Štaras, S., and A. Katkevičius. “Properties of Helical Structures Containing Periodical Inhomogeneities”.
Elektronika Ir Elektrotechnika
, vol. 99, no. 3, Mar. 2010, pp. 49-52, https://eejournal.ktu.lt/index.php/elt/article/view/9904.