Effect of second-harmonic superimposition on efficient induction of sonochemical effect

A new method of insonation for inducing sonochemical effects efficiently without using mechanical or acoustical agitation was investigated. When the second harmonic (1.5 MHz) was superimposed on the fundamental (750 kHz) at the optimum acoustical power ratio (1:1), the oxidation rate was one or more orders of magnitude higher than that obtained at the same total acoustic power when the fundamental or the second harmonic was used alone. Moreover, the second-harmonic superimposition reduced the threshold of acoustic power for the sonochemical reaction to half of the threshold when the fundamental alone was used.