Simultaneous measurement of elastic moduli, attenuation, density, and thickness of a layer by ultrasonic spectroscopy using point-focus transducer

This paper presents an ultrasonic technique for simultaneous determination of the complete set of acoustical and geometrical properties of a layer embedded between two known materials using point-focus transducer, which provides a high lateral resolution. The theoretical model of the two-dimensional spectrum R_t(θ,ω) of the layer is calculated as a function of six parameters: longitudinal and transverse velocities c_i, c_t, attenuation α_i, α_t, density ρ and thickness h, which fully determined the layer properties. The experimental spectrum R_e(θ,ω) can be measured by V(z,t) technique using point-focus transducer which is verified in our previous work. By minimizing the differences between the theoretical and experimental spectra at normal and oblique incidence, the six parameters of the layer can be derived. The full set of the properties of a 250μm thick stainless steel layer immersed in water are determined using this technique as an example. This measurement technique enables precise measuring of the local full set properties of layers.