EMC Best Practices: Part I
Astrodyne TDI
This application note from Astrodyne TDI, authored by Field Applications Engineer David Bourner, serves as the first part of a two-part series on EMC best practices for hardware designers. Rather than jumping straight to design rules, it builds understanding from the ground up by explaining the physical mechanisms behind electromagnetic interference. The document argues that circuit schematics are useful abstractions but fundamentally incomplete representations of real-world electrical behavior, and that effective EMC design requires designers to think beyond the schematic and account for the actual physical properties of conductors, traces, and component arrangements. It traces the history of EMC from its military origins in 1960s US defense programs to its current status as a legally binding requirement across commercial and industrial sectors. The core of the document walks through a progressive series of five design themes grounded in electromagnetics: that real components have parasitic properties beyond their intended function; that physical layout must be mapped to schematic to enable EMC mitigation; that signal frequency determines how current distributes within conductors; that conductors couple inductively with neighboring circuits even without physical connection; and that every signal or power trace requires a continuous, closely routed return path to minimize loop area and prevent unintended RF radiation or susceptibility. The underlying phenomena explored include DC and AC magnetic and electric fields, skin effect, and the reverse proximity effect in paired conductors and PCB ground planes. Part II, referenced but not included here, will address practical implementation strategies at the board, system, and enclosure levels.