Numerička karakterizacija efikasnosti zaštite kućišta sa otvorima na bazi sprege sa žičanim strukturama
Cvetković, Tatjana M.
Faculty:Универзитет у Нишу, Електронски факултет
Maleš Ilić, Nataša
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One of the fundamental tasks in designing electronic systems is to fulfill conditions of electromagnetic compatibility - EMC. EMC defines the capability of an electronic system to satisfactorily function in its electromagnetic (EM) environment not disturbing the operation of other neighboring devices. EMC has become one of the main aspects that has to be considered in the design of electronic systems because of the increasing number and rapid growth of EM intereference sources. It has been noticed that foreseeing the protection measures during the design phase is simpler and much more efficient than applying those measures on a completed system, which often becomes impossible. The fulfillment of EMC requirements is regulated by a set of standards. In Europe, all standards have to be harmonized with the Directive for Electromagnetic Compatibility (2004/108/EC). Those standards regulate limits of emission (the highest emission level of a source of EM interference), limits of immunity (the
highest level of EM interference on a device with no degradation or with acceptable degradation of its performances) and the measuring conditions and methods. One of the ways to reduce the emission and increase the immunity of an electronic system in its real environment is to place it in a protective metal enclosure. Characteristics of the enclosure regarding EMC are evaluated by a parameter called shielding effectiveness - SE. SE is the ratio between the field strength without and with the enclosure interposed, at the same observation point. SE can be defined for the electric field (the so-called electric SE) and for the magnetic field (the so-called magnetic SE). Regarding the EMC, performances of the electronic system, i.e. SE level, are influenced by: construction, shape, size and wall thickness of the enclosure, electric and magnetic characteristics of the construction materials (electric conductivity, relative permeability, magnetic susceptibility, etc.), frequency range of the system operation, size, shape and number of apertures, their position on its walls, parameters of excitation plane wave and coupling mechanisms between externaly generated EM interference and EM radiation generated within the various parts of the system. The paths by which external EM interference penetrates into the system are usually the same with the paths by which internally generated disturbances are radiated outside of enclosure. The protective enclosure walls contain apertures of various shapes and purposes, most often used to access and control the system, retract the input and output cables, for ventilation, cooling, etc. Through those apertures, EM radiation penetrates into the enclosure and also into the outer space, disturbing enclosure protective function. In addition to coupling through the apertures, there are also coupling by diffusion through shield walls, coupling with wire structures within the enclosure and with other parts of the system. For proper functioning of the system it is necessary to analyze and determine the nature and level of EM emissions generated by various parts of the system, the influence of externally generated EM interefrence on the system and its parts, as well as their mutual coupling, in order to undertake measures for reducing or eliminating the coupling paths. For determining the SE, various analytical and numerical methods are used alongside with experimental measurements. Analytical methods may be applied only in simple cases and with appropriate approximations. For an example an empty enclosure with apertures may be represented as an equivalent waveguide circuit, in which the enclosure is represented as a shorted waveguide, while the opening is represented as a coplanar strip line short circuited at both ends. The application of analytical methods on complex structures gives only approximate results. Numerical methods, which gained in importance by the use of high performance computers, have become an indispensable tool in modeling and simulation of various realistic EMC problems. By using these methods, research time can be significantly shortened, since the construction of prototypes which do not fulfill the established EMC requirements and thus need additional measurements and subsequent corrections in design can be avoided. The subject of the PhD scientific research is a numerical characterization of the metal enclosures’ protective characteristics, as well as analyses of the shielding effectiveness behavior in EMC relevant frequency range, depending on some of the previously mentioned factors (polarization type of the excitation plane wave and the azimuth and elevation angles under which the plane wave comes across the enclosure walls with apertures, the number of wall apertures and their mutual distance as well as their position with respect to the point in which the SE of enclosure is determined, etc.). Furthermore, the coupling of EM waves that penetrate into the enclosure interior with the wire structures, that can significantly affect the total EM field distribution within the shield and consequently affect its protective function expresses as SE, will be studied. As a numerical tool, a modeling method based on electric transmission lines (transmission line matrix method - TLM method) is used. Thanks to its characteristics, the TLM method has been widely used in solving various EM field propagation problems. The TLM method belongs to the group of differential numerical techniques in the time domain. It is based on the analogy between EM field components and electric currents and voltages in the transmission line network by which the concept of EM field is reduced to the concept of electric circuit theory. Enhancements of the TLM method, in the form of so-called compact models, suitable for efficient modeling of the mutual interaction between the excited EM field and geometrically small but in electrical sense important structures (thin wire structures, complex wView More
Keywords:efikasnost zaštite; shielding effectiveness; kućište; elektromagnetska kompatibilnost; sprega; pravougaoni otvor; TLM metod; prijemna antena; enclosure; electromagnetic compatibility; coupling; rectangular aperture; TLM method; receiving antenna