12D-6 A Study on the Dispersion Behaviors of Antisymmetric Flexural Modes Propagating Along Wedges Tips with Coatings

Acoustic sensors frequently rely on the detection of small mass changes that results from binding of a coated layer coupled to the active sensor surface. Antisymmetric flexural (ASF) modes are antisymmetric type of guided waves propagating along the tip of a wedge with displacement field much larger than surface acoustic waves (SAW). Effects of binding a layer of thin film on the wedge surfaces can be interesting and show feasibility of application in acoustic sensors. This paper describes a combined experimental and numerical study on the dispersion behaviors of ASF modes propagating along wedge tips with a layer of coating on one of the wedge´s surfaces. Two kinds of matrix/coating combinations are investigated, including slow coating (copper) on fast matrix (aluminum) and fast coating on slow matrix. A laser ultrasound technique is applied for the detection and generation of ASF modes. Also a general purpose finite element program (ABAQUS) is used to model the dispersion behaviors of ASF modes. It is found out that phase velocity of an ASF mode for the coated wedge (CW) starts at the ASF mode of the same order for the matrix wedge at the low frequency regime, and gradually influenced by the coating while frequency increases. Like SAW propagating along a flat surface with coating, loaded or stiffened phenomenon are also observed for the ASF modes in coated wedges. It also found out that enhanced loaded or stiffened effects due to the wedge tip geometry are founded. The loaded or stiffened effects for the ASF mode can be observed in wavelength regimes that are more than 10 times of the film thickness. The numerical results also show good agreement with other experimental studies.