Wireless-Friendly Microwaves

Makarand writes "According to this article on ABC News, scientists at the University of Michigan in Ann Arbor have stumbled upon a simple and elegant solution to keep your kitchen microwave from becoming a noisy nuisance to your home Wi-Fi network. They found that they could focus the microwaves into a single frequency and reduce noisy microwave emissions by placing ordinary magnets in specific patterns along the magnetron . New techniques to reduce microwave interference will be needed when Wi-Fi enabled entertainment systems will allow digital audio and video to be transmitted to different rooms of a house wirelessly. Packet drops in such a sytem would degrade the video and audio experience."

Comments

pdf here

[maharg]

Low-noise microwave magnetrons by azimuthally verying axial magnetic field - here

Re:pdf here

[hpmsource]

Up until four days ago, I was a graduate student in this laboratory. (Just graduated!) Here are some other links with more information, but the above PDF is probably the most detailed, being a journal article.

Press release after a recent APS conference

Extended summary of research (PDF) and

Research projects currently underway by the same U of Michigan group. Some cool stuff. Check it out. The microwave noise project is the first link. Nice PIC of the setup. Also a couple audio files showing the noise interference to a cordless phone before and after the modification.

Re:Or....

[Rosco P. Coltrane]

When you hit water with it, it will agitate the molecules and things get hot and cooked

You seem agitated and cooked enough without microwaves.

The difference is in power and concentration : a microwave oven is minimum 700W, concentrated on a lump of water, whereas an 802.11b is 100mW radiated in all directions. You'd need hundreds of wifi cards doing denial-of-services around a cage to even start incommodating the hamster inside.

Re:I've said it once and I'll say it again

[Chanc_Gorkon]

There may not be anything WRONG with the microwave. This is BS. First off, actually at power leakage is probable not occuring. It's REALLY hard to keep RF from getting out. First, you HAVE to have a door to put food in and take it out. You also have to have a window (because you need to see if your food is about to turn into flames). Most leakage could come from those two areas. If I can get a signal out of a public bus at 2m, I bet that even a nicely shielded microwave could have SOME leakage that could interfere with WiFi. Both of my microwaves are less then 3 years old. Only the one that is closest to the AP (about 10ft away) causes any issues with connectivity. Also, keep iin mind, most microwaves are pushing around a kilowatt or higher PEP output (if that's how they measure it). Most WiFi AP's are 1 watt or less. Two things I may try to increase my AP's profile:

Add a Linksys Stackable Amp (called a Signal Booster, but it's just an Amp) for 99 bucks.

Get rid of the rubber ducky antennas and either build my own halfwave antenna, or by a Diamond. Not known to many WiFi guys (except the serious ones), rubber ducks that ship with pretty much any radio equipment are usually compromise antennas. The typical SWR is closer to 2 then it is to 1 and it may be higher. The lower the SWR, the more power you are radiating. Rubber ducks are included because they do work, but they are probably not the best antenna you can get. Go spend some money and buy a Diamond antenna or find a homebrew design you can make that satisfies your requirements. After designing it, make sure to use a length of low loss coax and mount it near the ceiling.

Those two things would raise the profile or your AP and maybe not eliminate, bur probably reduce the amount of interference you get since your AP is now radiating more RF. I don't reccomend building your own amp. Stick to off the shelf as you'll be sure to be within the FCC power regs. If these regs state ERP, then be careful of your antenna also. To much gain may push you over that reg and while the FCC probably won't come to your house, it's being a good spectrum user to follow those guidelines.

Don't add a directional antenna unless your trying to establish a link say from building to building, or if you have an AP with Omnis and are setting up another AP to increase your footprint in a certain direction. Omni's would work better for most situations unless your trying to establish that link or establish a lobe in a certain direction. If the general idea is to provide better overall coverage, directional antennas like a yagi are not what you want. Go with a good omni.

Re:DIY?

[paganizer]

Actually, this is old news, it's just a variation on various things done with radar for a long, long time.
And you would have to design the "pattern" specific to each waveguide/magnetron/klystron and due to the low quality standards for oven grade waveguides & couplings, they vary quite a bit.
So, no magic bullet.
And yes, I AM an expert on the subject, according to the Navy.

NOT the resonance frequency of water!!!

[Anonymous Coward]

802.11 is not operating at the resonance frequency of water. Water as a liquid does NOT have any resonance, but do have an absoprtion maximum at 8-200 GHz, depending on temperature.

Water vapour has a resonance at approx. 22GHz.

More easy-to-read info at: http://www.zyra.org.uk/microw.htm
Follow links for hard-core Maxwell stuff.

Re:I've said it once and I'll say it again

[Skapare]

If the holes are smaller than about 1/20th wavelength, then the microwaves won't leak through, but you'll still be able to see in (light has a much smaller wavelength than those holes). The window in your oven door does have holes, right? If not, that probably explains why your brain is toast.

Re:Or....

[eggboard]

2.4 GHz is not the resonating frequency of water. That's way way up in the GHz chain. 2.4 GHz was chosen because that band is the junk band in which unlicensed users are subject to interference as part of the spec.

Microwaves work by oscillating water molecules, which are dipole. The magnetron cycles 2.45 billions times per second, which twists the water molecules. The interior of a microwave oven is coated with a microwave-reflecting material which allows a single beam to essentially paint the three-dimensional interior.

So many people write that water resonates at 2.4 GHz. It's just not true. Here's a nice explanation of how it works.

Try changing the channel

[adrianbaugh]

I got extremely poor link quality from my 802.11b network - like, it would barely connect - until I tried changing the channel (from 3 to 12). This improved things enormously; I haven't tested all the channels to find the best one yet but it might be worth it if you're having problems, it definitely seems possible to get variations in signal quality within the 11b band.