Electromagnetic testing emt-mft chapter 9b

Another magnetic method that uses a similar arrangement is the
measurement of Barkhausen noise. As the magnetic field strength, H, is
varied at a very slow rate, discontinuous jumps in the magnetization of the
material can be observed during certain portions of the hysteresis cycle.
These jumps are associated with the sudden growth of a series of magnetic
domains that have been temporarily stopped from further growth by such
obstacles as grain boundaries, precipitates, or dislocations. Barkhausen
noise is therefore dependent on microstructure and can be used
independently of hysteresis measurements, or in conjunction with such
measurements, as another method of magnetic testing. The experimental
arrangement differs from that shown in Fig. 7 in that a single sensor coil,
oriented to measure the flux normal to the surface of the specimen, is used
instead of the Hall probe and the flux winding.
Charlie Chong/ Fion Zhang