Slow Waves for Noise and Vibration Control

Acoustic/elastic waves can be manipulated through proper structural design to produce the so-called slow wave phenomenon. In flexible structures undergoing bending vibrations, slow waves can be generated by tailoring the structural thickness according to a power-law relationship, which reduces the phase/group velocity of the flexural waves while compressing the wavelength and enhancing the energy concentration. This phenomenon, known as "Acoustic Black Hole" (ABH), can be leveraged in many engineering applications such as the design of lightweight and highly damped structures, sound-proofing structures, dynamic absorbers and energy harvesting devices etc. For sound waves, the counterpart of the ABH is the so-called "Sonic Black Hole" (SBH), which can be realized inside a conduit by means of a series of spacers with reducing inner diameters. Due to the combined effects of wave compression and energy concentration, slow waves within the SBH waveguide allow for efficient sound absorption with proper boundary treatment. This talk review some of the recent advances in both ABH and SBH research made by the research team led by the speaker. Modeling and analytical tools, salient phenomena, underlying physical principles, and potential applications of slow-wave-based vibration and noise control techniques will be showcased and discussed.