How Does Axial Magnetization Work in Ring Magnet Sensing?

A sensor engineer is debugging a rotary encoder that uses a Ring Magnet. The encoder outputs a clean square wave at low speeds, but above 3,000 RPM the signal becomes distorted, and the counter loses pulses. The engineer checks the sensor, the wiring, and the power supply. All are within specification. The problem is the magnet. The axial magnetization pattern is not symmetric, and the field strength varies around the circumference. This variation causes the sensor to trigger at different points in each revolution, which distorts the waveform. This guide explains how axial magnetization works and why its uniformity is critical for reliable sensing.

1. What Is Axial Magnetization and How Does It Differ From Radial Magnetization?

Axial magnetization means the magnetic poles are on the flat faces of the Ring Magnet. One face is the north pole and the other face is the south pole. The magnetic field lines exit the north face, curve around the magnet, and enter the south face. Radial magnetization means the poles are on the inner and outer cylindrical surfaces. The field lines exit the outer surface and enter the inner surface. For rotary sensing, axial magnetization is often preferred because the sensor can be placed facing the flat face of the magnet. This allows a compact assembly with a small air gap. The table below compares the two magnetization directions.

In our factory, we produce Ring Magnet units with both axial and radial magnetization. The choice depends on the sensor configuration and the available space. For axial magnetization, the pole pattern is created by a specialized magnetizing fixture that applies a strong magnetic field to the flat face. The uniformity of the pole pattern is determined by the fixture design and the material properties. Xiamen Zhaobao Magnet Co., Ltd. has been manufacturing Ring Magnet units for over 15 years.

2. How Is the Pole Pattern Created on an Axially Magnetized Ring Magnet?

The pole pattern on an axially magnetized Ring Magnet is created by a magnetizing fixture that has multiple poles. The fixture is placed on the flat face of the magnet, and a high current is passed through the coils. The magnetic field aligns the domains in the material, creating alternating north and south poles around the circumference. The number of pole pairs determines the resolution of the sensor. A ring with 32 pole pairs will produce 32 electrical cycles per revolution. The table below shows the relationship between pole pairs and resolution for a typical encoder.

The uniformity of the pole pattern is critical. If the poles are not evenly spaced, the sensor will produce a non-uniform signal. This causes position error and speed ripple. In our factory, we use a laser inspection system to measure the magnetic field distribution around the circumference of every Ring Magnet. The field strength must be within ±5 percent of the average, and the pole spacing must be within ±0.5 degrees. Xiamen Zhaobao Magnet Co., Ltd. provides a magnetic field map with each high-precision ring magnet.

3. What Materials Are Used for Axially Magnetized Ring Magnets?

The material determines the magnetic strength, the temperature stability, and the corrosion resistance. The most common materials for Ring Magnet units are sintered neodymium iron boron (NdFeB), bonded NdFeB, and injection-molded ferrite. Sintered NdFeB has the highest magnetic strength but is brittle and requires a protective coating. Bonded NdFeB is less strong but can be molded into complex shapes and does not require a coating. Injection-molded ferrite is the least expensive but has the lowest strength. The table below compares the properties of these materials.

For high-resolution encoders, sintered NdFeB is the preferred material because of its high magnetic strength. However, the coating must be selected carefully. A nickel-copper-nickel coating provides good corrosion resistance but can affect the magnetic field distribution. An epoxy coating is less conductive and does not affect the field, but it is less durable. In our factory, we offer both coating options and can advise on the best choice for your application.

4. How Does the Air Gap and Sensor Position Affect Signal Quality?

The air gap between the Ring Magnet and the sensor affects the signal amplitude and the waveform shape. If the air gap is too large, the signal amplitude drops, and the sensor may not trigger. If the air gap is too small, the sensor may saturate. The optimal air gap depends on the magnetic field strength and the sensor sensitivity. The table below shows the recommended air gap for different magnetic materials and sensor types.

Summary for Sensor Engineers

Axial magnetization in a Ring Magnet creates poles on the flat faces, which allows a compact sensor assembly with a small air gap. The pole pattern determines the resolution, and its uniformity determines the signal quality. The material determines the magnetic strength and temperature stability. The air gap and sensor alignment affect the signal amplitude and waveform shape. By understanding these factors, engineers can design a reliable rotary sensing system. Xiamen Zhaobao Magnet Co., Ltd. has been manufacturing Ring Magnet units for over 15 years and provides full magnetic field mapping and application support.

Xiamen Zhaobao Magnet Co., Ltd. manufactures Ring Magnet units with axial and radial magnetization, in sintered NdFeB, bonded NdFeB, and injection-molded ferrite. We provide magnetic field maps, material certificates, and sensor interface recommendations for all of our products.