ULTRASONIC DETECTION BY PHOTO-EMF SENSOR AND BY WIDEBAND AIR-COUPLED TRANSDUCER

• Published in: Research in nondestructive evaluation 2004-07, Vol.15 (3), p.111-117
• Main Authors: Cerniglia, Donatella, Djordjevic, B. Boro
• Format: Article
• Language: English
• ISSN: 0934-9847; 1432-2110
• DOI: 10.1080/09349840490480783

Two non-contact remote ultrasonic detection systems are compared. The first consists of a continuous wave (CW) Nd:YVO 4 laser operating at 532 nm used in conjunction with a photo-induced electromotive-force (EMF) sensor. The second system employs an air-coupled capacitance transducer that has a bandwidth from 100 kHz up to 2 MHz. Both systems exhibit higher sensitivity to out-of-plane than in-plane measurements of stress wave signals. Ultrasound generation is carried out by an Nd:YAG pulsed laser at 532 nm in the thermoelastic regime in a 1.6 mm aluminum plate. A 0 Lamb mode is generated at frequency-thickness product with strong out-of-plane displacements. Ultrasonic waveforms acquired are reported and the performance advantages of the two remote non-contact detectors are compared with each other. For lower frequency tests (up to 2 MHz), better results have been achieved with the air-coupled transducer that also has superior overall performance and benefits. The tests enabled direct comparison of air-coupled transducer and photo-EMF detector.