Scientists develop new battery-free technology that draws energy from the air

In context: The air around us is thick with radio signals from Wi-Fi, Bluetooth, and 5G. These standards are great for transmitting data, but they’re also an untapped source of energy. Scientists have developed a new technology to collect ambient RF signals, or “waste,” and use them to power small electronic devices.

The key innovation is a nanoscale spin-rectifier that can convert extremely low-power RF signals, below -20 dBm, to a usable DC voltage. This device overcomes a major problem of existing RF energy-harvesting rectifiers that struggle to operate efficiently at low ambient power levels.

Professor Yang Hyunsoo of the National University of Singapore, who led the project, explained that traditional gigahertz Schottky diode rectifiers have stagnated for decades due to fundamental thermodynamic limitations at low power levels. Recent efforts have focused on improving antenna efficiency and impedance matching networks, which increase the surface area of ​​the chip, making miniaturization difficult.

And Yang’s team showed that nanoscale spin rectifiers offer a compact, sensitive, and efficient way to directly convert RF voltage to DC current.

“Our results demonstrate that SR technology is easy to integrate and scalable, facilitating the development of large-scale SR arrays for various low-power RF and communication applications,” Yang said.

To achieve this breakthrough, the researchers optimized the spin-rectifier devices in two configurations: a single rectifier operating from -62 dBm to -20 dBm and an array of 10 spin-rectifiers connected in series with 7.8 percent conversion efficiency. Integrating the array with an energy harvesting module allowed them to power a commercial temperature sensor with an input power of just -27 dBm.

The research, conducted in collaboration with scientists from Tohoku University in Japan and the University of Messina in Italy, was published in the journal Nature Electronics on July 24.

This is an exciting proof of concept, but spin-rectifier energy harvesting modules still have room for improvement. Yang’s team is now working on integrating an antenna on a chip, which could further improve efficiency and compactness.

The researchers also intend to work with industrial and academic partners to accelerate the development of self-sufficient smart systems with spin rectifiers on a chip. They hope that this will enable compact on-chip technologies for wireless charging and signal sensing systems based on collecting ambient radio signals.

In a similar study, Korean researchers optimized backscatter technology so devices can reflect modulated wireless signals to transmit data, extending battery life and resulting in a 40 percent improvement in energy efficiency.

Photo source: Duman Photography