The design and fabrication of high frequency poly(vinylidene fluoride) transducers

In this paper, stress and displacement fields inside a multilayered plate are analytically computed. For the theoretical modeling, individual layers of the multilayered plate are assumed to be elastic and homogeneous, but anisotropic. These theoretical computations are then experimentally verified in a qualitative manner. Experimental investigations are carried out on a ceramic composite plate that has 12 plies of fibers going in 0° and 90° directions, [0.90]\d3\i\ds. The incident angles and frequencies of the ultrasonic signal for generating different Lamb wave modes in this plate are obtained experimentally as well as from the theory. Displacement and stress fields inside the plate for some of these Lamb modes are then computed. Computation of stress and displacement fields inside the plate is useful for studying the internal damage. Internal stress distribution varies significantly from one Lamb mode to another. Hence, different Lamb modes should detect defects in different layers of the plate. The Lamb mode that produces maximum stress in a specific layer should be most sensitive for detecting defects in that layer. This is observed experimentally as well.

Guided Waves in Multilayered Plates for Internal Defect Detection

High-resolution ultrasonic methods are briefly reviewed. Special attention is paid to the principles underlying acoustic microscopy, since exactly they provide the high resolution necessary for modern technologies. Examples of acoustic images of fullerite ceramics, metals, and carbon materials are given.

High-resolution ultrasonic ultrasound methods: Microstructure visualization and diagnostics of elastic properties of modern materials (Review)

The inspection of the sliding surface and subsurface of plasma-sprayed ceramic coatings using scanning acoustic microscopy

The principle, design considerations, and operation of a C-mode, 100-MHz ultrasound backscatter microscope are described. Applications of the C-mode microscope, as well as of a new real time B-mode UBM, to the imaging of an in vitro tumor model and ocular tissue are presented. Central to these developments has been the construction of PVDF (polyvinylidene fluoride) transducers with sufficient sensitivity to detect the small backscatter signals from biological materials and bandwidth capable of giving an axial resolution of approximately 10 mu m. The lateral resolution achieved is 17.5 mu m in the C-scanner using an f/1.33 transducer and 36 mu m in the B-scanner, which uses an f/2 transducer. Future developments are also discussed. >

Ultrasound backscatter microscopy

A range of reflection acoustic micrographs that demon- strate how different contrast mechanisms can lead to images useful in materials science are discussed. The most important class of mecha- mism affecting contrast involves disturbance of the leaky Rayleigh wave propagating along the surface of the specimen. Pictures of very fine cracks (considerably smaller than the acoustic wavelength) and regions of plastic deformation can be obtained using this mechanism. The abil- ity of the scanning acoustic microscope (SAM) to image plastic defor- mation is a particularly important application to materials science be- cause there are serious limitations to existing techniques. Useful images may also be obtained in situations where Rayleigh-wave excitation does not predominate; in such cases interference between hulk waves can be responsible for the contrast observed. The conditions necessary for the production of various types of image are discussed, in terms of the elastic properties of and the boundary conditions close to the feature of interest.

S.D. Peck

Papers

Applications of the Scanning Reflection Acoustic Microscope to the Study of Materials Science