P. Osmokrovic

X-ray photoelectron spectroscopy study of Bi4Ti3O12 ferroelectric ceramics

Ferroelectric Bi4Ti3O12 ceramics have been prepared by the method of reactive sintering. The ceramics exhibit good ferroelectric properties with a remanent polarization Pr=5.5×10−2 C/m2 and a coercive field Ec=3MV/m. High resolution x-ray photoelectron spectra of the atomic constituents of Bi4Ti3O12 were recorded. The obtained results indicate that oxygen vacancies are preferentially sited in the vicinity of Bi ions, in the Bi2O2 layers.

Mechanism of electrical breakdown of gases at very low pressure and interelectrode gap values

The electrical breakdown mechanism of gases at very low pressures (from 10/sup -4/ to 10/sup 5/ Pa) and interelectrode gap values (from 0.1 to 1 mm) is considered. Comparing experimental results and theoretical analysis, the boundaries between areas of different breakdown mechanisms are established. The existence of edge breakdown, which was previously erroneously interpreted by the anomalous Paschens effect, is explained and proved. The avalanche hypothesis of vacuum breakdown is experimentally proved. >

Mechanism of electrical breakdown of gases for pressures from 10−9 to 1 bar and inter-electrode gaps from 0.1 to 0.5 mm

This paper discusses the mechanisms of gas breakdown at low values of pressure and inter-electrode gap, i.e. in the vicinity of the Paschen minimum. In this area of pressure and inter-electrode gap values, breakdown occurs either through gas or vacuum mechanisms, and also the so called anomalous Paschen effect appears. Electrical breakdown of electropositive, electronegative and noble gases has been investigated theoretically, experimentally and numerically. Based on the results obtained, regions in which particular breakdown mechanisms appear have been demarcated. Special attention has been devoted to the anomalous Paschen effect as well as to the avalanche vacuum breakdown mechanism.

Statistical properties of electrical breakdown in vacuum

The breakdown probability distribution function was determined for DC and impulse voltages, for conditions of gap pressure of 10, 0.1, and 10/sup -4/ Pa and gap length of 0.1 mm. It was found that DC and impulse voltages are associated with different types of probability distribution function due to different initiation mechanisms. The statistical influence of the number of previous breakdowns on the probability distribution of the breakdown voltage was investigated. By applying the U test for analysis of measured data, it was found that at lower gap pressure, the breakdown voltage probability changes after a smaller number of breakdowns than it does at higher gap pressure. >

Design of a SOI memory cell

In this paper a quantitative analysis has been used for describing and discussing design characterizations of an SOI flash memory cell. Mathematical expressions for the front gate threshold voltage of the SOI memory cell are derived using the equations for a standard SOI MOSFET. Coupling coefficients which exist between the control gate and source and drain regions, are the same as for the silicon body, through stored charge at the floating gate has to be included in these equations and the mathematical expressions for the flash memory cell can be obtained. Implementing this, the voltage of the front gate of a standard SOI MOSFET is equal to the voltage of the floating gate of the memory cell. During analysis, the emphasis is put on the case where the back channel is depleted, because then coupling between the front and back gate can control the threshold voltage of the control gate.

Mechanism of electrical breakdown left of Paschen minimum

The breakdown mechanism of a gas at small PD values is considered. Comparing experimental results and theoretical analysis, the limits of different breakdown mechanisms are established. For SF/sub 6/ and Ar gases the conditions for streamer and those for the Townsend breakdown mechanism are found, as well as those for vacuum breakdown. The pressure values characteristic for avalanche and emission mechanisms of vacuum breakdown are obtained. Left from the Paschen minimum in the vicinity of the minimum point, edge-type breakdown is dominating, which currently is misinterpreted as an anomalous Paschen effect. >

A novel approach for temperature estimation in squirrel-cage induction motor without sensors

In this paper, the authors present a coupled thermal and electromechanical model for squirrel-cage induction motor simulation and analyses. The effect of iron saturation, rotor parameter variation due to current displacement (skin-effect) and temperature variations of both stator and rotor resistances are taking into account simultaneously. A new device for the temperature measurement in the stationary as well as rotating parts of electric machines is built. The unique construction of the device for continuous rotor temperature monitoring is briefly described. This device is a part of a complete acquisition system, which is used for precise testing and investigating of a coupled thermal and electromechanical phenomena. An original thermal observer based on the direct stator temperature measurement under normal running condition with no additional sensors is proposed.

Triggered vacuum and gas spark gaps

This paper presents a comparative analysis of the characteristics for the gas insulated three-electrode spark gaps and vacuum insulated three-electrode spark gaps. The experimental part of this paper includes the testing of spark gap models. Two spark gap types were studied: one having the third electrode inside the main electrode and one having a separate third electrode, both being insulated by vacuum or gas (under pressure, providing the same operating voltage as for a vacuum insulated spark gap). Both types of spark gaps were theoretically sized in the optimal way. Several characteristics are determined experimentally: the influence of the gas and vacuum insulation parameters on the spark gap functioning, the influence of the rate of rise and injected energy of the triggering pulse on the spark gap functioning, and the degree of spark gap erosion vs. number of operations (long-time-stability). Two types of gases were applied: SF/sub 6/ gas, N/sub 2/ gas and three vacuum (residual) pressures: 10/sup -1/ Pa, 10/sup -4/ Pa, and 10/sup -6/ Pa. Three electrode materials were used: copper, steel and tungsten. The spark gap switching time and delay time are measured. It was found that the switching time decreases with application of pressure decrease, and the statistical dispersion of switching time raises with the pressure decrease. By comparison of results obtained for the vacuum insulated spark gap and the SF/sub 6/ or N/sub 2/ gas insulated spark gap, it was found that the vacuum spark gap has a slightly shorter switching time and a significantly higher corresponding statistical dispersion.

Calculation of impulse characteristics for gas-insulated systems with homogenous electric field

The possibility of generating a statistical sample of the pulse breakdown voltage random variable numerically is examined for arbitrary shaped pulses. Impulse characteristics are then determined on the basis of the generated statistical sample. Numerically generated statistical samples of the pulse breakdown voltage random variable are compared to the corresponding experimentally obtained statistical samples. Impulse characteristics obtained from the numerically generated statistical samples are compared to the corresponding impulse characteristics derived from the semi-empirical Area Law and the Time Enlargement Law. The set of impulse characteristics obtained in this way is compared to the results obtained experimentally for different shapes of the pulse voltage load. Gases used in the experimental and numerical models include SF6, N2 and Ar. Gas pressures range from 1 × 102 Pa to 6 × 102 Pa, and inter-electrode gaps from 0.1 to 10 mm. A homogenous electric field is considered.

Applicability of simple expressions for electrical breakdown probability in vacuum

Simple analytical expressions for the law of breakdown probability are suggested. They are tested by comparison with experimental data obtained by impulse breakdown in 10-Pa vacuum for very small gaps (d >