Design and calibration of a single-transducer variable-frequency sonication system

The design of a novel single-transducer variable-frequency sonication system capable of operating at constant acoustic power over the range 20-500 kHz is described. The system employs a mass-loaded sandwich transducer arrangement and a series of transformers to provide an accurate impedance matching circuit. Approximately 0-5 W of acoustic power are produced by the system at typical operating frequencies of 20, 40, 150, 200, 300, and 450 kHz. As a first test of the single-transducer variable-sonication system we have re-examined the frequency dependence of the sonochemical oxidation of potassium iodide. Previous investigators have monitored the frequency dependence using a multi-transducer system to obtain the different frequencies required. In accordance with the earlier findings, we have observed an eightfold increase in the rate of potassium iodide oxidation at 300 kHz compared to 20 kHz, as well as an inversion in the rate of oxidation for argon and air-saturated solutions at 300 kHz. Possible reasons for the rate variations are discussed.