Investigation of electromagnetic wave absorber based on carbon fiber reinforced aerated concrete using time-domain method

The electromagnetic wave absorbers prepared from autoclaved aerated concrete containing carbon fibers as additions in the shape of slabs with pyramids cut on one plane of these slabs were tested using dc microwave source and the time-domain method. It was demonstrated that autoclaved aerated concrete allows one to fabricate electromagnetic wave absorbers which have a reflection coefficient up to -30 dB in the frequency range from 2 GHz to 18 GHz

Fast two-stage protector against electromagnetic pulse based on electroresistance effect in polycrystalline La-Sr(Ca)-Mn-O films

The electroresistance (ER) effect in polycrystalline films of La0.83Sr0.17MnO3 and La0.7Ca0.3MnO3 was investigated in the temperature range of (5 – 290) K using high power sub-nanosecond rise time electrical pulses with amplitude up to 1 kV. It was obtained that conductance vs. voltage dependences are nonlinear and could be well fitted by empirical formula G = G0 + Gα · Uα; where G is conductance, U is the voltage applied across the sample, G0 is the conductance at low voltage, and Gα and α are the parameters related to the electrical transport mechanism. Parameters α for La-Ca-Mn-O and La-Sr-Mn-O were 1.5 and 1.33 respectively. It was obtained that there are two regions of the electroresistance vs. temperature dependence for both films: low temperature region where ER exhibits very slow dependence on temperature and high temperature region where ER significantly decreases with temperature. It was demonstrated that polycrystalline manganite films can be used for the development of protectors against short electromagnetic pulse (EMP), and fast twostage protector operating at cryogenic temperatures (80 K) is proposed

The Application of a CMR-B-Scalar Sensor for the Investigation of the Electromagnetic Acceleration of Type II Superconductors

In this paper, we investigated the behavior of a type II superconducting armature when accelerated by a pulsed magnetic field generated by a single-stage pancake coil. While conducting this investigation, we performed a numerical finite element simulation and an experimental study of the magnetic field dynamics at the edge of the pancake coil when the payload was a superconducting disc made from YBa2Cu3O7−x, cooled down to 77 K. The magnetic field measurements were performed using a CMR-B-scalar sensor, which was able to measure the absolute magnitude of the magnetic field and was specifically manufactured in order to increase the sensor’s sensitivity up to 500 mT. It was obtained that type II superconducting armatures can outperform normal metals when the launch conditions are tailored to their electromagnetic properties.This article belongs to the Special Issue Magnetic Sensors and Systems for Scientific and Industrial Application

Compact high-sensitivity potentiometer for detection of low ion concentrations in liquids

Project: European Regional Development Fund according to the supported activity “Research Projects Implemented by World-class Researcher Groups” under Measure No. 01.2.2-LMT-K-718The compact potentiometer, based on an electronic circuit protected from electrostatic and electromagnetic interference, was developed for the measurement of low ion concentrations in liquids. The electronic circuit of the potentiometer, consisting of analogous and digital parts, enables the measurement of fA currents. This makes it possible to perform reliable measurements of ion concentrations in liquids that are as small as 10−8-10−7M. The instrument was tested using electrodes that were selective for tetraphenylphosphonium (TPP+) ions. It was demonstrated that the characteristic response time of the potentiometer electronic circuit to changes in the concentration of these ions in a liquid was in the order of 10 s. An investigation of TPP+ absorption by baker yeast has shown that this device can be successfully used for long term (several hours) measurements with zero signal drift, which was about 1 μV/s. Finally, due to the small dimensions of the electronic circuit (7.5 × 2 × 1.5 cm), this potentiometer can be easily installed at a large apparatus in the laboratory condition (≈25 °C), such as high pulsed electrical generators of magnetic fields that are used in electroporation studies of biological cellsGamtos mokslų fakultetasValstybinis mokslinių tyrimų institutas, Fizinių ir technologijos mokslų centrasVilniaus Gedimino technikos universitetasVilniaus universitetasVytauto Didžiojo universiteta

Determination of the electroporation threshold for pulses from 95 ns to 20 us

The dependences of the fraction of electroporated mouse hepatoma MH-22A cells on the pulse intensity were obtained for the cells exposed to a single square-wave electric pulse with the duration from 95 ns to 20 μs. The amplitude of an electric pulse was varied from 0.4 to 12 kV/cm. Increasing the intensity of the electric field pulse increased the fraction of electroporated cells. The electric field, which lead to a given percentage of electroporation, decreased with increasing the pulse length. The dependence of the amplitude of the electric pulse required to electroporate 50 % of mouse hepatoma MH-22A cells on the pulse duration was also determinedBiologijos katedraFizinių ir technologijos mokslų centro Puslaidininkių fizikos institutasVytauto Didžiojo universiteta

Numerical Magneto-Mechanical Analysis of Destructive Coils with Reinforcement Cylinders of Various Thicknesses

The destructive laboratory device, generating half-period sinus-shaped magnetic field pulses of 0.15-2 ms duration is investigated numerically. The coil was placed into a steel reinforcement cylinder to resist magnetic forces, while influence of thickness of the reinforcement cylinder is considered in detail. The time-dependent non-linear magneto-mechanical model and the finite element software ANSYS are employed. On the basis of the mechanical analysis, reasonable explanation of the destruction nature is provided. The numerically obtained operation threshold value was in good agreement with experimental measurements

Measurement of the magnetic field distribution in railguns using CMR-B-Scalar sensors

Colossal magnetoresistance effect B-scalar magnetic field sensors with effective areas of 0.05 mm(2) were used very close to the rails for magnetic field measurements. These measurements were performed during static and dynamic railgun experiments. In static experiments three different rail materials were used and the results are compared to a finite element simulation

Inductors for high magnetic field generation

Inductors for high magnetic field generation are described. Pulsed magnetic field is generated discharging energy bank through the inductor during a short period of time. Axial magnetic field is calculated by equations using known values of pulsed current and geometric parameters of the inductor. The efficiency of energy transformation is analyzed. The possibility of non-destructive applications of single turn inductor, flux concentrator, helix inductor, and multi-section inductor is discussed. The design of pulsed magnetic inductors requires complex analysis of electrical, thermal and mechanical overloads, and the most limited factor is the destructive mechanical stress. For the first estimation the failure criteria of maximal available magnetic field inductor and the crosssectional distribution of stress intensity under action of Lorentz forces are presented. The multi-section inductor is chosen as the challenging long life construction for further experimentations in high magnetic field generation area

Numerical magneto-mechanical analysis of destructive coils with reinforcement cylinders of various thicknesses

The destructive laboratory device, generating half-period sinus-shaped magnetic field pulses of 0.15-2 ms duration is investigated numerically. The coil was placed into a steel reinforcement cylinder to resist magnetic forces, while influence of thickness of the reinforcement cylinder is considered in detail. The time-dependent non-linear magneto-mechanical model and the finite element software ANSYS are employed. On the basis of the mechanical analysis, reasonable explanation of the destruction nature is provided. The numerically obtained operation threshold value was in good agreement with experimental measurements

Influence of Sr content on CMR effect in polycrystalline La1-xSrxMnO3 thin films

The magnetoresistance of thin polycrystalline La1-xSrxMnO3 films deposited on lucalox substrate using metal organic chemical vapor deposition technique was investigated in pulsed magnetic fields up to 18 T in the temperature range 100-320 K. The influence of film preparation conditions, ambient temperature variation and Sr content is analyzed in order to determine the optimal conditions for the design of CMR-B-scalar magnetic field sensor based on thin manganite film, operating at room temperature