Investigating the Transient Sonochemical Efficiency of a Magnetostrictive Transducer under Resonant Conditions

Using ultrasound to increase the effectiveness of chemical disinfectants has become increasingly popular in water treatment systems. Irradiating an aqueous solution with intense ultrasound results in cavitation where the growth and collapse of micro-bubbles in the solution cause localised regions of extreme temperatures and pressures. Such conditions are sufficient to cause the dissociation of water and the production of free hydroxyl radicals which are highly reactive. Ultrasonic treatment is an energy intensive process and requires a control system to maintain optimal operation of the ultrasonic transducer. A magnetostrictive ultrasonic transducer was driven by a square voltage wave with a Class-D amplifier. Circuits were developed to produce feedback signals representative of the shape and amplitude of the current waveform. The shape of the current waveform was characterised by the amplitude of the 3rd harmonic obtained by an active band-pass filter. The current waveform amplitude feedback signal was found to better represent the resonant behaviour of the ultrasonic transducer and exhibited both resonant and anti-resonant characteristics. Experimental sonochemical results using potassium iodide dosimetry showed that operating the transducer at the anti-resonant frequency resulted in greater tri-iodide production, greater tri-iodide production rate, and higher sonochemical efficiency compared to the resonant frequency