A team of mechanical engineers from Virginia Tech have devised a way to 3D print piezoelectric materials that can be customized to convert movement, impact and stress into electrical energy. The ability to 3D print piezoelectric materials—which are used in cell phones, musical equipment and more—could expand their applications and drive new innovations in the field.
The research at Virginia Tech is being led by Xiaoyu ‘Rayne’ Zheng, an assistant professor of mechanical engineering at the College of Engineering and a member of the Macromolecules Innovation Institute. With his team, Zheng has developed a 3D printing technique to customize piezoelectric materials, which are essentially materials that convert stresses into electric charges.
Unlocking piezoelectric potential
Piezoelectric materials are made of brittle crystal and ceramic—a composition that makes them quite tricky to work with and often necessitates a clean room to produce piezoelectric structures. The 3D printing technique developed by Zheng and his team makes it possible to print the materials without any shape or size restrictions. The 3D printed material can also be activated, paving the way for next generation intelligent infrastructures and smart materials for tactile sensing, impact and vibration monitoring, energy harvesting and more.
The AM process enabled the engineers to manipulate and design arbitrary piezoelectric constants that allowed for an electric charge response to forces and vibrations applied to the 3D printed part by any direction. By utilizing 3D printed topologies, the researchers can effectively program voltage responses to be magnified, reversed or suppressed in any direction. This marks a clear step ahead for piezoelectric materials, which are conventionally prescribed their charge by their intrinsic crystals.
“We have developed a design method and printing platform to freely design the sensitivity and operational modes of piezoelectric materials,” Zheng explained. “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 engineers have found a way to design a structure that mimics the natural crystal structure of a natural piezoelectric material but also integrates a customizable lattice orientation.
“We have synthesized a class of highly sensitive piezoelectric inks that can be sculpted into complex three-dimensional features with ultraviolet light,” Zheng added. “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.”
To demonstrate the novel technique, the team 3D printed piezoelectric materials on the micro-scale. The printed materials had sensitivities 5-fold higher than flexible piezoelectric polymers and could be manipulated to have a particular stiffness and shape.
“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. 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.”
“The ability to achieve the desired mechanical, electrical and thermal properties will significantly reduce the time and effort needed to develop practical materials,” added Shashank Priya, associate VP for research at Penn State and former professor of mechanical engineering at Virginia Tech.
Creating new, smart applications
At this stage, the team has shown the 3D printing process’ potential for making wearables and consumer electronics, but there are other applications that could come into play as well. The technique, for instance, could be used to advance applications in robotics, energy harvesting, tactile sensing and intelligent infrastructure. The 3D printed piezoelectric material could be tailored to sense impacts, vibrations and other motions for monitoring purposes.
To illustrate these future applications, the engineers 3D printed a small-scale smart bridge with the ability to sense the locations of dropping impacts and magnitude and with the strength to absorb impact energy. Another example showed the method’s potential for producing smart transducers that convert underwater vibration signals to electric voltages.
“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 study. “Here, the structure itself is the sensor—it can monitor itself.”
The innovative research was recently published in the journal Nature Materials.