I'd be curious if anyone finds it worthwhile to have a smartphone while being so paranoid that you have to hide it in a Faraday bag. I understand the problem. I just don't understand the practical use case: every time you use the phone, you have to take it out of the Faraday bag, and it can be used to spy on you or report information about you. Assuming you're keeping it in the Faraday bag all day, when and why would you find it useful and worth the risk to take it out? And with that level of use, wouldn't it be more practical to have a dumb phone or a laptop?
Testing Phone-Sized Faraday Bags
101–110 of 205 posts
Re: Testing Phone-Sized Faraday Bags
#102Earlier quoted context omitted.
Biscuit tins and aluminium foil have layers of insulation on them, the varnish of the tin and the Al2O3 oxide layer for the foil. It is true that the gap in each case is small, but when you look for 10 orders of magnitude in attenuation - a little leakage goes a long way. Silver has the unusual property in that both the metal and it's oxide are both conductors = true silver foil made of thin metallic silver will make…
I think the biggest issue with cookie tin cans is that they usually don't close all the way around, because the lid or the box is always slightly oval and not round (they always "stick" just in two or three spots when opening), so it looks like there's a small gap around half the circumference long - far bigger than the wavelengths in question. Square tin can works better because those seem to usually scratch on the…
I had to do some testing with ble temp sensors once we're I needed to isolate them and then put them in a freezer. They were in advertising mode so I could tell at least if I could see them with a phone. A round tin that was used for green tea from Japan was the most reliable method I was able to improvise. It fit very snug and the lid was about an inch deep.
Re: Testing Phone-Sized Faraday Bags
#103I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1]. Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups t…
> The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. Maybe the hotels you stay in, Bond, James Bond.
I admit the vast majority of my experience with hotels consists of a single repeated data point: the staff[1] suite(s) we shared in the Hilton attached to the SJ convention center. They always had glasses/shaker/etc. You could probably ask for a shaker from roomservice or the hotel bar, if necessary.
[1] If you registered for FanimeCon 2000-2011, the weird software you had to use was my fault...
Re: Testing Phone-Sized Faraday Bags
#104The pink bag shown is actually a static dissipative bag, not a static shielding bag, so would not be expected to work. Though the article mentions trying other bags so no doubt some of those where static shielding (metallic appearance) bags. I've had a lot of fun in the past trying to shield Bluetooth devices for testing... metal filing cabinet? Practically no attenuation. Biscuit tin? Minimal attenuation like in the…
I noticed this as well.
> "Makeshift Pouch 1: Electrostatic Mylar Bag"
This is not a mylar bag. It's frustrating how often these two are confused, especially when said confusion can result in component damage.
Re: Testing Phone-Sized Faraday Bags
#105> 20 dB represents a change of a factor of 10 in amplitude (volts), while 40 dB is a factor of 100, 60 dB a factor of 1000, and so on. I always thought it was 10dB, or one B that was a change of factor 10. Have I missed something?
TIL: Two principal types of scaling of the decibel are in common use. When expressing a power ratio, it is defined as ten times the logarithm in base 10. That is, a change in power by a factor of 10 corresponds to a 10 dB change in level. When expressing root-power quantities, a change in amplitude by a factor of 10 corresponds to a 20 dB change in level. The decibel scales differ by a factor of two, so that the related power and root-power levels change by the same value in linear systems, where power is proportional to the square of amplitude.
Re: Testing Phone-Sized Faraday Bags
#106> 20 dB represents a change of a factor of 10 in amplitude (volts), while 40 dB is a factor of 100, 60 dB a factor of 1000, and so on. I always thought it was 10dB, or one B that was a change of factor 10. Have I missed something?
You're missing the distinction of power vs voltage. dB is defined in terms of power.
Power is proportional to voltage squared.
So a 10x increase in voltage == a 10^2 = 100x increase in power == a 20dB increase in power.
Re: Testing Phone-Sized Faraday Bags
#107I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1]. Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups t…
What's the physics behind being able to make a container light-tight with a couple of right angle corners yet radio waves seem to leak out like water?
Microwave wavelength lower than visible light. It interacts with atoms differently by interacting with magnetic fields in atoms more.
There is:
- lines-of-sight propagation in free space,
- reflect from the surfaces like light (spectacular reflection)
- microwaves can be channeled trough tubes (think sound waves). If you fold a conductive material like tin foil multiple times, it can still work as a wave guide and escape.
Re: Testing Phone-Sized Faraday Bags
#108I really like Snowden's recommended Faraday cage for phones or other devices of similar size: two drink-shaker cups[1]. Drink shakers are cheap and widely available. The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar. The simple two-cup style (as seen in [1]) is preferred over the fancier "strainer top" style because you can press the two cups t…
> The average hotel room in any medium/large hotel chain probably includes a shaker as a standard item as part of the minibar
I've stayed in dozens of hotels all over the world, and never once have I seen a cocktail shaker in the minibar?!
Re: Testing Phone-Sized Faraday Bags
#109This is a super cool blog post. However I think it alludes to a much larger problem. For many products today, it’s very difficult or impossible for most people to verify the product works. For a network switch, there are free and open source tools like iPerf to test and verify speeds are as advertised. For a faraday box, you have to go through all these steps (and knowledge learned) just to be able to test these. Wha…
This problem was most famously studied by Akerlof in The Market For Lemons. The prediction is that such a market will be overrun with low quality lemons.
Re: Testing Phone-Sized Faraday Bags
#110Earlier quoted context omitted.
If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result). In that sense, “infinity” acts as the opposite charge, does it not? I do not understand your question, otherwise. (Not a criticism, just an interested comment which may be very wrong though).
> If you consider the compactification of R^3 by a single point “at infinity”, an electric charge inside the surface is the same as the opposite charge at infinity (this is just Gauss’ result) This is a mental operation, not physically possible. The difference is real: for example, charge inside a perfect conductor cavity generates electrostatic field outside. A charge outside perfect conductor cavity does not genera…
This is what I wondered about back in physics class. Does that prove the universe is not compact? If it were, then inside-outside is the same. But surely that's not enough to know the shape of the universe. My 'resolution' of this was to say that the universe is surely very large and so the time to reach equilibrium will be very very long. So the experiment cannot really be run to completion.
But would a point charge outside a conductor cavity ever come to equilibrium where it does generate an electric field inside the conductor cavity? Assuming compact but very large universe. It seems strange but I guess it would.