How to Excite Anti-symmetric Modes in a Symmetric MEMS?

This study reports on an experimental investigation of modal interactions in a microresonator. The resonator is made of a clamped-clamped curved beam, electrostatically actuated via a side electrode. A two-to-one ratio exists by design between the first anti-symmetric and the second symmetric in-plane bending modes. Because the beam geometry and actuation are symmetric, anti-symmetric modes cannot be directly excited due to the negligible projection of the excitation force onto anti-symmetric modes. This study shows that these modes can be indirectly excited by channeling energy from a symmetric mode to the target anti-symmetric mode. The result is an M-shaped frequency-response curves, with stable trivial and large-amplitude branches. The latter branch combines contributions from both the directly and indirectly excited modes.