Titanium ultrasonic reactor tuned to 500 kHz

This study describes the design considerations, principles, and performance of a water-filled ultrasonic reactor formed by a 125 mm size titanium cylinder covered with 67 piezoelectric transducers, tuned as a system for peak emissions at 500 kHz. The total acoustic power measured by a radiation force balance is 107 W. The sound intensity is amplified by the cavity and focusing attributes of the cylindrical wall. The reactor can generate ZnO nanoparticles from ZnAc2 solution, and the nanoparticle are found fixated to an epoxy substrate as observed under a scanning transmission electron microscope. These indications are similar to a sonochemical reaction reported at 20 kHz, which validates that inertial cavitation has been reached. The titanium wall has a transmission efficiency of 51% compared to a well-matched POCO graphite-resin layer. The efficiency exceeds the value of 17% expected from a naïve calculation based on the impedance-translation theorem. The problem of optimal emission from a piezoelectric source is more complex than a simple reduction of reflections at the transducer boundary. COMSOL simulations show that the condition for optimal transmission requires consideration of elasticity and piezoelectric charge matrices instead of acoustic impedance. Approximated analytical calculation is suggested as a preliminary guidance for design of an optimal matching layer.