Phononic four-wave mixing
  We present the first experimental observations of phononic four-wave mixing (FWM) in a piezoelectrically actuated free-free beam microstructure. The FWM response is facilitated by the intrinsic coupling between a driven mode and an auto-parametrically excited sub-harmonic mode. Motivated by the experimental results, a dynamical model for FWM has been specified. 
Adarsh Ganesan, Cuong Do and Ashwin A. Seshia
cond-mat.mes-hall