Abstract
The standard analysis of power dynamics for a plane wave normally incident on the interface between two lossy media reveals an imbalance in local power density conservation at the interface, which is attributed to omission of the field interactions in conventional formulations. This omission further disrupts the conservation of global power flow across the interface. To address this, we introduce the concept of interaction power density, which ensures accurate conservation of both the local power densities at the interface and the global power flow across the interface between two lossy media. Our formulation is validated by demonstrating consistency between the global complex power flow derived from the revised local complex power density-including the interaction power density-and that calculated from electromagnetic fields and material properties. Additionally, we identify the extrema of the interaction power density and flow and relate them to the wavelength. Our numerical examples demonstrate the errors resulting from the neglect of interaction power density across a range of permittivity ϵ (F/m), conductivity σ (S/m), and frequency values f ∈ [300 MHz, 300 GHz]. The study reveals that field interactions can significantly impact local power density at the interface and global power flow over distances on the order of a quarter wavelength from the interface.