Scientists create battery-free device that harvests Wi-Fi energy

The team optimized the spin-rectifiers, ensuring effective operation across various power levels. FabrikaCr/iStock

A research team led by the National University of Singapore (NUS) has made a significant stride in energy harvesting technology. This innovation could potentially eliminate the need for batteries in various electronic devices.

They have developed a new type of rectifier that can efficiently convert ambient radio frequency (RF) signals, typically considered as “waste” energy, into usable direct current (DC) voltage.

For reference, their novel technology converts ambient RF signals from sources like Wi-Fi and cellular networks into usable electricity.

“RF energy harvesting technologies, such as this, are essential as they reduce battery dependency, extend device lifetimes, minimize environmental impact, and enhance the feasibility of wireless sensor networks and IoT devices in remote areas where frequent battery replacement is impractical,” stated the press release.

Harvesting ambient RF electromagnetic signals

The research demonstrated the use of nanoscale spin-rectifiers (SR) to achieve this conversion. They did it even at low RF power levels below -20 dBm, a threshold where existing technologies struggle.

“We optimized the spin-rectifiers to operate at low RF power levels available in the ambient, and integrated an array of such spin-rectifiers to an energy harvesting module for powering the LED and commercial sensor at RF power less than -20 dBm,” explained Professor Yang Hyunsoo of NUS, who spearheaded the project.

The team successfully powered a commercial temperature sensor using this technology.

“Harvesting ambient RF electromagnetic signals is crucial for advancing energy-efficient electronic devices and sensors,” said Yang.

“However, existing Energy Harvesting Modules face challenges operating at low ambient power due to limitations in existing rectifier technology.”

Overcoming existing challenges

Traditional rectifiers, like Schottky diodes, face thermodynamic constraints and parasitic effects at low power levels.

“Nanoscale spin-rectifiers, on the other hand, offer a compact technology for sensitive and efficient RF-to-DC conversion,” emphasized Yang. It offers improved sensitivity and efficiency.

The team optimized the SR devices, creating configurations that operated effectively across a wide power range.

“To improve output and achieve on-chip operation, the SRs were coupled in an array arrangement, with the small co-planar waveguides on the SRs employed to couple RF power, resulting in compact on-chip area and high efficiency,” mentioned the researchers.

Notably, an array of 10 SRs achieved an impressive 7.8% efficiency and high sensitivity.

Future plan of action

“Spin-rectifier technology offers a promising alternative, surpassing current Schottky diode efficiency and sensitivity in the low-power regime,” said Dr. Raghav Sharma, the first author of the paper.

“This advancement benchmarks RF rectifier technologies at low power, paving the way for designing next-generation ambient RF energy harvesters and sensors based on spin-rectifiers.”

The research team is now focusing on integrating an on-chip antenna to further enhance the efficiency and compactness of their technology.

They are also exploring series-parallel connections and on-chip interconnects to improve RF power harvesting, with the potential to generate enough voltage to eliminate the need for a DC-to-DC booster.

The research was conducted in collaboration with scientists from Tohoku University in Japan and the University of Messina in Italy.

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