Phenomenal advancements in non-contact ultrasound for composites characterization

摘要

Ultrasound for materials characterization has greatly progressed in recent decades. However, its modus operandi has been stagnant, at the very least. Conventional ultrasound is still stifled by the contact of transducer with the test medium. While Non-Contact Ultrasound (NCU) is highly desirable, in reality it is a very complex task. Not only does the enormous acoustic impedance mismatch between the coupling air and the test medium make NCU a difficult task, but the problem is further exacerbated at the high frequencies necessary for advanced NDE. In pursuit of NCU, piezoelectric transducers characterized by phenomenally high sensitivity in air have been developed (U.S. and international patents, pending). Consequently, it is now possible to propagate MHz frequencies through materials without any contact with them. Accompanying this is the development of an NCU analyzer that presents significant information about materials, such as velocity, thickness, density, delaminations, defects, microstructure, anisotropy, imaging, and more. Besides an introduction to NCU, in this paper we also present NDE applications for fibrous and particulate composites at various stages of processing and manufacturing.