Abstract

Excitation of ultrasonic waves can be done by numerous methods that induce time-dependent elastic deformation or pressure whereas receiving such waves requires means of converting time dependent displacements to an electric signal. Since piezoelectric crystals are offering a low cost, highly effective actuator/sensor materials they remained for many years the leading form of ultrasonic transduction. The most widely used commercial piezoelectric material is the various phases of lead zirconate titanate (PZT). Unfortunately, ceramic transducers are fragile and it is very difficult to produce them in large sizes. Further, these piezoelectric materials have a relatively high acoustic impedance requiring a complex damping and matching techniques to induce broadband signals. Polymer piezoelectric materials have been known to exist since the end of the twenties but the discovery of Polyvinylidene Fluoride, during the sixties, made them useful for commercial ultrasonic transducer applications. Piezoelectric polymers are associated with a low noise and inherent damping that makes them very effective receivers as well as broadband transmitters for high frequencies tasks. This paper reviews polymer piezoelectric materials, the origin of their piezoelectric behavior and their applications to ultrasonic NDE.

Content |Full Text|

INTRODUCTION - PIEZOELECTRIC SENSORS AND ACTUATORS
PIEZOELECTRIC POLYMERS
ORIGIN OF PIEZOELECTRICITY IN PVDF
SOME APPLICATIONS OF PIEZO-COMPOSITE PRODUCTS IN THE FIELD OF N.D.T
CONCLUSION
ACKNOWLEDGEMENT
REFERENCES

Authors:

Dr. Yoseph Bar-Cohen is a physicist with over 25 years experience in NDE, sensors and electroactive materials. He is a Technical Staff and the NDE/Advanced Actuators Principal Investigator at the Science and Technology Development Section of the Jet Propulsion Laboratory, Pasadena, CA.
Dr. Bar-Cohen received his Ph. D. in Physics (1979) and M.Sc. in Materials Science (1973), both from the Hebrew University at Jerusalem in Israel.
Dr. Bar-Cohen is the Editor of the NASA NDE Working Group (NNWG) Newsletter and in 95/96 he was the Chair of NNWG. He is an Adjunct Professor at the Department of the Mechanical and Aerospace Engineering, the University of California, Los Angeles (UCLA) and an Advisor for the NRC Research Associateship Program. He is also a Fellow of ASNT.
E-mail: yosi@jpl.nasa.gov
Home Page: NASA NDE Working Group

Dr. Tianji Xue is a Postdoc at the Jet Propulsion Laboratory (JPL), Pasadena Ca. He joined the NDE & Advanced Actuators Team in June, 1996 after he completed the requirements of his Ph. D. degree. Xue received his BS degree in Optical Engineering from the Beijing Institute of Technology, and his MS and Ph.D. degrees in Electrical Engineering from Iowa State University.
Xue has experience in ultrasonic wave propagation with application to nondestructive evaluation semiconductor and thin film devices design and characterization; optical system design, image formation and processing; and numerical modeling of electromagnetic. At JPL, Xue is working on NDE of Composites as well as the development of electroactive polymers for muscle actuators.

Dr. Shyh-Shiuh Lih is a mechanical engineer and a Member of the Technical Staff at the Technical Staff at the Science and Technology Development Section, JPL. He joined the NDE and Advanced Actuators Team at JPL in 1995. He is active in research and development of piezoelectric actuators and nondestructive evaluations (NDE) techniques for space applications.
Dr. Lih has been a Research Engineer at the Mechanical, Aerospace and Nuclear Engineering Department, UCLA from 1992-1994. His technical expertise are dynamic response of piezoelectric actuators, composite materials and structures, NDE of materials, adhesive joints and thin films, mechanics of advanced materials, finite element analysis, and modeling and analysis of aerospace structures and components.
Dr. Lih has been a consultant at JPL from 1993 to 1995, where he developed and performed a series of ultrasonic experiments to characterize the elastic properties of composite materials, adhesive joints, and damping of materials and demonstrated that the calculated wave forms based on the suggested models are in remarkable agreement with laboratory data.