On a similar note, Fishman produce a range of electric guitar pickups that use stacked PCBs for the sense coil, rather than the traditional loop of enamelled copper wire. It's not necessary (and it's undoubtedly more expensive), but it gives them far more precise control over inductance.
Uh ... cool! He says "48-layer circuit board", so my initial guess is those are not super-cheap, no. I think a regular PC motherboard (which is not a very simple board) has 8-10 layers. 48 is a lot.
https://www.youtube.com/watch?v=oZSS13d3vZs
https://www.fishman.com/products/series/fluence/