Researchers at the University of Washington have 3D printed a series of plastic connected devices that communicate with Wi-Fi receivers without electronics.
The devices use backscatter techniques, meaning ambient Wi-Fi signals are either absorbed or reflected to convey a zero or one.
Information embedded in those reflected patterns can then be decoded by a Wi-Fi receiver.
"Our goal was to create something that just comes out of your 3-D 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 Wi-Fi using only plastic? That's something that no one has been able to do before."
At the core of each device – the CAD models of which are being made publicly available – is a switch attached to a spring. A plastic gear presses against the spring to make contact with an antennae made of conductive filament.
Physical motion – be it pushing a button, a flow of liquid, turning a knob – triggers the gears and springs to cause a conductive switch to intermittently connect or disconnect with the antenna and change its reflective state.
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.
“Such a capability democratises the vision of ubiquitous connectivity by enabling designers to download and use our computational modules, without requiring the engineering expertise to integrate radio chips and other electronics in their physical creations,” Iyer added.
The researchers – part funded by Google – have developed a number of widgets built on the device including an anemometer, flow meter, button, turning dial and slider.
They suggested a number of use cases including 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.
"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," said senior author, associate professor Shyam Gollakota.
"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 system was described in the paper 3D Printing Wireless Connected Objects.