Acoustic nonlinearity parameter measurements in a pulse-echo setup with the stress-free reflection boundary.

This paper describes the acoustic nonlinearity parameter (β) determination for fluids using a pulse-echo method with the stress-free boundary. A newly derived β formula requires the measurement of the fundamental and second harmonic displacements with appropriate corrections for attenuation, diffraction, and boundary reflection. Measurements are composed of two steps: receiver calibration and harmonic generation. The β values calculated for water at several distances between the planar transducer and the water-air interface are in good agreement with literature, providing a validation for the method.