Why do Faraday bags for phones need an insulation layer, while Faraday cages in science museums with people inside don’t?
I understand the metal layer is required so EM charges have a conductive route to pass through without entering the Faraday cage/bag. I understand that Faraday bags have an insulation layer under the metal layer, that is placed between the metal layer and the protected object, so that EM charges are blocked and don’t pass through whatever’s in the Faraday bag.
What I don’t understand is why this layer is not required in Faraday cages in science museums, where a volunteer is placed inside the cage and then the cage is lit up with high voltage electricity around, arcing through the air. What’s there stopping the electricity, which is already arcing through the air due to the high voltage, from arcing into the Faraday cage and reaching whatever’s being protected?
Please let me know if more information is required.
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It boils down to scale and direct contact. In a science museum Faraday cage, you’re generally not touching the metal walls, so you’re not part of the electrical circuit. Faraday bags need an insulating layer because you’re often putting your device directly into contact with the bag.
So, Faraday cages in science museums and Faraday bags function on the same basic principle: they use a conductive shell to redistribute external electrical fields, thereby shielding the interior from electromagnetic radiation. The big difference is how they’re used. In a museum setting, the Faraday cage is often much larger, and people inside it are not in direct contact with the metal cage. This is key because the electrical charge is evenly distributed on the exterior surface of the cage. As long as you don’t touch the cage, you’re not part of the electrical circuit, so you don’t get zapped.
On the other hand, with Faraday bags, the device you’re trying to protect usually comes in direct contact with the bag. That’s where the insulating layer becomes important. This layer ensures that the device isn’t in electrical contact with the conductive outer layer of the bag. This keeps the device safe even as electrical charges are being redistributed on the exterior of the bag.
So yeah, it’s pretty much about scale and how you’re interacting with the Faraday device. Science museum cages are big, and you’re not touchin’ em. Faraday bags are small, and you’re stuffin’ your electronics right in there. The insulating layer is an extra precaution to ensure that the electronic device is truly isolated.
Pretty sure it’s just to stop the phone getting scratched or otherwise damaged, and to stop the conductive metal accidentally interacting with the touchscreen.
The Faraday Cage itself stops electricity from effecting anything inside it, that’s what they do.
Faraday cages are big metal structures. They can be built to sustain their own weight.
Little tiny strands of metal are very flimsy. If there was no insulation layer on the bag, the metal would buckle under any force.
Geometry is also very important for faraday cages. The spacing between the wires determines what frequencies of EMI are attenuated and reflected. If it was just metal, you could change that structure and ruin it’s properties. The plastic gives that structure the rigidity and flexibility required to handle everyday use.
The Faraday cage only protects things strictly inside. You will still get zapped if you touch the metal. But in those demonstrations the cage is at least an arms length away. There’s no such distance in a flat bag, so you have to add an insulating layer.
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