Hypersonic

Hypersonic is also over 1.000 MHz (Megahertz), thus over 1 GHz (gigahertz). It closes in the spectrum thereby upward to that on.

Starting from 1 GHz itself sound cannot do any more than mechanical in a medium. Hypersonic spreads only as Surface waves on the surface of out.

(the thing with the surface wave on the solid body should confirmed by a physicist again and/or. are corrected)

Popular-scientifically hypersonic designates also the speed range the far over (hyper) local or spacecraft with the reentry. Unmanned one reach up to 9,7-fache speed of sound (