Magnetism....it's well esoteric! (likewise Ross, I actually know very little about the science of magnetism...hence the trial & error aspect of making a good driver is my only option! I did find one magnetism forum, but didn't get much help there!)

OK, at the risk of straying well off all things CNC/Metalworking etc, for those that might not know, a guitar pickup typically has 'slugs' (mild steel 'cylinders') directly underneath each string with a ceramic magnet attached to the bottom. My (good) sustainer, emulates such a setup...the magnetism travels from the magnet attached to the bottom of the slug through the 'slug' & makes an appearance at the top (I don't yet have a gauss meter to measure the strength, but intend making my own gaussmeter with a PIC & a hall effect transistor soon).

The problem with a 'slug' design of sustainer is that a lot of guitars have different string spacings ....so for all this style performs well, if selling these eventually it's going to be a complete hassle establishing the guitar's string spacing & then having to make a custom bobbin to suit. (& Ross, since you ask....sting fade is not a problem when the string is bent between 'slugs')

The reason for wanting to now pursue a blade design is that it circumvents having to worry about the string spacing!