Mode localization and sensitivity in weakly coupled resonators

Abstract

Localization of normal modes is used in recent microelectromechanical systems (MEMS) technologies with orders of magnitude improvements in sensitivity. A pair of eigenvalues veer, or avoid crossing each other, as a single parameter of a vibrating system is varied. While it is well-known that the sensitivity ($s$) of modal amplitude ratio varies with strength of coupling ($\kappa$) as $s \propto\kappa^{-1} $ in the case of two identical coupled oscillators, recently, we showed that asymmetry $\alpha$ will also influence sensitivity according to $s \propto (\alpha \kappa)^{-1}$. Here, we show that further enhancements in sensitivity is possible in higher degrees of freedom ($n$) systems using energy analysis. In the case of $n-2$ uniformly coupled oscillators embedded between two oscillators, we show that $s \propto \alpha^{-1}\kappa^{1-n}$, if the blocked resonance spectra of the embedded oscillators and the end oscillators are well-separated. We also show that asymmetric coupled oscillators also enhance linear range in addition to sensitivity when compared to their symmetric counterparts. We do not use a perturbation approach in our energy analysis; hence the sensitivity and linear range expressions derived have a wider range of accuracy.