Low-frequency sound radiation characteristics of imperfect acoustic black hole in thin plate

The unique dynamic characteristics and energy focalisation of the acoustic black hole (ABH) have been confirmed. Meanwhile, an ABH composite structure covered with a damping layer exhibits excellent performance in vibration control. However, limited by machining accuracy and conditions, imperfect ABH is easier to obtain than ideal ABH. This study focuses on the sound radiation characteristics of an imperfect ABH thin plate without a damping layer in the low-frequency range. The imperfect ABH in this paper replaces the traditional curve with an oblique line near the centre of two-dimensional ABH. The vibration and acoustic changes of imperfect ABH plate are investigated based on three key variables: ABH diameter, residual thickness and centre position of imperfect ABH indentation. The finite element method (FEM) is used to calculate the radiation efficiency of various imperfect ABH plates at eigenfrequencies. The acoustic radiation efficiency is measured and estimated via a sound-intensity experiment. Both the simulation and experimental results show that the acoustic radiation efficiency of thin plates can be controlled by an imperfect ABH in the low-frequency band, which is associated closely with the geometric parameters and position of imperfect ABH.