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Microwaves and bluetooth

  1. Aug 22, 2008 #1
    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.
     
  2. jcsd
  3. Aug 22, 2008 #2

    mgb_phys

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    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.
     
  4. Aug 22, 2008 #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 ?
     
  5. Aug 22, 2008 #4

    mgb_phys

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    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
     
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