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Technology

Wireless-Friendly Microwaves 119

Posted by michael from the press-enter dept.
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."
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Wireless-Friendly Microwaves More

Wireless-Friendly Microwaves

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  • Noise? (Score:1)

    by Anonymous Coward
    Screw Wi-Fi. I'd be happy if my microwave just didn't whine and rattle because they didn't balance that turning thing. Damn, microwaves used to be fairly legit pieces of electronics. Now mine is about as well put together as one of those robot boxing games.
    • I'd be happy if my microwave just didn't whine and rattle because they didn't balance that turning thing

      Think positive, this noise is actually a useful feature : when your oven becomes quiet, you know it's high time you cleaned the inside, because globules of sticky food are stuck in the rollers.
    • You have to spend big bucks to get one that's not a POS!

  • pdf here (Score:5, Informative)

    by maharg ( 182366 ) on Sunday November 23, 2003 @07:37AM (#7541474) Homepage Journal
    Low-noise microwave magnetrons by azimuthally verying axial magnetic field - here [umich.edu]

  • DIY? (Score:4, Interesting)

    by LeoDV ( 653216 ) on Sunday November 23, 2003 @07:38AM (#7541476) Journal
    The article stresses that those microwave interferences can be curtailed with "ordinary magnets" placed "in a specific pattern" so why isn't there a DIY guide for figuring out that pattern and slapping the magnets on the side of the oven? I know I'm probably oversimplifying, but if you know the pattern at which your oven emmits the microwaves, it can't be too hard to figure out the pattern at which you can put the magnets. Am I missing something? Or is it simply because, as they mentioned, reducing microwave interferences is a huge market and "opensourcing" the method would stop that?

    • Re:DIY? (Score:5, Insightful)

      by mooface ( 674033 ) on Sunday November 23, 2003 @07:45AM (#7541494)
      Probably because the magnets have to be placed inside the microwave, close to the tube....and one doesn't want the average consumer messing around in there...

    • I know I'm probably oversimplifying, but if you know the pattern at which your oven emmits the microwaves, it can't be too hard to figure out the pattern at which you can put the magnets. Am I missing something? Or is it simply because, as they mentioned, reducing microwave interferences is a huge market and "opensourcing" the method would stop that?

      Maybe you're missing the fact that nobody really tried before, and THEY JUST FIGURED OUT HOW TO DO THIS?

      Have you found a replacement foil your tinfoil hat,

      • Re:DIY? (Score:3, Informative)

        by paganizer ( 566360 )
        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.
        • I disagree. If this were something that had been done with radar, then someone would have done it to magnetrons 20 years ago and we would have no noisy magnetron problems. The fact of the matter is that the scientific community has been working on this noise problem for decades. It was always thought that a axial magnetic field with no azimuthal variation was needed to minimize noise. Untrue. These researchers, whom I personally know, have found that the azimuthal variation reduces the noise. The pattern i
    • I believe that in order to change the frequency spectrum of the magnetron, it is the field INSIDE the magnetron, not the oven or waveguide (metal ducting into the oven chamber) that needs modification. The magnetrons I've seen all had the outside of the tube covered with alternating layers of ring magnets and thin aluminum heat-sink fins. There's no place to add anything, so you'd have to replace and redesign that structure completely. If attempting it, the really critical aspect is to have an effective

  • what about the millions of legacy microwaves? (Score:2, Insightful)

    by Anonymous Coward
    I will continue to have the people in the appartment next door toasting my WiFi.

  • Cook time? (Score:3, Funny)

    by Gothmolly ( 148874 ) on Sunday November 23, 2003 @07:41AM (#7541483)
    The summary sez:"Packet drops in such a sytem would degrade the video and audio experience."

    I'm much more concerned with interference from my WAN slowing down or altering the cooking time of my microwave!

    Geek1: Hey guys, want some microwave popcorn?
    Geeks: Sure!
    Geek1: OK, turn off all the 802.11 stuff so it will cook.

    • Re:Cook time? (Score:5, Interesting)

      by Chanc_Gorkon ( 94133 ) <.moc.liamg. .ta. .nokrog.> on Sunday November 23, 2003 @07:48AM (#7541507)
      More like be prepared to be booted as the microwave will cut off 802.11b. I did not have a problem with this until I bought my current microwave (it's a bit closer to the AP then the old one was). When ever the microwave is on, the signal drops to zilch and I disconnect. Makes me wonder how safe these things are! :)

      • Re:Cook time? (Score:1, Flamebait)

        by Gothmolly ( 148874 )
        Idiot, it was a joke.
      • I did not have a problem with this until I bought my current microwave (it's a bit closer to the AP then the old one was).

        Is it also controlled by an inverter? My new Panasonic is, and it cooks great, but, wow does it take down 802.11 alot worse than the old on/off magnetron did.

        (the inverter allows magnetron power output adjustment - the old power levels 1-10 were just all-on magnetrons, followed by periods of no power to the magnetron). You can actually cook stuff in a microwave with an inverter-cont

  • Even better ... (Score:5, Funny)

    by Rosco P. Coltrane ( 209368 ) on Sunday November 23, 2003 @07:43AM (#7541490)
    They found that they could focus the microwaves into a single frequency

    Why not go all the way and make the frequency and phase of the microwave oven's magnetron adjustable, add some kind of microcontroller to drive it, and a small cpu to implement the 802.11b stack. Then, from your laptop, run this script:


    WIFI_IF=eth0
    DATE=`date +%s`
    while [ ! $TIMEOUT ];do
    DATE_PREV=$DATE
    tcpdump -i $WIFI_IF -c 1
    DATE=`date +%s`
    let TDIFF=DATE-DATE_PREV
    if [ $TDIFF -gt 5 ];then
    TIMEOUT=1
    fi
    done
    echo "Coffee is hot!"

    Ah, the marvels of technology ...

    • You are seriously deranged (Score:2, Funny)

      by Anonymous Coward

      Nobody in their right mind would drink MICROWAVE COFFEE, right? Right??

      But if you like it, you might as well boil your sport socks and underwear, add a dash of pergamot and enjoy a hot cup of "coffee".

  • "Browsing the Internet, e-mail, or most of the things we do today with a wireless network of computers -- those are sporadic communications," says Eaton. "If you drop a packet of data due to interference, it gets recovered."

    "If you're watching digital video wirelessly and a data packet drops, you're going to notice picture degradation," says Eaton.

    What are they going to transfer the digital video over? And chances are, that'll be TCP, which should automatically send the packet, right?

    Unless it's anal

    • Video packets have to be delivered in a timely manner. Most streaming protocols, like video, audio, and gaming, use UDP, not TCP, because, to paraphrase a pioneer in realtime internet gaming, it's easier to write code to recover from lost packets than it is to write code that can travel back in time to deliever one that arrived late.

      The trouble with TCP is that it will deliver all of your packets, but it will never deliver one out of order. This means that if a packet gets dropped in the middle of the stre

  • Dangerous magents (Score:1, Funny)

    by Anonymous Coward
    Don't mess with magnets at home! I jest wraps my microwave in aluminium foil. If it's good enough for my head, it's good enough for my microwave. Not only does this stop interference with my WiFi, but the voices come in even clearer.

  • Is it safe? (Score:1, Interesting)

    by Anonymous Coward
    Great - any idea how long these leaking microwaves have been inducing microtumors in my brain? How much longer until they grew large enough to kill me? Or how much longer until they just weird me out and I go all Charles Whitman-like on your ass?

  • I've said it once and I'll say it again (Score:3, Interesting)

    by afidel ( 530433 ) on Sunday November 23, 2003 @07:51AM (#7541512)
    If your microwave is interfering with any WiFi device not adjacent to it then throw it out and get a new one. Any properly shielded microwave should NOT be interfering with your WiFi signal. I worked for 2.5 years with the guys at Cisco/Aironet and we could only find one 15 year old off brand microwave that we could get to cause any noticable loss of signal in our testing shacks (basically an RF isolated chamber enclosed by a Faraday cage). None of the microwaves in the building ever caused us any problems even though we had more WiFi equipment than any place on earth. And if you don't want to/can't replace the microwave then get an 802.11a capable radio, different spectrum =)

    • Re:I've said it once and I'll say it again (Score:4, Informative)

      by Chanc_Gorkon ( 94133 ) <.moc.liamg. .ta. .nokrog.> on Sunday November 23, 2003 @08:25AM (#7541569)
      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.

      • Yes (Score:1)

        by mindstrm ( 20013 )
        I also have worked in an RF lab, and tested the office microwave ovens, which were definately cheap. They did have SOME leakage, but it was nowhere near the power of the wifi and similar signals we were working with.. extremely unlikely for it to cause inteference.

        Yes, leakage happens around the door and window, but not if they are designed and built properly.

      • 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.

      • The wavelenght of a microwave is about 11 cm. Holes in the shielding smaller than about 1 quarter wavelenght cannot be penetrated by the microwaves: they are all reflected.
        Most microwaves actually have tamper proof door locks; if you try to jam them while the door is still open, the fuse is blown instead of radiation being emitted.
        If you don' t believe it: look it up yourself or dissect your microwave to see for yourself.

    • Actually it is more likelly that it will be a problem with Bluetooth because it operate at the exact same frequency as the ovens (1.4 GHz)
  • ...will finally be able to use Chris to wirelessly kill Lois in the new Family Guy season.
  • Microwaves DO interfere with WiFi. Case in point, when my wife is cooking here egg rolls in the microwave, my WiFi signal drops to zero. The microwave finishes and poof...11mb connections. If I can connect, I either get really really really SLOW connections, or I have to be ontop of the AP....literally! 2.4 GHz is what many call the garbage band...you got cordless phones, cellphones are close to it, microwaves, WiFi (both a and g), video units, intercoms, and just about anything you can think of all fighting for spectrum. 5GHz is going to be no better. I am waiting to see if the either start cleaning up 2.4 GHz which would be REALLY hard, or ramp up or down the frequency. I thing the 1.2 GHz ham band would be a good candidate for refarming. From Ham use, it's not even close to being useful for public service and even if there are radios, there's usually noone there even during rush hour. The range would be a bit better then 2.4Ghz and they could totally reserve it for WLANS of all types. As a ham, I am not usually in favor of killing a band (more in favor of addding ham bands), but almost no friends of mine work 1.2GHz and I am sure all of them would like a better WLAN connection! ;)

    • That microwave oven of yours is leaking. Your brain is well done by now.

    • As a ham who works satellites I would not just casually give away the 1.2 Ghz band. Rather, I would like to see WiFi move up to the 5 Ghz band rather than 1.2 Ghz. While I sort of agree that 1.2 Ghz is underutilized, 2.4 Ghz is where the primary downlink for AO-40 [amsat.org] is located, and used worldwide. The 2.4 Ghz downlink suffers from interference by microwave ovens, and increasingly WiFi appliances, as well as other services near the band. 1.2 Ghz is a good frequency to uplink to the bird, if you have the equipm

  • Noise (Score:2, Interesting)

    by FrostedWheat ( 172733 )
    Is the noise generated by an average microwave really that bad? Maybe it's just mine but it dosen't affect any of my wifi cards at all.

    It does however manage to wipe out the video sender which runs on 2.4GHz aswell.
  • the team had hoped their study would help create more efficient radar systems for the military.

    They said they didn't achieve what they set out to - I wonder if they came up with anything else.

    In this case, will the company get patent rights for commercial application since it was a military research investigation...
    apparently if it's being reported.
  • There are already 802.11 video transmitters [smartsightnetworks.com] out there... but they're a bit expensive.
    My x-10 audio/video sender gets nuked by my microwave, as does my linksys 802.11b access point's transmission signal. The microwave is brand new, and top of the line.
    Incidentally, even my neighbours microwaves nuke my signal (I live in a condo).
  • But can I use the within my foil hat design to stop them probing my mind?

    Rus
  • I know when I first got my WiFi, I couldn't figure out why I had such a bad signal. The AP was behind the microwave, with a wall in between. (New home, paper thin walls) I remembered that microwaves cause interference and I moved it to the other side of the computer room. The signal went to full. It is about time they did something about it.
  • How to build a MASER with your microwave oven using ordinary magnets.
  • I have the same problem, but with both devices. Was able to solve the phone interference by swithing channels on the WAP (unless you're standing on it and talking). The microwave is about 10 ft from the laptop I use to serve up my MP3's from my linux server, and it takes it out of service everytime. I've thought about switching to 802.11a, but afraid the signal level from oposite ends of the house might be an issue. Invariably, someone will decide to make popcorn on Friday night when we're listening to
  • Commission Apple to come up with a case for microwave ovens based on the TiBook casing.

    Voila - instant Faraday Cage.

  • Very interesting (Score:3, Interesting)

    by Anonymous Coward on Sunday November 23, 2003 @09:11AM (#7541660)
    I am sitting here testing a forward error correcting file transfer protocol and in a fit of boredom I turn to Slashdot. This article is very timely as I needed a way of injecting some noise into the system.

    Test environment:

    IBM T-21 laptop with Orinoco gold 802.11b wireless PCCard.

    SMC di-pole wireless AP (Forget the model number) which in testing has turned out to be a very good AP with range exceeding all of the standard 802.11b AP/routers we have tested.

    The test file is 4MB in size and we are sending it in both directions across the wireless network with and without error correction. No suprises here, with a perfect signal the file with error correction takes slightly longer to arrive due to the increase in size. Transfer rate is about the equivalent speed to a network file copy and slightly faster than ftp on the same network.

    After reading the article I moved the laptop to within two feet (as measured from microwave to the antenna of the access card) and re-ran the tests.

    With the microwave off, all tests ran as normal, with the microwave on I get the following results.

    Network file copy: Failed with network timeout, network not available
    Our FEC file copy: completed but very slow
    Our Non-FEC file copy: failed due to loss

    Time to look closer. I fired up the Orinoco client tools for site monitoring which allow you to view various network conditions. With the network off the signal was typically at -72db and the noise was measured at -92db. With the microwave on the signal would range between -72db and -60db and noise would range from between -90db and -63db. With the microwave on the signal quality would range between non-existent and 'good'.

    Running our tests produced the following results.

    Microwave off:

    -------- Transfer Summary --------
    Data bytes: 45638341
    Elapsed time: 91.93 seconds
    Effective rate: 3971.44 Kbps
    Packets lost: 11
    Packets sent: 46853
    Requested Rate: 10000
    Actual Wire rate: 4370.70 Kbps
    Average loss: 0.02%
    Average RTT: 35.88 ms

    Microwave on:

    -------- Transfer Summary --------
    Data bytes: 45638341
    Elapsed time: 390.71 seconds
    Effective rate: 934.47 Kbps
    Packets lost: 3225
    Packets sent: 50067
    Requested Rate: 10000
    Actual Wire rate: 1098.95 Kbps
    Average loss: 6.44%
    Average RTT: 85.03 ms

    The two important numbers are effective wire rate and packets lost. Keep in mind that repeated attempts at shell based file copies failed completely as did a non-fec file copy using udp and tcp. This looks like a problem that really does need a solution, at least for 802.11b.

    Oh, and my microwave is a two year old top of the line KitchenAid built in so it is surrounded by an additional metal frame and all of the wooden cabinets (and whatever they contain). Even with all that extra shielding it was massivly effecting the wireless throughput and presumably anything else within range, scary, I won't be standing too close to the microwave from now on when its on thats for sure.

    • Assuming the noise is all coming from the microwave, your peak noise reported is still less power (-63db) than the maximum strength signal you get from your network (-60db).

      I wouldn't be too concerned with getting cooked.

  • Hey, I already got Wi-Fi enabled with my crappy $100 Radio Shack unit that lets me broadcast the downstairs ReplayTV to the upstairs TV. Sure enough, the microwave makes loud and annoying static for it.

    However, if the microwave simply supported an IR remote, then I could reprogram one of my hackable Radio Shack remote's buttons to pause the ReplayTV and mute the TV everytime I pushed the "cook" button. (Hmmm, I think I would use Shift-Freeze to be the "cook" button. :-)

  • The full article uses the phrase "a specific pattern". The original /. poster says "patterns" plural. The actual paper covers precision adjustment and the methods and instumentation discussed in it show that there are quite a few variations, so the poster's capsule accout actually corrected an oversimplification in the popular press. Slashdot just committed accurate news reporting. What you want to bet that'll happen again?
    This is one of those cases where highly trained professionals with universi

  • Try changing the channel (Score:3, Informative)

    by adrianbaugh ( 696007 ) on Sunday November 23, 2003 @12:24PM (#7542534) Homepage Journal
    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.

  • Why should the microwaves be redesigned? (Score:2, Funny)

    by Anonymous Coward
    WiFi is an unlicensed, "Part 15" system. It has to accept all interference from all sources.

    I'm not going to pay $2 more for a microwave just so people who can't figure out how to run ethernet can avoid dropped packets every time I warm up my cocoa.

    JD
  • Every microwave I've ever taken apart just has the series of control parts (timer, switches, fuse) and the magnetron\waveguide assembly part of which is a feedhorn pointed directly into the cooking cavity.That's all it is. The metal chassis of the microwave reflects or grounds out the RF. The problem is not only does a microwave operate very,very close to the 2.5 gig band just like 802.11 spec it also has a crummy "see thru" screen on the front with holes punched out just slightly smaller than 1 or 2 mm. J
  • ...will I still be able to make an EMP gun from such a microwave?
    • yes but you can't do anything usefull with it.
      The most obvious targets procude lots of GHz anyway inside the box, and ar shielded pretty good anyway.
  • I worked out a microwave interference problem - it was the switching power supply that was causing it. Needed more common mode filtering.
  • These researchers are a bunch of complete idiots. Microwave ovens are DESIGNED to operate over a varying range of frequencies. BY DESIGN.

    The reason for this is that the variations in frequency mean that there are fewer "Hot Spots" in the oven where all the microwaves pass through, causing food to be cooked in a non-uniform manner.

    The other reason that I know these people are not as intelligent as they could be is that magnetrons are modulated at 50/60 Hz specifically. By removing this modulation many of t
  • The proper solution to the microwave interference problem is to just make the microwave a proper client to the WLAN and have it do RTS/CTS before each blast!
  • Here's their research [umich.edu], or some of it anyway. Oh, also here. [umich.edu]

    The US and UK came out with 10 centimeter radar in 1943 to sink U-boats. It turned the war around for us! God Bless you Magnetron.

    Anyway, that's more than 60 years ago. I've still not seen anything these guys have done that someone else should have already come up with by now.

    High frequency EM waves also travel around anything metal (skin effect), like sheet metal siding and power lines.

    Look at the headquarters for NORAD. It's deep inside a

  • if you change the antenna on a magnetron (for instance if you drive a tuning screw into the waveguide) you can change the frequency a bit, but also increase the noise on the sides of the peak enormously. Now recognise that the cooking space in a microwave oven is an integral part of the waveguide, and you will realize this 'reseach' is very hypothetical.
    I wonder how they would have fared if the used complete micowave ovens instead of just olde magnetrons from them. Just putting in metal racks /etc will incr
  • Just do all of your wireless networking within a gigantic Faraday cage!!!
  • ... you can show me how to hack my 802.11 stuff so it'll toast Pop Tarts and those little Red Baron pizzas.

    (The cup holder already works great)

  • The paper said they used a DC power supply, and only speculates about what would happen with a real el-cheapo microwave oven power supply.

    This matters because you can shift the frequency of a magnetron slightly off nominal resonance by varying the power input.

    Microwave ovens ship with the crudest imaginable high-voltage source and the magnetron voltage isn't even approximately constant.

    If the oven's frequency is bouncing around the spectrum, other users may not be able to stay out of the way.
  • Instead of investing thousands of euros in a Faraday shielding, I can just turn on the microwave and disrupt annoying cellphone calls!

    I think I will make a business of selling this 'incredible mobile phone jamming device' to restaurants and so.
  • This should only be done as a desperate last resort. If you have neighbors who ruin the quality of life in your home because they insist upon playing loud music on a disc player (or any other electronic device) and the law refuses to help and you cannot move because property values are destroyed by the niose pollution, you can fight back with microwaves. Make a parabolic chamber about 1 1/4" thick. It should consist of two flat parabolas with a focal length of about 11/16" and 20" long. You will have a
  • Comment removed based on user account deletion

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