Jonah Jin at OTIS

Polar-Anisotropic Ring Magnet

Explaining the benefits and design rules of polar-anisotropic multipole ring magnets can be a bit tedious. To make it easier for you, as an electric motor engineer, I’ve written a brief post listing the key points for quick understanding.

Advantages of Polar-Anisotropic Ring Magnets

  • Stronger magnetic field on rotor circumferential line surpasses traditional radially oriented ring magnets.
  • Reduced magnet mass is achieved through higher magnetic performance.
  • Reduced cogging torque achieved through a sinusoidal magnetic field on the rotor’s circumferential line.
  • Lower rotor weight by eliminating the need for a ferromagnetic yoke; alternative materials like copper or plastic can be used.
  • Cost reduction across the entire product system from the smaller motor size.

Design Guideline for Engineers

We have currently produced polar-anisotropic rings with outer diameters ranging from 4.5 mm to 43 mm. Larger or smaller magnets are not impossible but are waiting to be tested. The design, considering pole number and wall thickness, follows this formula:

Pole pitch / wall thickness ≥ 1.5

Pole pitch is the distance along the curved path between the centers of two neighboring magnetic poles, calculated by multiplying π (pi) by the outer diameter (OD) and dividing by the number of poles.

For additional details, kindly send an email providing information about your situation and your specific question.

Manufacturing Setup Costs

Two separate apparatuses are needed for magnetic-field-molding and final magnetization.

In the initial stage, magnetic-field-applying coils and molding dies are integrated for the pressing and orientation processes. The pole number is predetermined during molding. Following machining and coating, the ring magnet undergoes magnetization using a magnetizing fixture (coils) based on the predetermined pole number.

Including the apparatuses, the overall manufacturing setup costs amount to a few thousand dollars, varying depending on the specific project.

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