The shape of the gears and the speed at which they move control how long the backscatter switch makes contact with the antenna, creating patterns of reflected signals that can be decoded by a Wi-Fi receiver.
"As you pour detergent out of a Tide bottle, for instance, the speed at which the gears are turning tells you how much soap is flowing out. The interaction between the 3-D printed switch and antenna wirelessly transmits that data," says the paper's senior author Shyam Gollakota, an associate professor in the Paul G. Allen School of Computer Science & Engineering. "Then the receiver can track how much detergent you have left and when it dips below a certain amount, it can automatically send a message to your Amazon app to order more."
The researchers 3-D printed several different tools that were able to sense and send information successfully to other connected devices, including a wind meter, a water flow meter, and a scale. They also 3-D printed Wi-Fi input widgets such as buttons, knobs, and sliders that can be customized to communicate with other smart devices in the home and enable an ecosystem of "talking objects" that can seamlessly sense and interact with their surroundings.
The researchers also experimented with a different type of 3-D printing filament that combines plastic with iron, leveraging magnetic properties to invisibly encode static information in 3-D printed objects. This, they say, could be used in applications ranging from barcode identification for inventory purposes or providing information about an object that tells a robot how to interact with it.
"It looks like a regular 3-D printed object but there's invisible information inside that can be read with your smartphone," says Justin Chan, Allen School doctoral student and co-lead author of the paper.
For more, see "3D Printing Wireless Connected Objects."