Viscous fluid–structure interaction of micro-resonators in the beam–plate transition

Abstract

We numerically investigate the fluid-structure interaction of thin elastic cantilever micro-structures in viscous fluids. The Kirchhoff plate equation describes the dynamics of the structure, and a boundary integral formulation represents the fluid flow. We show how the displacement spectrum of the structures changes as the geometry is altered from a narrow beam to a wide plate in a liquid. For narrow beams, the displacement spectrum exhibits only a few resonance frequencies, which correspond to the vibrational modes described by the Euler-Bernoulli equation (Euler-Bernoulli modes). The spectrum of wide plates exhibits several additional resonance frequencies associated with the plate's torsional and higher-order vibrational modes. Wide plates in Euler-Bernoulli modes exhibit higher damping coefficients, but due to an increased added-mass effect, also higher Q-factors than slender beams. An investigation into the fluid flow reveals that for the Euler-Bernoulli modes of wider plates, the fluid flow and energy dissipation near the plate's edges increase, resulting in increased damping coefficients. Concomitantly, a region of minimal viscous dissipation near the plate's center appears for wider plates, resulting in an increased added-mass effect. Higher-order modes of wider plates exhibit lower Q-factor than the Euler-Bernoulli modes due to a decreased fluid flow at the plate's edges caused by the appearance of circulation zones on both sides of the plate. This decreased flow at the edge reduces the damping and the added-mass effect, yielding lower Q-factors. We anticipate that the results presented here will play a vital role in conceiving novel MEMS resonators for operation in viscous fluids.