| AVS 60th International Symposium and Exhibition | |
| MEMS and NEMS | Tuesday Sessions |
| Session MN-TuP |
| Session: | MEMS and NEMS Poster Session |
| Presenter: | L. Li, University of California, Santa Barbara |
| Authors: | L. Li, University of California, Santa Barbara L.A. Shaw, University of California, Santa Barbara K.L. Turner, University of California, Santa Barbara |
| Correspondent: | Click to Email |
The objective of this work is to develop a high frequency MEMS-based mass sensor capable of pushing the limits of sensitivity for the detection of explosive materials. The specific objective is to utilize a nonlinear microcantilever mass sensor functionalized with xerogel-based molecularly imprinted polymers (MIPs) for the selective detection of DNT. This paper reports the implementation of a novel control method for sensing which is based on the phase squeezing phenomenon present in the nonlinear dynamics of a parametrically driven microcantilever. It is expected to significantly improve the mass detection limits compared to bifurcation tracking [1], as well as reduce measurement time by over three orders of magnitude. Sensor speed, sensitivity, and selectivity are all important for ppt level DNT/TNT detection.
Previous work focuses on tracking the resonance frequency shift of the microcantilever due to DNT absorption using bifurcation tracking [1]. Bifurcation sensing is achieved by sweeping the frequency or voltage until a jump event occurs, and tracking is done by repeating the process to detect the frequency shift. However, bifurcation tracking is a time-consuming process which requires time to reset the system back to an appropriate initial condition after each jump event to avoid hysteresis before the next bifurcation occurs. This work reports a new method of sensing which concentrates on monitoring changes in the phase response as the device approaches the bifurcation point. Just prior to bifurcation, noise squeezing occurs due to a slowing down of the response component associated with the bifurcating eigenvalue near the bifurcation point. The statistical variance of the phase response serves as a precursor to activate the feedback control scheme, which employs frequency modulation to stabilize a parametrically-excited sensor at the edge of instability. By maintaining close proximity to the bifurcation, but not allowing the large amplitude growth necessary for existing bifurcation tracking methods, over three orders of magnitude measurement time improvements in the acquisition rate near the location of the bifurcation point can be made [2]. Initial results show that the controller is capable of tracking the resonance frequency based on the phase variance of the microcantilever with close proximity to the edge of instability and control parameters can be tuned to optimize the sensitivity of the sensor. DNT gas sensing using the controller is yet to be experimented and the sensitivity of noised squeezing bifurcation sensing of nonlinear MEMS microcantilever is expected to be presented at the conference.