Showing papers by "Ajit Mal published in 1991"
TL;DR: In this article, a leaky Lamb wave (LLW) technique was used to estimate the phase velocity and amplitude of a composite laminate in a broad range of frequencies and velocities.
31 citations
TL;DR: In this article, a measured acoustic material signature (AMS) for diamond-like films (DLFs) on silicon is used to determine the surface acoustic wave (SAW) velocity and the dispersion in the layered substrate.
Abstract: As the development of diamond-like films (DLFs) progresses and emerges from the research environment, the need for rapid, large-scale non-destructive inspection becomes ever more important. The metrology or reflectometer mode of the acoustic microscope is used to inspect the layered structure consisting of DLFs deposited on silicon substrates. A measured acoustic material signature (AMS) for DLF on silicon is used to determine the surface acoustic wave (SAW) velocity and the dispersion in the layered substrate. The variation of the measured SAW dispersion with film parameters, obtained in a completely non-destructive manner, may then be used to ascertain the film quality, such as film thickness, adhesion and texture. In the particular example of a DLF on a silicon substrate, the SAW velocity increases with frequency and film thickness (positive dispersion). The physics of the metrology mode (AMS) is described and applied to the determination of important film quantities in layered structures of gold and DLF on silicon. The measured SAW velocities of DLF on two crystalline orientations of silicon and with film thickness between 0.7 and 9.0 μm are reported at frequencies up to 600 MHz. These are compared with computed SAW dispersion based on the bulk properties of diamond. A preliminary interpretation of these results and the implications for material properties of these films are presented.
12 citations
01 Jan 1991
TL;DR: In this article, the authors combine the use of both leaky Lamb waves and polar backscattering (PBS) for material characterization, which can be used in conjunction with a C-scan system to provide images of various type of defects, or through various measurements to characterize defects and determine the material elastic properties.
Abstract: Application of composites to structural components of defect-critical systems, such as aircraft, requires adequate nondestructive evaluation (NDE) capability. NDE methods must be able to detect and characterize defects as well as determine the material properties. Various methods have been developed in recent years to support different aspects of this general need. Ultrasonic pulse-echo and through-transmission as well as radiography are widely used during manufacturing and service. By comparing the response to reference standards, these methods are used qualitatively to identify gross defects and areas with a questionable quality. This application does not take advantage of the quantitative NDE capability that has become available in recent years [see for example 1–4]. Examples of such methods are the leaky Lamb waves (LLW) and polar backscattering (PBS). Significant progress has been made in recent years in the theoretical analysis of the wave behavior in such transversely isotropic layered media. These methods can be used (a) in conjunction with a C-scan system to provide images of various type of defects [1], or (b) through various measurements to characterize defects and determine the material elastic properties [5]. Present work is directed toward combining the use of both LLW and PBS for material characterization.
4 citations