Capacitive air-coupled cylindrical transducers for ultrasonic imaging applications

This paper examines the development and characterization of an air-coupled ultrasonic capacitance transducer with a cylindrical geometry. Focusing is achieved using a shaped backplate and an attached thin polymer membrane. The design and construction of these transducers is described, together with the results of measurements to examine the frequency characteristics in pulse-echo mode. The sound pressure field is then examined, by scanning with a miniature detector, and compared to theoretical models. Further experiments are described to determine the lateral resolution and depth of field. Results from imaging experiments of surface features are presented, using two orthogonal devices in a pitch-catch mode