Problem description and significance:
Conventional resonant MEMS sensing devices rely on a change in resonant frequency of a MEMS resonator due to a change in its mass or stiffness by a physical quantity to be measured. An alternative resonant MEMS sensing paradigm, based on a change in mode shape of a weakly coupled MEMS resonator achieves orders of magnitude improvement in sensitivity. This sensing method also has the benefit of common mode rejection.
The high sensitivity of weakly coupled resonators results from mode localization due to a change in a parameter of the coupled system, for example, mass or stiffness of one of the resonators. In mode localization, vibrational energy localizes to certain resonators in the coupled system. Mode localization is accompanied by eigenvalue veering, wherein two natural frequencies of a system come close as a system parameter is varied and instead of crossing each other, they veer away. In the process, eigenvector rotates swiftly near the center of veering (location where eigenvalues come close to each other) and the eigenmodes associated with the veering frequencies get swapped.
We developed an energy-based framework that relates modal amplitudes of resonators in a coupled resonator system recursively. facilitating a convenient study of mode localization. A mode localized MEMS transducer with two coupled resonators operating in the air was also reported. Also, typically mode localized MEMS sensors reported in the literature are based on symmetric resonators. We show that carefully designed asymmetry can further enhance the sensitivity of a mode localized MEMS sensor. We also propose the use of linear electrostatic coupling based on shaped combs in coupled resonator system, instead of a typical parallel-plate based electrostatic coupling which may suffer from nonlinearity when vibration localization is strong.
Selected publications:
- Manav, M., Phani, A.S., and Cretu, E., 2017, ”Mode localized MEMS transducers with voltage-controlled linear coupling,” Journal of Micromechanics and Microengineering, 27(5), pp. 055010.
- Manav, M., Reynen, G., Sharma, M., Cretu, E., and Phani, A.S., 2014, ”Ultrasensitive resonant MEMS transducers with tuneable coupling,” Journal of Micromechanics and Microengineering, 24(5), pp. 055005.
- Manav, M., Reynen, G., Sharma, M., Cretu, E., and Phani, A.S., 2013, ”Ultrasensitive resonant MEMS transducers with tuneable coupling,” The 17th International Conference on Solid-State Sensors, Actuators and Microsystems (TRANSDUCERS & EUROSENSORS XXVII), Barcelona, Spain.
Funding:
The work is funded by Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), Canada Research Chairs and CMC Microsystems. This work is in collaboration with Prof. Edmond Cretu‘s lab at UBC.