UBC Theses and Dissertations

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UBC Theses and Dissertations

Vibration mode localization in coupled microelectromechanical resonators Manav


State-of-the-art resonant sensors rely on shift in resonant frequency due to a change in its mass or stiffness caused by a physical quantity to be measured. However, they require low damping operating environment. As a result, applications such as biomolecular detection in aqueous environment pose formidable challenges. A promising, alternative sensing paradigm, minimally affected by damping, is based on normal mode localization in a weakly coupled, symmetric resonator system due to parametric changes. The higher sensitivity of mode shape compared to resonant frequency in a weakly coupled, symmetric resonator system results from the phenomena of eigenvalue veering and associated mode localization induced by symmetry breaking parametric changes in the system. The method offers added benefit of common mode rejection. This thesis critically examines the mode localization based resonant sensing paradigm using a combination of energy based analytical theory, Simulink models, and experimental studies on planar MEMS devices. Built-in asymmetry in fabricated devices and its influence on achievable sensitivity are highlighted. Increasing the number of degrees of freedom (DOF) is shown to enhance sensitivity, but a trade-off exists with the size and complexity of the device. Similarly, decreasing coupling enhances sensitivity at the expense of measurable range of parametric changes. Two and three DOF coupled resonator MEMS devices with tuneable linear coupling were designed, fabricated and tested to verify the above conclusions. In summary, this thesis demonstrates that mode localization based sensing is orders of magnitude more sensitive compared to resonant frequency shifts. The sensitivity can be further increased by decreasing coupling between resonators, or increasing number of DOF in a resonant MEMS device, or both.

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