| High temperature sensors suitable for operating in harsh environments are needed in order to prevent disasters caused by structure or system functional failures due to elevated temperatures, for example, temperature monitoring of heat resistant tiles of the space shuttle and temperature monitoring of rotating bearings in the aircraft engine. Most existing temperature sensors do not satisfy the needs because these sensors require either physical contact or a battery power supply for signal communication, and furthermore, neither of which can withstand high temperatures nor rotating applications.; A novel passive wireless temperature sensor, being able to operate in harsh environments, has been developed in this research project for high temperature rotating component applications. A completely passive LC resonant telemetry scheme, which relies on a frequency shift output, has been integrated with the sensor, thereby eliminating the needs for contacts, active elements, or power supplies within the sensor. Consisting of an inductor and a temperature-dependent capacitor, this high temperature sensor forms a LC circuit, whose resonant frequency changes when the capacitance of the sensor changes in response to temperature.; Following a review of the state-of-the-art high temperature dielectric ceramics and substrates, schematic design of the capacitor was presented based on temperature sensitive ferroelectric dielectrics. These dielectrics were found to exhibit linear changes in electrical properties when exposed to temperature varying environments. Based on capacitance and inductance modeling and simulation, sensor design and modeling was conducted subsequently in order to limit the resonant frequency to the appropriate scope.; Moreover, sensor performance was analyzed to optimize the sensor configuration, maximize sensing distance, Q factor and sensitivity. The sensor prototype was then successfully fabricated to prove the concept of a temperature sensing device using passive wireless communication. The Low Temperature Co-fire Ceramic (LTCC) technology based on DuPont Green Tape(TM) was proposed for sensor packaging. Finally, the sensor prototype was calibrated up to 235°C in a laboratory setup. |
