Analysis of the edge finite element approximation of the Maxwell equations with low regularity solutions
Provides rigorous error bounds for finite element methods in electromagnetics when material heterogeneity causes low regularity, addressing a gap in existing theory.
The paper derives error estimates for edge finite element approximations of Maxwell equations that hold for solutions with very low Sobolev regularity (smoothness index arbitrarily close to 0), using new quasi-interpolation operators.
We derive $H_{\text{curl}}$-error estimates and improved $L^2$-error estimates for the Maxwell equations approximated using edge finite elements. These estimates only invoke the expected regularity pickup of the exact solution in the scale of the Sobolev spaces, which is typically lower than $\frac12$ and can be arbitrarily close to $0$ when the material properties are heterogeneous. The key tools for the analysis are commuting quasi-interpolation operators in $H_{\text{curl}}$- and $H_{\text{div}}$-conforming finite element spaces and, most crucially, newly-devised quasi-interpolation operators delivering optimal estimates on the decay rate of the best-approximation error for functions with Sobolev smoothness index arbitrarily close to $0$. The proposed analysis entirely bypasses the technique known in the literature as the discrete compactness argument.