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Wireless energy harvesting for IoT devices

Speed read
  • Nano-scale research is harvesting ambient AC energy
  • Retooled recharging will enhance performance of sensitive Internet of Things devices
  • Preliminary results show a 16x reduction in energy consumption

Wi-Fi is everywhere. In the grocery store, the bathroom, the car – practically everywhere we go we’ll find internet connectivity.

While wireless signals wash over us at all times, many bounce off their intended target objects, creating wasted heat in the process.<strong>Current affairs.</strong> Emre Salman's promising research has found large energy efficiency increases and practical methods to recharge difficult to access Internet of Things devices. Courtesy Emre Salman.

“The question is, could we use this ambient energy hidden within these wireless signals for some useful applications,” asks Emre Salman, director of the Nanoscale Circuits and Systems (NanoCAS) Lab at Stony Brook University.

The challenge researchers face is to be able to gather and develop methods that make the most use of this otherwise wasted energy. A nano-scale prototype is on the horizon, and Salman’s team, working together with Milutin Stanacevic’s team from the same university, has now achieved results verifying theoretical predictions.

What are these devices? Televisions, refrigerators, furnaces – many home items are connected and communicate wirelessly. Scientific instruments like unmanned aerial vehicles, bio-implanted medical devices, and climate-controlled research facilities also fall into this connected Internet of Things (IoT) category.

This domain is growing at a tremendous clip, but scalability is hampered by energy costs. Current growth projections indicate IoT devices will soar past 32 billion in the next three years. Within the next 10 years, 1 trillion sensor networks are expected to emerge. With the current power source technology, IoT devices will see 275 million battery changes per day –an unsustainable and woefully inefficient prospect.

Changing the battery in some of these wireless devices is also impractical, not only because maintaining the ability to continually process information is of critical importance, but also due to difficulty in physically accessing these devices.

We're seeing more than an order of magnitude increase in energy efficiency. ~Emre Salman

Consider implanted medical devices, or devices that monitor a structure or the environment. The hurdle of accessibility renders recharging or battery replacement unfeasible, and what’s more, these devices cannot do their own data processing with their current hardware configuration.

Salman’s team thinks that retooling these IoT devices to operate with the harvested wireless energy would reverse this inefficiency by enabling on-site data processing.

“The main problem is that, despite the abundance of wireless signals, the amount of energy is usually tiny. It would require a completely different approach to compute with such low levels of wireless energy.”

Typically, IoT devices convert the harvested alternating current (AC) power source to direct current (DC) source, a process known as rectification. Traditional computational requirements necessitate connection to a steady, DC source.

But in research funded by the US National Science Foundation (NSF), Salman and Stanacevic have crafted a method whereby processors within the wireless devices operate directly with the AC power source and recycle rather than dissipate electrical charge.

Salman’s method couples wireless energy harvesting with a novel charge-recycling mechanism that relies on AC, not DC, to power the computer processor in the IoT device. In Salman’s model, the harvested excess Wi-Fi signal is already in AC form and directed to computation with minimal energy loss.

<strong>Energizing results. </strong> A diagram illustrating the primary difference between the existing method and proposed approach for recharging wireless IoT devices. Courtesy Salman, Stanacevic, et al.

“In a sense, we go back to the ‘War of Currents’ of the late 19th century and propose AC computing for wirelessly powered devices,” says Salman.

“The result is more than an order of magnitude increase in energy efficiency.”

Combining these techniques in modified wireless devices has yielded a 16x reduction in power consumption.

Computational improvements in the wireless IoT devices will expand monitoring abilities far beyond the bounds of the current scientific cyberinfrastructure. Bio-implants will become smarter, having an ability to process information locally. Sensors will constantly monitor the reliability of buildings, bridges and inform us of any possible degradation before catastrophic incidents occur.  

In short, AC computing stands poised to revolutionize our wireless devices and their (our) energy consumption habits. Wireless energy harvesting and a reliance on AC for data processing will boost the reach of science.

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