Design and Additive Manufacturing of Multipermeability Magnetic Cores

Uneven distribution of magnetic flux in a conventional magnetic core limits the improvement of power density of the magnetic component. By making a magnetic core comprised of materials with different permeabilities, henceforth called multipermeability core, a more uniform flux distribution can be achieved without complex configuration and geometry of the core and winding. In this paper, we designed a three-ring toroid core to produce a flux uniformity factor, α, defined as Bmin/Bmax, in each of the three rings by increasing permeability from the inner to outer ring. With the same inductance, volume of the three-permeability toroid core was smaller than that of a single-permeability toroid core. For ease of fabricating multipermeability magnetic cores, a commercial multiextruder paste-extrusion 3-D printer was explored to process different magnetic pastes into 3-D structures. The magnetic pastes were formulated in our laboratory. Two types of magnetic paste systems, a high-temperature (>900 °C) pressure-less sinterable ferrite and a low-temperature (<250 °C) pressure-less curable powdered-iron, were developed and tested in the 3-D printer. By varying the magnetic/organic composition in each of the two material systems, we produced pastes that are compatible with the 3-D printer and can be processed into core materials with relative permeability ranging from 20 to 70. With the same dimensions, a 3-D-printed three-permeability toroid core had higher inductance than a single-permeability core.