## 4 Conclusions  
This paper presents three types of dry polarizable bioimpedance sensors, based on conductive polymer, PPY and hybrid nanocomposite PPY-Ag, with 10 and 20% Ag incorporated in the PPY matrix as sensitive materials, developed for electric bioimpedance measurements. The conductive polymer PPY was synthesized by chemical oxidative polymerization using FeCl\({}_{3}\)\(\times\) 6H\({}_{2}\)O like oxidizing agent in molar ratio polymer/oxidizing agent 1:2.33. For hybrid composites synthesis Ag/PPY, the colloid solution of Ag NPs was introduced in the pyrrole solution, followed by polymerization. The structure and morphology of the sensitive materials were assessed through a series of investigative methods, and it was found that the introduction of Ag NPs in the PPY leads to the formation of silver clusters covered by PPY, similar to a core-shell structure. In addition, an amorphization of the polypropylene should be considered in the presence of Ag NPs. From Raman spectra are resulted that a first important band appears at 1605 cm\({}^{-1}\), representing the vibration mode of the C=C bonds. The second band appears at 1321 and 1331 cm\({}^{-1}\) attributed to the stretching mode of the pyrrole ring and the third important band appears at 1040-1054 cm\({}^{-1}\), determined by the plane deformation of the C-H bond. For PPY, ATR FTIR spectra identified the functions: the peak at 780 cm\({}^{-1}\) is attributed to C-H out of plane of polypropylene ring, the peak to 1040 cm\({}^{-1}\) represents N-H in plane deformation, the peak located at 1186 cm\({}^{-1}\) is assigned to C-N stretching vibration. Ag NP's introduction into the PPY structure leads to some PPY FTIR characteristic bands' displacements, indicating specific interactions between Ag NPs and the PPY functional groups, especially those in the N-H group region. The SEM images show a classic polypyrrole structure consisting of globular units with average dimensions around 400 nm formed by the collision of smaller globular formations with average dimensions around 200 nm. In the cases of 10%Ag/PPY and 20%Ag/PPY hybrid nanocomposites the PPY covers the silver nanoparticles, as in the core-shell structure. Figure 20: Impedance fluctuation of polydimethylsiloxane (PDMS)-based flexible dry electrode with different area (13 pins, 16.59 cm\({}^{-1}\) and 21 pins, 10.27 cm\({}^{-1}\)) on forehead (adapted from [46]). In making the bioimpedance electrodes, the polypyrrole and Ag/polypyrrole hybrid nanocomposite powders were pressed in disk format. A layer of conductive silver paste on one side of the obtained disks was deposited. Each of the disks thus obtained are arranged on another silver disk of the same diameter. For obtaining the dry polarizable electric bioimpedance sensor, two electrodes arranged at 6 cm from each other were used. The electrical connection is making from the opposite side of each silver disk. The values obtained for the impedance of the electrode, for all the polymeric materials used, were much lower and almost constant in relation to the total bioimpedance (impedance measured for skin bioimpedance in series with two electrodes impedance), for the whole spectrum of frequencies. For this reason, the conclusions regarding the total bioimpedance can be considered true also for the skin bioimpedance in the first approximation. The skin electric bioimpedance measurements were performed at two points, by using the dry polarizable electric bioimpedance sensor made of two bioimpedance electrodes, glued on an adhesive strip, and applying a sinusoidal voltage of 2 V\({}_{\text{peak-peak}}\), in the frequency range of 1-300 kHz, at room temperature. The electric bioimpedance measurements were performed on six human subjects, both men and women, between 32 and 59 years old. For all cases, the bioimpedance decreased with frequency, more pronounced in the case of males. At the low frequency of 1 kHz, the bioimpedance values ranged between 16-65.7 k\(\Omega\) for male subjects and 58.7-155 k\(\Omega\) for female subjects.