Theoretical analysis of the microwave-drill near-field localized heating effect

Abstract

The microwave-drill principle ͓Jerby et al., Science 298, 587 ͑2002͔͒ is based on a localized hot-spot effect induced by a near-field coaxial applicator. The microwave drill melts the nonmetallic material locally and penetrates mechanically into it to shape the hole. This paper presents a theoretical analysis of the thermal-runaway effect induced in front of the microwave drill. The model couples the Maxwell's and heat equations including the material's temperature-dependent properties. A finite-difference time-domain algorithm is applied in a two-timescale numerical model. The simulation is demonstrated for mullite, and benchmarked in simplified cases. The results show a temperature rise of ϳ10 3 K / s up to 1300 K within a hot spot confined to a ϳ4-mm width ͑ϳ0.1 wavelength͒. The input-port response to this near-field effect is modeled by equivalent time-varying lumped-circuit elements. Besides the physical insight, this theoretical study provides computational tools for design and analysis of microwave drills and for their real-time monitoring and adaptive impedance matching.

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