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32 DESIGN007 MAGAZINE I JULY 2019 • Power and ground planes can be placed closely together to provide high-frequen- cy planar capacitance in high layer count boards • Return current can also excite the parallel plate resonance mode, causing significant electromagnetic radiation from the fring- ing fields • Plane pairs should be coupled closely to- gether to dampen the cavity resonance and provide high planar capacitance References 1. Olney, B. "Beyond Design: Stackup Planning, Part 1," The PCB Design Magazine, June 2015. 2. Olney, B. "Beyond Design: Stackup Planning, Part 2," The PCB Design Magazine, July 2015. 3. Olney, B. "Beyond Design: Stackup Planning, Part 3," The PCB Design Magazine, August 2015. 4. Olney, B. "Beyond Design: Stackup Planning, Part 4," The PCB Design Magazine, October 2015. Further Reading • Olney, B. "Beyond Design: Plane Cavity Resonance," The PCB Design Magazine, September 2017. • Olney, B. "Beyond Design: Faster Than a Speeding Bullet," The PCB Design Magazine, February 2016. • Olney, B. "Beyond Design: Signal Flight Time Varianc- es in Multilayer PCBs," The PCB Design Magazine, Decem- ber 2017. • Olney, B. "Beyond Design: Crosstalk Margins," Design007 Magazine, July 2018. • Olney, B. "Beyond Design: The Proximity Effect," Design007 Magazine, March 2019. • Johnson, H. W., & Graham, M. High-Speed Digital De- sign: A Handbook of Black Magic, Prentice Hall, 1993. • Ott, H. W. Electromagnetic Compatibility Engineering, Wiley, 2019. Editor's note: All numbered figures are attributed to Barry Olney. Barry Olney is managing director of In-Circuit Design Pty Ltd. (iCD), Australia, a PCB design service bu- reau that specializes in board-level simulation. The company developed the iCD Design Integrity software incorporating the iCD Stackup, PDN, and CPW Planner. The software can be downloaded To read past columns or contact Olney, click here. A new device developed by Stanford University re- searchers could make it easier for doctors to monitor the success of blood vessel surgery. The sensor, detailed in a paper published in Nature Biomedical Engineering, monitors the flow of blood through an artery. It is biode- gradable, battery-free and wireless, so it is compact, doesn't need to be removed, and it can warn if there is a blockage. "Measurement of blood flow is critical in many medical specialties, so a wireless biodegradable sensor could impact multiple fields in- cluding vascular, transplant, reconstruc- tive and cardiac surgery," said Paige Fox, assistant professor of surgery and co-senior author of the paper. Monitoring the success of surgery on blood vessels is challenging as the first sign of trouble often comes too late. By that time, the patient often needs additional surgery that carries risks similar to the original procedure. This new sensor could let doctors keep tabs on a healing vessel from afar, creating opportunities for earlier interventions. The sensor wraps snugly around the healing vessel, where blood pulsing past pushes on its inner surface. As the shape of that surface changes, it alters the sensor's capacity to store electric charge, which doctors can de- tect remotely from a device located near the skin but outside the body. In the future, this device could come in the form of a stick-on patch or be integrated into a wearable device or smartphone. (Source: Taylor Kubota, Stanford University) Stanford Researchers Develop Wireless, Battery-free, Biodegradable Blood Flow Sensor

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