IoT devices promise a myriad of benefits but could proliferate at a rate that makes powering them more challenging.
Now, a team at KAUST (King Abdullah University of Science and Technology) in Saudi Arabia proposes an inexpensive energy harvester that could recharge these Internet-connected smart devices using radio waves from wireless sources.
One way that researchers are miniaturising devices for IoT applications is through the system-on-package approach, which places entire systems onto a single chip-size package.
According to KAUST, recent work has shown that the protective packaging around microelectronic devices could accommodate components, such as antennas, for significantly reduced costs and space requirements.
Atif Shamim, a professor of electrical engineering, realised that system-on-package principles could help IoT devices become more self-sufficient. His team investigated strategies to build highly compact antennas that tune into the radiofrequency signals emitted from mobile and wireless devices. They then teamed up with Khaled Salama’s group at KAUST to convert this energy into electricity using semiconductor diodes.
Most radiofrequency harvesters can only utilise a single part of the wireless spectrum, such as the 3G standard but Shamim’s team produced a multiband device that can accumulate more energy from multiple sources of communication.
“Asking one antenna to do the job of several others simultaneously is tricky,” said Azamat Bakytbekov, the first author of a paper describing the work in Nano Energy. “You have to make sure the performance doesn’t drop at any one frequency point.”
The researchers turned to a cube-shaped package and fractals to build their energy harvester. First, the team 3D printed a square plastic substrate and then screen-printed fractal antennas on its surface using silver metal. They then glued five of the plastic pieces together to form a cube, roughly five centimetres in size.
Fractal antennas can introduce multiple resonances that allow access to broader parts of the radio spectrum. The symmetric geometry of the cube is said to have enhanced this effect by gathering radiation all around the cube. Subsequent wireless spectrum scanning revealed several distinct frequencies where energy harvesting could work.
Experiments in real-world environments proved that the energy harvester could gather enough radio energy to power small wireless sensors. According to co-author Thang Nguyen, the most interesting occurrence happened when smartphone users passed the cube.
“We saw the power gathered by the cube suddenly shoot up when a person nearby made a call,” said Nguyen. “With the increase in mobile communication, this concept enables more and more radiofrequency energy to be harvested.”
I hope that this energy harvesting method never becomes daily reality because it would only mean that I have to recharge my smartphone more often. The last paragraph is revealing: “We saw the power gathered by the cube suddenly shoot up when a person nearby made a call.” Smartphones are designed to minimize the emitted energy so that the battery lasts longer before recharging. All harvested energy has to be emitted extra.
So the cube effectively steals energy from wireless network devices that try to compensate for “weak” signals by increasing power?
Actually, this isn’t the case. The energy being recouped is ‘already’ being transmitted by the mobile phone. Cell phones simply ‘broadcast’ in a wide beam rather than a very tight node. So the energy being harvested is in fact ‘Wasted’ energy for the phone. Actually, phones transmit a lot of ‘waste’ energy when you think about it. But until Mobile companies etc come up with a means of making them home in on and ‘direct’ communications more effectively they will always waste too much energy.
Interesting device. I have heard of Rectenna (a very efficient device, consisting of a rectifier and an aerial, for capturing EM radiation – though diode more difficult for shorter wavelengths, such as visible light) being designed to capture a range of frequencies; they have higher efficiencies than conventional solarvoltaic devices).
This could be most useful for UAVs (original use of microwave rectenna in 60s or 70s, as I remember)
However if energy harvesting one would expect such a device to block signals (as this idea, effectively, can create a “shadow” – blocking out signal; so not so good for those who use expect to get a signal). I believe there was an instance were a farmer collected power from a long wave transmitter to power his chicken shed ; those who lived in the shadow were less than amused.