Ultrathin Acoustic Parity-Time Symmetric Metasurface Cloak

(a) The insonified portion of the cloak () is patterned by sound absorbing Helmholtz resonators. The angular dependence of their resonances has been tuned via the resonator neck width and depth . (b–d) The theoretically and numerically computed absorption and impedance match is presented in dependence to the angle , i.e., the position of the individual Helmholtz resonators.