Line-focus-beam

Fig. 8.4. (a) Wavefronts in a line-focus-beam microscope (b) structure of a line-focus-beam lens with dimensions for 225 MHz (Kushibiki and Chubachi 1985). 

In the line-focus beam analysis method, two fundamental assumptions are made regarding (8.21). First, it is assumed that the Rayleigh contribution is a perturbation on the total signal, i.e. that... 

The line-focus-beam technique with its associated analysis has been more extensively used than any other method for quantitative acoustic microscopy. 

Fig. 8.8. Analysis of line-focus-beam V(z) data for 31 different materials and orientations, compared with calculated values, (a) Normalized measured period of the oscillations in V(z) versus calculated fluid-loaded Rayleigh wave velocity the curve is eqn (8.17). (b) Normalized measured attenuation from (8.19) versus calculated attenuation the line corresponds to perfect agreement (Kushibiki and Chubachi 1985).

Anisotropic materials have been extensively measured using the line-focus-beam technique. These will be discussed further in Chapter 11, but some results are summarized in Fig. 8.8 to illustrate the range of materials over... 

Fig. 9.14. Buccal surface of human molar tooth. Rayleigh velocity and attenuation measured using a line-focus-beam lens at 225 MHz. The sketches indicate the approximate measurement angles at which the Rayleigh wave propagation was in the direction of the arrows... 

When studying a complex material such as tooth enamel it is invaluable to have accurate data on single crystals of the apatite of which it comprised. Figure 9.16(a) is a V(z) curve measured using a line-focus-beam microscope at 225 MHz, on the biggest crystal of hydroxyapatite in the world At least 12... 

Fig. 9.16. Single crystals of apatite compounds (a) V(z) measured with a line-focus-beam lens at 225 MHz (b) measured and calculated Rayleigh velocity in the surface of a hydroxyapatite crystal (c) measured and calculated Rayleigh velocity in the surface of... 

There are considerable difficulties in comparing theory and experiment even in such model experiments. The theoretical calculations are subject to the approximations inherent in the method, and also to uncertainties in the pupil function used to characterize the lens and in the two parameters used to characterize the crack. The experiments are subject to the difficulties of making a crack that is straight and flat to a fraction of the acoustic wavelength used, over the length measured by the line-focus-beam lens, and to the sensitivity of the results in some cases to small changes in x or z. Nevertheless, when all these considerations are taken into account it does seem... 

Kushibiki, J., Ohkubo, A., and Chubachi, N. (1982). Effect of leaky SAW parameters on V(z) curves obtained by acoustic microscopy. Electron. Lett. 18,668-70. [131] Kushibiki, J., Horii, K., and Chubachi, N. (1983). Velocity measurement of multiple leaky waves on germanium by line-focus-beam acoustic microscope using FFT. Electron. Lett. 19,404-5. [242]... 

Kushibiki, J., Asano, H., Ueda, T., and Chubachi, N. (1986). Application of line-focus-beam acoustic microscope to inhomogeneity detection on SAW device materials. IEEE 1986 Ultrasonics Symposium, pp. 749-53. IEEE, New York. [244]... 

Obata, M., Shimada, H., and Mihara, T. (1990). Stress dependence of leaky surface wave on PMMA by line-focus-beam acoustic microscope. Exp. Mechanics 30, 34-9. [148]... 

Yamanaka, K., Kushibiki, J., and Chubachi, N. (1984). Anisotropy detection in hot-pressed silicon nitride by acoustic microscopy using the line-focus beam. Electron. Lett. 21,165-7. [287]... 

Ganguly, S. Gao, J.Z. Application of On-line Focused Beam Reflectance Measurement Technology in High... 

A standard sealed tube has four Be windows located 90° apart around the circumference of the cylindrical body. One pair of the opposite windows corresponds to a point-focused beam, which is mostly used in single crystal diffraction, while the second pair of windows results in a line-focused beam, which is normally used in powder diffraction applications, see Figure 2.4. 

In general, the shape of the X-ray beam is chosen based on the analytical requirements. Conventional phase analysis, thin film work and high-resolution measurements typically employ a line focus beam, with a line shape elongation perpendicular to the diffraction plane. Point focus, where the beam has a point or oval shape, is typically used for texture, stress and general applications using two-dimensional (areal) detectors. 

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