Electromagnetic Pulse Aperture Coupling And Its Electromagnetic Topology Model

A practical electronic system is located within a metal shield cavity with unavoidable perforated apertures and conducting wires pass through the enclosure. Through an aperture and wires external electromagnetic pulse couples to the cavity, in which the transient current is induced on the lines and the transient voltage is induced on the line ends, and the interference formed by the transient current and voltage has destructive effect. With the increasing function of the electronic system and thousands of connecting wires, boundary geometric construction becomes more and more complicated, while the whole space is not a homogeneous medium, and the complicated electromagnetic interaction environment is also formed by the external electromagnetic pulse and the electronic system. The research on the above-mentioned problems used individual theories of the aperture coupling or the multiconductor transmission lines respectively to achieve approximate treatment. Obviously, in the method mentioned above there existed errors in practical situations. To solve the above problems, the aperture coupling theory and multiconductor transmission line theory should be combined to form a theoretics system to reveal essential rules of the complicated electromagnetic interaction.Electromagnetic topology divides the system in 3D space according to the system construction and shielding levels. The interactive relation can be represented as the electromagnetic topological diagram by using the orthogonal decomposition algorithm of the BLT (Baum-Liu-Tesche) equation to divide the whole system into the separate subsystems and therefore to reduce the computation of the systems'solution.Electromagnetic pulse (EMP) coupling through an aperture to multiconductor transmission lines inside cavity is considered by using electromagnetic topological theory in this dissertation. An electromagnetic topology theoretical model of multiconductor transmission-line aperture coupling is proposed. The topological diagram and the corresponding electromagnetic interaction sequence diagram in terms of the practical system are constructed. Using the equivalent theorem, the aperture is replaced by the equivalent magnetic sources. Utilizing boundary conditions and image theorem, the equivalent electric and magnetic dipole moments which can be exciting sources inside cavity are derivated. The calculation of the equivalent distribution sources on multiconductor transmission lines located inside the cavity can be expressed by the exciting sources. The theoretic calculation values and the measured waveforms for the electric field shielding effectiveness in frequency domain are obtained. The induced voltages vary with the aperture sizes and incident angles of the exciting sources, which describe the important characteristic parameters of the aperture coupling, obtained by finding the BLT equation solution.An electromagnetic pulse simulator, acting as the external high power electromagnetic pulse of the aperture coupling electromagnetic topological model, offers necessary technical support for the experimental research on the complicated electromagnetic interaction circumstance. The simulator controlled by the single chip microcomputer can generate five continuous double exponential pulse wavefroms, and pulse interval, voltage magnitude are adjustable. In order to compute the electromagnetic field of the simulator work volume, the electromagnetic field analytic expression of the simulator work volume is derived from the electromagnetic field tensor, and the computation problem of the electromagnetic wave analytic method is solved in the time domain for the exciting sources distributed in the abrupt bent construction. The computation result indicates that electromagnetic field distribution results from different retard potentials superimposed by the uniform currents from the front and back conical plates as well as middle parallel plate, and the field distribution has the feature of transverse electromagnetic wave.To the transient response experimental data of induced voltage on the lines located a metal shield cavity, the characteristic parameters are extracted for the transient later time response in low frequency by using the singularity expansion method (SEM) and the matrix pencil algorithm, and the characteristic parameters of the early time response in high frequency are also extracted by using the fractional Fourier transform technique, and coupling functions are obtained as well.The computation results are in good agreement with the electromagnetic topology theoretical model, indicate the feasibility and validity of the proposed model, and provide the foundation for further extensive research on and application to the electromagnetic topological theory.