Microwave oven leakage question

[TheNiceGuy]

Hi all
A couple of years ago I smashed the front glass out of our microwave. IIRC it was tempered tinted glass. The perforated metal sheet behind it was slightly dented, but otherwise undamaged, and none of the 1/8 (?) inch holes were compromised. I took it to a small appliance repair shop locally and they didn't seem to think it was a problem, and we could go on using it safely.
Besides making me a bit paranoid around it, it seems to work OK.
However, whenever we use the microwave it knocks our 2.4 cordless phones out, as well as wireless internet.
IIUC, these all use 2.4GHz, and therefore the interference. But I am wondering if that is normal to have the microwave leak enough to knock out other electronics.
For the life of us we can't remember if the interference was always there, or started after the broken glass.

Any ideas?

Thanks!

 

[C1]

You gotta be kid'dn.

Looks like a job for Bill Gaatjes

 

[PsiStar]

No. It is not normal to interfere with wireless devices.

So I guess the responses in the other thread you started was inadequate?:whiste:

Maybe make a poll asking who would use this microwave if it was theirs?

 

[Murloc]

microwaves aren't healthy anyway, they modify proteins and the food isn't genuine anymore.
Better that than risking to cook your brain

 

[TheNiceGuy]

No. It is not normal to interfere with wireless devices.

So I guess the responses in the other thread you started was inadequate?:whiste:

Maybe make a poll asking who would use this microwave if it was theirs?

Yes, absolutely inadequate. IIRC, I remember that OLD thread and there were a lot of paranoid people on it with no actual expertise in the described problem. The one guy who claimed to have done extensive work with industrial microwave technology said there was nothing to worry about at all.
I'm double checking here regarding signal interference. I and everyone else I know has no idea if that is normal or not. As I said in that other thread a licensed appliance repair shop took a look at it and said there was nothing to worry about.
Making emocon faces on this thread and rude condescending comments doesn't answer the question at all.

Anyone with actual expertise in this area?

 

[PsiStar]

Yes, absolutely inadequate. IIRC, I remember that OLD thread and there were a lot of paranoid people on it with no actual expertise in the described problem. The one guy who claimed to have done extensive work with industrial microwave technology said there was nothing to worry about at all.
I'm double checking here regarding signal interference. I and everyone else I know has no idea if that is normal or not. As I said in that other thread a licensed appliance repair shop took a look at it and said there was nothing to worry about.
Making emocon faces on this thread and rude condescending comments doesn't answer the question at all.

Anyone with actual expertise in this area?

I *told* you very nicely that continuing usage of this device is a bad idea. It is dangerous. I would never allow anyone's child anywhere near a questionable device much less one as clearly damaged as yours. Replacement is inexpensive. I do not know you nor likely ever will. My 1st born is not likely to ever know you much less anything else. I do not own stock in any manufacturer of microwave ovens. Therefore, I have nothing to gain nor to lose if you do or do not replace this damaged unit.

The ease in which you are offended is definitely clouding your judgement of your personal health as well as those you love.

 

[esun]

Interference is not unusual: http://www.wi-fiplanet.com/tutorials/article.php/3116531/Dueling-with-Microwave-Ovens.htm

If the Faraday cage was not compromised and you are short on cash, I would not worry. However, a new microwave is around $100 so it's a pretty cheap fix if for nothing else but piece of mind and cosmetics.

 

[TecHNooB]

I have an MSEE and have designed RF amplifiers & components from 1.6 MHz to over 200 GHz ... for a long long time. I was quoted in the NY Times a couple of decades ago relative to a microwave tower emissions.

I *told* you very nicely that continuing usage of this device is a bad idea. It is dangerous. I would never allow anyone's child anywhere near a questionable device much less one as clearly damaged as yours. Replacement is inexpensive. I do not know you nor likely ever will. My 1st born is not likely to ever know you much less anything else. I do not own stock in any manufacturer of microwave ovens. Therefore, I have nothing to gain nor to lose if you do or do not replace this damaged unit.

The ease in which you are offended is definitely clouding your judgement of your personal health as well as those you love.

200 GHz? You must be loaded.

 

[futuristicmonkey]

200 GHz? You must be loaded.

Someone's gotta design all the magical hardware inside spectrum analyzers

 

[TecHNooB]

Someone's gotta design all the magical hardware inside spectrum analyzers

That's not really 200Ghz now is it

 

[aceO07]

200 GHz? You must be loaded.

I believe he's talking about radio frequency and not processor speed...

Quick search shows that range is used in radio astronomy.

 

[PsiStar]

That's not really 200Ghz now is it

To be exact, 217 GHz pyramidal horn machined from gold & focused on a ZnSe lens. The "big" end of the horn was ~3.7 x 2.7 mm, 36 mm long.

Most of my bandwidth is below 100 GHz involving intended and unintended radiated RF as well as SI. Guess what I use multi-processor systems for?

I do have experience with EMC/EMI. And, *I* might use a damaged microwave oven, but I would not let anyone else use it. In my home I have 2 different cordless phone systems, WLAN, Bluetooth, & 2 very different microwave ovens ... an el cheapo & a ridiculously expensive Viking. I have not run a test as written about in the article as linked to by esun. Therefore I cannot say that I experience no interference as it only stands to reason that there is "some". But I experience nothing at all like the OP.

 

[futuristicmonkey]

That's not really 200Ghz now is it

I'm a power systems guy. I'll have my BSEE in May -- EM labs are fun, tho

 

[TecHNooB]

I'm a power systems guy. I'll have my BSEE in May -- EM labs are fun, tho

cool

the thing about spectrum analyzers with really high bandwidth is that they use random interleaved sampling (not real time). basically they sample the response from a slow squarewave and combine the samples to form 1 really high sampled wave (might be a step but i don't actually know). this process also has the benefit of adding less noise to the response because the A/Ds don't have to work as fast.

 

[futuristicmonkey]

cool

the thing about spectrum analyzers with really high bandwidth is that they use random interleaved sampling (not real time). basically they sample the response from a slow squarewave and combine the samples to form 1 really high sampled wave (might be a step but i don't actually know). this process also has the benefit of adding less noise to the response because the A/Ds don't have to work as fast.

Good to know, thanks. This sounds like the glitch capture feature on Fluke 190-series Scopemeters (I used one at a previous summer job - a beautiful 199C). I could never figure out the use for such a feature and I always disabled it. The max frequency I was ever looking at was ~680kHZ (emi given off by a variable-frequency drive) and the sampling rate of the 199C was more than enough to capture the signal.

Anyways, to get back on-topic; it's my understanding that you would instantly feel the microwaves cooking your skin if any of it leaked. The US military uses a device to irradiate an area with microwaves (of lower frequency) to cause people to disperse from the area. With the higher frequency of uwave ovens I'd expect the radiation to penetrate even less into a human's body (the dispersion device's "rays" only penetrate to 1/64th of a mm, IIRC) due to a decreased skin depth corresponding to higher frequency.

Edit: I only addressed whether it was safe to operate. It sounds like it's "leaking" enough to interfere with your other wireless appliances yet not enough for you to physically feel it.

 

[PsiStar]

It is great to see what comes out of computer simulation can be validated in the real world. It means that the computers are fast enough, the software is accurate, AND that both the computer model & real world setup make sense ... it is easy to botch the real world setup to get bad results. Both the good & the bad add a lot to intuition.

My thoughts about the OP's microwave is just intuition. My intuition tells me that he could easily be missing some important piece of information ... unaware, doesn't see, doesn't recognize ... whatever. BUT just based on this most recent post & the gross amount of obvious interference he is experiencing VS mine of nothing at all noticeable ... it just seems like a very bad idea to continue using this damaged oven.

As a consultant, it is not uncommon to experience argument when my opinion or analysis does not agree with the desired answer. C'est la vie

I have never gotten into instrumentation design & only a slight amount of experience with solar power systems. Nothing with high voltage high power ... there are only so many hours in the day.

 

[silverpig]

Just use the stove.

 

[Jeff7]

My understanding is that the mesh screen is what keeps the microwave radiation in the cooking chamber - due to the radiation's wavelength, the perforated screen behaves as an opaque sheet.

And any microwave I've been around has interfered with 2.4GHz wireless signals. There's more going on in there than just a microwave emitter, namely a powerful transformer.

 

[William Gaatjes]

You gotta be kid'dn.

Looks like a job for Bill Gaatjes

Thank you for having so much confidence in me. I am flattered. :awe:
But i am just a mere human with limitations as everybody else.

Before i can give a credible answer just as every other person on this planet, i would have to do research into the wavelength of the used microwaves (electromagnetic radiation) some parameters to adjust for the behavior of the microwaves with the specific material used and the hole diameter to do a theoretical prediction. Or i would have to encounter the situation and learn from it as i go.

I have a microwave at home and i know the basic school grade science stuff. But i have no details at the moment other then stating that it is a whirlpool microwave with a perfect design. It has only 2 rotary buttons, 1 for time and 1 for power settings. But no fail.

If i would profile myself as a microwave developer, i would choose the hole diameters of the perforated metal sheet at a size that there is no hazardous amounts of radiation leaking for life standing in front of it. A trade off between visibility and safety.
However, there are also EMC standards about how much radiation may leak from an electrical appliance. I think the window was to comply for the rf (is radio waves or electromagnetic radiation) interference. Which the niceguy encountered when the glass was no longer there. Is it hazardous , i do not know because it depends on the design of the microwave and even flawed designs can by some human error still be compliant. Thus i would say, do not stand in front of the microwave if you get a horrible pain sensation in the exposed body part.
But when it comes to rf interference , see it similar as a home made radio transmitter that transmits with a few watts by mistake on all radio rf bands, completely knocking out all the radio receivers in the vicinity but without danger.

EMC :

http://en.wikipedia.org/wiki/Electromagnetic_compatibility

EDIT:
I read the other thread, and i agree with Psistar,Paperdoc, bobsmith1492 and Modelworks.
The OP must let the microwave be tested by a qualified testing center. If they follow the exact quality guidelines, i expect this oven to fail even if it would not cause damage to body tissues over time. Because usually there is an explicit limit set far lower then the real threshold for danger.
And guidelines are usually developed to protect people. Stick to those guidelines, they allow for tolerance in the safety zone.

 

[William Gaatjes]

microwaves aren't healthy anyway, they modify proteins and the food isn't genuine anymore.
Better that than risking to cook your brain

All burning or heating changes the proteins. When you heat something, existing atomic bonds can brake and new atomic bonds can form, changing the chemical nature. Microwaves or infrared waves or heat transfer through conduction or convection, it is all the same.

 

[dkozloski]

Appliance repair shops have a simple go/nogo power meter that is used to measure leakage from a microwave oven. This is not rocket science and the measurement is so simple even a caveman could do it.

 

[William Gaatjes]

Appliance repair shops have a simple go/nogo power meter that is used to measure leakage from a microwave oven. This is not rocket science and the measurement is so simple even a caveman could do it.

For safety yes, but is it also about rf interference and signal strength from the leaking radiation ? If all your wireless technology stops working every time you make dinner, it is no danger but it is a nuisance.
I mean some of the glass windows may have some metallic inside them or some thin metal coating.

 

[Modelworks]

The legal limit for leakage from a microwave oven is lower than the radiated power level limit of a cell phone. It used to be much higher but in recent years was made even more restrictive. There is a reason the law requires not 1 but 2 safety interlock switches on the door. If either fails the microwave will not work.

If you have a microwave that when turned on kills your wifi, then have that microwave checked because it is leaking more than the legal limit, especially if it effects wifi in another room or over a distance. A properly working microwave forms a complete cage around the power entering the cavity. Any damage to the holes in the mesh on the door, or the holes in the cavity and the microwave should be discarded. The problem with just shrugging it off when it knock out wifi is you don't know how much power it is leaking. All you know is it is leaking enough to knock out the wifi signal. It could be leaking 1 watt or 50 watts.

 

[William Gaatjes]

The legal limit for leakage from a microwave oven is lower than the radiated power level limit of a cell phone. It used to be much higher but in recent years was made even more restrictive. There is a reason the law requires not 1 but 2 safety interlock switches on the door. If either fails the microwave will not work.

If you have a microwave that when turned on kills your wifi, then have that microwave checked because it is leaking more than the legal limit, especially if it effects wifi in another room or over a distance. A properly working microwave forms a complete cage around the power entering the cavity. Any damage to the holes in the mesh on the door, or the holes in the cavity and the microwave should be discarded. The problem with just shrugging it off when it knock out wifi is you don't know how much power it is leaking. All you know is it is leaking enough to knock out the wifi signal. It could be leaking 1 watt or 50 watts.

I agree. The safety specifications must be met. If this is not the case then the microwave should not be used. The retina are too important to loose.

 

[oynaz]

Just replace the damn oven. If it knocks out phones and wifi, it is clearly malfunctioning. You don't need to be an expert in electronics to figure that out.