High-temperature (> 1000 °C) acoustic emission sensor

Piezoelectric crystals have shown promising results as acoustic emission sensors, but are often hindered by the loss of electric properties above temperatures in the 500-700 degrees C range. Yttrium calcium oxyborate, (YCOB), however, is a promising high temperature piezoelectric material due to its high resistivity at high temperatures and its relatively stable electromechanical and piezoelectric properties across a broad temperature range. In this paper, a piezoelectric acoustic emission sensor was designed, fabricated, and tested for use in high temperature applications using a YCOB single crystal. An acoustic wave was generated by a Hsu-Nielsen source on a stainless steel bar, which then propagated through the substrate into a furnace where the YCOB acoustic emission sensor is located. Charge output of the YCOB sensor was collected using a lock-in charge amplifier. The sensitivity of the YCOB sensor was found to have small to no degradation with increasing temperature up to 1000 degrees C. This oxyborate crystal showed the ability to detect zero order symmetric and antisymmetric modes, as well as distinguishable first order antisymmetric modes at elevated temperatures up to 1000 degrees C.