Re: Inverse D squared v/s Inverse D sixth power ?
- From: Michael Gray <fleetg@xxxxxxxxxxxxxxxx>
- Date: Sun, 18 Sep 2005 16:12:59 +0930
On Sun, 18 Sep 2005 13:59:24 -0700, "Graeme Zimmer"
<gzimmer_NOSPAM_@xxxxxxxxxxxxxxx> wrote:
>Hi, (I posted this in sci.physics.electromag but didn't get a sqeak).
>
>For Electromagnetic Radiation, most text books show the power density
>(in watts per square meter) of a wavefront is inversely proportional to the
>square of the distance from the source.
>
>e.g. 1/r2
>
>However recent discussions of Near Field Communications (NFC) indicate a
>1/r6 relationship (inverse Sixth power).
>
>see http://www.radio-electronics.com/info/wireless/nfc/nfc_overview.php
>and http://www.auracomm.com/site/content/roll_off.asp
>
>Now I understand that this is in the special case where only a magnetic
>field is present (the electric field having been suppressed with shielded
>antenna) (or vice versa).
>
>The title suggests that this 1/r6 relationship only occurs in the Near
>Field, but I also understand that if you have just an alternating magnetic
>field, then the electric field is promptly re-created (and vice versa) (in
>the Far Field ?).
>
>So can anyone elaborate on just where and when this Inverse Sixth Power
>relationship applies please?
>
>
>Thanks ........... Graeme Zimmer
>
Auracomm's technical claims seem a trifle suspect to me.
Have you tried actually asking them directly?
.
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