Sensors powered by light, heat and movement could unlock the true potential of the IoT.
The ability to harvest energy from the air sounds like the superpower of one of Marvel’s lesser-known heroes, but if you paid attention in science class, you’ll know that radio waves, vibrations, light, heat and movement can all be turned into usable electric power. Solar panels, for example, absorb sunlight as a source of energy to generate electricity, while kinetic watches are powered by the movement of the wearer’s arm. But due to the limitations of current energy harvesting technologies, most ambient energy goes to waste.
Small solar cells or vibration harvesters can only capture a few milliwatts of energy, which is nowhere near enough to charge a smartphone or laptop. That might change if energy harvesting technologies improve and our gadgets’ power demands decrease. But there are already some devices that energy harvesters can power in an efficient and effective manner: the low power sensors that make up the Internet of Things (IoT).
Frank Schmidt, chief technology officer and co-founder of EnOcean, which has developed an energy harvesting wireless technology used primarily in building automation systems, says the number of sensors in the IoT will massively increase in future. “We are talking of billions to trillions of sensors in a few years,” he says. “As most of them will be connected wirelessly, we need to rethink how to power the sensors, otherwise the demand [for] batteries will increase into infinity.”
Even the most power-efficient sensor needs to have its battery changed or recharged at some point. But sensors that are effectively capable of powering themselves through ambient light, heat or motion could easily be built into walls, roads and roofs, or placed inside air ducts and other hard-to-reach places without anyone having to worry about how they’ll be accessed if the battery dies.
According to Schmidt, the IoT may not even reach its predicted magnitude without ambient-powered sensors capable of providing the data needed to optimise traffic flows or make buildings more energy efficient. “In addition, the environmental aspect of avoiding tons of battery waste by using self-powered sensors is an important consideration,” Schmidt adds. “Mountains of toxic battery waste should not be the price we pay for greater energy efficiency and wellbeing in our buildings.”
Self-powered sensors could also be applied to a variety of consumer products in the future. For instance, a company called Wiliot has developed a postage stamp-sized Bluetooth sensor tag that features an ARM processor powered by energy scavenged from ambient radio frequencies, such as Wi-Fi, Bluetooth and cellular signals.
“Recycling the radiation around us to power sticker-size sensors can enable new ways for consumers to interact with products that were previously not feasible,” Tal Tamir, CEO and co-founder of Wiliot, said recently. “Products can share when they are picked up, their temperature, or when they need to be replenished. Without batteries or other high-cost components, tags have unlimited power and lifespan, so can be embedded inside of products that were previously unconnected to the Internet of Things.”
Wiliot, which has received funding from Amazon Web Services and Samsung, claims its Bluetooth tags could communicate with washing machines to ensure whites never turn pink, or be applied during the production phase of consumer goods to allow for real-time tracking through the manufacturing process. But Joshua R. Smith, a professor of computer science and engineering and of electrical engineering at the University of Washington, is sceptical of claims that ambient Bluetooth or Wi-Fi can power devices. “Radios [radio frequencies] like Wi-Fi and Bluetooth are off most of the time, thus emitting no power,” he says, “and even when they are on, they put out very small amounts of power.”
Broadcast TV, which is on all the time, is the strongest ambient RF source in most urban areas, he says, adding that: “As mobile phone base stations get more densely packed, they may become the most useful and reliable RF power source – they are much stronger than Wi-Fi, but much more densely placed than broadcast TV towers.”
Jeeva Wireless, a start-up that has licensed technology created by Professor Smith’s lab, has developed multi-band RF harvesting technology that could make RF harvesting more practical by harvesting energy from multiple sources at the same time. ReVibe Energy, meanwhile, has developed products that can turn vibrations into a power source for industrial sensor and monitoring systems: as part of a pilot project with Deutsche Bahn its units were attached to railway tracks, drawing energy from the vibrations of passing trains to power the sensors that monitor track switches.
A company called Voltree has even developed a bioenergy harvester that can convert the metabolic energy of trees into electricity, which is then used to power wireless sensor networks that detect forest fires. While a Canadian company called Wibicom offers a combined solar power harvester and antenna called Enviro, which is equipped with sensors that can monitor environmental data such as temperature and humidity. In order to alleviate high R&D costs, energy harvesting technologies like Enviro need to achieve mass deployment, says CEO Mina Danesh, which requires a “big market push” that targets specific applications for it.
Schmidt believes that “a strong and communicative energy harvesting user community” like the EnOcean Alliance, which consists of more than 400 member companies offering over 1,500 products based on the EnOcean wireless standard, is also essential for the success and broad implementation of energy harvesting technology, which is still in its infancy in many ways. But given that University of Washington researchers have already invented a mobile phone that can harvest the power it needs from ambient radio signals or light, there’s no telling what the future might hold.
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