An ultrasonic circular array transducer for pipeline and borehole inspection

The circular array system was found to be a viable way to construct a rotating ultrasonic transducer without moving mechanical parts. Computer simulations were carried out to investigate the beam pattern related to this probe design. These indicated that subgroups should preferably consist of 8 to 16 elements. The beam pattern was found to be comparable to the beam pattern of a flat rectangular transducer when the phase shift related to probe curvature is compensated for by appropriate electronic delays on the respective elements within each subgroup. Furthermore, the viability of electronic focusing was demonstrated. A prototype probe consisting of 128 elements and operating at a frequency of 1 MHz was built. Measurements on multielement performance confirmed the results of computer simulations with regard to both beam rotation and focusing