Abstract:

In this paper an application of spatio-temporal array signal-processing techniques applied to broadband ultrasonic data gathered from a pulsed laser system is discussed. Using a laser source to heat a material specimen under test for flaws, a spatio-temporal processor capable of estimating the displacement field of the specimen is applied. The peak surface displacement is displayed as an image showing the initial source (displacement field) propagating throughout the material as well as any flaws (scatterers) that may be present within the specimen. Clearly, this method of imaging enables a unique methodology for nondestructive evaluation (NDE). Here, a pulsed laser generates an acoustic (ultrasonic) wave by heating the material and causing thermoelastic expansion. The resulting ultrasonic wave propagates throughout the material and is receied by an array of interferometers created synthetically. Assuming a spherically propagating wave field, the processor creates an image of the field by estimating the peak surface displacement at a given location. The resulting image displays valuable information about the material and its inherent flaws, providing an effective method of nondestructive evaluation. In this work, the results are shown of applying this method to data synthesized from a sophisticated thermoelastic simulation and specimen available in the laboratory are tested.