An Evanescent-mode Cavity Resonator Based Thermal Sensor

This paper reports the use of an evanescent-mode cavity resonator as a temperature sensor. The frequency loading is achieved by a capacitive post in the center of the cavity confining the electric field in a small volume. The resonant frequency of a loaded evanescent-mode cavity is related to the capacitance of the loading mechanism. As a sensing mechanism, a rectangular array of thermally actuated bilayered microcantilever beams on a silicon substrate has been fabricated using conventional microfabrication processes and placed inside the resonator. A temperature change causes the microcantilevers to deflect, changing the parasitic capacitance of the cavity and hence the resonant frequency of the resonator. Loaded microwave cavities have been fabricated using a layer by layer stereolithographic process and then metallized. The Si hosting the cantilevers is attached to the cavity. The resonant frequency of the sensor is monitored as a function of temperature and varies from 11.34 GHz at room temperature to 12 GHz at 90degC. At room temperature, the sensor has a temperature coefficient of frequency (TCF) of 0.029%/degC.