Experimental verifications of perforation-modulated slow-wave phenomenon

Slow wave phenomenon has been theoretically and numerically predicted inside a in a retarding based on the so-called sonic black hole (SBH). A perforation-modulated SBH (PMSBH) retarding structure is then proposed, in which the two physical processes (sound velocity reduction and absorption) can be balanced to enhance the black hole effects by modulating the perforation parameters. This work presents an experimental effort to confirm the theoretically predicted slow wave phenomenon as well as the ABH-induced sound absorption inside a PMSBH. Alongside some theoretical development, this study brings forward the concept of tunable design to improve the performance of SBH structures, which can benefit the design of sound wave manipulation and noise control devices.