High-Resolution, Far-Field, and Passive Temperature Sensing up to 700 °C Using an Isolated ZST Microwave Dielectric Resonator

Abstract

This paper presents a high-resolution, wireless and passive temperature measurement system up to 700 °C. The sensor is based on a metallization-free monolithic microwave dielectric resonator composed of zirconium tin titanate (Zr0.8Sn0.2TiO4) operating at 2.37 GHz. The external electromagnetic fields of the tracked single mode are adequate for the far-field coupling without the need to use any conducting part on the sensor surface. The measurements are conducted in a light weight refractory bricks oven at a distance of 1.20 m between the sensor and a reader planar antenna connected to a time-domain RADAR-based interrogation unit. This method allows to retain a quality factor ( $Q$ ) higher than 670 at 700 °C, while the $Q$ -factor from other electromagnetic cavity or microwave dielectric resonators degrades below 100, hence limiting the sensing resolution and increasing the sensitivity to the environmental echoes. The effect of temperature on the tracked sensor resonance frequency, signal-to-noise ratio, $Q$ -factor, thermal expansion, and sensing resolution is presented. The concept is suitable for applications working in extreme environments, such as aerospace applications.