Hello. I finished now building my Faraday cage, by glueing aluminium can's sheets around a shoebox. But when I tested, it didn't work. I've put one wireless home telephone inside it, and pressed the button on the base that makes the phone beeps, in order to allow the owner discovering where the hell is the telephone. It beeps as there was no aluminium around it... What have I done wrong?
OK, I connected the aluminium layer of the cage to the "ground" of the power outlet, and it still beeps. Whould I remove the external protection layer (anti-oxidation) of the aluminum sheet?
>What have I done wrong?
You should design an actual Faraday cage for the specific RF you want to block instead of merely putting something in a box covered with aluminium. That almost does nothing.
The first step is to acquire a little bit of autonomous problem solving capability: start like this: http://lmgtfy.com/?q=how+to+design+faraday+cage
A metal box will work. You don't need a "cage." The holes of the "cage" are normally sized to be smaller than what needs to be blocked. Making them solid will block everything.
It isn't properly grounded. Also, are all parts of the box grounded? Like is the lid grounded? You should solder the connections. A proper ground will be connected to several long copper rods driven at least 8 feet into the ground. Don't use the ground of your electrical system.
I've already read http://www.thesurvivalistblog.net/build-your-own-faraday-cage-heres-how/ , the first result.
>You should design an actual Faraday cage for the specific RF you want to block instead of merely putting something in a box covered with aluminium.
I want to block all RF.
The text I linked says:
>Therefore, wrapping a box in a couple of layers of heavy duty aluminum foil (typically about 24 microns thick) provides the necessary conductor thickness to protect against high-frequency radiated fields.
I think an aluminium can sheet has more than 24 microns.
>The bottom line is that an ungrounded cage protects the contents from harmful electromagnetic fields as well as a grounded one.
>What have I done wrong?
The gaps in aluminum interrupt induced current, causing voltage rise on them working as slot antenna.
For it to shield at any frequency it must have solid connection between sheets. Easiest and most sure way would be soldering or welding the sheets together. There are conductive glues and tapes but those will only work for certain frequency ranges.
Specifically with aluminum it's even worse - it has a constant layer of oxidation on top of it, denying good connection with any glues, tapes and making it nearly impossible to solder.
Also, generally, a solid metal cage must have walls thick enough to accommodate full skin-effect depth of your interested frequency range. Otherwise currents reach inner surfaces and cause radiation. So unless you have superconductor 24um is shit.
I'd start with getting nice sheets of steel that you can braze, copper clad boards you can solder together or lead sheets.
i haven't used it on a dect handset but i have put an fm radio in an old biscuit tin and it worked great.
you just have to make sure there are no gaps and that the whole thing is conductive.
if you glued the sheets together with a protective film on them then they will be insulated from each other.
try adding some solder joins between the different sheets for example.
look up about the electric potential inside a hollow charged sphere or something similar if you are interested in the maths and proof but the whole idea is that it only works if the entire surface is electrically connected.
>The gaps in aluminum interrupt induced current, causing voltage rise on them working as slot antenna.
I "glued" with paper adesive tape over it (white strips in the photo), and double-faced plastic adesive tape below it. The border of the aluminium layers are below another borders of aluminium layer, at least.
But I see the problem, one face is blank, but the other is covered with paint of the brewery...
I searched Google and found that one artisan soaks steelwool with acetone and rubs the painting, turning the paint into liquid and cleaning the cans. What to you think about this?
>unless you have superconductor 24um is shit
But... the text I linked here >>929135 says 24 microns is OK for aluminium foil!
That's for 200Mhz. Some older cordless home phones, walkie talkies etc can operate as low as 1.7MHz (62.8937um skin effect). And that's just the theoretical value (read - being optimistic about losses etc).
But mostly I'd choose more solid sheets just for their work-ability and smaller chance of damaging them. Just getting the paint off wont help much unless you can make contact that scrapes trough the oxidation (e.g. riveting).
Another point I'd look into is the lid. If there is a lot of tape creating it's shape it's not going to work. You decent need a wire connecting lid to rest of the case and some shielding strips. For DIY thing the same steel wool (or better yet - copper scourer) around the edge of box might provide enough seal. Or you could get crafty and make your own strips identical to the commercial ones (pic. related).
>i have put an fm radio in an old biscuit tin and it worked great
But I want to store hard disk drives. It's needed that it's big enough to handle some of them.
>look up about the electric potential inside a hollow charged sphere or something similar if you are interested in the maths and proof
I don't know... I can study that, but I guess I don't have the equipment to test if my cage follows the mathematical model...
>if you glued the sheets together with a protective film on them then they will be insulated from each other
>the whole idea is that it only works if the entire surface is electrically connected
Why not just use this?
I probably would have just went and found an ammo box.
>I probably would have just went and found an ammo box.
This, but you still have to solder a wire between the lid and rest of the box. Otherwise, they can be isolated due to paint or corrosion.
The reason your box and most faraday bags and boxes don't work is because of the signal strength.
I don't know the strength of the signal coming from your base unit. But you could move the handset farther away and determine the minimum distance required to block the signal. And compare that to an in shielded distance
Yes I said...
>>Faraday bags, boxes, cages don't work.
Here is link to a study I participated in when I was at Purdue. The study was done because cops had phones ringing inside the bags. Keep in mind this was prior to most phones having air plane mode.
Katz found taco wrappers from Taco Bell worked better then faraday bags.
It's not that people don't register, it's that, given few exceptions, only police and army can register guns... Or I get one box with them (presuming they have metal boxes, they can have only cardboard boxes, or no boxes at all), or I go to the drug dealers, which certainly do not have boxes (boxes are harder to hide than small amounts when someone transports them to sell to drug dealers), and will laugh at me and kill me for being an idiot. The only way to survive would be buying drugs from them, but I will not even discuss this possibility, because this isn't allowed in this chan.
There are no other people with guns, and who has them probably have small amounts of bullets, like 20 bullets at maximum, because they are very expensive (taxes, import, import taxes) and hard to get. It's needed to get approval from authorities for getting bullets, and you cannot use them in general.
It's not USA, where you can buy bullets in any market and receive guns as reward present for buying much bread in the bakery. Also, there are no amateur shooters or shooters clubs, at maximum olympic shooters, but even in this case I'm not sure, I don't like Olympics.
There are no military surplus stores. Aside from I already said here >>929359 , military-grade and police-military-grade guns and bullets are not allowed for normal people. It's not allowed to sell these things, and noone would buy aside from drug dealers, because normal people do not own military guns, so it's useless (and a crime) to have military bullets.
The surplus military ammo boxes don't contain actual ammo. They are left overs from the military and sold for other purposes. They make great project boxes. You can order them online.
I'm sure your country allows cookies right? There should be cookie tins. Some might even have cookies in them, which is a bonus.
I will consider searching for ammo boxes, but I still doubt the army has metal boxes. The budget isn't very high, to prevent coup d'etát, plus there are many intermediaries in the armys' transactions, and the more men, the more money is stolen, leading to even poverty in the equipments.
Cookies are not sold in metal cans. They are sold in blastic bags, or, if they are "premium", in cardboard boxes. Also, I imagine this cans as being too small for holding many hard disks.
cookies are most certainly sold in metal tins. It is very cheap to stamp shapes out of metal. Yes ammo cans are metal too.
Your faraday cage is probably not working because the aluminum cans you used are coated with an insulating layer so they can hold food.
I would not be surprised of you got better results with just plain ol' aluminum foil
i was told RF waves get reflected when they hit metal but you guys say it is getting used by the device in the box which makes zero sense. for example blocking 2.4ghz rf needs only holes less than 10cm cause the wavelength... i am so f-ing confused now