Optimization of transducer arrays parameters for efficient excitation of Lamb waves

Abstract

The guided waves are used for inspection of large industrial constructions. The Lamb waves are a sort of the guided waves propagating in planar structures. They can be used for inspection of such objects like metal plates and sheet piles. The regularities of the excitation of Lamb waves by single longitudinal and shear type transducers has bean determined using numerical modelling. The directivity patterns of the transducers arrays having different configurations have been investigated using the results of the numerical modelling. It was found out that the main problem is not the generation of guided waves, but generation of the desired mode of a guided wave. In the case of generation of various modes under the different angles to the main wavefront direction, it is complicate to interpret the results because the waveforms of the received signal become very complicated. The obtained results revealed several configurations of the transducer arrays which enable generation only the desired mode of the Lamb wave with a relatively low level of the parasitic, e.g., undesired waves. It was also demonstrated and explained the difference between application of the longitudinal and the shear type of the transducers in ultrasonic arrays. It was pointed out the advantage of the delay time technique of excitation of transducer arrays comparing to the simultaneous excitation of all elements of the array.