Airborne power ultrasonic transducers with stepped circular radiator for lyophilization at atmospheric pressure

The application of airborne power ultrasounds to enhance freeze drying processes has become a promising, green and efficient technology. It has been proved that this technology accelerates drying kinetics obtaining a good quality final product. The effectiveness of this process comes from the generation of a high-intensity ultrasonic field by an airborne power ultrasonic transducer (APUT) with an extensive radiator. A stepped circular plate, vibrating flexurally with seven nodal circles, has been used for this purpose. Its use allows a good impedance matching with the gas media because of the high surface of the radiator; and a coherent ultrasonic field due to the steps applied in the surface of the radiator and the high vibration amplitude of this surface.