22 January 2019
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Printed flexible sheet of piezoelectric material. Image: Virginia Tech
Piezoelectric materials can be custom-designed to convert movement, stress and strain into electrical energy
Scientists at Virginia Polytechnic Institute and State University (Virginia Tech) claim to have devised a novel technique to create piezoelectric materials using 3D-printing technology.
According to the researchers, the materials are not restricted by any size or shape and can be custom-designed to convert movement, stress and strain from any directions to electrical energy.
Piezoelectric materials are the materials that produce an electric current when placed under mechanical stress. There are several materials that demonstrate piezoelectric properties, including some proteins, bone, crystals (for example, quartz) and ceramics. This mechanism is also reversible, meaning that if an electric current is applied to a piezoelectric material, it slightly changes its shape.
Piezoelectric materials were first discovered in the 19th century. While scientists have made progress in the field of piezoelectricity in the past 100 years, some major issues hinder tapping into piezoelectricity as a practical method to produce electricity.
Producing piezoelectric materials is usually an expensive process. Moreover, such materials are made of brittle crystal and ceramic and come only in selected shapes, thereby limiting the ability to maximise the potential of the material.
The new technique developed by Virginia Tech researchers allows designing arbitrary piezoelectric constants in the material being produced. As a result, the material can produce electric charge movement in response to incoming vibrations and forces from any direction. 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," says Xiaoyu 'Rayne' Zheng, assistant professor in the College of Engineering at Virginia Tech.
Zheng explains that by programming 3-D active topology, it becomes possible to achieve almost any combination of piezoelectric coefficients within the material. The resulting material can then be used as strong and flexible sensors/transducers.
The team has also created a substitute for the natural crystal, which is currently used in fabrication of piezoelectric material. With natural crystal, the orientation of atoms remains fixed at the atomic level. The substitute created by the team mimics the natural crystal but allows for changes in the lattice orientation.
The researchers claim that they have 3D printed piezoelectric materials at a scale measuring fractions of the diameter of a human hair. Moreover, the material demonstrates five times higher sensitivities than flexible piezoelectric polymers.
The material can also be produced as a thin sheet resembling a strip of gauze.
"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 3-D printing technique has the potential to be used in robotics, creation of intelligent infrastructures, smart materials for tactile sensing, in energy harvesting and impact and vibration monitoring.
The details of the research are published in journal Nature Materials.
