Microwaves and bluetooth

  • Thread starter Abiologist
  • Start date
  • #1

Main Question or Discussion Point

Dear All,
Please excuse my ignorance of physics. According to some Russian research 1 mW of microwave radiation could be considered safe for the brain (ie. it won't cause brain damage). I therefore considered that if a 1 W cellphone is damaging to the brain then perhaps it's a good idea to use a 1 mW Bluetooth earphone (which has a range of 1 m) and carry the cellphone on a waist belt. My question is - how much microwave radiation will reach the brain anyway from the waist-carried cellphone ? In other words if the cellphone is giving out 1 W of microwaves - then how much (roughly) less will reach the brain if the cellphone is 50 cm away compared with only 1 cm ?

I look forward to your answers. Many thanks.
 

Answers and Replies

  • #2
mgb_phys
Science Advisor
Homework Helper
7,774
12
The radiation falls of as an inverse square law, so for every doubling of distance the radiation is 1/4 as much.

The easiest way to picture it is to imagine a sphere expanding out from the cell phone.
So at 50cm away the sphere will have a radius of 50cm and a surface area of 4 pi r^2 (or 32000cm^2) so each cm^2 at the distance of your head receives 1/32000 of the total energy, if you head is roughy 20x20cm, it has a cross sectiona area of 400cm^2 and so gets about 1% of the total area of the sphere and so 1% of the radiation.

In reality it's a bit more complicated depending on the exact pattern of radiation from the antennae.

There's no evidence of damage to your brain from a cell phone and no obvious mechanism. But keeping the phone on a belt and using a headset would reduce the power at your head.
 
  • #3
Many thanks for your reply. So I suppose that the difference between 1 cm and 32 cm is 5 doublings - which means that the radiation difference is 0.25 x 0.25 x 0.25 x 0.25 x 0.25 which would be about 1 mW from a 1 W cellphone. I suppose this is good news except that your brain would be receiving 1 mW from the bluetooth and 1 mW from the cellphone = 2 mW. On a similar note does anyone know the wattage of the microwave transmitter found in a Fujitsu Siemens laptop which can be used as wireless internet connection to a modem 5 m away ?
 
  • #4
mgb_phys
Science Advisor
Homework Helper
7,774
12
The power limit for Wifi is 1Watt, for bluetooth it is 100mw for 100m range class 1 devices or 1mw for class 3.
Agin it is complicated by the antenae design and the system can reduce the power if it can get an acceptable signal to noise
 

Related Threads on Microwaves and bluetooth

  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
2
Views
1K
  • Last Post
Replies
20
Views
3K
  • Last Post
Replies
6
Views
5K
  • Last Post
Replies
1
Views
2K
  • Last Post
Replies
8
Views
6K
  • Last Post
Replies
9
Views
21K
  • Last Post
Replies
6
Views
2K
  • Last Post
Replies
3
Views
3K
  • Last Post
Replies
7
Views
2K
Top