Surface acoustic waves confined to a soft layer between two stiff elastic quarter-spaces

• Published in: Wave motion 2021-03, Vol.101, p.102672, Article 102672
• Main Authors: Pupyrev, P.D., Nedospasov, I.A., Sokolova, E.S., Mayer, A.P.
• Format: Article
• Language: English
• Subjects: Acoustic propagation; Acoustics; Edge waves; Finite element analysis; Finite element method; Group velocity; Guided waves; Half spaces; Laguerre functions; Mathematical analysis; Modulus of elasticity; Nondestructive testing; Perturbation theory; Polymethyl methacrylate; Polynomials; Propagation; Surface acoustic waves; Surface waves; Wave propagation
• ISSN: 0165-2125; 1878-433X
• DOI: 10.1016/j.wavemoti.2020.102672

Propagation of acoustic waves is considered in a system consisting of two stiff quarter-spaces connected by a planar soft layer. The two quarter-spaces and the layer form a half-space with a planar surface. In a numerical study, surface waves have been found and analyzed in this system with displacements that are localized not only at the surface, but also in the soft layer. In addition to the semi-analytical finite element method, an alternative approach based on an expansion of the displacement field in a double series of Laguerre functions and Legendre polynomials has been applied. It is shown that a number of branches of the mode spectrum can be interpreted and remarkably well described by perturbation theory, where the zero-order modes are the wedge waves guided at a rectangular edge of the stiff quarter-spaces or waves guided at the edge of a soft plate with rigid surfaces. For elastic moduli and densities corresponding to the material combination PMMA–silicone–PMMA, at least one of the branches in the dispersion relation of surface waves trapped in the soft layer exhibits a zero-group velocity point. Potential applications of these 1D guided surface waves in non-destructive evaluation are discussed. •Surface waves were studied localized in a soft layer between two quarter-spaces.•Their dispersion relation and displacements were computed by FEM.•At small phase speeds they mostly behave like edge modes in plates with rigid walls.•Close to the cut-off speed they have the character of two interacting wedge waves.•They can be well described by a perturbation-theoretical approach.