Viscous Fluid Dissipation for Filtering Poor Bandgaps and Achieving Low‐Frequency Bandgaps in Metamaterials

Abstract Embedding viscous fluids in soft elastic metamaterials offers transformative potential for engineering applications, particularly in vibration control and acoustic filtering. Despite this promise, effectively leveraging fluid viscosity to achieve low‐frequency, high‐quality bandgaps remains a significant challenge. Specifically, fluid viscosity shifts local resonance modes to lower frequencies while mitigating negative dynamic effective properties, resulting in smoother transmission spectra. By incorporating viscous liquids as resonant units, it is demonstrated how vibrational acoustic coupling and viscous dissipation can be harnessed to engineer superior bandgap properties. The bandgap characteristics of locally resonant metamaterials with viscous liquid fillings are systematically investigated through theoretical analysis, numerical simulations, and experimental validation. The bandgap shifted to lower frequencies by up to 5.6% within the concerned viscosity range, accompanied by a 4.1% bandwidth expansion. This overturns the conventional notion that viscous dissipation reduces system performance, showcasing its positive impact on bandgaps. This work redefines viscous dissipation, usually considered a limitation, as a key enabler for achieving broadband, high‐performance low‐frequency bandgaps, unlocking new possibilities for advanced acoustic and vibration isolation technologies.