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UBC Theses and Dissertations

Flexible low-cost wireless temperature sensor using thermoresponsive Y5V capacitor chips Patel, Ronish


Temperature sensing is one of the most important abilities for monitoring and controlling thermal behaviors of target objects or environments, and the capability of its wireless reading largely expands the potential application areas. For example, biomedical and environmental applications are some of the promising areas for wireless temperature sensors. The use of inductor-capacitor (LC) resonant-tank circuits in which the capacitance or the inductance is designed to vary with temperature, is an advantageous approach for wireless temperature sensing given its reliable frequency-based reading and no requirement for having internal power sources. Type Y5V multilayer dielectric capacitors, commercially available in low-cost (e.g., ~$0.01-0.1/chip) surface-mount chips, exhibit significant capacitance variations over a wide range of temperatures (-30 to +85 ℃). Such capacitors can serve as the sensing elements in LC-tank circuits for frequency-based wireless temperature reading. The current work designs, fabricates, and demonstrates the first proof-of-concept device of a flexible wireless sensor that uses Y5V capacitor chips in combination with planar inductive coils microfabricated on thin polymer film, forming LC-tank-based devices. The physical flexibility and disposable nature of the devices makes them suitable for medical/healthcare applications, e.g., continuous remote monitoring of patient’s body temperature and feedback control of clinical hyperthermia treatments for various cancer therapies. This research presents the design, fabrication, and experimental validation of two prototype passive wireless LC temperature sensors of varying dimensions. The larger sized (20 mm²) sensor reported has a frequency response of 106-150KHz/℃ and a resonant frequency of 152 MHz at room temperature. Whereas, the miniature (~6 mm2) sized sensor reported demonstrates a frequency response of 77-119KHz/℃ and a resonant frequency of 1.5 MHz at room temperature. Moreover, a low-cost impedance analyzer is developed in this work. It consists of Raspi 3 host device and a Digilent PmodIA impedance analyzer has a low error of ~4% as compared to the Agilent network analyzer. The new analyzer is demonstrated and experimentally validated.

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