Measurement of liquid density by ultrasound backscattering analysis

Abstract

The ultrasound pressure backscattered by a wire depends on the density of the liquid in which it is immersed in which ultrasound waves propagate. To express this dependence, the classic resonant scattering theory (RST) is used. This theory shows that the influence of the liquid density on the backscattering ultrasound pressure is weak in absolute value but important in relative value. So, in this paper, we propose a new method of liquid density measurement based on the relation given by the RST in a relative way. The spectrum of the ultrasound pressure backscattered by a wire immersed in a liquid of unknown density is compared to the spectrum obtained from the same wire immersed in a benchmark liquid (water). The comparison of these spectra gives a curve which is a characteristic of the relative density of the test liquid with regard to the benchmark liquid density. Experimentally, a measurement is performed in four stages and needs two different wires. The first wire allows effective measurement, the second wire is used to calibrate the instrumental chain. The four stages consist in acquiring an echo for each wire in each liquid (the benchmark liquid and the test liquid). In this paper, the theory and the methodology of the measurement are developed. Some preliminary experimental results are also presented. These results confirm the theory.