Actuation of Higher Harmonics in Large Arrays of Micromechanical Cantilevers for Expanded Resonant Peak Separation

A large array of elastically coupled micro cantilevers of variable length is studied experimentally and numerically. Full-scale finite element (FE) modal analysis is implemented to determine the spectral behavior of the array and to extract a global coupling matrix. A compact reduced-order (RO) model is used for numerical investigation of the array's dynamic response. Our model results show that at a given excitation frequency within a propagation band, only a finite number of beams respond. Spectral characteristics of individual cantilevers, inertially excited by an external piezoelectric actuator, were measured in vacuum using laser interferometry. The theoretical and experimental results collectively show that the resonant peaks corresponding to individual beams are clearly separated when operating in vacuum at the third harmonic. Distinct resonant peak separation, coupled with the spatially confined modal response, make higher harmonic operation of tailored, variable-length cantilever arrays well suited for a variety of resonant-based sensing applications.

Simulation of electrical properties of quartz crystal microbalance using multi-resonance thickness-shear mode technique

The use of quartz crystal microbalance (QCM) in chemistry, biophysics, microbiology and electronics has grown tremendously in recent years. In this paper, the properties of a QCM sensor (a system include QCM device and viscoelastic medium) operating in the range of 5 MHz to 35 MHz of Multi-resonance Thickness-Shear Mode (MTSM, n = 1, 3, 5, 7) are described. We calculate the changes both in resonant frequencies and attenuation of the QCM. The penetration depth of the shear waves propagating from quartz into loaded thin film varies in different values due to the harmonics, from which we infer the properties of the loaded thin film. The multi-harmonic operation of QCM was presented to collect the information of the loaded thin film on QCM’s electrode. This enables a “virtual slicing technique” because a harmonic relates to a different penetration depth even with the same material. The theoretical analysis of MTSM has been developed to model and simulate the signature of the sensor responses at harmonic frequencies. The signatures of the evaporation- induced deposition processes were investigated by studying the effect of the thickness and stiffness of the medium.