Parametric Amplification in the Dynamic Radiation Force of Acoustic   Waves in Fluids
  We report on parametric amplification in dynamic radiation force produced by a bichromatic acoustic beam in a fluid. To explain this effect we develop a theory taking into account the nonlinearity of the fluid. The theory is validated through an experiment to measure the dynamic radiation force on an acrylic sphere. Results exhibit an amplification of 66 dB in water and 80 dB in alcohol as the difference of the frequencies is increased from 10 Hz to 240 kHz. 
Glauber T. Silva, Shigao Chen, Leonardo P. Viana