This Beetle-Inspired Color-Changing Humidity Sensor Is 10,000 Times Faster Than the Competition
Inspired by the Hercules beetle's color-changing shell, this sensor doubles up as a color display with anti-counterfeiting potential.
A team of researchers from the Pohang University of Science and Technology (POSTECH) and Electronics and Telecommunications Research Institute (ETRI) have developed a new ultra-fast humidity sensor, inspired by the Hercules beetle and offering a reaction time some 10,000 times better than current optical sensors — and suggest the technology could find its way into anti-counterfeiting systems.
The shell of the Hercules beetle, native to South America, changes color depending on external humidity. It's this ability, driven by a porous internal lattice structure made up of square holes, which inspired the new sensor that — like the beetle — changes its color depending on environmental humidity.
Optical humidity sensors aren't new, but what makes this beetle-inspired variant special is its speed: Its creators claim it responds to humidity changes some 10,000 times faster than equivalent sensors built around the Fabry-Perot interferometer principle. The new sensors can also be produced at a very low cost, opening up new use-cases — including anti-counterfeiting QR codes which are visible at certain humidity levels and invisible at others.
"This new humidity sensor is special in that it allows scalability of production at low cost even though nanomaterials and nanostructures were used," claims project lead Junsuk Rho, professor at POSTECH. "Introducing the humidity-responsive color pixels into security codes enables application toward security tags for humidity-sensitive electronic devices, banknotes, passports, and ID cards."
The team's creation is based on a triple-layer metal-hydrogel-metal sandwich, with a disordered nanoparticle layer followed by a chitosan hydrogel and a reflecting substrate on the base. As the humidity causes the inner hydrogel layer to swell, it changes how light is reflected — using the porous space between nanoparticles in the same way as the lattice of the beetle's shell.
The team's work has been published under open-access terms in the journal Science Advances.