helen-louise (baratron) wrote,
helen-louise
baratron

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mobile phones, they cook your head?

A few weeks ago when I had a cold, I sent Richard out to buy a new mammal thermometer, as the Feverscan forehead thermometer in the cupboard had an expiry date of 2005. For some reason he wasn't able to buy a new Feverscan thermometer - the only ones they had in Boots said they were only suitable for kids "up to age 12". So he bought a ridiculously sophisticated Braun in-the-ear thermometer that cost about £40, which is basically a home version of the type of thermometers they use to check your temperature in hospital. Just like the house thermometer we have, it is battery-powered and records temperatures to the nearest 0.1 degrees C. Unlike the room thermometer, it has a memory which stores the last N temperatures recorded, and came with 25 disposable plastic caps for hygiene between different users. Of course, we are geeks & technophiles, so it will probably be unsurprising that I've become completely obsessed with checking my temperature :)

So I can tell you that my normal waking temperature is 36.9 degrees C; my normal daytime temperature is 37.0 degrees C; and my normal just-before-sleep temperature is 36.6 degrees C. This confirms to me that the hospital was crazy to start panicking and feeding me paracetamol every time my recorded temperature was 37.0 on one of those thermometers - I'd thought it was entirely within the range of normal. Should I ever be unlucky enough to be in hospital again, I doubt they'll believe me if I tell them "37.0 is normal for me", but whatever.

It's an in-the-ear thermometer, right? So the results are influenced by anything hot I might have been placing close to my ear, like mobile phones. Now, the possible cancer-causing effects of mobile phones are highly controversial - basically because if it's true, it screws up a lot of basic wave physics. The danger of an electromagnetic wave is, as far as we know, directly proportional to the amount of energy it carries - which is directly proportional to the frequency of the wave. High-frequency e.m. waves like gamma rays and X-rays can penetrate the body and cause mutations in the DNA of cells. Ultraviolet can only penetrate skin, but the higher frequencies of UV are strongly implicated in aggressive skin cancers, like malignant melanoma. Gamma rays, X-rays and UV are all high enough energy to be able to knock electrons out of molecules in cells, and are therefore called ionising radiation. The e.m. waves that mobile phones use to communicate with satellites are in the microwave region of the spectrum - almost as low energy as you can get, and most definitely not ionising radiation.

There does seem to be some correlation between people who have used a mobile phone against the head for 2-3 hours a day every day and people who develop brain tumours, but proving cause and effect is difficult, as is getting an unbiased sample. (Bearing in mind the existing news reporting and human psychology, it's difficult to ask people diagnosed with brain tumours about their mobile phone use and be sure their answers are true.) The one thing that most researchers do agree on is that mobile phones cause heating of the head. The phones themselves get very hot after only a few minutes' use. Heat energy is infrared, another type of electromagnetic radiation, and this can travel as waves into the head. Also, any stray microwaves that don't get transmitted to the satellite can travel into the head - and as everyone knows, microwaves are used in cooking.

This is the point where the real world apparently disagrees with my memory. I was under the impression that microwave ovens used microwaves of wavelength 3.0 cm, while mobile phones used microwaves of wavelength 0.3 cm. Actually, the wavelength of both are closer to 0.3 m. The standard two frequencies of GSM in Europe are 900 and 1800 MHz, while Wikipedia claims the standard frequency of domestic microwaves is 2450 MHz. Some maths based on:
wave speed = frequency x wavelength

plus the knowledge that the speed of light & all other e.m. waves in a vacuum is
3 x 10^8 m/s

gives us:
wavelength in m = 3 x 10^8 / frequency in Hz
.
Applying this to the quoted frequencies gives:

 900 MHz = 9.00 x 10^8 Hz  -->   0.333 m = 33.3 cm
1800 MHz = 1.80 x 10^9 Hz  -->   0.167 m = 16.7 cm
2450 MHz = 2.45 x 10^9 Hz  -->   0.122 m = 12.2 cm


The frequency of cooking microwaves (2450 MHz or 2.45 GHz) is apparently slap bang in the middle of the band used for such things as Wireless LAN and Bluetooth. However, the power output by such devices varies tremendously. Typical domestic microwaves are rated at 600-900 W, whereas the power output by a wireless card in a PC is around 50 mW, 18000 times less. Hence our wireless devices aren't likely to cook us (unless, I suppose, you have 18000 of them all directed at you in unison... is that even possible?!). Mobile phones have a typical maximum power output of 125 mW, but the average value will typically be less than a tenth of that - around 12.5 mW. Also, even were we to assume maximum power output by the mobile phones, and minimum power output by a domestic microwave oven, that's 4800 mobile phones in a poor reception area to cook your head.

This is still (!) extremely over-simplified, because we need to take distance into account. The average distance of a magnetron in a microwave oven from the food would be about 20 cm. The average distance of the antenna in a mobile phone to your brain might be 2 cm. Power intensity varies according to 1 / distance ^2. So reducing the distance between the point source and the recipient cells by 10 would increase the intensity of radiation by 100, possibly meaning it would take a "mere" 48 mobile phones to cook your head.

However (!!), not all of the power output by a device is absorbed by human cells in proximity to it. The Specific absorption rate (SAR) is a measure of that. If you go out & buy a new mobile phone, the SAR for it will be specified all over the place. SARs have been dropping for modern phones because of adverse publicity. Also, it's believed that the skulls of older people that have finished growing are able to absorb a lot of radiation and stop it from reaching the brain. The skulls of children are softer and much less able to shield the brain, so if there is a danger from mobile phones, children are more likely to be at risk.

Why was I thinking about all this anyway? Well, I measured the temperature in my left ear, that had been against a hot phone for 20 minutes, and it was 37.6 degrees C. The corresponding temperature in my right ear was only 37.3 degrees C. Two minutes later, these had dropped to 37.3 degrees C (left ear) and 37.1 degrees C (right). Temperature, even quoted in kelvin, isn't on an absolute scale --> doubling the temperature doesn't mean there's twice as much heat energy present, so it's hard to know these numbers mean; let alone what difference an increase in my ear's temperature of 0.6 degrees C over 20 minutes could make to the long-term health of my cells. I still need to do a control run where I simply lie in bed with one ear pressed against the pillow for 20 minutes, as lying on one side is something the manual of the thermometer says will make a difference to recorded temperature. But it was enough of a difference for me to notice & sit here doing bad maths on for several hours.

I wanted to get you some references for all of the stuff mentioned below the cut, but Wikipedia's Electromagnetic radiation hazard and Wireless electronic devices and health both referenced the page The Dangers Of Electro Magnetic Radiation (EMF), which I am finding impossible to take seriously. Somehow, I tend not to trust "science" when it's spouted by a so-called medical professional in combination with such wonders as "You may choose not to wear a quartz-analog watch because it radiates pulsating EMFs along your acupuncture meridians." Riiiiight. Apparently, "Eyeglass frames should ideally be made from plastic with no wires in them, otherwise they can serve as an antenna to focus the radio and cellular phone waves directly into your brain." Uh-huh. I recommend aluminium foil helmets to anyone concerned about such things.

I do trust the World Health Organisation, but their factsheet Electromagnetic fields and public health: mobile telephones and their base stations dates from June 2000 and there's been a lot of new research since then. Wikipedia's Mobile phone radiation and health has more recent references, but I'm really far too tired to plough through them to see which seem reliable tonight.

Also, I can't believe I've been working on this since 9pm instead of posting any of the LJ entries I "owe" you, such as:

  • what Ludy & I did in Manchester - including a review of vegan eating & museums
  • a BiFest review
  • a Polyday review
  • a writeup of my Polyday workshop (an expanded version of the "crib sheet")
  • something or other about Sims 2 that's dropped out of my head
  • the question about my body temperature and allergies that sparked off all this temperature-measuring in the first place!


I am a nerd.
Tags: dangerously nerdy, science, the science of everyday life
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