A team of mechanical engineers at Virginia Tech have developed a new process for 3D printing energy harvesting, piezoelectric materials.
In an article published this week in the Nature Materials journal, Xiaoyu ‘Rayne’ Zheng, assistant professor of mechanical engineering in the College of Engineering and his team, have found a way to 3D print piezoelectric materials that can be custom-designed to convert movement, impact and stress from any directions into electrical energy.
Piezoelectric materials, made of brittle crystal and ceramic, are found in a range of devices such as mobile phones and come in only a few defined shapes. A complex and expensive manufacturing process and inherent brittleness of the material, has limited the ability to maximise the material’s potential. This latest research now makes it possible to 3D print these materials, unrestricted by shape or size, and could enable intelligent infrastructures and smart materials for tactile sensing, impact and vibration monitoring, and energy harvesting.
Zheng’s team have developed a model that enables them to manipulate and design arbitrary piezoelectric constants, which allows the material to generate electric charge movements in response to incoming forces and vibrations via a set of 3D printable topologies. The new method also means users can prescribe voltage responses to be magnified, reversed or suppressed 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."
At the atomic level, the orientation of atoms in the natural crystal used are fixed. Zheng’s team has produced a substitute that mimics the crystal but allows for the lattice orientation to be altered by design.
"We have synthesised 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 materials at a scale measuring fractions of the diameter of a human hair with sensitivities five times greater 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.
Zheng added: "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."
Shashank Priya, associate VP for research at Penn State and former professor of mechanical engineering at Virginia Tech commented: "The ability to achieve the desired mechanical, electrical and thermal properties will significantly reduce the time and effort needed to develop practical materials."