Calibration Methods of Acoustic Emission Sensors

Abstract

This study examined outstanding issues of sensitivity calibration methods for ultrasonic and acoustic emission transducers and provides workable solutions based on physically measureable quantities, laser-based displacement measurement in particular. This leads to mutually consistent determination of transmitting and receiving sensitivities of sensors and transducers. Methods of circumventing problems of extraneous vibrations on free transmitters are used, giving the foundation for face-to-face calibration methods. Working on many ultrasonic and acoustic emission transducers, their receiving and transmitting sensitivities are found to be always different, while their ratios exhibit unexpected similarity. This behavior is attributed to monopolar pulse generation and bipolar received signals due to electrical charge transfer during elastic wave motion and reflection on the back face. This is verified through a quantitative piezoelectric sensing experiment. Displacement vs. velocity calibration terminology is clarified, redefining the “V/µbar” reference for contact sensor calibration. With demonstrated differences in the transmitting and receiving sensitivities of transducers, the requirement of the Hill-Adams equation invalidates the basic premise of the currently formulated reciprocity calibration methods for acoustic emission transducers. In addition, the measured reciprocity parameter for the case of through-transmission significantly deviates from the approximate theoretical prediction. It is demonstrated that three methods provide reliable sensor calibration results that are complimentary among them.

Review on Structural Health Evaluation with Acoustic Emission

“…Recently, Ono [41,157,158] reexamined sensor calibration methods for different types of wave propagation. These new approaches incorporated laser interferometry as the basis for calibration and Vallen [159] took an initial step for their standardization.…”

“…It was also demonstrated that the so-called reciprocity calibration methods [160][161][162] have fundamental flaws. It was also found that most AE sensors fail to satisfy required reciprocity conditions [157,158].…”

An acoustic emission activity detection method based on short-term waveform features: Application to metallic components under uniaxial tensile test

“…Finally, the choice of the duration values of the window time, the threshold levels and the weighting factor for the noise analysis will a) b) be entirely determined by a prior calibration of the employed instrumentation as well as by the mechanical properties of the material. The calibration values of the comparative methods (see Table 1), was carried out following the recommendations of the related literature [26,[36][37][38][39][40] as well as the current standards [8,9,[41][42][43][44][45]) of the AE discipline. In Fig.…”

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

“…McLaskey & Glaser (2012) performed AE sensor calibration tests on a thick plate with two calibration sources (ball impact and glass capillary fracture) to estimate instrument response functions. Ono (2016) demonstrated detailed sensor calibration methods, including face-to-face, laser interferometry, Hill-Adams equation, and tri-transducer methods. Yoshimitsu et al (2016) combined laser interferometry observations and a finite difference modeling method to characterize full waveforms from a circular-shaped transducer source through a cylindrical sample.…”