In this paper, a novel electromagnetic negative-stiffness spring (ENSS) is constructed by coaxial permanent annular magnets and coils with rectangular cross section. The stiffness of the ENSS is negative when the coils carry exciting current. In the stiffness characterization study, the analytical model of the ENSS based on filament method is established and validated experimentally. With the stiffness model, the factors affecting the electromagnetic force and stiffness characteristics are investigated in a quantitative way. The effectiveness of a vibration isolator based on the ENSS is tested on a prototype isolator. The relationships between the transmissibility and the exciting frequency are measured under diverse amount of exciting currents. The experiment results demonstrate that the performance of the isolator can be easily tuned online.

This study presents a novel electromagnetic variable stiffness isolator that achieves bidirectional stiffness regulation, which means that the isolator experiences a reduced stiffness when the applied current is positive and an increased stiffness when the opposite current is applied. In addition, the stiffness variations are equal for two currents with the same magnitude but opposite polarities. The proposed isolator can not only ensure the vibration isolation performance in working frequency zone that is relatively far from the natural frequency, but also can realize high-damping-like effect for shock response attenuation, without introducing any additional damping components that may complicate the system. The bidirectional stiffness regulation was realized by combining mechanical springs with hybrid magnets (permanent magnets and coil windings). Variation in the overall stiffness of the proposed isolator occurred when the current was continuously adjusted. A prototype of the isolator was designed, fabricated and then tested with a round displacement step shock at the base. The theoretical analysis revealed that this device could be utilized as an active vibration isolator through certain control strategies. The experimental results proved the effectiveness of the proposed mechanism in shock isolation and revealed that it outperforms the conventional isolator in suppressing the residual vibration.