An Antenna for Visible Light

On Mon, 20 Sep 2004 07:23:06 +0000 (UTC), (Brian Tung) wrote:

1. Radio waves in the AM band, say, have frequencies within a
factor of two or so of 1 MHz. That means that the wavelengths
are in the neighborhood of 300,000,000 m/s (the speed of light)
divided by 1,000,000 Hz (that is, cycles/s), or 300 m. Yet
an AM radio needs an antenna no bigger than your pinkie finger.

Well, the general statement is still pretty accurate, that antennas need to be
close to the wavelength of the radiation they are collecting. As they get
shorter, they get less efficient. It just happens that there are sometimes
engineering solutions to less efficient antennas (like high gain, low noise
amplifiers). In the case of your AM radio, the small antenna is possible because
it isn't detecting the E field, but the magnetic field. A small piece of
ferrite, combined with a tuned coil, happens to produce a strong signal at AM
wavelengths. An aerial- a piece of wire that is 1/4 wavelength or longer- will
do better, but that isn't practical in most cases. A longer piece of ferrite
will also do better, but that is even less practical.

Overall, I think the Reuters article isn't bad at all (and I'm a physicist).
Even the comment about photons, while technically inaccurate, is pretty accurate
at reflecting the reality of radiation measurement: at wavelengths much longer
than light, it is almost never practical to think of EM as photonic; at shorter
wavelengths, it is seldom practical to treat EM as wavelike. Somewhere around
1mm wavelength is a bizarre hybrid zone of optics and electronics, but the
Reuters readers basically know about light and they know about radio. Detectors
for the former are fundamentally photonic; for the latter electronic. The
article is suggesting technology that would change this. As popular science
reports go, this one is a lot better than average.

_________________________________________________

Chris L Peterson
Cloudbait Observatory
http://www.cloudbait.com

Chris L Peterson wrote:
As popular science reports go, this one is a lot better than average.

Generally speaking, I agree with you. But when someone (in this case,
Greg) indicates that there are errors in a story, for some reason, that
makes the errors stand out all the more. (The antenna one didn't stick
out as far as the photon/wave thingie, though.)

Brian Tung
The Astronomy Corner at http://astro.isi.edu/
Unofficial C5+ Home Page at http://astro.isi.edu/c5plus/
The PleiadAtlas Home Page at http://astro.isi.edu/pleiadatlas/
My Own Personal FAQ (SAA) at http://astro.isi.edu/reference/faq.txt

"Clif" wrote in message
m...
No help from the manufacturer though, my warranty
period is way over.

Clif

Ever see "Minority Report"?

-- Mark

If I didnt know any physics and had a big mouth, I would resort to that too!

Greg Crinklaw wrote:

Marvin wrote:
whose basic errors? yours or theirs?

Oh, and Jerry, perhaps you weren't aware that your headers contain this:

Sender:

Have you considered venting your personal frustrations in less
personally embarrassing ways? Seems counter productive to me...

--
Greg Crinklaw
Astronomical Software Developer
Cloudcroft, New Mexico, USA (33N, 106W, 2700m)

SkyTools Software for the Observer:
http://www.skyhound.com/cs.html

Skyhound Observing Pages:
http://www.skyhound.com/sh/skyhound.html

To reply have a physician remove your spleen

"Mark Lepkowski" wrote in message news:
Ever see "Minority Report"?

-- Mark

Nope.
Clif

(Clif) wrote in message om...

I have a pair of those also. Very pleased overall. Autofocus,
autogain, single shot color, auto darks, excellent software, etc. The
only drawbacks I have encountered with the equipment are that the
autofocus range diminishes with time and use requiring external
refractive elements, and the blue light sensitivity is a good bit less
than when new. No help from the manufacturer though, my warranty
period is way over.

Clif

I expect the manufacturer has subcontracted to the CPR by now anyway.
But who needs a violet haze? I'd stick with the original equipment if
I were you. A regular soak in alcohol might free up that autofocus
problem. Though others dispute this. I'd also recommend that you keep
them in the original manufacturer's packaging for as long as possible.
Avoid amateurish modifications and abrasive cleaners.

Chris.B