Experimental investigation of a phase-cancelling slow-sound metamaterial with mean flow

Acoustic metamaterials have a wide variety of potential applications in various engineering disciplines. In many cases, the acoustic medium can be assumed to be at rest. However, for a lot of engineering applications a moving fluid is used to transport energy or substances, or to perform mechanical work. For those cases, acoustic waves are advected and acoustic energy can be dissipated or generated. These effects play a significant role for the design of acoustic metamaterials. In this work, an acoustic metamaterial with a low Mach number mean flow is presented. It is an array consisting of an even number of channels. Half of them are equipped with a slow-sound metamaterial, whereas the other half has unaltered sound propagation characteristics. Thus, the resonance frequencies of the channels are shifted. This results in a phase shift in the acoustic velocity response between both types of channels for a given pressure excitation, resulting in phase cancellation. However, this effect is weakened for higher mean flow velocities.