New Ultrasonic Torsional Waves for Sensing Applications

In this paper (inspired by a newly developed class of materials, i.e., elastic metamaterials) we will show that torsional surface elastic waves can propagate on the surface of a metamaterial elastic rod embedded in a conventional elastic space. In this work, we assume that the elastic compliance s
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(ω) of a metamaterial cylindrical rod varies with frequency ω according to Drude model. The proposed torsional ultrasonic surface waves can be considered as an elastic analogue of Surface Plasmon Polariton (SPP) electromagnetic waves propagating on the surface of a metallic rod embedded in dielectric space. An analytical expression for the dispersion equation the new torsional elastic surface wave was developed. The newly discovered torsional elastic surface wave inherits many of fascinating properties of electromagnetic counterpart such as: strong subwavelength concentration of the wave field in the vicinity of the cylindrical surface, low phase and group velocity etc. Therefore, the proposed new torsional ultrasonic surface waves can be used in: a) near-field subwavelength acoustic imaging (superresolution), b) amplification of the evanescent waves c) acoustic wave trapping (zero group and phase velocity)