Space-coiling Acoustic Metasurface with Independent Modulations of Phase and Amplitude

In this work, we propose a design of acoustic meta-surfaces in sub-wavelength scale enabling independent modulations of phase and amplitude. Each unit cell of the acoustic meta-surface consists of simple conventional space-coiling structure added with an air layer, which can be analyzed as two equivalent slabs with non-dispersion effective parameters. The amplitude depends on the space-coiling structure regardless of the air layer, and the phase can be further adjusted by the air layer independent to the amplitude. The acoustic meta-surface covers an entire phase change of 2-pi and amplitude change of one. We demonstrate an acoustic illusion effect by using the acoustic meta-surface screen, which works well as a full-control discontinuous boundary to support phase and amplitude differences between the original and illusion patterns. The incident field of a point source is transformed into a target field of the point source scattered by an object with shadow area behind it.