what material reflects microwave?

Graphite crucibles are absolutely beautiful for induction melting, especially of materials that don't normally work well, like copper and silver (which are too conductive and reflect most of the energy) or insulators (like if you wanted to do glass, or synthesize diamonds, etc.).

It also has a nearly flat tempco, whereas metals change by more than an order of magnitude before they melt. (Not to mention steel's additional hysteresis losses at low temperature.)

Tim

You could make a great close-to-parabolic reflector with one of those things just by sticking it to a round air tight frame and pulling a vacuum. In fact, even if the frame weren't perfectly round it'd probably still be an OK reflector.

The downside would be that you'd need to maintain the vacuum, but hey -- nothing in life is perfect.

Or you could take a big tank full of mercury, and slowly rotate it so the centrifugal force makes a parabolic shape, allowing you to dynamically adjust the focus. It has some drawbacks, but maybe you could sell it as 'green', and they would not notice :-)

When Hostess used to put HoHo's in foil, it made a electrical storm inside the microwave. I guess the foil could not take the current.

greg

snipped-for-privacy@zekfrivolous.com (GregS) wrote in news:i58ltj$q9h$ snipped-for-privacy@usenet01.srv.cis.pitt.edu:

no,you get standing waves and the voltage causes arcing,at sharp points. the metalization acts as an antenna.

Thank you for all your responses.

I am interested to learn the material that reflects microwave energy, cellular and wifi signals, and these specific wavelengths?

I also interested to learn what is best and low cost to collect cellular and wifi specific wavelength signals?

Mental note to self: Greg puts Ho-Ho's in microwaves. :)

Low cost (for collecting) would be an antenna. High cost (for reflecting) might be something like this:

Link:

Near Salt Lake City, UT. Up close, you can see they have little patterns cut into them to better reflect certain wavelengths. They use these as passive repeaters (no electronics whatsoever) to get around mountainous terrain and other obstructions. Sometimes you'll see them on old microwave relay towers (antennas on the ground, passive reflector panels at altitude on a tower)

You wouldn't think they'd work, but they actually work quite well. I recall in the early days of the space race, they launched a metal spehere and bounced radio waves off it while it was in orbit. Pretty much the same concept here.

-mpm

Oh, and I have 2 of them on my desk because I am assembling a "bug-out" bag

mpm, very interesting, can you tell me more about this kind passive signal reflectors? If I can build something myself? how do I figure out the patterns for WiFi and Cellular signals?

You can get spray-on nickel in aerosol cans. Fry's has/had it for electronic shielding. I've used it on radios with plastic cases to keep RF from leaking. I can't say for sure it is good at reflecting RF, but it seems like it should.

I thought it was GC electronics, but that doesn't seem to be the vendor.

Try this:

But they have a nice turn off feature, simply release the vacuum. It's been documented somewhere for a solar reflector whatsit hotspot heater.

Make a drum, metalised plastic for the skin and just add vacuum to focus.

Grant.

They make lossy coax for passive repeaters too.

Grant.

You don't need a big tank--mercury zenith telescopes use a really thin layer of Hg on top of a roughly parabolic support, with a small gutter running round the outer edge to prevent the mercury from breaking up into drops. You do have to watch out for the vapour from such a large area, of course.

Cheers

Phil Hobbs

If I make a flat metal sheet as antenna on window from inside my apartment, to improve sign reception and transmission, what kind of pattern should I use for Wifi (2.45GHz) and Cellular (GSM has 4 bands, do not know what is best frequency for rest others?)

To: snipped-for-privacy@sushi.com, why spray on Nickel? Is Nickel good in absorb or reflect microwave?

This would be a good starting place. The music leaves a bit to be desired.

There are easier ways to do it. Keep looking until you find something suitable for you. At least the music will never get worse.

mike

A lot of "silver" paints contain NO metal.

Pretty much any air pressure differential, use the other hookup on the household vacuum, and then spray the back with structural foam. After it hardens you are good to go.