Tong, Lihong

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Tong, Lihong

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  • Publication
    Negative Poisson’s ratio locally resonant seismic metamaterials vibration isolation barrier
    (Springer, 2024-05-07)
    Ding, Haibin 
    ;
    Huang, Nianyong 
    ;
    Gulzari, Muhammad 
    ;
    Xu, Changjie 
    ;
    Tong, Lihong 
    In recent decades, the application of seismic metamaterials to protect civil infrastructures being free of the damage of earthquakes has been attracting extensive attention. Specifically, the proposed locally resonant seismic metamaterials provide the probability of isolating the low-frequency seismic wave using a small-size isolation barrier. However, in previous studies, the energy absorption properties of locally resonant seismic metamaterials remain one of the least understood aspects of isolation. Benefit from the fascinating energy absorption characteristic of negative Poisson ratio (NPR) metamaterial, we creatively design a new seismic metamaterial structure by assembling the locally resonant seismic metamaterial and NPR metamaterial, to isolate seismic waves. The sound cone technique combining the transmission spectrum is employed to identify the surface wave from the hybrid waves. The generation mechanism of frequency bandgap and the isolation effectiveness of the proposed seismic metamaterial are discussed in detail. The results indicate that the generation of ultra-low and ultra-wide frequency bandgap with the range of 0.65 Hz–18.9 Hz is attributed to the locally resonant and energy absorption of the proposed seismic metamaterial structure and the excellent isolation effect is achieved by transforming the surface wave into the bulk wave. The frequency bandgap narrows as the distance increases between each resonator. In addition, the mechanical properties of the NPR bearing, such as the Poisson ratio, mass density, and elastic modulus, have remarkable impact on the frequency bandgap, especially on the upper bound frequency. In practical engineering, the NPR bearing with a low Poisson ratio, small mass density, and high elastic modulus is suggested for the design of the NPR locally resonant seismic metamaterial structures. Time domain analysis for the practical seismic wave verifies that the proposed seismic metamaterial has a promising application in isolating ultra-low and ultra-wide seismic waves, with the isolation effectiveness larger than 70%. This work contributes a new locally resonance seismic metamaterial design idea for isolating and adjusting the low-frequency seismic wave.
      1
  • Publication
    Valley edge states with opposite chirality in temperature dependent acoustic media
    (IOP Publishing, 2024-05-31)
    Gulzari, Muhammad 
    ;
    Zhang, Quan 
    ;
    King, Eoin A. 
    ;
    Tong, Lihong 
    ;
    Lai, S. K. 
    The valley degree of freedom in phononic crystals and metamaterials holds immense promise for manipulating acoustic and elastic waves. However, the impact of acoustic medium properties on valley edge state frequencies and their robustness to one-way propagation in valley topological phononic crystals remains unexplored. While significant attention has been devoted to scatterer design embedded in honeycomb lattices within acoustic and elastic media to achieve valley edge states and topologically protected nontrivial bandgaps, the influence of variations in acoustic medium properties, such as wave velocity and density affected by environmental temperature, has been overlooked. In this study, we investigate the effect of valley edge states and topological phases exhibited by topological phononic lattices in a temperature-dependent acoustic medium. We observe that a decrease in wave velocity and density, influenced by changing environmental temperature, shifts the topological valley edge states to lower frequencies. Therefore, alongside phononic lattice design, it is crucial to consider the impact of acoustic medium properties on the practical application of acoustic topological insulators. This issue becomes particularly significant when a topological phononic crystal is placed in a wave medium that transitions from incompressible to compressible, where wave velocity and density are no longer constant. Our findings offer a novel perspective on investigating topological insulators in variable acoustic media affected by changing thermodynamic and fluid properties.
      13