Berktay, H.O.; Smith, B.V.: 'End-fire array of virtual acoustic sources produced by the interaction of cylindrically spreading acoustic waves', Electronics Letters, 1965, 1, (7), p. 202-202, DOI: 10.1049/el:19650185
IET Digital Library, https://digital-library.theiet.org/;jsessionid=5e1fsfpw3t4uf.x-iet-live-01content/journals/10.1049/el_19650185