A high frequency amplitude-modulated magnetic field is realized by superposing a low frequency signal on the high frequency magnetic field. And the distribution of magnetic induction density

B

was measured by the small coils method. The results show that the higher B is observed in middle-bottom position

where that at the edge is higher than that of the center. The B can be increased with the increasing in amplitude-modulated value in the range of amplitude-modulated value of 0.5

7

V with amplitude-modulated signal frequency of 5 Hz. The B value of 0.029 T can be observed at the amplitude-modulated value of 7 V . The behavior of molten meniscus fluctuation in the magnetic field indicates that with the increase of magnetic induction density

the defined force is increased

which lessened the pressure between the molten and the crucible to result in the regular fluctuation of the meniscus.