Miniaturized Quarter-Mode Substrate Integrated Cavity Resonators for Humidity Sensing

This letter presents the substantial miniaturization of substrate integrated waveguide sensors using quarter-mode and ridged quarter-mode techniques, for detecting changes in relative humidity levels between 0%-80%. Miniaturizations of 73.3% and 86.2% are reported with resonant frequencies of 6 GHz and 6.9 GHz for the two techniques, respectively. Furthermore, an increase in humidity sensitivity is achieved almost four times greater than previously reported. Due to the reduced size and increased sensitivity, these two techniques open up new possibilities and applications for sensor design. To the best of the authors' knowledge, this letter also reports the first ridged quarter-mode resonant structure, providing even greater miniaturizations and improved quality factor of quarter-mode structures in the literature.