Enhanced energy transfer and multimodal vibration mitigation in an electromechanical acoustic black hole beam

Owing to their unique energy focusing capability and high-frequency damping effects, Acoustic Black Hole (ABH) structures show promise for numerous engineering applications. However, conventional ABH structures are mostly effective only above the so-called cut-on frequency, a bottlenecking deficiency that needs to be addressed if low-frequency problems are of concern. Meanwhile, achieving simultaneous high frequency ABH effects and low-frequency vibration reduction is also a challenge. In this paper, electrical linear and nonlinear shunts are intentionally added to an ABH beam via PZT patches to tactically influence its dynamics through electromechanical coupling. Both numerical and experimental results confirm that the effective frequency range of the ABH can be broadened as a result of the electrical nonlinearity induced energy transfer (ET) from low to high frequencies inside the beam. However, increased nonlinearity strength, albeit beneficial to energy transfer, jeopardizes the linear dynamic absorber (DA) effects acting on the lower-order resonances. Solutions are exploited to tackle this problem, exemplified by the use of negative capacitance in the nonlinear shunts with the embodiment of parallel linear electrical branches. On top of the nonlinear ET effects, simultaneous DA effect is also achieved for the low-frequency resonant vibration mitigation. Studies finally end up with a design methodology which embraces the principle of ET and DA to tactically cope with different frequency bands. The final outcome is the broadband multi-modal vibration reduction and the breaking down of the frequency barrier existing in conventional linear ABH structures.