In magnetic applications, one of the most critical factors in magnet selection is the air gap.
What is an Air Gap?
In magnet design and applications, the air gap refers to the non-magnetic separation between two components in a magnetic circuit. While the term “air” suggests empty space, the gap can also be filled with non-magnetic materials such as plastic, rubber, wood, coatings, or nickel plating.
Since these materials have very low magnetic permeability (close to that of air), they do not conduct magnetic flux. This creates higher reluctance (magnetic resistance) in the circuit, which reduces the effective magnetic flux density (B) reaching the target area. In practice, the larger the air gap, the weaker the magnetic field strength that can be achieved.
Interestingly, while large air gaps are often a challenge, in some designs—such as electric motors, transformers, or magnetic sensors—air gaps are intentionally introduced to control flux, prevent saturation, or fine-tune performance.
How Air Gap Influences Magnet Selection
1. Choosing the Right Magnet Material
- AlNiCo Magnets
AlNiCo magnets are valued for their excellent temperature stability. They perform reliably in applications that involve both air gaps and high operating temperatures.
Example: industrial sensors operating in extreme heat. - Ferrite Magnets
Ferrite magnets are cost-effective and chemically stable. They are suitable when the air gap is very small and only a moderate magnetic field is required.
Example: small DC toy motors where cost control is critical. - Neodymium Magnets (NdFeB)
NdFeB magnets are the strongest permanent magnets available today. They are the best choice when the air gap is relatively large and a powerful magnetic field is necessary.
Example: magnetic separators, magnetic couplings, and levitation devices, where strong flux density across a gap is required.
2. Effects on Magnet Size and Shape
- Magnet Size
A larger air gap typically requires a bigger magnet to compensate for flux loss and maintain field strength. - Magnet Shape
Complex or non-uniform air gaps may require custom magnet geometries (arc segments, rings, or multi-pole assemblies) to optimize the circuit and maximize flux efficiency.
At HSMagnet, we specialize in custom magnet manufacturing to help engineers overcome these design challenges.
3. Impact on Magnet Performance Requirements
- Magnetic Field Strength
Bigger air gaps weaken the magnetic field. Stronger magnets with higher remanence are needed to achieve performance. - Magnetic Permeability
Using soft magnetic materials (e.g., iron or laminated steel) in the circuit helps guide and concentrate flux, reducing losses across the gap. - Coercivity
In designs with large air gaps or harsh conditions, magnets are more prone to demagnetization. High-coercivity materials such as NdFeB with special grades are essential for stability.
Conclusion
The air gap is a critical factor in magnet design. Larger air gaps reduce magnetic strength, requiring careful selection of magnet material, size, shape, and circuit design to ensure performance.
Whether you choose AlNiCo for high-temperature reliability, ferrite for cost-effective designs, or NdFeB for maximum strength, understanding how air gaps influence magnet performance leads to greater efficiency, stability, and cost-effectiveness in your application.
👉 If you are an engineer, OEM, or industrial buyer, HSMagnet offers high-performance magnets and custom solutions to help you optimize designs for applications involving air gaps.
