Excitation of unidirectional SH wave within a frequency range of 50 kHz by piezoelectric transducers without frequency-dependent time delay

Abstract

Unidirectional generation of a pure guided wave mode is of practical importance in structural health monitoring (SHM). Currently, unidirectional propagation guided waves can only be generated by using transducer array in a phased array form, which is limited within a very narrow frequency range. If a variable-wavelength unidirectional wave source is required, both the transducer spacing and time delay usually need to be changed with frequency, which is against the permanent arrangement demand of transducers in SHM. In this work, inspired by the unique features of bidirectional SH0 wave (the fundamental shear horizontal mode) piezoelectric face-shear and thickness-shear transducers, a new method was proposed for generating unidirectional SH0 wave. Two types of transducer configurations (double-side and single-side) were designed to unidirectionally generate SH0 wave without frequency-dependent time delay. Both finite element simulations and experiments were conducted to validate the unidirectional features of the proposed double-side and single-side transducer configurations. Results shows that the double-side transducer configuration is capable of generating unidirectional propagation SH0 wave at the frequency range from 100 kHz to 150 kHz, while the corresponding working frequency range for the single-side one is from 100 kHz to 140 kHz. The proposed method provides a cheap way for generation of the unidirectional SH0 wave within a certain frequency range without adjusting the relative transducer spacing and the time delay with frequency, so it will have great potential applications in SHM.