Low Reflection Effects by 3D-Printed Functionally Graded Acoustic Black Holes
The acoustic black hole (ABH) effect produces drastic wave compression and energy trapping in thin-walled structures. Recent research has shown that the reflected wave in realistic ABH structures can be reduced by attaching specific wave concentration areas with thin absorbing layer. In this paper, the novel design and implementation of one-dimensional (1D) functionally graded acoustic black hole (FGABH) are presented, as an alternative to achieve low reflection effect. Two kinds of the FG-ABHs are demonstrated, i.e., an axially graded ABH and a thickness graded ABH. The FG-ABH beams are manufactured by 3D printing technology using an Objet Connex 500 printer. Materials with varying levels of rubber-like characteristics are produced using two base materials called TangoPlus and VeroWhitePlus. The FG-ABH beams have both diminishing thickness and elastic modulus from the uniform area to the tip of the wedge. Numerical investigation of wave propagation, attenuation and reflection are conducted utilizing a viscoelastic code: University of Michigan’s Local Interaction Simulation Approach (UM/LISA). The damping effect of the materials is included based on Kelvin-Voigt viscoelasticity theory. Finally, the process of wave propagation in FG-ABHs, traditional ABH and uniform beam are experimentally investigated using a scanning laser doppler vibrometer (SLDV) system. The reflection coefficients based on the ratios between the amplitude of reflected wave and incident wave are computed. Results indicate that the FG-ABHs enhance the ABH effects, and lower reflection is observed when compared to the traditional ABH structure.
