Holographic mirrors for spatial ultrasound modulation in contactless acoustic energy transfer systems

This work introduces and investigates a flat acoustic mirror capable of efficiently manipulating a wavefront and creating an arbitrary pressure pattern in a target plane using the sound reflection phenomenon. The mirror is a metallic holographic lens that performs as a spatial ultrasound modulator by introducing a relative phase shift to the reflected wavefront. The phase-shifting lens is designed using an iterative angular spectrum algorithm and 3D-printed from powdered aluminum through direct metal laser melting. The lens's capabilities to construct diffraction-limited complex pressure patterns under water are tested numerically and experimentally. The proposed holographic mirror design can drive immense improvements in applications involving contactless acoustic energy transfer, which is investigated in this Letter.