Mode conversion for elastic waves via anisotropic temporal interfaces

Customizing elastic wave polarization is a challenging task due to the complex interactions between waves and solids. In this work, perfect mode conversion from longitudinal to transverse waves is achieved by employing an isotropic-anisotropic-isotropic temporal interface. A general transfer matrix method is developed based on the continuity conditions at temporal interfaces, enabling the analysis of elastic wave propagation in temporally layered orthotropic structures. This method provides the calculations of transmission and reflection coefficients for both longitudinal and transverse polarization modes. Within this framework, a general route to complete elastic wave mode conversion is proposed and validated through finite-difference time-domain simulations. Furthermore, the underlying physical mechanism is elucidated through polarization trajectory analysis. This research provides a new approach for elastic wave control through time-varying materials.