Implementing guided wave mode control by use of a phased transducer array

A multi-channel time-delay system has been built and applied to a transduce r array for implementing guided wave mode control. The time-delay system ha s a capability of sending high energy controllable tone-burst signals from eight independent channels with arbitrary time delays from 0 to 30 mus with resolution of 0.025 mus. Software time delays are also provided for summin g up received signals of each channel. Theoretical discussions indicate the impact of the time delay capability on the bandwidth and sensitivity impro vement of a transducer array for guided wave generation. Determination of b oth physical and software time delay values is based on a knowledge of disp ersion curves and clement spacing. Based on reference signals, a non-knowle dge-based automatic time-delay searching algorithm was introduced for guide d wave mode selection. Experiments were conducted with a phased comb transd ucer array mounted on a carbon steel pipe. The experimental results show th at signal to noise ratio has been greatly improved by use of the time-delay system. Some other benefits Fig. of the phased array, including unidirecti on generation and mode control flexibility, are discussed.