Comment by ChuckMcM | Hacker News Reader

Comment by ChuckMcM | Hacker News Reader

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I particularly like "...strengths that did not raise animal body temperatures excessively." No sense microwaving the rats to death. For a 70kg person, that exposure (using the rat scale, 105 - 420 watts) for your entire life. Vs a cell phone which has an effective radiated power ERP of about 1 watt[1]. So somewhere between 1% and .25% of the power.

Cell phone signals fall off with the square of the distance so the bulk of the power of a cellphones RF energy that you are exposed to comes from the handset.

[1] "Meanwhile, the total power emitted from the cell phone itself ranges from 0.75 to 1 watt. According to the FCC (Federal Communications Commission), this is an acceptably safe amount of power for a cell phone since their cut-off or specific absorption rate is only 1.6 watts per kilogram (W/kg). As a result, the power radiated from a cell phone is considered as non-ionizing as opposed to ionizing." -- https://hypertextbook.com/facts/2006/EbruBek.shtml

Also, 2.5 W/kg in a shielded room is far, far more than 1.6 W/kg exposure. Cell phone radiation, when it even goes through your head, keeps on going right through to the other side[1]. In a shielded room, the radiation bounces off the walls until it's absorbed by the stuff in the room... ie the rats. The absorbed power in humans is microwatts. The rats were absorbing fractions of a watt.

[1]: as evidenced by the fact that cell phones actually work. When you cover them up with your hand, you don't suddenly drop the call.

No it isn't. W/kg is a measure of absorbed radiation.

No, it's just a unit. It's the output of your speakers to the amount of sugar I consume in a year if we want it to be.

We're talking about SAR obviously. Surely you could tell that?

Your original parent used the unit both for absorption and exposure; you replied claiming it wasn't a unit of exposure.

And a cell phone emits <1 W total, of which tens of millionths or less are absorbed. I was pointing out the difference between W/kg absorption and W/kg emission. These rats were absorbing tens of thousands of times more energy than you would experience holding a phone directly to your head.

I believe you added an extra "/kg" on emission.

No, he's pointing out that even (watts emitted)/(kgs of body region that is expected to absorb) is an over-estimate of watt/kg absorption.

Nope- It's a technical elision. An 80 kg man in an open field next to a 80 W transmitter is exposed to 1 W/kg, and absorbs microwatts/kg. Ionizing radiation is treated much more rigorously, and thickness and and frontal area are used to calculate the actual dosage, but for EM sources the wattage/kg is not unusual as a metric. It's useful for nearby transmitters, where exposure is focused on a single part of the body, vs simply being exposed to 80 watts of incident power.

> An 80 kg man in an open field next to a 80 W transmitter is exposed to 1 W/kg, and absorbs microwatts/kg.

That's not at all how it works.

https://en.wikipedia.org/wiki/Specific_absorption_rate#Mobil...

What if you’re around 105-420 people with cellphones radiating 1 watt each?

Again, the energy falls off with the square of the distance, so unless those hundreds of people have very long arms and decide to press their phone against you...

Not trying to be a troll -- Tokyo subways come to mind.

1 watt corresponds to an in-use phone. Heavy data use. Even a call has much lower power. Unless the phone is actively doing something, the cell pings are very brief and use very little power.

You're discounting the fact that cell phones are more used for data than for talking and data is always being transmitted, especially with apps that run in the background.

Nah, the amount of power used for data is just also low when not being actively used. I'm sure some people update over 4G, but not many.

But how many people use their phones for data while holding them against their heads? (Not to mention in a shielded cubicle?)

And how many can even get service in a crowded subway?

most. offline people doing podcasts and games probably don't emmit much less.

Even then, how many people can be within touching distance? 10? 20 if they’re making a real effort? So let’s say 20 within a meter, and let’s say they’re all actively using their cell phones... it’s going to be significantly less than 20 watts, so still nowhere close. If a few hundred people beyond that are using their phones it will add an asymptotically diminishing amount of energy, so you’re never going to come close to the exposure these rodents experienced.

Also, when my phone is in my pocket I'm exposed to 50% of the radiation in one small spot vs. let's say 10% of the antenna's radiation spread across the whole body of the rat. Hopefully they tuned the power in their experiment to account for that.

No, when they talk about watts per kilogram I am pretty sure that they mean these were absorbed. Like they literally built 21 big microwaves, 7 for mice and 14 for rats, and then turned them on: it's no different than your microwave at home, the waves bounce around the walls until they find some water to call home. They're presumably not concerned with any microwaves that escaped the resonator.

They can't get close enough to you to matter. The way to think of this is to imagine a bubble around each person's phone. Just like a bubble gum bubble, the bigger it gets, the thinner it gets. So if its dark pink when it is emerging from your lips, it is transparent by the time it is 6" in diameter.

The energy of the cell phone transmitter is spread out further and further as you move way, and because the 'bubble' is both taller and wider, each meter (about 3') you step away from the phone, the signal is 1/distance^2 less powerful. So 2 meters away, 1/4 as powerful, three meters, 1/9th etc.

I like the Tokyo subway image, and others have gone to the trouble of computing people densities[1], if you take their number of 7 people per square meter as a good maximum, then 100 people divide into 7 person groups and you get a box that is about 4 meters on a side (12' x 12'). You're only getting 10% of the energy from the phones that are 3 meters away.

[1] http://www.elsi.jp/en/blog/2015/11/blog1126.html

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