A reduced-order-model-based equivalent circuit for piezoelectric micro-electro-mechanical-system loudspeakers modeling.

Piezoelectric micro-electro-mechanical-system (MEMS) speakers are emerging as promising implementations of loudspeakers at the microscale, as they are able to meet the ever-increasing requirements for modern audio devices to become smaller, lighter, and integrable into digital systems. In this work, we propose a finite element model (FEM)-assisted lumped-parameters equivalent circuit for a fast and accurate modeling of these types of devices. The electro-mechanical parameters are derived from a pre-stressed FEM eigenfrequency analysis, to account for arbitrarily complex geometries and for the shift of the speaker resonance frequency due to an initial non-null pre-deflected configuration. The parameters of the acoustical circuit are instead computed through analytical formulas. The acoustic short-circuit between the speaker front and rear sides is taken into account through a proper air-gaps modeling. The very good matching in terms of radiated sound pressure level among the equivalent circuit predictions, FEM simulations, and experimental data proves the ability of the proposed method to accurately simulate the speaker performance. Moreover, due to its generality, it represents a versatile tool for designing piezoelectric MEMS speakers.

Experimental and theoretical study of processes leading to steady-state sound in annular thermoacoustic engines.

This paper gives a simplified analytical description of spontaneous generation and finite amplitude saturation of sound in annular thermoacoustic engines, and also provides comparison with experiments. The model includes the precise description of thermoacoustic amplification of sound (induced by interaction between an heterogeneously heated stack of solid plates and resonant gas oscillations), which accounts for the details of the temperature distribution in the whole thermoacoustic device (i.e., which does not only account for the mean temperature gradient along the stack). The saturation of the acoustic wave amplitude is described by taking into account both the reverse influence of high amplitude acoustic field on temperature field, and the dissipation of acoustic energy due to higher harmonics generation and minor losses (vortex generation). From the comparison between simulation results and experiments, it is demonstrated that the dynamical behavior observed in our experimental device is predominantly controlled by the effects of acoustic streaming and acoustically enhanced thermal conductivity tending not only to reduce the externally imposed temperature gradient along the stack, but also to change the shape of the temperature field.

Acoustic streaming in annular thermoacoustic prime-movers

The theory of acoustic streaming in an annular thermoacoustic prime-mover is developed. It is predicted that above the threshold for traveling wave excitation the device considered (which does not contain any moving parts or externally imposed pressure gradients) produces circulation of fluid. The heat flux carried by this directional mass flow inside the thermoacoustic stack exceeds (or is comparable with) the heat flux associated with the acoustically induced increase of thermal diffusivity of the gas. The effects investigated are important for optimization of the performance of thermoacoustic devices.