Märtens, O., T. Saar, M. Min, R. Land, and M. Reidla. “Fast Impedance Spectroscopy of Piezosensors for Structural Health Monitoring”. Elektronika Ir Elektrotechnika, vol. 103, no. 7, Aug. 2010, pp. 31-34, https://eejournal.ktu.lt/index.php/elt/article/view/9270.