Complete mode conversion of elastic waves by utilizing hexapole resonances in a double-scatterers structure

In recent years, the emergence of elastic metamaterial has provided new methods to manipulate the polarization of elastic waves, achieving elastic mode conversions. This paper theoretically investigates a complete mode conversion effect, where longitudinal waves are completely converted into transverse waves after being reflected by one layer of metamaterial slab. The slab structure contains a pair of cylinders, and the conversion is attributed to the out-of-phase coupled hexapole resonances of the two cylinders. Unlike the monopole, dipole, and quadrupole resonances, the hexapole resonances induce trivially, nearly constantly, effective parameters. The proposed design does not follow the recent popular “reversely designing parameters” method. The conversion based on the hexapole resonances is relatively broadband and wide-angle, which is beneficial for practical applications such as sound absorption.