Resin characterization by electro-acoustic measurements

Modeling analysis of ultrasonic attenuation and angular scattering measurements of suspended particles

A combination of two models previously developed by Faran, and Atkinson and Kytömaa (Faran-AK model) was used to calculate the ultrasonic attenuation and the backscattering signal of a suspension of particles. The model of Atkinson and Kytömaa yielded the viscoelastic contributions while the model of Faran yielded the scattering contribution. A comparison with the more fundamental model by Epstein, Carhart, Allegra, and Hawley validated the combination, where the combination used here proved to be computationally less intensive and more stable. The Faran-AK model outputs were also compared with ultrasound measurements of glass beads with two different particle size distributions and varying concentrations. The comparison showed a very reasonable agreement of model and experiment.

Acoustic spectroscopy: A powerful analytical method for the pharmaceutical field?

Acoustics is one of the emerging technologies developed to minimize processing, maximize quality and ensure the safety of pharmaceutical, food and chemical products. The operating principle of acoustic spectroscopy is the measurement of the ultrasound pulse intensity and phase after its propagation through a sample. The main goal of this technique is to characterise concentrated colloidal dispersions without dilution, in such a way as to be able to analyse non-transparent and even highly structured systems. This review presents the state of the art of ultrasound-based techniques in pharmaceutical pre-formulation and formulation steps, showing their potential, applicability and limits. It reports in a simplified version the theory behind acoustic spectroscopy, describes the most common equipment on the market, and finally overviews different studies performed on systems and materials used in the pharmaceutical or related fields.

Seismoelectric effect: a non-isochoric streaming current. 1. Experiment

Propagation of ultrasound through a porous body saturated with liquid generates an electric response. This electroacoustic effect is called the "seismoelectric current"; the reverse process, when an electric field is the driving force, is called the "electroseismic current." Seismoelectric currents can be measured with electroacoustic devices originally designed for characterizing liquid dispersions. Such electroacoustic devices must first be calibrated with a liquid dispersion and then used to characterize a porous body. We demonstrated such measurements of the seismoelectric current with electroacoustic devices in three different types of porous bodies. The first porous body was a deposit of solid submicrometer particles. We monitored the kinetics of the deposit formation on the surface of the electroacoustic probe. It allowed us to unambiguously confirm that the measured signal was generated by the deposit. We were also able to extract information about the porosity of the forming deposits. The second type of porous body was again a deposit, but instead of solid submicrometer particles, we used very large, porous glass spheres. According to classical theory, these glass particles are not supposed to generate any electroacoustic signal because colloid vibration current decays with increasing particle size due to the particles inertia. Nevertheless, we measured a strong signal, which was apparently associated with the pores of the particles. We were able to derive some conclusions about the dependence of the seismoelectric current on the pore size. The last tests were performed with cylindrical sandstone cores. These porous bodies have a very high hydrodynamic resistance that prevents measurement of the classical streaming current. We are able to measure a strong seismoelectric current that correlates with porosity of the cores.