“…Substituting (17) into (18), a bi-harmonic equation is obtained. When the components of the mechanical elastic stress,σ x , σ y , τ xy , are substituted into the compatibility equation, the homogenous bi-harmonic equation is also obtained since the magnetic field intensities H x (x, y, z), H y (x, y, z) are harmonic functions, and the same result is obtained [6].…”