Suppression of Eddy Current Loss in Multilayer NiFe-Polypyrrole Magnetic Cores Fabricated Using a Continuous Electrodeposition Process

Abstract

Metallic magnetic alloys are of interest as core materials in ultracompact or integrated inductors and transformers. However, when operated at high frequencies, such materials should comprise a multilayer stack of magnetic material laminations and electrically insulating interlayers to suppress eddy current loss. To achieve scalable and continuous fabrication of such a structure, sequential multilayer electrodeposition is an attractive approach. To achieve sequential electrodeposition, interlayer’s electrical conductivity should be sufficiently high to permit electrodeposition of subsequent layers, but sufficiently low to suppress eddy current loss. Polypyrrole, an electrodepositable polymer, was investigated as an interlayer material. Finite element modeling demonstrated a negligible difference in eddy current loss between NiFe/polypyrrole and NiFe/vacuum multilayers. Experimental verification of the efficacy was demonstrated as well. Compared with a single-layer NiFe inductor that has a comparable low-frequency (10 kHz) inductance value, a laminated ten-layer NiFe core showed higher inductance retention (88% of the low-frequency inductance for the laminated core versus 21% for the single-layer core) and lower ac resistance (1.68 versus <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$12.7~\Omega $ </tex-math></inline-formula> ) at 8 MHz, both of which are signs of suppressed eddy current. This scalable fabrication approach to high-frequency inductors will facilitate power converter miniaturizations.