Layer-Dependent Electromagnetic Field and Power Deposition in Bacillus Anthracis Spores: An Image-Based Study at 2.45 GHz

The inactivation of highly resistant pathogens, such as Bacillus anthracis spores, using microwave energy requires a precise understanding of electromagnetic interactions at the cellular level. This work presents a highfidelity two-dimensional Multiphysics study aimed at characterizing the layer-specific electric field distribution and power deposition within a single spore. High-resolution Transmission Electron Microscopy (TEM) micrographs were used to reconstruct realistic Finite Element Method (FEM) models including the exosporium, spore coat, cortex, and core. Frequency-dependent dielectric properties were described through the Debye relaxation equation to model the electromagnetic response of hydrated biological media at 2.45 GHz. The results highlight a pronounced layer-dependent redistribution of the electromagnetic field and deposited power. The spore coat and cortex emerge as the primary regions of enhanced absorption, exhibiting higher Joule heating density, whereas the inner core behaves as a relative cold spot, with electric field intensity and power deposition reduced to approximately 20–30% compared to the surrounding layers. These findings indicate that microwave inactivation mechanisms may predominantly involve preferential energy localization and structural alteration of the outer protective layers, rather than direct thermal damage to the spore core and its DNA.