In electromagnetism and magnetic circuits, residual flux density, also known as residual induction or remanence, refers to the amount of magnetic flux that remains in a material after an external magnetic field has been applied and then removed. It is a property of ferromagnetic materials, which exhibit hysteresis behavior in their magnetization curves.
When a ferromagnetic material, such as iron, is exposed to an external magnetic field, the material becomes magnetized and aligns its atomic dipoles in the direction of the applied field. As the field strength increases, the material's magnetization increases until it reaches a saturation point, at which further increases in the applied field produce little additional magnetization.
However, when the external magnetic field is reduced back to zero, the material does not return to an unmagnetized state immediately. Some amount of magnetic flux remains in the material, causing a non-zero magnetic field within the material. This remaining magnetic flux is the residual flux density.
Residual flux density is an important concept in the design and analysis of magnetic circuits and electromagnets. It affects the performance of devices such as transformers, inductors, and electric motors. The concept is closely related to hysteresis, which describes the lagging of magnetic effects behind changes in the magnetic field. Hysteresis loops are used to visualize the relationship between the magnetic field strength (H) and the resulting magnetic flux density (B) in ferromagnetic materials.
In summary, residual flux density is the magnetic flux that remains in a ferromagnetic material after the removal of an external magnetic field. It is a result of the hysteresis behavior exhibited by ferromagnetic materials and plays a crucial role in the behavior of magnetic circuits and electromagnets.