Medina, L., E. Moreno, G. González, and L. Leija. “Circular Ultrasonic Transducer Characterization: Theoretical and Experimental Results”. Revista Mexicana De Física, vol. 49, no. 6, Jan. 2003, pp. 511-0, https://rmf.smf.mx/ojs/index.php/rmf/article/view/3203.