An ultrasonic transducer for a pipe includes an ultrasonic source which produces plane waves. The transducer includes a housing having a face at least a portion of which is curved through which the plane waves produced from the source disposed in the housing are emitted and directed outward towards the pipe's interior wall so a full cross-section of the pipe's interior can be measured. A flow meter for detecting fluid flow rates in a pipe. A method for detecting fluid flow rates in a pipe.