One of the areas where the use of power ultrasound (PU) has undergone major development over the last two decades is food science and technology. Nowadays, PU is considered as one of the most promising emerging technologies in food industry together with high pressure processing, pulsed electric fields and ultraviolet radiation. This is because PU is considered as an environmentally friendly energy capable of reducing energy consumption in processes such as dehydration and extraction. To achieve this it is necessary to design, develop and validate efficient power ultrasonic systems, capable of working stably in continuous power conditions.
This paper presents the study of the nonlinear behaviour of a series of prototypes of power piezoelectric transducers developed to work at frequencies between 20 and 25 kHz. These prototypes have been designed and built with large radiating surfaces for application in food processing. We have characterized and identified nonlinear mechanisms that affect transducer behaviour, such as harmonic generation, combination of resonances, or modal interactions, and response saturation. Specifically, we have analyzed energy transfers between modes of the tuned systems as responsible for problems such as heating, noise and instabilities in the transducers.
