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Putting Wireless Power To Work

Smart sensors harvest radio-frequency energy

3 min read

When the U.S. Navy decided it needed to monitor the condition of its aging aircrafts' wings, it tried embedding wireless sensors inside them. Each sensor, attached to energy-harvesting circuitry, periodically checks the wings for damaging stress and strain, says Zoya Popovic, a professor of electrical engineering at the University of Colorado, Boulder, who worked on the project. To recharge or activate the sensors, a technician holds a transmitter a meter away from a wing to create a low-energy electric field within range of the sensors' energy-harvesting circuits.

In solving this problem, engineers dusted off a decades-old idea: radio-frequency energy harvesting, be it from strategically placed transmitters or from the ambient energy emitted by cellphone towers and television stations. The concept was once dismissed as unfeasible because of the rapid dissipation of electromagnetic waves as they travel from their source. But even microwatts, if trickled into a battery or supercapacitor, can be enough to power some sensors for more than a decade. The combination of extremely low-power microprocessors, increasingly affordable supercapacitors for energy storage, and budding markets for sensors that make buildings more energy efficient and monitor inventory has enabled a new generation of energy-harvesting devices.

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This photograph shows a car with the words “We Drive Solar” on the door, connected to a charging station. A windmill can be seen in the background.

The Dutch city of Utrecht is embracing vehicle-to-grid technology, an example of which is shown here—an EV connected to a bidirectional charger. The historic Rijn en Zon windmill provides a fitting background for this scene.

We Drive Solar

Hundreds of charging stations for electric vehicles dot Utrecht’s urban landscape in the Netherlands like little electric mushrooms. Unlike those you may have grown accustomed to seeing, many of these stations don’t just charge electric cars—they can also send power from vehicle batteries to the local utility grid for use by homes and businesses.

Debates over the feasibility and value of such vehicle-to-grid technology go back decades. Those arguments are not yet settled. But big automakers like Volkswagen, Nissan, and Hyundai have moved to produce the kinds of cars that can use such bidirectional chargers—alongside similar vehicle-to-home technology, whereby your car can power your house, say, during a blackout, as promoted by Ford with its new F-150 Lightning. Given the rapid uptake of electric vehicles, many people are thinking hard about how to make the best use of all that rolling battery power.

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