Lightweight bandgap tunable low-frequency local resonance structure

Local resonance (LR) structure can effectively suppress the low-frequency noise and vibration, but it is still a great challenge to design a kind of lightweight small-size structure with the low-frequency bandgap. This paper proposes a lightweight small-size LR structure with adjustable stiffness ratio, and there are two equivalent negative stiffness regions formed in the LR structure, which are not only greatly enlarged, but also coupled at last only by adjusting the stiffness ratio of the system (changing radius), and finally the negative stiffness region is successfully enlarged more than 2 times in this way. Based on the theory of regulating negative stiffness region, the mechanism of regulating the low-frequency bandgap within the lightweight small-size LR structure is further revealed. It is found that there are two low-frequency bandgaps in the LR structure, and its lower bound of the first bandgap is decreased from 54 Hz to 34 Hz only through adjusting the stiffness ratio (changing radius), and a low-frequency bandgap with 34–248 Hz is obtained by FEM at last. Most importantly, the mechanism of regulating the low-frequency bandgap only by adjusting the stiffness ratio can provide an important idea for designing the lightweight small-size LR structure since it can break out the limitation of the heavy mass and big structures in traditional methods, so it has great practical value for vibration isolation and noise reduction in engineering.