  Schroeder diffuser is a classical design, proposed over 40 years ago, for
artificially creating optimal and predictable sound diffuse reflection. It has
been widely adopted in architectural acoustics and it has also shown
substantial potential in noise control, ultrasound imaging, microparticle
manipulation, among others. The conventional Schroeder diffuser, however, has a
considerable thickness on the order of one wavelength, severely impeding its
applications for low frequency sound. In this paper, a new class of ultra-thin
and planar Schroeder diffusers are proposed based on the concept of acoustic
metasurface. Both numerical and experimental results demonstrate satisfactory
sound diffuse reflection produced from the metasurface-based Schroeder diffuser
despite it being one order of magnitude thinner than the conventional one. The
proposed design not only offer promising building blocks with great potential
to profoundly impact architectural acoustics and related fields, but also
constitutes a major step towards real-world applications of acoustic
metasurfaces.
