WAZIPOINT Engineering Science & Technology: Magnetic Hysteresis

## Magnetic Hysteresis

Magnetic hysteresis is a phenomenon observed in ferromagnetic materials, which are materials that can be easily magnetized. When a ferromagnetic material is subjected to a changing magnetic field, such as the alternating current in a transformer or the changing magnetic field in a magnetic circuit, the magnetic properties of the material exhibit a lag or delay in response.

The relationship between the magnetic induction (B) and the magnetizing force (H) in a ferromagnetic material is often represented by a hysteresis loop on a magnetization curve. This loop illustrates how the magnetic properties of the material change as the external magnetic field is varied.

Definition: Magnetic hysteresis refers to the lagging of magnetic induction behind the magnetizing force in a magnetic material.
Explanation: It results in a loop-shaped magnetization curve when plotting magnetic induction (B) against magnetizing force (H).

Area of Hysteresis Loop:
Definition: It is the area enclosed by the hysteresis loop on a B-H curve.
Explanation: The larger the area, the more energy is lost in the form of heat during each magnetic cycle.

Properties and Application of Ferromagnetic Materials:
Properties: High permeability, strong attraction to magnets, susceptibility to magnetization.

Applications: Transformers, inductors, magnetic cores in electronic devices.

Permanent Magnet Materials:
Materials: Alnico, Ferrite, Rare-earth magnets.
Applications: Speakers, electric motors, magnetic locks.

Steinmetz Hysteresis Law:
Statement: It relates the hysteresis loss to the frequency and maximum magnetic flux density in a magnetic material.

Energy Stored in Magnetic Field:
Formula: $�=\frac{1}{2}�{�}^{2}$, where $�$ is energy, $�$ is inductance, and $�$ is current.

Rate of Change of Stored Energy:
Formula: $�=��$, where $�$ is power, $�$ is voltage, and $�$ is current.

Energy Stored per Unit Volume:
Formula: $�=\frac{1}{2}{�}^{2}\mathrm{/}�$, where $�$ is energy density, $�$ is magnetic flux density, and $�$ is permeability.

Lifting Power of Magnet:
Depends on: Material, size, shape, and magnetization.
Application: Used in cranes, lifting systems.

Rise of Current in Inductive Circuit:
Explanation: When voltage is applied to an inductor, current gradually increases following an exponential curve.

Decay of Current in Inductive Circuit:
Explanation: When voltage is removed from an inductor, the current decreases following an exponential decay.

Details of Transient Current Rise in R-L Circuit:
Explanation: Describes the time-dependent increase in current when a resistor (R) is connected in series with an inductor (L).

Details of Transient Current Decay in R-L Circuit:
Explanation: Describes the time-dependent decrease in current when the voltage is removed from a series RL circuit.

Automobile Ignition System:
Function: Provides the spark needed to ignite the fuel-air mixture in the engine's combustion chamber.

Components: Ignition coil, distributor, spark plugs.

The hysteresis loop consists of two branches: the magnetization-increasing branch (when the magnetic field is increasing) and the magnetization-decreasing branch (when the magnetic field is decreasing). The loop shows that even when the external magnetic field is reduced to zero, the material retains some residual magnetization. This residual magnetization is known as remanence.

The width of the hysteresis loop is a measure of the energy loss in the material during each magnetic cycle and is related to the material's magnetic efficiency. Magnetic hysteresis is an important consideration in the design of magnetic circuits and devices, such as transformers and inductors, where energy losses due to hysteresis can have practical implications. Engineers aim to minimize hysteresis losses in these applications to improve the efficiency of magnetic devices.