Acoustic Blackbody Absorption: Transcending Causality Limits through Instability-Induced Softness

By coupling unstable components, we demonstrate a novel approach that reduces static modulus to zero, eliminating causality-imposed absorption limitations in acoustics. Our heuristic model simulations achieve ultra-broadband absorption over 99% for wavelengths greater than 132 times the absorber thickness. Theoretical analysis further proves this strategy can approach ideal blackbody behavior with infinitesimal thickness. These findings suggest fundamental physical laws no longer prevent true blackbody absorption realization; the only remaining obstacle is the material limitations.