In this paper we report the numerical design and experimental validation of a pentamode cloak for scattering reduction of elliptical targets in underwater acoustics. Despite being a well-known theoretical concept, experimental validations of transformation-based acoustic cloaking for non-axisymmetric targets have been hindered due to the difficulties related to the complexity of the required material distribution. We overcome these by adopting a linear quasi-symmetric map defined in elliptic coordinates that allows for the design of a pentamode cloak with constant anisotropic elasticity and a scalar inhomogeneous density. We then perform the long-wavelength homogenization based optimization of unit cells that implement the computed material distribution. Numerical validations allow to assess the working range of the designed microstructure, which depends solely on the ratio between the wavelength and the size of the microstructure, and is thus expressed in terms of the maximum normalized wavenumber $\kappa L_c$, being $L_c$ the characteristic length of the considered unit cell. The influence on the scattering performance of the cloak of a pentamode bandgap common to all the cells in the microstructure is also discussed, finding that it is actually detrimental for the scattering reduction. Finally, the specimen is fabricated and experimentally tested over the range $0.45<\kappa L_c<1.34$.

在本文中，我们报告了用于减少水声学中椭圆目标散射的五模斗篷的数值设计和实验验证。尽管是一个众所周知的理论概念，但由于与所需材料分布的复杂性相关的困难，非轴对称目标的基于变换的声学隐身的实验验证受到阻碍。我们通过采用在椭圆坐标中定义的线性准对称映射来克服这些问题，该映射允许设计具有恒定各向异性弹性和标量非均匀密度的五模斗篷。然后，我们对实现计算出的材料分布的晶胞进行基于长波长均质化的优化。数值验证允许评估设计的微观结构的工作范围，$\kappa {升}_C$， 存在 ${升}_C$所考虑的晶胞的特征长度。还讨论了微结构中所有单元共有的五模带隙斗篷对散射性能的影响，发现它实际上不利于减少散射。最后，制作样品并在范围内进行实验测试$0.45<\kappa {升}_C<1.34$.