Understanding Hysteresis Loss in Materials

Introduction to Hysteresis Loss

The concept of hysteresis loss is fundamentally important in materials science, particularly in the context of magnetic materials. It occurs when a system transitions between different states and the return to the initial state does not revert all the energy input, leading to a loss. This loss is due to the irreversibility of the process.

Visualizing Hysteresis Loss with a Rubber Band

A simple analogy to understand hysteresis loss is a rubber band. When you stretch a rubber band, it requires more force to stretch it compared to the force needed to release it. Similarly, the energy lost during the stretching process is not completely recovered when the band returns to its original shape. This is because not all the energy is returned to the source; instead, it is converted into internal energy, often in the form of heat. The difference in the areas under the force-time curves (blue and red) represents the energy lost.

Energy Conversion in Magnetic Domains

In magnetic materials, the energy conversion is more complex. Magnetic domains within a material store negative potential energy. To align these domains and produce bulk magnetization, the domain walls must rotate and realign. This process requires an external magnetizing field to supply energy, which is not returned entirely but is dissipated in the material. This dissipation forms the basis of hysteresis loss. The change in magnetic field (B) with respect to the magnetic field strength (H) is typically represented by a hysteresis loop, and the area within this loop represents the hysteresis loss.

Practical Example: Hysteresis Loss in an Electromagnetic Coil

To illustrate these concepts, let's consider a simple example of an electromagnetic coil. During the first half cycle, the coil is magnetized with a north-south (N-S) polarity. According to ideal conditions, the coil should be completely demagnetized during the second half cycle to return to its original state. However, in reality, some of the N-S poles remain, and to maintain the polarity as south-north (S-N), additional energy is needed. This energy is dissipated as heat, leading to hysteresis loss.

Conclusion

Hysteresis loss is a critical consideration in the design and operation of devices that involve magnetic fields, such as transformers, induction motors, and magnetic storage devices. Understanding the principles behind hysteresis loss can help in optimizing performance and reducing energy waste in such systems.