Dependence of microwave emissions from hypervelocity impacts on the target material

Microwave emissions due to hypervelocity impacts and their dependence on the target material are described. Microwave signals were measured for four kinds of target materials: aluminum, alumina ceramic, red brick, and polyurethane rubber. The signals were composed of two kinds of wave form: intermittent sharp pulses and white noise. The pulse signals were emitted strongly, especially with the aluminum target. The energy emitted from each target was estimated from the signal detected after calibrating the measuring system. The energy of the pulses was greater for conductors than for insulators. We hypothesized that the microwaves were emitted from a discharge along a microcrack in the target. The signals detected in the experiment agreed well with theoretical results.