Trends in the electronics industry are sometimes difficult to paint in broad strokes, given the truly massive number of applications they're used in. In general, however, there have been clear steps towards making circuits smaller and more flexible. Spurring these advancements are the demand for devices in the spheres of wearables and robotics. This combination of small, flexible circuits and the ruggedness required in wearable devices naturally leads to questions regarding durability and maintenance.
Researchers have been investigating the concept of self-healing circuits that could be used in these applications for years. Circuits that experience flex will eventually begin to break under fatigue, but self-healing components could, theoretically, mitigate these issues—or even one day prevent them entirely.
One example of a self-healing circuit in 2016 was a magnetic compound that would reattach itself once broken. While this research is important, its uses in electronic devices would be limited due to potential complications regarding electromagnetic interference, affecting not only the reliability of the self-healing mechanism but the reliability of the device as a whole.
Beginning in 2015, researchers from the University of Califonia, San Diego and the University of Pittsburgh developed a concept for self-healing electronics by utilizing what's called the Janus particle, utilizing individual nanoparticles to function as "nanorobots" that don't require a computer to program. Besides this technology still being in its infancy, implementing these particles in self-healing electronics would clearly require some rather large fundamental changes to circuit design and manufacturing.
Without further development, these concepts are not practical for current prototypes. New research on flexible self-healing circuits, however, could provide more attainable solutions.
A Practical Self-Healing Solution?
Researchers from Carnegie Mellon University have created a silicon-based material that not only demonstrates its self-healing property but also integrates multiple connections in the same piece of silicon. The researchers took a piece of silicon rubber and infused the material with micron-sized droplets of a gallium-indium alloy. This metal alloy (liquid at room temperature), is conductive but the suspended droplets do not form electrical contacts with each other. When external pressure is applied to the material the droplets are ruptured and bond with other nearby ruptured droplets resulting in a conductive path. This means that a simple device such as a pen plotter can be used to draw circuits into the material.
An example circuit drawn in the material. Screenshot courtesy of Carnegie Mellon.
How does this material self-heal? The brilliance in this material comes from the rupturing of droplets! When damage is done to the material (such as a hole punch) the droplets close to the damage are ruptured and this forms a new path around the damaged area.
A closeup of damage done to the tiny bot with a hole punch. Screenshot courtesy of Carnegie Mellon.
So, what happens if the material is stretched? Won’t this rupture the gallium-indium alloy droplets?
It turns out that this is not the case and the material can be manipulated and stretched without damage occurring to the electrical traces.
While this material is only a proof-of-concept for flexible self-healing circuits, it is certainly a strong candidate for wearable prototypes. The tracing of wires into the material demonstrate that creating custom circuits could be inexpensive to produce. The self-healing properties show that, if the material were to be punctured, the circuit could create alternative paths. However, the creation of alternative paths may cause issues if there are many conductive paths placed very close together so this type of technology is unlikely to be used in computing or data transfer using a parallel bus.
The flexibility of the material could see itself used in a number of applications, not just those involving wearable electronics. Aerospace applications could benefit from such a material due to the fact that probes cannot be repaired remotely. For example, micro-meteor impacts create small punctures, but such punctures could easily be repaired using a silicon-based circuit board.
Example of micrometeor damage. Image from NASA
Another possibility is that this material could be used as a "skin" for various robotics applications.
This demonstration of a self-healing flexible material that can have multiple circuit paths embedded is impressive and could be the key to future flexible materials. Of course, this material is still in the developmental stage but, considering that circuits can easily be printed and that puncture damage is mitigated against, it is arguable that this is the world’s first true self-healing electrical material.
What other advancements in self-healing circuitry have caught your eye? What applications do you think this technology could be used for? Share your thoughts in the comments below.
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- One Step Closer to Wearable Flexible Electronics