Electromagnetically induced localized ignition in secondary high explosives

A model for electromagnetically induced hot spots is developed from the well-established theories of dielectric mixtures, microwave absorption, heat transfer, and thermal ignition. This mathematical model is used to elucidate the interplay among these theories for a microwave heated system of secondary high explosive within which isolated electromagnetically lossy spheres are randomly distributed. Results are shown in this article for the specific case of pentaerythritol tetranitrate with embedded spheres of varying diameter and conductivity illuminated by a uniform time harmonic electromagnetic field of 1, 8, and 15 GHz. It is shown that for a given frequency and electric field strength internal to a particle embedded in a secondary high explosive, there exists a range of values for the particle's diameter and conductivity for which electromagnetically induced hot-spot ignition of the high explosive is possible. By providing an accurate estimate for the range of necessary geometric and electrical properties of the system, this idealized model can be used to guide potentially complex and otherwise less tractable computational and experimental studies of microwave-induced hot spots. We found that the condition of relatively large particles, with semiconductorlike conductivity, exposed to the highest possible frequency is most favorable for hot-spot ignition. (C) 2008 American Institute of Physics. [DOI: 10.1063/1.3002421]