Craiova University
Faculty of Electrical Engineering
Doctoral School of Electrical and Energy Engineering
CONTRIBUTIONS TO THE STUDY OF THE ELECTROMAGNETIC FIELD IN
ANECHOIC CHAMBER BY MODELING, SIMULATION AND EXPERIMENTAL
VERIFICATION
- PHD THESIS SUMMARY -
PhD Supervisor: Prof. univ. Dr. Ing. NICOLAE Petre-Marian PhD Sudent: Ing. DINA Livia-Andreea
CRAIOVA
2021
SUMMARY
Specialized test chambers play an important role in the process of assessing the effects of electromagnetic compatibility (EMC) and represent the main equipment used by engineers to perform measurements and checks so technically and biologically necessary in the industry.
In this context, research on the modeling and simulation of specialized EMC testing premises represents a current topic of great interest, widely debated worldwide.
In this doctoral thesis it was decided to carry out intensive research using the anechoic chamber, this being approached as a solution for the EMC testing environment, due to its advantages compared to other available solutions. The main reason why it was considered necessary to conduct this research is the presence of electrical and electronic devices in everyday life, devices that are the main source of radiation to which we are constantly exposed.
The main reasons why the anechoic chamber is preferred as a solution for EMC verification in various fields are the following: low costs compared to other alternative testing methods (such as outdoor testing), the advantage of multiple use of the site that was once calibrated without the need to recalibrate the equipment and last but not least the possibility to reproduce the environmental conditions relatively easily in case the repetition of the test is necessary.
One of the problems proposed for solving refers to the creation of a fundamental geometric model, a model that can be used as a starting point for various types of analysis and optimization of metal test chambers to be performed later.
Another problem is related to the analysis of the parameters and the distribution of the electromagnetic field inside the anechoic chambers, respectively.
Also, a problem of wide interest is related to the efficiency of these test environments, the determination of the effectiveness of the shielded enclosure being a major goal.
The research direction was chosen due to the studies previously carried out by the research team of which the doctoral student is a part in the field of electromagnetic field propagation and respectively of the researches regarding the specialized materials used in shielding. The main aim was to obtain a sufficiently complex anechoic chamber model so that it could be considered relevant in future attempts to develop unconventional test enclosures, usable in various EMC applications.
The results of the thesis can thus contribute to the development of new prototypes of EMC test models and tools. Through its content, the doctoral thesis is also a documentary material in this field.
The scientific and methodological support necessary for carrying out this research was constituted by consulting the multiple technical and scientific publications in the field, especially at those indexed in the international database IEEEXplore. Additionally, other databases were consulted, as well as prestigious specialized journals, doctoral theses, journals and scientific papers. Both national and international standards and legal provisions in the field were also consulted.
Thesis structure
The thesis is structured on 6 chapters and brings contributions in the field of electromagnetic compatibility through modeling, simulations and experimental determinations made and presented in it. In the structure of the doctoral thesis, 95 reports were presented, 80 figures were exposed, 10 tables were created and 181 bibliographical references were selected.
The first chapter investigates the propagation of the electromagnetic field, focusing on the field of specialized enclosures used for specialized EMC testing. Because the propagation of the electromagnetic field takes place in the form of electromagnetic radiation dispersed by contiguity (from point to point) with finite propagation speed, the Maxwell formulation was used to present the algorithm for determining the local structure of the electromagnetic field at each point in space at a certain moment, being thus determined the form of the solution of the electromagnetic wave propagation equation.
Also widely presented are the defining general relations regarding the propagation of the vacuum electromagnetic field (where, due to the lack of obstacles leading to the production of effects, the environment has no influence on the propagation of electromagnetic waves), and in environments with different properties where, due to differences between the spectral domains, multiple reflections arise when they encounter obstacles in their path, a consequence of this phenomenon consisting in the direct influence of the environment on the propagation module of the incident field.
A particular presented case addresses the propagation of the electromagnetic field in waveguides, guides that consist of transmission media delimited by the reflective inner walls of a solid tube, in which the propagation of electromagnetic waves takes place.
Electromagnetic waves are therefore guided by the walls of the tube which are made of a perfectly conductive material depending on how it propagates. The main modes of propagation of the electromagnetic field in waveguides are: transverse electromagnetic mode or TEM, if Ez = 0, Hz = 0; electric transverse mode TE or H mode, if Ez = 0, Hz ≠ 0;
transverse magnetic mode TM or mode E, when Ez ≠ 0, Hz = 0. For each of these modes the
formulations used to determine the components of the electric and magnetic field in the rectangular coordinate system based on Maxwell equations are presented.
At the end of the first chapter the particular calculation relations related to the different types of antennas used in the measurements performed are stated, the results of which are presented in Chapter 5 (frame antenna, horn antenna and biconical antenna), relations that describe the field propagation in cases particular.
In the second chapter a presentation of the modeling methods commonly used for the calculation and detailed analysis of the electromagnetic field is made, a methodological algorithm for modeling that is applicable to the case study approached in the doctoral thesis being presented in staged form.
Modeling an equipment, device or physical system is a fundamental action in the engineering field. This consists in the conception of an abstract image, of scientific-technical- mathematical nature of the object subjected to modeling in order to be able to estimate its functioning in different situations. Given the complexity of the calculations that need to be performed to model electromagnetic field problems, the most appropriate approach is the computer-assisted one.
The fundamental problems related to the modeling of the electromagnetic field in fixed or mobile environments are represented by the analysis problems, mainly the calculation or determination of the electromagnetic field. Assuming that the geometry of the domain, the characteristics of the materials in it, the spatial and temporal distribution of field sources and / or other additional conditions are known, in order to obtain a unique solution such as initial and boundary conditions, it is required to determine local and instantaneous field sizes ( E, D, B, H) in the space-time domain under analysis.
Electromagnetic field modeling is a multiphysical modeling that is carried out in stages according to the following algorithm: conceptual modeling, mathematical modeling, analytical modeling, numerical modeling and model validation, respectively.
Conceptual modeling represents the beginning stage in which simplifying hypotheses are established and some aspects that can be neglected are identified. Within the stage related to mathematical modeling, the basic model is formulated in exclusively mathematical terms.
Analytical modeling is the stage in which the relations between the input, state and output quantities are determined in analytical form, now an approximate variant of solving the model equations can be formulated. Numerical modeling is the step that complements the previous one by building numerical algorithms dedicated to solving model equations in order to obtain exact solutions. Model validation is the last stage of the modeling process, the one in which solving algorithms are implemented in computing systems and model simulations are performed in order to validate it.
If the results obtained from the simulations do not verify the equations of the conceived mathematical model, it is necessary to resume the stages starting with the analytical modeling.
Their resumption stops when the numerical model is checked.
The validation of the mathematical model is done by comparing the simulation results with those obtained experimentally. If the model does not show enough similarities and the deviations are not acceptable, then the mathematical model must be modified. These cycles are resumed until the model is validated.
Chapter 3 presents theoretical aspects regarding the simulation and modeling of anechoic chambers using dedicated software for the analysis of the electromagnetic field in the field of radio frequency. The main simulation and modeling tools used in academia and industry are also presented, including a comparative analysis of dedicated software in order to establish the differences between them and the capabilities they offer.
The systematic upgrade of the graphical interfaces of computing media today allows a particularly fast, suggestive, and efficient analysis of computational results, in the form of graphical representations and in-depth analysis of materials and bodies.
In the incipient phase, there is a worldwide tendency to develop computing programs based on the finite element method, which must be as general as possible and at the same time be very versatile, so as to offer the possibility to solve a wide range of types of computational problems.
This perspective has led to obtaining very large and, moreover, difficult to exploit programs.
The multitude of specific commands has made it difficult to learn them, many of which end up being morally worn out before they are sufficiently well mastered by the user. In this context, there is currently a tendency to design specialized programs, targeting smaller areas and simpler and easier to use menus.
At present there are numerous programs, generally specialized on different types of analysis problems, such as ANSYS, CST, FEKO, EMC Studio, MSC NASTRAN, COMSOL Multiphysics, MOSAIC, GffTS etc. Mainly, most are designed to allow the phased construction of geometric models by entering material information, meshing the geometric model, applying loads or demands, boundary conditions, actual solving, and post-processing calculations.
There are many dedicated software used to model and simulate electromagnetic compatibility problems, each of which has advantages and disadvantages. The choice of the most appropriate program to perform a simulation or modeling depends on the aspects related to the form and substance of the proposed problem to be solved.
The fundamental problems related to the modelling of the electromagnetic field in fixed or mobile environments are represented by the analysis problems, mainly being the calculation or determination of the electromagnetic field.
In most cases, the best solution proved to be the work combined with several simulation software, analyzing with each of them the aspects for which the best results are obtained, simultaneously with the possibility of performing a complex analysis.
Chapter 4 presents the modeling and simulation of the studied anechoic chamber in order to analyze the variation of the field sizes in shielded enclosures. The algorithm for making the chamber model using the CST Studio Suite software is presented in detail, the simulation of the efficiency of the electromagnetic field shielding and its distribution inside the enclosure being made based on the designed model. The obtained parameters and the performed type of analysis are also widely presented.
The purpose of modeling is to be able to estimate the distribution of the electromagnetic field inside and outside an anechoic measuring chamber for different imposed conditions.
In order to perform the physical modeling of the enclosure that is the subject of the research, it was necessary to perform an analysis on the principle of operation of the device and to identify the main phenomenon and causal relationships (internal and external field), to establish simplifying physical assumptions of the analysis and implicitly the regime of the electromagnetic field and to identify the main physical quantities that characterize the operation of the analyzed device, estimating the way in which they vary in time and space.
The modeled anechoic chamber consists of a modular construction made of prefabricated panels interconnected by means of fasteners, integrating in their overall structure, the power panel, which contains inputs for power and signal lines, fans for ventilation and access door.
The dimensions on the basis of which the geometric model was made, were calculated so as to respect at 1:3 scale the dimensions of the real enclosure.
Given the construction of the real anechoic chamber, it was found from measurements that the most common problems associated with the effectiveness of the Faraday cage occur when joining the components of the housing, door, fans and module joints from which the enclosure is made. For these reasons, the locations of interest selected were precisely those that show the highest probability of occurrence of electromagnetic field leaks.
The modeling process of the enclosure began with the geometric modeling stage, and once the geometric model was obtained, the customization of materials was continued. The material properties were applied according to the values presented by the physical equipment manufacturer, being defined using the dedicated commands provided by the CST Studio Suite software, with the help of which the simulation was performed. After the properties of the material were customized with the imposed values of the characteristic quantities, the excitation and the boundary conditions were applied, this being the last stage of the modeling process.
In order to compute the shielding efficiency of the modeled chamber, it was necessary to determine the values of the electric and magnetic field, two different cases (runs) were considered in the simulation structure. The first run simulated the case in which the influence
of the Faraday cage was not considered, thus determining the value of "direct electric field intensity", the second analyzed situation being the case in which the influence of the Faraday cage was taken into account, the electric field intensity being determined depending on the shielding level of the used screen.
In the case of determining the electric field intensity in a direct way, the running was performed after the geometry of the anechoic chamber was previously excluded from the simulation, so that it no longer had any influence on the propagation mode of the electromagnetic field. It was intended to simulate the field shielding efficiency without the influence of the metal casing on the distribution mode of the electromagnetic field. This was done by applying the boundary conditions so that the radiation of the electromagnetic field is achieved symmetrically along all the orientation directions of the coordinate axis system.
The results provided by the simulation, presented in detail in this chapter, revealed that the value of the electric field oscillates around 14 V/m and the magnetic field around 0.7 A/m.
The levels of the electric and magnetic fields, respectively, were evaluated and a result was obtained that varies around the values of 120 V/m and 80 A/m, respectively, which allowed to conclude that the shielding efficiency is satisfactory.
In order to be able to support the previously formulated conclusion regarding the values of the simulated electromagnetic field, a set of results obtained from measurements made on the real chamber whose geometry was simulated was presented, leading to the conclusion that on the whole frequency range for which the simulation was run, there was no maximum specific level exceeding of the electromagnetic field, the recorded values being close in order of magnitude and even in actual value.
The geometric model of the anechoic chamber used to simulate the field distribution in the enclosure in order to determine the uniformity of the field inside is the same as the one used to determine the effectiveness of shielding, the novelty of this simulation being represented by the horn antenna used as a signal source. The antenna was modeled so that it also correlated according to the 1:3 ratio with the actual size with which the measurements used as reference values for the comparative study were performed.
The distribution of the electric field on the surface was made according to the propagation mode of the waves in a TE guide type (TE) - electric transversal, the propagation direction being oriented along the x-axis. The cutoff frequency was 14.84 MHz and the accuracy was 1,332 × 10-16. The maximum value of the electric field recorded on the linear scale was equal to 742.2 V / m. Expressed in decibels, this value means 177. In the case of the magnetic field, the maximum value of the field recorded on the linear scale was 62.7 A / m, and on the logarithmic scale it was 156 dB µ A/m.
In the analyzed area of interest, values between the limits 165 and 177 156 dB µ V/m were recorded for the field. Thus the difference between the minimum and maximum value of the electric field is 12 dB µ V/m. In the case of the magnetic field, the difference between the minimum and maximum field values is only 7 dB µ A/m.
Analogous to the previously presented simulation, and in this case, in order to allow the comparison with real data, physical measurements were made for the uniformity of the field inside the chamber. These were performed in accordance with EN 61000-4-3, in the frequency range 80 MHz to 1 GHz, the frequency step used during the measurement being 1%. The electric field intensity was measured in 12 points in the analyzed field area, the measurements being performed at 3 meters.
The results obtained from the field uniformity measurements were centralized, both for horizontal polarization and for vertical polarization. The most unfavorable situations recorded in the 12 analyzed points were selected from the table obtained for the entire frequency range.
The deviation from the theoretical value for the measured environmental attenuation value is given in Figures 4.40 and 4.41. A positive value means that the transmission losses measured at the site are higher than at the reference environment. If equivalent antennas were used for measurement, a transmitting antenna was used in the simulation and a field sample for reception. The modeling and parameters of the two were previously specified.
Compared to the results of the previously presented measurement, it can be stated that a similar variation recorded the simulated electromagnetic field.
By means of these comparisons it was intended to make a correlation between modeling, simulation and experimental determinations for the determination of field sizes in the specialized chamber, in order to validate the results of the performed simulation. Thus, according to those demonstrated above, it can be concluded that the created model is a corresponding one, which is very close to the real object for which the simulation was intended.
It was thus shown that both the boundary conditions and the symmetries were well chosen, the material properties and the calculation constants were correctly defined, so that the model is very close to reality and thus the model can be considered optimal.
The CST STUDIO SUITE software with which the simulations were performed is one of the main high performance software packages used for simulations of the electromagnetic field distribution in all frequency bands. Numerical models of the investigated structure were developed in CST Microwave Studio. His principle is based on the description of electromagnetic problems by means of Maxwell's equations in differential form. The software includes four different solvents. To study the electromagnetic behavior of the analyzed structure, we chose the time domain (FDTD) and frequency (FDFD) solvents, these being considered to be the most appropriate in the case of shielding and absorption problems in the field of high frequencies. Spatial meshing of the structure was achieved by the Perfect Boundary Approximation (PBA) technology which allows a very good approximation even in the case of curved surfaces within meshed cubic cells. Thus the mesh is made by an automatic mesh generator, which also ensures an advantageous compromise between the accuracy of the provided solution and the simulation time.
A workstation with the following properties was used to perform the simulations: Windows 10, Dual Intel Xeon Gold 6244, 8 cores, 3.6 GHz base frequency, GPU graphics accelerator:
NVIDIA Quadro GP100 (16GB RAM ), 96 GB DIMM memory (12 x 8 GB) DDR4-2933
RAM, SATA hard disk capacity 1TB boot drive SSD. Using this tool, running the simulation takes approximately 13 hours. With the help of CST STUDIO SUITE, the modeling of the shielding efficiency and the distribution of the electromagnetic field inside the anechoic chamber was performed. Following the analysis of the obtained results, it was demonstrated that this configuration allows the realization of a large-scale simulation.
Chapter 5 presents the experimental results that were obtained following the tests for the studied anechoic chambers. The results of the experimental determinations of the shielding efficiency of some test chambers lined with rhodium-frequency absorbers are presented, being analyzed both individually and by comparison with those obtained from modeling, in order to formulate conclusions and observations regarding the research performed.
The principle of realization assumes a special construction that ensures optimal shielding, so that there are no external influences inside or outside of it. In most cases, the metal housing of the shielded enclosures is structured in many component parts, integrating the power supply panel containing inputs for power and signal lines, ventilation fans and the access door. The joining of the panels is done by screwing, and in order to ensure a sufficiently good shielding, sealing materials with special properties (gaskets) are used, which are applied in the joint area.
Some types of chambers may also include in their structure, in addition to the above components, panels made of materials that allow monitoring the behavior of equipment tested during the period in which tests are performed.
The component parts that are part of the studied anechoic chamber are presented in detail in the chapter, both in terms of construction and in terms of the risk it poses in terms of ensuring its effectiveness.
Another extremely important aspect presented in this chapter is the detailing of the necessary conditions for performing specific EMC measurements. These conditions require that all penetration doors and panels be closed during the measurements. Honeycomb inserts, line and feed filters must be checked for proper installation. Electric and electronic equipment must be switched off during testing, because otherwise, it could disturb the accuracy of the test result. Radiation-sensitive equipment must be removed to avoid possible flaws caused by the strong electric and magnetic field that will be produced during the test run. The resonance of the camera must be avoided by changing the position and orientation of the antenna, thus reducing the negative influences that would be reflected on the measurement results.
The first measurement was the experimental determination of the shielding efficiency of an anechoic chamber according to the IEEE 299 standard and took place inside the Electromagnetic Compatibility laboratory within the Center for Research in Applied Sciences - INCESA. The test site that was verified consists of an anechoic chamber E-CDC Energy and Coverage-aware Distributed Clustering Protocol, with the following dimensions: length 6100 mm, width 3400 mm, height 2550 mm.
The verification of the anechoic chamber shielding effectiveness was performed in the frequency range 9 kHz - 4 GHz, the measurements being performed in accordance with the provisions imposed by the IEEE Std standard. 299: 2006.
The field intensities were determined by means of two measurements, one being performed with a screen, and the other measurement being performed without a screen (this being found in the literature as “direct measurement”). The results were processed and used in computing the effectiveness of the enclosure shielding. The measured frequency range, between 9kHz and 4MHz, was subdivided as follows: range 9 kHz ÷ 20 MHz - low frequency range; 20 MHz range ÷ 300 MHz - resonant frequencies; 300 MHz range ÷ 4 GHz - high frequency range.
The obtained results are presented in tabular form and interpreted according to the IEEE Std standard. 299: 2006, the shielding effectiveness proving to be satisfactory. The tested semi- anechoic chamber is therefore a suitable test medium for performing EMC tests.
The second measurement performed for the experimental determination of the shielding efficiency of the semi-anechoic chamber took place inside the Electromagnetic Compatibility testing laboratory of an enterprise with activity in the machine building industry being performed in accordance with the provisions imposed in the standard in force EN 50147-1 The tested location consisted of a semi-anechoic chamber E-CDC - Energy and Coverage- aware Distributed Clustering Protocol, with a rectangular geometry with the following dimensions: length 6380 mm; width 5550 mm; having a height of 3750 mm.
The enclosure was tested at the following frequencies: in magnetic field: 10 kHz, 100 kHz, 1 MHz; in electric field: 100 MHz; for flat wave: 400 MHz, 1 GHz, 10 GHz, 18 GHz. Noise caused by the resonant frequency was avoided by changing the position and type of orientation of the antennas.
For the validation of the screen shield tested, the variation in decibel level of the indoor electromagnetic field according to EN 50147-1 shall not exceed the variation level of ± 6 dB between the recorded values. As the differences between the analyzed values varied in the range of minus 6, plus 6 decibels, not exceeding the minimum or maximum permissible level, it could be concluded that in this respect the acceptance criterion was met and the tested chamber can be considered optimal for measuring electromagnetic compatibility.
Chapter 6 presents the author's contributions and the conclusions drawn based on the research conducted in the doctoral thesis.
The conclusions of the thesis were structured in three categories, as follows: theoretical conclusions, conclusions on the modeling and simulation part and conclusions on the tests performed.
One of the drawn theoretical conclusions based on this doctoral thesis refers to the fact that the theory of electromagnetic field calculation is laborious and extremely cumbersome, very difficult to achieve without the help of modern computing techniques. However, many
methods of determination are available, depending on the type of analysis to be performed. In order to determine the local structures of the electromagnetic field and the mode of propagation of its component fields, the commonly used mathematical formulations are presented in chapters 1 and 2.
A computing algorithm was created based on the existing formulations in the specialized consulted literature , this being presented in detail in chapter 1, where the computing relations of the propagated electromagnetic field for different types of antennas used in the measurements performed and presented in the doctoral thesis are exposed;
The main software used in this field were mentioned, both in the scientific sphere and in the industrial environment, being amply presented in Chapter 3 for each one, their properties and particularities. Chapter 3 also presents a comparative analysis of the capabilities offered by these specialized software, depending on the type of analysis to be performed.
Regarding the performed modeling and simulations, it can be concluded that the analysis problems regarding the calculation or determination of the electromagnetic field in the conditions of knowing the geometry of the field, the characteristics of the domain materials, the spatial and temporal distribution of field sources and / or other additional conditions, for obtaining a unique solution as the initial and boundary conditions, involve the determination of local and instantaneous state quantities of the field (E, D, B, H) in the space-time domain under analysis.
So, in order to obtain exact solutions, in case of complicated configurations, numerical modeling is sometimes the best possible approach, based on the use of computers to evaluate the solution. CST STUDIO SUITE electromagnetic simulation software has proven to be an optimal high performance software package for electromagnetic simulation in all frequency bands, which includes tools for designing and optimizing devices operating in a wide range of frequencies offering efficient computerized solutions for the design and analysis of the electromagnetic field based on Maxwell's differential equations;
For the simulation were used: for transmission, a waveguide and for reception, a field sample, in order to reproduce the conditions created in the measurement where equivalent antennas were used. It was thus aimed that by comparison with the results of the performed measurements , to analyze in a realistic manner the variation of the quantities and the results obtained from the simulation, and their proximity (in order of magnitude) to the real ones.
Through the analysis procedure mentioned above, the doctoral student aimed, with the help of comparisons, to make a correlation between modeling, simulation and experimental determinations for determining field sizes in the specialized room, in order to validate the simulation results. Thus, according to those formulated above, it can be concluded that the created model is a corresponding one, which is very close to the real object for which the simulation was aimed.
Regarding the experimental results obtained by testing anechoic chambers used to perform measurements of conducted emission and radiated immunity in accordance with electromagnetic compatibility standards, in particular IEC / EN 61000-4-3, IEC / EN 61000-
4-20, CISPR 11 and CISPR 25, the conclusions of the thesis confirm that these anechoic chambers are safe to be used in various industrial applications, mostly in the automotive field because for the measurement presented in subchapter 5.2, the verification of the anechoic chamber shielding effectiveness was performed within the frequency 9 kHz - 4 GHz, was performed in accordance with the provisions imposed by the IEEE Std standard. 299, 2006 edition. Thus, the field intensities were determined by means of two measurements, performed with and without screen, the obtained results being subsequently processed to determine the attenuation calculation. The resonance of the camera was determined according to the standard methodology as having the value of 50 MHz, being avoided by changing the position and orientation of the antenna, thus reducing the negative influences that would have been reflected on the accuracy of the measurement results;
Directly, the values of the recorded magnetic field showed variations between 40 and 85 decibels. In the case of measurements made on either side of the wall in which the access door is mounted, for the frequencies in the resonant range, the shielding efficiency recorded values between 62 and 75 decibels.
- the maximum variation value of the electric field measured inside the camera was about 9 decibels, which proves a satisfactory shielding of the analyzed camera;
- for the high frequencies, from the measurement also made near the wall that includes the access door, values between 63 and 83 decibels resulted. And this time the values related to the field, which recorded variations between 5 and 8 decibels, are satisfactory, so the efficiency of shielding the anechoic chamber is high, its performance being high;
- the calculation of the camera shielding efficiency, for the second measurement was made without having radio frequency absorbers mounted on its floor, which is why the camera was considered as semi-anechoic. The verification of the effectiveness of its shielding was performed in the frequency range 10 kHz - 18 GHz, in accordance with the provisions imposed by the standard EN 50147-1. The maximum obtained dynamic values did not reach the limit values imposed on the field, the differences between the obtained values not being greater than the range minus 6, plus 6 decibels. It could thus be concluded that in this sense the acceptance criterion was satisfied, the tested chamber being optimal for performing electromagnetic compatibility measurements.
The contributions that emerged from the research carried out during the doctoral internship are structured in four categories as presented below.
As methodological contributions the physical quantities were established and interpreted with the help of which the components of the electromagnetic field can be determined, by:
personal observations during their presentation in Chap. 1, 2 and 3; by modeling the configuration of the studied anechoic chamber, in order to compare the results with standard values of the electromagnetic field in Chap. 4. and also by implementing the model and its simulation in the CST Studio Suite software in order to analyze the behavior manifested by the simulated equipment.
From a theoretical point of view:
- a classification of the most frequently used modeling methods in the calculation and analysis of the electromagnetic field in Chap. 2;
- a modeling algorithm was elaborated, based on the consulted specialized literature, to be the basis for the realization of the studied enclosure model;
- a classification of the equations of propagation of the electromagnetic field according to the type of antenna with the help of which it was produced in Chap. 2;
- different computing methods were synthesized based on the fundamental theory of wave propagation for various transmission media of the electromagnetic field in different states of its existence in Chap. 1.
From an applicative point of view, the results of experimental studies on the reliability of tested equipment relative to their shielding effectiveness, contribute to formulating conclusions on the veracity of the designed model and the correctness of the obtained results by simulating, by identifying and correlating existing standards and comparing with maximum admissible levels recorded in the measurements performed in the doctoral thesis so as to represent a standard both for the results of the latter and for the modeling and simulations performed.
Also, by reporting the results of experimental tests to determine the distribution of the electromagnetic field in specialized EMC testing premises with metal structure, at the levels imposed by norms and standards governing maximum permissible field limits for different types of analysis their reliability can be validated in order to obtain conformity certification.
The software contributions consist in the design of a geometric model of the equipment that is the object of the present research, a model with scale geometry. The parameters used to make the model are extensively detailed in Chap. 4 where are presented, moreover, the initial conditions and those of the adopted borders;
Contributions were also made in the field by performing simulations of the model designed to obtain results on how the electromagnetic field is distributed inside the specialized test chamber and determine the effectiveness of its shielding in Chap. 4;
Contributions were also made by performing an analysis on the reliability of the designed model based on the results obtained from its simulation, and its validation by performing a comparative analysis with the results obtained from physical measurements. And by performing at the same time the modeling of a constructive type of antenna (Pyramidal Horn antenna), used in the performed experimental determinations, in order to analyze the parameters and its propagation mode;
Originality elements of the doctoral thesis with the highest degree of interest are the following: realization of the geometric model of the room using the CST Studio Suite simulation program and its simulation in order to obtain graphical results on the distribution of the electromagnetic field inside the enclosure, and its variation mode depending on the type of excitation signal applied; simulating the effectiveness of shielding the anechoic chamber in locations prone to field leakage due to its realization, the graphical
representations related to each simulated area being presented and analyzed in detail in Chapter 4;
The results of the study carried out within the doctoral thesis, regarding the modeling and simulation of the propagation of the electric and magnetic field generated in shielded enclosures for the analyzed frequency range, contribute, together with other specifications in the literature, to improving the performance of existing equipment in order to optimize them, the simulation allowing adjustments in a much less expensive way than the effective realization of non-performing prototypes. The optimization, once performed at conceptual level, can allow the transition to the practical realization of an equipment at the level of laboratory prototype in order to develop new innovative equipment. The results of the performed experimental tests can confirm the possibilities offered by the equipment at the time of their performance, providing relevant information on the required standard procedures and how to perform the effective measurement for the type of analysis to be performed.
The obtained results during the thesis were disseminated in the international conferences of high scientific level where 13 scientific articles were published at specialized international conferences, 7 of them being presented. At national level, an article was published and supported.
The obtained results were also disseminated through the publication of scientific papers in prestigious journals, three of which in the annals of the University of Craiova (COPERNICUS magazine), one in ACTA ELECTROTEHNICA JOURNAL (CNCSIS B + magazine), one in the Bulletin of the Polytechnic Institute of Iasi COPERNICUS) and one in the AGIR Bulletin - (COPERNICUS indexing, ACADEMIC KEYS, GETCITED). A total of 6 articles were published.
The results obtained in the thesis are also due to the activity carried out prior to it, carried out during the elaboration of the dissertation project and respectively of the 5 research contracts in which the doctoral student was involved.
As a result of the research carried out, new research directions emerged regarding: the adjustment of the model conceived within the thesis, in such a way as to confer sufficient veracity to be suitably developed in a prototype of testing equipment; construction or acquisition of the unconventional metal enclosure prototype for specialized EMC measurements based on the model developed for its certification for its widespread use in the industry.
