[Fwd: MicroWave: RF equivalent of Photon?]

[David Rogers]

Just forwarded for interest
Dave (K9RKH)

-------- Original Message --------
Subject: MicroWave: RF equivalent of Photon?
Date: Thu, 09 Dec 1999 15:23:19 -0500
From: Tom Williams <tomw@aai.com>
Reply-To: Tom Williams <tomw@aai.com>
Organization: Millivision LLC
To: microwave list <microwave@wa1mba.org>

Mike asks:
 Is there a "photon" equivalent for RF?
===================================================

A photon is a quantum of electromagnetic energy.
Physicists think of electromagentic energy as having a
"dual nature", in that some experiments reveal its
nature as a particle which we call a photon and other
experiments reveal its nature as a wave. No doubt, it
is possible to continue this discussion ad inifinitum,
and better minds than mine have been at it for a long time.

When it comes to lower frequencies, such as microwaves,
VHF, and the like, it becomes much less convenient to
think of energy in the form of photons, but as far as I
know, there is no specific reason to decide that only
one nature exists at these longer wavlengths. I sometimes
refer to photons when describing an RF interaction with
matter. I do not know of any other word to describe the
particulate nature of a propogating RF energy field
except "photon". When the interaction with matter
converts the energy into a mechanical form, we sometimes
refer to the energy packets as "phonons", but this is not
a propogating EM field, but rather a sound wave.

In most antenna, transmission line, waveguide, and
quasi-optic
formulations, the EM field is described according to its
wave-like nature. When dealing with the interaction bewteen
a microwave field and a molecule of Oxygen (for instance),
in order to 
understand just why there are specific resonant frequencies
of
the molecule, a quantized nature re-appears, and the notion
of the field expressed as photons can make sense.

tomw WA1MBA at work



P.S. the interactions between matter and EM fields have
clearly
different properties when the interaction causes a change
in mechanical vibration as compared to causing a change in
electron orbital state. The first occurs in the microwave
and
millimeter wave range - such as the serious absorption of
22 GHz signals by water vapor in the atmosphere. Here the
interaction causes vibration and heat. To cause changes in
electron orbital states, infrared, visible and UV range
wavelengths
are involved - such as is evidenced by florescence and
lasers. 
In these cases much more than conversion to heat occurs. 
We call the  second group of wavelengths "light" and the
word "photon" is derived from Greek for light.