Soft magnetic composites (SMCs) were developed for induction heating, but the properties that made them useful there also matter anywhere AC magnetic fields are generated, guided or screened. This page sticks to what the published record supports: how SMCs compare with electrical steel laminations and ferrites, and where they have been applied outside conventional heat treating.
What an SMC is
An SMC has two parts. A soft-magnetic component, typically iron or iron-alloy powder, provides the path for magnetic flux. A dielectric component, usually an organic polymer binder, insulates the particles from each other to limit eddy currents. Particles are pressed at high pressure and cured or sintered, and the majority used in induction have an organic binder, which gives good machinability. Because each particle is insulated, the material does not provide a conductive path for large eddy currents.
SMC versus electrical steel laminations
Laminations are coated sheets of silicon electrical steel, typically 3 or 4% silicon, stacked in the plane of the field. The comparison from the ASM Handbook and Fluxtrol’s materials paper:
| Laminations | SMCs | |
|---|---|---|
| Saturation flux density | High (about 1.7 T) | Lower (see product pages) |
| Permeability | Very high | Lower, but sufficient in open circuits |
| 3D magnetic fields | Intense eddy-current heating | Perform well |
| Frequency | Up to about 30 kHz | 50 Hz to 13.56 MHz across types |
| Machining and assembly | Limited machinability, laborious assembly | Machinable; one or few pieces |
| Cooling | Complicated thermal management | Conduction or internal water channels |
| Size and cost | Very large simple parts; lower price | Plates up to 220 mm; higher price, though labor can offset it |
Laminations remain the right choice for very large, simple, low-frequency shapes. Many coils use both, with SMC at the end zones of seam annealers, where the field is 3D. For a direct drop-in, Fluxtrol LRM replaces laminations on low and medium frequency coils.
Why permeability is not the deciding number
SMCs have much lower permeability than laminations or ferrites, which raises doubts. Practical tests show a permeability of 20 to 40 is sufficient in most induction systems, because the magnetic circuit is open and the benefit stops growing above a limit. Gains are largest between 1 and about 10. High-permeability materials can even harm coil life by concentrating power in the copper corners.
Properties relevant to devices and sensors
- Linear behavior. SMCs are quasi-linear materials. Ferrotron permeability is almost constant over a wide range of field strengths, and a linear controller does not generate higher harmonics in coil voltage and current.
- High resistivity. Ferrotron 559H and Alphaform exceed 1 MOhm-cm. Alphaform can be applied to bare coil turns without shorting risk.
- Wide frequency coverage. Different SMC types cover 50 Hz to 13.56 MHz, with losses comparable to laminations at low frequency and to ferrites at high frequency.
- Shape freedom. Wall thickness under 1 mm has been machined, and formable grades fill irregular geometry.
- Surface treatments. Teflon, ceramic and plastic coatings, and impregnation, adapt SMCs to clean rooms, food packaging and demanding environments.
Documented uses beyond heating
The Fluxtrol materials paper lists biomedical treatment, food packaging, electronic clean-room processing and crystal growth among applications for SMCs, alongside heat treating and melting. Impregnated thin Ferrotron parts passed severe down-hole tests for oil and gas drilling. Fluxtrol’s R&D library includes electromagnetic processing of materials, where AC systems stir, cast, pour, transport and form melts at fields up to 12 T, and inductor design for hyperthermia research on magnetic nanoparticles. Core-loss research on SMCs to about 1 T near 150 kHz supports reliable design at high fields.
Sensors in induction systems
In induction equipment, SMCs also protect sensors and control components by eliminating the influence of the magnetic field on them. That is shielding, covered in detail on the shielding page .
Evaluate a new application
For a device or sensor application, define the frequency, flux density, geometry and environment first, because material and treatment follow from them. Contact Fluxtrol to discuss your application, or compare grades on the product page .
SMC families used in device work
Real-world results
Composite Materials for Magnetic Field Control in EPM (2009)
Overview of laminations, ferrites and SMCs (magnetodielectric materials) for AC magnetic systems used for stirring, casting, pouring control, transportation and forming.
- Fields from DC to several hundred kHz
- Intensities up to 12 T
Induction coil for cancer hyperthermia research (HES 10)
Inductor design for generating alternating magnetic fields to heat targeted magnetic nanoparticles in cell research.
- High-flux, high-frequency field in a relatively large volume
- Coil held between 35 and 39 degrees C for an hour or longer
Magnetic core loss at high fields (HES 19)
Calorimetric core loss measurements on SMCs up to about 1 T near 150 kHz, with discussion of the limits of traditional loss models.
- Core loss is a key factor in coil reliability prediction