3D printed objects connect to WiFi without electricty

pic: Mark Stone/University of Washington

University of Washington researchers have created 3D-printed objects and sensors that can collect data and communicate with other WiFi-connected devices entirely on their own. One typical application says the university is a laundry detergent bottle that can sense when it is running low on soap which will automatically connect to the internet to place an order for more.

With CAD models that the team is making available to the public, 3D printing enthusiasts will be able to create objects out of commercially available plastics that can wirelessly communicate with other smart devices. That could include a battery-free slider that controls music volume, a button that automatically orders more cornflakes from Amazon or a water sensor that sends an alarm to your phone when it detects a leak.

Our goal was to create something that just comes out of your 3D printer at home and can send useful information to other devices, said co-lead author and UW electrical engineering doctoral student Vikram Iyer. But the big challenge is how do you communicate wirelessly with WiFi using only plastic? That's something that no one has been able to do before.

To 3D print objects that can communicate with commercial WiFi receivers, the team employed backscatter techniques that allow devices to exchange information. In this case, the team replaced some functions normally performed by electrical components with mechanical motion activated by springs, gears, switches and other parts that can be 3D printed borrowing from principles that allow battery-free watches to keep time.

Backscatter systems use an antenna to transmit data by reflecting radio signals emitted by a WiFi router or other device. Information embedded in those reflected patterns can be decoded by a WiFi receiver. In this case, the antenna is contained in a 3D printed object made of conductive printing filament that mixes plastic with copper.

Physical motion pushing a button, laundry soap flowing out of a bottle, turning a knob, removing a hammer from a weighted tool bench triggers gears and springs elsewhere in the 3D printed object that cause a conductive switch to intermittently connect or disconnect with the antenna and change its reflective state.

Information in the form of 1s and 0s is encoded by the presence or absence of the tooth on a gear. Energy from a coiled spring drives the gear system, and the width and pattern of gear teeth control how long the backscatter switch makes contact with the antenna, creating patterns of reflected signals that can be decoded by a WiFi 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 3D printed switch and antenna wirelessly transmits that data, said 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 UW team also 3D printed plastic scroll wheels, sliders and buttons that can wirelessly interact with computers, phones and other WiFi-connected devices.

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