3-D printed plastic communicates without power or electronics

New material that reflects wifi signals, rather than emitting them, has numerous applications.
3-D printed plastics like these are able to send messages to wifi routers and phones without any electronics or batteries (University of Washington)

Imagine if your bottle of laundry detergent automatically ordered its replacement as it got nearly empty. All while just sitting on the shelf, with no buttons, subscriptions, or even electronics or batteries involved.

That's one small application of a new 3-D printed plastic that is able to connect to wifi networks and send information, with no circuitry or power.

The plastic is the creation of University of Washington engineering PhD students Justin Chan and Vikram Iyer.

The plastic works by reflecting the radio waves produced by wifi, using switches and copper embedded in the material. The reflected radio waves are known as backscatter, and can be interpreted as code.
Justin Chan (University of Washington)

So in the case of a detergent bottle, when a spindle in the container reaches a certain speed because of the liquid's flow rate, it trips a switch which reflects the changing wifi signal to a phone, triggering an app to order another container.
Vikram Iyer (University of Washington)

Their idea was inspired by old-style mechanical, automatic wristwatches, which work by using the kinetic energy created by the motion of the wearer's arm and don't require a battery.

"The design harvests mechanical energy to communicate wirelessly," Justin says.

So far they've made a flow rate sensor, wind speed sensor, and a scale. They've also made their designs freely available to anybody. "There are lots of people in the 3-D printing world who could do a lot with this," Vikram says, adding that anybody with access to a 3-D printer could try to make their own.

But perhaps more important, the material can be used in all sorts of larger scale applications, such as measuring how well critical urban infrastructure like underground pipes are working - all without requiring a costly installation that uses energy and needs maintenance.

"It can be deployed en masse, and you can just install these without any batteries so you can leave them there for years, without intervening," Justin says.