Quasi-zero stiffness resonators: Breaking low-frequency sound absorption limits.

Traditional acoustic resonators often face a fundamental trade-off between achieving low-frequency resonance and maintaining a broad sound absorption bandwidth, particularly without increasing the physical cavity volume. This limitation poses significant challenges for compact and efficient low-frequency noise control. To address this issue, the present study introduces a novel sound absorption mechanism based on a two-hollow magnet quasi-zero stiffness (QZS) structure. By introducing magnetic negative stiffness, the system's effective stiffness is significantly reduced, enabling wider bandwidth at lower frequencies, thus surpassing the sound absorption performance limits of conventional Helmholtz resonators. The research integrates theoretical modeling, finite element simulation, and experimental validation using an impedance tube to thoroughly investigate the underlying absorption mechanisms. The QZS resonator allows the resonator's effective cavity height Heff to exceed the upper limit of optimal performance seen in traditional resonators, achieving up to 1.6 times the physical length, without expanding the structural volume. The results of this study offer valuable theoretical and practical insights for designing compact, high-performance QZS-based sound absorbers, with potential applications in areas like aero-engine acoustic liners and underwater noise reduction systems.