Laminated bars are used to reduce eddy currents and a core with higher efficiency. In transformers you have higher efficiency with a minimum number of turns using insulated laminated sheets. Eddy currents are decreased in strength by using many thin sheets rather that a solid bar. The sheets should be insulated for optimum efficiency and to keep the laminates from shorting out with each other. Laminated blades have been used on Gretsch, Seymour Duncan custom and Bill Bartolini to retain the higher frequencies in a pickup.