22 December 2011
Self healing electronics could last longer and cut waste
Researchers have developed a self healing system that almost instantly restores electrical conductivity to a cracked circuit.
The research, published in Advanced Materials is designed to simplify systems, removing the need to build in redundancies or sensory diagnostic systems. Potential applications include instruments or vehicles for space or military functions, where electrical failures can't be replaced or repaired.
Engineers from University of Illinois were led by aerospace engineering professor, Scott White and materials science and engineering professor, Nancy Sottos. Sottos said the research addresses the problem of evolving electronic devices requiring as much density onto a chip as possible. This, in turn, creates reliability problems such as failure stemming from fluctuating temperature cycles as the device operates, or fatigue.
The team had previously developed a system for self healing polymer and adapted the technique for conductive systems. Microcapsules, as small as 10 microns in diameter, were dispersed on top of a gold line functioning as a circuit. As a crack propagated, the microcapsules broke open and released the liquid metal contained inside. The liquid metal filled in the gap in the circuit, restoring electrical flow.
"What's really cool about this paper is it's the first example of taking the microcapsule based healing approach and applying it to a new function," White said. "Everything prior to this has been on structural repair. This is on conductivity restoration. It shows the concept translates to other things as well."
A failure interrupts current for microseconds as the liquid metal immediately fills the crack. The researchers demonstrated that 90% of their samples healed to 99% of original conductivity, even with a small amount of microcapsules.
The self healing system also has the advantages of being localised and autonomous. Only the microcapsules that a crack intercepts are opened, so repair only takes place at the point of damage. Furthermore, it requires no human intervention or diagnostics, a boon for applications where accessing a break for repair is impossible, such as a battery, or finding the source of a failure is difficult, such as an air or spacecraft.
"In an aircraft, especially a defence based aircraft, there are miles and miles of conductive wire," Sottos said. "You don't often know where the break occurs. The autonomous part is nice – it knows where it broke, even if we don't."
The researchers plan to further refine their system and explore other possibilities for using microcapsules to control conductivity. They are particularly interested in applying the microcapsule based self healing system to batteries, improving their safety and longevity.
The research was supported as part of the Center for Electrical Energy Storage, an Energy Frontier Research Center funded by the US Department of Energy, Office of Science.
Author
Chris Shaw
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