Protection by open systems : an EMC study

Electromagnetic interference (EMI) is an important factor in the design of modern electronic equipment. A fully closed structure (Faraday cage) around the electronics would prevent the coupling towards and from the environment. However, practical considerations (accessibility, thermal characteristics, production costs etc.) seldom allow the implementation of such closed shields. This thesis presents the results of experimental and numerical investigation into the electromagnetic compatibility (EMC) properties of open systems of various levels and sizes. The ¯rst study involves metal conduits, which are used for mechanical support of cables and may provide protection against electromagnetic interference. Being the most common shape, an open U-shaped conduit has been chosen as basic con¯gu- ration. A number of wires inside the brass conduit represent the actual cables with their shields. This con¯guration is subjected to a plane wave excitation to determine induced currents in the wires. It is known that the open conduit can reduce the undesired coupling signi¯cantly. New in this study is the extended frequency range. Measurements and simulations agree up to frequencies where the wavelength is several time shorter than the conduit length, but still larger than cross-sectional dimensions. Another study concerns the coupling of printed circuit boards (PCB) with the envi- ronment, or the common-mode (CM) circuit. A nearby cabinet panel in°uences the signal transmission and radiation of PCB tracks. This in°uence has been studied for straight and meandering tracks by measurements and 3D calculations. If properly connected, a cabinet panel reduces the undesired CM coupling signi¯- cantly. An improperly connected cabinet may lead to enhanced coupling. The cou- pling is also a®ected by the shape of the cabinet panel, and by the way the signals are transported, either as a balanced signal via two tracks or unbalanced signal with a single track and the groundplane. A 2D model study showed the positive e®ects and also many possible situations where the coupling is enhanced. A novel technology allows production of fully shielded tracks on a PCB, by which the coupling can be extremely reduced. Even with partly open shields, the di®erential- mode (DM) and the CM coupling of tracks is considerably smaller compared to con- ventional transmission lines. The in°uence of manufacturing tolerances on character- istic impedance has been studied as well. In order to correctly perform the measurements on PCB, the in°uence of the connec- tors has to be minimized. Special attention has been paid to the interface between connector and both shielded and traditional transmission lines on a PCB. The simulations were performed with Schwarz-Christo®el mapping for simply and doubly connected polygonal regions, static 2D Method of Moments, dynamic 3D Method of Moments (CONCEPT by the Technical University Hamburg-Harburg and FEKO by EMSS), and Finite Integration Technique (Microwave Studio by CST GmbH). The experimental investigations on PCBs have been carried out in the TU/e groups EPS (up to 1.8 GHz), and EM (up to 18 GHz). The radiation measurements were performed in the EMC test facility of Philips Medical Systems in Best and the Philips Electromagnetic and Cooling Competence Center in Eindhoven, the Nether- lands. Various results were presented at a number of international conferences. Chapter 4 is accepted for publication in the IEEE Transactions on Electromagnetic Compatibility and Chapter 5 is published in the Journal of ElectromagneticWaves and Applications