A novel periodic beam with multilayer acoustic black holes for deep sub-wavelength vibration attenuation

Acoustic Black Hole (ABH) is a power-law taper in beam-plate structures that allows a smooth and progressive diminishing of the bending wave speed, even reduced to zero with no residual thickness. However, despite the use of viscoelastic damping layers, significant annulling of reflected waves only appears in mid-to-high frequency band. By contrast, acoustic metamaterials in local resonant mode can create relatively low-frequency band gaps for wave decay. This paper designs a sandwich beam combining the ABH features with local resonance mechanism to realize the sub-wavelength vibration reduction. To maintain the external shape, we resort to a double-leaf configuration with periodic ABH inclusions. It has been indicated that the newly designed structure opens a lower frequency band gap and wider bandwidth compared to its counterpart which made of only single material. The parametric analysis shows that increasing the ABH power and reducing the truncation thickness could further widen these gaps, while the add-on mass of the viscoelastic layer will benefit to the attenuation intensity. In what concerns the structural strength, stiffeners are inserted to alleviate the stress concentration with negligible modification to the transmission spectra. The results indicate that this approach will prompt the design of broadband acoustic devices at deep sub-wavelength scales and shed light on vibration control.

Automated summary

This paper presents a sandwich beam design that combines the features of Acoustic Black Hole (ABH) and local resonance mechanism for sub-wavelength vibration reduction. Parametric analysis shows that increasing ABH power and reducing truncation thickness can widen the frequency band gaps, while the mass of the viscoelastic layer benefits attenuation intensity. Inserting stiffeners to alleviate stress concentration has negligible impact on the transmission spectra.