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1

Piezoelectric effect on thermoelastic Lamb waves in functionally graded plates

Wang X., Ren X., Yu J., Zhou H., Zhang X., Leng J

Archives of Mechanics

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2023

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Vol. 75, nr 1-2

3--26

EN

Based on the Lord–Shulman thermoelectric elasticity theory, the piezoelectric effect on the thermoelastic Lamb wave propagation in the functionally graded material (FGM) plate is investigated. The coupled wave equations are solved by employing the Legendre polynomial series approach (LSPA), which poses the advantages of small scale of eigenvalues matrix and a convenient solution. It can directly obtain the complex wave number solutions without iteration. The obtained complex solutions, which represent the wave propagation and attenuation, are compared with those available data. Numerical examples show that the influence of gradient is profound. Results indicate that the piezoelectric effects on attenuation with the open and closed circuit condition are consistent for the S0 and S1 modes, but are inconsistent for the A0 and A1 modes. Although the piezoelectric effect is weak on the dispersion and attenuation of thermal waves, it is notable for their physical field distributions. In addition, the relaxation time is critical to electric displacements of a thermal wave mode, but is not essential for those of Lamb-like modes. The results can be used for the optimization of thermo-electric-elastic coupling structures.

2

Tłumienie sygnałów radiowych przez roślinność dla częstotliwości 28 GHz

Nikiforuk Maciej, Cichoń Krzysztof

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

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2022

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nr 4

511--514

PL

Rozwój systemów radiokomunikacyjnych powoduje poszukiwanie nowych, coraz wyższych, pasm częstotliwości dla zapewnienia rosnących potrzeb użytkowników. Wzmożone zainteresowanie tzw. pasmem fal milimetrowych wzmaga pytania o adekwatność dotychczas stosowanych modeli propagacyjnych dla wyższych zakresów częstotliwości. Jednym z interesujących aspektów jest tłumienie roślinności, które zostało poddane szczegółowej analizie w niniejszej pracy. Poza analizą komponentów tłumienia listowia w niniejszej pracy skupiono się na wykonaniu kampanii pomiarowej w otoczeniu budynków Politechniki Poznańskiej. Uzyskane wyniki porównano z zewnętrznymi pracami pomiarowymi i dokonano kalibracji współczynników tłumienia listowia odpowiednich dla rodzimych gatunków roślinności.

EN

The development of radio communication systems makes it necessary to seek for higher frequency bands to meet the growing needs of users. An increased interest in the so-called millimeter waves band raises questions about the adequacy of the use of propagation models for higher frequency ranges. One interesting aspect is radio signal attenuation in foliage, analyzed in detail in the paper. In addition to the analysis of the components of the foliage attenuation, the paper focuses on the implementation of the measurement campaign in the vicinity of the buildings of Poznań University of Technology. The obtained results were compared to external measurement works and there was performed the calibration of the foliage attenuation coefficients appropriate for native species of vegetation.

3

A Review on Feasible and Reliable Underwater Wireless Optical Communication System for achieving High Data Rate and Longer Transmission Distance

Joseph Lenin, Anandan Sangeetha

International Journal of Electronics and Telecommunications

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2022

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Vol. 68. No. 4

815--823

EN

Underwater Wireless Optical Communication (UWOC) offers significant research prospective with major challenges in the design and implementation. UWOC is capable of providing high rate of data transmission across large distances. This paper attempts to focus on the intricacies of practical implementations and open research issues of UWOC systems. Critical advances and progresses made in the field, modelling techniques and link design challenges are summarised. The purpose of this review is to give suggestions towards feasible and reliable UWOC design with improved performance. Finally the major points are summarized so that it will assist the future research in UWOC.

4

Attribute analysis as a tool for determining the areas of the late diagenetic Main Dolomite deposits and assessing the stability of the seismic signal parameters

Smalera Norbert

Geology, Geophysics and Environment

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2022

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Vol. 48, no. 2

111--132

EN

The results of the lithofacial analysis of data from the Moracz 3D seismic survey were among the main premises leading to the positioning of the new petroleum exploration well in that area. Unfortunately, the reservoir properties of the drilled part of the Main Dolomite carbonates differed significantly from those anticipated by the analysis of the amplitudes of the seismic signal recorded. Such surprisingly negative results impelled the reinterpretation of 3D seismic data. Hence, a number of analyses of the amplitudes, the frequencies, and the variability of phase shift were carried out in order to determine the influence of these parameters on the lithofacial interpretation of seismic data. The results revealed a fundamental error of amplitude with the extraction maps. It appeared that the distribution of amplitudes is not essentially controlled by the reservoir properties of the Main Dolomite carbonates but by the fault shadow effect coming from Mesozoic graben in the overburden. In addition, a large diversity of frequency spectra was found, which, combined with the small thickness of the exploration level, could have contributed to incorrect identification of seismic reflections. There was also a change in seismic signatures from the same reflection in different parts of the survey, raising doubts about the distribution of the phase rotation. In order to recognize phase rotation diversity, a new seismic data analysis was based upon the selected Triassic sediments of high impedance. The obtained maps demonstrated significant variability within the data volume due to attenuation. The reinterpreted data from the Moracz 3D seismic survey proved the uneven and unstable distribution of amplitudes, frequencies, and phase which resulted in erroneous conclusions of petroleum exploration. After modeling with the use of different frequency ranges, an analysis of the amplitude extraction of the horizons related to the Main Dolomite was performed. Then the amplitude ratio attribute was selected which eliminated the influence of the regional amplitude and frequency distribution and showed the distribution. of dolomite properties more reliably than the amplitude extraction maps.

5

The reflection and transmission of waves at interface between two nonlocal orthotropic thermoelastic halfspaces

Tung D. X.

Archives of Mechanics

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2022

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Vol. 74, nr 5

373--389

EN

The present article deals with the propagation of inhomogeneous waves in an orthotropic medium based on Eringen’s nonlocal thermoelasticity. For chosen directions of propagation and a real finite inhomogeneity parameter, a complex slowness vector is specified to define the propagation of inhomogeneous incident wave. Then the reflection, transmission of plane waves at a plane interface between two nonlocal orthotropic thermoelastic halfspaces are discussed. In this incidence, horizontal slowness determines the slowness vectors for all reflected, transmitted waves. For each reflected, transmitted wave, the corresponding slowness vector is resolved to define its phase direction, phase velocity and attenuation angle. Appropriate boundary conditions on this wave-field determine the amplitude ratios for reflected, transmitted waves relative to the incident wave. The numerical examples are provided to show the effect of the inhomogeneity of incident wave, nonlocal parameter on the propagation characteristic of the reflected, transmitted waves.

6

Deep-neural-networks-based approaches for Biot-squirt model in rock physics

Xiong Fansheng, Liu Jiawei, Guo Zhenwei, Liu Jianxin

Acta Geophysica

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2022

|

Vol. 70, no 2

593--607

EN

A new cost-effective surrogate model using deep neural network (DNN) for seismic wave propagation in rocks saturated with fluid is presented. In this field, the dispersion/attenuation analysis and wave-field simulation are two key measurements which can be carried out by solving wave equations. The Biot–squirt (BISQ) equation is a classical wave propagation model in geophysical forward modeling and has been widely used. The solution of such equation, especially by numerical method, is often complex and time-consuming. In this work, a DNN model is trained with the dataset of velocity and inverse quality factor generated from BISQ model. The results show that the relative mean square error between the predictions of DNN model and that of BISQ model on the test sets are all less than 3%. It indicates that the DNN model has learned the high-dimensional space well and then can realize the dispersion/attenuation analysis for any given rock physical parameters. Besides, the other well-trained DNN model is used to obtain the simulation results with second-order accuracy according to results by finite difference scheme with first-order accuracy. It reveals that the fast wave-field simulation can be implemented once the results with lower accuracy are obtained.

7

Enhanced feature extraction algorithms using oscillatory-mode pulsed Eddy Current techniques for aircraft structure inspection

Lysenko Iuliia, Kuts Yurii, Protasov Anatoliy, Redka Mykhailo, Uchanin Valentin

Transactions on Aerospace Research

|

2021

|

Nr 3 (264)

1--16

EN

A review of the existing literature shows that modern pulsed eddy current (PEC) technique for flaw detection in aircraft structure inspection is typically carried out in aperiodic mode. At the same time, the unstable characteristic points of the EC signal usually used as informative parameters can restrict the potential of this excitation mode due to significant measurement errors. This article considers an advanced PEC method of NDT based on the oscillatory mode. To obtain the conditions concerned with different modes of EC probe response oscillations, an equivalent scheme of the "testing object - EC probe" system was developed and analyzed. The frequency and attenuation coefficient of natural oscillations are proposed as the informative parameters of the probe signals. The obtained mathematical model of the probe signals allows for the dependence of proposed signal parameters on the characteristics of the testing object to be evaluated. Herein, we first develop algorithmic software for determining and analyzing the discrete amplitude and phase characteristics of PEC NDT signals based on the simulation results. The errors of the natural frequency oscillations and the attenuation coefficient determination as well as the optimal time for its determination are analyzed in order to minimize the possible errors. Next, the proposed informative parameters are experimentally investigated using a set of specimens. The obtained results confirm the possibility of the proposed methodology to enhance the inspection procedures related to the electrical conductivity and geometric parameters measurements as well as the detected defect sizing.

PL

Przegląd istniejącej literatury wskazuje, że nowoczesna technika impulsowych prądów wirowych (PEC) do wykrywania wad w inspekcji konstrukcji lotniczych jest zwykle prowadzona w trybie aperiodycznym. Przy tym, niestabilne punkty charakterystyczne w sygnale prądów wirowych, które zwykle są używane jako parametry informacyjne, mogą ograniczać potencjał tego trybu wzbudzenia ze względu na znaczne błędy pomiarowe. W niniejszym artykule rozważano zaawansowaną metodę PEC dla badań nieniszczących (NDT) opartą na trybie oscylacyjnym. W celu uzyskania warunków związanych z różnymi trybami oscylacji odpowiedzi sondy prądów wirowych, opracowano i przeanalizowano równoważny schemat układu „obiekt badany - sonda”. Jako parametry informacyjne dla sygnałów brano częstotliwość i współczynnik tłumienia drgań własnych.Tak powstały model matematyczny sygnałów pozwala na ocenęzależności proponowanych parametrów sygnałów od właściwości obiektu badanego. Najpierw na podstawie wyników symulacji opracowano algorytmiczne oprogramowanie do wyznaczania i analizy dyskretnych charakterystyk amplitudowych i fazowych sygnałów PEC NDT. Analizowano błędy wyznaczania częstotliwości drgań własnych oraz współczynnika tłumienia, a także optymalny czas jego wyznaczania w celu minimalizacji możliwych błędów. Następnie, zaproponowane parametry informacyjne badano eksperymentalnie z wykorzystaniem zestawu próbek. Otrzymane wyniki potwierdzają możliwość zastosowania proponowanej metody do usprawnienia procedur inspekcyjnych związanych z pomiarami przewodności elektrycznej, parametrów geometrycznych oraz oceny rozmiarów wykrywanych defektów.

8

Równoczesne tłumienie promieniowania gamma i neutronów w jednowarstwowej osłonie betonowej

Safamehr Majid, Izadinia Mohsen, Hashemi Seyed Hamid, Hoseini Seyed Jalil

Cement Wapno Beton

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2021

|

R. 26, nr 6

503--514

PL

Dzięki możliwości zastosowania różnych połączeń, beton jest jednym z najbardziej odpowiednich materiałów do konstruowania osłon przed promieniowaniem. W niniejszych badaniach kruszywo hematytowe i magnetytowe zastąpiło kruszywo zwykłe, oddzielnie i całkowicie w dwóch etapach. Dodatkowo zastępowano 2,5, 5 i 10% masowych cementu węglikiem boru. Przeprowadzono badanie gęstości, tłumienia promieniowania gamma z użyciem źródła Co 60 i promieniowania neutronowego z użyciem Am-Be 241. Zgodnie z wynikami, zastąpienie kruszywa zwykłego kruszywem hematytowym, poprawiło liniowy współczynnik tłumienia i makroskopowy przekrój czynny absorpcji neutronów betonu odpowiednio o 17% i 73%. Właściwości te poprawiły się odpowiednio o 37% i 105%, przy zastosowaniu kruszywa magnetytowego. Ponadto, przy dodaniu do składu betonu maksymalnie 10% węglika boru, makroskopowy przekrój czyny wzrósł o 120%, jednak liniowy współczynnik tłumienia zmniejszył się tylko o 5-8%. Oznacza to, że możliwe jest uzyskanie odpowiedniego tłumienia promieniowania gamma i wiązek neutronów jednocześnie, w jednej warstwie betonowej osłony. Ponadto stwierdzono dobrą zgodność wyników badań i symulacji Monte Carlo.

EN

The ability to create various compounds has made concrete one of the most suitable materials for constructing radiation shields. In this investigation, hematite and magnetite aggregates were used to replace ordinary aggregate, separately and completely in two stages. Boron carbide was also substituting cement at percentages of 2.5, 5, and 10 by mass. The density test, gamma irradiation with Co 60 and neutron irradiation with Am-Be 241 were performed. According to the results, the replacement of ordinary aggregates with hematite aggregates in concrete, improved the linear attenuation coefficient and macroscopic cross section by 17% and 73%, respectively. These parameters increased by 37% and 105%, respectively, by the use of magnetite aggregates. Moreover, with the addition of a maximum of 10% boron carbide to the concrete, the macroscopic cross-section increased by 120%, however, the linear attenuation coefficient decreased by between 5% and 8%. This means that it is possible to have a suitable attenuation of gamma ray and neutron beams in a single layer of concrete shield simultaneously. In addition, the results of the tests and Monte Carlo simulation were found to have good consistency.

9

A quadrature-free Legendre polynomial approach for the fast modelling guided circumferential wave in anisotropic fractional order viscoelastic hollow cylinders

Zhang X., Liang S., Shao S., Yu J.

Archives of Mechanics

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2021

|

Vol. 73, nr 2

121--152

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.

10

Distance attenuation and local magnitude scale based on constant geometrical spreading in Northern Punjab, Pakistan

Tahir Mohammad, Khan Ali, Mushtaq Muhammad Naveed, Iqbal Muhammad Tahir, Iqbal Talat, Shah Muhammad Ali, Khan Karam, Soomro Riaz Ahmed

Acta Geophysica

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2021

|

Vol. 69, no. 5

1567--1584

EN

Development and calibration of distance attenuation curve for local seismic data are requisite for better seismo-tectonic modeling and seismic hazard estimation. Local magnitude scale developed for Northern Punjab (Potwar Plateau and Salt Range) has been tested against diferent geometrical spreading values. Trade-of or linear inter dependence has been observed between local magnitude scale parameters. To address this issue, either nonparametric approach with proper smoothing factor or parametric approach with single parameter (a) as constant may be used. In this study, we fxed geometrical spreading parameter to eliminate parameters dependency and hence reduction in error was achieved. Geometrical spreading was observed to be distance-dependent factor rather than a constant parameter. A variance reduction of 11%, with zero error in anelsatic attenuation parameter was achieved by fxing geometrical parameter and performing parametric inversion. The new magnitude scale with distance correction factor is given by the expression; −logAo = log(R) + 0.0006(R) − 1.7419, where R is hypocentral distance, valid for R < 130 km and depth < 30 km. Lower attenuation (i.e., b = 0.0006) was observed in new magnitude scale as compared to previously developed magnitude scale (i.e., b = 0.00115) for the same area. The pronounced lower attenuation of seismic waves beneath the intraplate region of Northern Punjab is apparently owes to regional tectonics. Northern Punjab is relatively stable part of the Indian shield with Precambrian basement rock overlaid by varying thickness of salt diapirs and thick sedimentary cover.

11

A new acoustic traveltime approximation for attenuating transversely isotropic media

Xiao Han, Wang Deli

Acta Geophysica

|

2021

|

Vol. 69, no. 5

1611--1621

EN

Attenuation is one of the most important quantities in describing seismic wave propagation, which is also anisotropic because of the dispersion relationship between the seismic wave and the symmetry direction. Transverse isotropic media with titled symmetry-axis (TTI) is a widespread approximation of the Earth’s surface. For 2D TTI attenuating media, we frstly use the acoustic assumption to simplify the exact eikonal equation for the complex-valued quasi P-wave traveltime. Then we design a perturbation method to obtain the new approximation by solving the acoustic attenuating eikonal equation of TTI media and use Shanks transform to increase precision. Compared with former studies, the new approximation considers the symmetryaxis angles of the media as a factor, which will improve its robustness. The approximation is tested in several medium to demonstrate its efectiveness. The energy velocity which derived by the steepest-descent method is used to calculate the exact complex-valued traveltime. We test the accuracy of the approximations developed with and without Shanks transform in the following. Finally, we discussed the possibility to apply this approximation to the methods like fast marching methods.

12

Implementation of carbon fibre treatment couches in the XiO® and Monaco® Treatment Planning Systems

Reenen Van Christoffel Jacobus, Trauernicht Christoph Jan

Polish Journal of Medical Physics and Engineering

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2020

|

Vol. 26, Iss. 4

211--215

EN

Purpose: Carbon fibre treatment couches on linear accelerators provide a strong, rigid framework for patient support. Patient safety is a priority, therefore the dosimetric properties of treatment couches need to be accurately incorporated in treatment plans, to minimize differences between planned and delivered dose. This study aims to determine the attenuation effect of treatment couches for 3-D Conformal Radiotherapy (3-D CRT) and to validate the implementation thereof in the XiO and Monaco treatment planning systems (TPS). Material and methods: Attenuation measurements were performed on the ELEKTA Connexion couches of the ELEKTA Precise and Synergy-Agility linear accelerators. Measurements were made at 10° intervals in RMI-457 Solid water (30 cm x 30 cm x 30 cm) using a PTW Farmer-type ionization chamber (TW30013) positioned at the accelerator’s isocentre. The percentage attenuation was calculated as the ratio of the electrometer readings for parallelopposed fields. The Computed Tomography (CT) data sets of the set-ups were obtained on a Philips Big Bore 16-slice CT scanner and exported to the TPS. The individual couch structures were delineated and electron density (ED) values were assigned using the commissioned CT-to-ED curve. Test treatment plans were generated with 100MU per field at 10° gantry intervals. Results: The percentage attenuation was determined to be within 2% and 3% for beams perpendicular to the couch surface for XiO and Monaco, respectively. The maximum attenuation was observed for oblique fields which was significantly higher than the manufacturer specified values. TPS validation showed an agreement to 1% for XiO and Monaco. At extreme oblique angles, both planning systems overestimated this effect up to a maximum of 4%. Conclusions: Couch attenuation differs significantly with gantry angle and beam energy. As a result, the treatment couch models should be included in all treatment planning calculations.

13

Viscoelasticity expression and extension of seismic dispersion and attenuation in porous media with multiple fracture sets

Zhang Jinwei, Ding Renwei, Zhao Lihong, Wang Deying

Acta Geophysica

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2020

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Vol. 68, no. 6

1679--1688

EN

Intensive studies have been conducted on fuid-related seismic dispersion and attenuation in saturated anisotropic media. Most of the studies are concentrated on the transversely isotropy media. However, the fractures distribution in subsurface reservoirs is often complex. When there are multiple fracture sets developing in a porous background, the signatures of seismic dispersion and attenuation remain unclear. In this paper, we propose a method to calculate the frequency-dependent stifness matrix of a porous medium with multiple fractures sets from a perspective of viscoelasticity. Due to the favorable approximation performance of the generalized standard linear solid model and Chapman model, we use a modifed form of generalized standard linear solid model to simulate the frequency-dependent stifness tensor of porous media with multiple fracture sets. The representation of the stifness tensor utilizes the modulus defect to denote the efects the fractures including fracture density and geometry. With the procedure of calculating the stifness tensors at low- and high-frequency limits, we can easily calculate the frequency-dependent stifness tensor for media with multiple fracture sets with arbitrary orientations and directions. We then analyze the efects of the fracture parameters on the viscoelasticity characteristics taking orthotropic medium as an example. The results can help to understand the viscoelasticity and the mesoscopic seismic attenuation associated with fractures and fuids and can provide a practical rock physics model when dealing with reservoirs with complex fracture patterns.

14

Implementation of C-PolSK Modulation in FSO Network and Analysis of its Atmospheric Performance

Chattopadhyay Diptangshu, Bharti Manisha

Journal of Telecommunications and Information Technology

|

2019

|

nr 4

43--49

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.

15

Plane waves in thermo-viscoelastic material with voids under different theories of thermoelasticity

Tomar S. K., Goyal N., Szekeres A.

International Journal of Applied Mechanics and Engineering

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2019

|

Vol. 24, no. 3

691--708

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.

16

Frequency‑dependent energy attenuation and velocity dispersion in periodic layered media

Zhang Heng, Zhang Fanchang, Lu Yawei

Acta Geophysica

|

2019

|

Vol. 67, no. 3

799--811

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.

17

Estimation of the quality factor based on the microseismicity recordings from Northern Poland

Wandycz Paweł, Święch Eryk, Eisner Leo, Pasternacki Andrzej, Wcisło Miłosz, Maćkowski Tomasz

Acta Geophysica

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2019

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Vol. 67, no. 6

2005--2014

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.

18

Modele symulacyjne kanałów w systemach radiokomunikacyjnych i ich charakterystyki

Noga K. M.

Zeszyty Naukowe Wydziału Elektrotechniki i Automatyki Politechniki Gdańskiej

|

2017

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Nr 57

71--76

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.

19

Metoda pomiaru tłumienia EMC

Nowosielski L., Uljasz B.

Przegląd Telekomunikacyjny + Wiadomości Telekomunikacyjne

|

2017

|

nr 8-9

1099--1102, CD

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.

20

Badanie jednomodowych światłowodów telekomunikacyjnych pod kątem możliwości ich wykorzystania w rozłożonych czujnikach temperatury z rozproszeniem Rayleigha

Torbus S. A.

Przegląd Elektrotechniczny

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2017

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R. 93, nr 7

56--59

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.