Monitoring of structural health at high temperatures is required in many industrial applications, including turbine engines, automotive combustion systems, and aerospace propulsion systems. With recent scientific and technological developments, there is a pressing need for high-performance piezoelectric sensors for in-situ monitoring of the dynamic mechanics of such industrial systems for feedback control and system optimization, as well as for the monitoring of the health of structural components for safety improvements.

Extensive studies have been carried out to design different kinds of vibration sensors for high-temperature applications, including piezoresistive, capacitive, fiber optic and piezoelectric sensors. Piezoresistive sensors are less susceptible to electromagnetic interference than other types of sensors, but they are not suitable for high-temperature applications due to the inherent temperature dependence of material resistivity. Capacitive sensors can offer the advantages of low thermal drift, high resolution, and good noise performance, however, their use in high-temperature applications is often limited by the low working temperature (<400^oC) and the parasitic capacitance of the sensor itself. Fiber optic sensors have the advantages of high operating temperature and high tolerance of electromagnetic interference, but they are complex to fabricate and require expensive signal processing systems. Piezoelectric sensors have many advantages over the sensors mentioned above. Firstly, they usually have simple structures and fast response times. Secondly, they are robust and long-lasting, even in harsh environments. Last but not least, external power sources are not an essential requirement for piezoelectric sensors, which greatly facilitates their application in high-temperature environments.

In this report, several kinds of high-temperature piezoelectric crystals (LGS type, BTS type, and ReCOB type crystals etc.) are introduced and their potential applications for high-temperature (≥482^oC) sensing are discussed.

Fig.1 Temperature dependence of piezoelectric sensitivity (a) and the stability (b) of the fabricated high-temperature piezoelectric vibration sensors