Squeeze film damping in MEMS loudspeakers: Analysis of a clamped-clamped microbeam

Miniaturized micro-electro-mechanical systems (MEMS) loudspeakers is a current developmental trend for in-ear audio applications. However, when a loudspeaker shrinks to a size of a microelectronic chip, the involved physics starts to differ from the macroscopic world. At one side, an electrostatic mu Speakers benefits from small electrode gaps leading to high driving forces. At the same time, the fluid dynamics of the air can cause strong damping forces inside the microscopic cavities of a MEMS loudspeakers chip. Recently we have shown experimentally that the first Euler-Bernoulli bending mode is sufficient to reproduce the behavior of a Coulomb-actuated microbeam over the entire stroke with high accuracy. This leads to an ab initio modeling approach based on a novel Chebyshev-Edgeworth type expansion that leads to an accurate lumped parameter model (LPM) with a single degree of freedom for MEMS loudspeakers. In this work, we discuss the influence of microfluidics on the damping of a balanced nanoscopic electrostatic drive (NED) test loudspeaker design. With the help of the finite element method (FEM) we analyze how the pressure and velocity distribution is linked to the Euler-Bernoulli modes of a simple microbeam, with the aim of including the squeeze film damping in the LPM. Understanding the various sources of fluid dynamic damping is of great importance for the design of high fidelity MEMS based electrostatic audio transducers (mu Speakers).