Comparative study of wide-band ultrasonic transducers

Absolute Sensitivity of Air, Light and Direct-Coupled Wideband Acoustic Emission Transducers

“…In addition, Fig. 4 also shows the "thermal rattle" level for aluminum, the calculated noise floor for the HFHS electronics, the AE detection threshold and the measured sensitivity of a Michelson interferometer from reference [1].…”

“…Previous work has compared the relative performance of various wide-band ultrasonic transducers used as receivers [1]. Studies have also been made comparing the merits of various optical sensors [2] and evaluating their applicability to acoustic emission (AE) [3].…”

Optical Sensing of Ultrasound

“…Microradian beam deflections can be measured, although the technique has normally been used for only qualitative amplitude measurements. Quantitative measurements have required the use of interferometric instruments, and have evolved into many forms, They nearly all require some form of low frequency compensation to ensure that they are capable of measuring the relatively small amplitudes of ultrasonic events, Homodyne interferometers such as those based on a Michelson arrangement are capable of measuring out-of-plane ultrasonic displacements [25], Their frequency response is limited by the photo-detectors and subsequent electronic amplifiers, They can have a broad-band frequency response up to at least 150 MHz [13], If the frequency response is lower than this, optical arrangements can be made to enhance signal-tonoise performance levels, An example of this has been recently published by Holloway et at [3] and shown in Figure 5, Multiple paths within the interferometer increase the out-of-plane displacement sensitivity, Alternatively, improved signal-to-noise can be achieved with the use of a heterodyne device, in which the ultrasonic signal is superimposed onto a carrier wave at the shifting frequency, f b , For example, many systems based on a Michelson heterodyne interferometer have been described in the literature [e.g. 6,25], A Bragg cell operating as an acousto-optic cell is excited at frequency f b and is used to shift the optical frequency, Ultrasonic detection and calibration can be carried out in several ways [25,31],…”

“…• materials characterisation, such as residual stress, elastic moduli [8,II] • as a standard in the cross-calibration of transducers [12,13] • 2-D mapping of bulk defects in solids [14] • detection and sizing of surface-breaking cracks [15,16] 158 R. J. DEWHURST…”

Laser Ultrasonic and Photoacoustic NDE Using Front-Surface Piezoelectric Detection

“…In contrast. the piezoelectric transducers have the advantage of high sensitivity: several orders of magnitude higher than any alternate detection schemes [3][4][5]. This high sensitivity allows development of practical techniques which utilize these detectors [6,7].…”