Electric motor design has been shaped for a decade by the assumption that rare-earth permanent magnets are simply the cost of good performance. That premise is now colliding with volatile pricing, concentrated supply chains and a heavy extraction footprint, forcing a harder look at whether magnet-free alternatives can match permanent-magnet motors without pushing complexity into the rotor or onto a redesigned vehicle platform. What follows traces that argument from the range of magnet-free motor types through to the UESM’s system-level answer.
Exploring Magnet-Free Electric Motor Technologies
Magnet-free traction motors aren’t a single substitute for permanent-magnet machines; they’re a family of approaches, each moving the engineering burden somewhere else. Induction motors generate rotor field through currents induced in a conductive rotor; synchronous-reluctance machines produce torque by aligning a shaped, salient rotor with the stator’s rotating field; and wound-field synchronous machines create rotor flux with a DC field winding. Each replaces fixed magnet flux with electromagnetic design and control, and each trades that flexibility for losses, cooling demands, torque ripple or rotor-power delivery challenges. A review of rare-earth-free EV motors identifies induction, synchronous-reluctance and wound-rotor machines as viable alternatives, while noting the difficulty of matching permanent-magnet performance across the full operating range [1].
Wound-field architectures take the most direct route: three-phase stator windings create the rotating field, while separate rotor coils set field strength. ZF’s I2SM illustrates one method, transferring excitation energy inductively into rotor coils to avoid brushes and slip rings [2].
The Unique Design of the UESM
The UESM follows the wound-field route, replacing the rotor’s fixed magnetic field with electrically controlled excitation. Rather than relying on rare-earth magnets to establish flux continuously, it supplies rotor field strength only as the operating point requires, so torque production and field level can be managed together instead of fixed by material properties. Externally excited synchronous machines still need power to create that field [3].
The design goal, then, isn’t simply a different rotor: it’s a magnet-free synchronous motor that runs on a standard three-phase inverter and avoids adding rotor-side power electronics. That removes both the magnet material and its rotor-integration steps from the bill of materials, opening a route to lower cost without treating reduced performance as the price of supply resilience. Recycling initiatives address the incumbent magnet stream [4]; electrical excitation instead removes magnets from the motor’s field-generation mechanism entirely.
Limitations of Existing Designs
Permanent-magnet motors carry a materials-market exposure directly in the drivetrain bill of materials. When rare-earth availability or pricing shifts, manufacturers face a cost variable that motor control or production efficiency can’t resolve on its own. Concentrated processing capacity compounds the risk: a disruption at a handful of facilities can affect production schedules as well as margins.
Recycling can reduce dependence on newly mined material, but it doesn’t remove dependence on rare-earth magnets themselves. US Strategic Metals and Ionic Rare Earths’ planned Missouri facilities, for instance, would recover NdFeB and SmCo materials from spent magnets and scrap, at an initial investment of $100 million [4] [5]. That’s a meaningful supply-chain response, but unlike a design that eliminates the magnets altogether, it leaves motor adoption exposed to the same constrained material class it’s trying to manage.
Advantages of a Magnetless Approach
Where permanent-magnet motors carry that exposure structurally, a magnet-free architecture removes it rather than manages it. Eliminating rare-earth magnets takes out both an expensive material input and the manufacturing steps needed to shape, handle and assemble magnet components; unlike strategies that recover magnets for reuse, magnet-free designs don’t require a continuing magnet supply at all [4].
The trade-off shows up as heat. Reluctance and electrically excited machines can need higher current to produce comparable torque, raising I²R losses and making continuous output dependent on winding, cooling and control design. Rare-earth-free machines therefore face genuine thermal-management and torque-ripple challenges rather than an automatic performance advantage [1]. But when those constraints are designed into the motor from the outset rather than discovered afterward, removing magnets becomes a manufacturable route to lower material exposure, not a concession on viability.
Magnetless by Design: The Role of UESM
The engineering test for any electrically excited design is whether removing magnets simply relocates the cost and complexity elsewhere. Some wound-field machines solve rotor excitation with dedicated energy-transfer hardware; others avoid that hardware but carry a heavier thermal load as a result.
The UESM is built to avoid treating either penalty as inevitable. It uses electrically excited rotor operation without extra rotor components or rotor power electronics, and it runs from a standard three-phase inverter. [Magnetless Internal] That keeps field strength controllable across the full operating range rather than fixed by magnet material, while retaining synchronous-machine operation and avoiding the added rotor hardware that some competing wound-field approaches require. The result is that rare-earth removal becomes a design-level route to lower material exposure, achieved by treating rotor excitation, winding architecture and cooling as one problem rather than solving each in isolation.
A System-Level Approach to Motor Innovation
A credible magnet-free traction motor can’t be designed as a simple component swap. Since magnet-free designs typically draw higher current and carry higher I²R losses, that shift makes winding architecture, cooling, control and production tolerances part of the performance equation rather than afterthoughts. The broader rare-earth-free motor field faces this same multi-variable trade-off across power density, cost, manufacturability and vehicle-level performance [6].
That’s why the UESM is engineered as one system rather than a rotor swapped into an existing design: electrically excited rotor, windings, thermal path, control strategy and manufacturing process are developed together, while retaining compatibility with a standard three-phase inverter. The objective isn’t merely to eliminate a material, but to remove its cost and supply-chain exposure without transferring that complexity into additional rotor electronics or a redesigned vehicle platform, which is what would make magnet removal a genuine substitute rather than a trade of one constraint for another.
Sources
- Machines — mdpi.com
- press.zf.com
- Electric motors in electric vehicles an overview — felss.com
- USSM, Ionic plan $100M Missouri plant to recycle rare earth magnets – Interesting Engineering — news.google.com
- Interesting Engineering — interestingengineering.com
- IEEE Spectrum — spectrum.ieee.org