Active bandgap tuning of compression-torsion coupling metamaterials based on mode veering effects

Mode veering, a phenomenon where the frequencies of dispersion bands converge and then diverge while exchanging band characteristics, is critical for designing dynamic systems and predicting structural behaviour. Although extensively observed in chiral metamaterial systems, the underlying mechanism governing this phenomenon remains inadequately understood, hindering the development of effective active control strategies. This study presents an actively tunable metamaterial chain consisting of compression-torsion coupling oscillators with dual independent control mechanisms: dynamically adjustable inter-oscillator coupling stiffness and modifiable rotational inertia. Through precise parameters modulation, continuous and reversible regulation of energy redistribution and polarization switching between the torsional flat band and longitudinal dispersion band is achieved, enabling on-demand induction of mode veering. Further investigation of this process reveals that this phenomenon originates from an inherent conflict between band reversal and oscillatory incompatibility—a paradox resolved through shifts in the torsional natural frequency of the oscillator. Crucially, the interplay between this frequency shift and band trajectories is identified as the fundamental mechanism governing mode veering. Moreover, this study found that the nonlinear compression–torsion coupling effects can suppress the energy localization induced by the torsional flat band. These works establish a new paradigm for active elastic wave manipulation with promising applications in adaptive vibration isolation and programmable metamaterial design.