Nonlinear interactions in high-power ultrasonic processing systems

J.A. Gallego-Juárez, E. Riera, V. M. Acosta-Aparicio
Instituto de Acústica, CSIC, Serrano 144, 28006 Madrid, Spain.


Abstract

The use of high-intensity ultrasonic waves in industrial processing is a growing field with a great potential. In high-power ultrasonic processing a certain amount of mechanical energy is introduced into the processed medium to produce permanent changes in it. High-power ultrasound offers significant advantages for specific processes where a non-contaminating, non-ionizing and clean energy is required.

High-power ultrasonic processing is based on the exploitation of nonlinear phenomena linked to the large amplitude ultrasonic waves and includes a wide range of processes such as cleaning, drying, material processing, defoaming, extraction, etc. The introduction and escalation of such processes at industrial level requires the development of specific devices for the right generation of the high-intensities needed to activate the processing mechanisms.

Plate transducers, piezoelectrically driven, for applications in fluids and multiphase media represent a new ultrasonic technology which implements high-power capacity, efficiency and energy concentration. Such devices are multimode systems which work in one single selected mode at high frequency.

However, nonlinearity gives rise to a series of phenomena which are not present under linear excitation. In particular, the appearance of subharmonic, superharmonic and combination resonances as well as the interaction among different modes represent important limitations for the use of high-power ultrasonic transducers. Energy is exchanged among the different modes and the efficiency is drastically reduced. Additionally, the transducer modes may interact with the natural modes of the processing reactor causing lack of control of the process.

This paper deals with the experimental evidence of the production of undesired vibration modes and the interaction among them in high-power ultrasonic processing as well as on the development of some practical design problems to control or to palliate such important practical problem.



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