Analysis of the Quasi-Static Maxwell Equations in Resistive Solid-State Particle Detectors

We solve a boundary value problem arising from Maxwell's equations in the quasi-static approximation, which governs the time evolution of the so-called weighting potential $V_{\mathrm{w}}(t,x)$ in resistive solid-state particle detectors. The model reduces to the third-order time-dependent PDE $$ \varepsilon\,\partial_t \Delta V_{\mathrm{w}}(t,x) + \mathrm{div}\,\big(\sigma(x)\nabla V_{\mathrm{w}}(t,x)\big)=0 \quad\text{in } [0,T]\times\Omega,$$ supplemented with mixed Neumann-Dirichlet boundary conditions, possibly degenerate. Our analysis is based on the decomposition of the weighting potential into a static and a dynamic component. The static part solves a uniformly elliptic mixed boundary value problem, while the dynamic part satisfies a degenerate parabolic Cauchy problem. We also establish interior regularity results.