10 ms·
Testing phones from 5 millimeters away from the body may seem close, but for anyone carrying their phone in a pocket, the distance is closer to 2 millimeters. B
by jws 7y ago
Testing phones from 5 millimeters away from the body may seem close, but for anyone carrying their phone in a pocket, the distance is closer to 2 millimeters. Because wireless power falls off exponentially with distance, what might be a safe amount of RF exposure at 5 millimeters could be much higher at 2 millimeters.
They mean to say that you should expect a power about 6 times higher, (5^2 / 2^2). This is rubbish.
The square of the distance model is for a pair of points. Phones in pockets at such closed distances are more closely modeled by a pair of infinite planes where the power falls off not at all. The real result will be in between, but very much closer to 1 than 6.
- krastanov 7y agoSo it is doubly incorrect... They are completely misusing the word exponential to mean quadratic which is already incredibly annoying, but it is not even quadratic, it is constant.
- deleted 7y ago[deleted]
- whatshisface 7y agoNot squared, inverse square. That's faster than exponential.
- AnimalMuppet 7y agoYou may need to check your math. Inverse square does not fall off faster than exponential.
- whatshisface 7y ago1/x² has a singularity and rises faster than exponential as you approach it. We're talking about getting closer to the source, not further.
- AnimalMuppet 7y agoAh, I see. In that direction, you are correct.
- Retric 7y agoIt should be obvious that real world antenna don’t behave this way as they are not point sources. But, mathematically you’re correct.
- whatshisface 7y agoAs you get closer and closer to the surface of the phone, phenomena progress from a visible glow, to pair production, to the thermodynamic stability of quark-gluon plasma.
- krastanov 7y agoNo. All polynomials and rational functions fall off drastically slower than exponential.
- whatshisface 7y agoWe're talking about the rise in power as you get closer. 1/x² has a singularity, I doubt exp(x) can beat that...
- tomrod 7y agoGood point! -ln(x) may (would have to check), but exp(0) = 1 and 1/02 is defined as positive infinity (the Real numbers are not closed under division).
- enedil 7y agoNo, division just isn't a total function.
- tomrod 7y agoI think these may be the same thing in this case.
- fulldecent2 7y agoI'm following along in this thread here and double checking everybody's math. So... does this mean I will die from radiation or not?
- whatshisface 7y agoThis thread is actually irrelevant to the radiation question due to the plane radiator thing mentioned above.
- theseadroid 7y agoI wonder if we shall take exposure density into consideration? If RF is emitted in all directions, the closer the phone to the body, the same amount of RF will be received by a smaller area of skin?
- oefrha 7y agoYou’re still thinking about a point source, where the actual scenario is closer to two parallel plates, in which case the non-normal components cancel out, leaving only the normal component, except at the edges. The most basic example from electrostatics: http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesht.html http://hyperphysics.phy-astr.gsu.edu/hbase/electric/elesht.h...
- cdelsolar 7y agoI don't think the phone emits radiation from its entire body
- RL_Quine 7y agoThat's what the cuts around the metal band of the iPhone are for, to segment the edge into different tuned antennas.
- klodolph 7y agoIf you try to make an antenna too small compared to wavelength, it will become less efficient and more difficult to design. 900 MHz is the 33 cm band, so if you have a more standard size antenna on the order of quarter-wavelength size, you get an antenna that’s about 8cm.
- tyingq 7y ago"Phones in pockets..." The somewhat related study mentioned in the article was much more interesting in terms of "phones in pockets". https://www.jstage.jst.go.jp/article/tjem/248/3/248_169/_article https://www.jstage.jst.go.jp/article/tjem/248/3/248_169/_art...
- madengr 7y agoWell you are in the reactive near-field, so the antenna will de-tune, hence the power amplifier won't see it's ideal match, and not deliver as much power. All depends on antenna design and orientation, assuming they don't use active impedance tuning. The base station also tells the phone to back-off. If the TX were running at full power, the battery will die quickly. Leave your phone in a metal, security cubby and your battery will die quickly; no power control and worse-case antenna loading. Also the highly asymmetric data usage these days. Very little energy on the uplink. FWIW I design antennas and amplifiers for a living. The only time I'd worry about RF exposure is to the cornea; that is a proven hazard. RF burns are a right of passage for PA designers, and are harmless as it's the outer skin layers.
- johnr2 7y ago> RF burns are a right of passage for PA designers, and are harmless as it's the outer skin layers. A literal example of skin effect?
- madengr 7y agoYep. Put your finger on the corner of the output coupling cap on a 50 Watt S-band PA. It will turn your skin black from the charring, but doesn't penetrate into the live tissue. Just don't leave it on too long. Could probably gives non-permanent tattoos with this method.
- sjwright 7y ago> Leave your phone in a metal, security cubby and your battery will die quickly Which is the best selfish reason to remember to switch on flight mode on an aeroplane. (Also when you’re trekking in areas where you know cell coverage is nonexistent.)
- labawi 7y ago> If the TX were running at full power ... Leave your phone in a metal, security cubby and your battery will die quickly If the phone can't hear a network (not just faint signal like airplanes on certain heights), would it actually transmit? I think the battery drain would be from active RX searching for networks instead of sleeping. You get a similar though probably lower effect, when in roaming without setting a fixed network - an idle phone without crapware will burn way more energy.
- meekstro 7y agoWhy isn't it tested at 2mm if that is the standard useage? Why rely on a model? 20,000 phones are being sold an hour. Why not buy 200 phone's off 200 shelves and test them comprehensively at 0 mm, 1mm, 2mm, 3mm ..... The cost to volume sold is completely negligible and it is useful consumer information as 3 percent of the population is electrosensitive. An estimated 30 million people suffer from Myalgic Encephalomyelitis (chronic fatigue) in the world and the average diagnosis takes seven years. Chronic health conditions are increasing exponentially. Healthy people aren't sensitive to environmental stimuli but unhealthy people are and the number of chronically unhealthy people grows by the day as livers strain under the stressors and weakening of modernity. Turn your wifi off in your house at night and see if you sleep any better. Pretty simple anecdotal experiment. A house without the wifi on or excess electrical componentry on has a nicer feel. We did not evolve with this electromagnetic radiation and the cost of testing is negilible given the global population's growing exposure to it and something interesting may fall out of the research. The risk of Apple having to make slight design modifications if research raises an issue is not a huge concern of mine. One hours phone sales should cover it and then they could further differentiate their products and raise prices. How many electrical engineering schools are there in the world? Sounds like a great way for a university to get their staff free Iphones with a research grant.
- mopsi 7y ago> Turn your wifi off in your house at night and see if you sleep any better. This needs to be a blind test, e.g. you track your sleep quality over a longer period of time while a script turns wifi off on random nights.
- georgeburdell 7y agoExactly. Near field electromagnetic variations are not inverse square.
- doubleunplussed 7y agoFWIW when you're closer to an antenna than the wavelength, you're not just seeing normal Gauss's law drop off, you can be looking an an evanescent wave [1], which does indeed fall off exponentially (well, depends on the exact shape of the antenna). I've designed a short-range 'antenna' that is intentionally not impedance matched to the vacuum, and radiates very poorly - but the RF intensity close to the antenna is very high because of this effect. [1] https://en.m.wikipedia.org/wiki/Evanescent_field https://en.m.wikipedia.org/wiki/Evanescent_field
- jcims 7y agoCool. Could this be used for wireless charging and/or less snoopable RFID/contactless replacement?