New Invention: Harvesting Wi-Fi and Bluetooth Signals into Energy for Small Devices

Small devices like light sensors or networking components could soon harvest energy from Wi-Fi and Bluetooth signals using a new component that can turn the weakest electromagnetic waves into electricity.

Researchers have created a highly sensitive 'rectenna,' or rectifier antenna, a component that exploits the quirks of quantum physics to efficiently convert electromagnetic energy into direct current (DC). The researchers used this novel method to harvest electrons to power a commercial thermometer.

Radio signals can be converted into electricity using a new type of antenna based on the way electrons behave at the quantum level. (Illustration: Flavio Coelho)

In a study just published in the journal Nature Electronics, scientists argue that the technology could be expanded to power Internet of Things (IoT) devices and sensors by using a fraction of the excess radio frequency (RF) signals they use to communicate with each other.

Rectennas receive electromagnetic waves such as those found in radio frequency (RF) signals like Wi-Fi and Bluetooth or various wavelengths of light and capture them as alternating current (AC) electricity through an antenna. The device then converts this electricity into DC electricity through its rectifier circuit.

In these cases, the energy is transmitted directly to the device in the form of microwave energy. The surrounding RF signal is much weaker and not directed directly at the device.

To exploit the very weak ambient signals generated by Wi-Fi and Bluetooth networks, the researchers turned to a relatively little-known area of ​​quantum research. Called 'spintronics,' it studies the quantum spin of electrons and how it relates to magnetic fields.

The researchers relied on the properties of magnetic tunnel junctions (MTJs) , a component consisting of a very thin layer of insulating material sandwiched between two magnetic layers. MTJs are most commonly used in hard drives and have been used in other types of computer memory. RF signals can affect the MTJ, where the signal's current affects the spin of electrons inside the structure. This can be harnessed to generate electricity.

The team created a series of nanoscale 'spin rectifiers' (SRs) formed from MTJs, with full dimensions of 40 x 100 square nanometers and 80 x 200 nm2, that are sensitive to the frequencies of common ambient electromagnetic signals such as Wi-Fi (2.4 gigahertz frequency), 4G (2.3 to 2.6 GHz), and 5G (3.5 GHz).

In the future, the team hopes this method could be used to reduce the carbon cost of operating wireless networks by reducing battery reliance and power consumption in sensors and other small devices.