Ever been into a store, and had to walk between those sensors that beep when you forget to deactivate a tab? I took one apart recently, and took a few photos.
Outside is the drive coil, made from an aluminium strip wound into a massive coil, insulated with foam strip similar to double sided tape just not sticky. Wires are soldered to the ends and it is wrapped with clear tape. About 1kg of aluminium strip just in that coil alone.
In the middle you have the detector coils, at right angles to the drive coil ( for maximum rejection) and shielded with a wrapped aluminium shield and another plate to provide extra shielding.
Inside there you have the detection coils, around 100m of copper wire wound on a former, with a shielded cable to the sense electronics in a big pair of boxes separated from the coils, and connected by a mess of cabling.
