The impact of micromachined ultrasonic radiators on the efficiency of transducers in air

Abstract

The use of micromachined thin-film ultrasonic radiators to improve the efficiency of conventional in-air acoustic transducers is investigated. We conduct a theoretical investigation of the parameters that determine the efficiency of thin-film transducers, using a lumped parameter model, and show that the efficiency can be improved by choosing a radiating plate thickness that can be realized by micromachining. We also identified the problems that should be overcome to design and fabricate a micromachined ultrasonic transducer with the theoretically predicted efficiency. Based on the lumped parameter model, we showed that the problems can be resolved via an appropriate design scheme. A piezoelectric micromachined ultrasonic transducer is designed and fabricated to demonstrate the impact of the proposed design method. Test results for the fabricated radiator indicated that it provided an electroacoustic efficiency of 58.4%, up to 300% greater than either the unit previously fabricated by the authors or conventional unimorph ultrasonic transducers. An array of the proposed transducers was also designed, fabricated, and tested as a source transducer for a parametric array, since transducer efficiency is important for practical applications of a parametric array. The test results for the proposed transducer demonstrate its potential for improving the practicality of parametric array sources, such as parametric loudspeakers and directional ultrasonic ranging sensors.