Acoustic black holes: from generalization to realization

Abstract

This study starts with a simple question: can we efficiently reduce the vibration of plates or beams using a lightweight structure that occupies a small space? As an efficient technique to dampen vibration, we adopted the concept of an Acoustic Black Hole (ABH) with a simple modification of the geometry. The original shape of an ABH has a straight wedge-type profile with power-law thickness, with the reduction of vibration in beams or plates increasing as the length of the ABH increases [1]. However, in real-world applications, there exists an upper bound of the length of an ABH due to space limitations. Therefore, in this study, the authors propose a curvilinear shaped ABH using the simple mathematical geometry of an Archimedean spiral, which allows a uniform gap distance between adjacent baselines of the spiral [2]. In numerical simulations, the damping performance increases as the spiral length of the Archimedean spiral increases regardless of the curvature of the spiral in the mid- and high-frequency ranges. Adding the damping material to the ABH could strongly enhance the damping performance while not significantly increasing the weight. In addition, the authors experimentally investigate the effect of curvatures of the curved ABH on the vibration damping performance. The curved ABHs studied in this work are divided into two cases: (1) the curved ABH with the baseline of constant curvature, i.e., a circular arc shape, (2) the curved ABH with the baseline of varying curvatures. After manufacturing the spiral ABH with high precision, the authors perform experiments to investigate the effect of curvatures on the damping performance of the circular arc shaped ABHs [3]. An Archimedean spiral ABH, a particular form of the curved ABH of slowly varying curvatures is also investigated experimentally in order to create the possibility of using the spiral ABH as a new and efficient method of damping vibration in real-world problems.