On the Improvement of the Performance of Inexpensive Electromagnetic Skins by means of an Inverse Source Design Approach

TL;DR

The paper tackles the challenge of achieving high-performance static passive electromagnetic skins using low-cost substrates. It introduces an inverse source design that splits the radiating current into a pre-image component and a null-space component, optimizing the EMS layout and NS coefficients via an alternating minimization of a mismatch cost $\Phi(\mathcal{D},\underline{\beta})$. The method leverages a singular value decomposition of the forward operator to construct PI and NS currents and uses an offline database for efficient per-cell descriptor selection, complemented by a global NS optimization. Numerical results demonstrate up to about $28\%$ peak improvement in reflected power along the target direction (up to $38\%$ for small apertures), with robust performance for pencil-beam and contoured footprints; experimental validation on a paper-substrate prototype confirms the approach’s practicality. Overall, the work enables more efficient, scalable SP-EMS designs using inexpensive materials and modular tile concepts, with potential extensions to dynamic RIS-like architectures.

Abstract

A new methodology for the improvement of the performance of inexpensive static passive electromagnetic skins (SP-EMSs) is presented. The proposed approach leverages on the non-uniqueness of the inverse source problem associated to the SP-EMS design by decomposing the induced surface current into pre-image (PI) and null-space (NS) components. Successively, the unknown EMS layout and NS expansion coefficients are determined by means of an alternate minimization of a suitable cost function. This latter quantifies the mismatch between the ideal surface current, which radiates the user-defined target field, and that actually induced on the EMS layout. Results from a representative set of numerical experiments, concerned with the design of EMSs reflecting pencil-beam as well as contoured target patterns, are reported to assess the feasibility and the effectiveness of the proposed method in improving the performance of inexpensive EMS realizations. The measurements on an EMS prototype, featuring a conductive ink pattern printed on a standard paper substrate, are also shown to prove the reliability of the synthesis process.