Metshein, M., T. Parve, P. Annus, M. Rist, and M. Min. “Realization and Evaluation of the Device for Measuring the Impedance of Human Body for Detecting the Respiratory and Heart Rate”. Elektronika Ir Elektrotechnika, vol. 23, no. 3, June 2017, pp. 36-42, doi:10.5755/j01.eie.23.3.18330.