The lecture will present results of theoretical and experimental studies on non-contact fluids treatment by means of specially designed low-frequency (20..40 kHz) ultrasonic focusing device based on pressure amplification in acoustic cavities. At moderate powers (input electric power not exceeding 30 W) non-contact action of ultrasound enables generation of several practically useful physical and chemical effects including sonochemical reactions, bubble entrainment and excitation of regenerative gravitational-capillary waves. As it follows from FEM models, all elements of the considered acoustic system including ultrasonic transducer, air-filled cavity, fluid-filled volume and surrounding reservoir should be treated as coupled resonant elements and their natural frequencies should be synchronized in order to achieve maximum overall efficiency of the system. Nonlinear properties of the system result in several unusual and potentially useful physical effects including self-modulation of acoustic pressure and generation of frequency combs. These phenomena have deep analogy with physical effects observed in optomechanical cavities. The lecture will discuss potential practical applications of experimentally discovered effects, their existing analogies and prospects of future studies on non-contact ultrasonic treatment of fluids.

Dmitry Stepanenko is a professor of the Belarussian national technical university (BNTU) (Minsk, Republic of Belarus). He received his PhD and DSc degrees in engineering from BNTU in 2008 and 2020 respectively. His interests include biomedical engineering, applied mathematical and computer modelling, industrial and medical applications of power ultrasonics, modelling and design of power ultrasonic devices and ultrasonic motors. Current research interests include ultrasonic systems for non-contact treatment of fluids and biological tissues. Dr. Stepanenko published more than 50 scientific articles published in peer-reviewed journals in Republic of Belarus and abroad (including Ultrasonics, Applied Mathematical Modelling, Journal of Vibroengineering) and 2 monographs (including “Ultrasound in medicine” in Russian). He currently works as a professor of the department “Design and production of instruments” of BNTU reading lectures in 7 disciplines related to biomedical engineering, signal processing, physical basics of measurements and sensor technology. Dr. Stepanenko was a supervisor of 5 PhD students. He was invited as a reviewer by a number of peer-reviewed journals including Ultrasonics, Shock and Vibration, International Journal for Numerical Methods in Biomedical Engineering etc. He is a member of committee on defence of PhD and DSc dissertations in specialities “Mechanics of deformable solids” and “Biomechanics”.