An omnidirectional piezoelectric transducer for selective excitation and reception of high-order shear horizontal waves

Abstract

Guided wave tomography, as an advanced structural health monitoring (SHM) method, has offered a feasible solution to wall thickness quantification which is essential in petrochemical industries. However, previously used low-frequency Lamb waves (A0 and S0) limit the resolution of tomography. Recently, the first-order shear horizontal guided wave (SH1) was found very promising in tomography for its capability in resolution improvement. However, the SHM-required omnidirectional piezoelectric transducers for selectively generating and receiving the SH1 wave, namely OSH1-PT, are not available yet. In this work, a general method was developed to design an OSH1-PT based on the thickness-poled PZT half-ring configuration. Firstly, the excitation function of the OSH1-PT was explicitly derived and validated through finite element simulations. Secondly, a design formula was obtained and used to determine the size of the OSH1-PT. Then, the designed OSH1-PT was fabricated and tested by using a 2D laser Doppler vibrometer. Significant mode selectivity was observed in all directions (0 ∼ 90°) with the excited SH1 to SH0 ratio higher than 15 dB. Pitch-catch tests were conducted from 400 ∼ 520 kHz and the received SH1 to SH0 ratio was found higher than 19 dB at all frequencies and reached its maxima of 30.7 dB at 490 kHz, which is very close to the designed working frequency of 500 kHz. Finally, an OSH2-PT was theoretically designed and validated by FE simulations. Due to its simplicity and effectiveness in designing the OSHn-PT, the proposed method is expected to pave the road to wide applications of high-order SH wave tomography.