Multipole Ring Magnets

What Are Multipole Ring Magnets?

Multipole ring magnets are ring-shaped magnets with multiple magnetic poles distributed around the circumference, rather than just a single north pole and south pole. In motor applications, they are often used as a one-piece magnetic solution in place of segmented magnets such as arc magnets or other assembled rotor segments.

Based on magnetization direction, multipole ring magnets can be classified as axially multipole magnetized or diametrically multipole magnetized. In practice, anisotropic, diametrically multipole magnetized Neodymium ring magnets are more commonly used in motor designs.

Because the magnetization direction of anisotropic magnets is governed by their orientation direction, anisotropic multipole ring magnets are generally developed through either multipole orientation or radial orientation. These two routes correspond to polar anisotropic ring magnets and radially oriented ring magnets.

Multipole ring magnets can be classified by magnetization direction as axially multipole magnetized or diametrically multipole magnetized. For motor applications, diametrically multipole magnetized ring magnets are more commonly discussed because the magnetic poles are distributed around the circumference of the ring.

For anisotropic multipole ring magnets, magnetization direction is closely related to the orientation direction formed during production. Based on the orientation route, these magnets are generally divided into polar anisotropic ring magnets and radially oriented ring magnets.

Polar anisotropic ring magnets are oriented in multiple directions corresponding to the pole pattern. Radially oriented ring magnets, by contrast, are oriented along the radial direction of the ring. These differences affect not only the manufacturing route, but also the magnetic performance expected in the final motor design.

For multipole ring magnets used in motors, one of the most important evaluation points is the waveform of magnetic flux density. The peak value, angle, and area of the waveform are closely related to motor performance. Variations in peak value and angle can affect efficiency, cogging torque, temperature rise, and noise, while peak value and area together can also influence back electromotive force (BEMP), rated torque, and rated power.

Peak value is mainly related to magnet grade and the saturation level achieved during magnetization. In actual development, waveform quality is not determined by the magnet material alone. It also depends on the production process and the magnetizing fixture used. For this reason, waveform control is often a key part of multipole ring magnet development for motor applications.