The MEMS (microelectromechanical systems) and NEMS (nanoelectromechanical systems) market has been growing very fast over the past decade and worldwide sales of MEMS/NEMS devices are expected to reach $100 billion by 2009. Resonant sensors and filters are important MEMS/NEMS devices that can resonate at certain ranges of radio frequencies. They are widely used in the internet technology, wireless communication, mechanical and biomedical sensors, and digital electronics for making accurate frequency comparisons and for generating narrowband frequencies in the microwave region. However, operation of MEMS/NEMS resonators and filters at high frequencies usually involves damping-related energy dissipation processes. Minimization of the energy loss or achieving high quality factor (Q-factor) is often a key design objective.

There are various sources of damping in MEMS/NEMS. The investigation of the energy loss caused by thermoelastic damping in MEMS/NEMS is relatively very recent, being prompted by the pursuit of low energy dissipation in designing and fabricating high-precision actuators, sensors and filters (Lifshitz and Roukes 2000).

The mechanism of thermoelastic damping can be explained briefly as follows: Change of temperature in a material system will cause thermoelastic deformation, and this process can also occur in the opposite way: that is, mechanical deformation may cause a change of local temperature. During the compression and decompression of an oscillating system, the coupling between heat transfer and strain rate will induce a sort of irreversible heat dissipation. This phenomenon is called "thermoelastic damping" or TED.

My current interest in this area is to use the reduced-order finite element models to simplify those problems with geometric symmetries, such as resonant beams, plates and rings. The following figure shows the different TED mode patterns of a resonant MEMS ring using a reduced-order model.

Many commerical codes have also incorporated the capabilities of computing eigenfrequencies and quality factors for TED. The following figure shows a screenshot of the dominant TED mode of a rectangular MEMS plate using COMSOL Multiphysics(C).

Reference

Yi, Y. B., 2007, Geometric Effects on Thermoelastic Damping in MEMS Resonators, Journal of Sound and Vibration, accepted for publication.

Yi, Y. B. and Matin, M. A., 2006, Eigenvalue Solution of Thermoelastic Damping in Beam Resonators Using a Finite Element Analysis, ASME Journal of Vibration and Acoustics, 129, 478-483.

R. Lifshitz and M.L. Roukes, 2000, Thermoelastic damping in micro- and nanomechanical systems ,Physical Review B, 61, 5600-5609.