The low-frequency and broad bandgap characteristics of two-dimensional phononic crystals embedded with acoustic black hole structures

Abstract To address the challenge of controlling low-frequency vibration noise, a coupling phononic crystal model embedded with the acoustic black hole (ABH) structures has been designed. By comprehensively studying the complex dispersion curves, vibration modes, and transmission loss, we numerically demonstrate that this coupling structure exhibits good sound insulation performance in the low-frequency range of 64.3 Hz∼665.4 Hz, the bandgap coverage reaches 92.7%, while the effective sound insulation range achieves 89.6% within the frequency range of 1000 Hz. The torsional vibration of the scatterer component is more conducive to the lowering of the first starting frequency, and a larger torsion angle further contributes to this reduction. However, the cutoff frequency of the first bandgap is predominantly caused by the oscillating along the z-direction of the ABH structure. Evanescent waves exist in all the studied frequency bands exhibiting a strong correlation with the complex dispersion curve and the transmission loss. The intensity of the evanescent wave depends on the activated state of the ABH structures, the lower imaginary part of the complex dispersion curve corresponding to the passband yields the lower energy loss caused by the evanescent wave. Damping materials benefit the energy loss caused by evanescent waves. Parameters dependence of the ABH truncation thickness, the length of bending component and uniform part are analyzed, which are expected to provide theoretical design guidance for the control and attenuation of low-frequency vibration and noise.