Abstract: Aiming at wide range nondestructive testing of plate structure, the technique of Lamb wave transducer array based on software virtual focusing is developed, i.e. based on the principle of equiphase superposition in the phased array, through the software processing of the data received by the array, the directional focusing of beam of array is implemented without needing for hardware system of phase control. By using the simulation data, the influences of diameter of array, number of array elements and number of beams on the circumferential resolution and side lobe noise of virtual focusing image are studied. It is found that the spacing of array elements should be smaller than half-wavelength of Lamb waves in order to avoid the obvious side lobe noise. Lamb wave experiments are conducted for detecting the plate structure by using array of electromagnetic acoustic transducer (EMAT). The results show that by selecting appropriate diameter of array, number of array elements and number of beams, and through virtual focusing processing of the signals detected by the transducer array, defect detection and identification of structural features of plate in any direction (such as boundary) can be realized.

Key words: Array, Beam directional focusing, Electromagnetic acoustic transducer, Lamb wave, Virtual focused method