A theory for magnetic hysteresis, magnetization potential model was introduced, which was based on the motion of magnetic domain wall. The magnetization potential model can be applied to the description of the magnetic hysteresis of both isotropic and anisotropic ferromagnetic material in almost all range of magnetic field.
Hysteresis and harmonics generated during magnetization of 3% Si-Fe were experimentally measured along magnetization angle, and were compared with those calculated from the model. For the magnetization angle of 0 degree, the theoretical hysteresis, first and third harmonics agreed quantitatively with those experimentally obtained. As the magnetization angle increased, the theoretical hysteresis and harmonics agreed qualitatively with those of experimentally obtained result.
Analysis of the harmonics generated during magnetization of grain-oriented 3% Si-Fe specimens with 3 different grain sizes provided the information about the micro-structure. The first harmonic signal increased greatly than third harmonic signal with the increase of saturation magnetization, whereas the third harmonic signal increased greatly than 1st harmonic signal with the increase of magnetic moment coupling constant. The 9th harmonic signal also increased and cut-off harmonics shifted toward lower order harmonics as anisotropy energy increased. Therefore it can be said that first and third harmonic signals can be used in determining the micro-structural state of ferromagnetic materials for a nondestructive testing method.
The micro-structure of the steel plate was qualitatively analyzed by comparing the contrast of two-dimensional gray level images obtained by scanning through a hole defect made artificially and black lines on a steel plate. The two-dimensional gray level images were obtained by detecting the first and third harmonic signals generated in a single core active induction coil in the course of scanning the surface of specimens. The results indicated that this method can be applied to the on-line monitoring for whole surface inspection of steel plate.
A new method suitable for a single core flux-gate magnetometer has been developed. The method makes use of the coupling property of odd and even harmonics generated by the self-product of induced voltage during the magnetization of ferromagnetic material by an external field superposed on the AC driving magnetic field. The power difference between the two half-periods of magnetization was expressed by the coupling of odd and even harmonics, which was found to be proportional to the external field under the condition that $H_{ext}l《 H_{AC}$, where $H_{ext}$ and $H_{AC}$ are the external magnetic field and AC driving field amplitude, respectively. This method provides a linearity in the wide external field range, high sensitivity, good reproducibility and also provides the vector detection without phase detection.
