Low-Profile Wireless Passive Temperature Sensors

This thesis explores design challenges and promising solutions for temperature sensors for high temperature environments such as combustion turbines. To survive this high temperature environment of over 1000 °C the sensors are required to be robust in their electrical and mechanical properties. Wire connections for these high temperature environments are a complex problem due to the physical limitations of most materials at those high temperatures. In this thesis, robust ceramic sensors based on microwave resonators are demonstrated for high temperature environments, with some studies into optimizing the techniques used to measure them, as well as the distance at which their responses can still be measured. Two types of temperature sensors are realized using rectangular reflective patches with different dielectric substrates. The sensors are realized with either alumina substrate or yttria-stabilized zirconia (YSZ), both of which have temperature dependent dielectric constants. The temperature is wirelessly detected by measuring the resonant frequency of the reflective patch. The reflective patch sensor works simultaneously as a resonator and a radiative element. The sensors were tested up to 800 °C. In these high temperature environments, it is important to be able to interrogate the sensor from a distance safe for the interrogating antenna, for this reason, the sensors must be designed with a high enough Q factor that their responses can be measured up to at least 2 inches of distance away from the interrogating antenna. While exploring designs of temperature sensors, a few measurement techniques on the vector network analyzer are studied to optimize the identification of the resonant frequency of the reflective patches. These measurements include the start and stop time of the time domain gating window, the start and stop frequency of the frequency span of the interrogating signal, and the gain/size of the interrogating horn antenna