Intentional Nonlinearity Design Extends to Nanoscale
Mechanical Science and Engineering Professors Min-Feng Yu and Alexander Vakakis, and Ph.D. Student Hanna Cho, along with Aerospace Engineering Professors Lawrence Bergman and Michael McFarland, have designed and demonstrated a conceptually new nonlinear nanomechanical resonator that offers significantly expanded resonance bandwidth and high sensitivity sensing performance. They describe their work in a paper accepted for publication and posted online this week in the journal Nano Letters.
Traditional nanomechanical resonators typically operate in the linear dynamic regime and achieve high sensitivity sensing to added mass by exploiting high quality-factor resonance at high frequency. The problem is that in order to maintain the resonance system in the linear regime, the resonance amplitude has to be kept extremely small, comparable to the nanoscale diameter of the resonance beam. This makes developing the measurement system for monitoring the resonance very difficult and, more importantly, limits the sensitivity of the nanoresonator to added mass or other perturbations, especially under ambient and room temperature environments.
The new nanoresonator design overcomes such problems by intentionally incorporating an inherent geometric nonlinearity in the resonance system by the use of a center-concentrated driving force to drive a doubly clamped nanowire. This intrinsic geometric nonlinearity has a nonlinear force-displacement dependence of pure cubic order and prescribes that the resonance system has no preferential resonance frequency and is thus broadband. They demonstrated its operation by integrating a carbon nanotube as the mechanical beam and realized its broadband resonance over tens of MHz, over three times its natural resonance frequency. They further achieved high sensitivity sensing to femtogram (10-15 g) added mass at room temperature.