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Old 01-01-2010, 03:32 PM   #1
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A Little Microwave Science (Very little)

There was recently a thread where the topic of microwave ovens became a source of contention. I have some scientific background and physics background as well. As a matter of point, I have a B.S. in Electrical Engineering Technology. It's what I'm trained in. And with that said, I would like to share some little known info about microwave radiation.

First, microwave energy, as the stuff emitted in a microwave oven, is the very same kind of energy emitted by your cell phone, by television transmitters, by radar, by lasers, by radio antennas, and a host of other common place facets of our modern civilization. Even the older computer screens and televisions, i.e. cathode ray picture tubes, emitted the same kind of energy. And what is this mysterious stuff anyway? You might have heard of it on the show Ghost Hunters, where it's referred to as EMF, or as an electro-magnetic-field.

Electro-magentic fields are produced any time an eletric current passes through a conductor, such as a piece of wire. So when you are turning on the lights in your home, you cause electro-magentic fields to radiate throughout your home.

The frequency of the field, or how many times it goes from its positive peak to its negative peak in one second, determines how it is percieved, and what it's called. Also, if you map that field postive-to-negative journey on a graph per unit time, you find that each frequentcy has a distance that it travels in each second before the cycle is completed. This veries from very long waves, in the order of meters of length per cycle (or much greater), to very small waves, in the order of microns per cycle. The higher the frequency, the shorter the wave. Microwave energy is electro-magnetic waves of a high enogh frequency so that the physical distance of each wave is measured in nano-meters, hence the name.

How does the eletro-magnetic energy of a microwave create heat? It has to do with molecular structues wherein the mloecules have a atoms with a characteristic called a dipole. In such a molecule, the direction of rotaion, of electrons around the nucleous of an atomic particle reverses when it is influenced by the microwave energy. This causes motion within the molecule, which in turn creates friction, which turns the microwave energy into heat energy. Every material that has a dipole has a specific frequency range that will cause this energy change. The microwave oven uses a kind of tube called a magnetron to create the frequency emitted and radiated at the food, or anything else in the oven. The magnetron is a tunable tube and the fequency is carefully tuned so that the energy affects water. That's why so many things that are placed in the oven are unaffected, such as glass, ceramics, paper, and other items. But foods have a high amount of water in them, which heats and cooks the foods containing them. The cellulose in plants, and protiens in meats are really not affected by the microwave energy. Rather, they become heated by the water that is part of the meat, or veggie, or soup, etc.

It just so happens that the frequency of microwaves is similar to that used by the military in radars, hence the early name of radar range.

A unique feature of electromagnetic energy is that when it passes accross a conductor, such as metal, it creates an electric current in that metal. This is called induction. It's what makes the steel or cast iron pan heat up on an induction cook top. That is the same energy as produced in a microwave, but at a different frequency. When you place metal into a microwave oven (say a DVD disc that's coated with a metalic film), the microwve energy is creating powerful electrical currents within that metal so that a very high voltage is created. There is a difference between the voltge on the disc and that of the surounding metal shell of the appliance that quickly grows strong enough to create mini-lightning bolts within the applieance as the voltages try to equalize. It makes a pretty dazzling display, but can harm the appliance. That's why you can't place a metal bowl, for instance, into a microwave oven and cook in it.

Microwaves don't change the DNA or atomic structure of elements or compounds. They do heat water, and very efficiently. And so why do radar guns that cops use cause sterility if not handled with care? Well, the guns' business ends were somtimes pointed at the wrong area of the human male anatomy, and the microwave energy tended to cook those little critters responsible for fertilizing eggs, and the organs that produced them.

Are microwaves dangerous? Certainly, if misused, or used carelessly. They are powerful electro-magnetic waves that can interfere with sensitive electonic devices, such as pacemakers, hearing aids, and other low current devices. If the oven leaks energy, then it can cause problems. But just as the electro-magnetic energy given off by your television isn't going to kill you, niether is the energy emitted by a micro-wave oven.

This was a very simplistic explanation of microwave energy. Anyone who wants to be more specific, and show documentation is welcom to join in.

Seeeeeeya; Goodweed of the North


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Old 01-01-2010, 11:18 PM   #2
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There was some website I ran across that had videos of all sorts of things being
microwaved, from peeps to cds to small appliances. Some were really impressive!


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Old 01-03-2010, 05:15 PM   #3
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Re Goodweed of the North - while your answers are correct in large part, there are some errors. (I am a microwave scientist and this is my 50th year working with microwave ovens and microwave heating.) Here are a few corrections:
1. common microwave wavelengths are not in nanometers but in millimeters (mm) or centimeters (cm) - for example, the free space wavelength of the microwaves generated by domestic microwave ovens is 12.2 cm @ a frequency of 2,450 MHz +/- 50 MHz.

2. a cooker magnetron is not tunable but rather is a fixed frequency tube constructed to deliver microwves in the frequency range noted above. By the way, the frequency was not chosen because water heats best at this frequency - it is in fact a compromise. Water couples best with microwaves at 22 GHz at room temperature, but that wavelength is so short it would be useless for cooking.

3. Dry Cellulose will heat and burn in a microwave oven, especially when hot - that's what makes drying wood with microwaves or radio frequency dangerous - it leads to fires. Water and dipoles are not the only heatable materials or mechanisms. Oils, for example will heat, even though their dielectric properties suggest they won't.

4. Induction heating is due to the magnetic portion of the electromagnetic waves, and at lower frequencies than a microwave oven; food cooks by interacting with the electric field component.

5. the comment on sterility from microwave radar is just wrong - there would have to be significant heating of the gonads to do that - and that doesn't happen. I know what microwave heat feels like - it also takes time and is not instantaneous like a flame.

6. It is also incorrect that microwaves interfere with pacemakers - that was a tale that came about more than 20 years ago and no microwave oven interference was ever reported and verified. However, those older pacemakers did have reported and verified interference problems due to automobile ignitions, lawnmower engines and more. Today's pacemakers are protected from stray radiation.
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Old 01-03-2010, 05:21 PM   #4
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Thanks for the info microwaveguru.

Any information on the fears some people have that microwaving food changes it in some way to make it hazardous to your health?
"If you want to make an apple pie from scratch, you must first create the universe." -Carl Sagan
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Old 01-07-2010, 07:07 AM   #5
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Thanks for the info, microwaveguru. I am much better versed on electric componants than on microwave theory. For instance, I'm not even sure if it's a magnetron or klystron that's used to create the microwave energy, or if waveguides are used to direct that enery. I have a basic understanding of electromagnetic radiation at best, but know that works wonders in transformers, induction stoves, and other such applications, not to mention radar, antennae, lasers, and masers.

Seeeeeeya; Goodweed of the North
“No amount of success outside the home can compensate for failure within the home…"

Check out my blog for the friendliest cooking instruction on the net. Go ahead. You know you want to.- http://gwnorthsfamilycookin.wordpress.com/
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