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UBC Theses and Dissertations

Tunable microwave resonator using liquid metal and 3D printed fluidic channel for the development of microwave spectroscopy Rafi, Md. Abdur


This thesis presents an innovative and practical approach to developing planar resonant-based spectroscopy in microwave sensor technology. Resonant based microwave sensors have drawn attention for decades now in terms of sensing and measuring materials dielectric properties because of demonstrating a higher accuracy, precision, and sensitive measurement compared to non-resonant based sensors. This method has been mostly used on binary solvents due to their ability to display a highly delicate response to the materials under test. This thesis presents a comprehensive analysis of the sensor design and fabrication, sensor characterization, and testing samples to achieve the materials' frequency selective response. Microwave resonator sensors are limited in their current form to a single fixed resonant frequency, leading to issues in selectivity among materials or mixtures with similar dielectric properties. The first study presents a successful effort of achieving a frequency-tunable resonator circuit by utilizing the liquid metal and 3D printed microchannel with a modified split ring resonator. The resonator utilizes liquid metal in a microfluidic channel to change the resonant frequency of the resonator over a wide, continuous spectrum by changing the effective capacitance of the sensor. In the second study, highly sensitive interdigitated capacitive traces have been added with the designed sensor structure for material sensing. The designed and fabricated sensor demonstrated an operating resonant frequency that could be tuned between 2.1 and 2.8 GHz for both solid and liquid sensing. The sensitivity of the designed sensor structure is investigated by sensing standard solid samples, and sensitivity variation was noticed due to the increased reactive loading introduced by the liquid metal. Experimental validation of the sensor and standard liquid mixtures confirmed that the frequency tunability enables similar dielectric materials to be distinctly identified using multiple frequency spectra. Specific attention was made towards materials with identical dielectric properties at specific frequencies, simulated with the Debye model, and matched experimentally with dielectric probe validation. The device enables multi-phase material detection with the ability to investigate dielectric properties over a frequency spectrum rather than a single point.

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