By using reflected Wi-Fi signals, a chipless smart tag can put touch-responsive controls on almost anything
Despite the modern world’s fixation with touchscreen smartphones and tablets, most homes and businesses remain cluttered with objects that lack any digital interfaces. Now, those ordinary objects could get an upgrade thanks to new smart tags that harness reflected Wi-Fi signals to add touch-based controls to any surface.
The idea of an inexpensive tag capable of transforming any object into a smart device is not necessarily new. But most cheap smart tags that lack batteries or complicated electronics can only perform simple functions, such as passively storing and sharing identifying information about an object.
By comparison, new LiveTag technology allows for interactive controls or keypads that can stick onto objects, walls, or even clothing, and let people remotely operate music players or receive hydration reminders based on the amount of liquid remaining in a water bottle.
“These tags can sense the status of everyday objects and humans, and also sense human interactions with plain everyday objects,” says Xinyu Zhang, assistant professor in electrical and computer engineering at the University of California, San Diego.
Zhang and his colleagues at the University of Wisconsin—Madison developed the LiveTag technology after brainstorming about ways to easily incorporate ordinary objects into the Internet of Things without adding costly hardware and batteries. Their LiveTag designs and early prototypes are detailed in a paper [PDF] posted on the University of Wisconsin website.
The basic LiveTag technology seems deceptively simple: copper foil printed onto lightweight paper-like materials without any batteries or discrete electronic components. The key is in the geometric copper foil patterns that are designed to absorb Wi-Fi signals of specific frequencies, even as the overall tag generally reflects 2.4/5 GHz signals from nearby Wi-Fi device transmitters.
Each pattern’s selective signal absorption in the midst of the overall reflection creates a “notch” at a specific frequency on the spectrum that can be detected by Wi-Fi device receivers. Together, all of those notches for each specific tag create a unique spectrum signature that makes individual LiveTags stand apart from one another.
Once those notches have been established for each LiveTag, a person’s touch on various points of the tag will change the overall Wi-Fi spectrum signature of the individual tag. Such touch-based change can be detected and interpreted as specific button presses or control inputs—such as hitting the start/pause button on a music controller LiveTag or using a sliding bar for volume control—by customized software or apps running on nearby Wi-Fi devices.
Figuring out the right design for the printed copper foil patterns was no easy task. Zhang and his colleagues had to experiment with many different combinations of shapes, sizes, and materials for the LiveTags and run all those combinations through computer simulations. [READ MORE]
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