We use vibration localization as a sensitive means of detecting small perturbations in stiffness in a pair of weakly coupled micromechanical resonators. For the first time, the variation in the eigenstates is studied by electrostatically coupling nearly identical resonators to allow for stronger localization of vibrational energy due to perturbations in stiffness. Eigenstate variations that are orders of magnitude greater than corresponding shifts in resonant frequency for an induced stiffness perturbation are experimentally demonstrated. Such high, voltagetunable parametric sensitivities together with the added advantage of intrinsic common mode rejection pave the way to a new paradigm of mechanical sensing.
In recent years, the concept of utilizing the phenomenon of vibration mode-localization as a paradigm of mechanical sensing has made profound impact in the design and development of highly sensitive micro-and nanomechanical sensors. Unprecedented enhancements in sensor response exceeding three orders of magnitude relative to the more conventional resonant frequency shift based technique have been both theoretically and experimentally demonstrated using this new sensing approach. However, the ultimate limits of detection and in consequence, the minimum attainable resolution in such mode-localized sensors still remain uncertain. This paper aims to fill this gap by investigating the limits to sensitivity enhancement imposed on such sensors, by some of the fundamental physical noise processes, the bandwidth of operation and the noise from the electronic interfacial circuits. Our analyses indicate that such mode-localized sensors offer tremendous potential for highly sensitive mass and stiffness detection with ultimate resolutions that may be orders of magnitude better than most conventional micro-and nanomechanical resonant sensors.
We use the phenomena of mode localization and vibration confinement in pairs of weakly coupled, nearly identical microelectromechanical (MEMS) resonators as an ultrasensitive technique of detecting added mass on the resonator. The variations in the eigenstates for induced mass additions are studied and compared with corresponding resonant frequency shifts in pairs of MEMS resonators that are coupled electrostatically. We demonstrate that the relative shifts in the eigenstates can be over three orders of magnitude greater than those in resonant frequency for the same addition of mass. We also investigate the effects of voltage controlled electrical spring tuning on the parametric sensitivity of such sensors and demonstrate sensitivities tunable by over 400%.
Abstract-Measuring shifts in eigenstates due to vibration localization in an array of weakly coupled resonators offer two distinct advantages for sensor applications as opposed to the technique of simply measuring resonant frequency shifts: (1) orders of magnitude enhancement in parametric sensitivity and (2) intrinsic common mode rejection. In this paper, we experimentally demonstrate the common mode rejection capabilities of such sensors. The vibration behavior is studied in pairs of nearly identical MEMS resonators that are electrically coupled, and subjected to small perturbations in stiffness under different ambient pressure and temperature. The shifts in the eigenstates for the same parametric perturbation in stiffness are experimentally demonstrated to be over three orders of magnitude greater than corresponding resonant frequency variations. They are also shown to remain relatively constant to variations in ambient temperature and pressure. This increased relative robustness to environmental drift, along with the advantage of ultra-high parametric sensitivity, opens the door to an alternative approach to achieving higher sensitivity and stability in micromechanical sensors.
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