ABSTRACT
Dynamic micro/nanomechanical systems are devices employing mechanical elements (e.g., a beam, a membrane, etc.) at micro/nanometer scales, designed to exhibit mechanical motions usually at or near their resonance frequencies; these are called “micro/nanomechanical resonators” or just “micro/nanoresonators.” The mechanical elements are often accompanied by electrical or optical functionality to achieve the ultimate design objectives originating from their unique mechanical motion. The attributes that the tiny size provides are high resonant frequency and low damping, which make micro/nanomechanical systems appealing for many
applications including extremely sensitive sensors and high frequency RF electronic components. One of the major research directions with the goal of achieving higher performance has been toward decreasing the device size in order to reach higher frequencies and lower damping. Building such tiny devices relies on remarkable development in micro-and nanofabrication techniques. The main difficulties in decreasing the device size do not originate from fabricating a small device but from realizing the required operation combined with actuation and detection techniques. Extensive research over the last two decades has overcome such difficulties by developing effective schemes to actuate these tiny devices and detect the resulting small motion with extreme sensitivity. However, the operation of these devices is still limited by the intrinsic traits of readily realizable nonlinear characteristics in micro/nanomechanical systems.A mechanical resonator at micro/nanoscale can easily transit from linear to nonlinear resonance operation, because of its remarkable properties, namely small size and low damping. There are many sources of system nonlinearity such as nonlinear dissipative mechanisms, geometric/kinematic nonlinearities, nonlinear potential force-laws, etc. Moreover, as the device size decreases and, accordingly, the corresponding damping becomes very small, the system becomes vulnerable to such sources of nonlinearity and may exhibit strongly nonlinear behavior whether this is by design and wanted or not.Early studies on micro/nanomechanical systems, however, were concerned with their operation in the linear dynamical range. As the systems were designed to operate within the linear regime from the beginning, the operation naturally strayed from the original design specifications when nonlinear effects appeared, leading to performance degradation. In fact, in order to restrict the dynamics within the linear regime, the resonant amplitude was restricted to be smaller than the critical amplitude for the onset of nonlinearity, which is often comparable to the amplitude of thermal vibration for nanoscale devices. As a result, the dynamic operational range was narrowly confined and, thus, performance and applications were also limited.
