External Mean Flow on Sound Radiation of Active Mechanical Metamaterials

Sound pressure level (SPL) is one of the significant parameters of the acoustic-structure coupling for the elastic wave metamaterial. This paper presents the use of the external mean flow and the active feedback control system. Based on the locally resonant mechanism, the dynamic effective mass density is also discussed and the negative density appears at a lower frequency region. From the results, it can be seen that both the SPL and the effective mass density can be controlled by the active feedback system. As the frequency region of the negative density increases obviously, it emerges two negative regions with the changing of the displacement feedback control action and leads to the changing of the SPL. Besides the Mach number of the external mean flow, other influences on the SPL are also discussed, such as the structural damping, lattice constants, excitation position, elevation angle, and azimuth angle. Finally, these interesting effects on the elastic wave metamaterial are presented and explored.