Analysis of flexural mode focusing by a semianalytical finite element method.

Focusing is one of the most promising techniques for the detection of small defects in pipe works, in which guided waves including longitudinal and flexural modes are tuned so that ultrasonic energy can be focused at a target point in a pipe, and analysis of reflected waves gives information on defects such as location and size. In this paper, the focusing technique is discussed by way of a simulation of guided wave propagation in pipe by a semianalytical finite element method (SAFE). Experiments and SAFE calculations were compared for waveforms transmitted by a single transducer and received at different circumferential positions initially, and then the focusing phenomena were experimentally observed using focusing parameters obtained by calculations. Calculation and visualization were conducted to clarify focusing phenomena in pipe in investigating the potential of the focusing technique. These results show that the time-reversal idea helps in understanding focusing and that resolution of focusing is strongly affected by incident waveforms as well as the number of channels available in an experiment.