The microwave-drill thermal-runaway analysis

The microwave-drill employs an open-end coaxial applicator generating a localized hot-spot in the drilled material. This paper presents a theoretical analysis of the coupled thermal-electromagnetic phenomena involved, whereas the material's temperature-dependent properties (e.g. the dielectric permittivity and thermal-conductivity variations) play a dominant role in the thermal-runaway evolution. The numerical simulation employs a finite-difference time-domain (FDTD) method in a cylindrical symmetry, The temporal and spatial temperature evolution profiles are simulated for mullite. The equivalent microwave-drill impedance is found as a lumped circuit with varying resistive and reactive components. This analysis is applicable for open-end coaxial microwave applicators in general.