In Kirchhoff migration, this is done by using the Kirchhoff integral representation of a field at a given point as a (weighted) superposition of waves propagating from adjacent points and times.
According to the superposition principle and the second kind of complete ellipse integral, the magnetic field current circle was calculated.
运用磁场的叠加原理及第二类完全椭圆积分，给出了椭圆形稳定电流环垂直轴上的磁感应强度。
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Then the eigenvalue problem of free vibration of annular sector plates is transformed into the eigenvalue problem of integral equation by using superposition theorem.