Study Of Perturbed Magnetic Fields Caused By Mechanical Stress

In recent years research works on the interaction between magnetic fields and stress or deformation of elastic solids received more and more attention because of the development of non-destructive test (NDT) technologies and their application in the production of microelectromechanical system (MEMS). Development of magnetism based non-destructive test (NDT) technologies calls for investigation of quantitative relation between deformation, stress, damage or fracture of structures and their induced magnetic quantities. In MEMS technology, because of the size effect of thin film, the coupling between magnetic fields and mechanics becomes much more obviously. So it is necessary to analyze the coupling effect between magnetism and force in the MEMS thin film structure.Based on linearized magnetoelastic theory and focusing our attention on common used steel or other ferromagnetic structures working in Earth magnetic field, governing equations and boundary conditions to determine the perturbed fields were derived by neglecting effect of the magnetic field on deformation of the structures but coupling the displacements into governing equations of perturbed magnetic field. Effect of mechanical deformation on the magnetic fields was taken into account by coupling structural displacement into the perturbed magnetic fields continuous conditions on the boundary of the structure.The results of the infinite plane showed that projection of displacement gradient on the normal of the boundary of structures plays a dominating role. If the projection is zero, then there is no perturbed magnetic field.The perturbed field of a half-plane magnetism structure caused by a point force was calculated by the Fourier transform method. The results show that the calculated magnetic intensity component normal to the structure boundary reaches its maximum at the point the force acted while the component tangent to the boundary inverses its direction sharply. The magnetic induction of the perturbed fields is proportional to the applied force.The perturbed magnetic fields of infinite plane with a circle hole were obtained by the separate variable method. The results show the magnetic intensities of the perturbed fields are proportional to the applied force. And the perturbed magnetic fields are different from the rigid magnetic fields with three magnitude and there is a break along the 45o direction in the hole side. The perturbed magnetic field have stronger local character.