2007-03-12 11:48:37 · 2 answers · asked by JAMES 4 in Science & Mathematics ➔ Engineering
Microwaves do not really move inside a metal because the good conductivity of metal will zero out the electric field to reflect it back. Even lower frequency currents have a tendency to get out to the skin of the metal. Microwaves need a non-conductive medium to propagate but a metal boundary channel to guide them.
Waveguides can be hollow rectangular tubes or they can also be filters such as comblines, interdigitals, etc... Coax, microstrip and strip lines are also "waveguides." Coax cables and microstrip have the ground conductors covering/bracketing a metal line. Strip line circuits have traces just like other PCB circuits, but a microwave do not travel on those metal traces, rather it bounces between the traces and the ground plane underneath them. This may give a wrong perception that a microwave travels in the metal.
What determines a microwave speed is not the metal which only determines the insertion loss. The speed is determined by the dielectric material between the metal boundaries. The most typical PCB and coax material is Teflon. The speeds of RF and microwaves in Teflon are about 70% of the speed of EM waves in vacuum. For another material, you need to look up its relative index of refraction, which is the relative geometric mean of the material's permittivity and permeability, and which is the speed reduction ratio relative to the speed of light in vacuum.
2007-03-12 12:45:46 · answer #1 · answered by sciquest 4 · 0⤊ 0⤋
Microwaves do not run in metal they flow in wave guides something like pipes. The move at the speed of light.
2007-03-12 12:00:49 · answer #2 · answered by Bullfrog21 6 · 0⤊ 0⤋