Neale Banks wrote:

Something like the packaging CityLink E-tags are delivered in?

Looks like metalised film - but much more metalised than anti-static bags, and much more robust than Al-foil.

Yes; just the thing; obviously E-tags can't be switched off; so they have to ensure, they won't trigger charges in transit ! ....but where do I get the stuff ? regards Rohan McLeod

Graeme Cross wrote:

Rohan, Do a search for MIL-B-81705 spec packaging. There are plenty of suppliers, in a variety of form factors. Regards Graeme Yes ; that looks like it would work; there seem to be a variety of suppliers; eg. http://www.grofitpl.com/html/grid_shield.htm; not finding many sources in melbourne in particular street fronts, though; may still finish up with old space-blanket ! thanks Rohan McLeod

Trent W. Buck wrote:

Rohan McLeod wrote:

...

I am investigating making a flexible faraday-cage for my mobile phone; I don't have experience myself, but everyone seems to be doing it. I presume you already tried these: Thanks I was actually just looking for fabric with a conductive coating; it is many years since I dropped out of Electrical Engineering; but enough must have penetrated to register, that there seems to be much confusion out there !

https://en.wikipedia.org/wiki/Faraday_cage

The Wikipedia article seems to have basically the right idea; it starts with static charges in hollow conductors; then talks about static charges in earthed hollow conductors. My take on the AC shielding effect is: A spacial oscillation of the charge would produce a spacial oscillation of it's electrostatic field; but since the voltage on the outside of the hollow conductor, must be everywhere the same with respect to earth and zero if it is earthed; no evidence of it's oscillation is transmitted beyond the enclosing conductor. It would have been useful to have the analytical expression for the ratio of the intensities of a pure sinusoidal electromagnetic wave of frequency 'f '; inside and outside a conducting sphere with a single hole of dia, 'D'. Seems to be ~ k.(2.pi.f.D)^6, but there is no derivation

https://duckduckgo.com/lite?q=cell+phone+faraday+cage

They seem very confused at duckduckgo; the essential problem seems to be the transparency of faraday-cages to static magnetic fields; but their known opacity to EM radiation.The simple explanation seems to be that one only needs to attenuate one component ; in this case the electric field to attenuate the EM radiation thanks Rohan McLeod

Trent W. Buck wrote:

.......................

So work out what the wavelength is for 3G or LTE or whatever, get mesh of the appropriate gauge, fold it in half and sew it together. There are two issues here: 1/ We established that aluminium foil works as a faraday-bag ;( even a single layer) and chip packets don't; by simply ringing the same phone first unwrapped and then unwrapped to see if it answered. -empirically it might be better if a simpler more robust test could be designed which by-passed cell phone technology; eg.some kind of radio-wave power meter in roughly the range of mobile phones? 2/ I'll keep the fine woven metal mesh (I assume that is what you proposed ?)idea ;as a fall back ; because I am still thinking of a 'bag'; after all a 0.6mm Al metal box would obviously also work

............ I doubt spotlight is hipster enough to stock something like that, but you could always call and find out. Well ready made bags from the fabric with an integral metal mesh seem to be available on eBay; Perhaps a fine chain-maille would also work ?

Further:

| A booster bag (shopping bag lined with aluminium foil) [...] is | often used by shoplifters to steal RFID-tagged items.^[4]

...sounds like a solution you can test without any special equipment, by getting off the sofa and walking into the kitchen. Note the "booster bag" article further clarifies that multiple layers of foil are apparently used. Well I'm merely avoiding embarrassment; not arrest !

The Talk:Faraday_cage article also mentions people testing cellphone reception from within an (inactive) microwave oven's faraday cage; this may be a useful reference point.

...

...

https://duckduckgo.com/lite?q=cell+phone+faraday+cage They seem very confused at duckduckgo; ddg.gg is a search engine -- like google except

http://dontbubble.us and http://donttrack.us

I'm not enthusiastic about them,................snip thanks I'll have a look; regards Rohan McLeod

Arjen Lentz wrote:

Hi Rohan

................snip Solution might depend on purpose.

If you want to prevent your own mobile phone from doing anything 2G/3G/wifi/bluetooth, you can put it in airplane mode. Is that not sufficient? From the particular to the general: 1/ I have an ancient NextG ZTE phone selected for it's extended coverage when TELSTRA closed the CDMA network; I am almost certain 'airplane mode' is not an available option.When for example I am in a hurry to avoid the embarrassment of having the opening bars of the 'William Tell Overture'( aka the Lone Ranger theme)...my ring-tone; play I 'boot the phone down'. That way I am certain it won't ring. Unfortunately booting it up is comparable in duration to booting up that other OS on a slow 386 cpu. 2/ As to why I persevere with such obsolete technology; partly laziness I have learned all it's quirks and partly stinginess ! I kept the analogue till they closed down analogue; the same with CDMA; if the phone breaks or NextG folds; I may try something else ! regards Rohan McLeod

Robin Humble wrote:

wouldn't the radio on a rf shielded phone ramp up to maximum to try to talk to a cell tower? ie. if you shield it, the battery use will go up. possibly not ideal... Yes that did cross my mind; if it flattened he battery with a 2hour use say ; I would consider it unusable; but providing I still have some charge left; it might still be acceptable; After making it and using it I will; report back ! regards Rohan McLeod

Brian Parish wrote:

I suspect that the phone may handle this a bit like a mail server - try hard for a while, then decrease the frequency of connection attempts to preserve battery. So the net effect may be quite subtle.

I admire your optimism, expecting cellphone vendors to have heard of exponential backoff. Personally I would expect the base system to have it, and then for all the telcos to turn it off in their branded versions so that the phone is "more responsive"... * * * Since nobody has suggested it before -- why don't you just remove the battery, so that the device is unpowered? Most RF equipment is effectively unreachable without a power source.

Trent W. Buck wrote:

Since nobody has suggested it before -- why don't you just remove the battery, so that the device is unpowered? Most RF equipment is effectively unreachable without a power source. Problem is that while quicker than 'booting-down'(also glacial); it is a bit fiddly; I want a quick,simple, certain way of shutting it up ! may even upset the phone......phones have feelings to :-) ; I joke ! no flames or digressions into machine consciousness please ! ; anyway the main reason is to avoid the long boot-up; but thanks Trent and others for the many ideas; regards Rohan McLeod

Hello Rohan, On Wed, 2012-10-10 at 15:47 +1100, Rohan McLeod wrote:

Trent W. Buck wrote:

...

Since nobody has suggested it before -- why don't you just remove the battery, so that the device is unpowered? Most RF equipment is effectively unreachable without a power source. Problem is that while quicker than 'booting-down'(also glacial); it is a bit fiddly; I want a quick,simple, certain way of shutting it up ! may even upset the phone......phones have feelings to :-) ; I joke ! no flames or digressions into machine consciousness please ! ; anyway the main reason is to avoid the long boot-up; but thanks Trent and others for the many ideas; regards Rohan McLeod

This thread has gone on while I have needed meatspace time. You do need a faraday cage, yes, but you need to understand how it works. It shorts the electric field component of the electromagnetic radiation, but needs sufficient thickness of conductive material. The issue is "sealing" the joints. Since it is difficult to get a good electrical contact, you can end up with an excellent waveguide that will "leak" signal. The way the microwave oven gets around that is a controlled gap where the door shuts into the oven cavity. By carefully controlling the width of the gap, and the length, you end up with the right electrical characteristics at the inner boundary. With the multiple frequencies for a mobile, a labyrinth seal that may have effective waveguides in parts, but discontinuous, should be effective. To make one, you could have a basic sheetmetal box, but soldered around the fixed seams, and then a similar box fitting over as a lid. With a thin sheet of adhesive plastic film to insulate them from one another, you can put the mobile in the box and put the lid on, and have it effectively shielded from the outside radio environment. The other material is 'muMetal", or radio metal, which impedes the magnetic component. I know of it, but not enough details to hand. You might find details on wikipedia, or such. There were other comments, and it might be worth while keeping an eye out on what is on offer. My mobiles were initially secondhand, a Motorola, then a Nokia, but then bough new, but as prepaid items, with the current one I never used the prepaid SIM card, just put in my Telstra postpaid SIM. They expect you to pay for the prepaid phone by using it on their network as prepaid, but you can use on the same network with the postpaid SIM. I type this with consideration of wanting a basic phone, but that the current phones are almost all so much more. Regards, Mark Trickett