Printable metal tags have been developed that could be attached to everyday objects to turn them into “smart” Internet of Things (IoT) devices. The tags are made from patterns of copper foil printed onto thin, flexible, paper-like substrates that reflect WiFi signals. The tags work essentially like mirrors that reflect radio signals from a WiFi router. When a user's finger touches the mirrors, it disturbs the reflected WiFi signals in such a way that can be remotely sensed by a WiFi receiver, like a smartphone.

Thin, flexible LiveTag tags in comparison with a piece of photo paper (far left). (Xinyu Zhang)

The tags can be tacked onto plain objects that people touch and interact with every day, like water bottles, walls, or doors. These plain objects then essentially become smart, connected devices that can signal a WiFi device whenever a user interacts with them. The tags can also be fashioned into thin keypads or smart home control panels that can be used to remotely operate WiFi-connected speakers, smart lights, and other IoT appliances.

The LiveTag technology consists of low-cost, battery-free, chipless, printable sensors that only reflect specific signals within the WiFi frequency range. By changing the type of material they're made of and the pattern in which they're printed, the tags can be redesigned to reflect either Bluetooth, LTE, or cellular signals.

As a proof of concept, LiveTag was used to create a paper-thin music player controller complete with a play/pause button, next-track button, and sliding bar for tuning volume. The buttons and sliding bar each consist of at least one metal tag so touching any of them sends signals to a WiFi device. The LiveTag music player controller was tested to remotely trigger a WiFi receiver, but it could remotely control WiFi-connected music players or speakers when attached to a wall, couch armrest, clothes, or other ordinary surface.

LiveTag also was adapted as a hydration monitor. It was attached to a plastic water bottle and showed that it could be used to track a user's water intake by monitoring the water level in the bottle. The water inside affects the tag's response in the same way a finger touch would, as long as the bottle is not made of metal, which would block the signal. The tag has multiple resonators that each get detuned at a specific water level. The tag could be used to deliver reminders to a user's smartphone to prevent dehydration.

For more information, contact Liezel Labios at This email address is being protected from spambots. You need JavaScript enabled to view it.; 858-246-1124.


Tech Briefs Magazine

This article first appeared in the December, 2018 issue of Tech Briefs Magazine.

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