Experimental measurement for assessing pseudo-sound effect in parametric array

The parametric array that generates narrow beams at low frequencies with apertures shorter than the wavelength and has been widely investigated when measuring the acoustic characteristics of materials, such as sound transmission and reflection properties. Because the parametric array utilizes nonlinear interaction across the frequency components, nonlinear phenomena arise in both the acoustic medium and the hydrophone. The unwanted nonlinear sound generated in the hydrophone and instrumentation is termed pseudo-sound. This work devised an experiment to measure the pseudo-sound for the purpose of isolating the “real” nonlinear difference frequency sound from the total nonlinear sound. Experimental results were validated by comparing its results with the pseudo-sound measured with a truncator (i.e., acoustic filter) to identify hydrophone nonlinearity.