Ultra-low-frequency reflection mode conversion from compressional to shear waves enabled by periodic inclined slits

TL;DR

This paper demonstrates a novel low-frequency elastic wave conversion technique using periodically inclined slits on a surface, enabling efficient transformation from compressional to shear waves through geometry-induced coupling.

Contribution

It introduces a new method for low-frequency wave mode conversion using inclined slits, with detailed analysis of the boundary coupling effects in a 2D elastic model.

Findings

Achieves near-complete conversion efficiency at very low frequencies.

Shows inclined geometry induces strong boundary coupling enabling wave mode conversion.

Provides a simple, geometry-controlled mechanism for elastic-wave polarization control.

Abstract

A periodically patterned free surface with inclined slits can convert an incident compressional wave into a reflected shear wave with nearly complete efficiency at very low frequency. The system is described by two-dimensional in-plane linear elasticity, and the slits are treated as voids. The conversion is quantified by the ratio between the reflected shear-wave energy and the incident compressional-wave energy, obtained from mode decomposition and energy-flux evaluation below the surface. The results indicate that the inclined geometry introduces strong coupling between normal and tangential motions at the boundary, enabling suppression of the ordinary compressional reflection while redirecting the reflected energy into the shear channel. This simple, geometry-controlled mechanism provides a compact route for low-frequency elastic-wave polarization control.