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I'm curious. I think I'm confused because I don't really understand the way ionizing radiation works.

So the Wifi radiation passes through my body, but has no ionizing effects within my body?

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Curious is bad with electronics! Things get fried. [I speak from experience.] –  Annonomus Penguin Nov 29 '13 at 3:14
    
@AnnonomusPenguin: At the same time, all electronics, and all technology have ultimately been created as a result of curiosity. Don't put down people's attempts to learn. –  whatsisname Jun 8 at 21:52

3 Answers 3

up vote 27 down vote accepted

Ionizing radiation is a little complicated, so stay with me as I try to explain it in an easy way...

When talking about ionizing radiation, scientists talk about energy levels. But this refers to the energy level of the photon of electro-magnetic energy, not the quantity of photons. All electromagnetic energy (radio waves, light, x-rays, etc.) can be thought of as either a wave or a particle. The shorter the wavelength, the higher the energy. So when scientists talk about the energy level of ionizing radiation they are talking about the wavelength.

Here's a wiki page showing the electromagnetic spectrum.

Only the higher energy waves are ionizing. Specifically, stuff in the UltraViolet and above (X-Rays and Gamma Rays). Stuff in the visible spectrum and below (including radio waves and microwaves) are non-ionizing.

Wifi signals, which are in the 2.4 to 5.something GHz range are not ionizing.

I should point out that if something isn't ionizing then simply having more of it (at the same frequency/wavelength) is not going to make it ionizing. It doesn't work that way.

Non-ionizing radiation can have an effect on your body, however. It can cause heating. A microwave oven, for example, operates near 2.4 GHz and obviously heats up food. But a microwave does not ionize food.

But let's put all of this into perspective. A typical WiFi device can output about 0.1 watts of energy. A typical LED flashlight will output about 1 watt of light. They are both non-ionizing energy and will have a similar heating effect. The main difference is that the flashlight will heat you 10 times faster and in a more concentrated spot on your body. Yet you wouldn't think twice about shining a flashlight on your hand-- and you shouldn't worry about it.

On the equator at noon the sun puts out approximately 1,000 watts of energy per square meter of ground. The vast majority of this is non-ionizing (the UV part is ionizing). This is about 1,000 times more "radiation" than the LED Flashlight, and 10,000 times more than the WiFi signal. You run more risk going outside than sitting in your house playing on the iPad. Even so, just put on some sunscreen and enjoy the outdoors!

Some electro-magnetic radiation will pass through your body. The higher wavelengths and lower wavelengths in particular will pass through more easily. But passing through means that their energy did not interact with your body. It's the stuff that doesn't pass through that you're interested in. Even so, what I said above assumes that 100% of the energy gets trapped in your body and it still isn't an issue.

Conclusion:

A WiFi signal is non-ionizing and is thousands of times less energy than going outside in the sun. Don't worry about it. It's not going to harm you.

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Very nice answer, examples are sometimes more effective than facts for most people, although skeptics will do what they do. :) –  Kenny Robinson Mar 15 '12 at 5:14
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+1 for "just put on some sunscreen and enjoy the outdoors!". Priceless in an EE site :) –  clabacchio Mar 15 '12 at 7:14
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While I agree with your descriptions, you are ignoring the possibly different effects of different wavelengths. The 5 inch wavelength of WiFi and microwave ovens can do very different things to us than light with its waves 250k times smaller. There is still much debate and conflicting studies about microwave and longer radiation on the human body. This is not a resolved issue. Saying catagorically to not worry about it is irresponsible because we don't currently know for sure. –  Olin Lathrop Mar 15 '12 at 13:13
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There is still legitimate scientific uncertainty. Just because we can't see a immediate mechanism for microwaves to cause harm other than by heating doesn't mean it's not happening. There was a paper in the journal of the American Medical Association (jama.ama-assn.org/content/305/8/828.full) that showed brain activity linked to cell phone proximity. Even they admit they don't understand the mechanism or what it means, but it shows we don't understand everything. Long time ago microwaves were linked to increases in cataracts, so maybe we should be careful until this is understood. –  Olin Lathrop Mar 15 '12 at 14:27
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@OlinLathrop That study only involved 47 people and didn't control for the effect of the phone itself getting warm due to use and warming up the area of the head near the ear-- heating unrelated to RF energy. It is known that metabolism increases at higher temps, so the results of their experiments are not surprising. You'd probably get similar effects by just placing a small non-electric heat pack on the side of your head. While you're correct that there are lots of things we don't know, I prefer to not stress out about it. After all, we can't explain gravity either. –  user3624 Mar 15 '12 at 15:05

Your Wi-Fi equipment most likely does not emmit ionizing radiation. I suggest to read ionizing radiation in the Wikipedia for more information on that topic.

To roughly test whether the signal of a Wi-Fi device can pass through your body, just cover its antenna with your hands and test with another Wi-Fi Device whether the receive signal strength declines. Wi-Fi uses Frequencies around 2.4 GHz or 5 GHz (802.11a). This frequencies are non-ionizing (see non-ionizing radiation in the Wikipedia for a nice graphic of the spectrum). The radiated energy typically is in the hundreds of milliwatts and by most considered to cause no health effects.

But as there even are (very few) people allergic to water, there also may be people that experience electromagnetic hypersensitivity...

I don't think, your health is likely to be affected by Wi-Fi. But your network security may be depending on whether you use unencrypted protocols.

P.S.: Some hyperlinks are cripled because of this sites anti-SPAM measures.

Edit: You really should read the faster answer above mine :-)

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WiFi uses the spectrum around 2.4 GHz because this is one of the ISM bands, which allows use without a licence.

The ISM band in this range exists because microwave ovens operate at 2.5 GHz, because this is the resonant frequency of water, and energy is absorbed to a large degree by water molecules, such as the ones in the skin.

The radiation is thus caught in the outer layers of the skin, which is fine because it is the same thing it already does for sunlight.

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You're sliding off topic here...you didn't even mention ionization –  clabacchio Mar 15 '12 at 8:22
    
The other answers already did, my point was to highlight the special property of this band. –  Simon Richter Mar 15 '12 at 8:34
    
2.5 ghz is not the resonant frequency of waters. This is an often cited, but false, claim. Microwave ovens work due to dielectric heating. –  whatsisname Jun 8 at 21:58

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