Communications of the ACM
Structural Electronics Come Online
A structural supercapacitor developed at Vanderbilt University, which stores electricity by assembling electrically charged ions on its porous surface.
Credit: Joe Howell/Vanderbilt University
From tires that report low air pressure to bridges that alert engineers to structural weakness, various pieces of complex systems are increasingly being asked to do double duty by not only fulfilling their traditional roles, but thanks to sensors or other electronics, also performing some "smart" function such as information processing or energy storage.
Such multipurpose assemblages have been dubbed "structural electronics," which a recent report from research and consulting firm IDTechEx defines as "electronic and/or electrical components and circuits that act as load-bearing, protective structures, replacing dumb structures such as vehicle bodies or conformally placed upon them."
Peter Harrop, chairman of IDTechEx, is quick to point out that multipurpose structures are far from new. "For example, your car windshield probably has an antenna in it, so it's not a regular piece of glass any more," he says. "It's a load-bearing, weather-resistant structure that has an electronic function." Similarly, new buildings are often built with integrated photovoltaic electricity-generating systems. As such technologies start to become ubiquitous, Harrop believes the field has reached a tipping point.
That trend has also been noticed by Cary L. Pint, assistant professor in the Department of Mechanical Engineering at Vanderbilt University. Pint says, "Structural electronics is a melting pot of people who run into each other from different disciplines and fields," including electrochemistry, electronics, and mechanical engineering. "In recent years, there's been a focus on making everything multifunctional--to have a system that not only performs some really great function, but does it while also being a structural material."
Antennas and solar cells are still passive, isolated systems. The true tipping point will come as the world becomes filled with sensors interacting with each other and generating data to which other devices respond. Those developments will require computer systems capable of processing the data they generate and of controlling the response.
Battery replacements
One of the most active areas in structural electronics research is in replacing standalone batteries with structural energy storage systems. In 2012, Lola Group and Drayson Racing Technologies introduced a prototype all-electric racing car that ran on a battery that also served as the car's airfoil. Also, researchers at Imperial College London have worked with Volvo to develop a combination car trunk and super-capacitor.
Pint's group at Vanderbilt is also working on energy storage, mainly for mobile phones, laptop computers, and other such portable devices. "You have these massive batteries that contain really toxic substances and weigh quite a bit," he says. "What if you integrate that into components that are already there?"
His group started by trying to integrate energy storage and silicon chip technology. They demonstrated they could use standard semiconductor material processing techniques to make a porous silicon wafer, which they then infiltrated with a polymer. The result was a composite material that was strong, but also had onboard energy storage. The group has since applied its technique to solar cells and, as Pint explains, has literally converted unused space in that solar cell into energy storage. "Most solar cells are made of silicon and are much thicker than they need to be. We’ve taken solar cells, etched off the back aluminum coating, then etched material into the back of the solar cells."
The inspiration for Pint's composite materials came from aerospace systems in which carbon fibers are combined with polymers to make very strong composite materials. Harrop also points to aerospace as a source of structural electronics innovation. The carbon composites used in the fuselages of modern aircraft do not conduct electricity, so manufacturers have been embedding copper wires in them to use as lightning conductors. Yet those wires can also conduct information, so manufacturers could essentially "embed the whole plane's nervous system in the fuselage," Harrop says, giving aircraft so equipped a "smart skin" that will be able to detect and evaluate foreign objects. "Here's a world where suddenly the fuselage of an aircraft isn't just a cigar of aluminum or carbon composite, but has all manner of intelligence inside and out."
Information overload
As structures increasingly become smart and sensors proliferate, they will generate huge amounts of information. There is a debate, Harrop explains, about whether it is better to have structures and sensors talking to each other, or to pull all the data back to a central server and process it there (the latter approach will appeal to companies that want to mine the data). Still, both scenarios will require computer systems to evaluate and analyze the data and respond accordingly.
Also, with so many wireless devices in use, Harrop says we already have a problem with signals interfering with each other, or saturating the bandwidth. "There is a data overload, but also a wireless signaling overload issue, and that will require all kinds of computer workarounds, such as frequency hopping and sensing which frequencies are available at a given moment."
Both Harrop and Pint believe the field of structural electronics is poised for significant growth. "It's really an emerging area," says Pint. "Somebody who stands out in front of the community and provides some really exciting routes is probably going to end up leading it."
Logan Kugler is a freelance technology writer based in Tampa FL. He has written for over 60 major publications.
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