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EN
Compared to the traditional integer order viscoelastic model, a fractional order derivative viscoelastic model is shown to be advantageous. The characteristics of guided circumferential waves in an anisotropic fractional order Kelvin–Voigt viscoelastic hollow cylinder are investigated by a quadrature-free Legendre polynomial approach combining the Weyl definition of fractional order derivatives. The presented approach can obtain dispersion solutions in a stable manner from an eigenvalue/eigenvector problem for the calculation of wavenumbers and displacement profiles of viscoelastic guided wave, which avoids a lot of numerical integration calculation in a traditional polynomial method and greatly improves the computational efficiency. Comparisons with the related studies are conducted to validate the correctness of the presented approach. The full three dimensional spectrum of an anisotropic fractional Kelvin–Voigt hollow cylinder is plotted. The influence of fractional order and material parameters on the phase velocity dispersion and attenuation curves of guided circumferential wave is discussed in detail. Moreover, the difference of the phase velocity dispersion and attenuation characteristics between the Kelvin–Voigt and hysteretic viscoelastic models is also illustrated. The presented approach along with the observed wave features should be particularly useful in non-destructive evaluations using waves in viscoelastic waveguides.
EN
Free Space Optical (FSO) communication is a quickly developing technology that is designed to handle high data rates while maintaining a good quality factor (Q-factor). Many novel techniques have been implemented to cope with atmospheric attenuating factors, such as fog and rain. Here, we have introduced circular polarization shift keying (C-PolSK) modulation to produce a stable and uniform light beam. The plane of polarized light keeps rotating along with the propagation vector, which helps reduce phase variations and cross-channel effects. C-PolSK provides higher penetrating power and attenuation resistance over linear polarization shift keying (L-PolSK). Two different C-PolSK models have been proposed and graphical comparisons, relying on such parameters as Q-factor, transmission distance and inputoutput power, have been made. The cases of moderate fog and rain attenuation are taken to verify the model’s efficiency. Polarized light is split into two orthogonal components and then modulated using the Mach-Zehnder modulator. One of the models also employs the principle of orthogonal differential phase shifting. Eye diagrams have been provided to verify the bit error rate (BER). The orthogonal differential phase shifted C-PolSK model proves to be the most suitable implementation prototype.
EN
Propagation of time harmonic plane waves in an infinite thermo-viscoelastic material with voids has been investigated within the context of different theories of thermoelasticity. The equations of motion developed by Iesan [1] have been extended to incorporate the Lord-Shulman theory (LST) and Green-Lindsay theory (GLT) of thermoelasticity. It has been shown that there exist three coupled dilatational waves and an uncoupled shear wave propagating with distinct speeds. The presence of thermal, viscosity and voids parameters is responsible for the coupling among dilatational waves. All the existing waves are found to be dispersive and attenuated in nature. The phase speeds and attenuation coefficients of propagating waves are computed numerically for a copper material and compared under different theories of thermo-elasticity. The expressions of energies carried along each wave have also been derived. All the computed numerical results have been depicted through graphs. It is found that the influence of CT and GLT is almost same on wave propagation, while LST influences the wave propagation differently.
EN
According to Brajanovski periodic layered model, a fractural medium can be equivalent to layered media with periodic distribution of fractural layers and background layers, but the analytical solution given by Brajanovski can only interpret the dispersion and attenuation effects of single characteristic unit model. In order to study the dispersion and attenuation features of multiple characteristic units, forward modeling methods are needed. Based on the theory of two-phase medium, Biot deduced the propagation equation of longitudinal waves in fluid-saturated porous media. However, there are two problems in the forward modeling using time-domain equation. One is the influences of boundary reflection, and the other is the introduction of cumulative error. For convenience, time-domain equation is rewritten in the frequency domain, thus constructing a one-dimensional rock physics model. Then, forward method is used to study the dispersion and attenuation features of fluid-saturated medium. Numerical simulation results are found to be in good agreement with the analytical solution. Furthermore, the frequency-domain forward method can analyze the velocity dispersion and energy attenuation of longitudinal waves in any multilayered fracture medium. By analyzing those numerical simulation results, it can be obtained that, as the length of characteristic unit increases or the number of characteristic unit decreases, both the starting frequency of dispersion and the peak frequency of attenuation shift to low, whatever the attenuation peaks are equal. In addition, the effects of porosity, permeability and fluid saturation on energy attenuation and velocity dispersion are also studied. Finally, the stress field and displacement field distributions of fluid-saturated fractural medium are given by the frequency-domain forward modeling method.
EN
We use the peak frequency method to estimate effective P- and S-wave quality factors (QP and QS) based on the recorded waveforms of microseismic events. We analyze downhole datasets recorded during the hydraulic stimulation of the two unconventional gas reservoirs located in the northern part of Poland. The effective attenuation is lower in the deeper reservoir consistent with higher compaction. In both cases, we observe high QS values relative to QP which is consistent with attenuation coefficients of saturated reservoirs.
PL
W artykule przedstawiono wybrane zagadnienia z zakresu symulacji kanałów radiokomunikacyjnych, tj. matematyczne modele propagacyjne, statystyczny opis szybkich zaników i powolnych fluktuacji. W artykule omówiono kanał wielodrogowy, mobilny Rayleigha oraz Wattersona. Jako narzędzie symulacyjne wybrano pakiet Vissim.
EN
The wireless channel can be described as a function of time and space. The received signal is the combinations of many replicas of the original signal. Multipath propagation produces several effects on the received signal, like time and frequency dispersion, amplitude fluctuation. The use of mathematical models describing the propagation of radio waves allows to simulate the propagation of different environment. In this paper fast and slow fading models and their characteristics are presented. A Rayleigh, mobile multipath and Watterson channel model are also described in this paper.
PL
W niniejszym artykule przedstawiono metodę pomiaru tłumienia filtrów używanych do tłumienia zakłóceń w liniach energetycznych i telekomunikacyjnych. Procedura oparta jest o standard CISPR 17:2000. W artykule przedstawiono układ pomiarowy dla tłumików o standardowej impedancji 50 Om. Impedancja linii w sieciach energetycznych zwykle nie jest dokładnie znana, wobec czego trudno przeprowadzić jest w typowy sposób pomiary. Artykuł przedstawia metodę kalibracji pomiaru oraz zasadniczą metodę pomiaru charakterystyk tłumienia filtrów EMC.
EN
The aim of this work is to present the attenuation measurement procedure measurement and laboratory stand for filters used to interference suppression in power and telecommunication lines. The procedure is based on the CISPR 17:2000 standard. The article describes the attenuation measurement system for filter with impedance different then 50Ω. The article presents the measured attenuation characteristics of set of EMC filters which are offered on the market. The calibration of measurement method is presented too.
PL
W części teoretycznej niniejszej pracy przedstawiono definicję, budowę, zasadę działania, parametry oraz obszary zastosowań światłowodowego rozłożonego czujnika temperatury wykorzystującego w swym działaniu wymuszone rozproszenie Rayleigha. Praktyczna część pracy zawiera wyniki eksperymentów polegających na badaniu wpływu temperatury na wartość tłumienia jednomodowego światłowodu telekomunikacyjnego, w zależności od jego standardu oraz długości fali świetlnej – okna pomiarowego. Zawiera ona również analizę uzyskanych wyników i wynikające z niej wnioski.
EN
In the theoretical part of this work are presented the definition, design, operation, parameters and application areas of fiber optic distributed temperature sensor uses in its operation forced Rayleigh scattering. The practical part of the work contains the results of experiments involving the study of the effect of temperature on attenuation value of single mode optical fiber depending on the standard and the wavelength – measurement window. It also includes an analysis of the results and conclusions.
9
Content available remote Influence of the core size on light propagation in photonic liquid crystal fibers
EN
In this paper analyses of mode distribution, confinement and experimental losses of the photonic crystal fibers with different core sizes infiltrated with liquid crystal are presented. Four types of fibers are com-pared: with single-, seven-, nineteen-and thirty seven solid rods forming the core in the same hexagonal lattice of seven “rings” of unit cells (rods or capillaries). The experimental results confirming the influence of the core diameter on light propagation are also included. The diameter of cores determines not only the number of modes in the photonic liquid crystal fiber but also is correlated with experimentally observed attenuation. For fibers with larger cores confinement losses are expected to be higher, but the measured attenuation is smaller because the impact of liquid crystal material losses and scattering is smaller.
EN
Underwater Wireless Sensor Networks are deployed to explore the world under the water, measure different parameters and communicate the data to the surface, in the widespread applications. The main operating technology of these networks is the acoustic communication. The communication among the sensors and finally to the surface station requires a routing protocol. The sensors being battery limited and unfeasible to be replaced under the water requires an energy efficient routing protocol. Clustering imparted in routing is an energy saving technique in sensor networks. The routing may involve single or multi hop communication in the sensor networks. The paper gives a comparative study of the benchmark protocol multi-hop LEACH with the proposed Sensor Hop-based Energy Efficient Networking Approach (SHEENA) for the shallow as well as deep water in three dimensional Underwater Wireless Sensor Networks. The network energy model for the Underwater Wireless Sensor Networks is based among the different acoustic channel characteristics. The proposed approach is found to give better response.
EN
Seismic and geodetic studies were carried out before, during, and after underground exploitation of a coal bed in Katowice - Kleofas Coal Mine, located in the Upper Silesia Coal Basin, Poland. Development of a subsidence trough was completed approximately 3 months after passage of a longwall exploitation in the coal seam. This was the time required for the subsidence trough to appear on the surface, which was confirmed by levelling measurements. Sharp changes in the elastic parameters were observed on each profile during subsidence trough development. This observation can result from changing tension and compression forces caused by increase and/or decrease of the elastic parameters of the rock mass. After completion of subsidence trough development, the rock mass appeared to return to its isotropic state and the observed changes ceased. Some minor fluctuations were noted, but they probably resulted from changes in groundwater levels, which might have affected the measured parameters.
PL
Podziemna eksploatacja górnicza wywołuje niebezpieczne deformacje powierzchni terenu. W rejonie prowadzonej ścianowej eksploatacji górniczej przez KWK Katowice – Kleofas wykonano dwuletnie, cykliczne pomiary sejsmiczne oraz geodezyjne. Największe wartości składowych pionowych przemieszczeń punktów osnowy geodezyjnej zaobserwowano 3 miesiące po przejściu frontu eksploatacji ścianowej w pokładzie węgla kamiennego na głębokości ponad 600 metrów poniżej poziomu terenu. Podczas procesu wykształcania się niecki obniżeniowej stwierdzono występowanie gwałtownych zmian parametrów sprężystych płytkiego ośrodka geologicznego. Zmiana tych parametrów wynika ze zmiennego w czasie stanu naprężeń ściskających i rozciągających w skałach. Po zakończeniu procesu wykształcania się niecki obniżeniowej mierzone parametry generalnie ustabilizowały się, co świadczy o powrocie środowiska geologicznego do stanu izotropowego. Występujące wtedy niewielkie wahania parametrów wynikają ze zmiany poziomu zwierciadła wody.
EN
Adopting the method of forced oscillation, attenuation was studied in Fontainebleau sandstone (porosity 10%, permeability 10 mD) at seismic frequencies (1–100 Hz). Confining pressures of 5, 10, and 15 MPa were chosen to simulate reservoir conditions. First, the strain effect on attenuation was investigated in the dry sample for 11 different strains across the range 1 × 10-6–8 × 10−6, at the confining pressure of 5 MPa. The comparison showed that a strain of at least 5 × 10-6 is necessary to obtain a good signal to noise ratio. These results also indicate that nonlinear effects are absent for strains up to 8 × 10-6. For all the confining pressures, attenuation in the dry rock was low, while partial (90%) and full (100%) saturation with water yielded a higher magnitude and frequency dependence of attenuation. The observed high and frequency dependent attenuation was interpreted as being caused by squirt flow.
13
PL
W artykule została przedstawiona szybka metoda pomiaru tłumienności z wykorzystaniem szybkiej transformaty Fouriera (FFT). Istotną cechą tej metody jest możliwość uzyskania quasi-ciągłych charakterystyk tłumienia obiektów ekranujących dzięki widmowej analizie odpowiednio ukształtowanych przebiegów w dziedzinie czasu.
EN
This article presents a quick method of attenuation measurement using Fast Fourier Transform (FFT). An important feature of this method is possibility to obtain a quasi-continuous attenuation characteristics of shielding objects by spectral analysis of the selected signals.
EN
The loss of elastic energy to the medium can be quantified by the quality factor Q. Acoustic full waveforms log from Winna Góra1 borehole were used to estimate P-wave quality factor. Data used in this paper were analyzed with usage of GeoWin software. Interpretation of acoustic full waveforms was performed for the one pair of waveforms. The most important part in the interpretation of data is manual picking of P wave arrival, calculation of semblance function, and picking anomalies of P wave on amplitude spectrum. Using data from interpretation of acoustic full waveforms, we calculated quality factor. Based on provided analysis it is concluded that the highest attenuation ( so the lowest Q) is observed in Rotliegend strata.
EN
CO2 laser treatment can increase the surface roughness of plastic optical fibres (POFs) with the diameter of 0.5 mm and enhance the input intensity and attenuation coefficient accordingly, which is supposed to weaken the side emission of POFs in long distance above 375 mm. TiO2 particles were applied to improve the increasing optical loss of POFs by laser treatment. POFs were first modified with fine TiO2 particles and then treated by CO2 laser with the pixel time from 30 to 120 ìs. The surface morphology was observed by scanning electron microscopy to investigate the changes of micro-structure before and after laser treatment and the distribution of TiO2 particles. The illumination intensity and attenuation coefficient were calculated and compared in two methods. It is visible that the evaluation by model LLF2 with two parts is more suitable for the fitting of experimental data and shows higher input intensity and lower attenuation than that by standard power function. Both the evaluation methods exhibit that the utilization of TiO2 particles could play an active role in the enhancement of side emission of POFs treated by CO2 laser.
EN
The paper presents results of measuring attenuation coefficient of the Al-20 wt.% Zn alloy (AlZn20) inoculated with different grain refiners. During experiments the melted alloys were doped with Al-Ti3-C0.15 refining master alloy. Basing on measurements performed by Krautkramer USLT2000 device with 1MHz ultrasound wave frequency it was stated that grain refinement reduces the attenuation coefficient by about 20-25%. However, the examined alloys can be still classified as the high-damping ones of attenuation greater than 150 dB/m.
EN
This article presents an efficient method of modelling acoustic phenomena for real-time applications such as computer games. Simplified models of reflections, transmission, and medium attenuation are described along with assessments conducted by a professional sound designer. The article introduces representation of sound phenomena using digital filters for further digital audio processing.
EN
Prony filtering is a method of seismic data processing which can be used to solve various geological and production tasks, involving an analysis of target horizons characteristics and a prediction of possible productive zones. This method is based on decomposing the observed seismic signals by exponentially damped cosines at short-time intervals. As a result, a discrete Prony spectrum including values of four parameters (amplitude, damping factor, frequency, phase) can be created. This decomposition occurs at many short-time intervals moving along an observed trace. The combined Prony spectrum of the trace can be used to create images of the trace through a selection of some values of the parameters. These images created for all traces of a seismic section provide an opportunity for locating zones of frequency-dependent anomalous scattering and absorption of seismic energy. Subsequently, the zones can be correlated with target seismic horizons. Analysis and interpretation of these zones may promote understanding of the target horizons features and help to connect these features with the presence of possible reservoirs.
PL
W artykule przedstawiono wyniki prowadzonych w Laboratorium Urządzeń Elektronicznych prac związanych z zastosowaniem typowych absorberów EMC w aplikacjach innych niż komory bezodbiciowe. Wybrane modele absorberów funkcjonujących na rynku zostały sprawdzone pod względem tłumienności oraz potencjału zastosowań innych niż branża EMC.
EN
This paper presents the results of works carried out in Laboratory of Electronic Devices on the use of absorbing materials for other than anechoic chambers’ applications. The chosen existing on the market absorbers have been evaluated for their attenuation characteristics and possible use for others than EMC trades.
EN
This article applies to modelling the propagation of electromagnetic waves. The use of mathematical models describing the propagation of electromagnetic waves allows you to simulate the propagation of any environment such as a building. The paper shows problem of selecting the appropriate propagation model for the analysis of the propagation environment.
PL
Artykuł dotyczy modelowania rozchodzenia się fal elektromagnetycznych. Zastosowanie matematycznych modeli opisujących rozchodzenie się fal elektromagnetycznych pozwala na symulowanie dowolnego środowiska propagacyjnego np. budynku. Celem artykułu jest przedstawienie problemu doboru odpowiedniego modelu propagacyjnego do analizowanego środowiska.
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