[Ti] Laptop Health Warning!

[Bob Jacobsen]

At 1:13 PM -0600 11/23/02, luke wrote:
>
>your right - the .3 milliwatts might not be enough to cook a 8 pound 
>turkey or pop pop-corn, but it is enough to cook single cells... 
>the ones at the surface.
>
>the more power you have the more mass you can heat, or the faster 
>you can heat it...
>
>cells have very little mass individually...  you CAN harm cells (of 
>which we are all made)... you may not be able to cook your entire 
>head with a cell phone/laptop but you certainly can affect a certain 
>number of cells nearer to the surface...
>
>if the  microwaves in a microwave oven were PWM to square waves 
>(digital) they would cook even more efficiently and faster... 
>remember the waves from your phone and notebook are digital and more 
>efficient than sinusoidal analogue waves...  similar to a digital 
>audio amplifier being able to create more volume, more cleanly, 
>with less power (90% efficiency compared to analogue amps at like 
>maybe 70% or less)... and if the frequencies of the signal are in 
>resonance w/ ANY component of the cells the damage will be even more 
>possible.

The above is not correct.

When interacting with biological materials, microwaves spread their 
effects over a constant volume, regardless of power level. Basically, 
they penetrate by a certain distance into water-bearing materials. 
That's why a microwave oven heats a baked potato from the inside.  If 
you reduce the power, you are still spreading that reduced power over 
the same volume, so you're reducing the rate of energy deposition 
into any given cell.  You are _not_ increasing, or even keeping 
constant, the heating of surface cells.

"Square wave" and "digital" microwave signals are still GHz sine 
waves.  They are just turned on and off at some rate to modulate 
them.  Biological heating is done by the total power, and modulation 
only reduces that.

A "digital audio amplifier" is actually a switching amplifier.  That 
can cause it to reject less energy as heat, but it will produce the 
same energy in the outgoing signal.  For a given amount of sound 
output, a speaker will receive the same power from any type of 
amplifier. The type of electronics does not significantly effect the 
radiated power from a card that is deliberately radiating a signal.

As to resonance of a microwave signal with part of the cells:  That 
resonance is already well-tuned in a microwave oven.  They are 
effective because they efficiently excite the water-bond resonance; 
their frequency is chosen for that.  Phones, laptops and other 
devices that work at different frequencies are _less_ effective at 
coupling their energy into biological material, not more.

Bob
-- 
--------------
Bob Jacobsen (Bob_Jacobsen at lbl.gov, 510-486-7355, fax 510-495-2957)