2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/29280The nonlinear surface impedance of a thin superconducting strip carrying a microwave current has been calculated numerically from first principles based upon flux penetration due to a current-induced critical state. The calculations approach analytic results in the appropriate limit. The technique is useful for design of passive superconducting microwave circuits.4 pages, 7 PostScript figures, Submitted to IEEE Transactions on Applied Superconductivity. More details and related publications are available at http://sagar.physics.neu.edu/Superconductivitytext