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Maleki Gargari, Ali

University of British Columbia

Materials exhibit diverse electromagnetic responses across a broad spectrum, characterized by parameters such as permittivity, permeability, and refractive index. This thesis investigates microwave resonant structures as high-sensitivity sensors for material property detection. The limitations of traditional cabled connections, restricting accessibility and introducing errors through cable bending, drive the development of wireless systems. Furthermore, integrating these structures with light-sensitive materials extends their sensitivity to optical properties. To address cabled limitations, two periodic resonant structures were designed for antenna-based passive material detection. The first design features a passive multi-layered structure based on a mushroom high-impedance surface, enhancing sensitivity and enabling a low-profile antenna-based material detection system. This system wirelessly tracks resonance frequency shifts caused by changes in the effective permittivity of the sensing layer. Notably, it achieved a sensitivity of 150 MHz per unit relative permittivity (ɛᵣ). Subsequently, a new sensor design was proposed, increasing the sensitivity up to 1.46 GHz per ɛᵣ while maintaining a minimal sensing layer profile (0.033λ₀). Moreover, this thesis introduces integrating low-cost light-dependent resistors (LDRs) into a microwave double-gap split ring resonator (DGSRR), enabling optical property tracking within the microwave frequency range. Illuminating the structure with red light (intensity of 27.46 mW/m²) induced an 85 MHz frequency downshift and a 13.9 dB amplitude reduction. In an experiment involving 3600 uL water and 20 uL commercial green food coloring, the LDR-integrated structure demonstrated the potential to distinguish liquid colors at microwave frequencies. Additionally, a passive photosensitive microwave structure was developed to simultaneously monitor light intensity variation in three wavelength regions (green, red, and blue) for visible light sensing. Finally, an LDR-integrated periodic resonant structure was designed for non-contact material detection beyond the resonator's near-field by placing a thin layer of dust at 1 cm, 5 cm, and 10 cm above the resonant surface. The resonant profile was remotely monitored by a horn antenna situated 30 cm above the resonant surface. Differences in the measured resonant frequency and amplitude of the structure in the presence and absence of visible light showcased the potential of LDR-integrated microwave resonators for non-contact material detection within wireless microwave sensing systems.

Text

2024-11-30

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/86757

Electrical Engineering

University of British Columbia

UBCO

http://creativecommons.org/licenses/by-nc-nd/4.0/