Ultrasonics: A Technique of Material Characterization

The material science and characterization is a field concerned with inventing new materials and improving previously known materials by developing a deeper understanding of properties under different physical conditions. The properties of materials depend upon their composition, structure, synthesis and processing. Many properties of materials depend strongly on the structure, even if the composition of the material remains same. This is why the structure-property or microstructure property relationships in materials are extremely important. On the basis of different physical properties, the materials are classified mainly into five categories: (a) metals and alloys, (b) semi-metals and semiconductors, (c) ceramics, glasses and glass-ceramics, (d) polymers, and (e) composite materials. Functional classification of materials includes aerospace, biomedical, electronic, energy and environmental, magnetic, and optical (photonic) materials. The structural classification of materials are of two types as (a) crystalline (single crystal and polycrystalline), and (b) amorphous. The selection of a material and the potential to be manufactured economically and safely into useful product is a complicated process. It requires the complete knowledge of constituent material not only after production but also in processing. Increased competition and need of higher productivity and better products from material producing industries are creating more stringent requirements for process and quality control. This demands the characterization of materials. The topic material characterization essentially includes the evaluation of elastic behaviour, material microstructure and morphological features, associated mechanical properties etc. The destructive, semi-destructive and non-destructive testing (DT & NDT) techniques are available for the complete characterization. These characterization techniques are the basic tool for the quality control and quality assurance of the material or component or product. Ultrasonics, which is a sub category of acoustics deals with acoustics beyond the audio limit. The application of ultrasonics falls into two categories as high frequencylow intensity and low frequency – high intensity. The low intensity application carries the purpose of simply transmitting energy through the medium in order to obtain the information about the medium or to convey information through the medium. High intensity application deliberately affects the propagation medium or its contents. So, the low intensity and high