Seismic metamaterials are an emerging vibration-damping technology, yet concentrating the bandgap in the low-frequency range remains challenging due to the constraints imposed by lattice size. In this study, we numerically investigated seismic metamaterials connected by auxetic (negative Poisson’s ratio) slender strips, which exhibit an exceptionally wide low-frequency band gap for vibration isolation. Using a finite element method, we first performed a comparative analysis of several representative seismic metamaterial configurations. The results showed that the auxetic thin strip-connected steel column structure demonstrated outstanding performance, with the first complete band gap starting at 1.61 Hz, ending at 80.40 Hz, spanning a width of 78.79 Hz, and achieving a relative bandwidth of 192.15%. Notably, while most existing designs feature lattice constants in the ten-meter range (with the smallest around two meters), our proposed structure achieves these results with a lattice constant of only one meter. We further analyzed the transmission characteristics of the steel column structure, both with and without concrete filling. Interestingly, significant vibration attenuation, approaching 70 dB, was observed below the first complete band gap (approximately 0.22–1.17 Hz), even without the use of concrete. By comparing the flexural wave band gap with the transmission spectrum, we attributed this attenuation primarily to the presence of the band gap, a phenomenon often overlooked in previous studies. This attenuation at lower frequencies highlights the potential for effectively reducing low-frequency vibration energy. To further enhance the attenuation, the number of periods in the propagation direction can be increased. Additionally, we systematically explored the influence of geometric parameters on the first complete band gap. We found that optimal results were achieved with a slender strip length of 0.05 m, its width between 0.05 and 0.1 m, and a steel structure width of 0.1 m. Our findings underscore the critical role of auxetic thin strips in achieving broadband low-frequency vibration isolation. The approach presented in this study, along with the discovery of low-frequency flexural wave band gaps, provides valuable insights for seismic engineering and other applications requiring effective vibration reduction strategies.
