[HN Gopher] Building a Faraday cage with data passthrough for ES...
___________________________________________________________________
Building a Faraday cage with data passthrough for ESP32 reverse
engineering
Author : signa11
Score : 62 points
Date : 2024-01-14 15:29 UTC (7 hours ago)
(HTM) web link (esp32-open-mac.be)
(TXT) w3m dump (esp32-open-mac.be)
| alright2565 wrote:
| The detail here is really great!
|
| I thought that maybe aluminum foil would work here. I found this
| paper:
| https://www.acsu.buffalo.edu/~ddlchung/Materials%20for%20ele...
|
| > electrical conductivity is not the scientific criterion for
| sheilding ... Metals ... function mainly by reflection.
|
| > A secondary mechanism of EMI sheidling is usually absoprotion.
|
| > The absorption loss is a function of the product srmr, whereas
| the reflection loss is a function of the ratio sr/mr, where sr,
| is the electrical conductivity relative to copper and mr is the
| relative magnetic permeability.
|
| > The reflection loss decreases with increasing frequency,
| whereas the absorption loss increases with increasing frequency.
|
| So it turns out aluminum foil wouldn't actually be much good,
| with srmr=.61 and sr/mr=.61. The commercial material listed says
| it uses copper & nickel: nickel's srmr=20, copper's sr/mr=1.
|
| So my thought here is completely wrong. Who would have figured
| the commercial product has gone through more thought than my
| random guesses!
| slicktux wrote:
| Wrap it in foil and stick it in the oven!
| qwertox wrote:
| Not sure if it was a joke, but shouldn't a microwave oven
| shield the 2.4 GHz band pretty well?
| bonzini wrote:
| The article says
|
| > I also tried putting my phone in a (turned off!) microwave,
| but this did not work either, it was still connected to the
| Wi-Fi access point.
|
| But yeah I would have thought the same.
| HALtheWise wrote:
| > I also tried putting my phone in a (turned off!) microwave,
| but this did not work either, it was still connected to the
| Wi-Fi access point.
|
| Apparently modern wifi chips are just too good at picking up
| faint signals.
| ComputerGuru wrote:
| Implying faint microwave signals also make their way out,
| of course.
| BenjiWiebe wrote:
| I have heard of WiFi slowing down when a microwave is
| running.
|
| Also when a phone is in a microwave, the RF noise is also
| attenuated, so that helps a little (amplifier noise is
| unaffected).
| MauranKilom wrote:
| My wireless headphones get an unbearable amount of pops
| and cracks when I'm wearing them close to my (running)
| microwave. But since I wear them virtually always, I am
| in effect virtually never next to my microwave when it's
| on :)
| myself248 wrote:
| The TitanRF fabric isn't super durable, so a shell around it is a
| good idea.
|
| I've had great luck with Ecofoil NT material, which is somewhere
| between cardstock and cheap poly tarp material in handling
| properties. (It's a polyethylene weave with foil on both faces.)
| Easy to work with, easy to fold and tape, easy to cover with
| other materials for durability. Super cheap in big rolls.
|
| For 120VAC passthrough, the Delta 20DBAG5 is cheap and cheerful.
| Screw it into a metal junction box and tape all sides of the box
| to the chamber wall. But a battery in the box is simpler and
| quieter.
|
| If you need windows/vents, avoid the hobby-store copper mesh
| that's meant as a stiffener for clay models; the way it's woven,
| it isn't guaranteed to have connections to itself in adjacent
| rows. It's good at first but any surface corrosion ruins it.
|
| Go with punched or "expanded metal" sheet, even if you can't find
| copper, aluminum or stainless works fine in practice. Just make
| it significantly larger than the window opening and use plenty of
| foil tape at the edges; I suspect that capacitive coupling
| through the surface oxide layer means it's an RF short even if it
| looks open at DC.
|
| I've been wondering if ITO-coated glass would work as a window
| but have not tried it. But it's no good for ventilation anyway so
| I'm not sure it's worth the bother.
| ph4te wrote:
| I worked for a service provider doing some cellular testing and
| we had a special clear box that did this. It was probably
| expensive at the time. I wonder how well those faraday bags or
| boxes for $20 work from amazon or ebay.
| H8crilA wrote:
| Don't the pcap dumps contain signal strength for each frame? Is
| it unreliably measured?
| crtified wrote:
| Layperson question : does it help if the Faraday cage is
| grounded, so that the waves it picks up have somewhere to "go"?
| or does it not work that way? (I fully expect it does not work
| that way!)
___________________________________________________________________
(page generated 2024-01-14 23:00 UTC)