Research on flexible, wearable electronic devices is already well under way, with products such as the Wove Band attracting a great deal of attention. In fact, it’s a field of increasing research interest due to many potential applications. These include monitoring health and fitness, functional clothes, as well as many mobile and internet uses.
Such technology could have many implications in several areas of life. These might involve more effective and immediate monitoring of patients outside hospital, potentially reducing response time if something were to go wrong, and moving communications technology into an entirely new age. The smartphone as we know could be a thing of the past once this technology takes off.
Given the plethora of uses and the high profile of the research, it’s no surprise that many materials have already been considered. Silver nanowires, carbon nanotubes, and conductive polymers have all been explored in relation to flexible electronics. Unfortunately, problems have been reported in each case, such as high manufacturing costs in the case of silver nanowires and stability issues for some polymers.
But fear not my fellow science enthusiasts! Another material has appeared to save the day. It’s one you’re probably quite familiar with by now – Graphene! This two-dimensional hexagonal array of carbon atoms has great potential in the field of flexible electronics due to its unique properties, which include great conductivity and stability. However, known production methods for the Graphene sheets that would be needed give structures with a rather high surface resistance, which is not ideal.
Luckily, the invention of conductive Graphene inks provided a way to overcome this problem. This allows for sheets of superior conductivity, greater flexibility, a lighter weight, and a lower cost. That sounds VERY good for a wearable, flexible electronic device. These inks can also be prepared with or without a binder, a chemical that helps the ink stick to a surface. This also brings advantages and disadvantages, as a binder can improve the sheets conductivity, but also requires high temperature annealing processes. This limits its use on heat sensitive substrates such as papers and textiles.
Well, a new paper published in Scientific Reports in December claims to have found a production method that doesn’t require a binder and has a high conductivity. The research was conducted by scientists at the University of Manchaster, United Kingdom, and it represents and important step forward in making flexible Graphene based electronics a reality. The production method first involves covering a surface with an ink containing Graphene nanoflakes, then drying it at 100oC. This forms a highly porous coating, which is not ideal since it leads to high contact resistance and an unsmooth electron pathway.
The authors overcame this problem by compressing the dry coating, which led to a thin, highly dense layer of Graphene. This not only improved the adhesion of the nanoflakes, but the structure became much less porous, improving its conductivity. It is also noted that greater compression led to higher conductivity values, with the highest being 4.3×104 S/m. But the science didn’t end there! The authors then went on to test how flexible electronic components made from this material would perform with regard to communications technology. Both transmissions lines (TLs) and antennae were created from the Graphene sheets, and tested in various scenarios.
TLs are conductors designed to carry electricity or and electrical signal, and are essential in any circuitry. The ones created here were tested in three positions: unbent, bent but not twisted, and bent and twisted. This was done to determine if the material performed well in various positions; a necessity for a wearable, flexible device. Turns out the TLs performed well in all three positions, with data showing only slight variations in each case.
The Graphene based antennae were also tested in various positions, both unbent and with increasing amounts of bending. In each case the antennae were found to function in the frequency range matching Wi-Fi, Bluetooth, WLAN, and mobile cellular communications. This is an excellent indication that this material could be ideal for use in wearable communications technology. It was also tested in a pseudo-real life scenario, with antennae being wrapped around the wrists of a mannequin. These results were also promising, showing that an RF signal could be both radiated and received.
So, you can hopefully see that this work represents a real step forward towards wearable electronic devices, as it shows that Graphene is truly a prime candidate. That said, there is still a great deal of work to do, such as incorporating all these components into a complete device and figuring out how to produce the technology on a commercial scale. There would also need to be more research to see if these Graphene sheets could be modified in some way to include applications outside of communications. But putting that aside, I’m quite excited about this research bringing us a little bit closer. Keep an eye out to see where it goes from here.
- Fuente, J. (2016). Properties Of Graphene. Graphenea. Retrieved 18 January 2016, from http://www.graphenea.com/pages/graphene-properties#.VpzceyqLSwV
- Huang, G.-W. et al. Wearable Electronics of Silver-Nanowire/Poly(dimethylsiloxane) Nanocomposite for Smart Clothing. Sci. Rep. 5, 13971; doi: 10.1038/srep13971 (2015).
- Huang, X. et al. Highly Flexible and Conductive Printed Graphene for Wireless Wearable Communications Applications.Sci. Rep. 5, 18298; doi: 10.1038/srep18298 (2015).
- Matzeu, G., O’Quigley, C., McNamara, E., Zuliani, C., Fay, C., Glennon, T., & Diamond, D. (2016). An integrated sensing and wireless communications platform for sensing sodium in sweat. Anal. Methods, 8(1), 64-71. http://dx.doi.org/10.1039/c5ay02254a