A temperature sensor based on a whispering gallery mode resonator

This paper deals with a microwave temperature sensor based on a whispering gallery mode (WGM) resonator whose dielectric medium is a cylindrical sapphire crystal. The performance as temperature sensor were investigated a three WGMs resonant frequencies over the temperature range from −40 °C to 85 °C. It was found that the quality factor for these WGMs can be in excess of 1.7⋅10⁵, potentially enabling high-resolution measurements. The temperature repeatability, stability, hysteresis, frequency-vs-temperature sensitivity of the WGM temperature sensor are reported. Moreover, two sapphires, which have the same nominal characteristics, were investigated in order to assess the system reproducibility and the results reported.