Momentum - The Magazine for Virginia Tech Mechanical Engineering Vol. 4 No. 1 Spring 2019 | Page 19

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3D printing of piezoelectrics, sensors and transducers
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 the lattice orientation to be altered by design.
“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 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 has sensitivities 5-fold higher 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.
“The ability to achieve the desired mechanical, electrical and thermal properties will significantly
reduce the time and effort needed to develop practical materials,” said Shashank Priya, associate
VP for research at Penn State and former professor of mechanical engineering at Virginia Tech.
New applications
The team has printed and demonstrated smart materials wrapped around curved surfaces, worn
on hands and fingers to convert motion, and harvest the mechanical energy, but the applications
go well beyond wearables and consumer electronics. Zheng sees the technology as a leap into
robotics, energy harvesting, tactile sensing and intelligent infrastructure, where a structure is
made entirely with piezoelectric material, sensing impacts, vibrations and motions, and allowing
for those to be monitored and located. The team has printed a small smart bridge to demonstrate
its applicability to sensing the locations of dropping impacts, as well as its magnitude, while robust
enough to absorb the impact energy. The team also demonstrated their application of a smart
transducer that converts 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 con-
nectors,” 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 team’s work is supported, in part, by the National Science Foundation, Air Force Office
of Scientific Research, the Office of Naval Research and the Virginia Tech Institute of Critical
Technology Junior Faculty Award.
The paper in Nature Materials features the following authors: Huachen Cui (Mechanical En-
gineering), Ryan Hensleigh (Virginia Tech Macromolecules Innovation Institute), Desheng Yao
(ME), Deepam Maurya (ME), Prashant Kumar (ME), Min Gyu Kang (ME), Shashank Priya, (ME
& Penn State’s Materials Research Institute), and Zheng.
Zheng is also an affiliate faculty member of the Department of Materials Science and
Engineering.