CAD models have been developed that enable objects to be 3D-printed out of commercially available plastics; these objects can wirelessly communicate with other smart devices, including a battery-free slider that controls music volume, a button that automatically places an order with Amazon, or a water sensor that sends an alarm to a smartphone when it detects a leak.
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, some functions normally performed by electrical components were replaced 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, liquid flowing out of a bottle, turning a knob, or 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.
Several different tools were 3D-printed that could sense and send information successfully to other connected devices: a wind meter, a water flow meter, and a scale. A flow meter was printed that was used to track and order laundry soap, and a test tube holder was printed that could be used for either managing inventory or measuring the amount of liquid in each test tube.
WiFi input widgets such as buttons, knobs, and sliders also were 3D-printed that can be customized to communicate with other smart devices, and enable a rich ecosystem of “talking objects” that can seamlessly sense and interact with their surroundings.
Using a different type of 3D printing filament that combines plastic with iron, magnetic properties were leveraged to invisibly encode static information in 3D-printed objects, which include barcode identification for inventory purposes, or information about the object that tells a robot how to interact with it.