Date of Award
Doctor of Philosophy (PhD)
Todd H. Hubing
Anthony Q. Martin
Electromagnetic interference (EMI) is a problem of rising prevalence as electronic devices become increasingly ubiquitous. EMI filters are low pass filters intended to prevent the conducted electric currents and radiated electromagnetic fields of a device from interfering with the proper operation of other devices. Shielding is a method, often complementary to filtering, that typically involves enclosing a device in a conducting box in order to prevent radiated EMI. This dissertation includes three chapters related to the use of filtering and shielding for preventing electromagnetic interference. The first chapter deals with improving the high frequency EMI filtering performance of surface mount capacitors on printed circuit boards (PCBs). At high frequencies, the impedance of a capacitor is dominated by a parasitic inductance, thus leading to poor high frequency filtering performance. Other researchers have introduced the concept of parasitic inductance cancellation and have applied this concept to improving the filtering performance of volumetrically large capacitors at frequencies up to 100 MHz. The work in this chapter applies the concept of parasitic inductance cancellation to much smaller surface mount capacitors at frequencies up to several gigahertz. The second chapter introduces a much more compact design for applying parasitic inductance cancellation to surface mount capacitors that uses inductive coupling between via pairs as well as coplanar traces. This new design is suited for PCBs having three or more layers including solid ground and/or power plane(s). This design is demonstrated to be considerably more effective in filtering high frequency noise due to crosstalk than a comparable conventional shunt capacitor filter configuration. Finally, chapter 3 presents a detailed analysis of the methods that are used to decompose the measure of plane wave shielding effectiveness into measures of absorption and reflection. Textbooks on electromagnetic compatibility commonly decompose shielding effectiveness into what is called the Schelkunoff decomposition in this work with terms called penetration loss, reflection loss, and the internal reflections correction term. In experimentally characterizing the shielding properties of materials, however, other decompositions are commonly used. This chapter analyzes the relationships between these different decompositions and two-port network parameters and shows that other decompositions offer terms that are better figures of merit than the terms of the Schelkunoff decomposition in experimental situations.
McDowell, Andrew, "Design and Analysis of Electromagnetic Interference Filters and Shields" (2014). All Dissertations. 1368.