Fig. 1: Schematics of a unidirectional focusing lens (UFL).
From: Unidirectional focusing for broadband Lamb guided wave based on mode conversion
a Forward incident S0-mode Lamb waves are converted into A0-mode waves and focused on the right side of the lens. Inset: 3D view of a unidirectionally-transmitted elastic meta-atom (UTEM) composed of a mode converter and a mode selector, respectively. The geometric parameters a1 (a2), w1 (w2), and h1 (h2) correspond to the periodicity, width, and depth of the asymmetric groove (symmetric groove), while H represents the plate thickness of the UTEM. b Backward incident S0-mode Lamb waves are largely unable to transmit to the left side.
