title: Whispering Gallery Mode Thermometry.
abstract: This paper presents a state-of-the-art whispering gallery mode (WGM) thermometer system, which could replace platinum resistance thermometers currently used in many industrial applications, thus overcoming some of their well-known limitations and their potential for providing lower measurement uncertainty. The temperature-sensing element is a sapphire-crystal-based whispering gallery mode resonator with the main resonant modes between 10 GHz and 20 GHz. In particular, it was found that the WGM around 13.6 GHz maximizes measurement performance, affording sub-millikelvin resolution and temperature stability of better than 1 mK at 0 °C. The thermometer system was made portable and low-cost by developing an ad hoc interrogation system (hardware and software) able to achieve an accuracy in the order of a few parts in 10⁸ in the determination of resonance frequencies. Herein we report the experimental assessment of the measurement stability, repeatability and resolution, and the calibration of the thermometer in the temperature range from -74 °C to 85 °C. The combined standard uncertainty for a single temperature calibration point is found to be within 5 mK (i.e., comparable with state-of-the-art for industrial thermometry), and is mainly due to the employed calibration setup. The uncertainty contribution of the WGM thermometer alone is within a millikelvin.
authors: Department of Electronics and Telecommunications, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino 10129, Italy. simone.corbellini@polito.it.
authors: Simone
authors: S
authors: Corbellini
authors: Department of Electronics and Telecommunications, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino 10129, Italy. chiara.ramella@polito.it.
authors: Chiara
authors: C
authors: Ramella
authors: College of Electrical Engineering and Control Science, Nanjing Tech University, Nanjing 211816, China. lili.yu@njtech.edu.cn.
authors: Lili
authors: L
authors: Yu
authors: Department of Electronics and Telecommunications, Politecnico di Torino, Corso Duca degli Abruzzi 24, Torino 10129, Italy. marco.pirola@polito.it.
authors: Marco
authors: M
authors: Pirola
authors: Istituto Nazionale di Ricerca Metrologica, Strada delle Cacce 91, Torino 10135, Italy. v.fernicola@inrim.it.
authors: Vito
authors: V
authors: Fernicola
keywords: high-accuracy thermometry; microwave resonance; sapphire-based dielectric thermometry; temperature sensors; whispering gallery mode resonators