THESIS
2019
xiv, 166 pages : illustrations ; 30 cm
Abstract
Resonators made from micro-/nanoelectromechanical systems are of great importance for
their applications ranging from ultra-sensitive measurement to fundamental researches. In this
work, we study the coupling between two mechanical modes in MEMS and NEMS resonators
as well as the self-sustained oscillations that arises from the mode coupling.
In the NEMS resonators made from MoS
2 thin flakes, the internal resonance enables
effective energy transfer between two modes and thus up-convert the input signals to its higher
order harmonics. The dispersive coupling can act as a probe to detect the vibrations of
mechanical modes that are hard to access. By parametrically modulating the mode coupling,
the quality factors of the two modes are enhanced simultaneously and this provides an
o...[
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Resonators made from micro-/nanoelectromechanical systems are of great importance for
their applications ranging from ultra-sensitive measurement to fundamental researches. In this
work, we study the coupling between two mechanical modes in MEMS and NEMS resonators
as well as the self-sustained oscillations that arises from the mode coupling.
In the NEMS resonators made from MoS
2 thin flakes, the internal resonance enables
effective energy transfer between two modes and thus up-convert the input signals to its higher
order harmonics. The dispersive coupling can act as a probe to detect the vibrations of
mechanical modes that are hard to access. By parametrically modulating the mode coupling,
the quality factors of the two modes are enhanced simultaneously and this provides an
opportunity to improve the performance of such 2-dimension devices in room temperature.
In the MEMS resonators, by pumping at the sideband of high frequency mode, additional
linear or nonlinear friction force show up on the low frequency mode depending on the
frequency of the modulation. The negative nonlinear friction leads to various of new
phenomenon such as non-Lorentzian mode shape, energy-dependent dissipation and an isolated
branch on top of normal driven response.
Self-sustained oscillations take place once the additional linear friction or negative
nonlinear friction is strong enough to overcome the intrinsic energy dissipation. In the former
case, self-sustained oscillations build up spontaneously by amplifying thermal fluctuations
while in the latter case, zero amplitude is also stable and an excitation is required to activate the
self-sustained oscillations. In both cases, the phase of two modes diffuses randomly and they
add up to a constant due to the discrete time translation symmetry. The self-sustained
oscillations can be used in signal transduction and frequency tuning element.
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