RF Energy Exposure

Even 802 GHz photons don’t reach 1 electron volt.

Are you concerned that your Wi-Fi router is causing cancer? Worried that your smart electric meter is giving you headaches?

There is a lot of pseudoscience, crazy theories, and false information out there when it comes to the effects of RF energy emissions. There are hundreds and hundreds of websites out there which use human paranoia and ignorance to their advantage by using just enough techno-speak. This kind of apocrypha uses the right kind of big words, acronyms, abbreviations, and clever imagery to sway the non-technical minded to their side. Some of them border on the supernatural, selling crystals and charms to guard against “electrosmog”. The erroneous example to the right (in regards to Wi-Fi frequency) is not only wrong, hilarious, but illustrates the common lack of understanding which is all too efficient in propagating nonsense. It is actually quite difficult to find real, accurate, scientific articles online on this subject due to the proliferation of vapid text presented as fact.

I’m not here to ridicule personal beliefs. You are free to believe what you choose, and if you choose to believe that your crystals help you in combating anything that makes you uneasy, including this “electrosmog”, then that’s great, but it’s still scientifically incorrect, unproven, immeasurable, and as far as I’m concerned, they belong in the same department as the HAARP and NEXRAD weather manipulation theories. Just google those for a real treat.

Ionization

One of the core fundamentals of understanding why exposure to RF energy isn’t just exposure to “radiation” (containing all of the negativity that word generally comes along with thanks to the 1950’s and Hollywood), is understanding the different energy levels involved in various types of electromagnetic radiation. Not all electromagnetic radiation is the same.

The electromagnetic spectrum is made up of many different types of radiation. Without getting into Quantum Electrodynamics, in current physical theory, electromagnetic waves are fundamental in and of themselves, but can be described as being made up of quanta called photons. Photons can be thought of as small packets of energy that make up the electromagnetic wave. Photons have an energy that is dependent on the frequency of the radiation. This is illustrated in the above diagram, and according to the formula that photon energy (E) is equal to Planck’s Constant (h) times the speed of light (c), divided by the wavelength (lambda). Since Planck’s constant and the speed of light are constants, the only variable is the wavelength (c/frequency), so energy possessed by photons in a given radiation must increase as the frequency of these photons increases.

It is common knowledge that gamma rays can cause cellular damage, since gamma rays are of the highest energy levels, and highest frequency. It is also well-known that excessive X-rays can be bad for you, but your Wi-Fi router didn’t come with a radiation warning. It is important to understand the basics of two different types of radiation.

Ionizing Radiation is radiation which has enough energy to strip electrons from atoms. This is a process called ionization, hence the term. Stripping electrons from atoms within DNA, or other cellular systems can cause mutations, cellular death, growths, tumors, etc, without any noticeable thermal effects. Some forms of Ionizing radiation include gamma rays, X-rays, high frequency ultra-violet rays, and high energy radiation from nuclear reactions.

Non-Ionizing Radiation is radiation which does not have enough energy to strip electrons from atoms. There is no damage at the atomic level caused by this radiation, and no damage to tissues unless exposed to very large levels which cause damage via heating effects. Examples of Non-Ionizing radiation include radio waves, microwaves, infra-red, visible light, and low-frequency ultra-violet.

Click to enlarge

Each element in the periodic table has its own ionization energy. This is the energy level that has to be absorbed by that given element to cause a release of one of its electrons. A list of all of the elements sorted by their ionization energy (in electron volts) is available here. The element with the lowest required molar ionization energy is caesium, which requires about 3.9 keV, or 3,900 electron volts to separate an electron from each atom in the mole. Radiation with this kind of energy sits squarely in the soft X-ray region of the electromagnetic spectrum. Have a look at the image to the right for reference.

With single atom ionization, the threshold is much lower. The ionization energy of a hydrogen atom is 13.6 eV, so a level around 10 eV is taken as the approximate bare minimum threshold for single-atom ionization.

Lets compare this to the energy of a 2.4 GHz Wi-Fi router emission:

A full wavelength at 2.4 GHz is 12.5 cm, or 0.125 meters. And, using the formula above, we can calculate its photon energy to be 0.000009925597292486 eV, which is 9.9 millionths of an electron volt. The 900 MHz frequency commonly used by smart electric meters has a photon energy of 0.000003722098984682 eV, which is 3.7 millionths of an electron volt. This is over a billion times less than the energy required to strip one electron from an mole of caesium, and over 2.6 million times less than the bare minimum energy of 10 eV required to strip an electron from a hydrogen atom.

The conclusion being that radio frequency and microwave radiation does not cause ionization, and therefore no cellular damage through this mechanism.

We’ve established that RF emissions have a very low photon energy in contrast to other forms of ionizing radiation like X-rays and high frequency UV, but what about radiation that we are subjected to every day? An extremely common radiation, which has a photon energy a million times that of a 900 MHz radio wave?

Sunlight

Our friendly neighborhood galactic thermonuclear reactor emits a wide spectrum of electromagnetic radiation, and we’re lucky enough that some of it is in the visible and infra-red spectrum, else we’d be cold and dark, and probably not alive right now. It is widely known that the sun also emits radiation in the ultraviolet spectrum, and that UV can cause skin cancer, sun burn, and other issues. This is due to high frequency UV radiation being high energy, ionizing radiation.

Consider the following images. The first image is from the Oklahoma Mesonet, and shows the current amount of radiation (in watts per square meter) that is arriving at the ground on that date and time. The next image shows a typical mix of wavelengths which make up sunlight.

Solar Radiation (W/m2)

Solar Spectrum

So, you’re looking at almost 1,000 watts per square meter where the sun is shining (see surface power density later on), and most of this is in the areas between 350-750 nm, which works out as a photon energy between 1.6 to 3.5 eV. That is 161,000 to 354,000 times more powerful than the photon energy which makes up the average Wi-Fi router RF emission. You’re exposing yourself to thousands and thousands of times more radiation, and much more damaging radiation by walking outside than you are sitting across the room from your Wi-Fi router.

Dielectric Heating

Dipole molecule in a microwave oven. Click for animation.

One way that damage to tissue can occur via RF energy is via dielectric heating. This is the mechanism which microwave ovens use to heat food. Dielectric heating requires a high-powered RF source, and in the case of the microwave oven, they use a type of vacuum tube called a cavity magnetron which emits anywhere from 500 to 1500 Watts of RF power at 2.4 GHz into a small tuned cavity. This power penetrates the food you have placed in the oven from the surface to a depth which varies depending on the dielectric constant of the food, the container, the temperature of the food, the type of material used to hold the food, and several other factors. The food likely contains a lot of water, which is a dipolar molecule, and since the 2.4 GHz is an alternating field generated by an alternating current, it causes the molecules to rotate to match the field polarity as it alternates back and forth between positive and negative, 2.4 billion times a second. This causes friction between the molecules and in turn, this causes the material to heat up. Microwave ovens do not cook from the inside out! The microwave oven has its history based in World War II, during radar research at Raytheon, by Percy Spencer. He noticed that equipment he was working on had melted a candy bar that was in his pocket. You can read here for more information on that. Percy Spencer lived until the age of 76, despite being subjected to powerful electromagnetic fields in his radar research.

Surface Power Density

Since we’re picking on microwave ovens, lets look at RF leakage from microwave ovens. Since there is a very high power RF transmitter inside the oven, it makes sense that there may be a concern as to the RF emissions surrounding it.  See the bottom of this article for a CST Studio white paper on microwave oven shielding mechanisms.

When a microwave oven is new, the RF emission limit is 1 mW/cm2 at a distance of 5 centimeters from the oven. The limit for existing ovens, or ovens throughout their operational lifetime is 5 mW/cm2 at a distance of 5 centimeters from the oven. This is a measurement of surface power density. In the solar radiation image above, you can see that on a sunny day, the surface power density from the sun approached 1000 W/m2. That’s equivalent to 100 mW/cm2 which is 20 times the maximum limit for microwave oven leakage.

5 mW/cm2 translates to approximately 500 milliwatts of RF energy.

The average power radiating from the human body is 0.0003 mW/cm2. Yes, human beings radiate energy from bio-electrical signals, yet nobody ever worries about the cumulative effect of being exposed to thousands of these fields in a stadium or concert.

One area where humans do need to be careful with large magnitude RF fields is the eyes. Exposure to high power RF energy can cause dielectric heating of the retina, and with no blood flow to take this heat away from the affected area, damage can occur (read here). So, don’t remove the door from your microwave oven and stare inside, don’t stand in front of a radar transmitter or climb on television and radio broadcast transmitters, and you’ll be ok. Sounds reasonable.

There is no risk to your bodily tissues from dielectric heating via your Wi-Fi router or smart meter. The output power of a typical Wi-Fi router is in the order of a hundred milliwatts, or 0.1 Watt. This is 10,000 times less than a microwave oven, and it is not all concentrated a couple of wavelengths away in a cooking chamber.

RF energy levels dissipate from their source. The intensity is inversely proportional to the square of the distance from the source. Read about the inverse square law here. That’s a physical law, and it doesn’t change. It applies to all electromagnetic radiation.

As you can see by looking at the images to the right, as you move away from an RF source, the field strength tapers off dramatically. So, in a nutshell, you can stop worrying about small, short-range RF devices which are common in the home and workplace, like microwave ovens, Wi-Fi routers, smart electric and gas meters, wireless keyboards, mice, wireless thermostats, etc, etc.

A good power density calculator relating to the FCC’s MPE (Maximum Permissible Exposure) limit which will give you a result in mW/cm2 from your power and distance to source metrics is located here. A Windows-based utility for calculating the same is located in the downloads section of this website.

Cell Phones

Image via CST

Some of the more popular victims of the “electrosmog” conspiracy are cell phones, and while personally I’m not the world’s biggest fan of holding a radio transmitter against my head for long periods of time, I am confident that the limits have been set using good science and reason.

When cell phones undergo certification testing, they have to pass a SAR test, or Specific Absorption Rate test. Cell phones are tested under the most severe, worst-case (and highest power) operating conditions for all the frequency bands used for that cell phone (including Wi-Fi, bluetooth, etc), and the maximum is stated on the test result.

SAR is a measure of the rate of RF energy absorption by the body from the source being measured. Many people mistakenly assume that using a cell phone with a lower reported SAR value necessarily decreases a user’s exposure to RF emissions, or is somehow safer than using a cell phone with a high SAR value. While SAR values are an important tool in judging the maximum possible exposure to RF energy from a particular model of cell phone, a single SAR value does not provide sufficient information about the amount of RF exposure under typical usage conditions to reliably compare individual cell phone models. Rather, the SAR values collected by the FCC are intended only to ensure that the cell phone does not exceed the FCC’s maximum permissible exposure levels even when operating in conditions which result in the device’s highest possible (but not its typical) RF energy absorption for a user.

The FCC’s SAR limit for cell phones is 1.6 W/kg. Cell phones vary their power depending on where they are in relation to the tower, using minimum power when in close range to a tower, and ramping up to use their maximum power when you’re in a very low signal service area. So unless you’re permanently in a poor signal area making a call, simultaneously streaming a YouTube video to your phone using Wi-Fi, your cell phone won’t approach its maximum SAR level as indicated on the test report.

If you want to find out the SAR rating for your personal cell phone, visit this link. Or head over to the FCC’s own page on cell phone SAR ratings.

Websites and articles which assert that the FCC limits are too high often mention the fact that Russia’s power density limits are much lower than the limits in the rest of the world, and use that as an example of a safer limit. Russia’s limits were developed before the era of modern mobile telecommunications and the spread of mobile devices, and back then, the rationale for determining compliance was very different.

In Summary

  • Ionizing radiation can cause damage to cells by altering their structure (stripping electrons from atoms).
  • Non-ionizing radiation can cause damage to tissue through dielectric heating effects, but it requires exposure to high levels of this type of radiation, for a significant amount of time.
  • Common household sources of RF energy are in the order of 10,000 times smaller than the energy used inside a microwave oven, often even much less than that.
  • Even a short distance from an RF source attenuates it greatly.
  • Exposure to fields which do not possess enough energy to ionize, nor possess enough magnitude to cause significant dielectric heating can likely be regarded as harmless.
  • I’m not a physicist, I know there are a lot of gaps in this post, so don’t trust one source, educate yourself, and make up your own mind.

Unit Conversion

If you want to convert between power and field strength units, check out these handy conversion sheets.

Microwave Oven Shielding Mechanisms

Here is a very nice white paper from CST on that subject.

 

 

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