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22 DESIGN007 MAGAZINE I DECEMBER 2022 netic fields around the trace. "Where exactly is the signal?" is a false choice. When we design a board, we must pay attention to all the ele- ments of the system: • e physical characteristics of the trace (including its impedance) • How close the signal path is to the return path • e material environment around the trace • e electrical environment around the trace (proximity of other signal paths) Do not pay too much attention to anyone who tells you that only one part of this system matters and the rest does not. DESIGN007 References 1. I have written about what current "is" several times. For example, see: PCB Currents; How They Flow, How They React, Section 1, Chapters 1-3, Prentice Hall, 2013, and "What Is This Thing Called 'Current', Electrons, Displacement, Light, Or What?" reprinted in UltraCAD's Best Articles and Applica- tions Notes 2022, Chapter 1. 2. Do a search on Google for the definition of electrical current and you will find an uncountable number of hits saying this or something close to this. 3. I will try not to let my bias show through here. But it has been my observation that many such engi- neers think they are superior to all others because they think that they understand Maxwell's equations and that you don't. Nonsense. As you will see, there is no choice of "either/or" here. And the dirty little secret is that most of them can't solve a set of Max- well's quations either. 4. Maxwell's Equations Without the Calculus, by Doug Brooks. This booklet describes how these principles are the basis for Maxwell's equations. Side note: James Clerk Maxwell was a mathemati- cian, not an engineer or physicist. His contribution to all of us was recognizing that these same laws could be combined into a "closed" system and he wrote the equations for them. An outstanding biog- raphy related to Faraday's work as well as Maxwell's contribution is Faraday, Maxwell, and the Electro- magnetic Field: How Two Men Revolutionized Phys- ics, by Nancy Forbes and Basil Mahon, 2019. 5. Ampere's Law and Faraday's law combined together explain the principles behind motors and generators. 6. The situation is slightly different in electronic transmission (as from an antenna) where we account for energy loss through a virtual radiation resistance. Douglas Brooks, PhD, is a vet- eran signal integrity instructor and the founder of UltraCAD Design in Issaquah, Washington. Researchers at Stanford University say they have created a simple, effective chip-scale isolator that can be laid down in a layer of semiconductor-based mate- rial hundreds of times thinner than a sheet of paper. "Chip-scale isolation is one of the great open challenges in photonics," said Jelena Vučković, a professor of electrical engineering at Stanford and senior author of the study. The nanoscale isolator is promising for several reasons. First, this isolator is "passive." It requires no external inputs, complicated electronics, or magnetics. The new isolator is made from common semiconductor-based material and can be manu- factured using existing technologies. The new isolator is shaped like a ring. It is made of silicon nitride, a material based on silicon. The strong primary laser beam enters the ring and the photons begin to spin around the ring in a clock- wise direction. At the same time, a back-reflected beam would be sent back into the ring in the oppo- site direction. The primary laser then exits the ring and is "iso- lated" in the desired direction. Vučković and team have built a prototype as a proof of concept and were able to couple two ring isolators in a cascade to achieve better performance. (Source: Stanford University) New Stanford Chip-Scale Laser Isolator Could Transform Photonics

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