A new inerter-based acoustic metamaterial MRE isolator with low-frequency bandgap

Acoustic metamaterials are capable of generating bandgaps at specific frequency ranges, which makes them have good applications in the field of vibration isolation. The bandgaps can be further broadened with active control, nonlinear components and graded structures, such as: controllable stiffness by magnetorheological elastomer (MRE) and graded stiffness. However, the current approaches to reducing the bandgaps have limitations. Both the reduction in structural stiffness and the increase in mass will reduce the overall stability of the acoustic metamaterial. In this research, a novel inerter-based acoustic metamaterial MRE isolator (IAM-MREI) was designed and prototyped to lower the bandgap. Inerters can generate a large equivalent mass with very light weight. Moreover, it is discovered that elements containing quadratic frequency terms are added to the dispersion matrix of the IAM-MREI due to the frequency-independent force applied to the resonators, which is generated by the inerters. By this way, the bandgap calculated by this dispersion matrix is greatly lowered and broadened, which cannot be achieved only with extra equivalent mass. The effects of the inerters on the overall performance of the IAM-MREI was thoroughly investigated and validated both theoretically and experimentally. The evaluation experiments confirmed that the IAM-MREI possesses a low-frequency bandgap and can provide great vibration isolation performance.