In this work, total conversions between longitudinal and transverse modes are achieved within an elastic metamaterial plate with thickness two orders smaller than the wavelength. The ultrathin metamaterial plate consists of an array of anisotropic dipolar resonators obliquely oriented, which can transfer the longitudinal movement into the transverse one, or vice versa, accounting for this effect. A mass-spring model is developed to depict analytically the mode conversion with a quantitative agreement with the simulation. The conversion rate of the metamaterial plate remains above 95% in varying solids, showing good adaptability in practical applications.

In this work, we study the conversions between longitudinal and transverse modes by one layer of oblique anisotropic dipolar resonators, whose size can be orders smaller than the wavelength. The mode conversions are found for both transmitted and reflected waves by such small resonators with a normal incidence. A mass-spring model is proposed to depict analytically the mode conversion, giving simplified analytical expressions for the conversion rates. The reflected conversion will gradually increase to the maximum while the solid material behind resonators becomes soft, or vice versa. It may provide theoretical guidance for practical application.

In this work, we propose a design of a double-scatterer structure to achieve complete conversion for elastic bulk waves. Every unit of the elastic metamaterial slab contains a pair of scatterers with a relatively oblique direction. When the slab attaches on a semi-infinite solid background, it can completely convert the normal incident longitudinal wave into the reflected shear wave, or vice versa. The conversion can be attributed to the in-phase coupling of the double scatterers’ quadrupolar resonances. The coupled two quadrupoles could interact with the background and bring oblique displacements. Consequently, the oblique displacements generate horizontal displacements for reflected waves.