Mehran University Of Engineering & Technology SZAB Campus Khairpur Mir’s Hysteresis Loop & Some Magnetic Properties (Topic) Subject: Theory Of EMF Presenting Roll No: K-12 EL 28

Outline: Hysteresis Hysteresis Loop Some Magnetic properties

Hysteresis When an external magnetic field is applied to a ferromagnetic such as iron, the atomic dipoles align themselves with it.  Even when the field is removed, part of the alignment will be retained: the material has become magnetized. This lagging behind of flux density(B) or magnetization to magnetizing force(H) is called Hysteresis or Hysteresis Loss. Some compositions of ferromagnetic materials will retain an imposed magnetization indefinitely and are useful as "permanent magnets".

Hysteresis Loop A hysteresis loop shows the relationship between the induced magnetic flux density (B) and the magnetizing force (H). It is often referred to as the B-H loop or curve The loop is generated by measuring the magnetic flux of a ferromagnetic material while the magnetizing force is changed. This property of ferromagnetic materials is useful as a magnetic "memory".

B & H Magnetic flux density (B): The amount of magnetic flux through a unit area taken perpendicular to the direction of the magnetic flux. It is expressed by the force per unit length on a conductor carrying unit current at a point near it. Magnetizing Force (H): It is the force which depends upon the current which is passed through a magnetic material to magnetize it.

Comparing two Hysteresis loops

Another example of hysteresis loop is shown below:

Magnetic Properties Retentivity :It is a material's ability to retain a certain amount of residual magnetic field when the magnetizing force is removed after achieving saturation. Residual Magnetism or Residual Flux : the magnetic flux density that remains in a material when the magnetizing force is zero. Coercive Force : The amount of reverse magnetic field which must be applied to a magnetic material to make the magnetic flux return to zero.

Magnetic Properties Permeability (m):  It is a material property that describes the ease with which a magnetic flux is established in a component. It is the ratio of the flux density (B) created within a material to the magnetizing field (H) and is represented by the following equation: m = B/H Reluctance : It is the opposition that a ferromagnetic material shows to the establishment of a magnetic field. Reluctance is analogous to the resistance in an electrical circuit.

References: Internet Links: http://en.wikipedia.org/wiki/Hysteresis#Magnetic_hysteresis http://magician.ucsd.edu/essentials/webbookse26.html http://wiki.answers.com/Q/What_is_hysteresis_loss http://hyperphysics.phy-astr.gsu.edu/hbase/solids/hyst.html http://www.ndt-ed.org/EducationResources/CommunityCollege/MagParticle/Physics/HysteresisLoop.htm