Wavefront shaping with a tunable metasurface: Creating cold spots and coherent perfect absorption at arbitrary frequencies

Modern electronic systems operate in complex electromagnetic environments and must handle noise and unwanted coupling. The capability to isolate or reject unwanted signals for mitigating vulnerabilities is critical in any practical application. In this work, we describe the use of a binary programmable metasurface to (i) control the spatial degrees of freedom for waves propagating inside an electromagnetic cavity and demonstrate the ability to create nulls in the transmission coefficient between selected ports, and (ii) create the conditions for coherent perfect absorption. Both objectives are performed at arbitrary frequencies. In the first case, an effective optimization algorithm is presented that selectively generates cold spots over a single-frequency band or simultaneously over multiple-frequency bands. We show that this algorithm is successful with multiple input port configurations and varying optimization bandwidths. In the second case, we establish how this technique can be used to establish a multiport coherent perfect absorption state for the cavity.