**4. Conclusion and outlook**

In this chapter, an overview of key metasurface concepts such as diffusion, anomalous reflection and refraction has been carried out, and their use in wavefront shaping and beamforming applications, followed by a discussion of polarization conversion in few-layer metasurfaces and their related properties have been discussed. An overview of diffusion coding metasurface reveals their ability to realize unique functionalities to reduce the radar crosssection. We also describe diffusion coding metasurfaces that can improve the field uniformity in reverberation chambers. Finally, we conclude by providing our opinions on opportunities and challenges in this rapidly developing research field. These works presented herein provide a glimpse of the opportunities available for advanced EM functional devices based on geometric phase coding metasurface, which may find applications in the future. Moreover, scalability of these coding metasurfaces to frequencies in the range of THz or optical is possible, allowing for the controllability of reflection, and scattering of EM waves in these frequency domains [11].
