Physical Mechanisms of Magnetic Field Effects on the Dielectric Function of Hybrid Magnetorheological Suspensions

In this paper, we study the electrical properties of new hybrid magnetorheological suspensions (hMRSs) and propose a theoretical model to explain the dependence of the electric capacitance on the iron volumetric fraction, ΦFe, of the dopants and on the external magnetic field. The hMRSs, with dimensions of 30 mm×30 mm×2 mm, were manufactured based on impregnating cotton fabric, during heating, with three solutions of iron microparticles in silicone oil. Flat capacitors based on these hMRSs were then produced. The time variation of the electric capacitance of the capacitors was measured in the presence and absence of a magnetic field, B, in a time interval of 300 s, with Δt=1 s steps. It was shown that for specific values of ΦFe and B, the coupling coefficient between the cotton fibers and the magnetic dipoles had values corresponding to very stable electrical capacitance. Using magnetic dipole approximation, the mechanisms underlying the observed phenomena can be described if the hMRSs are considered continuous media.

Increasing the reliability of electrical equipment in the agricultural and industrial complex based on measuring the electrical capacitance of capacitors

The article presents elaborated technical suggestions for increasing reliability of electrical equipment of agro-industrial complexes. The analysis of the already known ways of measuring electric capacitance is carried out and it demonstrates the necessity of withdrawing a capacitor from a working circuit for sufficient accuracy of determining electric capacitance. The urgency of developing a method for measuring electric capacitance without removing the capacitor from а working circuit to reduce the average recovery time is shown. Theoretical foundation of the possibility to measure electric capacitance without a capacitor being withdrawn from a working circuit in smoothing filter mode is worked out; a structural electric circuit of an electric capacitance measuring device is elaborated and the principle of its operation is described; methods of measurement by means of the given device are elaborated; conditions for creating and maintaining the measurement mode of the device are substantiated. The validity of the received results is checked with the help of the programmed package Mathcad, as well as on electric models of the main blocks of the device. The obtained results can be used to measure electric capacitance of electrolytic capacitors during maintenance and electrical equipment renovation and also can promote its reliability.

Substantiation of rational parameters of the sensitive element of the grain moisture indicator

Annotation Purpose. Improving the efficiency of harvesting work based on the development of information tools for determining grain moisture. Methods. Method of regression analysis, method of planning and processing of experimental data using software packages – “Microsoft Office Excel 2010”, Microsoft Visual Studio Community 2015 in C ++, statistical method of processing research results. Results. Regression model of the dependence of the electric capacitance of the capacitor on the working area of the plates of the capacitor of the sensing element and the distance between the plates of the capacitor. Rational values of the parameters of the sensitive element of the grain moisture indicator. Conclusions 1. The NSC “IAEE” has developed a simple and reliable indicator of grain moisture, the principle of which is based on the change in dielectric constant between the plates of the capacitor. 2. A regression model of the dependence of the electric capacitance of the capacitor on the working area of the capacitor plates of the sensing element and the distance between the plates of the capacitor, which allowed to determine that at a capacitor plate area of 200 mm, the rational value of the distance between capacitor plates is 0.69 mm. 3. The values of the rational values of the distance between the plates of the capacitor of the sensitive element of the grain moisture indicator, which are obtained in theoretical calculations and experimental studies, differ by 15%. Keywords: grain, humidity, grain moisture indicator, primary converter, rational parameters.

Polymer matrix ferroelectric composites under pressure: Negative electric capacitance and glassy dynamics

This report presents the results of high-pressure and broadband dielectric spectroscopy studies in polyvinylidene difluoride (PVDF) and barium strontium titanate (BST) microparticles composites (BST/PVDF). It shows that the Arrhenius behaviour for the temperature-related dynamics under atmospheric pressure is coupled to Super-Arrhenius/Super-Barus isothermal pressure changes of the primary relaxation time. Following these results, an explanation of the unique behaviour of the BST/PVDF composite is proposed. Subsequently, it is shown that when approaching the GPa domain the negative electric capacitance phenomenon occurs. Graphical abstract