OT: uneven cooking in microwaves

Heated in a checkerboard pattern.

I can't remember detail=

When I put it in my mouth there were alternating parts that were warmer and colder.

Yes, one would think a rotating carousel would get rid of all that, but it didn't.

all nukes have reflectors around the food, they're called the walls.

Stirrers are reflectors, but as they rotate they vary the internal rf pattern, moving hot & cold spots about, thus improving heating evenness. The best nukes have both turntable & stirrer.

that's not the cause. The outer food absorbs the microwaves leaving less to heat the centre. This can be somewhat solved by going to a lower frequency eg 915MHz, but 915 isn't used for domestic ovens generally because, being longer wavelength, it's not absorbed much by small food items.

yes. But the cooker would cost a lot more.

for once I think you're right. Cook mostly with 915MHz but switch to 2.45 if the food is small/light.

I don't think that's legal in the UK, certainly caused a scandal before now.

NT

True. I would like to find better data.

That graph shows the atmospheric properties between 1 and 3 terahertz, not gigahertz, so I don't really see how it is relevant.

Well, we both seem to be having trouble producing good quality data to support our positions, so maybe there is some point.

I found an old electronics magazine that had an article about building a "macrowave oven" that would cool food electronically. It used a superconducting device called a "krystron" that works best in a vat of liguid nitrogen.

Although my device used negative entropy.

Before class one day, a student had the idea that light doesn't really exist but is an illusion caused by the lack of darkness. This led to the invention of the DED (dark emitting diode). Somehow I don't expect a DED flashdark to recharge its batteries.

Talk to the molecules in the food and threaten them with dire consequences if they don't calm down :-)

(written while remembering some much more serious nonsense)

I've heard about those. With a fuse in each plug, so the higher capacity is safe.

I needed one of those "double male" cords once (for the purpose of running a hardwired appliance from a generator). I was so careful that it was actually saver than normal operation.

I've gotten so used to a DVR that when I miss something, I'll often look for the "replay" button on the car radio.

That paper has nothing whatsoever to do with absorption by water. If you search the pdf the word "water" does not appear in it at all.

The following document is much more useful:

This shows clearly that the 2.45GHz band is very suitable for long-range radio transmission as it has very LOW absorption due to water vapour. There is no hint of a resonance around 2.45GHz in water vapour.

John

Yip, we did away with individual circuits a long long time ago. It's unbelievable you still have unfused plugs. Clearly a table lamp will use a thinner wire than a heater, so it has to have a smaller fuse. So either you plug it into a different outlet (very inconvenient), or it's not properly protected.

Explain.

That reminds me - I have a two minute memory of everything I've heard. I'm quite surprised when I meet someone who doesn't. They seriously can't spool back and listen to what was said a minute ago.

Anaximander would approve.

It's those damn dipoles; they are gender fluid or something.

About the only broadcast TV I watch is some of the PBS programming. I find myself looking for the pause button when I need to take a leak.

We'll see...

But has no spectrum of absorption at anything even remotely like enough of a resolution at around 2.4GHz. so it isnt possible to see if there is a peak at 2,4GHz

Its as useless as your original second link.

That?s nothing even remotely like food being heated in a microwave.

You can do that with live TV if you are watching with a PVR.

There can be a number of reasons.

The one most often mentioned is the lack of a turn table or some kind of deflector to spread the ?pattern? evenly in the food.

Certainly these are valid but I doubt any but the cheapest ovens lack either a turn table or some simple deflector system these days.

If the food, especially meat, has areas of fat they will heat differently to lean areas as the fat has a dipole structure and that is more responsive to the effect of the EM radiation. It is a myth it is only water which is heated, a number of dipole structures in food respond to EM radiation, including water, fat, and sugars (or compounds made of sugars). If the food was frozen, as it defrosts, once once part is defrosted it will heat more quickly than a still frozen part.

The local hot spots can help the overall cooking process, which is partly why rest time is sometimes recommended.

I don?t especially like cooking with a microwave. No real reason. I certainly don?t think they are dangerous etc. I use one to heat milk for coffee, defrost things sometimes, initially cook baked potatoes before crisping in the oven (we have a combi microwave / fan oven ), plus it makes good porridge.

That is true about EM radiation. To even out the heating you have to allow convection to take place as outer surfaces absorb faster. A defrost cycle calls for long times at low settings, otherwise you cook the outer part and leave the center frozen.

EM is not that different from conductive heating where you put item on hot surface. Outer part heats faster.

Yes, I do that all the time. Someone comes into the room and interrupts - I pause it. Confuses the hell out of people if it's the news, and they later see the clock on the screenm when it's been time shifted about 10 minutes.

That's with an old HDR Fox-T2.

Yes it is. The document states: This Recommendation provides methods to estimate the attenuation of atmospheric gases on terrestrial and slant paths using: a) an estimate of gaseous attenuation computed by summation of individual absorption lines that is valid for the frequency range 1-1000 GHz;

So are you are suggesting that the International Telecommunications Union are incompetent and don't know about an absorption line at 2.45GHz? The starting point of the document is the known absorption lines of all the relevant atmospheric gases including water vapour. If there was an absorption line at 2.45GHz it would be shown in that document.

Its part of the story. Various people have asserted that the 2.45GHz band contains a water-molecule related resonance and one claim is that this makes the band unsuitable for outdoor communication. The ITU document makes it very clear that the water molecule itself does NOT have any such resonance of its own and that atmospheric attenuation is extremely low in this band.

Clearly there are other loss mechanisms at work otherwise the food would not get heated, but they are not narrow-band water molecule resonances centred on 2.45GHz.

Have a look at:

Please don't suggest that the 2.45GHz absorption line is so narrow that it doesn't show up on the graphs. I have measured the frequency of a microwave oven with a spectrum analyzer while heating a glass of water. The frequency wanders over much of the 2.4 to 2.5GHz band as the turntable rotates. If there was a very narrow absorption band that doesn't show up on the graphs I linked to it would be so narrow that the frequency of the microwave oven would miss it much of the time.

John

Good for scrambled egg too. Put the beaten egg in a glass bowl in the microwave: take it out every quarter minute or so and stir it with a wooden spoon until the desired consistency.

That?s not the food cooking we are discussing.

Food is a lot more than just water.

Nope, that atmospheric gases are nothing even remotely like FOOD.

It isnt even that.