What type of magnet can generate radial magnetic field?

In motors, sensors, and various rotating components, the radial magnetic field represents a critically important form of magnetic field. A radial magnetic field refers to magnetic flux lines distributed outward from the center or inward from the periphery, rather than the conventional axial distribution along the shaft. Magnets capable of stably generating this field rely on radial magnetization and possess structural shapes suitable for forming radial magnetic fields.

First, radially magnetized ring magnets represent the most typical and widely applied form. These magnets feature a circular ring structure with magnetic flux lines uniformly distributed radially. They can be manufactured from sintered ferrite, bonded neodymium iron boron, or molded ferrite, and are extensively used in applications such as brushless motor rotors, external rotor fans, electric water pumps, and Hall effect sensors.

Second, radially multipole magnetized rings represent a further refinement of single-radial magnetization. The ring is magnetized circumferentially into multiple alternating N and S poles, though each pole's magnetic field direction remains radial. Increasing the number of poles enhances magnetic field frequency variation and detection resolution, making them common in magnetic encoders, high-precision speed and position feedback systems, and brushless motors employing FOC control.

Radially bonded neodymium magnetic ring

Additionally, the radial magnetization structure of segmented magnets (magnetic segments) is another key method for generating radial magnetic fields. By assembling multiple segmented magnets in a circular arrangement to form a ring, each magnetic segment is magnetized either toward or away from the center. This segmented design not only reduces manufacturing complexity and cost but also facilitates installation and maintenance. For instance, a typical permanent magnet motor rotor may consist of 8 or 12 segmented magnets. Each magnet is individually magnetized before being bonded or snapped onto the rotor core, collectively generating a nearly uniform radial magnetic field.

Beyond these common types, irregularly shaped radially magnetized magnets are also prevalent in injection-molded magnets, such as cross-shaped, spline-shaped, or multi-tooth plastic-magnet rotors. These magnets are formed in a single mold shot and undergo radial multi-pole magnetization, enabling stable radial magnetic fields within complex spaces. They are particularly suited for applications like small water pumps, flow sensors, and household appliance micro-motors.

In summary, magnets capable of generating radial magnetic fields are not limited to any single material but are defined by the core characteristic of “radial magnetization.” Whether in the form of discs, rings, wedges, or irregularly shaped plastic-molded magnets, they can all generate radial magnetic fields in practical applications.

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