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

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 OSH_n-PT, the proposed method is expected to pave the road to wide applications of high-order SH wave tomography.