Changing the way to design sensors


US engineers have  3D-printed piezoelectric materials. Samantha Page reports.


A printed flexible sheet of piezoelectric smart material.

A printed flexible sheet of piezoelectric smart material.

H Cui, Zheng Lab

If you use voice-activated software – like iPhone’s Siri or voice-to-text – tiny, brittle pieces of crystal or ceramic are converting the vibrations of your voice to electric impulses.

Now, researchers at Virginia Tech University in the US have developed a method to custom-design materials – flexible and strong, thick or thin – that could replace the delicate crystal and ceramic that were previously the only materials able to convert pressure to electricity in what is known as the piezoelectric effect.

These materials are smart, and they can sense stress and monitor impact in any direction, says research leader Xiaoyu Zheng, a member of the Macromolecules Innovation Institute.

"We can tailor the architecture to make them more flexible and use them, for instance, as energy harvesting devices, wrapping them around any arbitrary curvature," he says. "We can make them thick, and light, stiff or energy-absorbing."

A paper detailing the team’s work is published in the journal Nature Materials.

The previously available crystal and ceramic piezoelectric materials can only work in certain orientations, because of the atomic structure.

The 3D ink designed by Zheng’s team copies the natural “lattice” of the crystal but allows for the orientation to be changed around. The materials can be printed using UV light in thicknesses only a fraction of the diameter of a human hair.

"The inks contain highly concentrated piezoelectric nanocrystals bonded with UV-sensitive gels, which form a solution - a milky mixture like melted crystal - that we print with a high-resolution digital light 3D printer," Zheng says.

The possibilities for use go well beyond voice activation. While previous piezoelectric materials were limited by their stiffness and delicacy – needing a clean room for manufacturing – the robustness and flexibility of the new process means Zheng and his team envisage using the materials as sensors for nearly anything.

They have already demonstrated the materials’ use in wearables, but also suggest they could be used in infrastructure and other areas where pressure and vibration are important.

"Traditionally, if you wanted to monitor the internal strength of a structure, you would need to have a lot of individual sensors placed all over the structure, each with a number of leads and connectors," says first author Huachen Cui. "Here, the structure itself is the sensor - it can monitor itself."

“This will change the way we design sensors,” Zheng says.

  1. https://www.electronicdesign.com/power/what-piezoelectric-effect
  2. https://www.nature.com/articles/s41563-018-0268-1
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