Publications

Numerical investigations on a frequency selective surface using metalized strips deposited on high resistive silicon in a millimeter waves are presented in this paper. High resistivity Si substrate was chosen due to the very good transparence in millimeter waves. For simulations, normal incidence of millimeter waves alongside Floquet modes and ports are considered. Dependence of the frequency response with the geometrical parameters of the unit cell is discussed.

The aim of this study was to investigate the influence of new hybrid composites of TiO2 or SiO2 nanoparticles with poly(2,2'-bithiophene) on 50% cotton/50% polyester fabric and sheep skin leather surface properties. The dispersion-based newly made nanocomposites were analyzed to determine conductivity, particle size, polydispersity and Zeta potential. The finished textile and leather materials were characterized in terms of functionalization treatments performance by: surface resistivity, water contact behaviour, physical-mechanical characteristics and photocatalytic properties. SEM analysis was used to investigate the distribution of nanoparticles on the textile and leather materials surface. Textile materials treated with SiO2/poly(2,2'-bithiophene) nanocomposite with concentration 98 wt% nanoparticles of SiO2 and leather treated with poly SiO2/poly(2,2'-bithiophene) nanocomposite with concentration of 95 wt% nanoparticles of SiO2 showed lower resistivity values, confirming the conductive properties of silica. The higher photodegradation efficiency of functionalized materials has been obtained for textile material treated with poly TiO2/(2,2'-bithiophene) with concentration of 95 wt% nanoparticles of TiO2 and for leather material treated with TiO2/poly(2,2'-bithiophene) with concentration of 98 wt% nanoparticles of TiO2, respectively.

We found previously how to estimate the density of the adsorbed surface species in the case of the molecules interacting to the oxide support surface by one type of bond. Here this algorithm is developed for the case of the molecules which can be bonded to the support surface by two types of bonds. The adsorption assumptions are similar to those considered in the case of only one type of bond. The calculation is exemplified for some composites of cyanophenyl alkylbenzoates (CPnBs) (n is the number of carbon atoms in the alkyl chain) interacting with Aerosil A380. The interaction takes place by hydrogen bonding between the -OH groups or the support and the functional groups of the CPnB molecules. The estimated values of the total surface density of CPnBs agree well with those found for the composites containing related but simpler molecules.

The Polovragi Cave-Oltetului Gorge karst area is about 3 km(2) in size and is traverse by the Oltet River through a spectacular narrow gorge, which represents the natural boundary between Parang Mountains to the west and Capatanii Mountains in the east. These mountains are part of the Southern Carpathian. Focul Viu Caving Club surveyed the Polovragi Cave between 1975 and 1985. In parallel with the survey activities in the main cave developed on the first level, several smaller caves were identified on both sides of the Oltetului Gorge. These caves are located on the second and third levels, which are interrelated with different peneplanation events that occurred in the Carpathians. In 2000, Focul Viu began working in the cave again, replacing gates, removing trash, digging to open new passages, and performing underwater explorations. By the end of 2011, new passages were found in the Hope Chamber and Costin Gallery, extending the total length of the cave to 10,793 and 92 m in vertical range. The Polovragi Cave along with two other smaller caves is presented in this chapter. The Polovragi Cave is the third longest cave in the Southern Carpathians and the eleventh in Romania. One of the smaller caves hosts an important bat colony, and the other one, with 800 m of passages, hosts Ursus spelaeus bones and deposits of saltpeter. The Bones Cave (Pestera cu Oase) located on the western side of the gorge (opposite side of Polovragi Cave) at a higher elevation is an old meander of the Oltet River.

Lead zirconate titanate doped with iron and niobium (PZFNT) was prepared by conventional processing technique, solid state synthesis method. The influence of dopants on the microstructure, ferroelectric and pyroelectric properties was investigated. XRD data reveals a perovskite structure near to the lead zirconate phase. The relative density of PZFNT is approximate 90%, with average grains size of 6.45 mu m.

Barium strontium titanate (BST) ferroelectric layers were deposited on high resistivity Si substrates by Pulsed Laser Deposition and Radio Frequency sputtering. The stoichiometry was measured by using the Rutherford Backscattering technique at 3.041 MeV. For sub-THz measurements of Si samples, a new resonant method placing the sample between two flanged waveguides is proposed. In the THz range, the Time Domain Spectroscopy proved to be a reliable method. Both methods show effects due to the dielectric losses of BST in that frequency range.

Cyber security threats have escalated dramatically in the past few years, this being the main reason why the development of Internet of Things (IoT) devices was hindered and the full potential of their utility was not reached. A major step forward could be taken only by providing reliable and cheap protection against unauthorized interference from malicious users and other threats so that people can feel safe keeping their devices connected to the cloud. This paper is focused on the development of a robust cyber security solution for IoT. The device developed and presented in this paper has the capability of solving cyber security problem by using a simple and low-cost solution, that comes with the advantage of being less intrusive and easily adaptable to any Ethernet connected IoT device. The developed device has two embodiments, the first one being a simple hardware control of the communication line using a parallel channel, and the second one extending the features of the first by using the physical unclonable functions (PUF) generated by a controlled memristor for securing the data sent over the communication channel.

Ferroelectric field effect transistors (FeFETs) based on lead zirconate titanate (PZT) ferroelectric material and amorphous-indium-gallium-zinc oxide (a-IGZO) were developed and characterized. The PZT material was processed by a sol-gel method and then used as ferroelectric gate. The a-IGZO thin films, having the role of channel semiconductor, were deposited by radio-frequency magnetron sputtering, at a temperature of similar to 50 degrees C. Characteristics of a typical field effect transistor with SiO2 gate insulator, grown on highly doped silicon, and of the PZT-based FeFET were compared. It was proven that the FeFETs had promising performances in terms of I-on/I-off ratio (i.e., 10(6)) and IDS retention behavior.

High speed high pressure torsion (HSHPT) a patented new approach is proposed to fabricate nanocomposites. The goal of this work is to investigate the NiTi/NiFeGa bilayer hybrid material with nano- and submicrocrystalline structure under the influence of HSHPT. Apart from the grain refinement, the effectiveness of the joint are revealed scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The mechanical properties of the composite layers in bulk and after severe plastic deformation are investigated. Bi-layered composite disks consisting of NiTi shape memory alloy and NiFeGa - Heusler type alloy, exhibit thermoelastic structural martensitic transformation. Submicrocrystalline structure is formed in the both layers of the hybrid material. It is also ascertained significant hardening of each layer of the hybrid as a result of HSHPT. The results highlight market differences between the bulk and the hybrid and the role of severe plastic deformation on martensitic transformation.