A comparison of laser ultrasound measurements and finite-element simulations for the dispersion behavior of antisymmetric flexural modes propagating along wedge tips with coatings

Antisymmetric flexural (ASF) modes are antisymmetric types of guided waves propagating along the tip of wedge-shaped waveguides. Acoustic sensors frequently rely on the detection of small mass changes that result from binding a coated layer coupled to the active sensor surface. While a layer is coated on one of the wedge's surfaces, another type of sensor can be potentially developed based on detecting the change of ASF velocity. This paper describes a study on the effects of ASF dispersion behavior for a wedge with a layer of coating using a combined numerical and experimental investigation. In this study, the frequency range is from 0.5 MHz to 10 MHz, and the effective wave propagation length along the wedge tip ranges from 3 mm to 13 mm. Brass wedge tips coated with aluminum layer are studied for the case of slow matrix with fast coating, while aluminum wedge tips with copper coatings are studied for the case of fast matrix/slow coating combination. Like surface acoustic waves propagating along a flat surface with a layer of coating, loaded and stiffened phenomena are observed for the ASF modes traveling along coated wedges. Moreover, the wedge tip geometry is found to have an effect in enhancing the loaded and stiffened phenomena. The numerical results show good agreement with experimental results.