A team of scientists from the National University of Singapore (NUS) has developed an innovative energy-harvesting module that can convert ambient radiofrequency (RF) signals, such as those from Wi-Fi, Bluetooth, and 5G, into direct current (DC) voltage.
This groundbreaking technology can power small electronic devices without the need for batteries, potentially transforming the future of wireless electronics.
Wireless technologies like Wi-Fi and Bluetooth rely on RF signals to transmit data. However, these signals often go to waste.
The new energy-harvesting module captures these ambient RF signals and converts them into usable power, making it an eco-friendly solution that reduces battery dependency and extends the life of devices.
This is especially useful for wireless sensor networks and Internet of Things (IoT) devices in remote areas where replacing batteries is difficult.
One of the main challenges in RF energy harvesting has been the low power of ambient RF signals, typically less than -20 dBm.
Traditional rectifier technology, which converts RF signals to DC voltage, struggles to operate efficiently at these low power levels.
Improving antenna efficiency and matching the impedance can help, but this increases the size of the technology, making it hard to integrate into small devices.
To overcome these challenges, the NUS team, along with researchers from Tohoku University (TU) in Japan and the University of Messina (UNIME) in Italy, developed a compact and sensitive rectifier technology using nanoscale spin-rectifiers (SR).
These SR devices can convert ambient RF signals into DC voltage even at very low power levels, below -20 dBm.
The researchers designed two configurations: a single SR-based rectenna that works between -62 dBm and -20 dBm, and an array of 10 SRs in series that achieved 7.8% efficiency and high sensitivity.
When integrated into an energy-harvesting module, the SR-array successfully powered a commercial temperature sensor at -27 dBm.
“Harvesting ambient RF signals is crucial for advancing energy-efficient electronic devices and sensors,” said Professor Yang Hyunsoo from the Department of Electrical and Computer Engineering at NUS.
“Existing energy-harvesting modules face challenges at low ambient power due to limitations in current rectifier technology. Nanoscale spin-rectifiers offer a compact solution for efficient RF-to-DC conversion.”
Prof. Yang and his team optimized the spin-rectifiers to operate at low RF power levels found in the environment. They integrated an array of these rectifiers into an energy-harvesting module, successfully powering an LED and a commercial sensor with ambient RF power.
Their results show that SR technology is easy to integrate and scalable, making it suitable for various low-powered RF applications.
The research, published in Nature Electronics on July 24, 2024, involved collaboration with Professor Shunsuke Fukami’s team from TU and simulation work by Professor Giovanni Finocchio from UNIME.
The study demonstrated that SR technology could outperform traditional rectifiers like Schottky diodes, which have remained stagnant due to thermodynamic restrictions at low power levels.
Dr. Raghav Sharma, the first author of the paper, emphasized the significance of the findings. “Despite extensive global research on rectifiers and energy-harvesting modules, fundamental constraints remain for low ambient RF power operation.
Spin-rectifier technology offers a promising alternative, surpassing current Schottky diode efficiency and sensitivity in low-power regimes.”
The NUS research team is now working on integrating an on-chip antenna to improve efficiency and compactness. They are also developing series-parallel connections to tune impedance in large arrays of SRs, aiming to enhance RF power harvesting and generate significant rectified voltage without needing a DC-to-DC booster.
The team hopes to collaborate with industry and academic partners to advance self-sustained smart systems based on on-chip SR rectifiers.
This could lead to new, compact technologies for wireless charging and signal detection systems, paving the way for a battery-free future in electronics.
