W. PAJEWSKI, P. KIEŁCZYŃSKI, and M. SZALEWSKI, “Radiation of piezoelectric rings into the air through cylindrical waveguides”, Arch. Acoust., vol. 20, no. 4, pp. 361–372, Jan. 2014, Accessed: Apr. 26, 2025. [Online]. Available: https://acoustics3.ippt.pan.pl/index.php/aa/article/view/1276