Figure 3

The scattering patterns of sound scattering around acoustic cloaks. (a) Polar plot of directivity pattern of the existing cloak¹ in stationary medium. (b) and (c) Polar plots of directivity patterns of the convective cloaks⁷ in moving media for M = 0.1 and M = 0.2, respectively. The directivity patterns are calculated in dB scale by using equation (5) at r = 10R₁. The incident angles and the Helmholtz numbers are set as α = 0 and kR₁ = 3. A large deviation from 0 dB in directivity plot indicates that we have more scattering unwanted. In (b) and (c), the blue lines indicate the results of the present formulation using equation (2), and the red lines indicate the results of the previous formulation⁷ using equation (1). There is a clear difference between the scattering patterns of the previous and present formulations, and the difference becomes larger as the Mach number increases.