Abstract
In this work, an all-ceramic passive wireless inductor–capacitor (LC) resonator was presented for stable temperature sensing up to 1200 °C in air. Instead of using conventional metallic electrodes, the LC resonators are modeled and fabricated with thermally stable and highly electroconductive ceramic oxide. The LC resonator was modeled in ANSYS HFSS to operate in a low-frequency region (50 MHz) within 50 × 50 mm geometry using the actual material properties of the circuit elements. The LC resonator was composed of a parallel plate capacitor coupled with a planar inductor deposited on an Al2O3 substrate using screen-printing, and the ceramic pattern was sintered at 1250 °C for 4 h in an ambient atmosphere. The sensitivity (average change in resonant frequency with respect to temperature) from 200–1200 °C was ~170 kHz/°C. The temperature-dependent electrical conductivity of the tin-doped indium oxide (ITO, 10% SnO2 doping) on the quality factor showed an increase of Qf from 36 to 43 between 200 °C and 1200 °C. The proposed ITO electrodes displayed improved sensitivity and quality factor at elevated temperatures, proving them to be an excellent candidate for temperature sensing in harsh environments. The microstructural analysis of the co-sintered LC resonator was performed using a scanning electron microscope (SEM) which showed that there are no cross-sectional and topographical defects after several thermal treatments.
Highlights
Publisher’s Note: MDPI stays neutralReal-time temperature awareness is vital for every industrial process, and the temperature sensor is one of the most widely used sensors in most industries
Conventional temperature sensors have been predominantly fabricated with refractory metals and metal alloys, such as Ni, Cr, Si, Mg, Pt, and Rh, which are prone to oxidation/corrosion and lead to the necessary frequency calibration or replacement [3]
Since the multi-layer capacitor structure was co-sintered at 1250 ◦ C, it is vital to analyze the interface of the ITO and
Summary
Publisher’s Note: MDPI stays neutralReal-time temperature awareness is vital for every industrial process, and the temperature sensor is one of the most widely used sensors in most industries. Based on the working temperature region, temperature sensors can be classified as low to moderate (25–300 ◦ C), moderate to high (300–1200 ◦ C), and very high to ultra-high (1200–2000 ◦ C) [1]. Thermometers and optical sensors (infrared sensors) are used in sensing applications for low-temperature regions (−250 to 300 ◦ C). Conventional resistance temperature detectors (RTDs) and thermocouples are extensively used in moderate (500 ◦ C) to ultra-high temperature regions (2000 ◦ C) [2]. Thermocouples have limited applications where a cold and hot junction should be maintained for accurate temperature measurement. This leads to numerous challenges during interconnecting the sensors with sophisticated furnaces, gasifiers, reactors, and nonstationary parts (such as turbine blades and rotors) [2,3]. Conventional temperature sensors have been predominantly fabricated with refractory metals and metal alloys, such as Ni, Cr, Si, Mg, Pt, and Rh, which are prone to oxidation/corrosion and lead to the necessary frequency calibration or replacement [3]
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