How are these coils so thin for a pulse metal detector? Can they be replicated for hobbyist use?

[CrizzyD]

Hi all,
I was looking at this industrial metal detector (I assume that it's pulse due to all the rocks) and noticed how thin it was. How are these coils so skinny? I have assumed that the wider the coil, the better as it means that the material is within the field for longer. If the coil is too thin then the return current path affects the magnetic field. Is it possible to make an ultra thin metal detector? How would that manifest in a DIY scenario? Could it be possible to make a single loop coil for a pulse design?
Link:
https://youtu.be/tqrwYeA3jqo?si=GVD4oE0YWOyc20KG

[Carl-NC]

Most likely the coil wraps all the way around the conveyor. That is, the rocks move through the center of the coil.

[pito]

LOOP SENSOR - MAGNETIC VEHICLE DETECTION - 10' LEAD
those loops have about 5 turns


my skinny coils , 10 mm

[CrizzyD]

Most likely the coil wraps all the way around the conveyor. That is, the rocks move through the center of the coil.

That was my first thought but the top and bottom have thicker sides that are more box-like. The system can also be disassembled. Metal travelling through the coil would be the ideal scenario but I don't think that's the case here. I would assume that there's separate tx and rx coils here.