★ Study of the acoustical nonlinearity of water using a variation of the finite amplitude method. ★ No need for a priori knowledge of the absorption in the material of interest. ★ No approximations related to the effect of absorption needed. ★ Direct measurements of pressure of the fundamental and that of the second harmonic. ★ Investigated the effect of transmitter–receiver distance on acoustical nonlinear parameter.
The acoustic nonlinearity of water is investigated using a variation of the finite amplitude method with harmonic generation. The finite amplitude method provides information on the coefficient of nonlinearity, β, through the ratio of the amplitude of the fundamental and that of the second harmonic. The pressure of both the fundamental, p1, and that of the second harmonic, p2, are determined experimentally at different transmitter–receiver separation distances, eliminating the need for knowledge of the sound absorption in the medium. It was found that the experimental relationship between the slope of p2(x)/Symbol(x) and transmitter–receiver separation distance, x, follows a linear relationship only in the near-field, in good agreement with theoretical predictions. A β of 3.5 ± 0.1 is determined for water at room temperature, in good agreement with previous results from both the isentropic equation of state and finite amplitude method.