Kybernetika pro materiálové vědy

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    Measurement of thermal depolarization effects in piezoelectric coefficients of soft PZT ceramics via the frequency and direct methods
    (Elsevier Ltd., 2016-09-01) Fialka, Jiří; Beneš, Petr; Michlovská, Lenka; Klusáček, Stanislav; Pikula, Stanislav; Dohnal, Přemysl; Havránek, Zdeněk
    Depolarization at high temperatures around the Curie point constitutes an important yet difficultly measurable material property of piezoelectric (PZT) ceramics. The common vibrometric technique (d33 meters) is not suitable for the measurement of temperature dependences, and therefore we used the frequency method to perform the desired procedures. The indicator selected to show the depolarization state in the piezoelectric ceramics consisted in the piezoelectric charge coefficient, whose value can be effectively measured via the above-mentioned frequency technique. The accuracy of the method was verified via comparing a d33 meter constructed by the authors (as described in this paper) and also by means of differently sized cylinders of ceramics NCE51, which are designed for longitudinal length modes. Based on the obtained results, we established a measurement methodology to exactly determine the value of the Curie point that corresponded to the phase transition to a cubic crystallographic structure. The experiment also confirmed the applicability of progressively controlled depolarization of PZT ceramics by high temperature in the range of between 350 and 370 °C, and it defined the temperature limits at which there occur irreversible changes of the piezoelectric properties of PZT ceramics. In the measured NCE51 material, the limit for irreversible changes was equal to 95% of the Curie temperature (368 °C).
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    Comparison of Methods for the Measurement of Piezoelectric Coefficients
    (IEEE, 2013-04-03) Fialka, Jiří; Beneš, Petr
    The charge constant of piezoelectric material is one of the crucial constant values. At the present time, the measurement of this value is mostly realized by means of three techniques: the frequency method, the laser interferometer technique, and the quasi-static method. These techniques have been practically applied to piezoelectric ceramic samples. Our paper presents comparison of the individual methods with regard to their accuracy and the demands placed on the instrumentation and preparation of the piezoelectric material samples. A soft ceramic product marketed under the production code of NCE51 was used in the experiments. The methods are described in detail, including the process of sample preparation, description of the experiments, and procedure of alculating coefficients from the measured values.
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    A Heuristic Algorithm to Compute Multimodal Criterial Function Weights for Demand Management in Residential Areas
    (MDPI, 2017-07-20) Kaczmarczyk, Václav; Fiedler, Petr; Bradáč, Zdeněk
    We present the conceptual design of a collective control scheme for appliances within a smart home. Based on the relevant energy acquisition procedures, three appliance groups are defined, modeled, and completed with an energy storage as well as a generator using renewable sources. At the following stage, a mixed quadratic optimization problem is presented, with the solution consisting in a time plan to regulate the operation of the individual devices. Importantly, the paper also proposes a heuristic algorithm securing consistent functionality of the computational process even despite the varying input and user conditions given in the receding horizon.
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    Optimal Scheduling of Domestic Appliances via MILP
    (MDPI AG, 2015-01-08) Kaczmarczyk, Václav; Fiedler, Petr; Bradáč, Zdeněk
    This paper analyzes a consumption scheduling mechanism for domestic appliances within a home area network. The aim of the proposed scheduling is to minimize the total energy price paid by the consumer and to reduce power peaks in order to achieve a balanced daily load schedule. An exact and computationally efficient mixed-integer linear programming (MILP) formulation of the problem is presented. This model is verified by several problem instances. Realistic scenarios based on the real price tariffs commercially available in the Czech Republic are calculated. The results obtained by solving the optimization problem are compared with a simulation of the ripple control service currently used by many domestic consumers in the Czech Republic
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    Solvability of a close to symmetric system of difference equations
    (Department of Mathematics, Texas State University, 2016-06-27) Stevič, Stevo; Iričanin, Bratislav; Šmarda, Zdeněk
    The problem of solvability of a close to symmetric product-type system of di erence equations of second order is investigated. Some recent results in the literature are extended.