Re: those folks at MIT (fwd)

["Tesla list" <tesla@xxxxxxxxxx>]

---------- Forwarded message ----------
Date: Tue, 12 Jun 2007 15:37:50 -0700
From: Ed Phillips <evp@xxxxxxxxxxx>
To: Tesla list <tesla@xxxxxxxxxx>
Subject: Re: those folks at MIT (fwd)

    On a more positive note I have yet to find the source paper you have
>read.  Is it available on line?


http://www.sciencemag.org/sciencexpress/recent.dtl

June 7th edition.

gotta pay for it, unless you're at an institution with a 
subscription, or you're a member of AAAS


Did some analysis on their revised numbers in the supplementary 
material (1 MHz instead of 10 MHz, single turn loop).

Using practical materials (silver plated copper, polypropylene 
capacitors) the single turn loop (2 ft diameter) would have an 
unloaded Q of about 1400.

Doesn't change the fact that the authors of the paper (and the 
editors of Science) should be embarrassed about their lack of useful 
quantitative data, and an obvious unfamiliarity (or willful 
ignorance) of the relevant literature.  Some coworkers of mine here 
are casually looking for the oldest references that describe the 
phenomena reported in this paper.  They're not sure if they can get 
back before 1850, but they are hopeful, since Faraday described 
experiments with magnetic induction between two coils in 1831.  His 
coils were untuned and on an iron core, though.


It's the editors of Science who really deserve opprobrium here.."

Jim:

	Thanks for the link.  I've been an AAAS member for over 50 years so didn't have to pay.  Somehow I missed that it was in ScienceXpress and was waiting for the June 8 Science to arrive.  It did yesterday but the article wasn't there.  I notice that there is a statement on the ScienceXpress home page that these are "pre-publication" articles and presume that means that this one will appear in Science some day but I didn't find anything to indicate whether their download articles are already peer reviewed.  If it passes the Science peer review I suspect they'll get ripped later even though most readers aren't engineers or physical scientists.   Of course, Science has published a few suspect papers over the years.I believe the guys' experimental data and still find the paper trivial and ludicrous - I hope your colleagues find a really old reference covering the same subject. Certainly the work Lodge and others did with Leyden jars connected to parallel lines qualifies but there is probably something earlier.  The authors' acute observation that the power transfer falls off rapidly with detuning of either coil is really astonishing!  Brilliant guys!

	They had a bunch of references including a Tesla patent which doesn't really apply, but a single reference to any issue of The Radiotron Designer's Handbook would have sufficed.  If they had read it and understood it they wouldn't have published [maybe - they're on an ego trip so who knows?].  Their equation for coil resistance is too complicated for me to bother to understand but their value of 950 for Q is very close to what I get using formulae in the third edition which I used in college back in 1944 although I ignored coil capacitance in the calculation.  Just for kicks I went through a calculation similar for the case of  24" diameter coils consisting of 20 turns of #10 wire in a total length of 4 inches.  k (the conventional one without their superfluous omega in it) works out to abe 0.00757 for 120 inches center to center spacing and to 0.00441 for the 144" spacing Terry's "10 R" challenge would use.  Pretty high coupling when you think about it.  Here are some Excel calculations I made using a simplified coil analysis program based on the RDH formula and ignored self capacitance or self resonance to make the job simpler.

f(MHz)	Q	kQ 120"spacing	kQ 144"spacing
0.1	362	2.74034		1.59642
0.3	647	4.89779		2.85327
1	1204	9.11428		5.30964
3	2106	15.94242	9.28746
10	3780	28.6146		16.6698

Even assuming my Q calculations are off by a factor of more than two any frequency of 1 MHz or above should provide enough power transfer to win Terry's prize - I thought he made it too easy but never bothered to run these calculations!

Regards,

Ed