Electronic sensors built into cartons may make it easier to tell when it's time to toss out funky milk or orange juice. And that's just the start.
At least that's the goal for researchers working on putting electronics into paper. They're trying to figure out how to combine the flexibility, low-cost and recyclability of paper with the information-carrying ability of electronics.
Daniel Torbjork, a physics graduate student at the Abo Akademi University in Finland, has been working on the problem. He's published a review of the field in the May issue of the journal Advanced Materials.
Much research has been focused in this area. While most electronic applications require patterned conducting structures, conducting paper could be used in applications such as energy storage devices, sensors, electric heaters, electric field emitters, antistatic coatings and electromagnetic shields, according to Torbjork.
"You could even have some interactive functions in magazines," Torbjork said via Skype. "You could put a simple game in a package. If you want a touch screen, press a button and then something happens. Sensors in paper could tell us when something has gone bad."
Additional applications, such as information storage and security paper, have been suggested for magnetic papers containing magnetite. At the Massachusetts Institute of Technology, researchers in the lab of professor Karen K. Gleason have figured out how to put a solar cell into a piece of folding paper and have posted a video of such a device put into a paper airplane.
German researchers have also embedded electronic chips in paper bank notes to thwart counterfeiters.
Paper makes a good substrate but printing electronics also requires low-cost manufacturing. As many U.S. and European papermakers lose market share to cheaper paper from China, these big paper companies are looking for added value products.
That's where electronically souped up paper devices could make a difference.
Torbjork and professor Ronald Osterbacka at the university's Center for Functional Materials are developing a low-voltage organic transistor as well as a special roll-to-roll printing system for electronic devices. Some of their work to develop sensors in packaging is supported by the Finnish paper firm Stora Enso.
The major obstacles are paper's large surface roughness, porosity and chemical impurities, Torbjork says. But others in the field think that electronic sensors in paper are still far from the consumer marketplace.
"I don't think it's going to happen," said Roy Horgan, co-founder of Dublin-based SolarPrint, which is developing wireless solar-powered sensors for homes and offices. "You need a conductive surface. It could be 10 years out. What we are looking for are solutions that you can commercialize today. The best substrate is glass, then plastics, beyond that there are also metal solutions."
Solar Print is partnering with Italian automaker Fiat to develop a unique auto glass with tiny photovoltaic cells that can capture electricity from the sun, enough to power 10 percent of the car's energy needs. The prototype is on track to roll out by 2013, Horgan said. In the meantime, using paper to conduct electricity is still a "blue-sky" project.
"I would love to see someone prove me wrong, because that means that it's actually happening," Horgan said. "If someone comes up with conductive paper, then that's a very interesting patentable technology."
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