Ultra-Broadband Acoustic Metasurface for Manipulating the Reflected Waves

We have designed and experimentally realized an ultra-broadband acoustic metasurface (UBAM) capable of going beyond the intrinsic limitation of bandwidth in existing designs of optical/acoustical metasurfaces. Both the numerical and experimental results demonstrate that the UBAM made of subwavelength gratings can manipulate the reflected phase-front within a bandwidth larger than 2 octaves. A simple physical model based on the phased array theory is developed for interpreting this extraordinary phenomenon as well as obtaining deeper insight to the underlying physics of our design. We anticipate the UBAM to open new avenue to the design and application of broadband acoustical devices.