Acoustic nonlinear parameter measurement in solid with a contact phase modulation method

In this work, a new method to measure in contact the nonlinearity parameter β of solid plates is presented. This method is based on an idea developed by Barriere and Royer (2001) to measure the nonlinearity parameter in liquids. A high frequency (HF) tone-burst signal of 20 MHz is inserted in the material by a contact-transducer (with a suitable coupling). A low frequency (LF) pulse (2.5 MHz) is applied to the other face, in the opposite direction, such that the nonlinear interaction of the two waves takes place during the back propagation toward the HF transducer. This collinear interaction creates a phase modulation of the HF tone-burst which is directly proportional to the β coefficient and the particle velocity of the LF wave. To determine this particle velocity a self reciprocity calibration of the contact LF transducer is used, as proposed by Dace et al. (1991). A numeric phase demodulation has been performed, giving the beta coefficient of the sample. The proposed method is validated by nonlinearity parameter measurements in Fused Silica.