RF-Based passive wireless sensor for harsh environment application

Fabrication of RF-based Passive Wireless Sensors for High Temperature Application

Monitoring the health of a high temperature system are numerous in the energy technology (steam and gas turbines, nuclear reactors), manufacturing industries (chemical reactors, furnaces, boilers, and blast reactors/furnaces), and aerospace industry. The aforementioned systems operate in a harsh environment which has a temperature ranging from 1000 – 2000°C, pressing reaching up to 1000 psi, varying pO ₂ levels, and some environments are corrosive in nature such as molten inorganics and/or reactive gases, etc. Conventional sensor systems such as a thermocouple, spallation sensors, thermistor, and optical sensors cannot be used in a sophisticated reactor/furnace due to various reasons. The major issue involves the frequent replacement of the sensor and the cost involved during the replacement. Therefore, there is a great demand for advanced sensing technologies, particularly for use at high-temperatures and harsh environments. Research is on-going to overcome the issues by developing a passive wireless sensing technology that can efficiently tackle several problems in monitoring the health of a high temperature system. In our sensing vision, passive wireless sensors are developed based on ceramic and electro-ceramic materials. Owing to the excellent high temperature stability, compatibility with other ceramic materials, good electrical conductivity electro-ceramic can replace noble metals such as Pt, Rh, Ir, Re for high temperature application. Electro-ceramic systems such as conducting oxides (ITO, LaCrO ₃, La ₂NiO ₄), transition metal silicides, nitrides, and carbides are being developed to overcome the disadvantages of noble and refractory metals for high temperature application. Current work focused on developing an electro-ceramic system with different fabrication routes which also includes polymer derived ceramics (PDC). High molecular weight inorganic polymers such as polysilazanes, siloxanes, silanes can form respective ceramics such as SiC, SiCN, SiOC, etc. based on the chemical structure and the composition of the polymer. Current work involves modifying/adding ceramic particles within the polymer matrix to control the formation of desired electro-ceramic compound. The work also focuses on the structural, chemical and electrical characterization of the PDC after pyrolysis. The developed electro-ceramic system will be used for the fabrication of RF-based passive wireless sensors. The capacitor (C) and inductor (L) pattern were deposited on a refractory dielectric substrate such as Al ₂O ₃, YSZ, or HfO ₂ to realize the LC circuit. Two different fabrication approach was developed: 1) micro-casting of ceramic ink and 2) direct ink writing on the substrate. Micro-casting involves a combination of photolithography patterning of the substrate with desired LC pattern and the electro-ceramic ink will casted into the micro-molds and pyrolyzed. Direct ink writing is based on a nozzle based inkjet/robocasting technology to pattern the substrate with the LC pattern. The wireless testing of the sensors was performed in a high temperature furnace with the in-situ electrical acquisition.