Ultrasonic method of materials characterization for recognition buried objects

Among the ultrasound based NDT methods and techniques, some are used for materials characterization. In a typical situation, some of the measurable properties of a tested object’s material are used as a data set for characterization. The basis of measurements are properties of an ultrasonic pulse that can propagate through the object. In order to obtain intense enough registered ultrasonic pulse, one should have relatively low transfer losses and relatively high signal to noise ration in the system. In order to obtain large enough extractability of information about the tested object material, one should know the changes in the pulse that occur during its propagation [1]. Information about the tested object material, gained through signal processing, contains, e.g. values of the elastic constants and pulse attenuation coefficients, as well as other quantities that could not be so straightforwardly related to the ultrasound propagation properties [2]. In the context of the characterization, usually there was no differentiation among various object’s parts, based on differences in their properties. As will be shown later, one may obtain different results depending on whether the object bulk or surface response is used in characterization. Starting from the achieved level in ultrasonic based materials characterization, the approach is further being developed for the purpose of unknown, buried objects’ material type determination [2-5]. Appropriate transfer of the ultrasound pulse is essential for the ultrasound based materials characterization. In the appropriate setup, the ultrasonic pulse transfer is realized as the pulse’s propagation from the transducer to the buried object to be characterized, and back to transducer again. The signal received is a complex combination of characteristics of both the transfer entity and the characterized object. If one does not know quantitatively how much a transfer entity influences the ultrasonic pulse propagation, the possibility of the buried object characterization is drastically lowered. Therefore, the transfer entity influence on the ultrasonic pulse should be known in order to enable one to use the ultrasound for buried object materials characterization. That influence could be modeled and the object containing transfer medium appropriately designed. Following this line of thought, the ultrasound could not be used in the characterization if it propagates through a bulk of the buried object’s material, because then the object’s structure and shape would affect the pulse properties. Because of the facts presented, the ultrasonic pulse should propagate through a characterized transfer entity, and be influenced only by the surface of the buried object to be characterized.