AVS 51st International Symposium
    MEMS and NEMS Tuesday Sessions
       Session MN-TuM

Paper MN-TuM7
Frequency-Tuning for Control of Parametrically-Resonant Mass Sensors

Tuesday, November 16, 2004, 10:20 am, Room 213C

Session: MEMS and NEMS: Enabling Tools for Scientific Research
Presenter: W. Zhang, University of California, Santa Barbara
Authors: W. Zhang, University of California, Santa Barbara
K. Turner, University of California, Santa Barbara
Correspondent: Click to Email
Parametric-resonance based mass sensing leads to increased sensitivity over other resonant methods@footnote 1@. In this work, we present a frequency-tuning approach to measuring mass change in an ultra-sensitive mass sensor. This scheme drives the oscillator using an electrical signal with fixed frequency and tunes the natural frequency to match the driving frequency by feeding back a DC offset to the sensor. Instead of monitoring frequency shift of oscillation in a micro-oscillator, mass change in the sensor can be detected by measuring the DC offset shift, making the sensor amenable to closed-loop control. Different from conventional harmonic resonance based mass sensor, this mass sensor detects mass change in a micro-oscillator based on parametric resonance phenomenon@footnote 1@. In a prototype mass sensor with natural frequency of 83k Hz, less than 1 Hz of frequency shift has been measured at air pressure, which is equivalent to 0.0012% of the mass of the micro-oscillator (less than 1 pg mass change in this prototype mass sensor). Due to the configuration of the micro-oscillator, which is driven by a pair of non-interdigitated electrodes, the natural frequency can be tuned by changing the DC offset in driving electrical AC signal. Since the frequency of parametric resonance at the stability boundary is related to natural frequency (doubled), the parametric resonance frequency can be tuned by DC offset feedback as well. By matching the fixed frequency of driving electrical signal with parametric resonance frequency using DC offset, the actual natural frequency change, and the mass change, can be found from monitoring shifts in the DC offset. This scheme and the prototype mass sensor has been built and tested. Potential applications include water quality monitoring, gas leakage sensing, and bio sensing, such as DNA, protein, and virus assay. @FootnoteText@ @footnote 1@W. Zhang et al, Sens. Actuators A, Phys., 102/1-2 (2002).