Z. Roubal

Energy Sources for an Experimental Electrical Network: PV Panel and Micro-Hydroelectric Power Plants

Abstract The authors present energy sources for an Experimental Electrical Network (E.E.N). The main sources applied are photovoltaic and hydroelectric power plants. For the purposes of modelling the experimental network, the authors describe the measured values of the output power provided by the plants. The performance of the photovoltaic station was measured for the period of three weeks; as expected, the resulting value is strongly dependent on the weather. In the small hydroelectric station, we monitored the relation between the turbine output power and the water level in the weir. Moreover, we also produced a six-hour record of the performance of the station. Based on this characteristic, the relation between the water level and the output power was determined using approximation of the exponential function. The paper also describes the perspectives of remote sensing of the data acquired from a power plant and analyzes the possibilities of storing the data to an SQL server.

Analysis of magnetic properties measurement in closed samples

This paper contains an analysis of magnetic properties of a coil core material. Methods of demagnetizing the sample before measurement are discussed. Static and dynamic hysteresis loops, initial magnetization curve, and normal magnetization curve are measured. The authors show the corrections of systematic errors for all measurements and indicate the specific conditions under which the measurement of the characteristics is realized.

Testing an Impedance Non-destructive Method to Evaluate Steel-Fiber Concrete Samples

Abstract Steel-fiber reinforced concrete is a composite material characterized by outstanding tensile properties and resistance to the development of cracks. The concrete, however, exhibits such characteristics only on the condition that the steel fibers in the final, hardened composite have been distributed evenly. The current methods to evaluate the distribution and concentration of 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 tests related to the evaluation of the density and orientation of fibers in a composite material. Compared to the approaches used to date, the proposed technique is based on the evaluation of the electrical impedance Z in the band close to the resonance of the sensor–sample configuration. Using analytically expressed equations, we can evaluate the monitored part of the composite and its density at various depths of the tested sample. The method employs test blocks of composites, utilizing the resonance of the measuring device and the measured sample set; the desired state occurs within the interval of between f=3 kHz and 400 kHz.

A Non-Destructive Impedance Method Using Resonance to Evaluate the Concentration of Steel Fibers in Concrete

Abstract Steel-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.

Mini- and microgenerators applicable in the MEMS technology

The article presents certain general conclusions obtained from an investigation of a vibration-powered milli- or microgenerator functioning as a harvester. In this context, the authors summarize the parameters that are critical in designing optimal generators to retrieve the residual energy contained in an electromechanical system and transferred through the vibrations of an independent structure. The discussion exploits our previous results, which theoretically define the properties characterizing the models of individual basic configurations of a generator based on Faraday’s law of induction.

A methodology for measuring air ions in medical caves

The complex and time-consuming measurement the concentration of light air ions in therapy caves requires a suitable methodology to prevent the measured patterns from being corrupted by spurious charges or the actual distribution of the electrostatic field.

An impedance non-destructive method to evaluate the steel fibers in composites

Steel-fiber reinforced concrete is a composite material characterized by outstanding tensile properties and resistance to the development of cracks. The concrete, however, exhibits such characteristics only on the condition that the steel fibers in the final, hardened composite have been distributed evenly. The current methods to evaluate the distribution and concentration of 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 the tests related to the evaluation of the density and orientation of fibers in a composite material.

Practical application of electrical impedance tomography and electrical resistive tomography

Usage of electrical impedance tomography and electrical resistance tomography will be in the article. The electrical impedance tomography is a widely investigated problem with many applications in physical and biological sciences. Medical imaging can be used primarily for the detection of pulmonary emboli, non-invasive monitoring of heart function and blood flow, and for breast cancer detection. Electrical resistive tomography is use in the geophysical imaging is used for searching underground conducting fluid plumes near the surface and obtaining information about rock porosity or fracture formation. Another application of electrical impedance tomography is for example in non-destructive testing and identification of material defects like cracks or identification of corrosion in production materials. The principle of electrical impedance tomography and Electrical resistive tomography is based on the back image reconstruction, which is highly ill-posed inverse problem. The aim of both methods is to reconstruct, as accurately and fast as possible, the internal impedance or conductivity distributions in two or three dimensional models.

The NQR RF decoupler construction based on transformer

This paper will present some experiments with improving one of crucial parts of nuclear quadrupolar resonance (NQR) spectrometer, the RF decoupler. This part decouples the high power rf excitation signal from receiver port of low detected signal preamplifier. In the position of decoupler usually some LC filters and back-to-back diodes are used. We have tested rf impedance transformers of different types in rf decoupler construction, suitable for our experimental NQR spectrometer with the working frequency range from 0.5 to approximately 50 MHz. Obtained results show very good applicability of this transformers in NQR circuitry. The measured impedance and transition times between on and off state of the proposed decoupler will be discussed in this paper.

The efficiency of a microgrid hydrogen circuit

The paper discusses the efficiency of a microgrid hydrogen circuit. We measured and calculated the energy efficiency values to describe two main sources of low efficiency. The principle of the proposed design consists in improving the stability of a direct current microgrid and enabling the maximum exploitation of the electric energy produced by renewable sources. The circuit is composed of a microhydropower plant, solar panels, and wind power plants. In this respect, we present a module to save the energy, proposing an efficiency calculation procedure for the hydrogen circuit.