Effect of positive electrode coverage ratio on SH0 mode in thickness-shear piezoelectric transducers

Abstract

Piezoelectric-based ultrasonic guided wave transducers often extend the negative electrode to the same plane as the positive electrode to facilitate circuit connections. This study examines the effect of the positive electrode coverage ratio on SH0 mode excitation in d₁₅ thickness-shear piezoelectric transducers. First, a qualitative analysis based on the direct and inverse piezoelectric effects evaluates the effect of the electrode coverage ratio on SH0, A0, and S0 modes. Subsequently, a finite element (FE) model is developed using the explicit-implicit co-simulation method to further analyze the effect of the electrode coverage ratio on mode excitation. The results indicate that increasing the electrode coverage ratio enhances the amplitudes of the SH0 and S0 modes while reducing the amplitude of the A0 mode. Partial electrode coverage introduces a small amount of the S0 mode and a significant amount of the A0 mode in the primary propagation direction of the SH0 mode. This shift in mode composition is identified as the primary factor contributing to the deterioration of the signal-to-noise ratio (SNR) of the SH0 mode. Further analysis of the frequency tuning curves shows that increasing the electrode coverage ratio enhances the SH0 mode response at the operating frequencies while reducing the amplitudes of the A0 and S0 modes in the dominant propagation direction of the SH0 mode. The A0 and S0 modes are nearly absent in this direction with 100 % electrode coverage ratio. Finally, experiments measure the SH0 frequency tuning curves and wavefields in the dominant propagation direction for the d₁₅ thickness-shear piezoelectric transducer at four different electrode coverage ratios. The agreement between the experimental results and the FE simulations confirms the accuracy of the FE model.