Here Comes ‘Smart Dust,’ the Tiny Computers That Pull Power from the Air
A world covered in sensors that don’t require batteries is near at hand.

By Christopher Mims

The idea of a perpetual machine—one that, once set in motion, never stops—is preposterous. The energy it needs must come from somewhere. But a twist on the idea, where energy is sponged from the environment to power ultra-efficient devices, isn’t a fantasy. Some people even call it perpetual computing.

These energy-harvesting machines can already be as small as a stack of three quarters, and there’s no law of physics that says they couldn’t someday shrink enough to hide anywhere. Imagine tiny sensors—for sound, vibration, chemicals, light, motion—that don’t require power lines or battery changes.

The first wave will be unobtrusive sensors with onboard computing and wireless radios with a range of as much as a kilometer. Most early applications people have in mind for them are already being accomplished by their wired or battery-fed brethren—the kinds of sensors that make factories, homes and our wearables “smart.”

Eventually, researchers believe these tiny, always-on devices could enable us to do things that aren’t realistic today, such as sticking small security cameras wherever we like, instrumenting every square meter of a farm, or filling our cars and homes with sensors that increase both our safety and the usefulness of our most expensive assets. They’ve coined a term to describe the potential ubiquity of such sensors: “smart dust.”

There are challenges. Current microchips are for the most part too power hungry to be useful in untethered sensors. The performance and longevity of the nascent technology being used to power them is still unknown. And when those issues are resolved, the self-powered, microscopic monitoring devices will likely give rise to new concerns over privacy and surveillance.

Power Dynamics

Smart dust is becoming possible now because of new techniques for lowering the amount of power electronics require.

“If we look at it from the power consumption side, the energy efficiency of microelectronics has improved by more than a factor of a trillion from ENIAC [one of the world’s first electronic computers] to today,” says Joshua R. Smith, a professor at the University of Washington who specializes in low-power systems and wireless communication.

A whole cottage industry of chips that consume miniscule amounts of energy has sprung up, including startups like Ambiq Micro, which specializes in wearables, sensors and smart cards, and PsiKick, which is building batteryless industrial internet of things systems using its custom low-power microchips. Where the processor in your smartphone uses about one watt of power, the power consumption of some of these chips is measured in microwatts—a million times less.

There are now also better ways to harvest energy from the environment. A handful of startups are working on wireless communication systems that need so little power that remote units can harvest energy from the base station they communicate with.

Such technology is already in use in RFID tags, which respond to a reader’s wireless signal by bouncing back a unique identification number. But RFID development has stalled, and there’s room for improvement, says Gregory Durgin, a Georgia Institute of Technology professor and expert on wireless power transmission. “We’re not anywhere close to the physical limits of what we can do for [radio frequency] energy harvesting for computation and communication,” he adds.

One promising development, so-called passive Wi-Fi, uses “ambient backscatter” communication. This technology works like a mirror if a mirror could do useful computation on the light bouncing off of it, reflecting back signal after it’s been modified by low-power electronics. Prof. Smith is one of the founders of a startup, Jeeva Wireless, that is among the companies pioneering its use for ultra-low-power communication across long distances for industrial applications, environmental sensors on farms and many other applications.

Another promising source of energy for smart dust is heat. As scientists have long known, a temperature difference on two sides of particular materials can generate a current. The Matrix Power Watch from Matrix Industries runs off its wearer’s body heat. Matrix has netted $30 million in investment since its founding in 2011, and its investors include 3M

The company currently has technology that can power sensors in factories where things like motors and boilers produce plenty of heat.

In Pakistan, The Hub Power Co. wants to make its power plants run more reliably by collecting and sending vibration and heat data wirelessly to General Electric Co. , which then makes maintenance recommendations. But changing all the batteries in hundreds of sensors or else wiring them all to power would be labor intensive, says Aly Khan, a Hub Power director. When leaders of the firm heard about Matrix’s technology, they decided to try it. The company is in the process of verifying Matrix’s technology claims, and plans to roll out sensors at one of its power plants sometime next year, with more to follow.

Matrix is also developing a system that can generate power just from the daily fluctuation of air temperatures from night to day, says chief executive and co-founder Akram Boukai. With a daily fluctuation of 20 degrees Fahrenheit, it can generate on average 5 to 10 milliwatts. That’s enough to power a variety of sensors and beam their data back to a cell tower every 5 to 10 minutes.

Wearables for Cows

The bulkiness of the air-temperature-powered system—it’s about the size of an Amazon Echo speaker, though the company hopes to shrink it to the size of a Coke can—illustrates one of the many challenges on the path to creating smart dust. Thermoelectric heat generators are going to have to shrink a great deal before they can power sensors meant to be scattered throughout the home.

In the meantime, there are plenty of applications for which something the size of a soda can is perfectly workable, and still more for which warm objects can power smaller, coin-size perpetual sensors. Cows, for example, produce a lot of body heat, and could easily power their own smart, watch-size health wearables. (Health wearables for cows are, believe it or not, an investment many farmers have made already.) And spies who want to eavesdrop behind enemy lines wouldn’t have to worry about risking life and limb to recharge a remote microphone.

As the technology improves, and Dr. Durgin of Georgia Tech believes it will, it could mean not just novel applications but a re-thinking of our largely wired world. For example, the average car has about 50 pounds of wiring in it—you could probably do away with a lot of that using independently powered wireless sensors. And smart homes could be configured without all the wires and power lines currently needed.

As wonderful as that sounds, someone could use this technology to develop a perpetual, coin-size location tracker, microphone or camera to stick on our vehicle or person—or anywhere else, really. While no one has publicly disclosed the existence of such devices yet, the likelihood they will should give us all pause.

Write to Christopher Mims at christopher.mims@wsj.com