Two technologies compete for the same job in modern power electronics: laminated electrical steel, the incumbent for a century, and soft magnetic composite (SMC), a pressed iron-powder material that allows three-dimensional flux paths. The choice is not about loss density alone — it is about shape freedom, frequency, and how the part is assembled.
1. The material comparison
| Property | Laminated steel (e.g. 35A300) | Soft magnetic composite |
|---|---|---|
| Saturation flux density | 1.6–1.9 T | 1.2–1.6 T |
| Permeability | High, anisotropic (in-plane) | Isotropic, lower (typically 100–500) |
| Loss at 50–400 Hz | Low | Moderate to high |
| Loss at 1–20 kHz | Rises sharply with thickness and frequency | Comparable or better due to particle insulation |
| Shape freedom | 2D laminations, stacked | True 3D pressing, near-net shape |
| Eddy current path | Constrained to lamination plane | Isolated between particles in all directions |
| Tooling | Stamping die, low cost at volume | Press tool, moderate cost, shape-dependent |
2. Where laminated steel still wins
At 50/60 Hz and at high flux density — distribution transformers, large inductors, line-frequency chokes — nothing beats grain-oriented steel. Its permeability is an order of magnitude higher, so a given inductance needs far fewer turns, and its loss at power frequency is lower per kilogram. If the design runs below roughly 400 Hz with a sinusoidal flux, SMC is usually the wrong answer.
3. Where SMC wins
Three situations favour SMC:
- Three-dimensional flux paths. Axial-flux motors, claw-pole machines and some transformer geometries cannot be built from stacked laminations at all.
- Higher frequency with thick steel. At 1–10 kHz, a 0.35 mm lamination develops significant eddy loss; SMC’s particle insulation keeps loss per unit volume competitive.
- Part consolidation. An SMC part can combine a core, a mounting feature and an air-gap structure in one pressing, removing assembly steps and tolerance stack-ups.
4. The design trap: isotropic but low permeability
Because SMC permeability is lower and its saturation lower, an SMC inductor needs more turns or a larger cross-section for the same inductance and energy storage. The part can therefore be heavier than the laminated alternative even though the material is lighter per unit volume. Model this before choosing: the correct comparison is wound-part mass and loss at the operating point, not material datasheet loss.
5. Practical selection checklist
- Frequency and flux waveform — sinusoidal or PWM with DC bias?
- Required energy storage or flux swing, and the resulting saturation margin.
- Whether the flux path is genuinely three-dimensional.
- Assembly cost: does SMC remove a stacking and bonding operation?
- Volume: stamping dies amortise well above 50k pieces; SMC pressing tolerates lower volume with more shape flexibility.
For power inductors above 20 kHz with DC bias, neither material is usually the answer: ferrite or a distributed-gap powder core from the Magnetic Core series will be smaller and cooler. Shaanxi SiRui Technology supplies iron powder, sendust, high flux and ferrite cores for those cases, and can advise on the boundary where SMC or laminated steel becomes the better engineering choice.
Send your frequency, flux and volume assumptions to sales@sirui-tech.com.