Researchers from the University of Washington have 3D-printed objects and sensors that are able to communicate with Wi-Fi devices such as smartphones or computers without needing to be powered by batteries or a wall socket. Examples include an attachment that can sense when laundry detergent is about to run out and place an online order for more, an anemometer and a connected test tube holder.

At the heart of the development are reflection of waves techniques known as backscattering, where ambient radio signals are reflected from a Wi-Fi router via an antenna printed using a plastic and copper mix, and onward to a wireless receiver. Rather than use batteries to power the 3D-printed object or sensor, the researchers tapped into mechanical motion.

When flowing liquid turns a wheel or a button is pushed, gears and springs activate or deactivate a conductive switch, changing the reflective state of the 3D-printed antenna. Data can be hard-coded into an object by way of teeth on the gear – with the presence or absence of a tooth determining how long a switch remains in contact with the antenna. Signal patterns thus created can then be translated into readable output by the 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," said senior author of the team's paper Shyam Gollakota. "The interaction between the 3D-printed switch and antenna wirelessly transmits that data. 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 team from the University of Washington's Networks & Mobile Systems Lab has created a number of objects capable of successfully sensing and transmitting to other connected devices, including a detergent flow meter, wind and water flow meters, a scale and a test tube holder.

Input devices such as buttons, knobs and sliders were also printed, which could be custom made to talk to smart devices in the home – controlling the volume on a connected music system, for example, or placing an order for groceries from an online store at the push of a button.

Not content with creating battery- and electronics-free objects able to wirelessly talk to smart devices, the team also toyed with magnetism to encode information in 3D-printed objects. Identification information similar to barcodes could be embedded in an object printed using a plastic/iron filament and read using a smartphone.

A paper detailing the research was presented at the Association for Computing Machinery's SIGGRAPH Conference and Exhibition on Computer Graphics and Interactive Techniques in Asia last week. A video outlining the project can be seen below.

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