We experimentally demonstrated the 2D broadband acoustic cloak by the design paradigm of conformal mapping and coordinate transformation. 2D cylindrical acoustic cloak with anisotropic mass density was designed and fabricated by a 2D array of sub-wavelength cavities and connecting channels with spatially tailored geometry, that significantly reduce the visibility of the hidden object from underwater acoustic waves (shown in Figure).

Figure (a) The sketch of acoustic cloaking measurement; (b) and (c) Pressure field distribution without/ with acoustic cloaking, respectively.