The recent introduction of a new generation of airborne ultrasonic piezoelectric transducers with extensive radiators opened up new possibilities in food industry, environment and manufacturing. Relevant features of these systems, besides their green and sustainable character, are the capacity to act synergistically with other forms of energy in order to promote, accelerate or improve existing processes as well as their ability to produce a variety of effects in different media. Among the processes which benefit from ultrasound we mention extraction of substances with supercritical fluids, drying and dehydration of foodstuff at moderate and low temperatures, agglomeration of fine aerosol particles, defoaming, and atomization. Nevertheless, to allow an effective scale up of this technology there are crucial problems to overcome such as controlling the nonlinear behaviour of tuned ultrasonic systems exhibited at high power.
In the present paper, nonlinear effects such as resonant frequency shifts, hysteresis phenomena, amplitude saturations, modal interactions are experimentally investigated in the tuned responses of several devices. To mitigate the nonlinear behaviour of such airborne transducers, for practical purposes, different strategies have been developed and applied. The experimental results obtained by applying these strategies will be presented and discussed. The improvement in the dynamic response of such transducers will be shown.
