Metamaterial with Perforated Auxetic Core for Ultra-Low-Frequency Vibration Isolation of Lamb Waves

Low-frequency vibration isolation metamaterials (LFVIMs) remain challenging in generating ultra-low-frequency bandgaps around 10 Hz and below. For this issue, a novel LFVIM composed of a square steel auxetic core perforated with orthogonally aligned peanut-shaped holes and a silicone rubber coating is proposed, leveraging the auxetic core's unique resonance behavior. The superiority in bandgap creation of the peanut-shaped perforations is illustrated by comparing them to elliptical and rectangular perforations. Furthermore, a filled auxetic core is explored as well, to enhance its wave attenuation potential. The wave propagation mechanisms of both the unfilled and filled LFVIMs are comparatively studied by finite element simulation validated against an existing LFVIM design and scaled-down vibration testing. Compared to the unfilled LFVIM, the filled case merges smaller bandgaps into three wider full bandgaps, increasing the relative bandgap width (RBW) from 44.25% (unfilled) to 58.93% (filled). Subsequently, the role of each design parameter is identified by parametric analysis for bandgap tuning. The coating material shows a significant influence on the RBW. Particularly, optimizing the coating's Poisson's ratio to 0.2 yields a maximum RBW of 93.95%. These findings present a successful strategy for broadening LFVIM applications in the regulation of ultra-low-frequency Lamb waves.