October 6, 2011
Stevens PZT Nanofibers Published in Advanced Materials as Frontispiece.
Keeping tabs on the condition of our public infrastructure and high-performance materials is critical, but presents many challenges to existing technologies. A recent article by researchers from Stevens Institute of Technology, led by Dr. Yong Shi, reveals a remarkable solution to this urgent problem. Their research paper demonstrates the new concept of using piezoelectric (PZT) nanoactive fiber composites (NAFCs) as embedded sensors for structural health monitoring. With support from the National Science Foundation, Dr. Shi and Mechanical Engineering graduate students Xi Chen, Jinwei Li, and Guitao Zhang have realized NAFCs offering nanoscale size, low weight, flexibility, low cost, and anisotropic sensitivity—meaning that they are sensitive to the specific direction of acoustic emission (AE) signals and therefore more accurate than current techniques.
Acoustic emission testing is one of the most popular methods currently employed to monitor the internal health of structures. By measuring specific elastic waves that emanate from imperfections within a material, AE sensors can pinpoint the location and severity of potentially perilous damage. Since these sensors operate by passively "listening" to the effects of everyday stresses, they are an ideal solution for "always-on" monitoring that can relay information about the health of a structure to a remote location.
Embedding sensors for more precise measurements is highly desired, but the current generation of sensors is simply not suitable for this application due to their size, cost, and ceramic material properties. Matters are worse due to the complexity of advanced composite structures, which have anisotropic properties that are not well resolved by traditional AE sensors. The need to power such devices for long-term use makes embedded applications even more problematic.
Dr. Shi's research team has addressed all of these issues by taking AE sensing to the nanoscale. PZT nanofibers developed by his group exhibit an extremely high piezoelectric voltage constant (g33, 0.079 Vm/N), high bending flexibility, and high mechanical strength. With added piezoelectric properties, the NAFCs have the opportunity to make self-powering devices. The team's nanofibers can produce much higher voltage and power output than other semiconductor type of piezoelectric materials. Such a nanogenerator would be excited by the acoustic waves to produce electricity, thereby powering the sensors indefinitely without batteries.
The research team has previously published papers in this subject area in Applied Physics Letters and Nano Letters.
"This technology has the potential to become a public safety breakthrough by introducing embedded intelligence into critical infrastructure such as roads, bridges, and buildings," reports Dr. Constantin Chassapis, Deputy Dean of the Schaefer School of Engineering and Science and Department Director for Mechanical Engineering at Stevens.
This exceptional set of characteristics makes the material a breakthrough for structural health monitoring, saving time, money, and lives by delivering current and precise information about the health of millions of structures worldwide.