Development of Pb-free piezoelectric sensor technology for condition monitoring under nuclear environments

Lead-free piezomaterials and condition monitoring sensors built on them need to be developed in order to replace toxic lead-based piezoelectric materials, represented by Pb(Zr,Ti)O₃ (PZT), and their electrical components and devices. Also, lead-free piezoelectric sensors to be developed should be operated under nuclear environments with high-performances and reliability. For this purpose, the material technologies to make high-performance ring-type piezoceramics with piezoelectric coefficient d₃₃ of more than 300 pC/N and Curie temperature T_C of 330 ^oC for making sensor module were developed by employing our own lead-free (K,Na)NbO₃ (KNN)-based piezoceramic composition (KNN-x-y). Optimal vibration sensor (accelerometer) module designs were obtained through the work on meta-modeling and piezoelectric analysis and used to fabricate the lead-free piezoelectric accelerometer. The technologies of design, fabrication and assembly for making high-performance lead-free piezoelectric accelerometer were established. The fabricated sensor module had excellent sensing performances: sensitivity of 95 pC/g, mounted resonant frequency of 22 kHz, charge-to-acceleration linearity of 1 and frequency range of 10Hz~12.7kHz (at ±3dB). The obtained performances were not only much higher than target values of this project (sensitivity ~80 pC/g, resonant frequency ~10 kHz) but also exceeded those of commercial sensor (SKF accelerometer, Sweden). Finally, four kinds of designs and prototype sensor modules (D25, D30, D35, D40) were proposed