Selective Lamb mode excitation by piezoelectric coaxial ring actuators

This paper describes an omnidirectional multi-element transducer for selective Lamb wave mode excitation. It is composed of several coaxial ring-shaped piezoelectric elements actuated by n-cycled sinusoidal tone bursts. Mode selection is achieved through a special choice of the amplitudes and time delays of the input driving signals. The method for the determination of these parameters is based on strict analytical consideration. In the limiting case of an infinite number of cycles and with a sufficient number of actuators one can generate a single required mode and completely eliminate all undesired ones. It is shown that within the range of applicability of a simplified model for the piezoelectric elements, i.e. when the actuating contact traction is replaced by a pair of concentrated opposite ring tangential forces, no time delays are needed, and the mode selection is achieved through an appropriate choice of the driving input-signal amplitudes applied in phase or out of phase to different transducer elements.