# Opportunities in magnetic materials for high-frequency power conversion

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## Abstract

Power converters are increasingly being operated at switching frequencies beyond 1 MHz to reduce energy storage requirements and passive component size. To achieve this miniaturization, designers of inductors and transformers need magnetic materials with good properties in the MHz regime. In this paper, we argue that available materials are not optimized for MHz power conversion applications—even those that are marketed as such—and that further development of magnetic materials is needed. In particular, we review how magnetic components are used in power converters and demonstrate that reducing core loss should be the main target of future material development, as existing permeabilities and saturation flux densities are substantially higher than necessary. The progress of power conversion technology will depend in part on how well new magnetic materials can be optimized—properly—for the MHz regime.

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## Notes

1. Most students have learned in electromagnetics that larger $$N$$ leads to more B field. This is true, all else equal. In design, however, the target inductance is usually fixed and larger $$N$$ is necessarily accompanied by larger reluctance $$\mathcal{R}$$. Because gap length must scale more than $$N$$ to maintain inductance $$\left(L\propto \frac{{N}^{2}}{\mathcal{R}}\right)$$, the B field in the resulting structure is actually smaller. This result is captured more directly in (2).

2. The choice of notation for performance factor is fraught. Script $$\mathcal{P}$$ is commonly used for permeance, script $$\mathcal{F}$$ is commonly used for magnetomotive force, and PF is commonly used for power factor. Both $$\mathcal{F}$$ and PF have been used for performance factor in the literature; we opt for $$\mathcal{F}$$ because the abbreviation MMF is readily available for magnetomotive force.

3. Another class of components likely to be saturation-limited are pulsed components, i.e. those that are expected to carry very high current for a short amount of time. We only consider continuously-operated components in this paper.

4. Core loss density would be unaffected; technically the core volume is negligibly smaller when the gap length is increased, which leads to a negligible decrease in total core loss.

5. Higher component quality factors are almost always desirable, hence the lower limit on typical values. The upper limit comes partly from feasibility and partly from the diminishing returns on having extremely low losses in the magnetic component compared to other components in the system.

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## Funding

This work is not related to any funded research.

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Correspondence to Alex Hanson.

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Hanson, A. Opportunities in magnetic materials for high-frequency power conversion. MRS Communications 12, 521–530 (2022). https://doi.org/10.1557/s43579-022-00225-1