Ústav teoretické a experimentální elektrotechniky
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- ItemDesigning an Improved Method to Determine the Anhysteretic Curve in Soft Magnetic Materials via the Jiles-Atherton Model(POLISH ACAD SCIENCES INST PHYSICS, 2024-08-01) Roubal, Zdeněk; Smejkal, VítThe article discusses a novel procedure for measuring the anhysteretic curve in soft magnetic materials. This curve frequently finds use in diverse applications, such as the Jiles-Atherton hysteresis model. The actual method is characterized in detail, including sample calculations for materials exhibiting various hysteresis loop shapes (ferrites, grain-oriented steel, and nanocrystalline material). To illustrate the benefits of the proposed approach, the authors compare the measurement-based and the simulated curves, the latter being obtained through an optimal interleaving of the model.
- ItemCorrosion of calcite speleothems in epigenic caves of Moravian Karst (Czech Republic)(Springer, 2024-03-14) Faimon, Jiří; Baldík, Vít; Štelcl, Jindřich; Všianský, Dalibor; Rez, Jiří; Pracný, Pavel; Novotný, Roman; Lang, Marek; Roubal, Zdeněk; Szabó, Zoltán; Hadacz, RomanCorrosion processes were studied in epigenic caves of the Moravian Karst (MK). Samples of naturally corroded speleothems and carbonate rocks collected in various MK caves were compared with limestone and calcite standards that were corroded under well-controlled conditions in the laboratory. Two stages of corrosion were distinguished: (1) an early stage of pitting and linear corrosion predisposed by point and line defects in the standards, and (2) an advanced stage characterized by deep corrosion of the entire standard surface. During the second stage, the internal structure of the corroded substrate remained partially preserved, however, if the water was extremely aggressive, the corrosion progressed to depth en-bloc regardless of the structure. In this paper, we (1) proposed a new corrosion mechanism based on the binding of aqueous calcium by clays and tested it experimentally in the cave, (2) characterized conditions that generally favor the formation of aggressive waters (water undersaturated with calcite) into seven categories incorporating them into a conceptual model of the karst vertical profile, and (3) discussed anthropogenic influences on these processes.
- ItemApplication of an electromagnetic numerical model in accurate measurement of high velocities(Lublin University of Technology, 2015-03-01) Fiala, Pavel; Friedl, MartinThe velocity of various objects measured within a large number of disciplines and activities. This paper presents the process of designing an accurate method and equipment for the measurement of velocity in one-shot nonlinear processes, which occur only once and are thus characterized by zero repeatability. The measurement methods must therefore enable the recording, saving, and retroactive evaluation of the processes at a pre-defined accuracy; all these operations are performed to facilitate comparison of the recorded event and other similar processes. However, the electromagnetic method described in the paper does not include the disadvantages of known optical methods. We therefore present the design of an inductive sensor equipped with an electronic signal processing system. This design is based on numerical evaluation of the relativistic effect occurring during the application of the electromagnetic principle in sensing the position and velocity of an object J. Van Bladel. The final section of the paper contains a discussion of the measured results. The authors investigate the use of a coupled model of the magnetic field and analyze the motion of a conductive object in this field. The analysis shows that, for an exact evaluation of the influence of all effects, it is necessary to consider the phenomena related to the movement of a system relative to the other one. It is shown that related distinctive effects affect the resultant electromagnetic field distribution already at the relative velocity of v0= 1ms-1.
- ItemA Non-Destructive Impedance Method Using Resonance to Evaluate the Concentration of Steel Fibers in Concrete(DE GRUYTER POLAND SP ZOO, 2018-10-08) Bachorec, Tibor; Fiala, Pavel; Steinbauer, Miloslav; Roubal, ZdeněkSteel-fiber reinforced concrete is a composite material characterized by outstanding tensile properties and resistance to cracking. The concrete, however, exhibits such characteristics only on the condition that the steel fibers in the final, hardened composite are distributed evenly. Current methods to evaluate the distribution and concentration in a fiber composite are either destructive or exhibit a limited capability of evaluating the concentration and orientation of the fibers. In this context, the paper discusses auxiliary techniques and laboratory tests that evaluate the density and orientation of the fibers in a composite material, presenting an innovative approach to impedance-based non-destructive testing. The actual methodology utilizes the resonance of the measuring device and the measured sample set; the desired state occurs within the interval of f = 10 kHz and 2 GHz.
- ItemPredicting the Optimum Corn Harvest Time via the Quantity of Dry Matter Determined with Vegetation Indices Obtained from Multispectral Field Imaging(MDPI, 2023-06-16) Janoušek, Jiří; Marcoň, Petr; Dohnal, Přemysl; Jambor, Václav; Synková, Hana; Raichl, PetrEstimating the optimum harvest time and yield embodies an essential food security factor. Vegetation indices have proven to be an effective tool for widescale in-field plant health mapping. A drone-based multispectral camera then conveniently allows acquiring data on the condition of the plant. This article examines and discusses the relationships between vegetation indices and nutritiolnal values that have been determined via chemical analysis of plant samples collected in the field. In this context, emphasis is placed on the normalized difference red edge index (NDRE), normalized difference vegetation index (NDVI), green normalized difference vegetation index (GNDVI), and nutritional values, such as those of dry matter. The relationships between the variables were correlated and described by means of regression models. This produced equations that are applicable for estimating the quantity of dry matter and thus determining the optimum corn harvest time. The obtained equations were validated on five different types of corn hybrids in fields within the South Moravian Region, Moravia, the Czech Republic.