TIME-DELAY AND PHASE-SHIFT MEASUREMENTS FOR ULTRASONIC PULSES USING AUTOCORRELATION METHODS

At the interface between two media, a monochromatic ultrasonic pulse separates into two waves, a reflected one and a transmitted one. A simple hypothesis is to consider the phase shift, introduced by the reflection, as equal to 0 or pi. But, in many cases, it becomes necessary to know the phase shift precisely. This is done by a Fourier analysis of the different signals. This article deals with mathematical methods that can be used for time and/or phase shift measurements. A new method, based on an analysis of the anaLytic signal of the autocorrelation function, is described and compared to existing phase slope and autocorrelation methods. An application of this method is given in the case of a ''long bar'' mode propagation at the interface between alumina and glass.