Search

Magnetic diffusion is of great importance in the domain of electromechanical energy conversion since it can be a performance-limiting mechanism. This paper deals with magnetic diffusion in the case of the rails of a railgun. The experiments benefit from the use of a new type of high magnetic-field sensor based on thin (< 1 [micro]m) manganite films, which exhibits a colossal magnetoresistance (CMR) effect and has very small sensitive areas (e.g., 0.5 mm x 50 [micro]m). Some basics about CMR and the design of the sensor are given. Several sensors were used and calibrated in the course of static transient railgun experiments. Here, varying spatial field distributions due to the use of different rail materials were recorded. Magnetic-field measurements during railgun operation with projectile velocities exceeding 1000 m/s have been successfully performed. By comparison with 3-D finite-element calculations, interesting results concerning magnetic diffusion have been worked out. Index Terms--Magnetoresistance, railguns, sensors, skin effect.

The accurate measurement of the magnetic field distribution during electromagnetic launch experiments is an ambitious task. Loop sensors are widely used for detecting the change in magnetic flux. However, this technique is mostly used only for qualitative purposes, e.g., for triggering various devices. This paper deals with the use of another type of high magnetic field sensor based on thin (< 1 [micro]m) manganite films, which exhibit the colossal magnetoresistance (CMR) effect. This sensor measures the magnitude of the magnetic induction and can have very small sensitive areas (e.g., 0.5 mm x 50 [micro]m). Some basics about CMR and the design of the sensor are given. Several sensors were used in experiments performed with the ISL-launcher EMA3 (Eprim = 0.6 MJ, l = 3 m, cal = 15 mm x 30 mm). Transient magnetic field profiles with rise times of approximately 50 [micro]s and amplitudes up to 4 T were recorded. The results obtained with the CMR sensors are compared with those of conventional loop sensors. Also, some metrological peculiarities due to high-frequency coupling to the detector circuit are mentioned. The highly local measurements of these CMR sensors were validated by results obtained from 3-D finite element (FE) calculations of the magnetic field distributions. Index Terms--Magnetoresistance, railguns, sensors, skin effect.

The electric and magnetic properties of microbridges made from 440 nm thick Y–Ba–Cu–O films prepared on Al2O3 substrates with CeO2 sublayers by the pulsed injection metal organic chemical vapor deposition (MOCVD) method were studied in temperatures ranging from 20 K to 300 K in order to investigate the possibilities of using these microbridges as fast fault current limiters. The application of an external magnetic field () causes the flux flow induced magneto-resistive effect, which is proportional to and to at low and high temperatures, respectively. The experimentally obtained S-shaped I–V characteristic and the change of the microbridge resistance over time when affected by a step-like magnetic field can be well explained using a thermo-electrical model based on Joule heating and the flux flow nature of the resistive state (RS). The transition from the superconducting to the RS, studied using ns duration rectangular waveform electrical pulses able to create up to ≈2106 A cm−2 current densities without rises of microbridge temperatures, demonstrated that the I–V characteristics of the RSs consisting of an assembly of straight lines corresponding to the different pinning centers. At temperatures close to the critical temperature of superconductivity, the number of these lines increases, and the I–V characteristics can be described with high accuracy by a power law. It was concluded that microbridges made from these films can be used as protectors against complicated waveform electromagnetic pulses having short rise times, high voltage peak amplitudes and long low-value over-current 'tails'. [ABSTRACT FROM AUTHOR]

The 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 cells. [ABSTRACT FROM AUTHOR]

The electrical field-induced changes of the yeast Saccharomyces cerevisiae cells permeabilization to tetraphenylphosphonium (TPP+) ions were studied using square-shaped, nanosecond duration high power electrical pulses. It was obtained that pulses having durations ranging from 10 ns to 60 ns, and generating electric field strengths up to 190 kV/cm significantly (up to 65 times) increase the absorption rate of TPP+ ions without any detectible influence on the yeast cell viability. The modelling of the TPP+ absorption process using a second order rate equation demonstrates that depending on the duration of the pulses, yeast cell clusters of different sizes are homogeniously permeabilized. It was concluded, that nanosecond pulse-induced permeabilization can be applied to increase the operational speed of whole cell biosensors. [ABSTRACT FROM AUTHOR]

Copyright of Electronics & Electrical Engineering is the property of Electronics & Electrical Engineering and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

A new fast high-power fault current limiter made from epitaxial and polycrystalline \La0.83\Sr0.17\MnO3 thin films and operating at 80 K has been demonstrated. An epitaxial film that exhibits a current-induced increase in its resistance is connected in series with a 50-\Omega-impedance transmission line, while a polycrystalline film whose resistance decreases with an increase in current is connected in parallel. It has been demonstrated that, when the fault current pulse has an amplitude of 200 V, a rise time of 0.5 ns, and a pulselength of 18 ns, the limitation of its amplitude is 3.5 dB after the rise time and 8 dB at the end of the pulse. [ABSTRACT FROM AUTHOR]