Approach to nonlinearity parameter in liquids calculation based on the scaling theory of thermodynamic fluctuations

The nonlinearity parameter B/A is a characteristic of liquids and soft matter, which gains growing attention due to its sensibility the composition materials. This makes it prospective indicator for nondestructive testing applications based on ultrasound sounding suitable variety from physic chemistry biomedical studies. At same time, thermodynamic definition requires extensive measurements at elevated pressures that are not always available; in addition, there known certain contradiction such data with obtained by methods nonlinear acoustics. Objective. In this work, we consider recently proposed approach prediction speed sound high pressures, uses property invariance reduced pressure fluctuations normal ambient only. method generalises classic Nomoto model, however gives only qualitative picture, results quantitative correspondence experimental values within their range uncertainty. Methods. Analytical theory applied parameters equations acoustics as well numerical simulation COMSOL Multiphysics® environment. Results. Expressions calculating acceptable accuracy were using atmospheric pressure. Numerical calculations performed toluene. discrepancy between via acoustic routes analysed solution Westervelt equation; revealed deviation emerges when effects absorption finite-amplitude waves properly taken into account.