Estimation of Electrical Properties of Hidden Objects Using Microwave Signals

Pulsed excitation of a horn antenna for generating large B wideband electromagnetic pulses was used. The antenna was excited by electrical pulses with rise time of 200 ps and pulse voltage of 15 V. The spectral properties of the electromagnetic pulses were investigated using different wide band antennas and (0 – 18) GHz passband sampling oscilloscope. It was found that the signal spectra is wide and ranges from 0.3 GHz to higher than 12 GHz. Hollow cylinders made from opaque for visible light materials were used to hide other cylinders with certain electrical properties. To reveal their presence we employ the electromagnetic pulses. Transmitted through and reflected from investigated objects pulses were received by several antennas having different frequency ranges and detected to obtain needed information. The experiments show that analyzing this information leads to conclusions about the presence of the object and its electrical properties. This methodic supposedly can be employed to disclose electrical properties of objects having complex electrical properties if broadband amplifiers and digital oscilloscopes are used. DOI: http://dx.doi.org/10.5755/j01.ms.20.2.6331</p

Reflecting and Polarizing Properties of Conductive Fabrics in Ultra-High Frequency Range

The system based on ultra-wide band (UWB) signals was employed for qualitative estimation of attenuating, reflecting and polarizing properties of conductive fabrics, capable to prevent local static charge accumulation. Pulsed excitation of triangle monopole antenna of 6.5 cm height by rectangular electric pulses induced radiation of UWB signals with spectral density of power having maximum in ultra-high frequency (UHF) range. The same antenna was used for the radiated signal receiving. Filters and amplifiers of different passband were employed to divide UHF range into subranges of 0.3-0.55 GHz, 0.55-1 GHz, 1-2 GHz and 2-4 GHz bands. The free space method, when conductive fabric samples of 50x50 cm2 were placed between transmitting and receiving antennas, was used to imitate a practical application. Received wideband signals corresponding to the defined range were detected by unbiased detectors. The fabrics made of two types of warps, containing different threads with conductive yarns, were investigated. It was estimated attenuation and reflective properties of the fabrics when electric field is collinear or perpendicular to thread direction. In the UHF range it was revealed good reflecting properties of the fabrics containing metallic component in the threads. The system has advantages but not without a certain shortcoming. Adapting it for specific tasks should lead to more effective usage, including yet unused properties of the UWB signals.</p

Phase separation and microwave response of epitaxial and polycrystalline manganite films

The resistance, magnetoresistance, and resistance response under microwave irradiation (f=10 and 35GHz) were measured for epitaxial and polycrystalline La 0.67 Ca 0.33 MnO 3 and La 0.67 Sr 0.33 MnO 3 thin films in the temperature range 78÷300K. The microwave induced resistance increase observed for the epitaxial films in a narrow temperature range below the ferromagnetic to paramagnetic transition temperature T c certifies coexistence of low resistance (ferromagnetic) and high resistance (paramagnetic) regions in the manganites. Resistance of polycrystalline films decreased under microwave irradiation in a wide temperature range below T c . The effect was explained in terms of microwave assisted hopping of carriers in high resistance regions formed at grain boundaries of the polycrystalline films

Recent Progress in Perovskite Tandem Solar Cells

Tandem solar cells are widely considered the industry’s next step in photovoltaics because of their excellent power conversion efficiency. Since halide perovskite absorber material was developed, it has been feasible to develop tandem solar cells that are more efficient. The European Solar Test Installation has verified a 32.5% efficiency for perovskite/silicon tandem solar cells. There has been an increase in the perovskite/Si tandem devices’ power conversion efficiency, but it is still not as high as it might be. Their instability and difficulties in large-area realization are significant challenges in commercialization. In the first part of this overview, we set the stage by discussing the background of tandem solar cells and their development over time. Subsequently, a concise summary of recent advancements in perovskite tandem solar cells utilizing various device topologies is presented. In addition, we explore the many possible configurations of tandem module technology: the present work addresses the characteristics and efficacy of 2T monolithic and mechanically stacked four-terminal devices. Next, we explore ways to boost perovskite tandem solar cells’ power conversion efficiencies. Recent advancements in the efficiency of tandem cells are described, along with the limitations that are still restricting their efficiency. Stability is also a significant hurdle in commercializing such devices, so we proposed eliminating ion migration as a cornerstone strategy for solving intrinsic instability problems

A Method for Measuring the Specific Electrical Conductivity of an Anisotropically Conductive Medium

The paper deals with the ways of finding an electrical conductivity tensor of a plane and anisotropically conductive sample. Application of the Van der Pauw method to investigate the conductivity of anisotropically conductive media makes the basis of research. Several models of distribution of the electric field potential are presented, their merits and demerits are discussed, and the necessary physical measurements are indicated. On the basis of these models, the respective calculation expressions of the specific conductivity tensor are derived and algorithms for their realization and error calculation are developed

Įmagnetintų puslaidininkių ir feritinių bangolaidžių tyrimas

In this paper we describe the method that allowed us to arrive at a dispersion equation for the electrodynamical analyses ofopen layer cylindrical gyrotropic waveguides. We numerically investigated dispersion characteristics of longitudinally magnetized semicon-ductor p-Ge and n-lnSb waveguides at several free charge carrier concentrations A for several modes. We analyzed the n-lnSb waveguide's dispersion dependences on the extemal constant magnetic field strength. We also analyzed cutoff frequency dependences of the main HE i and the first higher mode EH i on the IV. We discovered that the vvaveguide wideband at the beginning decreascs and then by a sudden change it increases when the concentration N is increased. We analyzed the dispersion charactcristics of'the longitndinally magnetized ferrile-dielectric vvaveguide on different electrodynamical parameters. We discovered that the vvorking frequency band be-comes wider for a microvvave with a right-hand polarization when the fem'te magnetization is increased. Thc same dependencc Ibr a micro-vvave with a left-hand polarization has the opposite effect. The experimental and calculated difterential comparison ofthe phase shift ofthe ferrite waveguide on the value ofthe territe magnetization show that these results were in agreement with each other

A method for measuring the specific electrical conductivity of an anisotropically conductive medium

The paper deals with the ways of finding an electrical conductivity tensor of a plane and anisotropically conductive sample. Application of the Van der Pauw method to investigate the conductivity of anisotropically conductive media makes the basis of research. Several models of distribution of the electric field potential are presented, their merits and demerits are discussed, and the necessary physical measurements are indicated. On the basis of these models, the respective calculation expressions of the specific conductivity tensor are derived and algorithms for their realization and error calculation are developed

Электродинамический анализ пустотелых диэлектрических и метаматериальных волноводов

Development of computer algorithms for electrodynamical analyses of different waveguides is important nowadays due to the fact that these can be created from the newest materials with complicated dependences of the permittivity and the permeability on frequencies and waveguides can have nanometers sizes. We present the dispersion equation for analyzes of dielectric and metamaterial hollow-core cylindrical waveguides (HCWs). The main objective of our work is to analyze dispersion characteristics of the dielectric and metamaterial HCWs. We have analyzed dispersion characteristics of single−mode and many−mode dielectric and metamaterial HCWs. Dependencies of normalized propagation constant values on waveguide radiuses have been analyzed for dielectric and metamaterial HCWs. We have compared properties of the dielectric HCWs with metamaterial HCWs using obtained graphical results.Lietuviška santrauka. Kompiuterinių algoritmų, skirtų įvairių bangolaidžių elektrodinaminei analizei atlikti, plėtra dabar yra labai aktuali, nes bangolaidžiai gali būti pagaminti iš naujausių medžiagų, turinčių sudėtingas dielektrinės ir magnetinės skvarbos priklausomybes nuo dažnio, ir gali turėti nanometrinius dydžius. Pristatoma dispersinė lygtis, skirta dielektrinių ir metamedžiaginių tuščiavidurių cilindrinių bangolaidžių (TCB) elektrodinaminei analizei atlikti. Plačiai aprašoma dielektrinių ir metamedžiaginių TCB dispersinių charakteristikų analizė. Pateikta vienmodžio bei daugiamodžio dielektrinių ir metamedžiaginio TCB dispersinių charakteristikų analizė. Normuotos išilginės sklidimo pastoviosios priklausomybės nuo bangolaidžio spindulio buvo gautos dielektriniam bei metamedžiaginiam TCB. Naudojant gautus grafinius rezultatus, buvo atliktas dielektrinių bei metamedžiaginio TCB savybių palyginimas

Applicable damage of high-Tc YbaCuO superconducting tapes by current and laser pulses

Damage and irreversible damage of YBaCuO tapes with high density current after switching from superconducting to normal state are investigated. Quasi-homogeneous current distribution across the tape in superconducting state can cause perfect tape damage or irreversible damage when current is slightly above critical value. The model of the tape heating during the optically initiated switching from superconducting to normal state is proposed. Analysis of causes inducing damage shows necessity to consider 0.5Tm damage criterion because of strong current influence on the damage processes. Possible damage mechanisms are described and crack tips motion simultaneously with switching from superconducting to normal state is considered. Application of optically illuminated YBaCuO tapes with nanosecond duration current pulses on the base of the described mechanisms is proposed

Electric field distributions of the fast and slow modes propagated in the open rod SiC waveguide

Here we present the electrodynamical analysis of the ceramic circular rod silicon carbide (SiC) waveguide with the radius R = 2.5 mm at the temperature 1800° C. We present dispersion characteristics of the SiC waveguide in the frequency range 1−100GHz. We show the losses of two slow and one fast waveguide modes. We give here the electric field distributions of the slow and fast modes propagated in the investigated waveguide. We present a table with magnitudes of the electric and magnetic field components in the fixed point of the SiC waveguide cross-section