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78 DESIGN007 MAGAZINE I DECEMBER 2022 it might seem quite unnecessary to explore those that lay beyond; yet today, that is exactly where I intend to take you. A Vast Highway of Opportunity Heater Circuits ere are countless design opportuni- ties that lie outside the generally perceived realm of flexible circuits, but far too oen we simply don't see them. For example, consider the flexible heater circuit. in flexible heaters are used in numerous invis- ible applications. ese heater circuits are oen found in such items as fog and frost- free mirrors. ey are a simple, yet very practical flexible circuit application that can be found anywhere—from the automobile to the bathroom—where relatively low tem- peratures suffice to accomplish the objec- tives. ese low-power circuits can be made relatively inexpensively using materials such as polyester films and polymer thick film inks. However, higher temperature flexible circuit heaters are also possible. Such high- temperature heaters can be made using highly resistive metal films or foils such as nickel-chrome, Iconel, or stainless steel—in combination with high temperature mate- rials, such as polyimide, that are capable of withstanding and putting out significant wattage and heat. Smart Cards Another area where flexible circuit tech- nologies have played a significant role over the years is in the manufacture of smart cards. is is not a new application for flexible cir- cuits, but it is clearly an emergent technology as we press on into the age of the internet, where nearly every individual item ever man- ufactured can have a unique, trackable iden- tity. Smart cards have become the backbone of the internet of things (IoT). Such devices generally have a chip attached to provide their identity. Metal coils etched into the copper foil of the flex circuit material are typical fea- tures on such devices, used to both send and/ or receive wireless data. Because of the huge and growing volume of such circuits, roll-to- roll processing—a process that flexible circuits are naturally suited to—is generally employed to manufacture these increasingly ubiquitous circuits. Wearable Electronics Yet another area of gathering potential for flex circuits is wearable electronics, an indus- try that has exploded in recent years due to the growing interest in personal health moni- toring. Typically, these devices include both electronic devices with thinned integrated circuit chips and passive devices that con- form to the anatomical features of the wearer. Such devices can monitor many bodily func- tions, including heart rate, respiration, elec- trolytes, blood sugar, and many others; this data can then be transmitted to a smartphone, for example. ese expanded capabilities have inspired developers to label these more inte- grated assemblies "flexible hybrid electron- ics" (FHE). ey have been integrated into another area of investigation: stretchable cir- cuits, which use elastic or elastomeric sub- strates; this technology opens doors to even more practical and fanciful electronic product innovations. is brief column may have fallen short of covering the usefulness of flexible circuits in its entirety, but for those not yet familiar, it has hopefully provided a taste. e simple reality is that flexible circuits offer an unending range of opportunities to solve problems. is column has been an exercise in trying to inspire you to consider flexible circuits as an alternative "road" to your next electronic design destina- tion and implementation. Circling back to where I started this column, I'd like to share the poem that has inspired me many times over my life as a courtesy to those who may never had an opportunity to read and enjoy it.