In this work we investigate the feasibility of two-directional switching of an initially curved or pre-buckled electrostatically actuated microbeams using a single electrode fabricated from the same structural layer. The distributed electrostatic force, which is engendered by the asymmetry of the fringing fields in the deformed state, acts in the direction opposite to the deflection of the beam and can be effectively viewed as a reaction of a nonlinear elastic foundation with stiffness parameterized by the voltage. The reduced order model was built using the Galerkin decomposition with linear undamped modes of a straight beam as base functions and verified using the results of the numerical solution of the differential equation. The electrostatic force was approximated by means of fitting the results of three-dimensional numerical solution of the electrostatic problem. Static stability analysis reveals that the presence of the restoring electrostatic force may result in the suppression of the snapthrough instability as well as in the appearance of additional stable configurations associated with higher buckling modes of the beam that are not observed in "mechanically" loaded structures. We show that two-directional switching of a pre-buckled beam between two stable configurations cannot be achieved using quasistatic loading. Furthermore, we show that switching is both associated with the dynamic snapthrough mechanism and possible within certain interval of actuation voltages. Using a single-degree-offreedom (lumped) model, estimation voltage boundaries are obtained. Theoretical results illustrate the feasibility of the suggested operational principle as an efficient mechanism in the arena of non-volatile mechanical memory devices.
Large amplitude flexural vibrations have been excited in single layer silicon-on-insulator micromechanical cantilever beams in ambient air environment. Our driving approach relies on a single co-planar electrode located symmetrically around the actuated grounded cantilever. Electrostatic forces are created via tailored asymmetries in the fringing fields of deformed mechanical states during their electric actuation, with strong restoring forces acting in a direction opposite to the deflection. This results in an effective increase in the structure stiffness in its elastic regime. The devices had been fabricated using deep reactive ion etching based process and their responses were characterized in a laser Doppler vibrometer under ambient conditions. Harmonic voltages applied to the electrode result in the periodic modulation of the effective stiffness and lead to strong parametric excitation of the structure. As opposed to close gap actuators, where high-amplitude drives are severely limited by pull-in instabilities, squeezed gas damping, and stiction, our resonators exhibit very large vibration amplitudes (up to 8 in terms of the amplitude to thickness ratio in the strong parametric regime), with no apparent damage, via the application of highly tunable distributed forces. A reduced order model, based on the Galerkin decomposition, captures the main dynamical features of the system, and is consistent with the observed beam characteristics.
We report on an experimental observation of synchronization and abrupt transitions between standing wave patterns in arrays of micromechanical oscillators. The architecture of flexible cantilever arrays parametrically excited by and interacting through time-dependent fringing electrostatic fields allows tuning of an interaction potential and supports traveling waves. The arrays consisting of 500 μm long and 5 μm thick single crystal Si cantilevers were fabricated from silicon on insulator substrates. The out-of-plane resonant responses were visualized by time-averaged temporally aliased video imaging and measured by laser Doppler vibrometry. Our experimental and reduced order model results collectively demonstrate that under a slowly varying drive frequency the standing wave patterns remain unchanged in certain frequencies intervals, followed by an abrupt change in the pattern.
We have performed in situ real time mass sensing of deposited liquid volatile droplets and sprays using plate-like microstructures, with robust and reusable performance attained over harsh conditions and multiple cycles of operation. A home-built electrooptical sensing system in ambient conditions has been used. The bimorph effect on the resonant frequency of altered mass loading, elasticity, and strain had been carefully compared, and the latter were found to be negligible in the presence of nonviscous liquids deposited on top of our microplate devices. In resonant mode, the loaded mass has been estimated from measured resonant frequency shifts and interpreted from a simple, uniformly deposited film model. A minimum submicrogram detectable mass was estimated, suggesting the system's potential for robust, fast, and reusable sensing capabilities, in the presence of volatile liquids under harsh operation conditions.
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