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Gene Fuller wrote:
"Figure 8.3.2 Propagation of a circularly polarized pure direct (in the +z direction) travelling wave with phase velocity vf = c." Whether Cecil did not see this caption, did not understand it, or was again trying to pull a fast one remains unknown. It matters not in any case. If I was trying to pull a fast one, I wouldn't have posted the reference along with the graphic. The phasors associated with a traveling wave rotate in opposite directions for forward and reflected traveling waves, i.e. in their exponential notations, they are indeed polarized. If the forward and reflected waves didn't rotate in opposite directions, the standing waves wouldn't stand. That graph is a reasonable graph of a uniform plane wave in exponential notation. My graph of the superposition of forward wave phasors and reflected wave phasors still stands at: http://www.w5dxp.com/EHSuper.JPG The Re part of those phasors (the fields) are 180 degrees out of phase. Quoting "Optics" by Hecht, concerning a traveling wave: "... a phasor rotating counterclockwise at a rate omega is equivalent to a wave traveling to the left (decreasing x), and similarly, one rotating clockwise corresponds to a wave traveling to the right (increasing x)." The graphic I posted is a reasonable representation of a traveling wave illustrated in exponential form. The fields of a circularly polarized waves are virtually identical to the phasors of a uniform plane traveling wave. You can observe the rotation of a traveling wave by downloading http://www.w5dxp.com/rhombicT.EZ and turning on the current phase option. What is immediately observed is that the Poynting vector for an ordinary standing wave is zero only for specific locations or for specific times. At other locations and times the Poynting vector is non-zero. Only the time or space *average* is zero. Which is exactly what I have been saying. The instantaneous Poynting vector is of limited usefulness. The time-averaged Poynting vector is the one that is useful and the one I have been talking about, as I stated a couple of times previously. Every time I have used the words, "Poynting vector", I have been referring to the average Poynting vector. As you know, I have been using the word "net" as in, "there is no net energy flow in a standing wave". We both agree that in a traveling wave the voltage and current are in phase for forward waves and 180 degrees out of phase for reflected waves. The E-field and H-field are 90 degrees apart in both traveling wave cases. A traveling wave is an example of a uniform plane wave. The technical fact that the voltage and current in a pure standing wave are 90 degrees out of phase proves that the standing wave is NOT a uniform plane wave. In fact, in an earlier posting, a standing wave failed all 7 properties of a uniform plane wave. V*I*cos(A) = average Poynting vector = 0 for a standing wave. -- 73, Cecil http://www.w5dxp.com |
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