Development of industrial models of high-power stepped-plate sonic and ultrasonic transducers for use in fluids

The extension of the high-power applications of sonic and ultrasonic energy in industrial processing requires the development of efficient and powerful transducers. Years ago some of the authors of the present paper proposed a new concept of ultrasonic transducer for use in fluids (more specifically in gases) based on a stepped-plate radiator. This concept was successfully applied to the design and development of a series of circular plate transducers of small and medium power capacities (lower than 1 kW) and radiating surfaces smaller than 0.5 m/sup 2/. Nevertheless, the scale of a great part of industrial applications requires higher powers and larger radiating surfaces. Looking for such applications (i.e. fume precipitation, defoaming, drying and dewatering, etc.) we have designed and developed an industrial model of transducer with a rectangular plate radiator of double-stepped profile. The design of the new model was made with the help of the finite element method (FEM) and the acoustic field was computed by the boundary element method (BEM). In such a way the distribution of displacements and stresses as well as the corresponding radiated field could be known previously to the real construction of the unit. The industrial prototype of macrosonic transducer was designed with a radiating plate of 1.8/spl times/0.9 m/sup 2/ for an estimated power capacity of about 3500 W. Previously a first scale model was developed and tested with a radiating plate of 0.6/spl times/0.3 m/sup 2/ for a frequency of 20 kHz and a power capacity of about 400 W. The industrial prototype was constructed by scaling up the first model in a factor of three. Typical problems faced in the development of the industrial transducers were, the adequate selection and characterisation of the plate material, the excitation of the useful vibration mode without interference of the closer modes of the plate, the decrease of the maximum stress by improving the uniformity of the vibration amplitude, etc. The industrial prototype, constructed initially with an aluminium plate and eventually with a titanium alloy plate, presents an electroacoustic efficiency of 67% and it has been operated in air with an applied power of two kilowatts in continuous wave.