An ultrathin acoustic carpet cloak based on resonators with extended necks

By employing a set of resonators with extended necks, an ultrathin acoustic carpet cloak with a thickness of about 1/30th of the operation wavelength is proposed to achieve effective cloaking around a bump at 1000 Hz. The cloak is composed of a periodic array of supercells. The supercell is constructed by a solid unit and seven inhomogeneous resonators with different extended necks. The elements in the supercell are capable of achieving distinct phase shifts ranging from 0 to 2π in a phase increment of π/4. To demonstrate the effectiveness of the cloak, both normal incidence and oblique incidence (incident angle equals to 30^°) plane waves impinging on a cloaked triangular bump are investigated numerically and validated experimentally. The results show that it is possible to conceal the bump by wrapping over the surface of the bump through using the proposed ultrathin carpet cloak. As a resonant-element based acoustic device, the cloak exhibits invisibility in the frequency range from 980 to 1070 Hz. The proposed acoustic metasurface offers a simple and compact solution for acoustic cloaking and may hold promise in realistic applications. (paper)