17-11-2020 | | By Robin Mitchell
A team of researchers have developed a circuit board that provides true flexibility and can be easily recycled. What challenges do flexible electronics face, what have the researchers developed, and what advantages does the new design provide?
While electronics have been able to take over most of daily life, one area that they continue to struggle to infiltrate is wearable items. The major reason for this is that electronics are ridged solid structures, while clothes and other wearable items are flexible. If a traditional PCB is made to flex, the result is often traces cracking over time, components falling off, and pads being ripped from the PCB. As a result, modern electronics are rarely found, if at all, inflexible applications. Instead, electronics used in such applications are generally mounted onto a ridged PCB which is then housed into a ridged case and then attached to a flexible strap (such as smartwatches or health monitor bands). Other challenges that wearable electronics also face include flexible power sources that can be worn unnoticed. Still, small coin-cells can be integrated into clothing such as buttons and the clothes label while going unnoticed.
If, however, flexible electronics in clothes and other wearables could be achieved commercially, then the technological ramifications would be vast. For instance, clothes could be turned into medical monitors that provide large amounts of data for medical AI systems. From there, peoples health could be actively monitored to look for anomalies and thus provide, for the first time in history, active health care instead of passive health care whereby diseases and conditions are treated before they show symptoms instead of after.
Researchers from the University of Colorado Boulder have demonstrated a new electronic skin that allows for a high degree of flexibility. The new skin allows for normal components to be mounted in place, but the skin itself not only allows for electronic signal routing but can be stretched by as much as 60% of its original size. The skin also demonstrates self-healing abilities whereby a cut in the material is healed if the skin is pinched together at the site of damage. The reformed bonds are covalent in nature, meaning that the healed skin is as strong as it was before, thus not creating weak points as the material is repeatedly used.
The skin substrate is made from a material called polyamine while the electrical connections are made using liquid metals wires that are screen printed onto the skin. From there, normal components are placed, and the circuit is sandwiched between the polyamine layers. To demonstrated the effectiveness of the skin, the researchers created a simple health monitor that can measure body temperature and the number of steps taken (i.e. a pedometer). The temperature sensor used in the design was the MCP9700 while the ADXL335 was used as the triaxial accelerometer. While the device also integrated an AD8505 which is used for ECGs, it is not clear whether the flexible system can indeed measure heart rate. The flexible nature of the device
“If you want to wear this like a watch, you can put it around your wrist. If you want to wear this like a necklace, you can put it on your neck not only makes it comfortable to wear. It can also be worn on any other part of the wearer.” - Jianliang Xiao, associate professor in the Paul M. Rady Department of Mechanical Engineering.
The features boasted by the electronic skin make it an ideal candidate for creating future wearable electronics, but one feature that was arguably not given enough attention was its recycling ability. Traditional electronics are recycled as much as they can be, but components are generally thrown away with the PCB as these generally cannot be reused. This is often because removing components from a PCB is a difficult process, and the cost of trying to salvage capacitors and resistors far exceeds the price of brand-new parts.
However, the new electronic skin developed by the research team is easily broken apart using a recycling solution that allows for the electronic skin to be reused. But the components drop to the bottom of the solution, effectively allowing them to be reused. Such an ability of a consumable electronic product could see large amounts of waste diverted from landfills assuming that such electronics become popular.
“Our solution to electronic waste is to start with how we make the device, not from the endpoint, or when it’s already been thrown away. We want a device that is easy to recycle.” - Jianliang Xiao, associate professor in the Paul M. Rady Department of Mechanical Engineering.