Advances in wide bandwidth air-coupled capacitance transducers

Investigations into the field characteristics of an air-coupled ultrasonic capacitance transducer have been performed for a range of transducer configurations. The pressure field of a wide bandwidth silicon backplate capacitance transducer has been scanned in air, and compared to theory based on a plane piston approach. New devices have been fabricated, using laser-machined backplates and an electret film, and are described. The devices have also been used in an air-coupled tomographic imaging experiment.