Electromagnetic Near-field Characterization & Occupational Exposure to RF Waves in Industrial Environment

Abstract : The analysis of radiated emissions from a source throughout the space, is very essential for both dosimetric and electromagnetic interference analysis. The concerns about the latter are growing because of the need to have prediction of the system reliability of the electronic circuits. Moreover the everyday use of devices and systems emitting radio frequency electromagnetic fields is continuously increasing. Some of these devices are operating in the vicinity of human body, and operators are in the near-field region of the radiating source, and they are exposed to electromagnetic fields. For this reason, dosimetric analysis, that shows the necessity of having three dimensional (3D) field mapping in the vicinity of the radiating source, should be performed. For this kind of applications, several scans of the near fields should be done within different planes in order to build the 3D field mapping. Being a challenging process in electromagnetic compatibility studies, near field characterization is being treated by several algorithms that propose different approaches to achieve the required scanning on the radiating source.In this work, we introduce a 3D scanning system with a low cost three axis magnetic field probes. Having such probes allow the simultaneous measure of the three components of the magnetic field based on a single planner scan above the device under test. The designed probes consist of three orthogonal loops combined together; the first probe contains three conventional loops joined in a plastic cube with a total dimension of 10×12×13 mm3, whereas the second probe is a PCB probe printed on an FR4 substrate of 3.2 mm with a reduced dimension of 9×9×3.2 mm3. The designed probes were calibrated with a TEM cell and the corresponding antenna factors were extracted. The presented scanning system uses an oscilloscope as a measuring instrument that gives the possibility of both time and frequency domain measurements. The second part of this thesis presents a reconstruction algorithm based on plane wave spectrum method. In order to reduce the number of scans and hence the time requirements, the presented algorithm requires just a 2D near field scan of the field components, to reconstruct the 3D magnetic field distribution above the radiating device.The third part of the thesis is devoted for the dosimetric analysis of the radiated electromagnetic fields near RFID systems and RF-welding machines. The near-field exposure assessment of the radiated fields from RFID reader antennas operating at 13.56 MHz and used in Libraries was performed. The measurements of the magnetic field near the antenna were established using the designed probes. The results are then analyzed and compared to the regulations in European Directives and ICNIRP Guidelines. Moreover, the exposure to RF electromagnetic fields of workers near RF-welding machines in industrial environment is studied. These machines, operating at 27 MHz, emit strong radiation and the exposure takes place in the near-field region. The spatial distribution of the electromagnetic fields in this region is studied in both numerical simulations and measurements.
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Kassem Jomaa. Electromagnetic Near-field Characterization & Occupational Exposure to RF Waves in Industrial Environment. Optics / Photonic. Université Grenoble Alpes, 2018. English. ⟨NNT : 2018GREAT111⟩. ⟨tel-02146578⟩

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