Analysis and Mitigation of Electromagnetic Noise in Resonant Cavities and Apertures

Title of Dissertation: ANALYSIS AND MITIGATION OF ELECTROMAGNETIC NOISE IN RESONANT CAVITIES AND APERTURES Lin Li, Doctor of Philosophy, 2004 Dissertation directed by: Associate Professor Omar Ramahi, Mechanical Engineering The trend of low voltage in electronics circuits and boards makes them vulnerable to electromagnetic interference (EMI). Furthermore, higher speed (clock rate) leads to faster switching which increases the potential for higher radiation from circuits and boards. These inevitable trends collectively compromise the electromagnetic compatibility of electronic systems by increasing their electromagnetic susceptibility. In this work, radiation from enclosures and apertures is studies and characterized and radiation mitigation techniques are proposed. High-speed circuit radiation within an enclosure leads to cavity resonance that can have critical impact on other electronic components housed within the same enclosure. The amplified electric field in the enclosure can couple to critical circuits leading to either hard or soft failures. One measure to gauge the resonance of an enclosure is through the determination of S-parameters between certain ports connected to the enclosure. In this work, different numerical methods for efficient prediction of Sparameters are proposed and evaluated for their effectiveness and accuracy. Once an efficient procedure is established for calculating S-parameters, novel topological variations within the enclosure can be tested before manufacturing using accurate numerical prototyping. The proposed numerical S-parameters calculation algorithms are validated by comparison to laboratory measurements. Radiation from resonant apertures present in the walls of enclosures represents a second major source for radiation. In this work, a novel analysis of aperture radiation is presented based on the interpretation of the aperture as a transmission line. Once the transmission line analogy is established, a novel aperture resonance mitigation technique is proposed based on the use of material coating that mimics the behavior of matching loads that typically terminate transmission lines. The technique consists of adding resistive sheets in selected places in, or around the aperture. The effectiveness of the proposed method is demonstrated by first using numerical simulation of an aperture present in an infinite perfectly conducting sheet, and then by designing an experiment where the novel technique proposed here is tested on resonant apertures present in a metallic box. Both radiation measurements in an anechoic chamber and S-parameters measurements were conducted to test the validity of the proposed mitigation techniques. ANALYSIS AND MITIGATION OF ELECTROMAGNETIC NOISE IN RESONANT CAVITIES AND APERTURES