New heat-shrinking method integrates electronic circuits on irregular shapes

 

Most electronics are built on flat, stiff boards, which makes it incredibly difficult to fit them onto curved and irregular shapes we find in the real world, such as human limbs or curved aircraft wings. While flexible electronics have made some progress, they are often not durable enough or are too complex to manufacture for everyday use.

But now scientists from Tianjin University and Tsinghua University in China have developed a way to integrate high-performance circuits into irregular 3D surfaces. Their findings are published in the journal Nature Electronics.

Shrink to fit

The solution the researchers developed is a simple heat-shrinking method. First, they printed a circuit onto a common thermoplastic that shrinks when heated, so it can snugly wrap around objects. Then, instead of copper wires that could snap when the plastic shrinks, they used a semi-liquid metal. This mixture of gallium, indium and copper is thick enough to stay exactly where it is printed and liquid enough to bend without losing its electrical connection.

The next step was to ensure that, once the thermoplastic film shrinks and conforms to an object, it doesn't do so haphazardly. To solve this, the team used computer simulations to predict how the film would warp, enabling them to calculate the optimal design for each curve.

Once the design was ready, they used either a blast of hot air or warm water (about 70°C) to pull the film tight and mold the liquid circuit to the target object without damaging it.

Then came the testing. To prove the material was tough enough for real-world use, they took a strip of thermoplastic film with the wires printed on it and put it through thousands of bending and twisting cycles. While traditional wires would have most likely developed cracks, the circuit showed almost no change in its ability to conduct electricity.

"We have developed a cost-effective method for fabricating shape-adaptive electronics with high durability, demonstrating good conductivity even after 5,000 bending and twisting cycles," wrote the researchers in their paper.

Potential applications

Following the successful lab testing phase, the scientists moved their invention onto real-world objects. Because the method is so versatile, they were able to add functionality to surfaces that are usually difficult to wire up.

They shrunk sensors onto fresh fruit to monitor temperature and humidity during shipping, and on model aircraft wings to create an in-built heating system that melts away potentially dangerous ice. They also created smart bandages that can check their own status.

The team believes they have only scratched the surface with their breakthrough. Refining the process will allow them to fit their circuits to an even wider range of complex shapes and surfaces.