Visualization of surface wave generation and tail wave formation in acoustic Wood anomalies

Acoustic Wood anomalies are phenomena characterized by sharp amplitude peaks and dips at specific frequencies in the spectra of the waves reflected from periodic surfaces. Theoretical studies proposed the double mode conversion theory, suggesting bulk waves convert to surface waves at periodic rough surfaces and reconvert to bulk waves, which then interfere with specular reflections (main waves) as delayed reflected components (tail waves). However, experimental validation remains incomplete. This study clarifies the relationship between surface waves and tail waves through visualization of wave propagation processes and identifies causes of changes in tail wave formation due to periodic surface geometry. Pulse-echo experiments were conducted using carbon steel specimens with rectangular periodic profiles of varying pitch and depth. Finite-difference time-domain simulations visualized ultrasonic wave propagation under identical experimental conditions. Simulation data showed good agreement with experimental data, validating the simulation approach. Amplitude spectral analysis revealed that the surface waves and tail waves had common frequency characteristics, confirming the double mode conversion assumption. The simulations successfully visualized surface waves generation, propagation, and reconversion to bulk waves, demonstrating tail wave formation from surface waves in detail.