Whispering Gallery Mode Resonators for Precision Temperature Metrology Applications

Abstract

In this work, the authors exploited the whispering gallery mode (WGM) resonator properties as a thermometer. The sensor is made of a cylindrical sapphire microwave resonator in the center of a gold-plated copper cavity. Two coaxial cables act as antennas and excite the WGM standing waves in the cylindrical sapphire at selected resonance frequencies in the microwave range. The system affords a high quality factor that enables temperature measurements with a resolution better than 15 µK and a measurement standard uncertainty of 1.2 mK, a value approximately three times better than that achieved in previous works. The developed sensor could be a promising alternative to platinum resistance thermometers, both as a transfer standard in industrial applications and as an interpolating instrument for the dissemination of the kelvin.

Equivalent Circuit Model Extraction for a SAW Resonator: Below and above Room Temperature

“…In the literature, there are different strategies in order to increase the accuracy of the determination of f r and Q r [ 42 , 43 , 44 ]. For instance, a Lorentzian fitting can be performed on the acquired data points so that f r , Q , and the other parameters can be derived from the fitted equation analytically and with higher accuracy [ 45 , 46 ].…”

“…In this work, a Lorentzian function ( L ( f )) in the form of Equation (14) [ 46 ] was employed to perform a fitting of the Y 11 and Y 22 parameters. where a 0 and f 0 are two complex coefficients estimated by the selected best fit algorithm.…”

“…In order to improve the quality of the fit, a background signal ( B ( f )) is usually included beside the Lorentzian peak [ 46 ]. It is a complex polynomial function expressed as: where N is the polynomial order, b n are complex coefficients, and f c is a real quantity.…”

Design and Test of a New Dielectric-Loaded Resonator for the Accurate Characterization of Conductive and Dielectric Materials

“…In particular, and differently from many other works, we put a strong focus on the analysis and improvement in the metrological characteristics. In fact, it is clear how materials characterization methods at microwave frequencies were an evolving field in the last years: these techniques had great success in the experimental investigation of the e.m. properties of matter [ 64 , 65 , 66 , 67 , 68 ], and nowadays, microwave measurements are instrumental both for the design and testing of devices and complex systems whose performances can be particularly sensitive to the so-measured quantities [ 24 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 ] and in metrology [ 77 , 78 , 79 ]. This is the general framework into which this work fits: it shows a novel configuration of a dielectric-loaded resonator, and its possible applications, with a thorough evaluation of the measurement uncertainty.…”

On the design and characterisation of a microwave microstrip resonator for gas sensing applications

“…A better fitting approach consists in using a Lorentzian function [33], [34], which allows achieving a good estimation of the resonant parameters fR, Q, and AR. A more accurate result can be achieved by using a complex function to fit both real and imaginary parts of the spectrum [35], [36]. This technique can be useful in several applications in which the calibration procedure is impracticable (e.g., in cryogenic measurement systems) [36].…”