3 August 2001 High-frequency noncontact ultrasonic analysis of materials: introduction and applications
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Abstract
High frequency Non-Contact Ultrasonic (NCU) analysis of materials has been a persistent dream of materials engineers and scientists. However, a natural impediment to NCU is the exorbitant acoustic impedance mismatch between air and the test materials. The magnitude of this obstacle is further exacerbated in the Megahertz frequencies, necessary for high resolution, detectability, and sensitivity. This air- material acoustic impedance barrier has been successfully broken by virtue of our phenomenally high transduction piezoelectric transducers (from 100 kHz to 5 MHz) and equally high sensitivity non-contact analyzer (> 150 dB dynamic range and nano-second time-of-flight accuracy). It is now possible to transmit ultrasound in virtually all materials and all states of matter (with the exception of vacuum) without any contact with them. Unlike the conventional contact ultrasound, with NCU, characterization of materials is easy in the early stages of their formation and processing. This includes powders, green ceramics, consolidated powder metals, composite pre-pregs, and polymerization process. In this paper we provide a systematic introduction to the significant of materials characterization, NCU transducers and an analyzer. Also provided are a number of examples of NCU analysis of a wide range of materials, including their internal and surface characteristics. Materials are characterized for thickness, velocity (density and mechanical properties), microstructure, delaminations, defects, etc.
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Mahesh C. Bhardwaj, Mahesh C. Bhardwaj, Gary F. Stead, Gary F. Stead, } "High-frequency noncontact ultrasonic analysis of materials: introduction and applications", Proc. SPIE 4336, Nondestructive Evaluation of Materials and Composites V, (3 August 2001); doi: 10.1117/12.435556; https://doi.org/10.1117/12.435556
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