Radio power from mobile phones could enable sensors on printed smart labels for Internet of Things applications
The scientists at Linkoping University, along with industry partners, have produced an all-printed diode which can harvest radio waves at 1.6GHz, using them to generate electrical power, according to a paper published at the Proceedings of the National Acadamy of Sciences (PNAS) of the US. The resulting label operates at more useful frequencies than previous efforts, and loks like a serious contender for IoT use.
Internet of things applications place sensors on everyday objects, so they can be tracked, monitored and controlled. It requires low energy devices, and works best if they can be powered indefinitely using energy gathered from the environment. Radio energy havesting has always looked a good contender for the job, as it is widely available in the air, and can be gathered using electromagnetic induction, by spiral-shaped printed electrodes.
The researchers, backed by industrial partners from De La Rue in the UK and Acreo in Switzerland improved on previous work by Acreo, which used frequencies in the region of 100MHz, where signals carry lower energy, and are less widely available. Moving up to 1.6GHz takes the technology into the domain of mobile phone communications, and the group hopes to reach 2.4GHz where Bluetooth and Wi-Fi (and microwave ovens) produce a fair amount of energy.
“This is the first time anyone has done anything like this in the gigahertz region,” says Göran Gustafsson, a materials scientist at the Norrköping branch of the Acreo Swedish ICT research institution quoted in IEEE Spectrum. “This is the starting point of having paper connected to the Internet.”
The researchers took crystalline silicon, doped it with antimony and crushed it into tiny particles around 1 micron across. These were printed onto an aluminium electrode and coated with niobium silicide microparticles and linked to a carbon electrode and silver paste. The large antenna which gathers the power is made of aluminium.
The whole device likes 1.6GHz waves best, but could still get 19 microAmps from a 1.8GHz smartphone signal, if it was used right up against the label.
That is still quite a long way from anything really usable, as the range and frequency need tweaking. The researchers also hope to reduce the need for expensive niobium and silver in the labels. But the manufacturing process eliminates the vaccuum and temperature extremes required by earlier experiments, and marks a major step towards labels which could make Internet of Things applications more practical.