Equivalent optically transparent circuits: an optimization-driven methodology for the design of optically transparent sensors and antennas

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Touch sensors are indispensable components of the user interface of personal electronic devices such as smartphones, tablet computers and wearable health monitors. These sensors are ordinary circuits, whose usual copper wires are replaced by optically transparent (practically invisible) conductors such as Indium Tin Oxide (ITO). The use of optically transparent conductors, which suffer from higher losses compared to copper, makes the design of these circuits a challenging task. Circuit designers have by and large dealt with this challenge on a trial-and-error basis, using a combination of circuit models and electromagnetic simulations to derive topologies that trade performance for optical transparency. With the market for personal and wearable electronic devices as competitive as ever, new touch sensors are expected to support high-rate sensing of multi-tasking gestures with low latency. These stricter specifications test the limits of current design tools, motivating further research on the optimal performance bounds of transparent circuits and the topologies that meet those bounds under given fabrication constraints.The present proposal addresses this urgent need by introducing the concept of equivalent optically transparent circuits (EOTCs). These two and four-port circuits are synthesized by optimization aimed at minimizing the difference between their performance and the performance of their copper-based counterparts. Leveraging advances in convex optimization of electromagnetic structures and uncertainty quantification techniques, this project is aimed at deriving a "dictionary" of building blocks for transparent circuits made with standard (ITO) and emerging (silver nanowires, graphene) materials, just as one/two-dimensional microstrip lines are for copper-based ones. In addition to touch sensors, applications of the EOTC concept to the design of transparent antennas and multi-functional touch-input/antenna surfaces will be explored.