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Mud-Fueled Smart Sensors for the Bottom of the Ocean

Engineers power a microprocessor-equiped sensor platform using dirt, germs, and a lack of air

2 min read
Mud-Fueled Smart Sensors for the Bottom of the Ocean
Bacteria in mud power tiny sensors.
Photo: University of Michigan, Ann Arbor

If you put tiny electrodes in the mud on the ocean floor, you can harvest enough energy to power a tiny sensor platform that can monitor what’s going on at those depths.

So say researchers from the University of Michigan at Ann Arbor, in a recent issue of IEEE Transactions on Circuits and Systems I. Together with collaborators from Korea and California, they have designed a self-sustaining sensor platform for oceanic sensing applications that is powered entirely by small-scale benthic microbial fuel cells.

“We wanted a platform that could run off very small harvesting sources,” Michigan electrical engineering professor and IEEE Fellow David Blaauw tells IEEE Spectrum. “If you can get power consumption down enough, there are all sorts of things you can use. Even plants produce little bits of voltage,” he says.

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When benthic bacteria are in an anaerobic environment, their metabolism produces electric current. “It’s been well studied,” says Blaauw, “but in the past, people have struggled to get enough current to run something.”

 According to Blaauw, laboratory experiments confirmed that if a microbial fuel cell sits in the sediment, with the cathode floating in a water column where it is exposed to oxygen, it can deliver enough energy to run the platform perpetually.

Though using electrodes with larger surface areas generates more power, the researchers say that it is more challenging to maintain the anaerobic environment with larger electrodes. “If the anode pops out, the whole thing stops working,” Blaauw says, adding that large-size microbial fuel cells also require human divers and sophisticated deployment equipment in order to be properly installed in the ocean floor.

The sensor platform draws just 2 nanowatts

But his team’s setup has very little in the way of complications. “We have much lower power requirements. Just shoot a small dart into the mud, wait a couple of days for the oxygen deprived environment to establish itself, and then you get current.”

Blaauw explains that the sensor platform features a microprocessor, a radio, and few kilobytes of memory. Its power management unit helps keep the draw from its battery to a minuscule 2 nanowatts.

“When the system is in standby mode, it retains data, but consumes little power,” he says. “Very low power timers allow it to wake up occasionally, take readings, then check, store, or transfer data. Low power consumption enables us to work with obscure, small harvesting sources. We can now deploy sensors in the oceanic floor easily and cheaply, and we don’t have to provide batteries that will run forever.”

Blaauw told Spectrum that the prototype system was designed to track changes in temperature, but that it’s easy to imagine it measuring other things such as changes in coral reefs suffering from decay due to pollution.

He explains that this platform is part of a broader portfolio of work focused on powering electronic systems with low energy sources. “These platforms could be used inside the human body, by oil companies investigating fissures in the ground, or by security systems where you need something unobtrusive that fits into the surrounding décor,” he says. “We’ve had interest from a university that wants to study snails, and another that is studying bees. Make a platform really small, and it opens up all sorts of new avenues.”

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Why Functional Programming Should Be the Future of Software Development

It’s hard to learn, but your code will produce fewer nasty surprises

11 min read
A plate of spaghetti made from code
Shira Inbar

You’d expectthe longest and most costly phase in the lifecycle of a software product to be the initial development of the system, when all those great features are first imagined and then created. In fact, the hardest part comes later, during the maintenance phase. That’s when programmers pay the price for the shortcuts they took during development.

So why did they take shortcuts? Maybe they didn’t realize that they were cutting any corners. Only when their code was deployed and exercised by a lot of users did its hidden flaws come to light. And maybe the developers were rushed. Time-to-market pressures would almost guarantee that their software will contain more bugs than it would otherwise.

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