This is the last of the hazardous environmental factors research blogs for this project, subsequent blogs in this challenge will deal with hardware builds, software programs, functional tests and test results.
Microwaves are used for cell phones, Wi-Fi, Bluetooth, Zigbee, GPS, some cordless phones, and microwave ovens. The microwave oven is proof that a high enough exposure can be harmful. But what is the mechanism that makes microwaves cook food?
It is pretty common knowledge that it is heating up the water molecules in food, but it turns out it is not exciting the resonant frequency of water molecules, (the resonant frequency of water molecules is over 21 GHz) the oscillating electromagnetic field is acting on the water molecule dipoles. Water molecules conceptually have a plus side and a negative side so they try to align with the prevailing electric field – as the field oscillates (reverses), the molecules flip to stay aligned. This rapid rotation of molecules causes friction between molecules and thus heat. If 2 tires on a vehicle were touching as they rolled along a road, they would generate extreme friction and heat because although they are turning in the same direction, at the point of contact the tires are traveling in opposite directions. It isn't just water that responds to oscillating fields, other dipole molecules and salt ions also are also affected.
There is also nothing magic about the frequency used in microwave ovens, a fairly wide range of frequencies would have similar results. It is mainly regulations that dictate the frequency used. (2.45 GHz)
Humans can dissipate well over 100 Watts, so it takes significant rf radiation (over 4 W/kg) to cause excess heating. Regulations (0.4 W/kg) were developed long ago to keep human exposure well below levels where excess heating would become a problem. And if heat from microwaves is occurring, you would feel it as heat – it would heat the outer 1 cm of your skin – not much would penetrate further. Although your eyes are more susceptible especially to ionizing radiation.
Okay, so the risk of getting cooked by microwaves is very low and you would feel it if it was occurring, but lower levels of microwave are still causing dipole molecules in our bodies to vibrate or rotate rapidly – what effect does this have on our physiology?
There are lots of studies on this, often finding some correlation with adverse effects at exposure levels orders of magnitude below regulatory limits, but generally not dramatic influences. It may speed up activity in some cells, but I don't have much info on this.
We know that DNA is affected by electric fields and in fact electrophoresis is a technique that uses this property to selectively move DNA around. So DNA can probably be jostled around by electromagnetic oscillations. There doesn't seem to be much literature around on whether DNA is too constrained to be spinning and flipping, but it is conceivable that every once in a while the jostling is severe enough to overstress some DNA and cause breaks or mutation and some studies show this. I could go on with further speculation, but I don't have enough data to support it so I will get back to real studies and measurements.
There is concern that cell phones cause brain cancer and there are some serious studies investigating this possibility. Some significant studies indicate that heavy cell phone use could double the risk of brain cancer, but symptoms might not show up for one or more decades. Keep in mind that deaths from brain cancer are about 1/375th of the chance of death from other types of cancer, so doubling the risk still makes it a relatively small risk.
I have collected a lot of data and reports correlating cell phone emissions with a myriad of symptoms from obesity and headaches to autism and insomnia. Some study the effects all the way down at the cellular level while some are just statistical correlations. One thing that seems to be common is when people are discussing the subject, they tend to dramatize the results, playing down statistics that would provide a better contextual perspective. I don't want to regurgitate all that, but there is one case where the evidence seems to be more widely accepted: When men carry cell phones in their pockets, they tend to have lower testosterone levels and lower sperm counts. In many species, reduced fertility is an early warning of environmental stress so these results are troubling. The process involved when DNA and RNA precisely replicate themselves is complex and fantastic and it is not hard to believe that it doesn't take much interference to mess it up.
I have been trying to determine if it is possible to shield a person with a cell phone in their pocket, but it is difficult to do with the setup I have. The cell phone is only periodically transmitting and the power levels seem to be very dynamic. I think I would need at least 2 fast power level sensors and a data acquisition system that could simultaneously sample both sensors. Right now, if I insert a shield, and the readings change, I don't know if they have changed because they were about to change anyway or if the shield caused the change.
That being said, I did find some trends that seem to be occurring. The radiation seemed a bit stronger coming from the edges of the phone I was testing and putting a metal shield between an edge and my meter, caused the reading to drop more significantly than doing the same test on the face of the phone. I'm not sure if there any huge conclusions, but wearing metal underwear would likely reduce exposure. These phone shield pockets that are being sold work, but they stop the phone from receiving and you get pretty much the same performance by simply putting the phone in airplane mode. My tests suggest it might be possible to design a directional shield that reduces exposure of the owner while allowing communication with a cell tower, but I need to think a bit more on how to prove performance of such designs.
As mentioned, I have collected a pile of information and studies on the hazards of low level EM radiation and much of it is worrisome if not downright scary, but although many symptoms have been linked to EM radiation, the risks do not appear to be high enough and the symptoms do not appear to be severe enough (with proven causality) to warrant immediate regulatory intervention. However, just because the light is green doesn't mean there is no risk to crossing the street. Sometimes it is worth looking both ways before crossing anyway.
I won't re-print all the data but here is an example table of some potential symptoms and effects from low-level EM radiation:
- RFR is Radio Frequency Radiation
- To convert mW/cm2 to mW/m2 multiply by 10
In the next section, which shows some actual readings I have been taking around the house, I will list a few practical tips to reduce exposure. One of the main reasons for doing this project is to use the instrumentation to explore my environment and find ways to make it as safe as possible.
This image show readings from a decent microwave oven (I've seen worse). The readings drop from 232 mW/m2 at 1 foot to 1 mW/m2 at 6 feet.
Safety Tips: It is easy to stay at least 6 feet from running microwave ovens.
This image shows readings from a cell phone coming out of airplane mode and reconnecting to a cell tower to get email.
- keep the phone in airplane mode whenever it is not in use or expecting an urgent call
- when exiting airplane mode, keep the phone a few feet away
- when making a call, use a headset rather than putting the phone to your ear
- if you don't have a headset, use speaker phone mode
- try to make calls where reception is good – the phone will throttle back on transmit power
- use text instead of voice – it keeps the phone further from your body and can reduce transmit time
- use a land line when possible
- when driving, use a hands free system and put the phone away from your body
- put the phone in airplane mode at night while it is charging or keep it a reasonable distance from your body
This image shows readings from a Wi-Fi hotspot measured from 6 inches away.
This image shows readings from a Wi-Fi hotspot measured from 54 inches away.
- Turn the Wi-Fi router off when it is not needed (when you are sleeping for example)
- locate the Wi-Fi router away from commonly occupied spaces, but close enough that client devices do not need to crank up to full power to access the router
This image shows a tablet using Wi-Fi to update its game.
- use a big tablet at full arms length from your body – on a table not your lap
- operate it close enough to your router to get all signal strength bars lit
- use a wired Ethernet connection if possible
This image shows a couple of Buetooth devices communicating.
- move to Bluetooth low energy (BLE)
- keep devices at arms length when possible
- Bluetooth headsets are better than putting a phone to your ear, but not as good as a wired headset
This table summarizes some of the readings I took around my house:
Magnetic Field (mG)
Electric Field (V/m)
RF Strength (mW/m2)
HV Power Lines
Res Power Lines
Note that distance is a big factor in power levels and exposure, a few extra feet from the source can cut exposure levels by orders of magnitude.
All links to blogs related to this project can be found in the first blog here: