Quantitative methods in acoustic microscopy

An overview of current methods is provided. Two well-established methods of quantitative analysis are the line-focus-beam system for measuring the velocity and attenuation of leaky surface acoustic waves, and the inversion of the complex-valued V(z) to yield the reflectance function. Now at least three other methods are available. The first involves the use of very short pulses to resolve echoes from different interfaces or from different interactions with the specimen. The Fourier inversion of V(z) has been extended to signals measured through a diode detector, from which the phase information has therefore been lost. A phase retrieval method based on the Gerchberg-Saxton algorithm enables the complex reflectance function to be reconstructed from a modulus only V(z), and the results seem to reproduce the phase change around the Rayleigh angle rather faithfully. Finally, the analysis method used for the line-focus-beam system has been generalized for spherical lenses, and results have been obtained with isotropic materials at frequencies up to 1.5 GHz