How do I detect a Faraday bag coming into or leaving my store?
The intention of detecting Faraday bags is to be aware of customers who have the ability to walk out of the store with an RFID-tagged product that hasn't been paid for.
How do I detect a Faraday bag coming into or leaving my store?
The intention of detecting Faraday bags is to be aware of customers who have the ability to walk out of the store with an RFID-tagged product that hasn't been paid for.
First, the problem/challenge. The Faraday bag suppresses RF energy in both directions: RF to the tag, which energizes it, and RF return from the tag.
A classic conductive Faraday cage works by distributing RF energy across its surface, cancelling any effect on the interior. These may be grounded (like a shield room) to shunt energy away, or ungrounded, relying only on distribution of charge and skin effect.
More about Faraday cages here: https://nationalmaglab.org/about/around-the-lab/what-the/faraday-cage
In practice, a shield bag won't be a Faraday cage, but instead will be made of a lossy, absorptive material which converts RF to heat.
Example: https://slnt.com/products/faraday-bag
Anyway, I suppose you could sniff out such a lossy bag by measuring the overall return signal with a beam aimed at bag-height. If you see a dip in this signal compared to a person walking through without such a bag, then you might have something to act upon, assuming you have other evidence (such as surveillance footage showing them placing the item in the bag) that would legally entitle you to stop them.