Earlier, we discussed why motor stator cores need to be “sliced”—to interrupt. Vortex The engineer cut an entire block of iron into hundreds or even thousands of thin sheets.

However, when silicon steel sheets have already become as thin as cicada wings—0.2 mm or even thinner—and physical processing has reached its limits, how can we further reduce losses and maximize motor performance?

Table of Contents

01 Advanced Insulation: Say Goodbye to Soldering and Rivets—The “Black Tech” of All-Surface Self-Adhesive Coatings

02 Lane-Changing Overtaking: The “Benefits” and “Costs” of the New Materials Corps

03 Fine-tuning Magnetic Domains: Performing a “Laser Minimally Invasive Surgery” on the Magnetic Field

04 Ingenious Structural Design: Magnet Splitting and Litz Wire

05 Source Control: Don't Let the Current Be “Too Dirty”

06 Conclusion: The Ultimate Journey from Macro to Micro

07 Advanced Insulation: Say Goodbye to Soldering and Rivets—The “Black Tech” of All-Surface Self-Adhesive Coatings

We often talk about “stacking sheets,” but how can hundreds of slippery silicon steel sheets, when stacked together, be transformed into a strong, tightly integrated whole?

The traditional industrial practice is typically: Rivet buckle 、 Welding Or Threaded screw 。
Although these methods are low-cost, in high-end applications, they bring... Two fatal “side effects” ：

L Insulation breakdown (short-circuit risk) Riveting involves deforming the sheet metal pieces through stamping to join them together, while welding uses high temperatures to melt the metal. Both processes directly damage the insulating layer on the surface of the silicon steel sheets, artificially creating... Interlayer conductive point It’s as if several holes had been dug in a dam that had taken so much effort to build—the eddies would then “reignite” along these conduits, leading to localized overheating.

Insufficient rigidity (vibration and noise) The traditional fixed mounting method is essentially a “point-to-point connection.” The individual pieces do not fully fit together. When the motor spins at tens of thousands of revolutions per minute, tiny frictional movements occur between the iron sheets, generating high-frequency squealing—a type of energy loss itself—and also hindering heat conduction.

To thoroughly address this pain point, a disruptive process has been born— Full-surface coated self-adhesive coating 。

Figure 1: Comparison of Coating Processes: Traditional Rivet/ Welding vs. Full-Surface Self-Adhesive Coating

Note: The conventional methods on the left—such as riveting, welding, and screw fastening—create physical holes on the surface of the steel sheets, directly damaging the insulation layer and providing a “short-circuit path” for eddy currents. Moreover, the sheets only make contact at a few discrete points, leaving air gaps between them, which makes it difficult to dissipate noise and heat. In contrast, the full-surface self-adhesive coating on the right eliminates physical connections altogether. It uses a special epoxy resin to completely cover each steel sheet at the molecular level, achieving complete electrical isolation. At the same time, the resin fills even the tiniest gaps, enhancing thermal conductivity.

What is “full-surface self-adhesive”?

This process eliminates physical connections. On the surface of each silicon steel sheet, we uniformly coat a ultra-thin layer. Special thermosetting epoxy resin After lamination, this resin layer undergoes a chemical cross-linking reaction upon heating and curing, fusing hundreds or even thousands of steel sheets together at the molecular level.

How powerful is the performance?

This coating is a “specialized piece of equipment” designed for extreme operating conditions:

Ø Withstands temperatures up to 180℃ When a high-performance motor is running at full speed, the inside of the iron core becomes like an oven. Ordinary materials would have long since softened and failed, but specially formulated epoxy resin coatings available on the market can withstand such conditions. 180℃ high temperatures—even some self-adhesive coatings can withstand temperatures as high as Above 220℃ Under high temperatures—such as the aerospace-grade self-adhesive coating from HuaCi Technology—the bond strength remains as strong as steel, ensuring that the motor does not fall apart or deform even under extreme thermal loads.

  Ø Pull-out force Its vertical tensile strength can reach 2–4 N/mm² Does this number seem abstract? Let’s do a conversion: This means that on an adhesive surface only the size of a fingernail (about 100 mm²), it can withstand— 20 to 40 kilograms The tensile strength! After the entire iron core has been cured, its mechanical strength rivals that of solid steel.

The core logic behind reducing consumption:

Electrical isolation The pieces are completely isolated from each other by resin, with no metal contact points whatsoever—leaving eddy currents with absolutely no path to follow.

    Ø High damping and high thermal conductivity The iron core has been transformed into a highly damped monolithic structure, eliminating micro-motion friction and significantly reducing noise. Meanwhile, the resin has filled the tiny gaps that were previously occupied by air, enabling heat to dissipate more smoothly and further lowering temperature rise.

02

Switching to Overtaking: The “Benefits” and “Costs” of the New Materials Corps

As the physical potential of silicon steel materials has been fully exploited, scientists have begun searching for alternatives. But remember: in materials science, there’s no such thing as a perfect hero—every new material has its own quirks and challenges.

I. Amorphous Alloy: Metal Like Glass

[Principle] Through rapid quenching technology, molten metal is instantly solidified, leaving atoms insufficient time to arrange themselves in an ordered manner and thus forming a disordered structure similar to that of glass.

【Bonus】 Its thickness is only one-fourth that of A4 paper (about 0.025 mm), and it has an extremely high resistivity. Compared to conventional silicon steel, its no-load loss can be reduced. 70%-80% It is the “energy-saving champion” in the field of distribution transformers.

【Cost】 ： Extremely brittle, high hardness It is extremely difficult to process and tends to crack easily even under slight stress. Moreover, its saturation magnetic flux density is relatively low, resulting in a larger device size for the same power output.

II. Nanocrystalline alloy The evolutionary version of amorphous.

[Principle] A special annealing treatment is performed on an amorphous base to precipitate nanoscale microcrystals.

【Bonus】 It boasts both high permeability and low loss, making it ideally suited for high-frequency transformers and precision current transformers.

【Cost】 The process is extremely complex and the manufacturing cost is high.

3. Soft Magnetic Composite Materials: Iron Powder Coated with an Insulating Layer

[Principle] The surfaces of tiny iron powder particles are coated with an insulating film, and then the coated particles are compressed into shape just like tablets.

【Bonus】 Because each particle is insulating, eddy currents are confined within the micrometer-sized particles and cannot form macroscopic circuits. It is ideally suited for... High-frequency motor Moreover, since it’s produced by powder compaction, it can be shaped into complex 3D topologies (such as claw-pole motors)—a feat that cannot be achieved with laminated steel sheets.

【Cost】 After all, it’s made by pressing powder into shape. Relatively low mechanical strength Moreover, since the spaces between particles are entirely insulating (equivalent to having only tiny air gaps), the magnetic permeability is lower than that of solid steel plates, requiring a larger current for excitation.

4. Ferrite: Magnets That Resemble Ceramics

[Principle] A metal oxide ceramic that is essentially a semiconductor or an insulator.

【Bonus】 Its resistivity is tens of thousands of times higher than that of metals, and eddy-current losses are virtually zero. It is the preferred choice for ultra-high-frequency (MHz-level) switching power supplies.

【Cost】 The saturation magnetic flux density is extremely low (easily saturated), making it completely unsuitable for the demanding task of driving high-power, high-torque motors.

Figure 2: Performance Comparison Table of Four New Magnetic Materials

Note: Although amorphous alloys can reduce losses by 70% to 80% and are thus the “energy-saving champion” for distribution transformers, they are extremely brittle—any slight mechanical stress can cause them to shatter—and are extremely difficult to process. Nanocrystalline alloys, on the other hand, incorporate nanoscale microcrystals precipitated within an amorphous matrix, combining high permeability with low losses, making them ideal for high-frequency applications. However, their manufacturing process is complex and costly. Soft magnetic composites (SMC), which consist of iron powder particles coated with insulating films and then compacted into shape, can be used to create intricate 3D structures—but they have relatively low mechanical strength. Ferrites are ceramic materials with nearly zero eddy-current losses, making them the preferred choice for MHz-level switching power supplies. Yet, they have extremely low saturation magnetic flux density and cannot handle high-power motors.

03

Domain refinement: Performing a “laser minimally invasive surgery” on the magnetic field.

In addition to handling materials and insulation, The high-end grain-oriented silicon steel sector (primarily used in large-scale transformers) Scientists have also tinkered with the magnetic field itself.

There are many inside the silicon steel. Magnetic domain You can think of them as little “magnet squads.” If these squads are too large (with broad magnetic domains), when the direction of the current changes and they’re required to “turn around,” their movements will be extremely slow and accompanied by tremendous internal friction, which in turn generates... Abnormal Eddy Current Loss 。

Thus, Laser scribing technology Emerging with the times:
By rapidly scanning the surface of silicon steel sheets with a high-energy laser, we create traces that are barely visible to the naked eye, introducing microscopic stress. This stress acts like a wall— “Chop” the originally broad magnetic domains into narrow, flexible small teams.

Once narrowed, the magnetic domains respond extremely quickly, significantly reducing “friction” during rotation. With just this one technique, transformer iron losses can be reduced by another roughly 10% on top of their already very low baseline levels.

Figure 3: Working principle of magnetic domain refinement: A comparison between the wide magnetic domains of conventional silicon steel and the refined magnetic domains after laser scribing.

Note: On the left, the magnetic domains in conventional silicon steel are large and thick. When the direction of current changes, these “little magnetic squads” must all flip simultaneously—much like a massive army turning around. This results in significant friction and corresponding energy losses. On the right, after laser engraving, a high-energy laser scans the surface of the steel sheet, leaving microscopic traces that are barely visible to the naked eye. These traces introduce microstress, acting like invisible “walls” that divide the large magnetic domains into countless tiny, narrow squads. With these refined domains, the response becomes much quicker, dramatically reducing friction during flipping. Just this one simple step alone can further reduce iron losses by another 10%.

04

Clever Structural Design: Magnet Segmentation and Litz Wire

Reducing eddy currents isn't just a matter for the iron core—it's also relevant in motors. Other components Also a victim of eddy currents.

I. Segmentation of Magnets:

In permanent-magnet motors, although rare-earth permanent magnets have a higher resistivity than copper, they still generate eddy-current heating under the harmonic magnetic fields produced by high-speed rotation. Once overheated, the magnets will suffer permanent demagnetization, rendering the motor irreparably unusable.

The engineer’s approach is simple and straightforward: Cut a large magnet into several small pieces, insulate the spaces between them, and then reassemble them. It’s as if the highway has been cut off, completely severing the vortex’s large-scale circulation loop within the magnet.

II. Leeds Line:

For copper windings, high-frequency currents tend to flow along the surface (skin effect), resulting in wasted material in the center and increased resistance. Litz wire transforms a single thick conductor into... Hundreds or thousands of individually insulated, fine enameled wires are twisted together. Together, they force the current to distribute evenly, significantly reducing copper losses and eddy currents at high frequencies.

Figure 4: Ingenious Structural Design: A Comparison of Two Vortex-Reduction Approaches—Segmented Magnets vs. Litz Wire

Note: The magnetic segmentation approach for the upper half: A single large rare-earth permanent magnet would generate significant eddy currents when exposed to a high-speed, harmonic magnetic field. To address this issue, engineers adopted a straightforward yet effective solution—cutting the large magnet into several smaller pieces and separating them with insulating materials. This is akin to cutting off a highway: without a continuous, large-scale current loop, eddy currents are forced to break down into weak, microscopic loops instead. As for the lower half—the Litz wire approach: In conventional thick conductors, high-frequency currents tend to flow only near the surface due to the skin effect, leaving the central portion underutilized and contributing significantly to increased resistance. The genius of Litz wire lies in its design: it transforms a single conductor into hundreds or even thousands of thin, individually insulated enameled wires twisted together. This forces the current to have no escape route and obliges it to distribute evenly across each individual wire, thereby delivering outstanding high-frequency performance. The underlying logic behind both approaches is the same: “segmentation and isolation”—breaking up large current loops, eliminating the skin effect, and leaving no place for energy to hide.

05

Source Control: Don't Let the Current Become "Too Dirty"

All the techniques discussed earlier represent “passive defenses” implemented within the motor itself. Yet there’s one critically important dimension that’s often overlooked— Power supply purity 。

This is “source-based governance.”

Eddy-current losses follow a harsh physical law: Loss is proportional to the square of the frequency. (Pe∝f ² ).

This means that as the frequency increases, eddy-current losses will increase exponentially.

Most modern motors are now made of Driven by a variable-frequency drive (VFD). The output from the VFD is not perfect. Sine wave rather, it consists of countless square-wave pulses (PWM waves). This waveform is rich in higher-order harmonics.

I. What are harmonics?

Think of electric current as food for a motor. The fundamental wave—the main frequency—is like nutrient-rich rice that generates torque; whereas higher-order harmonics are like sand and stones mixed in with the rice.

These high-frequency “sand grains” contribute almost nothing to the motor’s rotation, yet their frequencies are extremely high—possibly tens or even hundreds of times that of the fundamental frequency. According to the square-proportionality law, these high-frequency components induce intense eddy currents on the surface of the iron core, causing the motor to heat up inexplicably.

Figure 5: Relationship between Current Waveforms and Harmonics: Comparison of Sine Wave and PWM Waveforms, as well as the Relationship Between Eddy Current Loss and Frequency Squared.

Note: The upper part of the figure compares an ideal sine wave (a clean 50/60 Hz fundamental wave) with the PWM wave output by the inverter (a complex waveform rich in higher-order harmonics). Frequency spectrum analysis reveals that, in addition to the fundamental frequency, multiple harmonics such as the 3rd, 5th, and 7th also appear. The key pattern in the lower part is that Pe ∝ f²—eddy-current losses are proportional to the square of the frequency. This means that when the frequency doubles, the losses increase by a factor of four. While the fundamental frequency contributes to motor rotation, the higher-order harmonics are like “sand mixed into the rice”—they merely induce intense eddy-current heating within the iron core.

II. How to treat it?

This requires a combination of software and hardware.

Hardware-wise : Install between the inverter and the motor Sine wave filter or Reactor Filter out high-frequency noise and turn “brown rice” into “white rice.”

On the software Optimizing the inverter Control algorithm (Such as the SVPWM modulation strategy) actively reduces the harmonic content in the output waveform (lowering THD).

If the motor “eats cleanly,” the iron core naturally won’t “get overheated.”

06 Conclusion: The Ultimate Journey from Macro to Micro

Now, we’ve finally put together the complete puzzle for combating eddy-current losses. Looking back on this invisible battle, we realize it’s an extraordinary journey that spans across all scales:

Figure 6: Comprehensive Framework of the Five Major Energy-Saving Key Strategies

At the source (control layer) We use algorithms to purify the current and eliminate interference from high-frequency harmonics.

On the surface (micrometer layer) We use 220℃ High-Temperature Resistant, Full-Surface Self-Adhesive Coating Replacing damaged insulation with riveted buckles achieves both electrical isolation and mechanical strength—a triumph of the manufacturing process.

In the ontology (material layer) We select based on the scenario. Amorphous, SMC Leverage the material’s inherent physical properties to deliver a decisive blow by reducing dimensionality.

At the microscopic (quantum) level We utilize Laser scribing Refine magnetic domains and reduce friction during magnetic moment flipping.

Reducing eddy-current losses isn't just about saving a few degrees of electricity.

It means electric vehicles can travel dozens of kilometers farther; it means industrial robots can stop with pinpoint accuracy at the hair-strand level; and it means massive transformers no longer have to be so noisy or generate so much heat.

The precise control of every micrometer-thick coating, the incremental increase in bonding strength by every newton, and the bold experimentation with each new material—all represent engineers’ relentless exploration at the very edge of physical limits. It is precisely these converging “black technologies” that enable our energy heart to beat cooler, stronger, and longer.

The above information is excerpted from the WeChat public account “Motor Core Researcher.”