Visco-thermal effects on an acoustic cloak based on scattering cancellation

Recent research has shown that the performance of acoustic metamaterials can be greatly influenced by the effects of viscous and thermal dissipation. In the worst case, an isentropic assumption can lead to an undesired performance. To further investigate the impact of losses on novel acoustic devices, an already known acoustic cloak is validated numerically, including the viscous and thermal dissipation effects. The specific cloaking device is realized using 120 small aluminium cylinders distributed around a larger cylindrical object, in such a way, that plane waves incident to the cloak will appear to be undisturbed, at the operational frequency of 3061 Hz. The initial optimization procedure for determining the positions of the small cylinders assumes isentropic conditions neglecting dissipative effects, meaning that the actual realization of the cloak might behave differently than intended. Through numerical simulations the acoustic cloak performance is compared with and without dissipation, giving an estimate of the differences that can be expected in similar cases. The results show that losses have very little impact on the key performance characteristic, the averaged visibility.