Transmission loss of plates with embedded multi-scale and tuned acoustic black holes

Abstract

The Acoustic Black Hole (ABH) is an emerging method for developing lightweight, high-loss structures and has recently drawn extensive attention. Unlike many conventional methods, ABH implementations are typically able to reduce structure vibration and sound radiation without a net addition of mass. Transmission loss (TL) is a key criterion for panel structure in the noise and vibration industry. Many noise and control applications demand panel structures with high TL and low weight. Plates with embedded ABH cells have the potential to act as good candidates for TL applications. In this work, the transmission loss (TL) of an embedded multi-scale ABH plate was studied. The embedded large and small ABH cells were particularly designed to cut on below and above the critical frequency of the plate, respectively. The results were compared with a uniform plate and an embedded single-scale ABH plate. Discrete tuning masses were attached at the ABH cells' center to manipulate the ABH cut-on modes to increase the TL further. The results show that the damped multi-scale ABH plate achieved a 10 dB TL increase, flattened the TL curve, and nearly eliminated the plate coincidence dip. Manipulating the high loss ABH modes by adding tuning masses (20 g each) demonstrated a 2 dB increase at low frequencies within the mass-law range. Although damping material was applied, adding some mass and an overall weight advantage were still attained compared to the uniform plate. The damped multi-scale ABH plate is 7% lighter than the uniform plate.