Experimental modal analysis for microelectromechanical systems

The structural dynamics behavior of microelectromechanical systems (MEMS), which include moving, overhung, and compliant subcomponents, plays a pivotal role in determining their performance and reliability. Traditionally, experimental modal analysis is used to characterize the dynamic behavior of structures, as well as to derive, validate, update, and correct analytical and numerical models. Due to their small size, however, conventional modal testing methods cannot be directly applied to microstructures. In this paper we provide an overview of modal testing techniques for microsystems. A particular experimental modal analysis methodology that includes base excitation via a piezoelectric shaker and measurement through a laser interferometer is then described and evaluated. A distinguishing characteristic of the methodology is its simplicity, including its simple setup and off-the-shelf components. The modal model is derived for the base excitation of microcantilever beams. The effectiveness of the methodology is illustrated through various experiments on polysilicon microcantilevers for different geometries and ambient pressures. Analysis of the damping data for different pressures has confirmed the well-documented fact that the structural damping in microsystems can be considerably less than damping arising from interaction with the ambient gases.