Excitation of single mode shear horizontal (0,1) guided wave in a narrow plate waveguide using d24 piezoelectric wafers

Abstract

Piezoelectric ultrasonic transducers are widely used for exciting shear-horizontal (SH) guided waves in narrow plate waveguides (NPW) for high-temperature wall thickness monitoring. The SH(0,1) mode in NPW exhibits nearly nondispersive propagation, making it ideal for monitoring. However, achieving high modal purity and ensuring optimal size matching between the transducer and NPW remain challenging. Existing studies approximate NPW behavior using dispersion curves of plates with infinite width (PIW), leading to inaccuracies in transducer excitation parameter selection. To address this issue, this study develops a dispersion-based excitation parameter selection method for single-mode SH(0,1) wave generation using face-shear (d₂₄) PZT wafers. First, dispersion analysis of SH waves in NPW is conducted using the Floquet periodic boundary conditions method, comparing NPW and PIW dispersion curves to evaluate their differences. Results indicate that in NPW, the cutoff frequency of the SH wave decreases with increasing plate width but remains independent of plate thickness—this contrasts with PIW, where the cutoff frequency varies with plate thickness. Next, based on the dispersion characteristics of SH waves in NPW and SH(0,1) mode shapes, a transducer design optimization approach is proposed. The optimal width and excitation frequency of a symmetrically double-sided d₂₄ PZT wafer transducer are determined. Finite Element simulations and experimental validation are employed to assess the impact of wafer length on excitation performance. Results show that wafers of 6–36 mm length can excite the SH(0,1) mode in a 30 mm wide NPW, with excitation purity and signal-to-noise ratio maximized when the wafer length matches the SH(0,1) mode shape (18–24 mm). A transducer-to-NPW size ratio of 0.6–0.8 enables nearly nondispersive, single-mode SH(0,1) wave excitation. This study provides theoretical guidance for transducer design and has potential implications for broad engineering applications.