Theory And Application Of Transient Electromagnetic Field In Cylindrical Medium Of Multilayer

Transient electromagnetic fields excitated by a pulse of current which have very short duration and long cycle, have a wide frequency spectrum from direct current to microwave. The process of interaction between transient electromagnetic field and medium can be followed directly in time domain. Through the transient response, we can obtain a great lot information rapidly in a wide frequency spectrum. At present, the study of transient electromagnetic field theory mainly concentrate on horizontal medium of multilayer. In recent years, the theory of transient electromagnetic field in cylindrical medium being required, due to the studying of engineering defend of electromagnetic pulse and well logging using electromagnetic pulse have got the attention gradually. This thesis, based on Maxwell equation of harmonic electromagnetic field, analysed the harmonic electromagnetic response in cylindrical medium of multilayer; based on the harmonic electromagnetic response and the one by one corresponding relationship, using G-S inverse Laplace transform method, analysed the propagation of the transient electromagnetic field in the cylindrical medium of multilayer. The conclusions as follows: (1) The integrated formulae of the shielding effectiveness of the shielding body with any layers, perfected the shielding theory system primely. The formulae are simple and have transparent signification. (2)The G-S inverse Laplace transform method is introduced to the calculation of electromagnetic shielding problem. The shielding effectiveness of cylindrical shielding body with multilayer to transient electromagnetic field is calculated. The thesis analysed the shielding problem of cylindrical shielding body with multilayer to transient electromagnetic field, and showed the shielding effectiveness of cylindrical shielding body with any layers to the transient electromagnetic field excited by step current, and discussed the relationship between electromagnetic and the layers of shielding body and the thickness and the parameter of any layer. These results provided academic foundation for the engineering defend to electromagnetic pulse. (3)The thesis simulated the propagation of the electromagnetic field, excited by the magnetic dipole which be inspired by rectangular pulse, in the homogeneous and axial symmetrical lossy medium. The method in this thesis can be used for the studying in exploration using electromagnetic pulse .