Automation of ultrasound velocity scanning for concentrated dispersions

Abstract

There have been a number of reports of the scanning of concentrated emulsion and suspension systems to obtain ultrasound velocity profiles which are subsequently converted to concentration profiles. These have contributed significantly to the understanding of sedimentation and creaming behaviour. The systems described have generally required manual intervention to measure the ultrasound velocity at each vertical level. For scans which can possess upwards of 100 individual measurements, each taking a significant time (minimum 30 s), the approach is tedious and limiting for dynamic systems. This paper describes an approach to an automated system which utilises an inherently highly accurate ultrasound velocity measuring technique, the sing-around technique. The method is modified to deal with problems of variable ultrasound attenuation and interference, which potentially present some limitations to the application of even the sing-around technique. The result is a “black box” which provides the basis of an automated ultrasound velocity scanner system without the need for relatively expensive signal generation equipment. The results obtained in terms of concentration profiles compare well in terms of volume fraction values with the established manual technique, with each scan point being obtained at least an order of magnitude faster than by the manual technique. Measurement of times of flight to within 1 ns in 30 μs is possible using the modified sing-around approach, compared with 5 ns in 30 μs for the manual pulse comparison technique.