The quest for sustainable and efficient power solutions has become paramount in the Internet of Things (IoT), where billions of devices are expected to be connected by 2030.
A recent study by the International Energy Agency (IEA) highlights that the energy consumption of IoT devices could reach 1,700 Terawatt hours (TWh) by 2030, surpassing the current combined annual electricity consumption of the U.S. and Japan.1
As traditional batteries pose environmental and logistical challenges, the emergence of battery-free IoT devices powered by innovative energy-harvesting technologies is set to revolutionize the industry.
Harnessing the Power of Radio Waves
The secret lies in ambient radiofrequency (RF) signals. These low-power waves are all around us, emanating from sources like Wi-Fi routers, cell towers, and Bluetooth devices. Researchers from the National University of Singapore have figured out a way to efficiently convert these RF signals into usable DC power.(ref)
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Radio waves carry energy that can be harvested and converted into electricity. The power available in radio waves is relatively low, on the order of microwatts to milliwatts. However, with efficient antennas, impedance-matching circuits, and rectifiers, this low power can be captured and accumulated to power small electronic devices.
The frequency range of harvestable RF energy spans from a few hundred MHz to several GHz, covering common wireless technologies like TV broadcasts, cellular networks, Wi-Fi, and Bluetooth. The lower frequencies provide longer range but require larger antennas, while higher frequencies enable more compact designs but have shorter range.
A Miniature Marvel
At the heart of this innovation is a tiny device called a spin-rectifier (SR). It’s so small, you could fit hundreds of them on the tip of your finger. But don’t let its size fool you – this little wonder can capture and convert RF signals with remarkable efficiency.
The researchers optimized the SR design and even created an array of 10 SRs working together, achieving an impressive 7.8% conversion efficiency.
Spin-rectifiers are based on spintronics, an emerging field that exploits the intrinsic spin of electrons in addition to their charge. SRs can rectify low-power RF signals more efficiently than conventional semiconductor diodes, which suffer from high turn-on voltages and reverse leakage currents.
The NUS team’s SR device consists of an ultra-thin ferromagnetic layer sandwiched between two non-magnetic electrodes. When an RF signal is applied, it induces spin-polarized currents that are rectified into DC voltage due to the asymmetric spin-dependent transport properties of the device.
Powering the Internet of Things
This breakthrough could revolutionize the world of wireless sensors and Internet of Things (IoT) devices. Imagine sensors in remote locations monitoring everything from weather to wildlife without ever needing a battery change or smart home devices that never go offline due to a dead battery. The possibilities are endless!
The Internet of Things is rapidly expanding. Powering this vast network of devices is a major challenge, as frequent battery replacements are impractical and environmentally unsustainable.
RF energy harvesting offers a compelling solution for IoT devices, especially those in hard-to-access or hazardous locations. By scavenging energy from ambient radio waves, these devices can operate autonomously for extended periods without relying on batteries.
Wireless sensor networks, wearable devices, and smart infrastructure are prime candidates for RF energy harvesting. For example, structural health monitoring sensors embedded in bridges or buildings could continuously monitor conditions without requiring manual battery servicing.
Future Implications
The research team isn’t stopping here. They’re already exploring ways to integrate on-chip antennas and optimize SR arrays to boost power output. The goal is to generate a few volts of power, enough to eliminate the need for additional voltage boosters. With industry partnerships on the horizon, we could soon see self-sustained, battery-free devices becoming the norm.
Integrating antennas directly onto the chip alongside the SR rectifiers can improve efficiency and enable ultra-compact designs suitable for IoT and wearable applications. On-chip antennas, however, face challenges in terms of size, efficiency, and impedance matching.
To further increase the output voltage and power, the NUS team is developing series-parallel connections of SR arrays. By carefully designing the interconnects and impedance matching networks, they aim to achieve rectified voltages of several volts, sufficient to directly power sensors and microcontrollers without additional power management circuits.
Collaborations between academia and industry will be crucial in translating this technology from the lab to real-world applications. Standardization efforts, such as the recently announced AirFuel RF wireless power standard, can foster interoperability and accelerate adoption.
So, prepare for a future where dead batteries are a thing of the past. Thanks to these brilliant minds, our devices might just keep going and going, powered by the invisible waves that surround us daily.
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Davin is a jack-of-all-trades but has professional training and experience in various home and garden subjects. He leans on other experts when needed and edits and fact-checks all articles.