Design and Experimental Validation of Fiber-Steered Acoustic Black Hole Beam for Suppression of Bending Resonances

Abstract

Acoustic black hole (ABH) beams are lightweight tapered structures that damp bending vibration modes by reducing the reflection coefficient of bending waves. ABH beams suppress bending resonances only above the cut-on frequency, leaving the modal loss factors of lower-order modes low. This study aimed to design ABH beams capable of mitigating all bending resonance peaks from the first mode. To achieve this, we proposed a fiber-steered ABH beam that addresses the trade-off between a stiff host structure and a low cut-on frequency. The geometry of the ABH wedge with curvilinear carbon-fiber paths was optimized to maximize the minimum modal loss factor within a target frequency range. The host beam length was tuned such that the first bending mode was above the cut-on frequency. The feasibility of this design was examined under various boundary conditions. The reflection coefficient was calculated using the impedance matrix method, and the advantages of the curvilinear fiber paths were evaluated through comparison with other ABH configurations. Frequency response functions and modal loss factors were obtained through finite element analysis and hammering tests. The results demonstrated that a properly designed fiber-steered ABH beam achieved high modal loss factors from the first bending mode.