Ultrasound Spectrometry

In-situ characterization of Microstructure

The Method

Ultrasonic Spectroscopy is a unique technique in its ability to interact with material structure. At its core is the ultrasonic determination of the absolute frequency dependant velocity and attenuation of liquids and soft solids. Since ultrasonic waves are the propagation of a mechanical wave through a medium, the interaction of the wave with the material is a function of the material structure and the thermo elastic properties. Specifically in liquids this is a mechanical propagation is through a longitudinal (compression) wave

Ultrasounds great advantage is that unlike optical methods, is not limited by the opacity of the sample and is hence able to work at high concentration or in coloured liquids such as pigments. In addition the technique is sensitive particle size over a wide range of mean particle sizes approximately 10nm to 1mm. Outputs from the method include information on concentration, particle size and the rheology of the bulk.

The system is composed of a measurement module controlled from a computer (usually a PC) and a sensor fitted to a pipe. The sensor contains two ultrasound transducers which convert the signals to ultrasound energy and back again.

Interaction with Particulate Materials

As ultrasound passes through a suspension, colloid, or emulsion, it is scattered and absorbed by the discrete phase with the result that the intensity of the transmitted sound is diminished. The attenuation coefficient is a function of ultrasonic frequency and depends on the composition and physical state of the particulate system. The measurement of the attenuation spectrum is described in Part 1 (ISO 20998-1).