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Schubert
Antenna Wizard

Joined: 08 Apr 2009
Posts: 161

 Posted: Wed Feb 23, 2011 4:52 am    Post subject: Cell Phones Affect Areas of the Brain, Study Shows Here's an interesting article, which notes cell phones do impact the brain when in use: http://www.businessweek.com/lifestyle/content/healthday/650150.html The study is quick to point out that they have no evidence that the effects of cell phone use are harmful. It simply states that the metabolism of glucose is 7 percent higher when a cell phone is used. I'm actually pretty surprised by this. This is the first direct evidence I've seen that using a mobile phone has some impact on the brain. Assuming this study is had no incorrect biases, I think this study in some way justifies the SAR limits set by the FCC. SAR is discussed here: http://www.antenna-theory.com/definitions/sar.php SAR is simply a measure of the amount of energy absorbed by nearby tissue, so for mobile phones they turn the power all the way up and measure the power absorbed. Since there are no known or proven health effects, where does the FCC limit (1.6 W/kg) come from? Simple: they guessed. There really is no magic number, they don't know. Maybe these studies will help to find a way to determine if this limit is reasonable or not. The current state of human knowledge does not have an answer.
rtso
Antenna-Theory.com Newbie

Joined: 03 Apr 2011
Posts: 6
Location: Los Angeles

 Posted: Sat Apr 09, 2011 3:23 pm    Post subject: I read somewhere that the limit was based on keeping the temperature rise of the brain below a certain limit, for a certain talk time. 1.35kg is the average human brain mass. The human brain is 85% water. The specific heat of water is 4.2J/gram-C so if we makes some approximations, we can say the average brain would take about 6kJ to raise its temp by 1 degree C (assuming uniform heating, which we know does not happen) So if SAR = 1.6W/kg => 1.6 W/kg x 1.35kg = 2.16 W 6kJ / 2.16W = 3000 seconds = 50 min of talk time. This assumes adiabatic heating, which we know does not happen as there is bloodflow to and from the brain, which would tend to keep it cooler. So it would seem from a thermal heating perspective, the guideline would seem reasonable. But as you say, no one really knows the possible biological effects - such as brain tumors that might be encouraged by microwave exposure to the brain, which could have nothing to do with a heating effect.
bigSteve
Antenna Wizard

Joined: 14 Mar 2009
Posts: 265

 Posted: Sat Apr 09, 2011 11:10 pm    Post subject: Interesting analysis rtso. To add some more layers of complexity: In Europe, the SAR limit is defined by averaging the power absorbed over 10 grams of tissue. In the USA, the SAR limit is defined by averaging the power absorbed over 1 gram of tissue. Both USA and Europe have a SAR limit of 1.6 W/kg. Guess which limit is more difficult to achieve? The US limit is much more difficult. The fields die off extremely quickly with distance from the phone within your head - i.e., they are not uniform. Hence, the larger the area you average over, the easier it is to achieve the spec, since the fields are concentrated at the edge. Hence, you could further your analysis by figuring out the temperature rise in a local region of the brain where the power absorbed close to 1.6 W/kg (it isn't uniform throughout the whole brain mass).

Joined: 03 Jan 2007
Posts: 199

 Posted: Mon Dec 19, 2011 7:32 pm    Post subject: more on SAR and RF Energy Scare Here's a new "radiated electromagnetic energy scare" article. In San Francisco, the power company PG&E has installed smart meters, which wirelessly transmit the used power at residences. This saves the power company from sending people around to read the meters, a good use of 21st century technology. The article is somewhat scary as people are saying they are feeling pressure in their head and other symptoms that are alleviated when the smart meter was removed. This is pure placebo effect, since the neighbors all still use the smart meters and WIFI at the same frequency is continuously broadcast as well. More concerning, and to which I emailed the author about, is his statement that "the notion that wireless technology can have such effects remains in deep dispute among researchers". This is an example of a journalist just not knowing the facts but typing an article anyway. I emailed him for comment, but I highly doubt he responds. In general, I'm a little troubled by the level of fear raised by wirelessly transmitted devices. Given enough irrationality, the whole system could one day be shut down by a bunch of ignorant activists. Here's hoping it won't come to that. The article is here: http://www.sfgate.com/cgi-bin/article.cgi?f=/c/a/2011/12/16/BULC1MD1MA.DTL&tsp=1
DeboraLee
Antenna-Theory.com Newbie

Joined: 16 Oct 2014
Posts: 1

 Posted: Thu Oct 16, 2014 9:19 am    Post subject: This assumes adiabatic heating, which we know does not happen as there is bloodflow to and from the brain, which would tend to keep it cooler.
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