A novel auxetic acoustic metamaterial plate with tunable bandgap

Two-dimensional phononic metamaterials, consisting of plates with resonant cylinders, can significantly attenuate waves by opening a subwavelength bandgap, though their characteristic unit cell size is small. To realize the real-time adjustment of the bandgap, external excitations including mechanical load, temperature field, electric field and magnetic field could be introduced, of which applying mechanical load is the most practical way. In this work, an acoustic metamaterial plate based on the negative Poisson's ratio structure (NP-AMP) is proposed and feasible to achieve lower frequency, wider bandgap, and tunable bandgap compared with traditional ones (T-AMP). A counterpart based on the positive Poisson's ratio structure (PP-AMP) is also introduced for comparison. Studies have indicated that the newly designed structure has a lower frequency bandgap and wider bandwidth. With the increase of compression strain, the initial bandgap of PP-AMP gradually moves to a higher-frequency range. In contrast to PP-AMP, the NP-AMP exhibits lower frequency, which is beneficial for the further research of low-frequency bandgap. Moreover, the bandgap variation range can be enlarged by the enhancement of the auxetic behavior. Finally, the variation range of the NP-AMP initial bandgap frequency increased by 62%. The findings in this work will broaden the design of low-frequency broadband acoustic devices used in a dynamic environment, while providing new ideas and methodologies for real-time adjustment of bandgaps.