The Modal and Harmonic Analysis of a Cylindrical Horn Designed for an Airborne Ultrasonic Dryer

The extensive radiating surface of horn is an imperative part for amplifying the ultrasonic airborne waves generated for drying of foodstuffs. However, the radiation of high-intensity waves may lead to frequency shift, interaction of modes and reduced efficiency of ultrasonic system. Furthermore, the excitations may also be harmful to the transducer, horn and the joints. In this study, a finite element model is developed for the dynamic analysis of a cylindrical horn. In the modal analysis, the natural frequency of horn is found to be 19,498 Hz which is very close to the working frequency of the ultrasonic generator i.e., 20 kHz. At this frequency, the amplitude of non-beneficial longitudinal mode is negligible compared with that in main radial mode shape and there is no risk for interaction of modes. According to the harmonic analysis, the generated von Mises stresses in the horn are much lower than the endurance limit of constructing material and the horn can safely radiates the waves. The experimental data measured by a laser vibrometer are also used for validating the results of numerical simulation.