Battery-Free Low-Cost Printable Flexible Circuits Turn Paper, Card Into Interactive Gadgets

Researchers at Purdue University have unveiled a technique for printing battery-free human-machine interfaces (HMIs) directly onto paper, creating self-powered ultra-slim gadgets based on existing paper and cardboard materials.

"This is the first time a self-powered paper-based electronic device is demonstrated," claims Assistant Professor Ramses Martinez of the team's work. "We developed a method to render paper repellent to water, oil, and dust by coating it with highly fluorinated molecules. This omniphobic coating allows us to print multiple layers of circuits onto paper without getting the ink to smear from one layer to the next one."

These "omniphobic paper-based electronics" need no external power, the researchers claim, and aren't affected by moisture, liquid stains, dust, or fingerprints. Better still, they're extremely low-cost: The researchers estimate a cost of less than $0.25 per device, while the weight is little heavier than the plain paper or card on which they're printed.

The devices, dubbed Rᶠ-SPEs, act as pressure sensors which harvest energy from the act of the user pushing down — hence not requiring any form of external power, a fact which combined with the ease of printing the circuit offers potential for a range of different use cases.

"I envision this technology to facilitate the user interaction with food packaging, to verify if the food is safe to be consumed, or enabling users to sign the package that arrives at home by dragging their finger over the box to proper identify themselves as the owner of the package," Martinez explains. "Additionally, our group demonstrated that simple paper sheets from a notebook can be transformed into music player interfaces for users to choose songs, play them and change their volume."

The team's work has been published under closed-access terms in the journal Nano Energy.