Aleksandrovas, A., A. Rodriguez, L. Svilainis, M. Angel de la Casa, and A. Salazar. “Ultrasound-Based Density Estimation of Composites Using Water-Air Interface”. Elektronika Ir Elektrotechnika, vol. 22, no. 6, Dec. 2016, pp. 28 -32, doi:10.5755/j01.eie.22.6.17219.