Scientists have developed means to make soft, flexible and stretchy electronic circuits and radio antennas by manually, just by writing on highly specialized sheets of material.
This means may assists people draw electronic devices based on demand for customized devices, researchers said in a new study explaining the method.
As old electronics are stiff, new soft electronics are flexible and easily stretchable and foldable. Researchers worldwide are looking at applications of soft electronics such as wearable and implantable devices. [5 Crazy Technologies That Are Revolutionizing Biotech]
The new method researchers developed makes circuits by fusing, or melting, together small bits of metal to make electrically conductive wires.Even though this newly developed process make no use of heat, as is usually the case with fusing. Instead, this method involves soft sheets made of silicone rubber with numerous small droplets of liquid metal embedded within them. Pressing down on these sheets using, for instance, the tip of a pen, ruptures the capsules, much like popping miniature water balloons, and the liquid metal inside can come together to form circuit elements.
"We can make conductive lines by hand just by writing," said study co-senior author Michael Dickey, a chemical engineer at North Carolina State University in Raleigh.
The researchers used a metal called eutectic gallium indium (EGaIn), a massively conductive electrical alloy,liquid at about 60 degrees Fahrenheit (15.5 degrees Celsius). They enclose droplets of EGaIn that were only about 100 nanometers, or billionths of a meter, wide into sheets of the type of silicone rubber known as PDMS.
When these droplets come together, their electrical conductivity increases tremendrously about tenfold compared to when they are separate, the researchers said. To understand why, imagine a hallway covered with water balloons.
"If you covered a floor with water balloons, you could not make a conductive path between balloons," Dickey told Live Science. However, if the balloons get popped, they merge to form a continuous electrically conductive pathway, he explained.
These mechanically fused metal pathways could also serve as radio antennas. Researchers could tune the frequencies these antennas pick up simply by changing the length of the pathways.
"An antenna can be created on the fly simply with a magic marker," Dickey said.
Normal circuit boards consist of circuits of electrically conductive foil laminated onto stiff electrically insulating boards. The fabrication of such circuit boards requires multiple steps, and the circuits must be designed in advance of use. In contrast, these new soft circuit boards can be created simply by writing on them, which means the circuits can be built on demand, the researchers said.
"We live in a world with lots of soft materials — our bodies, clothing," Dickey said. "Most electronics are made from rigid materials and are therefore mechanically incompatible with our 'soft world.' Rigid electronics also tend to fail catastrophically when deformed — I've seen plenty of cracked phones, as an example. The circuit boards we made are soft and deformable."
The soft circuit boards can easily be cut into desired shapes, the researchers said, and it is also possible to connect rigid components, such as lights, simply by inserting them into the sheets. For instance, using this new technique, researchers created Christmas trees that could be lighted.
One drawback of this approach is that droplets may sinter accidentally if they're exposed to excessive pressures. The researchers discovered that one way to solve this problem is to brush a clear glue onto the sheets. The glue dries and forms a rigid protective layer that could prevent unwanted sintering after the circuits are written, the scientists said.
Another limitation of this approach is that the wires are only as thin as the stylus used to create them and thus are nowhere as narrow as the wires in traditional microchips. The scientists noted that commercial desktop lasers could lead to more complex patterns, although this does make the fabrication process more complicated. Another possible way to form straight, thin channels involves embedding the droplets in orderly patterns within the silicone rubber, such as in microscopic rows.
However, "Many advances are still needed to make this commercially viable," Dickey said. "This is a simple demonstration to illustrate the concept of soft circuits."
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