Local Field Enhancements of Periodical Metallic Powders in Microwaves

The temperature spike or sparking is vital to the catalytic effect with metallic powders in microwaves, but the mechanism is still unclear. In this article, the local field enhancement (LFE) of periodical metallic powders in microwaves is studied. It shows that microwaves can get through the separations among metallic powders with the LFE, which provides a preliminary understanding of the temperature spike or sparking among metallic powders. First, for simplicity, metallic powders are simplified to 2-D periodical metallic bars, which can be analyzed by the transmission line model and full-wave simulations. When the incident electric field is perpendicular to the separations among metallic bars, the electric field can be compressed. Specifically, even with the volume fraction of 99% metals, microwaves can pass through the separations well with intensive LFEs. Then, metallic powders are simplified to 3-D periodical spherical metallic powders. In this case, microwaves propagate at the slow wave mode with the LFE. Finally, the proposed models are validated by measuring reflectivity and observing the discharge in neon (Ne) gas at atmosphere in a rectangular waveguide at the TE
₁₀
mode. This work provides a way of controlling LFEs for enhancing reaction reactivity and creating plasma.