Shear viscoelasticity of ultrasonic couplers by broadband reflectivity measurements

The acoustic shear wave velocity and attenuation of ultrasonic couplers were investigated by broadband reflectivity measurements at around room temperature and 15-30 MHz. The feature of the present technique is to use impulsive pulse and normal incident waves against a reflective interface. Its characteristics are compared with the inclined incident wave technique used so far. It is found that the normal incident wave technique is nearly free from the effects of diffraction in contrast with the inclined incident wave technique. In the present work, the acoustic shear properties and their temperature dependence were investigated for nine commercial couplers at 15, 25, and 35°C. The shear wave velocity dispersion was clearly observed in every measurement in the investigated frequency range; these data are useful for design in ultrasonic shear wave experiments. Furthermore, a linear relationship was found between the rigidity and Q value for hydroxyl carbons and naphten oils. The difference in the physical properties can be attributed to differences in the chemical properties of the samples. Therefore, the present technique is useful for investigating both the macroscopic and microscopic properties of viscoelastic materials.