## 4 Conclusions
The measurement of the useful signal can be influenced by noise. In the case of measurements of the useful signal in order to obtain total electric bioimpedance by using a precision LCR meter, AGILENT E4980 A type, the measuring probe TL09A ensured an accuracy of 1%. However, to develop ECG equipment that uses the dry polarizable electric bioimpedance sensors made with sensitive materials 10%Ag/PPY or 20%Ag/PPY hybrid nanocomposite it was necessary for the useful signal to be taken in differential mode and the input impedance to be of MM values. The problem of shielding and filtering the signal by using bandpass filters must also be solved. Both AgNPs/PPY hybrid nanocomposites presented a tendency to decrease the measured skin bioimpedance with frequency, but compared to the behaviour of PPY, the bioimpedance values were higher due to the obstruction of the polymer electron gaps by Ag NPs. For hybrid nanocomposites 10%Ag/PPY and 20%Ag/PPY the results obtained indicate the best tendency of quasi-linear decrease of the electric skin bioimpedance with frequency compared to the PPY material. For the nanocomposite 20%Ag/PPY, the tendency of decreasing the electric skin bioimpedance with frequency was observed but compared to the behaviour of PPY and 10%Ag/PPY the electric skin bioimpedance values were higher, because a higher quantity of Ag NPs inserted in polymer obstructs the hopping of electrons in polymer. The importance of measurements for skin bioimpedance is given by the possibility of performing studies related to monitoring wound healing in post-operative phases. The results obtained indicate that both sensitive materials the hybrid nanocomposite 10%Ag/PPY and 20%Ag/PPY can be considered for obtaining the bioimpedance sensors. Future developments will study the possibility of using the dry polarizable electric bioimpedance sensors at frequencies lower than 100 Hz as well as higher than 300 kHz, in order to take over the signals of the ECG (electrocardiogram), EMG (electromyogram) and EEG (electroencephalography) types. These studies and further developments will be performed for a larger number of subjects and will involve statistical data processing. [PERSON] performed the synthesis of the polypyrrole (PPY), made three types of dry polarizable electric bioimpedance sensors and provided the first draft of the paper while the other authors contributed technical input in their areas of specialty. [PERSON] performed the conceptualization and investigation activities, provided the guidance for the analysis and the design of the experiments, performed the experiments, analyzed the data and supported the design of the three types of dry polarizable electric bioimpedance sensors. [PERSON]-[PERSON] performed the RAMAN spectrometry, the FTIR spectroscopy and provided the present draft of the paper. These first three authors have an equal contribution and are considered the principal authors. [PERSON] performed the synthesis of the sensitive material 10%Ag/PPY and 20%Ag/PPY hybrid nanocomposites. [PERSON] performed the SEM microscopy and elemental analysis EDX. All authors have read and agreed to the published version of the manuscript. This research was funded by the Romanian Ministry of Education and Research grant number 46N/2019, PN19310301 and The APC was funded by the authors of the paper. This study did not require ethical approval. Informed Consent Statement: Informed consent was obtained from all subjects involved in the study. This work was financially supported by the Romanian Ministry of Education and Research, Program NUCLEU, Contract 46N/2019, PN19310301, \"Complex Bioimpedance Measurement System as Support for Vital Function Monitoring and Development of Cardiovascular Impedance Clinical Techniques\", signed with National R&D Institute for Electrical Engineering ICPE-CA. The authors declare no conflict of interest.