Fabrication of a high performance acoustic emission (AE) sensor to monitor and diagnose disturbances in HTS tapes and magnet systems

An acoustic emission (AE) technique was introduced as a non-destructive method to monitor sudden deformation caused by local heat concentrations and micro-cracks within superconductors and superconducting magnets. However, the detection of AE signals in a high temperature superconductor (HTS) tape is not easy because of its low signal to noise ratio caused by the noise from boiling liquid cryogen or mechanical vibration from the cryo-cooler. Therefore, high performance piezoelectric ceramics are needed to improve the sensitivity of the AE sensor. The aim of this study was to improve the piezoelectric and dielectric properties to enhance the performance of an AE sensor. This study examined the effects of Nb2O5 addition (0.0 wt.% to 2.0 wt.%) on the properties of high performance piezoelectric ceramics, Pb(Zr0.54 Ti0.46)O3 + 0.2 wt.% Cr2O3, sintered at 1200 °C for 2 h. The performance was examined with respect to the acoustic emission response of AE sensors manufactured using the specimens with various Nb2O5 contents. Superior sensor performance was obtained for the AE sensors fabricated with the specimens containing 1.0 wt.% to 1.5 wt.% Nb2O5. The performance and characteristics of the AE sensors were in accordance with their piezoelectric and dielectric properties.