FRACTAL CHARACTERIZATION OF ULTRASONIC SIGNALS FROM POLYCRYSTALLINE MATERIALS

For the first time the concept of fractal geometry is introduced to characterize discrete time domain ultrasonic signals scattered from polycrystalline materials aluminium and brass using the pulse echo method. The fractal dimension of these scattered signals was evaluated using the box counting method and power spectral method. These signals possess unique fractal dimension which remains invariant with the change in sampling rate of signal capturing. The fractal dimension evaluated by the above two methods remains constant in case of aluminium but gives remarkably different values for brass. This observation is interpreted on the basis of the variation of scattering mechanism in these two materials.