High frequency sound waves can be used to discriminate and quantify some basic mechanical, structural, or compositional
properties of solids and liquids. Ultrasonic material analysis is based on a simple principle of physics: the motion of any
wave will be affected by the medium through which it travels. Thus, changes in one or more of four easily measurable
parameters associated with the passage of a high frequency sound wave through a material -- transit time, attenuation,
scattering, and frequency content -- can often be correlated with changes in physical properties such as hardness, elastic
modulus, density, homogeneity, or grain structure in metals, plastics, ceramics, and composites. Eddy current instruments
that monitor conductivity can be used to verify heat treatment and to qualify alloy composition, grain size, and hardness in
metals.