Dr. Raghav Sharma holds a chip integrated with 50 spin-torque oscillators. The new technology converts Wi-Fi signals into energy, which can power small devices. (Image Credit: National University of Singapore)
Researchers from the National University of Singapore and Japan's Tohoku University developed a new technology that utilizes spin-torque oscillators (STOs) to collect and convert Wi-Fi signals into energy, powering small electronics. During their demonstration, the team managed to harvest energy to power up an LED without using a battery.
"We are surrounded by Wi-Fi signals, but when we are not using them to access the Internet, they are inactive, and this is a huge waste. Our latest result is a step towards turning readily available 2.4GHz radio waves into a green source of energy, hence reducing the need for batteries to power electronics that we use regularly. In this way, small electric gadgets and sensors can be powered wirelessly by using radiofrequency waves as part of the Internet of Things. With the advent of smart homes and cities, our work could give rise to energy-efficient applications in communication, computing, and neuromorphic systems," said Professor Yang Hyunsoo from the NUS Department of Electrical and Computer Engineering.
STOs generate microwaves and can be integrated into wireless communication systems. Unfortunately, its application is limited due to low output power and broad linewidth. Although mutually synchronizing multiple STOs helps solve this issue, existing methods like short-range magnetic coupling have spatial restrictions. Meanwhile, long-range electrical synchronization utilizing vortex oscillators has a few hundred MHz frequency responses limit. This needs dedicated current sources for each STO, making the on-chip integration more complex.
To solve the spatial and low-frequency limits, the team designed an array with eight series-connected STOs. The array converted the 2.4 GHz electromagnetic radio waves into a direct voltage signal, which was transmitted to a capacitor that lit up a 1.6V LED. After turning off the wireless power, the capacitor, when charged for 5 seconds, lit the LED for one minute.
The team highlighted the electrical topology importance for designing an on-chip STO system and compared the series configuration with the parallel one. Their findings show that the parallel design has useful wireless transmission capabilities due to improved time-domain stability, spectral noise behavior, and impedance mismatch control. Series connections provide a benefit for energy-harvesting due to the STOs diode-voltage additive effect.
Dr. Raghav Sharma, the first author of the paper, said, "Aside from coming up with an STO array for wireless transmission and energy harvesting, our work also demonstrated control over the synchronizing state of coupled STOs using injection locking from an external radio-frequency source. These results are important for prospective applications of synchronized STOs, such as fast-speed neuromorphic computing."
To improve the energy-harvesting capability, the team plans on integrating more STOs in their array. They also want to test the energy harvester to determine if it can wirelessly charge other electronic devices and sensors. Additionally, the team hopes to collaborate with industry partners to explore on-chip STOs development for smart systems. Doing so could help pave the way toward wireless charging and wireless signal detection systems.
Have a story tip? Message me at: http://twitter.com/Cabe_Atwell