Jan 23, 2019 | By Thomas
The piezoelectric materials produce an electric current when placed under mechanical stress and can be found in everything from our cell phones to musical greeting cards. However, they have their limitations.
Producing piezoelectric materials is usually an expensive process. It requires clean-rooms and a complex procedure that produces films and blocks which are connected to electronics after machining. Moreover the highly-useful materials are made of brittle crystal and ceramic and come in just a few selected shapes. Now scientists at Virginia Polytechnic Institute and State University (Virginia Tech) claim that the piezoelectric material will be able to be 3D printed in ways that will not restrict them by shape or size.
A 3D printed flexible sheet of piezoelectric smart material (Photo by H. Cui of the Zheng Lab)
Xiaoyu 'Rayne' Zheng, assistant professor of mechanical engineering in the College of Engineering, and a member of the Macromolecules Innovation Institute, and his team have developed methods to 3D print piezoelectric materials that can be custom-designed to convert movement, impact and stress from any directions to electrical energy.
They developed a model that allows them to manipulate and design arbitrary piezoelectric constants, resulting in the material generating electric charge movement in response to incoming forces and vibrations from any direction, via a set of 3D printable topologies. The new technique also enables users to programme voltage responses to be magnified, suppressed or reversed in any direction.
"We have developed a design method and printing platform to freely design the sensitivity and operational modes of piezoelectric materials," Zheng said.
"By programming the 3D active topology, you can achieve pretty much any combination of piezoelectric coefficients within a material, and use them as transducers and sensors that are not only flexible and strong, but also respond to pressure, vibrations and impacts via electric signals that tell the location, magnitude and direction of the impacts within any location of these materials."
The 3D printed flexible sheet of piezoelectric material. Credit: Virginia Tech
A factor in current piezoelectric fabrication is the natural crystal used. At the atomic level, the orientation of atoms are fixed. Zheng's team has produced a substitute that mimics the crystal but allows for changes in the lattice orientation.
"We have synthesized a class of highly sensitive piezoelectric inks that can be sculpted into complex three-dimensional features with ultraviolet light. 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 said.
The team demonstrated the 3D printed piezoelectric materials at a scale measuring fractions of the diameter of a human hair. "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," Zheng said. "We can make them thick, and light, stiff or energy-absorbing."
The material demonstrates five times higher sensitivities than flexible piezoelectric polymers. The stiffness and shape of the material can be tuned and produced as a thin sheet resembling a strip of gauze, or as a stiff block.
"We have a team making them into wearable devices, like rings, insoles, and fitting them into a boxing glove where we will be able to record impact forces and monitor the health of the user," said Zheng.
Researchers suggest that the material created using 3D printing technique has the potential to be used in robotics, energy harvesting, tactile sensing and intelligent infrastructure, where a structure is made entirely with piezoelectric material, sensing impacts, and impact and vibration monitoring.
A 3D printed, flexible energy harvester (Photo by H. Cui of the Zheng Lab)
"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," said Huachen Cui, a doctoral student with Zheng and first author of the Nature Materials paper. "Here, the structure itself is the sensor - it can monitor itself."
The details of the research are published in journal Nature Materials.
Posted in 3D Printing Application
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