Mechanical behavior and sound generation efficiency of prestressed, elastically clamped and thermomechanically driven thin film sandwiches

A model of thermomechanically driven plates as used, e.g., for acoustic mic roresonators is reported. The model describes the quasibuckling, excitation , fundamental frequency and vibration mode of multilayered plates under pla ne strain. The plates consist of stacked thin films with individual elastic modulus, Poisson's ratio, prestress, heat capacity and coefficient of ther mal expansion. Membrane edges are elastically clamped to lateral supports. In thin plates two driving mechanisms are identified: the first couples the thermomechanical bending moment to the curvature of the vibration mode; th e second couples the thermomechanical line stress to the periodic length ch ange of the vibrating quasibuckled structure. Results of the model include vibration amplitude, sound held pressure, emitted power and quality factor as functions of the membrane properties. Maximum output is obtained close t o the quasibuckling transition of the structures, where their resonance fre quency is minimum. Largest sound pressures are generated by structures with rigid supports or with vanishing initial bending moment. The model shows e xcellent agreement with experimental data from micromachined resonant silic on membranes.