Magnetic Bearings: Active vs Passive, AMB Systems & Applications
A magnetic bearing supports a shaft through magnetic forces rather than normal rolling contact. An active magnetic bearing (AMB) regulates these forces using position feedback and a controller. Passive magnetic support uses an uncommanded magnetic field, but a complete machine can still require active damping or other supporting components.
On this page11 sections ⌄
Active, passive and permanent-magnet-biased are not synonyms
Classify how supporting force is controlled before comparing product names.
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| Term | Meaning | Do not infer |
|---|---|---|
| Active magnetic bearing | Position feedback regulates electromagnetic support | That the actuator works without its sensor, controller and power system |
| Electromagnetic-biased AMB | Electrically generated bias and variable control fields | A universal current, force or gap from the term alone |
| Permanent-magnet-biased AMB | Permanent magnets supply bias while an active field provides control | That permanent magnets make the complete bearing passive |
| Passive magnetic support | Supporting magnetic force does not require active position control | That the whole machine needs no electronics, damping or other restraint |
The control loop and backup support
Position sensing → controller → power amplifier and actuator → supporting force → updated position. This is a functional explanation, not a wiring or tuning procedure.
SKF's published blower example includes auxiliary ball bearings and a backup-power strategy. That demonstrates why power-loss behavior must be assessed as part of the machine. It does not mean every magnetic bearing shares that backup geometry or shutdown sequence.
After a touchdown or overload, use the machine's inspection criteria. Normal non-contact running does not prove that a backup bearing has remained undamaged.
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| Part of the system | Role in a comparison |
|---|---|
| Radial and axial actuators | Which directions of shaft movement are supported |
| Position and speed sensing | What the control system measures and uses |
| Controller and power electronics | How current, force and fault handling are managed |
| Backup / touchdown bearings | Support when magnetic suspension is inactive or cannot carry the load |
Real series and application examples
The examples distinguish architectures. They are neither interchangeable bearing numbers nor a best-product ranking.
Manufacturer examples include blowers and compressors. Calnetix also discusses passive-support applications such as flywheels and centrifuges. An application category explains where a technology is used; it does not identify a spare part for a particular chiller, turbine or generator.
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| Published example | Architecture or use | Remaining model-level evidence |
|---|---|---|
| Calnetix PowerFlux | Homopolar, permanent-magnet-biased active magnetic support | Exact actuator/controller/rotor combination |
| Calnetix XcelFlux | Heteropolar, electromagnetic-biased active support | Specified interfaces and operating envelope |
| Calnetix Duraflux | Permanent-magnet support used with an active electromagnetic damper | Complete damping and supported-axis arrangement |
| SKF integrated blower example | Magnetic shaft support with motor, controls and auxiliary bearings | Current machine-specific documentation, not historical example ratings |
Check the meaning of magnetic before searching for a replacement
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| Search description | Correct next question |
|---|---|
| Non-magnetic bearing | Is the requirement a material property rather than magnetic shaft suspension? |
| Magnetically stabilized fan | Does a lubricant film still carry the shaft load? |
| Magnetic bearing heater or isolator | Is this a tool or sealing component rather than a support bearing? |
| Bearingless drive | What support and drive functions are integrated in the exact machine? |
Does a magnet anywhere in a fan make its bearing an AMB?
No. Identify what actually supports the shaft and whether there is an active position-control loop. Magnetic motor components or a magnetic-assistance label alone do not establish an active magnetic bearing.
Does frictionless mean zero power loss?
No whole-system zero-loss claim is established by non-contact support. Compare the actual bearing electronics, motor, damping, cooling and operating point.
Can a same-size rolling bearing replace a magnetic bearing?
Nominal dimensions do not establish an equivalent support system. Rotor dynamics, controls, lubrication, loads and backup behavior require a verified machine-level assessment.
Are superconducting and permanent-magnet systems covered by the same design rules?
No. This guide distinguishes common catalogue architectures; it does not supply a superconducting bearing design, cryogenic specification or stability proof.
What the evidence can — and cannot — tell you
| Observation or context | Interpretation to consider | Verification needed |
|---|---|---|
| Active magnetic bearing | A controlled rotor-support system | Identify actuators, position sensing, controller, power supply and backup support. |
| Permanent-magnet bias | A constant magnetic bias may coexist with active control | Do not classify a PM-biased AMB as passive merely because it contains magnets. |
| Passive magnetic bearing | The supporting element does not use active position control | Check the complete system's stability, damping and supported axes. |
| Magnetic fan or non-magnetic bearing | Potentially a different meaning of magnetic | Distinguish magnetic assistance, material properties and full magnetic suspension. |
A practical investigation sequence
Identify and record
Identify the machine and the support function. Distinguish the motor's torque production from the bearing's radial and axial support.
Check the context
Record the complete rotor, actuator, sensor, controller and auxiliary-bearing arrangement. Keep software and hardware revisions with the mechanical identity.
Verify before acting
Review normal-speed, startup, shutdown, overload and power-loss conditions against the supplied system documentation. Do not replace this with a nominal bore comparison.
Keep the decision traceable
Retain operating logs and validated limits. Treat a proposed controller, backup bearing or rotor substitution as an unresolved integration change until verified.
Capture the information a model search cannot guess
Keep this checklist with your inspection or comparison. Checking a box only records that you have collected the item; it does not certify the bearing.
0 of 4 information groups recorded.
Technical basis & editorial scope
Original BearingScope workflow, written for catalogue research and comparison. Manufacturer material is used to check principles, not copied as a product endorsement or substituted for model-specific instructions. Reviewed 1 October 2026.
- Calnetix — Magnetic bearing terminology — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- Calnetix — Active magnetic bearing series and system components — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- Calnetix — Passive support with active damping — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
- SKF Evolution — Integrated magnetic-bearing blower example — Principles and explicitly named examples only; not an equipment fitment or universal rating. Source reviewed 3 October 2026.
Source addresses and collection status are retained in the internal audit. No unpublished dimensions, torque settings, service intervals or interchange approvals are inferred.