Vibration isolation using inerter-induced negative effective mass: An experimental and theoretical study

In vibration control, tuning a structure’s natural frequency to avoid resonance is a widely adopted strategy for passive isolation. Inerters are typically employed to increase a system’s effective mass via large inertance. This study investigates whether they can also be configured to reduce effective mass. To explore this, we develop and experimentally validate an Inerter-based Negative Effective Mass (INEM) system that enables both mass amplification and reduction. The INEM connects an inerter to a host mass-spring-damper system via a secondary spring, generating an inertial force that interacts with the host’s dynamics. Above a critical frequency, this interaction produces an inertial force opposing the host’s acceleration, reducing effective mass and shifting the natural frequency. Near the resonance of the internal resonator, the force becomes strongly out of phase, leading to negative effective mass behaviour. This induces anti-resonance and stop bands that suppress wave transmission and improve isolation by cyclically exchanging energy between the excitation source and the inerter. While the configuration of the INEM bears similarity to the Tuned Mass Dampers Inerter and Tuned Inerter Dampers, the INEM offers a new insight to inerter-based vibration isolation through the lens of negative effective mass. Theoretical modelling and experimental results confirmed that the INEM introduces a low-frequency negative effective mass region (minimum –17 kg), reducing transmissibility by up to –6.3 dB compared to the baseline system. Through the negative effective mass framework, we also reveal the coupling stiffness between the inerter, and the rest of the inerter-based system play a role in determining resonance behaviour.