Ultrasonic characterization of stratified media with independent measurement of wave velocity and thickness

Ultrasonic pulse-echo systems are well established tools for non-destructive evaluation, optimal measurement design and geoacoustic inversion techniques. Distance measurements must take into account the differences in wave velocities along the propagation path. This work presents an ultrasonic method to characterize the layers of a stratified medium, from independent measurements of wave velocity (c) and thickness (Z) of each layer. The model, based on Geometrical Acoustics, includes refraction. Two transducers are used: one active (3.4 MHz) and a hydrophone as a receptor, which is moved laterally through 15 positions. The distance between the transducers and the delay between the echoes, from, the interfaces separating the layers, received by them are used to calculate c and Z. A three-layered phantom containing acrylic (Z=9.1 mm), water (Z=13.1 mm) and PVC (Z=9.6 mm) was immersed in. a water tank and tested. The experimental results for the acrylic, water and PVC layers have a percentage rms error of 2.2, 4.2 and 6.7, for thickness,. and of 2.1, 4.0 and 6.2, for wave velocity, respectively.