text: From Rayleigh–Plesset equation one can derive the bubble resonant frequency:
  Where  is the fluid density,  is the rest radius of the bubble,  is the polytropic index,  is the ambient pressure,  is the vapor pressure and  is the surface tension constant.
  Bubbles with resonance frequency above the acoustic driving frequency travel up the pressure gradient, while those with a lower resonance frequency travel down the pressure gradient. 
  The dependence of the resonant frequency () on the rest radius of the bubble predicts that for standing waves, there is a critical radius  that depends on the driving frequency. Small bubbles () accumulate at pressure antinodes, whereas large bubbles () accumulate at pressure nodes.