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Richard Clark wrote:
Cecil Moore wrote: Wave cancellation in a transmission line redistributes the energy in the opposite direction as constructive interference. It is established there is "some" amount of energy in the "second" medium (in other words, beyond the match point as I have demonstrated); it then follows there is not a total reflection (same demonstration), and certainly not as constructive (to what?) interference. What's wrong with this picture? Looking at it upside down? With the source on the left, the second medium is to the right (load side) of the first medium. Of course, there is energy to the right of the match point - because of standing waves, more energy than exists in the first medium to the left of the match point. There's no reflected energy in the first medium to the left of the match point. It appears to look something like my earlier example: 1w | 1/4WL | laser-----air-----|---thin-film---|---glass---... 1st medium | 2nd medium | 3rd medium n=1.0 n=1.2222 n=1.4938 Pfor=1w Pfor=1.0101w Pfor=1w Pref=0w Pref=0.0101w Pref=0w Reflected energy is eliminated at the air to thin-film interface because of wave cancellation (total destructive interference). According to Hecht and every other reference I've seen, the reflected energy involved in the wave cancellation event at the match point joins the forward wave in the 2nd medium. Of course, that increases the amount of energy in the 2nd medium beyond what exists in the 1st medium. The necessary (total constructive inter- ference) energy is contained in those standing waves in the 2nd medium. www.mellesgriot.com/products/optics/oc_2_1.htm "Clearly, if the wavelength of the incident light and the thickness of the film are such that a phase difference exists between reflections of p, then reflected wavefronts interfere destructively, and overall reflected intensity is a minimum. If the two reflections are of equal amplitude, then this amplitude (and hence intensity) minimum will be zero." [total destructive interference] "In the absence of absorption or scatter, the principle of conservation of energy indicates all 'lost' reflected intensity will appear as enhanced intensity [constructive interference energy] in the transmitted beam. The sum of the reflected and transmitted beam intensities is always equal to the incident intensity. This important fact has been confirmed experimentally." [my notes] In the above example, the laser's transmitted beam intensity is 1w. In the 2nd medium, the reflected beam intensity is 0.0101w. The incident intensity upon the 3rd medium is 1.0101w. "This important fact has been confirmed experimentally." The above example is equivalent to a matched 1/4WL transmission line section having the following lossless characteristics. 1w XMTR--50 ohm coax--+--1/4WL 61.2 ohm coax--+--75 ohm coax--75 ohm load Pfor=1w Pfor=1.0101w Pfor=1w Pref=0w Pref=0.0101w Pref=0w -- 73, Cecil http://www.qsl.net/w5dxp ----== Posted via Newsfeeds.Com - Unlimited-Uncensored-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 100,000 Newsgroups ---= East/West-Coast Server Farms - Total Privacy via Encryption =--- |
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