Hysteresis

Ehysteresis

Hysteresis sharp curve

Elastic Hysteresis

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Hysteresis is a phenomenon observed in physics and engineering where the state of a system depends not only on its current environment but also on its past history. This concept is widely applicable across various fields, including magnetism, ferroelectricity, mechanics, and control systems, among others. Hysteresis can manifest in different forms, such as magnetic hysteresis in materials science, mechanical hysteresis in elasticity, and thermal hysteresis in thermodynamics.

Definition

Hysteresis is derived from the Greek word ὑστέρησις (hysteresis), meaning "deficiency" or "lagging behind". It describes systems where the output does not directly follow the input, creating a lagging effect. This lag results in a looped graph when the system's input and output are plotted, known as a hysteresis loop. The area within the loop is often related to the energy dissipated by the system.

Types of Hysteresis

Magnetic Hysteresis

In magnetism, hysteresis refers to the lagging of the magnetization of a material behind the magnetizing force applied to it. This is a critical concept in the design of magnetic recording devices, transformers, and inductors. The hysteresis loop for magnetic materials displays the relationship between the induced magnetic field (B) and the magnetizing field (H).

Mechanical Hysteresis

Mechanical hysteresis occurs when there is a lag between the applied stress and the resultant strain in a material, often due to internal friction. This phenomenon is significant in materials science, particularly in the study of viscoelasticity and damping materials that are used to reduce vibrations.

Thermal Hysteresis

Thermal hysteresis is observed in systems where the temperature response of a material or process lags behind changes in the thermal environment. This can be seen in phase change materials (PCMs) that are used for thermal energy storage, where the material's change from solid to liquid (or vice versa) does not occur precisely at the melting point.

Applications

Hysteresis has both beneficial and detrimental effects, depending on the application. In control systems, hysteresis is intentionally introduced to prevent oscillation or "chattering" in switches and relays. In contrast, in systems where precision and repeatability are critical, hysteresis can lead to errors and inefficiencies.

Magnetic Storage

Magnetic hysteresis is exploited in the design of hard drives and magnetic tapes, where bits of data are stored in magnetic domains that resist changes to their orientation, thus preserving data integrity.

Sensors and Actuators

In sensors and actuators, hysteresis can affect accuracy and repeatability. However, understanding and designing for hysteresis can improve the performance of devices such as thermostats and pressure switches.

Modeling and Control

Modeling hysteresis is challenging due to its non-linear and path-dependent nature. Various mathematical models, such as the Preisach model and the Jiles-Atherton model, have been developed to predict hysteresis behavior. In control systems, algorithms that account for hysteresis are used to improve system stability and performance.

Conclusion

Hysteresis is a complex phenomenon that plays a crucial role in the behavior of many physical systems. Understanding and managing hysteresis is essential for the design and operation of a wide range of devices and materials, from electronic components to structural materials.

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