Klein tunneling for Lamb waves in elastic phononic crystal plates

Klein tunneling is an intriguing phenomenon in quantum mechanics, which refers to the unity transmission of particles through a higher energy barrier without hindrance in the case of normal incidence. The introduction of phononic crystals enables the direct observation of this phenomenon from a different point, giving rise to a broader application prospect. In this paper, we aim at realizing the Klein tunneling for elastic plate waves. To this end, we combine two kinds of Y-shaped phononic crystals with different Dirac point energies to structure a sandwich-like plate, which supports the propagation of Lamb waves while artificially introducing a potential barrier. Under such a configuration, perfect wave transmission regardless of the barrier in a wide frequency range can be realized, which also enables the numerical prediction and experimental observation of the Klein tunneling phenomenon in Lamb waves. The results of this work provide a direction and reference for the design and applications of phononic crystal devices, such as the chip-scale elastic waveguides.