Eigenmode-Guided Amplification via Spatiotemporal Active Acoustic Metamaterials

Abstract: We present a spatiotemporal gain-loss framework for selective acoustic mode amplification illustrated using coupled Helmholtz resonators. In our scheme, the gain or loss in each resonator is determined by the amplitude in adjacent cavities, forming a non-Hermitian yet energy-conserving system. Our scheme enables the system to collapse toward the eigenstate of an effective linear Hamiltonian with the eigenvalue of largest imaginary part, serving as a fixed-point attractor. In dimer systems, we identify exceptional points that separate oscillatory and convergent regimes, allowing controllable switching between mode collapsing and Rabi-type oscillation. By modulating the gain-loss profile over time, we achieve programmable transitions between eigenmodes, with strategically introduced symmetry-breaking perturbations accelerating convergence. Full-wave simulations validate our approach and highlight its potential for acoustic switching, signal processing, and analog computation. Our results establish a new paradigm for sustainable wave control by bridging non-Hermitian physics and time-varying physics in resonant metamaterials.