Engineering perspectives on spin-induced wave steering in elastic media

Spin phenomena are well known in quantum mechanics, but recent works have shown that spin can also be found in continuum mechanics. Spin angular momentum (SAM) can be a mechanism for steering elastic waves through phase-shifted external excitations. While spin-related phenomena have been mainly addressed in physics-oriented studies, an engineering perspective supported by analytical tools remains lacking. Previous studies have demonstrated that combined shear and bending excitation with suitable magnitudes and phases can induce one-sided propagation. In this work, we interpret the wave steering phenomenon in beams from an engineering perspective using a frequency-domain wave propagation solution. Furthermore, we derive analytical expressions for the magnitude and phase relation of the shear force and bending moment that cause SAM in Euler–Bernoulli beams. These analytical expressions are dependent on the excitation frequency and wavenumber. It is shown that the required phase angle for optimal unidirectional propagation is 90 degrees. Spectral and time-domain numerical simulations and experiments confirm that switching the sign of the SAM reverses the propagation direction, and that the ratio of shear to bending moment for optimal wave steering varies with frequency. These results establish a consistent engineering perspective on spin-driven wave control and pave the way for practical applications.