Anomalous Thermomechanical Softening-Hardening Transiti ons in Micro-oscillators

We report a transition in the response of a doublyclamped micromechanical oscillator with linear inertial forcing. The experimental response of the oscillator changes, counter-intuitively, from softening to hardening on increasing the power of an incident laser beam. A novel response structure, that simultaneously displays characteristics of both softening and hardening resonances, is observed at intermediate laser powers. Using a dynamic nonlinear thermomechanical model, we show that the transition is explained by opposing responses of linear and cubic stiffness terms to temperature.