Advanced negative stiffness absorber for low-frequency noise insulation of panels

The sound transmission loss of conventional means of passive acoustic treatment in the low-frequency range is governed by two physical mechanisms: the inertia, as stated by the mass density law, and the local resonances of the structure. Since usual partitions are flexible and lightweight, their acoustic performance is poor, especially below 300 Hz. Although conventional acoustic meta-materials can offer excellent acoustic properties, they also perform poorly in this range. Therefore, novel meta-structures are required to overcome these limitations. This proposed novel absorber optimally combines the concepts of KDamper (KD) and inertial amplification mechanisms (IAMs). The novelty of the KD-IAM absorber lies in the generation of equally deep but significantly wider attenuation bands surpassing the mass density law while requiring only a small fraction of additional mass. The absorber is implemented and demonstrated as an elastic mount for retrofitting existing panels, essentially manipulating the resonant response of the structure by controlling the panel’s boundary conditions. It is also shown that increasing the panel’s rigidity and, consequently, its fundamental eigenfrequency utilizing stiffeners results in further improvements in the bandwidth and depth of noise attenuation. A wide and deep attenuation band is demonstrated in the resonance region below 120 Hz, up to 13 dB above the reference level. An indicative design and implementation for a case study are presented. It is further demonstrated that the same concept can be utilized for the formation of meta-structures by periodic repetition of KD-IAM unit cells, leading to significant additional attenuation of the lowest vibration modes.