Vjera Krstelj

Contribution to classification of buried objects based on acoustic impedance matching.

Determination of material the buried objects are made of could contribute significantly to their recognition, or classification. This is important in detecting buried antipersonnel landmines within the context of humanitarian demining, as well as in a variety of other applications. In this article the concept has been formulated of the approach to buried objects material determination starting with ultrasonic impulse propagation analysis in a particular testing set configuration. The impulse propagates through a characterized transfer material in such a way that a part of it, a reflected wave, carries the information about the buried objects surface material acoustic impedance. The limit of resolution capability is theoretically analyzed and experimentally evaluated and the influencing factors described. Among these, the contact between clean surfaces of the transfer material and buried object is emphasized.

Mathematical modeling of disk reflector response as a contribution to the in situ ultrasonic inspection

The possibility of mathematical modeling of ultrasonic beam, the most influencing factor in the ultrasonic methods in quality control of materials and constructions, is considered. We have focused attention on the distribution of acoustic energy in inspected material, since a reliable estimate of the reflector size is possible only if the former is known. In the experimental part we used an ultrasonic pulse-echo method and piezoelectric probes, as well as two basic types of reflectors that cross the ultrasonic beam and the reflectors that are within the beam, as representative for the flaw in inspected materials. In the modeling we have included real in situ conditions and factors influencing the results, and the results were selected using the proposed optimal criteria.