Emerging nanofiber technology establishes tiny, self-powering sensors and actuators with compelling commercial applications

Dr. Yong Shi of the Mechanical Engineering Department at Stevens Institute of Technology is a pioneer in the fabrication and control of Piezoelectric (PZT) fibers at the nanoscale. He has inventively combined techniques and materials to arrive at a unique and useful technology, for which he has recently been awarded US Patent 8,093,786: Piezoelectric Composite Nanofibers, Nanotubes, Nanojunctions/ Nanotrees.

Dr. Yong Shi“Dr. Shi’s innovations are ingenious and enterprising,” says Dr. Christos Christodoulatos, Associate Provost of Academic Entrepreneurship. “His far-reaching expertise and boldness of vision to synthesize these PZT nanofibers will mark the genesis of a new segment of the multi-billion dollar market for piezoelectric materials.”

Piezoelectric materials accumulate electrical charge in response to mechanical pressure. This property allows them to be used both as sensors (which convert motion into electric signals that record or detect motion) or actuators (which convert electric energy into mechanical work). However, existing PZT materials break easily because of their rigid structure. Dr. Shi has patented the process of transforming ceramic piezoelectric material into nanofibers, which are strong but also provide more design flexibility, thus expanding the possible sensing and actuating applications. As a nanoscale fiber, the materials are flexible and damage-resistant, much like how glass is light and strong in fiber form but brittle on a larger scale.

Dr. Shi demonstrates that the nanoscale fibers preserve and even enhance piezoelectric properties, and the potential applications are wide-ranging. Sensors built upon the PZT nanofiber technology can be used to monitor aircraft or bridges for structural fatigue in real time. Because the sensors can also harvest and store energy, they could power themselves indefinitely, eliminating the need for external power or a battery. Mechanical energy could potentially be gathered from heartbeats or body motion to create a self-powering pacemaker. In the future, clothes woven with a combination of thermoelectric and piezoelectric fibers could harvest energy from movement for athletic or military applications.

The PZT nanofibers are well-suited to sensing and actuating applications because of their unique structure. They are composed of several elements in ion form (having a net positive or negative electrical charge). When force is applied, the positions of the elements shift, releasing electricity, which can be measured to establish the sensing capability. Conversely, researchers can apply electricity, forcing the ions and the structure itself to move, thus establishing the actuating functionality.

Dr. Shi ingeniously extracts the PZT nanofibers from the raw material with a well-known technique called electro-spinning. Researchers put the PZT material in an organic solution and then apply an electric field to generate the nanofibers. The nanofibers are then placed in a special-purpose oven at high temperatures to complete the fabrication process.

“This advance will unlock numerous opportunities for commercialization of PZT technology,” says Dr. Michael Bruno, Dean of the Charles V. Schaefer, Jr. School of Engineering and Science. “It dramatically enhances the science of piezoelectric materials and builds a new foundation for future research.”

Dr. Shi is also designing PZT nanotubes with electrodes on their internal/external surfaces that act as standalone actuators and sensors. They can change their position, morphology or configuration in response to an electric field, mimicking the micro-environment of a cell in vitro and potentially promoting cell growth or aiding in the repair of a damaged neuro-network.

“Dr. Shi is a pioneering researcher and innovator who successfully imparts these qualities to the students in his lab,” says Dr. Costas Chassapis, Deputy Dean of the School of Engineering and Science, and Director of the Department of Mechanical Engineering. “His patented technology will lead to new avenues for entrepreneurship.”

Dr. Shi continues to pursue even more applications with the aid of collaborators and students. “The work of master’s and doctorate students has been essential to the development and application of the nanofibers,” he says. “The active role of students in research at Stevens fosters a culture of innovation and entrepreneurship.”

Dr. Shi is the head of the Active Nanomaterials and Devices Lab at Stevens. He was also recently awarded a grant from the National Science Foundation for his project, “MEMS Umbrella-Shaped Actuator with Active Structure for Medical Applications.”

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