[akiselev]

Miles of copper wire, thick titanium tube, large neodymium magnet, and C4. The hard part is the simulations/experimental design of the titanium part such that the exploding C4 and melting wire don't disintegrate the whole device before the magnet has had a chance to pass through the whole coil.

Last time I did the math though, you'd only get a few tens of kilometers of effect radius with an 20ft shipping container sized device so realistically, EMPs are only deployable using nuclear weapons detonated in the atmosphere.