Pulse Signal Propagation Research Articles

Simulation of Propagation of Video Pulse Signals of GPR in the Earth’s Lithosphere

Simulation of Propagation of Video Pulse Signals of GPR in the Earth’s Lithosphere

Propagation of pulsed signals in a lossy waveguide line

Propagation of pulsed signals in a lossy waveguide line

Simulation of propagation of video pulse signals of GPR in the Earth's lithosphere

Представлены результаты моделирования прохождения негармонических сигналов от расположенной на поверхности Земли антенны через верхний слой литосферы и отражения этих сигналов от различных неоднородностей в литосфере в случае, когда на антенну подается видеоимпульсный сигнал специальной формы. Используемая в работе модель основана на явной схеме численного интегрирования уравнений Максвелла. В этой схеме электрическое и магнитное поля вычисляются в одни и те же моменты времени в одинаковых узлах пространственной сетки, а также используется расщепление по пространственным направлениям и физическим процессам. В работе изучается, какую информацию о характере неоднородности литосферы можно извлечь из формы отраженного сигнала. Также исследуется влияние параметров видеоимпульсного сигнала на амплитуду и форму отраженных от типичных неоднородностей литосферы сигналов. Показано, что некоторые типы неоднородностей можно определить по форме отраженного сигнала.

Experimental Testing of the RAY Computational Program for Solving Acoustic Ranging Problems on Long Trajectories Including Shelves and Deep Seas

The results of studies of the features of the formation of pulse characteristics on the axis of an underwater sound channel in waveguides with different hydrological and bathymetric conditions of the Sea of Japan and the Sea of Okhotsk are discussed. The results of model calculations and experiments characterizing the regularities of propagation of low-frequency pulse signals in complex waveguides including shelf and deep sea for hundreds of kilometers are presented. It is shown that one of the main effects that determines long-range sound propagation in complex waveguides including the shelf and deep sea is the acoustic “landslide” effect. It is also shown that numerical modeling of the process of signal propagation from the shelf to the deep sea on acoustic traces in the Sea of Japan and the Sea of Okhotsk using the RAY program provides good convergence of the calculated and experimentally obtained impulse characteristics.

МАТЕМАТИЧЕСКИЙ АППАРАТ ДЛЯ АНАЛИЗА ПОМЕХОПОДАВЛЯЮЩИХ ПОЛОСКОВЫХ УСТРОЙСТВ С АСИММЕТРИЧНОЙ СТРУКТУРОЙ

A mathematical apparatus that is used to analyze protective devices based on a meander line (ML) turn. The apparatus takes into account the effect of asymmetry of cross-section on the propagation of pulse signal in a turn The developed mathematical apparatus includes: a model for calculating radiated emissions from a turn with an arbitrary cross-section; an analytical model for calculating the time response at the turn output; models for obtaining conditions that ensure the complete ultrashort pulse (USP) decomposition in multistage devices The proposed apparatus was evaluated on the example of structures with broad-side and side coupling (by the comparison with the results of computer simulation). As a result of comparison of frequency dependences of the maximum electric field strengths obtained using the model and numerically were produced ambiguous results. For the ML turn with broad-side coupling, the dependences were found to be in good agreement qualitatively in the frequency range up to 2.5 GHz. However, they can differ significantly in terms of quantity. More specifically, at some frequencies, there are pronounced maxima of the frequency dependences obtained numerically. For the turn with side coupling, the amplitudes of the maximum field strengths calculated by the model were found to be higher in the entire frequency range (with the exception of several maxima) than those calculated numerically. The constructed directional diagrams of the turn confirm the quantitative discrepancies. Meanwhile, the analysis of the obtained results allows us to claim that the real field strengths will be lower than those calculated by the model, so the model is applicable for preliminary estimates. As a result of evaluation of the analytical model for calculating the time response at the turn output revealed a complete coincidence of the time responses obtained on the basis of the model and numerically. Finally, the models to obtain the conditions for the complete pulse decomposition were evaluated on the example of 3-stage devices. The results demonstrated that the developed models were correct. The case was also considered when the conditions obtained using the models are not met, which leads to an increase in the signal amplitudes at the output of the devices. Thus, the entire presented mathematical apparatus can be used to analyze protective devices based on an ML turn with an asymmetric cross-section.

Analysis of the pulse signal propagation in a turn of a meander line of two segments based on lattice diagrams

The analysis of the propagation of a pulse signal in a turn of a meander line of two segments is carried out. For this purpose, the plotting of lattice diagrams for the even and odd modes is carried out, as well as their subsequent comparison with the time responses to the pulse excitation in each node of the line. A complete coincidence of the amplitudes and arrival times of pulses obtained by different methods was obtained.

Model sub-ionospheric ELF – VLF pulses

The propagation of natural wide-band pulsed radio signals in the spherical Earth – ionosphere cavity is numerically simulated. The frequency band considered is 1–10,000 Hz. We address the TM waves originated from a vertical lightning stroke of the Bruce and Golde, Williams, or Jones model. Major data are based on the Williams’ lightning model. The upper boundary of the cavity is horizontally stratified and the conductivity of each stratum depends on its altitude. We apply several models of vertical conductivity profile, and all of them adequately describe the global electromagnetic (Schumann) resonance. The electromagnetic fields are expanded into a series of normal waves (modes). The frequency dependence of the complex propagation constant of each mode is found by using the full wave solution in the form of Riccati equation. The roots of this equation are found by iterations. Various source–observer distances are used in the waveguides with different height conductivity profiles. The Fourier transform of complex spectra provides the time domain realizations of the wide-band pulsed signals. The results of different model profiles are compared and their correspondence to the known observational data is demonstrated. Computations show that the model pulses similar to either tweek or to slow tail atmospherics. They acquire the form of slow tail atmospherics when the conventional night or day conductivity profiles are used. In this case, a train of VLF oscillations precedes a typical Q-burst. The delay of Q-burst from the VLF precursor grows in proportion to the source – observer distance. The tweek atmospheric emerges combined with the Q-burst when the mesosphere conductivity profile has a section of rapid conductivity increase by 4–5 orders of magnitude in the altitude interval of a few kilometers around 90 km.

Monitoring the difference in liquid levels in adjacent tanks

The possibility of synchronous monitoring of coolant levels in the cooling systems of nuclear and thermal power plants before and after the barrier mesh using a specialized level gauge is considered.
 The block diagram of a level gauge providing current synchronous control of liquid levels in two adjacent channels (reservoirs), as well as the difference in liquid levels in them, is presented. A feature of the structural diagram of a specialized acoustic level gauge is the use of a radiation source common to both channels and a device for dividing the common waveguide path into two channels.
 An algorithm for the functioning of a specialized level gauge has been developed, in which, based on time diagrams, it is shown how the level is controlled in each channel and the difference in liquid levels before and after the barrier grid is calculated. The description of the algorithm is accompanied by calculated expressions for determining the levels and the difference in liquid levels.
 For a level gauge made in the acoustic wavelength range, a condition is given that is necessary for the creation of a device that provides matching when dividing a common channel into two independent channels of pulse signal propagation. This condition made it possible to establish the relationship between the inner diameters of cylindrical pipes used as waveguide paths of an acoustic wave.
 Variants of the implementation of a specialized level gauge based on two modifications of the ZOND-3M level gauge are proposed, in which cylindrical pipes are used as waveguiding systems. It is shown that when using the AP-7VT transceiver, the level gauge will have an operating range of up to 10m with a level resolution of ± 1mm, and when using the AP-70T transceiver, it will have an operating range of up to 20m with a level resolution of ± 1cm.

Study of pulse signal propagation in Vityaz Bay of Sea of Japan based on experimental and model data

Study of pulse signal propagation in Vityaz Bay of Sea of Japan based on experimental and model data

Light propagation in nanophotonic waveguides considering graphene's saturable absorption

We study saturable absorption in graphene-comprising nanophotonic waveguides taking into account the finite relaxation time as well as the carrier diffusion due to the nonuniform, tightly confined spatial profile of the guided modes. We discuss various details of graphene SA and comment on the necessary conditions that allow for directly comparing our model with available experimental. The mathematical framework is based on the nonlinear Schr\odinger equation which provides a strict framework for our analysis and is developed for two optical channels. We explore the propagation of cw, long and short pulsed signals in a silicon slot waveguide and show the importance of our model in order to capture the ultrafast dynamics of graphene and the spatial distribution of guided modes. Finally, we demonstrate how cross absorption modulation can be exploited in order to imprint data from a high power optical channel to a low power channel.

Conditions for Separation Rays by Their Arrival Time at Large Distances and Low Frequencies

Abstract—The results of experimental studies on the propagation of low-frequency pulsed signals in deep- and shallow-water areas of the World Ocean are presented. Sufficient conditions have been obtained for separation rays based on their arrival time at the reception point: displacement of the ray under the influence of the downward sound velocity gradient directed exceeds displacement of the ray in the opposite direction under the influence of the gradient due to gravity; the emitter and receiver are at different depths; the emission is pulsed for a pulse duration smaller than the difference in the ray arrival times at the reception point. The experiments validated the hypothesis that the aggregate conditions are sufficient to detect rays by their arrival time.

Means and Methods for Hydrological–Acoustic Support of High-Precision Long-Range Positioning of Underwater Objects

The article discusses the application of methods and means of general and satellite oceanology for the high-precision acoustic positioning of autonomous underwater vehicles (AUVs) at distances of hundreds of kilometers from control stations. The authors present the results of analyzing their long-term acoustic ranging studies, which revealed the specific features of low-frequency pulsed signal propagation in different hydrological–acoustic conditions in which underwater sound channels (USCs) of different origin form. Special attention is devoted to the possibility and efficiency of using long-term oceanological observation databases to form the spatiotemporal characteristics of USCs in areas for long-range navigation support to AUVs. Additionally, the authors consider the possibilities of sea surface observation by means of satellites to provide the unit that computes the AUV coordinates with data on the integral (effective) sound speed in the near-surface sound channel (NSSC), which forms in winter. The experimental testing results on applying oceanographic technical tools in the Sea of Japan have shown that they improve the accuracy and reliability of AUV navigation support at distances of hundreds of kilometers from coastal control stations. It is been shown that in summer–autumn and winter hydrological conditions, it is possible to determine the AUV coordinates with errors not exceeding hundredths of a percent at distances of hundreds of kilometers.

Study of Acoustic Signal Propagation from Sea to Land

The features of propagation of low-frequency tonal and pulsed acoustic signals generated at sea to land have been experimentally and theoretically studied. The accuracy in determining signals characteristics and, in particular, transmission losses using relatively simple measuring instruments (a hydrophone placed in a small water-filled container) is shown. The results of the calculating estimates for the sound field parameters on the coast formed by a source operating in the water layer are demonstrated. The calculations done by a program that uses a parabolic equation in the horizontal plane and vertical waveguide modes.

Intense Pulses in Relaxing Media with Limited “Memory Time,” Power-Law and Nonanalytic Nonlinearities

Processes that accompany propagation of time-limited pulsed signals in a relaxing medium are investigated for the case of a nonlinear medium with power-law (quadratic or cubic) nonlinearity or nonanalytic nonlinearity (modular or quadratically cubic one). Instead of ordinary integro-differential equations with exponential or fractional-power kernels, a simplified model of a medium with finite “memory time” is used. Such a medium “remembers” its prehistory within a limited time interval, and the corresponding kernel of the integral term is nonzero only within a finite interval. For this model, the problem is reduced to solving a difference-differential equation, which considerably reduces the amount of calculations, as compared to the initial integral equation. The processes that accompany evolution of pulses, namely, the formation of compression and rarefaction shock fronts and the appearance of triangular and trapezoidal nonlinear structures, are described. Effect of relaxation time on these processes is revealed.

Contactless Modal Phenomena Based Approach to Detecting, Identifying, and Diagnosing of Electrical Connections

This paper presents a unified description of a new approach for contactless detection, identification, and diagnostics of electrical connections and describes an idea and principles of using modal probing for these tasks. Simulation and experimental results on pulsed signal propagation through flat cables demonstrate the modal decomposition of a pulsed signal, which varies depending on the state of the probed wire. It is shown that the presented tasks can be solved by modal probing. The article also considers the analysis of modal distortions in frequency domain and gives the formula for its practical use. This formula can be useful when the pulse duration time is longer than the minimum of mode delay difference. In conclusion, we present further development ideas of the modal probing.

Analytical Calculation and Numerical Modeling of Temporal Characteristics of a Short Pulse Propagating in a Planar Waveguide with Rough Boundaries

We present the results of numerical modeling by the Monte-Carlo method of the pulse signal propagation in a planar waveguide with smooth rough boundaries during bistatic sounding. The results of the numerical and analytical calculations in the case of single reflection are compared. Temporal characteristics of the received signal with multiple reflection and a low grazing angle are analyzed.

Features of the propagation of pseudorandom pulse signals from the shelf to deep water in the presence of gyre formation on the acoustic track

The paper discusses the results of an experiment conducted in the Sea of Japan in March 2016 on an acoustic track 194 km long in winter hydrological conditions. The most complex case of propagation of pseudorandom pulse signals from the shelf to deep water in the presence of gyre formation on the acoustic track. An analysis of the experimentally obtained pulse characteristics show that at all points, a maximum, in terms of amplitude, first arrival of acoustic energy is recorded. This is evidence that at a given depth horizon, pulses that have passed the shortest distance through a near-surface sound channel at small angles close to zero are received first. The calculation method of mean sound velocity on the track, based on the satellite data of surface temperature monitoring, is proposed. We expect that the results obtained with this method can be successfully used for the purposes of acoustic range finding and navigation.

Modeling of acoustic pulse signal propagation in deep sea using the Maslov canonical operator

An asymptotic solution to the problem of sound pulse propagation in deep sea is derived using the Maslov canonical operator. An example of a waveguide with the Munk sound speed profile and a point source is considered, and an asymptotic expression for the pulse signal time series at the receiver is obtained. The asymptotic solution is compared with the solution computed using the normal mode theory.

Low-Loss and Low-Dispersion Transmission Line Over DC-to-THz Spectrum

Transmission lines or waveguides are the most fundamental building blocks of all electronic and photonic circuits and systems. Efforts have been made to incrementally evolve and improve existing transmission line structures to meet the increasingly stringent demands for signal transmission bandwidth and performance. However, a potentially revolutionary scheme or disruptive concept is required in support of future technological needs and bridging the gap between electronics and photonics. In this paper, we report on a fully integrated transmission line with simple structure that overcomes the long-standing bottleneck problems of high attenuation, strong dispersion, and low mode confinement in the guided-wave signal transmission from dc to terahertz (THz). This so-called mode-selective transmission line (MSTL) supports super-broadband and/or ultrafast pulse signal propagation, making it a disruptive solution for building future high-performance analog and digital integrated electronics and photonics. To demonstrate this scheme, an MSTL on fused silica substrate is designed, fabricated, and experimentally measured from near-dc to 0.5 THz, showing less than 0.35 dB/mm attenuation and low dispersion characteristics over the entire frequency range.

Transverse compactlike pulse signals in a two-dimensional nonlinear electrical network.

We investigate the compactlike pulse signal propagation in a two-dimensional nonlinear electrical transmission network with the intersite circuit elements (both in the propagation and transverse directions) acting as nonlinear resistances. Model equations for the circuit are derived and can reduce from the continuum limit approximation to a two-dimensional nonlinear Burgers equation governing the propagation of the small amplitude signals in the network. This equation has only the mass as conserved quantity and can admit as solutions cusp and compactlike pulse solitary waves, with width independent of the amplitude, according to the sign of the product of its nonlinearity coefficients. In particular, we show that only the compactlike pulse signal may propagate depending on the choice of the realistic physical parameters of the network, and next we study the dissipative effects on the pulse dynamics. The exactness of the analytical analysis is confirmed by numerical simulations which show a good agreement with results predicted by the Rosenau and Hyman K(2,2) equation.