Uneven distribution of magnetic flux in aconventional magnetic core limits improvement of power densityof the magnetic component. By making a magnetic corecomprising materials with different permeabilities, henceforthcalled multi-permeability core, a more uniform flux distributioncan be achieved without complex configuration and geometry ofthe core and winding. In this work, we designed a three-ring toroidcore to produce a flux uniformity factor, α, defined as Bmin/Bmax,in each of the three rings by increasing permeability from inner toouter ring. With the same inductance, volume of the threepermeabilitytoroid core was significantly smaller than that of asingle-permeability toroid core. For ease of fabricating multipermeabilitymagnetic cores, a commercial multi-extruder pasteextrusion3D printer was explored to process different magneticpastes into 3D structures. The magnetic pastes were formulated inour laboratory. Two types of magnetic paste systems, a hightemperature(> 900°C) pressure-less sinterable ferrite and a lowtemperature(< 250°C) pressure-less curable powdered-iron, weredeveloped and tested in the 3D printer. By varying themagnetic/organic composition in each of the two material systems,we produced pastes that are compatible with the 3D printer andcan be processed into core materials with relative permeabilityranging from 20 to 70. With the same dimensions, a 3D-printedthree-permeability toroid core had a higher inductance than asingle-permeability core.
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