Ultrasonic broadband characterization of a viscous liquid: methods and perturbation factors

The perturbation factors involved in ultrasonic broadband characterization of viscous fluids are analyzed. Precisely, the normal incidence error and the thermal sensitivity of the properties have been identified as dominant parameters. Thus, the sensitivity of the ultrasonic parameters of attenuation and phase velocity were measured at room temperature in the MHz frequency range for two reference silicone oils, namely 47V50 and 47V350 (Rhodorsil). Several methods of characterization were carried out: time of flight, cross-correlation and spectral method. These ultrasonic parameters are measured at room temperature. For this family of silicone oil, the dispersion of the attenuation spectrum is modeled by a power law. The velocity dispersion is modeled by two dispersion models: the quasi-local and the temporal causal. The impact of the experimental reproducibility of the phase velocity and acoustic attenuation was measured in the MHz frequency range, using a set of ultrasonic transducers with different center frequencies. These measurements are used to identify the dispersion of the ultrasonic parameters as a function of the frequency. A first experimental and descriptive approach is developed to assess the reproducibility of the normal incidence between the acoustic beam and the viscoelastic material. Thus, the relative error on the measurements of velocity and attenuation are directly related to the angular deviation of the ultrasonic wave, as well as the sampling and signal-to-noise ratio. A second experimental and phenomenological approach deals with the effect of a temperature change, typical of a polymerization reaction. As a result, the sensitivity of the phase velocity of silicone oil 47V50 was evaluated around -2 ms(-1) K(-1).