New Invention Harvests Ambient Wi-Fi and Bluetooth Signals to Power Small Devices

Wasted radio signals can now be transformed into electricity using an innovative antenna based on quantum electron behavior. This advancement can potentially power small devices like light sensors or network components by harvesting energy from background Wi-Fi and Bluetooth signals through a sophisticated component that even converts faint electromagnetic waves into electricity.

Researchers have developed a highly sensitive "rectenna" or rectifying antenna, which leverages the principles of quantum physics to efficiently convert electromagnetic energy into direct current (DC) electricity. This technology showed its potential when it was used to power a commercial thermometer by harnessing electron dynamics.

According to a study published on July 24 in Nature Electronics, the technology is scalable enough to power Internet of Things (IoT) devices and sensors, utilizing only a minuscule portion of the excess radiofrequency (RF) signals exchanged between these devices. Rectennas absorb electromagnetic waves from RF signals such as those from Wi-Fi and Bluetooth, and convert the alternating current (AC) generated into DC via its rectifier circuit.

While rectennas have been known to generate low levels of electricity since the 1960s—demonstrated by wirelessly powering model vehicles—this mostly involved direct microwave energy transmission aimed at the device. Ambient RF signals, on the other hand, are much weaker and dispersed, not focusing on the devices directly.

To put things into perspective, ambient RF signals can be well below minus 20 decibel-milliwatts (dBm). For comparison, smartphones transmit signals at 27 dBm, and microwave ovens operate at 60 dBm. To manage such weak ambient signals from Wi-Fi and Bluetooth, researchers ventured into "spintronics," an area of quantum research that studies electron spin in relation to magnetic fields.

For their demonstration, they utilized magnetic tunnel junctions (MTJs)—components featuring a thin insulating layer between two magnetic layers, commonly found in hard disk drives. Ambient RF signals can influence MTJs by shifting electron spins, converting this dynamic into electricity.

The team crafted nanoscale "spin rectifiers" (SRs) from MTJs sensitive to the frequencies common in Wi-Fi (2.4 GHz), 4G (2.3 to 2.6 GHz), and 5G (3.5 GHz) signals, with dimensions as small as 40 x 100 nanometers squared and 80 x 200 nanometers squared. They successfully demonstrated the SR array’s capability by powering a temperature sensor using only minus 27 dBm of ambient RF.

Looking ahead, the researchers hope this method could significantly reduce the carbon footprint of wireless networks by diminishing dependence on batteries and lowering the energy consumption of sensor-based and other small devices.

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