High temperature langasite surface acoustic wave sensors.

摘要

High temperature sensors are a key enabling technology for advanced control and optimization of many industry processes. This thesis reports on the development of the langasite surface acoustic wave (SAW) temperature and oxygen sensors for sensing applications in high temperature, harsh environments.;The conductivity-based surface acoustic wave sensor was selected for the high temperature oxygen sensing application in this work. A series of finite element simulations of surface acoustic wave propagation in langasite SAW devices were performed to understand the effect of sensing and spacer layer on the sensor sensitivity.;Langasite SAW sensors with Pt/Ti as the IDT metallization, and ZnO and SiO2 as the oxygen sensing layer and spacer layer materials, respectively, were designed, fabricated and packaged for high temperature sensing applications. Langasite SAW temperature sensors were tested successfully from room temperature up to 700 °C in wireless mode and 900 °C in wired mode. The ZnO/langasite SAW oxygen sensors were tested in wired mode and showed effective oxygen sensing response up to 700 °C. A multi-sensor with both temperature and oxygen sensing capability was also designed and tested. Understanding the input characteristic of the transducer is important when designing the SAW sensor for wireless operation. Langasite SAW device IDT transducers were characterized in frequency domain at room temperature. Conductance loss caused by the finite resistance of Pt electrode finger was observed and investigated.