Browsing by Subject "Materials--Microscopy."

Now showing 1 - 4 of 4

Open Access
Characterization and imaging of single layered materials by the Lamb wave lens
(1991) Değertekin, F. Levent
The Lamb wave lens, which was introduced earlier as a new kind of lens for scanning acoustic microscope, is analyzed theoretically. A simulation program capable of handling single layered materials with different material parameters and bonding conditions is developed. The validity of theory is investigated by comparing the simulation results with the experimented ones for speciidly prepared samples. Parameter sensitivity of V{f) curves are used to test the characterization ability of the lens in layered materials. Sul)surface imaging ability of the Lamb wave lens is also investigated by forming amplitude and peak frequency images of some samples.
Open Access
Data acquisition system design for acoustic microscopy
(1996) Baştürkmen, Nadir Zafer
Conventional acoustic microscopes suffer from the complexity and low speed of their scanning mechanisms. The frame rates of these instruments are low, while their cost are high. In this work, a data acquisition system for acquiring raster image data at precise positions was designed for an acoustic microscope which uses a high speed, simple, and hence low cost scanning mechanism. The design is based on a data acquisition integrated circuit which is specifically designed to be used in this system. The implementation was done in sucha way that the system can be mounted to a standard personal computer. It is possible to obtain acoustical images on the monitor of the personal computer at rates as high as 50 lines per second, using this system.
Open Access
Material characterization by using high velocity modes
(1994) Yaralıoğlu, Göksen Göksenin
Acoustic microscopy is one of the most powerful tools for non-destructive material characterization. Excited modes on the materials are responsible for the high contrast obtained in the images. However, conventional lenses suffer from multi-mode excitation. Lamb wave lens proposed earlier overcomes this difBculty. It insonifies material surface at only one incidence angle. In this thesis, material characterization ability of high velocity modes for loaded single layered materials by using Lamb wave lens is investigated. The validity of the theory is checked by comparing simulated and measured V(z) curves obtained from specially prepared sample.
Open Access
The V-Groove lens
(1994) Bozkurt, Ayhan
Primarily designed for imaging purposes, the acoustic microscope finds application in the qualitative evaluation of materials, too. The lens response as a function of defocus, which is known as the V{z) curve, is formed by the interference of various wave components reflected from the material surface. Leaky wave velocities of the material can be extracted from this interference pattern. The accuracy of the measurement is heavily influenced by the leaky wave contribution to the V(z) curve. Hence, lens geometries capable of efficiently exciting leaky wave modes need to be designed. If a particular geometry is to be used for measurements on materials exhibiting crystalographic anisotropies, it must be able to couple to modes only in a single direction, as well. The proposed V-Groove lens, combines the directional sensitivity of the Line Focus Beam lens and the efficiency of the Lamb Wave lens. The geometry is able to accurately measure the direction dependent leaky wave velocities of anisotropic materials. A new model based approach improves the accuarcy of the extracted velocities. In this study, the V-Groove lens has been analyzed theoretically. A mathematical model describing the lens response has been developed. The performance of the V-Groove lens has been tested by simulations. A new leaky wave velocity extraction algorithm based on fitting the model curve to actual curves using Nelder-Meade search has been proposed. A prototype lens has been manufactured and performance figures have been verified experimentally. The accuracy of the lens has been compared with those of other various geometries.