Ambient energy emitted by cellular phones and modems can be captured and converted into electricity using unusually shaped technology according to researchers from King Abdullah University of Science and Technology (KAUST) . Radio waves from wireless sources can reportedly help recharge an inexpensive energy harvester developed at KAUST for Internet-of-things (IoT) gadgets.
The researchers helped miniaturize energy harvesting device using a system-on-package approach in which the protective packaging around microelectronics is used to accommodate components, including communication antennas, for considerably reduced costs and space requirements.
Atif Shamim, a professor of electrical engineering and an authority in energy harvesting, recognized that system-on-package design could help IoT devices become more self-sufficient. His team looked into strategies to construct highly compact antennas that tune to the radiofrequency signals emitted from wireless and mobile devices. They then worked with Khaled Salama’s group at KAUST to convert this energy into electricity using semiconductor diodes.
While most radiofrequency harvesters can only get energy from a single part of the wireless spectrum, like the 3G standard, Shamim’s team, however, wanted to produce a multiband device that could accumulate more energy from multiple sources of communication.
“Asking one antenna to do the job of several others simultaneously is tricky,” notes Azamat Bakytbekov, the first author of the paper. “You have to make sure the performance doesn’t drop at any one frequency point.”
To build their energy harvester, the researchers applied a cube-shaped package and employed the mathematical concept of fractals—patterns that repeat from small to large scale. First, the group 3D printed a square plastic substrate and then used screen printing to fabricate fractal antennas on its surface with a silver metal. Lastly, they glued five of the plastic pieces together to construct a cube that is about five centimeters in size.
Fractal antennas can allow multiple resonances giving access to broader portions of the radio spectrum. The symmetric geometry of the cube helped further enhance this effect by gathering radiation all around the cube. Subsequent scanning of the wireless spectrum showed several distinct frequencies that could work for energy harvesting.
Tests in real-world environments demonstrated that the harvester could accumulate enough radio energy to power small wireless sensors. However, the most remarkable phenomenon, according to co-author, Thang Nguyen, occurred when smartphone users passed by the 3D cube.
“We saw the power gathered by the cube suddenly shoot up when a person nearby made a call,” says Nguyen. “With the increase in mobile communication, this concept enables more and more radiofrequency energy to be harvested.”
Bakytbekov, A., Nguyen, T.Q., Huynh, C., Salama, K.N. & Shamim, A. Fully printed 3D cube-shaped multiband fractal rectenna for ambient RV energy harvesting. Nano Energy 53, 587-595 (2018).| article