This paper presents a comprehensive material invariant analysis on asymptotes and resonances of absorbed power distribution. A closed-form solution for absorbed power in the presence of distributed microwave source has been derived from the first principle, which shows the existence of two distinct asymptotic regimes: thin and thick samples. Within thin samples, absorbed power is shown to be weak function of position, while it decays exponentially within thick sample. In between thick and thin samples, absorbed power is shown to exhibit resonances, where a detailed analysis has been performed to reveal various resonating characteristics of average power. The main purpose of the analysis is to predict the occurrence of resonances and establish correlations for a priori prediction of resonating sample dimensions in the presence of various distributed microwave incidences. The closed-form analysis has been shown to be useful in forecasting the heating characteristics: hot spot vs uniform heating. It has been shown that the heating characteristics can be tuned by suitable distribution of microwave source towards optimal material processing. (c) 2006 Elsevier Ltd. All rights reserved.