Slit-Induced Reflection Mode Conversion Between Fundamental Lamb Modes in Elastic Plates with Low-Frequency and Broadband Response

We present a compact slit-based interface that enables reflection mode conversion in an elastic plate by transforming an incident lowest-order antisymmetric Lamb mode into a reflected lowest-order symmetric Lamb mode. The interface is realized by introducing inclined vacuum slits along the lateral sides of the plate. This geometry intentionally breaks symmetry and produces a strongly localized, vortex-like deformation near the slit tips, which provides an efficient coupling pathway from the antisymmetric incident response to a symmetric reflected component. The conversion is quantified in a consistent, field-based manner by extracting the reflected antisymmetric level from the standing-wave envelope on a probe line placed sufficiently far from the slits, and then inferring the converted symmetric energy under a lossless assumption with only two reflected propagating channels. The proposed design delivers strong low-frequency conversion and sustains broadband half-power operation, while parametric studies confirm that the performance is tunable and robust over a wide range of slit angles and widths.