optimized, because of the difference in each laser pulse length.…”

Section: T Sequencementioning

confidence: 99%

“…Finite Element (FE) models allow to indagate the features of low-power laser US as can be done in those cases in which high power lasers are used [17][18][19]. FE analysis does not cover the experimental practice, where a high number of pulses and high randomness in the TTLs driving the laser are necessary [15,20]: an optimum in SNR can be reached adjusting parameters directly connected to the ultrasonic PtP value and the input sequence's randomness.…”

Section: Introductionmentioning

confidence: 99%

“…Low-power laser US are generated feeding (driving) the diode with TTL signals, especially PseudoNoise (PN) or pseudo-random sequences [10][11][12][13][14][15], consisting of several pulses with different lengths. PN codes have a perfectly centred auto-correlation, because of their high randomness characteristic; however, even if this can be an advantage considering only the cross-correlation post-processing purpose, pulses with different durations generate an US with different frequency content [16].…”

Section: Introductionmentioning

confidence: 99%

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Random Sequence for Optimal Low-Power Laser Generated Ultrasound

Vangi

Virga

Gulino

2017

J. Phys.: Conf. Ser.

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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.

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Section: Distance Between Pulsesmentioning

confidence: 99%

Section: T Sequencementioning

confidence: 99%

Section: T Sequencementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Random Sequence for Optimal Low-Power Laser Generated Ultrasound

Vangi

Virga

Gulino

2017

J. Phys.: Conf. Ser.

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Signal Enhancement in Surface Crack Detection with Gas-Coupled Laser Acoustic Detection

et al. 2021

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Ultrasonic signal enhancement resulting from constructive interference between direct Rayleigh waves and same waves reflected by a surface defect is exploited to increase crack identification capabilities of the Gas-Coupled Laser Acoustic Detection (GCLAD) non-contact detection technology. Highlights from simulations are provided regarding the interference phenomenon in the solid and its propagation in air, where GCLAD detection occurs. Experimental campaigns are preliminarily performed on a bar to evidence the effect of cracks on the GCLAD acquired signals. Then, a signal enhancement of +30% is reached on a plate, implying that defects are efficiently scanned by moving the GCLAD in proximity of the discontinuity. Since the GCLAD allows monitoring points of a piece belonging to the same line at once, its translation in one direction is sufficient to perform a two-dimensional scan, entailing reduction of inspection time and simple automation of the interrogation layout compared to other traditional or signal enhancement-based techniques.

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