Sensors that use their energy are all the rage

PERCHED LIKE IT Perched above a harbor on the Dingle Peninsula on Ireland’s Atlantic coast, Mike Fitzgerald’s office has an unparalleled view of the territory he hopes to conquer: the open sea. As the founder and CEO of Net Feasa, a name derived from the Irish word for knowledge, Mr. Fitzgerald’s goal is to equip each of the millions of shipping containers moving around the world with a sensor. By using these to track the locations and conditions of those containers and sending that information back to the people who need to know when a container is at sea via satellite and via a cellular network when it is in port or on land he believes companies will be able to maximize supply chain efficiencies.

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And monitoring the supply chain is just one of the benefits that small, remote-controlled sensors can bring. People are already interacting with many of them – sometimes knowingly, for example in smartwatches, sometimes less, for example with those who regulate the temperature and light in their offices. Indeed, some people pompously talk about the result being an interconnected network, akin to an “Internet of Things” (IOT).

Irrespective of this, there will be many more such sensors in the future. In 2017, researchers at POOR, a chipmaker, predicted the world would have a trillion of them by 2035. Even more sober estimates are in the tens or hundreds of billions. And they will all need power. To keep battery makers from rubbing their hands over this new market, Mr. Fitzgerald and others like him have another idea. Your version of this future will not be battery powered. Instead, the sensors that populate it will make a living.

Net Feasa builds sensors to do just that. Powered by vibration, heat and light, they use technology developed in collaboration with Mike Hayes of the Tyndall National Institute in Cork. The electricity generated in this way is then stored in so-called supercapacitors, where it is immediately available. The system only has to fall back on the built-in backup battery in the event of an acute lack of energy. Consequently, this battery should never need to be replaced. All of this is packed into a device just a few centimeters tall, designed to fit unobtrusively on the doors of a shipping container. And these devices have already proven themselves in initial tests.

secret source

Net Feasa is not alone. Sensors that draw energy from the environment, either to supplement or replace a battery, are beginning to proliferate. The managers of EnOcean, a German company that is one of the leaders in this field, estimate that around 20 million of the company’s products have been installed in one million buildings around the world.

The most advanced are those that use light. Their powerhouses are similar to solar cells, but are tuned to ensure that the indoor artificial light they capture is both dimmer than sunlight and a different color. Such photovoltaic sensors are used to measure illuminance, temperature, air pollution and even (of particular interest for the moment) airborne pathogens. Automatic systems fed with this data can then adjust lighting, heating, ventilation and air conditioning accordingly.

Photovoltaic sensors can also track products on the assembly line and monitor quality during manufacture. They provide eyes and ears in sterile chambers and provide early warning of bottlenecks or leaks. They also generate vast amounts of data that can be used to maximize efficiency — although companies that use them in this way tend to keep the details secret. A study published in 2019 on the industrial applications of all sensor types in Germany, Switzerland and Austria by EYa consulting firm, estimates that the combined increase in revenue from their extensive use could be as high as 34%, depending on the sector affected.

Obviously, photovoltaic harvesting has limitations, as it is only suitable where the lights are normally on. This works for offices and the parts of factories where people work. But for many industrial applications, particularly those conducted in the dark, heat is a more useful source of purified energy. The trick to converting this into electricity was discovered two centuries ago and has been improved ever since. It’s usually a device called a thermocouple, made up of plates of two suitable materials placed opposite each other. When one side is hotter than the other, electrons move between the sheets, creating a current.

Turn up the heat

One company that makes power harvesters that work this way is Perpetua Power in Oregon. His devices are designed for inaccessible places where changing batteries would be inconvenient. Perpetua’s sensors were installed on oil wells in the frigid conditions of Alaska and the desert heat of California to measure wellhead pressure. They were also placed on steam flow meters beneath New York’s streets to ensure customers were correctly billed for use of the city’s district heating system.

FIG, a Swedish-Swiss company, also manufactures temperature sensors based on thermoelectric harvesting. Customers in the food industry can use it to ensure that ovens are sufficiently hot, while owners of industrial plants can check their cooling systems for proper functioning. And thermal harvesters can even be embedded in the concrete foundations of buildings or attached to internal beams to reveal structural weaknesses and mechanical problems.

Another area where energy absorbing sensors are used is in traffic. This is where vibration and movement come into their own. Perpetuum, a company spun off from the University of Southampton in the UK in 2004 and bought by Hitachi Rail in 2021, develops sensors powered by piezoelectricity. This is a phenomenon where certain materials generate electricity when stressed or deformed. Perpetuum’s products monitor the condition of rail vehicles – a rich source of vibration. Sensors installed in wheels, transmissions and engines can assess the health of these components by looking for thermal and vibration-related indicators of mechanical failure. You can also monitor the condition of the track. The railway networks of several countries use them to varying degrees, including those of America, Australia and India.

Shake, rattle and roll

ReVibe Energy, a Swedish company, has similar goals. Its sensors, which use electromagnetic induction rather than piezoelectricity to convert vibrations into energy, can be attached to wagon wheels to monitor their position and the stress on their bearings. ReVibe’s technology is also used in mining to look for unusual movement patterns in machines involved in crushing and hauling aggregate.

There is also another source of motion that could be exploited to power sensors. This is the human body itself, which it is becoming increasingly fashionable to decorate with sensors. A plausible way to convert body motion into electricity is through the use of devices called triboelectric nanogenerators (TENS). These convert friction into electricity by rubbing two so-called triboelectric materials (the Greek word for amber) together electronand wool were once popular) to generate static electricity. TENs turn this party trick into a useful resource by dissipating the charge so generated as electricity.

TENs, which were only invented a decade ago, could plausibly be integrated into sensors attached to human bodies or clothing. Bodies are continuous generators of movement, whether it’s breathing, gesturing, or running for a bus. The flexibility of many triboelectric materials makes them ideal for sewing into fabrics, where they could use the body’s movement to power sensors that monitor important statistics like breathing and heart rate during exercise. Such sensors could also do well in the hands of savvy marketers, with the phrase “batteries not included” not being a warning, but a boast.

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This article appeared in the Science & Technology section of the print edition under the heading “Scavenger Hunt”

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