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Re: Secondary Theory (Was Bipolar Coil)-Heretical view
-----Original Message-----
From: Tesla List <tesla-at-pupman-dot-com>
To: tesla-at-pupman-dot-com <tesla-at-pupman-dot-com>
Date: Wednesday, May 26, 1999 6:06 PM
Subject: Re: Secondary Theory (Was Bipolar Coil)-Heretical view
>Original Poster: "Malcolm Watts" <MALCOLM-at-directorate.wnp.ac.nz>
>
>Hi Terry, all,
>
>> Original Poster: Terry Fritz <twftesla-at-uswest-dot-net>
>
><snip>
>
>> There are two questions we should consider:
>>
>> 1. Is it POSSIBLE to make a true 1/4 wave operating Tesla coil??
>
>An excellent question. The question I would like answered is whether it is
>possible to make a low loss 1/4 wave open resonator - i.e one that
>radiates poorly? If my conjecture is right, spacing between turns
>must be >> Dwire and as this happens, radiation losses increase as
>operating frequency reaches skywards.
Accelerating (and decelerating) charges radiate. Nothing you can do about it
except catch the radiation and send it back with a "perfect" reflector
(which is what a cavity does, but, I assume it wouldn't meet your
requirement of an "open" resonator). A superconductor would reduce IR
losses, but, you'd still radiate.
Now, if you have a pair of perfectly matched charges of opposite sign,
accelerating in just the same way, the radiated field will cancel, at least
at some boundary surrounding the charges. Of course, getting those perfectly
matched charges in the same place at the same time is physically impossible.
But, you can get close, which is what twisted pair and coaxial cable are all
about, and why they don't radiate (or receive, for that matter, radiation
and reception being reciprocal).
If you have some current oscillating, then the charge is accelerating as it
moves back and forth, so it will radiate.
For the more math inclined:
Pradiated = mu^2 * q^2 * vdot^2 / (6 * pi * Z)
where:
mu is permeability of medium (Henry/meter)
q is charge (coulombs)
vdot is acceleration ( m/s^2)
pi is 3.14....
Z is impedance of medium in ohms
also(for substituting in above): Idot * length = Vdot * q
Idot is change in current (amps/sec)
length in meters
q in coulombs
vdot is acceleration (m/s^2)