Electromagnetic wave velocities: an experimental approach

Abstract

We describe experiments with coaxial transmission lines for the study of some of the velocities used to characterize the propagation of electromagnetic waves in a medium, namely phase, group and signal velocities. The experiments are suitable for undergraduates at advanced laboratory level. Their purpose is to acquaint the students with the fact that in a dispersive medium there are many possible definitions for the speed of light, and that the measurement of these different velocities is important for general understanding of wave propagation.

A Resonant Ring Topology Approach to Power Line Communication Systems within Photovoltaic Plants

“…The previous documents mentioned regarding single-cable transmission in Section 1 considered frequencies of transmission above 50 MHz (higher than the ones we worked with in this first demonstration stage for our PV-PLC system), whose current distribution is expected to be flowing superficially or in a thin layer close to the surface of the cable (skin effect), with propagation described to be carried out by a surface wave whose phase velocity is c (the speed of light). Our direct measurements of the phase velocity over a line of single PV cable at a frequency of 20 MHz showed speeds around 0.6 c, closer to what is observed in typical coaxial cables [14], even when the propagation mode is different in our single-cable medium (TM) than the one in coaxial cables (TEM). The lower frequency used in our single-cable support suggests that the current distribution flows in a thicker layer inside the conductor, and the influence of the material lowers the phase velocity with respect to the previously mentioned Sommerfeld surface wave.…”

On the Counterpropagation of Waves

“…The wave phenomena permeate many areas of physics such as mechanics, thermodynamics, electromagnetism, relativity, and quantum mechanics. One important theme associated with wave phenomena is propagation [1,2]. Essentially, wave propagation can be affected by the changing of the physical medium properties (for example, in electrodynamics the electrical permittivity , the magnetic permeability µ, among others), by the changing of the physical medium geometry (the changing in boundaries or the inclusion of another, as obstacles), by the existence of another waves, or by the existence of the matter.…”