The narrow band gap width caused by local resonance is the shackle for the further development of conventional metamaterials. In this paper, a novel type of hierarchical metamaterial containing parallel multiple resonators is presented, whose ultra-broadband vibration suppression property originates from a rational gradient design. Characterization of dispersion relations and bandgap characteristics of the one-dimensional outward-hierarchical lattice system reveals the variation of bandgap boundaries with relevant parameters. Thus, two gradient design approaches are proposed to overlap and merge the bandgaps. These designs are verified on the analogous continuum models by finite element simulations, and the ultra-wide wave/vibration attenuation band is consistent with the prediction of band gap diagram. Moreover, the range of the total band gap is determined by the boundary parameters of the gradient design, and its integrity is affected by the setting of gradient interval. In particular, the relationship between the gradient interval setting and the generation of overlapping gaps is analyzed. The gradient outward-hierarchical metamaterial is demonstrated to be an effective solution for elastic wave bandgap engineering, which can also be considered as a complement to existing inward-hierarchical configurations.

局部共振导致的窄带隙宽度是常规超材料进一步发展的桎梏。在本文中，提出了一种包含并联多个谐振器的新型分层超材料，其超宽带振动抑制特性源于合理的梯度设计。一维向外分层晶格系统的色散关系和带隙特性的表征揭示了带隙边界随相关参数的变化。因此，提出了两种梯度设计方法来重叠和合并带隙。这些设计通过有限元模拟在类似的连续介质模型上得到验证，超宽波/振动衰减带与带隙图的预测一致。而且，总带隙的范围由梯度设计的边界参数决定，其完整性受梯度间隔设置的影响。特别分析了梯度间隔设置与重叠间隙的产生之间的关系。梯度向外分层超材料被证明是弹性波带隙工程的有效解决方案，也可以被视为对现有向内分层配置的补充。