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March 2014 • The PCB Design Magazine 41 the town crier DIFFERENTIAL EDuCATION 101 FOR PCB DESIGNERS continues Instead of just reading more personal obser- vations, it is far more productive for me to offer you, the PCB designers and managers, a chance to supply some of your thoughts by participat- ing in an e-mail survey. Editor Andy Shaugh- nessy and I want to hear your collective voices, and we will publish the results for all to see. Thank you for reading this column, and more importantly, thank you in advance for your feedback. To take this short survey on PCB design and design education, click here. Next month, we'll go over the results. See you next month! PCBDESIGN Ed: This series on design education will continue for the next few months. Dan wants your feedback, so don't be shy. You may even see your name in an upcoming edition of "The Town Crier." Daniel J. smith is a principal technologist for raytheon Missile systems. he has taught multiple aspects of the PCB design pro- cess internationally, and he has authored several PCB-related patents, articles, and standards over the past 30+ years. To contact him, click here. For futuristic applications like wearable body sensors and robotic skin, researchers need to ferry information along flexible routes. electron- ics that bend and stretch have become possible in recent years, but similar work in the field of optics--communicating with light instead of electrons--has lagged behind. now a team of Belgian researchers reports progress on this front with what may be the first optical circuit that uses interconnections that are not only bendable, but also stretchable. These new interconnections, made of a rubbery trans- parent material called PDMs (poly-dimethyl- siloxane), guide light along their path even when stretched up to 30% and when bent around an object the diameter of a human finger. until now, the re- searchers say, no one had discovered a way to enable these ma- terials to carry light while stretched. Past efforts also included embedding waveguides made of semi-rigid glass fibers into a stretchable substance. in the new method, the stretchable substance itself is the waveguide. The new connector consists of two materials, both made of PDMs: a transparent core through which the light travels, surrounded by another transparent layer of PDMs with a lower refrac- tive index, a characteristic of the material that describes how light moves through it. Bending a waveguide beyond a certain point causes some of the light trapped in the core to escape, a process called optical loss. The Belgian team tested how far they could bend and stretch their new optical connector before too much light escaped. "We were surprised that stretching had so little influence on the waveguides and also that their mechanical performance was so good," Missinne said. The guide's reliability was also "remarkable," he said. This work has been performed at the Cen- tre for Microsystems Technology (CMsT), a laboratory associated with imec and Ghent university. Optical Circuits Flexing Their Way to the Forefront