Hysteresis Hysteresis loop,
Magnetism
Hysteresis loops happen when you repeatedly wiggle the
system back and forth (cycle the field up and down). The magnetization of a
tape will ``lag behind'' as the field sweeps up and as it sweeps down. The
memory in the tape is the magnetization remaining as the field is released
to zero from a large value
When a ferromagnetic material is magnetized in one
direction, it will not relax back to zero magnetization when the imposed
magnetizing field is removed. It must be driven back to zero by a field in
the opposite direction. If an alternating magnetic field is applied to the
material, its magnetization will trace out a loop called a hysteresis loop.
The lack of retraceability of the magnetization curve is the property called
hysteresis and it is related to the existence of magnetic
domains in the material
Hysteresis can be used to filter signals so that the
output reacts slowly by taking recent history into account. For example, a
thermostat controlling a heater may turn the heater on when the temperature
drops below A degrees, but not turn it off until the temperature rises above
B degrees. Thus the on/off output of the thermostat to the heater when the
temperature is between A and B depends on the history of the temperature.
This prevents rapid switching on and off as the temperature drifts around
the set point.
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