Bayesian waveform-based calibration of high-pressure acoustic emission systems with ball drop measurements

Abstract

Acoustic emission (AE) is a widely used technology to study source mechanisms and material properties during high-pressure rock failure experiments. It is important to understand the physical quantities that acoustic emission sensors measure, as well as the response of these sensors as a function of frequency. This study calibrates the newly built AE system in the MIT Rock Physics Laboratory using a ball-bouncing system. Full waveforms of multi-bounce events due to ball drops are used to infer the transfer function of lead zirconate titanate (PZT) sensors in high pressure environments. Uncertainty in the sensor transfer functions is quantified using a waveform-based Bayesian approach. The quantification of in situ sensor transfer functions makes it possible to apply full waveform analysis for acoustic emissions at high pressures. methods only work under ambient conditions, and not within a pressure vessel where rock physics experiments are sometimes carried out. To calibrate the AE amplitudes under high-pressure conditions, Kwiatek et al. (2014) proposed an in situ ultrasonic transmission calibration (UTC) method to correct relative amplitudes under high pressure. McLaskey et al. (2015) developed a technique to calibrate a high-pressure AE system using in situ ball impact as a reference source. This design enabled the determination of absolute source parameters with an in situ accelerometer.This study aims to advance these calibration methodologies by quantifying the uncertainty of sensor transfer functions using a waveform-based Bayesian approach. Instead of using the waveform of a single ball bounce, our approach is able to use the waveforms of multi-bounce events. Inferring an in situ sensor transfer function, and its associated uncertainty, makes it possible to apply full waveform analysis for acoustic emissions under high-pressure conditions. The method is tested using the newly built AE system of the MIT Rock Physics Laboratory.

Revisiting Piezoelectric Sensor Calibration Methods Using Elastodynamic Body Waves

“…We used the single impact of spherical ball as the mechanical active source to excite body waves in our transfer plate while the multibounce scenario of ball drop is outside the scope of this study [53]. In Fig.…”