  Sonochemical reactors are used in water treatment, the synthesis of fine
chemicals, pharmaceutics and others. The low efficiency of sonoreactors have
prevented its massive usage at industrial scales. Controlling the appearance of
bubbles in place and time is the most limiting factor. A novel type of
sonochemical reactor was designed making use of micro-fabrication techniques to
control the nucleation sites of micro-bubbles. The efficiency was increased
first by locating the nucleation sites in the most active region of a
micro-chamber; additionally the desired chemical effect was significantly
higher at the same powers than when not controlled. Silicon substrates were
micromachined with "artificial nucleation sites" or pits, and placed at the
bottom of the micro-chamber. The pits entrap gas which, upon ultrasonic
excitation, sheds off a stream of microbubbles. The gas content of the pits is
not depleted but is replenished by diffusion and the emission of microbubbles
can continue for hours.
