| When a continuous or pulsed wave of ultrasound is scanned over an object an echo emanating from the object may be detected. If the echo has an irregular variation in amplitude versus position of the sound source, the resulting variation is referred to as acoustical speckle. A theory of acoustical speckle interferometry is presented which parallels the data analysis in pointwise filtering in laser speckle interferometry. Displacement measurements are made utilizing the correlation of reference and displaced ultrasonic signals. Effects of strains and rotations on the minimum of the cross-correlation function are discussed by the illustration of theoretical and experimental examples.; A computer aided data acquisition system is developed to make acoustical speckle interferograms. Computer programs, written in Fortran and assembly languages, are developed for the data acquisition experimentation and the two-dimensional cross-correlation. Several numerical and experimental examples are presented to test the theory of the displacement measurements. Experiments, using pulse-echo scanning, are used to illustrate the comparison of measured to calculated value of displacements. The experimental data analysis is also discussed. |
