Quantitative assessment of ultrasound-induced resistance change in saline solution

The purpose of the study was the experimental assessment of the interaction coefficient characterising the influence of pressure on the conductivity of electrolyte solutions. Pressure pulses were applied to samples of 9 gl⁻¹ sodium chloride contained in cuboid measurement cells of identical cross-sectional dimensions but different thickness along the acoustic beam axis. The magnitude of the changes induced in cell resistance was recorded for three values of applied pressure increment (ΔP=0.94, 1.39 and 1.78MPa) and three values of cell thickness (e=0.58, 1.13 and 1.62mm). A thick, focused transducer generated short (0.1μs), unipolar pressure pulses. A model accounting for the characteristics of the pressure pulse and the geometry of the measurement cell was developed to predict the ultrasound-dependent changes in the measured electrical resistance. Despite some discrepancy between theoretical and experimental results, discussed in the paper, the results validated the order of magnitude of the interaction coefficient (10⁻⁹ Pa⁻¹). The predictions varied from about 50% (e=1.62 mm, ΔP=0.94MPa) to 77% (e=0.58mm, ΔP=1.78MPa) of the experimental values.