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22 DESIGN007 MAGAZINE I NOVEMBER 2022 Ralph Morrison was a physicist who pro- moted the belief that electromagnetic energy flows in spaces, not the traces. at energy does not flow in the copper traces of a PCB, but rather the energy follows the traces act- ing as a waveguide and propagates through the dielectric material. is explains many elec- tromagnetic (EM) effects such as radiation from outer microstrip layers and from stripline fringing fields, how components can be mag- netically coupled, and why crosstalk is created by overlapping EM fields. But it also raises a few questions. e simplistic approach to analyzing elec- tronic circuits is to use the lumped element model. is methodology assumes that the attributes of the circuit—resistance, capaci- tance, and inductance—are concentrated into idealized electrical components connected by Forget What You Were Taught a network of perfectly conducting wires. How- ever, that is not the case. As the frequency and rise time increase, these elements become dis- tributed continuously through the substrate along the entire length of the trace. e cop- per trace and the adjacent dielectric materi- als become a transmission line, the skin effect forces current into the outer regions of the conductor, and frequency dependent losses impact the quality of the signal. e PCB trace now behaves as a distributed system with para- sitic inductance and capacitance characterized by delay and scattered reflections. e behav- ior we are now concerned about, occurs in the frequency domain. We were taught in circuit theory (and still are) that electric energy is made up of electrons moving in the conductors. Unfortunately, cir- cuit theory does not consider the flight time of Beyond Design Feature Column by Barry Olney, IN-CIRCUIT DESIGN PTY LTD / AUSTRALIA