Выражение встречается в следующем контексте:

Данное выражение встречается в статье, описывающая явление излучения радиочастоты при воздействии гиперзвуковой скорости.

First observations of RF(radio frequency) emissions were reported by Bianchi et al. in 1984 [1]. They impacted aluminum projectiles of around 1 g of mass onto hard leucitite rock with about 10 km/s and detected electromagnetic between 100 and 200 kHz with a system of 300 kHz bandwidth. They argue that rock fracture rather than the generated impact plasma yields responsible for the signal because the small cloud dimensions do not allow for low frequency generation. Furthermore, the signal frequency was not changing as expected for a rapidly expanding plasma.

Заранее спасибо.