Selection of magnets for permanent magnet synchronous machines in all-electric aircraft by applying decision science techniques

Permanent magnets are ubiquitous in aerospace applications, specifically in modern environment-friendly and high efficiency electric machines for energy conversion power generation, as in more-electric and all-electric aircraft. Since the last century, the industrial production of permanent magnets matured from steels through magnet alloys, ferrites, alnicos, and platinum-cobalt alloys to rare-earth-based permanent magnets. The permanent magnets for design and materials engineers for wide applications continually expand, including magnetic high-entropy alloys (HEAs). The selection of an apt permanent magnet catering to the application’s demands, as in permanent magnet synchronous machines in all-electric aircraft, is critical. The attribute specifics included long-term performance in harsh conditions, long service life, miniature sizes, reduced weight, superior retention force, etc. We analyzed the permanent magnets in the current literature by applying decision science techniques. Several interaction-based, utility-based, and distance-based multiple attribute decision-making methods (MADM) sorted and ranked the magnets based on the performance requirement of the intended application. Principal Component Analyses (PCA) consolidated the ranks of the magnets, while Hierarchical Clustering (HC) identified similarities (or differences) among the magnets. The ranks assigned by several MADMs, viz. including WASPAS (weighted aggregated sum product assessment), DEMATEL (decision-making trial and evaluation laboratory), WEDBA (weighted Euclidean distance approach), etc., were concurrent―the Spearman's correlation coefficients (S_ρ) was > 0.75! The decision science-driven technique identified variants of cobalt samarium and neodymium magnets as the top choice, followed by alnicos, ferrites, Pt-Co alloys, and magnetic HEAs. The investigation provided perspectives on critical properties for consideration, permanent magnet selection, substitute magnets, and potential existing materials to focus on further research and development.