Calibration of acoustic emission sensors with laser-generated ultrasonic wave.

Abstract

Laser-generated ultrasonic wave is employed as a standard acoustic emission (AE) source to calibrate sensors. Characteristics of ultrasonic wave concerning its genera tionefficiency and directivity were investigated. By covering a transfer block with water layer, a unipolar planar pulse with 80 ns duration was efficiently generated. The surface excitation was interrogated by an optical interferometer, and subsequently measured by AE sensors. Comparing these outputs, the sensitivity of AE sensors can be determined in the wide frequency range. Experimental results on five commercial sensors are demonstrated.

Rayleigh Wave Calibration of Acoustic Emission Sensors and Ultrasonic Transducers

“…The trend of different RW and NW sensitivities found here is consistent with the behavior observed by Matsuda et al [34,35], using direct laser interferometry, as shown in Figure 2. However, it disagreed with the finding of Sause and Hamstad [23], who found that the receiving sensitivities to four wave types were identical.…”

“…( a ) Laser interferometric calibration results of Matsuda et al [34,35]. NW (solid curve) and RW (dash curve) receiving sensitivities for AE900M sensor.…”

“…At this time, however, this calibration method [24] is supported by no national standards agency, and secondary calibration [25] can only be conducted using primary calibration of more than ten years old. Another study by Matsuda et al [34,35] used laser interferometry directly on an aluminum transfer block, receiving Rayleigh waves generated by a line-focused Q-switched YAG laser. This reference source provided ±1 dB flatness over 0.06 to 3 MHz and eight sensors were characterized.…”

“…This reference source provided ±1 dB flatness over 0.06 to 3 MHz and eight sensors were characterized. However, sensor types remain unknown except for three, which also were evaluated for NW sensitivities [34,35]. Presently, these three are the only commercial AE sensors that have been calibrated for both NW and RW receiving sensitivities with laser references.…”

Transmission Sensitivities of Contact Ultrasonic Transducers and Their Applications

“…For ultrasonic works in SHM and industrial NDE, low MHz frequencies are typically used, and many applications utilize contact transducers because of practicality and cost. For UT and AE transducers, their calibration utilizes optical interferometry, capacitive sensing and substitution methods [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 , 21 , 22 ]. The transmission sensitivity (displacement or velocity per unit input voltage) can be readily determined by pulse excitation plus laser interferometry, but was not reported for broadband UT transducers until recently [ 21 , 22 ].…”