Characterization of Fiber-Waviness in Composite Specimens using Deep Line-Focus Acoustic Microscopy

Abstract

A line-focus transducer used as the transduction element in an acoustic microscope forms the basis of a powerful materials characterization tool. When such a transducer is excited with rf-burst signals the transducer output voltage V exhibits strong amplitude variations which are related to the transducer’s defocus distance z, that is, the distance between the transducer’s focal point and the sample surface. These amplitude variations result from the interference between the leaky surface wave and the direct-reflected wave from the surface of the specimen. Analysis of such V(z) curves permits determination of the wavespeed and attenuation of the surface wave which is the basis of the materials surface characterization measurement. Developed by Chubachi and Kushibiki [1] the line-focus beam has been used by a number of investigators to detect and characterize material anisotropy and stresses. Using a small aperture and high f-number lens as well as high-frequency excitations, the system is capable of high spatial resolution on a specimen. It forms the basis of an acoustic microprobe for determining near-surface material properties. Scanning the transducer permits the map** of material properties over a region of the specimen, cf. [2]-[6].