This paper suggests a design for a Film Bulk Acoustic Resonator (FBAR) which utilizes a secondary piezoelectric layer for purposes of tuning the FBAR's resonant frequency. Currently, many ceramic resonators have difficulties in on-chip integration, power handling and electrode fabrication. FBARs are not only simple to fabricate and capable of full integration with CMOS/RF IC circuitry, but are also compact and can achieve high frequencies (GHz) with high quality factors. It is widely accepted that piezoelectric actuators encounter a significant change in mechanical stiffness between their open-circuit and closed-circuit states. In addition, it has been previously shown that the resonant frequency of a multi-layer FBAR is a function of the acoustic impedances and, correspondingly, the acoustic velocities, of its respective layers. Since the effective modulus term of the acoustic velocity of an FBAR layer is dependent on both the mechanical properties and electromechanical coupling of its piezoelectric element, and since electromechanical coupling can be altered by means a previously investigated shunt capacitor tuning concept, the stiffness of the piezoelectric tuning layer can be adjusted to vary the resonant frequency of the FBAR. Since difficulties have existed in matching FBAR resonant frequencies to specified values or making the frequencies stable during temperature variations, an active tuning capability for FBARs could offer many possible improvements. This work describes the application of the shunt capacitor tuning to a FBAR resonator and looks at the effects that varying different FBAR parameters have on the frequency range and degree of tunability of the device.
Damage detection and prediction is essential for structural health monitoring. Vibration based methods have been used in health monitoring. In this work damage is proposed to be a nonlinear dynamical phenomenon and can be analyzed by utilizing the bifurcation theory. A methodology for predicting failure is proposed which utilizes the concepts of distance to stability boundary as estimated by bifurcation analysis. The proposed methodology is illustrated by developing bifurcation boundary for a two degree of freedom nonlinear mass-spring-damper system. Two damage models are investigated to illustrate the utility the proposed methodology in capturing and estimating the evolution of damage phenomenon.