Date of Award

Fall 2013

Document Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Electrical and Computer Engineering

First Advisor

Josse, Fabien J.

Second Advisor

Heinrich, Stephen M.

Third Advisor

Nigro, Nicholas J.

Abstract

Dynamically driven prismatic microcantilevers excited in the in-plane flexural mode have been investigated and used in liquid-phase sensing applications. However, the performance is restricted due to their limited surface sensing area and higher stiffness in shorter and wider prismatic microcantilevers. To increase the surface sensing area, and further improve sensing characteristics, it has been proposed to investigate symmetric hammerhead microcantilevers vibrating laterally in viscous liquid media. In this work, a theoretical model is proposed and the characteristics of the microcantilevers with symmetric shaped hammerheads (isosceles trapezoid, semi-circle, uniform rectangle and composite rectangle) are investigated. In the analysis, the stem of the structure is modeled as an Euler-Bernoulli beam while the head is modeled as a rigid body. Since the arbitrary, symmetric head has a varying width, 2b2(x), in the length direction, a new semi-analytical expression for the hydrodynamic function in terms of the Reynolds number, Re(x), and aspect ratio, h/[2b2(x)] is obtained and the resonance frequency, quality factor and mass sensitivity are investigated as a function of both the hammerhead microcantilever geometry and liquid media properties. For the investigated geometries, the results show that, for a hammerhead microcantilever with a fixed head area, as the mass center of the head moves towards the support end of the stem, the resulting resonance frequency and mass sensitivity will first increase and then decrease, because the total kinetic energy will first decrease and then increase. The quality factor will keep increasing, due to a more rapid decrease in the energy dissipation. It is also found that, hammerhead microcantilevers with wider heads tend to have higher quality factors. For instance, the highest quality factors are found for the hammerhead microcantilevers with the isosceles trapezoid-shaped, uniform rectangular and composite rectangular head as 140, 72 and 129, respectively, due to the possible shift of the mass center of the head towards the support end of the stem. Such trends can be used to optimize sensor device geometry and frequency stability. By further increasing the surface sensing area (additional mass), the resonance frequency and the mass sensitivity will significantly decrease. Such trade-offs must be considered when designing the geometry of the hammerhead microcantilever devices. For appropriately designed hammerhead microcantilevers, the improvement in the sensing area and quality factor are expected to yield much lower limits of detection in (bio) chemical sensing applications.

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