Air gaps and other non-magnetic regions, including spacers and structural parts, are non-magnetic sections of the circuit that may still carry a significant portion of the flux. Together with the surrounding low-permeability media such as air, they define the working area and influence both field strength and field distribution. Not all flux remains in the intended main path, and some forms parasitic paths, resulting in leakage flux and fringing flux around edges and gaps.
Taken as a whole, the permanent magnet, magnetic core, air gaps, non-magnetic regions, and the inevitable leakage and fringing paths determine the actual flux distribution and overall performance of a permanent magnetic circuit, and they need to be considered together in permanent magnet design.
Magnetic circuit design is similar to electric circuit design: it focuses on planning and controlling the path of magnetic flux so the required field strength and direction occur at the right place. Different applications create different design goals. Some demand uniform, stable magnetic fields, while others prioritize maximum strength, complex three-dimensional field patterns, or precise dynamic control. Based on these needs, magnetic circuits can be divided into several main types.
Basic magnetic circuits are often discussed in terms of two familiar forms: open-circuit and closed-circuit configurations. In an open circuit, a standalone permanent magnet generates field lines that spread directly into free space. This layout is simple and cost-effective but has higher magnetic reluctance because air has low permeability. As a result, it is most suitable for basic demonstrations, simple holding devices, or sensing applications where field shape and efficiency are less critical.
In a closed-circuit configuration, the magnet is integrated into a high-permeability path—such as an iron or steel yoke—that guides the magnetic flux and forms a complete loop. This greatly improves flux utilization, providing a more uniform and efficient magnetic field for precision work. By focusing on guiding and controlling magnetic flux, closed circuits deliver stable field distribution and high efficiency, making them well suited for tasks such as multi-pole experimental field alignment, electron beam control, and the evaluation of precision instruments.
Flux enhancement magnetic circuits include designs that boost magnetic strength by combining permanent magnets with flux-guiding components, such as steel yokes or backing plates. These parts direct the magnetic flux toward a specific working area, creating strong attraction or a locally intensified field. When used on their own, the magnets and yokes concentrate the field in one main direction and usually operate in a semi-open-circuit mode. Once they are attached to a matching steel surface or counterpart, the circuit behaves more like a closed loop, further improving efficiency. This type of magnetic circuit is widely used in holding applications, especially pot magnets, where concentrated magnetic strength is needed for secure attachment.
Another form of flux enhancement uses pole pieces placed between magnets with like poles facing each other (for example, N–pole piece–N or S–pole piece–S). The repulsion between the same poles intensifies the magnetic field in the gap and around the pole piece. This arrangement is commonly used in magnetic bars for magnetic separation, where a high-gradient field is required, and in products like shuttering magnets that need very high holding force.
Array magnetic circuits are best represented by the Halbach array, where multiple permanent magnets are arranged in a specific pattern with rotated magnetization directions. This design strengthens the magnetic field on the working side while greatly reducing it on the opposite side, achieving targeted field enhancement or shielding that single magnets cannot provide. As a result, Halbach-type array magnetic circuits offer high efficiency, compact size, and precise control of the magnetic field distribution.
Energy conversion magnetic circuits generate stable, controllable magnetic fields that interact with coils or other magnets to convert energy between electrical and mechanical forms, or to transfer mechanical energy from one part to another. In permanent magnet (PM) motors, permanent magnets are arranged on the rotor or stator with alternating N–S poles to create multi-pole fields that drive rotation or linear motion. In voice coil motors, a radial magnetic field in an annular gap enables precise linear movement of the coil. In magnetic couplings, specially designed push–pull magnetic circuits transmit torque without physical contact, providing leak-proof drive solutions for sealed systems.
Switchable magnetic circuits use mechanical or electrical control to change the external magnetic field while maintaining their “on” or “off” state without continuous power. In permanent magnetic chucks and magnetic lifters, rotatable internal magnets switch the circuit between an open-circuit “on” condition and a closed-circuit “off” condition, allowing the magnetic force to be applied or removed as needed.
Electro-permanent systems, also known as hybrid magnetic circuits, use short electrical pulses in a coil to reverse the polarity of low-coercivity magnets such as AlNiCo, or to counteract the field of other permanent magnets with an opposing coil flux. This approach combines the reliability of permanent magnets with the controllability of electromagnets, providing precise, repeatable operation without the need for constant power.
The core of magnetic circuit design can be simply summarized as delivering the right magnetic field to the right place at the right time. Magnetic circuits can range from simple to highly complex, depending on the device’s performance requirements. In many cases, magnetic flux must be guided from the permanent magnet source to a specific working area, while in others, magnetic shunts or shielding are used to divert fields away from sensitive components. In permanent magnetic circuit design, parameters such as magnet material, magnet size, core geometry, and air gap length are selected together to balance force output, efficiency, and performance stability for the target application.
For simple designs, practical experience and rules of thumb often provide reliable guidance. For more complex configurations, numerical methods such as finite-element analysis (FEA) are essential to account for leakage, saturation, and fringing effects. Contact WZ Magnetics for expert guidance, custom simulations, and prototypes to optimize your magnetic circuit.
