Naslov (srp)

Razvoj i primena postupaka za efikasnu karakterizaciju elektromagnetske sprege ostvarene posredstvom otvora u oklopljenim kućištima

Autor

Milutinović, Vesna

Opis (srp)

Datum odbrane: 29.06.2015.

Opis (eng)

Electromagnetic compatibility (EMC) is essential for the design and operation of electronic systems in real time, as a form of equipment behavior in such a way that it is resistant to a certain level of interference from the environment, and which at the same time emits an acceptable level of EM radiation. From EMC point of view performance of electronic systems dominantly depend on the existence and nature of interconnecting paths, through which the coupling between EM energy sources and sensitive electronic systems is achived dominantly, in addition to the character of excitated EM radiation and configuration of wire and dielectric structures within the system. Major role in the elimination or reduction of these interconnecting paths have shielded enclosures. This enclosures, made of conductive material with adequate thickness and with different EM characteristics, affect on the level of EM radiation that reaches the electric circuit from the environment, but also determine how much energy is radiated by the circuit to the environment. Because enclosures have individual apertures inevitably, which are commonly used to access the system (connectors, power supply/shortening cables, CD/DVD-ROM, and others), and/or more apertures of the same shape for cooling and removal of excess heat from the system (e.g. air-vent apertures), EM radiation penetrates through the apertures in the space inside and outside the enclosure, degrading the basic function of shielding. The role of the shielded enclosure is that depending on the frequency, thickness and EM material characteristics of which is made, reduces the amount of EM energy which penetrates into the space inside and outside the enclosure and is usually expressed in term, which is called the shielding effectiveness (SE). This measure is usually defined as the ratio in dB between the level of the incident field in the corresponding point in the system in the absence of enclosure and in the presence of enclosure and it can be defined as well as for the electric (the so-called electric shielding effectiveness) and for the magnetic field (the so-called magnetic effectiveness). The aim of the doctoral dissertation is to analyze the influence of different effects such as: increasing the thickness of the front metal wall with apertures, a number of apertures, changing the shape and size of apertures, as well as their mutual distance on the shielding effectiveness of enclosure, on the example of enclosure of certain size in a certain frequency range. Accordingly, both individual apertures and air-vent apertures were considered with different shapes (rectangular, circular and square), which are usually located on the walls of shielded enclosures. In addition to the incident plane wave, an oblique wave in which the angle of polarization, azimuth and elevation is changed, was discussed also, as well as calculated values for SE in the different observation points within the enclosure. For most practical EMC issues, excitation in the form of a plane wave is only an approximation of the real excitation and is mainly used for the calculation of the shielding effectiveness. An excitation is placed inside the enclosure, when it is necessary to estimate the level of EM emissions, using numerical simulation, which is radiated from the shielded enclosure and the degree of its impact on other electronic systems in the environment. The internal excitation in enclosure, in the form of wire, was examined in the doctoral dissertation and how it affects on the external environment for the different shape of the apertures on the front wall calculating the electric field in the far field. Considering that for the purposes of conducting measurement a receiving antenna is being used, which is located inside the enclosure, it is necessary to take into account the impact of receiving antenna on the SE. The receiving antenna of finite size can significantly change the propagation of EM fields inside the enclosure and thus affects on the result of the SE. The effect of the presence of the receiving dipole, as well as monopole antenna on the SE was examined in this doctoral dissertation, in terms of how changes in antenna parameters, such as the radius and the length of the antenna position within the enclosure and its orientation, affect on the enclosure SE. Research methods that were applied in this doctoral dissertation are: analytical method for modeling using equivalent circuit and numerical modeling method using electrical lines (Transmission Line Matrix - TLM). The method of equivalent circuit was used for the analysis, in order to consider more apertures at many walls and oblique incident wave, and it was enhanced by the author to consider the presence of the receiving antenna inside the enclosure, which is used in the measurements process for calculating SE. Therefore, the main subject of this doctoral dissertation is development of analytical model and the development of equivalent model in order to calculate SE of enclosure with apertures. The basic advantage of this improved analytical model is his ability to precisely modeling antennas inside the enclosure. In fact, at some point within the enclosure receiving antenna was presented with appropriate impedance in the observing point of equivalent model. From this reason, the obtained results for the input impedance of a receiving antenna, for obtained equivalent model, were presented in the doctoral dissertation. The TLM method with the compact wire model was used also, for consideration of the receiving antenna presence in the measurement process, while in the case when an enclosure have air-vents, so-called a compact TLM model for the air vents on the metal walls, was applied, owing to calculate distribution of the EM field around a large number of apertures. Analytical and numerical model were compared in the dissertation in terms of their ability to calculate a different number of air-vent apertures, with a different mutual spacing on the front wall. A comparison of analytical and numerical results with the obtained measurement results was presented in detail, in order to verify and investigate the possibility of applying the proposed method for modeling the receiving antenna. The efficiency of the proposed analytical method was discussed in the example of enclosure with apertures on the front wall and the receiving antenna located at different points within the enlosure. The accuracy of the method was verified by comparison with numerical values, for a different length and diameter of the receiving antenna and with the corresponding measurement results. In this context, to what extent there is a difference between results obtained by analytical and numerical model, was shown in the doctoral dissertation, depending on the size of the receiving antenna. The corresponding numerical results, which represent the shielding effectiveness of enclosure, for a number of different wire diameters used as a receiving antenna, were illustrated in the framework of the doctoral dissertation. Among the expected results, which represent the original scientific contribution of the dissertation, can be extricate as following: computation of impact for various factors: the number and shape of apertures, their mutual spacing, wall thickness, changes in the excitation parameters of plane EM wave, on the SE using numerical differential method in time-domain for analysis of practical EMC problems; computation of excitation influence in the form of wire inside the enclosure on the EM field in the far field using numerical method; application of improved TLM method with compact wire model for generating a numerical model in order to analyze the impact of the receiving dipole antenna on the SE; application of analytical and numerical models for calculation the SE of enclosure with apertures and receiving antenna inevitable in the measurement process especially at the resonant frequencies; calculation of the SE with and without receiving antenna with different diameters using improved numerical and analytical models. The conclusions are based on analyzes and calculations, in which it was highlight the most important features and advantages of the proposed methods. It was indicated on the differences of analytical and numerical models with and without receiving antenna of various diameters, that must be taken into account during the experimental characterization, in order to correctly calculate the level of SE and the position of resonant frequencies.

Jezik

srpski

Datum

2017-03-01T09:16:54.220Z

Licenca

Ovo delo je licencirano pod uslovima licence
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