Elastic metamaterial with multiple resonant modes and asymmetric structure design for low-frequency vibration absorption

In this work, an elastic metamaterial (EMM) structure with multiple resonant modes that can generate bandgaps is proposed. Through proper geometrical adjustments, the resonant frequency and sequence of the resonant modes can be tuned to form continuous bandgaps. This is in contrast to commonly used elastic metamaterial configurations with only one primary local resonance mode for bandgap opening, resulting in relatively narrow bandgap widths. The effect of geometrical parameters on the bandgap property is investigated via numerical simulation. Numerical results verify the accuracy of dispersion relation prediction on the bandgap location and width. A bandgap with maximum width of 100.2 Hz in the low frequency range (< 300 Hz) is found numerically. Prototype samples of the proposed EMM are fabricated, and experimental tests have been conducted. Testing results for all prototypes validate the formation of an even larger bandgap than numerically predicted. The largest bandgap measured is about 256 Hz. The damping allows the bandgaps to merge and form a broad continuous one. The utilization of asymmetric structure design is proposed in this present work to enlarge the bandgap width through enhancing the interaction between the relevant resonant modes and the incident wave. With a proper geometrical parameter selection, the bandgap associated with the torsional resonant mode can be enlarged by about 64.4%. This work confirms that the breaking of self-balance condition in the symmetric EMM structure can enhance the torsional mode-related bandgap performance. It thus provides a new design pathway for the bandgap enlargement for elastic metamaterials for applications in structural vibration control.