I Beg to Diffract: RF Field Programming With Edges

In this paper, we propose a new paradigm in intelligent surface design for field programming and multi-point focusing. We approach this problem from an entirely different vantage point by leveraging edges and the corresponding Geometrical Theory of Diffraction (GTD), allowing us to avoid the use of highly specialized and expensive element designs. More specifically, we show that a lattice of edge elements (i.e., cheap, thin, rectangular metal plates with length long enough as compared to width) can provide a rich repertoire for programming the RF field. When a wave is incident on an edge, a cone of outgoing rays emerges, known as a Keller cone. When considering a lattice of such edge elements, we then have a rich set of "knobs" for RF field programming, via changing the orientation of the edge elements and exploiting the exiting Keller cones. We then show how to electromagnetically model and design a practical edge element. We further propose an efficient algorithm to configure the orientations of the edges to achieve the desired multi-point focusing. We build sample prototypes of our proposed paradigm, using off-the-shelf material (i.e., 7 cent metal plates). We then show several real-world experiments in three different indoor areas, where an edge lattice focuses the transmitted wave of a WiFi card of a laptop on up to and including 4 focal points (maximum achieved in the literature albeit with much more expensive element designs). Overall, the paper shows the rich potential of edges for RF field programming.