Nanomechanical Motion Transducers for Miniaturized Mechanical Systems
Reliable operation of a miniaturized mechanical system requires that nanomechanical motion be transduced into electrical signals (and vice versa) with high fidelity and in a robust manner. Progress in transducer technologies is expected to impact numerous emerging and future applications of micro-and, especially, nanoelectromechanical systems (MEMS and NEMS); furthermore, high-precision measurements of nanomechanical motion are broadly used to study fundamental phenomena in physics and biology.
... hysics and biology. Therefore, development of nanomechanical motion transducers with high sensitivity and bandwidth has been a central research thrust in the fields of MEMS and NEMS. Here, we will review recent progress in this rapidly-advancing area. A miniaturized resonator oscillating in one of its modes can be modeled as a one-dimensional damped harmonic oscillator under a time-dependent driving force F(t): (1) Here, x(t) is the modal coordinate, f r is the resonance frequency of the mode, and γ is the dissipation -typically, described in terms of the quality factor, Q = 2π f r /γ. The dissipation experienced by a vibrating nanostructure can come from a variety of sources. Some well-studied examples include clamping losses, thermoelastic damping, and damping from surrounding fluids          . Since dissipation (Q-factor) is an important parameter in both fundamental and engineering aspects of miniaturized resonators  , there have been attempts to control and enhance Q-factor, for example, via chemical surface treatment  , external circuits  and parametric amplification  . The resonance frequency f r is determined by the geometry-e.g., cantilevered or torsional structures-and the linear dimensions of the device as well as the device material. The stress field within the structure, either intrinsic or induced externally, also affects f r and γ, and can thus be used for tuning    .