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Magnetic Hysteresis (Loop)

Published Date
Author Cadence PCB Solutions

Key Takeaways

  • Magnetic hysteresis, often called magnetic hysteresis (loop), describes how ferromagnetic materials' magnetization (m) responds to changes in an applied magnetic field (h).

  • Magnetic hysteresis is essential in engineering and design applications, as it can impact the efficiency and performance of magnetic devices.

  • Magnetic hysteresis affects PCB design by influencing the selection, performance, and efficiency of magnetic components like inductors and transformers.

The main magnetic hysteresis (loop) and initial magnetization curve calculated using Stoner-Wohlfarth theory for an isotropic system of identical single-domain magnets

A theoretical model of the magnetic hysteresis (loop) showing magnetization m against magnetic field h. Beginning at the origin, the upward curve shows the initial magnetization. The downward curve after saturation and the lower return curve form the main loop. The intercepts hc and mrs are the coercivity and remanence.

Magnetic hysteresis, often called magnetic hysteresis (loop), describes how ferromagnetic materials' magnetization (m) responds to changes in an applied magnetic field (h). This phenomenon is essential in understanding the behavior of materials used in various magnetic devices such as transformers, inductors, magnetic cores, and permanent magnets. The magnetic hysteresis (loop) is represented graphically as a plot of magnetization (m) versus the applied magnetic field (h). It shows how the material's magnetization changes as the magnetic field increases or decreases.

Regions of a Magnetic Hysteresis (Loop)

Magnetization Saturation

At low magnetic field strengths (h), the material's magnetization (m) increases linearly with the applied field. This region is called the initial magnetization or saturation region.

Magnetic Susceptibility

As the magnetic field strength is further increased, the rate of change of magnetization for the field strength decreases. This region represents the material's susceptibility to magnetization.

Saturation

The magnetization reaches a maximum value at high magnetic field strengths and becomes saturated. Further increases in the magnetic field have little effect on the magnetization in this region.

Remanence

The material retains some magnetization after the magnetic field is reduced to zero. This remaining magnetization is called remanent magnetization or remanence. Residual magnetization remains in the material when no external magnetic field is applied.

Coercivity

A reverse magnetic field must be applied to demagnetize the material and bring its magnetization to zero. The intensity of this reverse field is called coercivity. It represents the material's resistance to demagnetization.

Repeatable Loop

When the applied magnetic field is cycled back and forth, the magnetization follows a closed loop, known as the hysteresis loop. The width of this loop, or the enclosed area, represents the energy losses in the material due to magnetic hysteresis and is a critical consideration in the design of magnetic components.

Magnetic hysteresis is essential in engineering and design applications, as it can impact the efficiency and performance of magnetic devices. Engineers and scientists study the hysteresis behavior of materials to choose the appropriate magnetic materials for specific applications and minimize energy losses. Materials with narrow hysteresis loops are desirable for applications where energy efficiency is critical, while those with wide hysteresis loops are used in applications like permanent magnets.

Implications of Magnetic Hysteresis (Loop) for PCB Design

Magnetic hysteresis affects PCB design by influencing the selection, performance, and efficiency of magnetic components like inductors and transformers. The shape and width of the hysteresis loop in these components can significantly affect their energy losses, thermal considerations, and suitability for high-frequency applications. PCB designers must carefully choose components with appropriate hysteresis characteristics to meet design requirements while considering their effects on size, electromagnetic interference, and temperature sensitivity. The implications of magnetic hysteresis for PCB design include:

  • Component Selection: When choosing magnetic components like inductors or transformers for your PCB design, it's essential to consider their magnetic properties, including the hysteresis loop characteristics. The shape and width of the hysteresis loop can affect the component's performance and efficiency. You may need to select components with specific hysteresis characteristics to meet your design requirements.
  • Size and Form Factor: Magnet components' size and form factor can be influenced by their hysteresis properties. Components with wide hysteresis loops may require larger cores to achieve the desired performance, affecting the PCB's physical layout and packaging.
  • Energy Loss: Magnetic hysteresis results in energy losses in the magnetic core material of components. These losses manifest as heat, which can impact the overall thermal design of your PCB. If your application is sensitive to heat generation, you may need to choose components with lower hysteresis losses or implement additional cooling measures.
  • Temperature Considerations: Magnetic properties, including hysteresis behavior, can be temperature-dependent. PCB designers must account for temperature variations and choose components with stable magnetic characteristics over the expected operating temperature range.
  • Switching Frequencies: The effects of magnetic hysteresis become more pronounced for PCBs that operate at high frequencies, such as those found in power converters or RF circuits. The core material in magnetic components may not have enough time to respond to rapid changes in the magnetic field fully. Component selection, core material choice, and the magnetic circuit design become critical in such cases.
  • Saturation and Core Material: Understanding the saturation characteristics of magnetic components is important in PCB design. Saturation occurs when the magnetic core material becomes fully magnetized and can no longer store additional magnetic energy. It is essential to choose components and core materials that can operate within their specified saturation limits to avoid performance degradation.
  • Electromagnetic Interference: Magnetic components can emit electromagnetic interference (EMI), affecting nearby components and circuits. The hysteresis loop of the core material can impact the levels and frequencies of EMI emissions. Proper PCB layout and component placement can help mitigate EMI issues, but understanding the core material's hysteresis properties is essential in EMI management.

Managing magnetic hysteresis is crucial for achieving optimal performance and minimizing unwanted consequences in electronic circuits and systems. It affects the selection, performance, and efficiency of magnetic components used on a PCB. Designers must consider the hysteresis loop characteristics of these components to ensure that the overall electronic system meets its intended specifications and performance requirements. 

Cure Magnetic Hysteresis Headaches with Cadence Tools

Magnetic hysteresis (loop) can be a headache for PCB designers, but it can be mitigated with the right tools. Cadence’s PCB Design and Analysis overview page provides tools ideal for minimizing voltage hysteresis, including the OrCAD PCB Designer.

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