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I recently bought some cellphone accessories, and as a free gift, the merchant gave me a "24K gold plating electromagnetic shielding sticker", whose instructions are all in Chinese, but I guess you're supposed to stick it onto your cellphone, and that's supposed to protect you from nasty E-M radiation.

My initial reaction is that this is total quackery, but let me ask those more knowledgeable in the field: is there any substance to these things?

Shaul Behr
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    There was a similar question on Skeptics a while ago (http://skeptics.stackexchange.com/questions/2693/can-products-that-claim-to-to-reduce-electromagnetic-radiation-from-mobile-phones), those stickers don't do anything, it's pure quackery. –  Sep 27 '11 at 11:59
  • For comparison, cell phones output a maximum of about 2 W of non-ionizing radiation. The human brain outputs about 20 W of (thermal) non-ionizing radiation. – endolith Sep 27 '11 at 16:04
  • Generally, they are quite effective at separating kooks from their money. – Connor Wolf Dec 08 '15 at 03:56

4 Answers4

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I call quackery. You don't want to shield the electromagnetic field, because that's what makes the phone work. If you would stop the EM field you wouldn't have communication.

The "24 carat gold" should also ring a bell. I bet there's not a \$\mu\$g gold in it. Even if you want to make a shield there are much cheaper materials which perform almost as well as gold does, aluminium for instance. Despite what some people think you don't need a magnetic material like steel (iron) to shield off alternating electromagnetic fields. (Besides, gold isn't magnetic either.) For shielding you need a good conductor. Gold is one, but so are copper and aluminium. The magnetic field passing the shield creates eddy currents which in turn create a field countering the first one.

stevenvh
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    To shield off static magnetic fields you need more than a good conductor. A superconductor will do! But you're obviously referring to _alternating_ fields. – leftaroundabout Sep 27 '11 at 09:14
  • @leftaroundabout - yes, alternating fields are the context, but you're right, I'll add it to my answer. – stevenvh Sep 27 '11 at 09:20
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I guess you're supposed to stick it onto your cellphone, and that's supposed to protect you from nasty E-M radiation.

Electromagnetic radiation can be nasty at some energies, but the EM radiation from your cell phone isn't dangerous. Radiation is dangerous as such when it is ionizing radiation - capable of removing electrons from an atom, creating an ion. Ions are chemically reactive, and it's the reaction that causes harm.

Take a look at this image of the electromagnetic spectrum from Wikipedia:

http://en.wikipedia.org/wiki/File:EM_Spectrum_Properties_edit.svg

Your cell phone operates between the radio and microwave frequencies. Ultraviolet light (such as that created by the sun) is the lowest-frequency ionizing radiation.

My initial reaction is that this is total quackery, but let me ask those more knowledgeable in the field: is there any substance to these things?

If you're not convinced by or don't understand the ionizing vs. non-ionizing radiation argument, note that visible light is closer to being a "nasty" ionizing form of radiation than radio waves. Don't worry about it.

leftaroundabout points out that radiation can also be dangerous at high frequencies due to thermal effects. However,

  • Low power levels,
  • Large thermal mass in your head, and
  • High conductivity of any thermal effects by your blood

combine to make this a non-issue.

Kevin Vermeer
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    Ionizing is certainly the most immediate kind of harm that radiation can commit, but you can't _conclude_ from this that non-ionizing kinds of radiation are per se harmless. If you stick your head in a microwave oven, no molecule is directly ionized by the microwaves, and it's still deadly since your brain doesn't like to be boiled. – leftaroundabout Sep 27 '11 at 11:12
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    @leftaroundabout - Brain boiling power requires a lot more transmitted power than your phone antenna could ever approach. Your microwave outputs somewhere around 1000W, but your cell phone outputs less than 1W, which is not enough to cause a significant rise in temperature. Holding your hand to your ear will cause more heating than your phone would. – Kevin Vermeer Sep 27 '11 at 11:23
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    Yeah, I didn't say phones boil your brain. I just said it's a wrong conclusion to say \$x\in A\$ are dangerous, \$B\not\subset A\$, therefore any \$y\in B\$ are harmless. – leftaroundabout Sep 27 '11 at 11:35
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    @leftaroundabout - OK, I'll bite. Added to answer, should be comprehensive now. (Unless you want to consider the effects of a phone accelerated to a high velocity, or ingested...) – Kevin Vermeer Sep 27 '11 at 11:59
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    My $0.02 - conflicting studies are absence of proof. In general, absence of proof is not proof of absence. Adding some common sense (non-ionizing radiation, lower power levels on newer phones) makes me judge there to be no risk - [Wikipedia article](http://en.wikipedia.org/wiki/Mobile_phone_radiation_and_health) – Adam Lawrence Sep 27 '11 at 12:57
  • Just to add a little bit to what @leftaroundabout said: EM radiation from cell phones can and probably does warm the body, but since a cell phone transmits at much less than 1 watt, the effects are tiny. By comparison, the light from the sun strikes the earth with approx. 1,000 Watts/meter2. So the sun has much more warming ability than a cell phone could possible have-- and the sun outputs UV light, which _IS_ ionizing radiation. From that we can conclude that the non-ionizing radiation from a cell phone is less harmful than the sun. –  Sep 27 '11 at 13:01
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Summary:

  • The stickers don't help at all

  • If you care a Bluetooth headset is liable to be the best solution.

  • It is possible but by no means certain that there are any significant health effects from using cellphones. Very heavy use may be more liable to hurt, but even this is uncertain.

The stick on "shields" do nothing useful and probably nothing even measurable.

You could produce shielding for a cellphone - but for it to have any significant effect on user field strength levels it would have to severely impact the phone's radiation pattern and would have a good chance of affecting how effective the phone was as a communicator. To be useful (if usefulness is in fact needed) and also not affect the phone's operation would require it to be designed for a specific phone's spatial and functional layout.
There is also a prospect that adding "shielding" may make any effects that do exist worse by altering the field shape and maybe causing an area that is more sensitive to have increased exposure. This is extremely unlikely, but worty noting for completeness.

If you must have shielding then the most effective and cost-effective method is either

(1) to use an external antenna. At the distances of phone to body the user is very much in the near field and coupling will be largely magnetic. Magnetic shielding is harder than RF. But, magnetic field strengths drop (notionally) with the cube of distance. If you could move a phone a few hundred millimetres from your head you'd get great reductions in field level. Or

(2) Use a remote connection to the phone - which is what a Bluetooth headset does for you. Bluetooth has its own transmit field but it is very substantially smaller

Even a wired earpiece/microphone will achieve a similar result. You'll get some RF transfer along the wire but it will be much much less than than the affect from close proximity to the cellphone. If a wired headset is used then adding a ferrite RFI shield (eg a purpose designed ferrite toroid or clamp around the cord outer - no electrical connection - would further reduce RF reaching the headset.

But

There has been ongoing effect over many decades re the biological hazards from EM fields. There have been numerous scientific studies and consequent peer reviewed papers that concluded that there were statistically significant hazards in some cases - and about as many others that concluded just the opposite.

One of the more disturbing (to me) was the suggestion that very heavy users developed certain carcinomas in the head, significantly more on the side closest to common cellphone use and overall significantly more than for the general population. BUT I understand that even this claim is subject tonthe normal debate and uncertainty.

My practice and advice in this and similar areas is "prudent avoidance" - do what you can to avoid what may be risk situations but don't let them wreck your life. There is usually not any sensible need to let such things overly even influence your life. eg

  • If you use a cellphone a lot Bluetooth makes sense anyway.

  • Locating the mains transformer equipped alarm clock away from your pillow when you sleep is of minimal effort.

  • Not buying a house near or under HV powerlines makes sense because of what others think as that will affect prices regardless of whether there is any effect or not.

    And rental accomodation under a powerline will usually not be cheaper than similar accomodation elsewhere.

    If your children have left home and you are older than younger and favor house per $ over resale value then buying under powerlines may make much sense. if there are effects they take decades to manifest and are almost ij the noise when/if they do.

So - ignore the stickers, get a Bluetooth headset (and Bluetooth equipped phone).

Russell McMahon
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    Re the research: It has been discovered that research causes cancer in lab rats. – Majenko Sep 27 '11 at 09:55
  • I don't know if it's the research or the researcher, but I would get in between the two. – kenny Sep 27 '11 at 11:52
  • @Majenko 4.3 years on :-) - ... by some researchers paid by some people under some conditions. Change various parameters and the results disappear. Also, too often the conditions required to produce some effect prove far from representative of human reality. eg rats may have had cell phones inserted in their brains or broadcasting stations strapped to their heads and operated at full power fro 25 hours per day :-). Whatever. | I am NOT saying the effects are not real but that they appear if they exist to mostly be down in the noise of civilisations other ills and that prudent avoidance ... – Russell McMahon Jan 07 '16 at 11:56
  • ... will get most of us to the end of an average life with a range of eg cancer sources possibly having been what killed us and no strong single certain cause. Yes? – Russell McMahon Jan 07 '16 at 11:57
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Most cell phones already have internal shielding. They are tested and must meet emissions standards. For example the FCC sets limits for cellphones sold in the USA. The shield layer may be a piece of light weight metal, but it can also be conductive paint.

Adding additional shielding, if the "gold" sheet is even real shielding, would do very little.

Jim C
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