Theoretical analysis of nonlinear surface wave absorbing metasurfaces

In this paper, we provide a theoretical analysis and discussion of the fundamental principles of nonlinear surface wave absorbers, in which ideal diodes are used to rectify surface currents to produce nonlinear harmonic terms including DC, and higher order modes (2f0, and 4f0, …). Interestingly, we find rectification converts most of the power to DC that can be completely absorbed by resistance in the surface, leading to advantages of nonlinear absorbers over conventional linear surface wave absorbers in both bandwidth and attenuation. We demonstrate the full-wave rectification case, and diode-rectifier-based nonlinear absorbing metasurfaces possess obvious advantages and can exceed the performance of linear absorbers, which relates the bandwidth and attenuation rate to the substrate thickness. For nonlinear metasurfaces, even with very thin substrates (for instance 0.35 mm thickness which is λ₀/143 for center frequency 6 GHz), we can potentially achieve more than 60% relative bandwidth, three times of that in linear metasurfaces. To visualize the practical working mechanism, the distributed nonlinear network using ideal diode model is presented, and the full-wave simulations are demonstrated with nonlinear advantages. Differences between the theoretical case and practical case are addressed as well.