Re: NEC-LIST: E-M demos/simulations/animations

Hello all,

>From: Jos R Bergervoet <Jos.Bergervoet_at_philips.com>
>To: nec-list_at_ece.ubc.ca
>Subject: Re: NEC-LIST: E-M demos/simulations/animations
>Date: Wed, Apr 19, 2000, 1:17 AM
>
> Steve Inge wrote:
>>
>> I have just come home from ACES-2000. Ed Miller and John Schaeffer
>> gave a full day short course on "Where does the radiation come from".
>>
>> The cute answer, but accurate, is "radiation is caused by the
>> acceleration of charge."
>>
>> For a half wave dipole, this is where the travelling charge reverses
>> at the dipole ends ...
>
> But there are no travelling charges at the dipole ends. The current is
> zero at those points. You have to go about 1/4 wavelength away from
> the ends. For a half wave dipole, this is its center! The current,
> and also its time-derivative (accelleration of charge) are highest in
> the centre. If Ed and John are right, the radiation should come from
> the centre.
>
> See: http://home.iae.nl/users/bergervo/gouy/dipole.html

The results to which Steve referred were for rather longer current
filaments and wire antennas. The resolution of Shaeffer's results is
limited to 1/4 to 1/2 wavelength, so the bright spots near the end of
a filament cannot be interpreted to be exactly at the ends.

Miller's (my) results obtained using FARS (Farfield Analysis of
Radiation Sources) do exhibit a first peak at about a quarter
wavelength from the end for these longer current distriubtions. For
shorter antennas, the FARS results are peaked at the center, falling
to zero at the ends. But to say there are no charges at the ends
seems incorrect to me. The current goes to zero at the physical end
of a wire because the charge is reflected there where there is a
charge pileup. This phenomenon is shown clearly in time-domain
solutions.

Best wishes,

Ed

--
Dr. Edmund K. Miller
3225 Calle Celestial
Santa Fe, NM 87501-9613
505-820-7371 (Voice & FAX)
e.miller_at_ieee.org