Selective excitation of high-order shear horizontal wave (SH1) by using a piezoelectric interdigital transducer

Abstract Shear horizontal (SH) waves have received more and more attention in structural health monitoring (SHM) and nondestructive testing (NDT) since the fundamental mode (SH0) is non-dispersive and only has one displacement component, which is very convenient for signal identification and simulation. In recent years, great progress had been made in exciting single-mode SH0 wave for SHM. However, it is still difficult to excite high-order SH wave modes at present. In this work, a piezoelectric interdigital transducer, named SH-IDT, was proposed for selective excitation of the SH wave. By simplifying the bonded SH-IDT to distributed shearing line forces, an explicit formula for the far-field wave displacement was derived and validated through finite element simulations. Then, two SH1-IDTs working at 1 MHz on a 3 mm-thick plate and 3 MHz on a 1 mm-thick plate were designed and fabricated for exciting the SH1 mode and suppressing other wave modes. Their performances were examined by using a homemade 2D laser Doppler vibrometer. Nearly perfect wave mode selection and high energy concentration were observed. The displacement amplitude ratios between all the unwanted waves and the SH1 wave are smaller than 1/10 and this value turned to be as lower as 1/50 when using another SH1-IDT as the receiver. The half radiation angle of the SH1-IDT was only about 10°. All the experimental results are in good agreement with the simulation results, which validated the design of the SH1-IDT. The high selective capabilities of the designed SH-IDT make it very promising for tomography in SHM and it is expected to be widely used in near future.