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This paper presents the verification of indoor propagation channel simulations based on an intelligent ray launching algorithm (IRLA) in the Ka‐band of the millimeter‐wave (mmWave) spectrum in various indoor environments, including a classroom, an office, and a corridor, by radio channel measurements. Power delay profiles (PDPs), path loss, and root‐mean‐square (RMS) delay spreads were obtained from both the simulation results and the measurement results. Moreover, parameters of two site‐general path loss models, the close‐in free space reference distance path loss model and the floating‐intercept path loss model, were estimated based on the measured and simulated path loss. The comparison between the simulation results and the measurement results indicates that the IRLA‐based simulation can accurately describe the main characteristics of the indoor propagation channel in the Ka‐band. Key Points: Intelligent ray launching algorithm (IRLA) based channel simulations in three‐dimensional (3‐D) indoor environment modelsRadio channel measurements in indoor environments in the Ka‐band of the millimeter‐wave (mmWave) spectrumComparison of power delay profiles (PDPs), path loss, and root‐mean‐square (RMS) delay spreads between simulation and measurement results [ABSTRACT FROM AUTHOR]

With the increasing number of mobile phone users, new services, and mobile applications, the proliferation of radio antennas has raised concerns about human exposure to electromagnetic waves. This is now a challenging topic to many stakeholders such as local authorities, mobile phone operators, citizen, and consumer groups. Thus, the prediction of exposure map at urban scale is a very important requirement to find a relevant indicator of the real exposure. In this paper, we propose a monitoring solution for electromagnetic field (EMF) exposure based on a numerical modeling of the radio wave propagation radiated by mobile telephony base stations. The accuracy of this tool directly depends on the input data precision, such as location of base station antennas or their radiation pattern, which are often poorly known. These data are therefore refined by an optimization algorithm fed by a lot of information, such as the indication of the received signal strength (RSSI) measured directly from users' smartphones, which are used as probes. Results show that this method significantly improves the precision of unknown data concerning mobile base stations and the accuracy of exposure maps at urban scale. [ABSTRACT FROM AUTHOR]

For many laser machining applications, an assist gas is required. However, for applications with high pressure or temperature gradients, the density of the assist gas is not homogeneous. Thus, the laser propagation is influenced by the density properties within the turbulent gas. In this article, an overview and example results of the influence of a nozzle geometry on the light propagation in two dimensions are presented. [ABSTRACT FROM AUTHOR]

Radio propagation prediction simulation methods based on deterministic technique such as ray launching is extensively used to accomplish radio channel characterization. However, the superiority of the simulation depends on the number of rays launched and received. This paper presented the indoor three-dimensional (3D) Minimum Ray Launching Maximum Accuracy (MRLMA) technique, which is applicable for an efficient indoor radio wave propagation prediction. Utilizing the novel MRLMA technique in the simulation environment for ray lunching and tracing can drastically reduce the number of rays that need to be traced, and improve the efficiency of ray tracing. Implementation and justification of MRLMA presented in the paper. An indoor office 3D layouts are selected and simulations have been performed using the MRLMA and other reference techniques. Results showed that the indoor 3D MRLMA model is appropriate for wireless communications network systems design and optimization process with respect to efficiency, coverage, number of rays launching, number of rays received by the mobile station, and simulation time. [ABSTRACT FROM AUTHOR]

Validating a 3D indoor radio propagation model that simulates the signal strength of a wireless device can be a challenging task due to an incomplete or a faulty environment model. In this paper, we present a novel method to simulate a complete indoor environment that can be used for evaluating a radio propagation model efficiently. In order to obtain a realistic and robust model of the full environment, the OctoMap framework is applied. The system combines the result of a SLAM algorithm and secondly a simple initial model of the same environment in a probabilistic way. Due to this approach, sensor noise and accumulated registration errors are minimised. Furthermore, in this article, we evaluate the merging approach with two SLAM algorithms, three vision sensors, and four datasets, of which one is publicly available. As a result, we have created a complete volumetric model by merging an initial model of the environment with the result of RGB-D SLAM based on real sensor measurements. [ABSTRACT FROM AUTHOR]

In this paper, an inhomogeneous human body model was presented to investigate the propagation characteristics when the human body was used as an antenna to achieve signal transmission. Specifically, the channel gain of four scenarios, namely, (1) both TX electrode and RX electrode were placed in the air, (2) TX electrode was attached on the human body, and RX electrode was placed in the air, (3) TX electrode was placed in the air, and RX electrode was attached on the human body, (4) both the TX electrode and RX electrode were attached on the human body, were studied through numerical simulation in the frequency range 1 MHz to 90 MHz. Furthermore, the comparisons of input efficiency, accepted efficiency, total efficiency, absorption power of human body, and electric field distribution of different distances of four aforementioned scenarios were explored when the frequency was at 44 MHz. In addition, the influences of different human tissues, electrode position, and the distance between electrode and human body on the propagation characteristics were investigated respectively at 44 MHz. The results showed that the channel gain of Scenario 4 was the maximum when the frequency was from 1 MHz to 90 MHz. The propagation characteristics were almost independent of electrode position when the human body was using as an antenna. However, as the distance between TX electrode and human body increased, the channel gain decreased rapidly. The simulations were verified by experimental measurements. The results showed that the simulations were in agreement with the measurements. [ABSTRACT FROM AUTHOR]

Deterministic field prediction has been widely used to provide channel data for coverage analysis. Among these prediction tools, point cloud-based methods have been developed for millimeter-wave frequencies in order to characterize the environment with higher precision, but they have not taken into account all the necessary propagation mechanisms. In this paper, we present the implementation for predicting both specular reflections and diffraction as well as the total channel, including the aforementioned mechanisms along with scattering and shadowing. Both line-of-sight (LOS) and non-LOS channels are predicted and validated against measurements in a cafeteria. The result shows excellent agreement between prediction and measurement in terms of power delay profiles, power angular spectra, path loss, mean delay, delay spread, and azimuth spread. [ABSTRACT FROM PUBLISHER]

Luby transform (LT) codes were the first practical rateless erasure codes proposed in the literature. The performances of these codes, which are iteratively decoded using belief propagation algorithms, depend on the degree distribution used to generate the coded symbols. The existence of degree-one coded symbols is essential for the starting and continuation of the decoding process. The absence of a degree-one coded symbol at any instant of an iterative decoding operation results in decoding failure. To alleviate this problem, we proposed a method used in the absence of a degree-one code symbol to overcome a stuck decoding operation and its continuation. The simulation results show that the proposed approach provides a better performance than a conventional LT code and memorybased robust soliton distributed LT code, as well as that of a Gaussian elimination assisted LT code, particularly for short data lengths. [ABSTRACT FROM AUTHOR]

The article presents a study on the prediction quality of the ITS HF Propagation application suite: VOACAP (Voice of America Coverage Analysis Program), ICEPAC (Enhanced Profile Ionospheric Communications Circuit Analysis and Prediction Program) and REC533 (ITU Recommendation RS 533) for point to point connections of the NVIS (Near Vertical Incidence Sky-wave) type. The simulation results were compared to the measurements obtained on a NVIS direction carried out in Romania and with the measurement results obtained and published by Walden in [1] for a NVIS network established in the UK. Compared with the measurement data obtained in Romania, the results predicted by the three applications have achieved average values of the correlation factors. These low values regarding the quality of a predictive application are due to the short observation period of the ionospheric channel. In these circumstances, REC533 achieved the lowest mean value of the standard deviations compared to VOACAP and ICEPAC. Regarding the measurement results published by Walden, the three applications have achieved strong values. These results lead to high values of the coefficient of determination, ensuring a very good power of prediction. REC533 provided the most correlated values and the lowest average value of standard deviations. The results provided by ICEPAC and VOACAP are highly correlated for each month under review. Of the three applications analysed, the best predictions were obtained by REC533. [ABSTRACT FROM AUTHOR]

Acoustic tracking with propagation delay is a challenging problem for the following reasons: 1) It is difficult to perform an accurate state prediction, as the time interval between the current state and the previous state is varying and unknown due to the propagation delay; and 2) the target time (signal emission time) needs to be estimated in addition to the target position and velocity. With the state augmented with the target time, the state transition cannot be described by the commonly used explicit Gauss?Markov model. In this paper, we propose a new approach to solving this difficult problem by using the Gauss?Helmert model for the state transition, which consists of an implicit equation between two consecutive states. An unscented Gauss?Helmert filter is then developed based on this formulation. The new approach is applied to the bearings-only tracking problem with state-dependent propagation delay. Simulation tests are conducted to demonstrate the performance of the unscented Gauss?Helmert filter, which is shown to outperform other approaches in terms of estimation accuracy, especially when a target is moving at high speed. [ABSTRACT FROM PUBLISHER]

Soliton-like nonlinear SPPs have shown to posses intensity dependent propagation characteristics. Two different dispersion relations with arbitrary parameters being input field intensity and position of soliton-like peak were derived and coupled using self-consistent calculations to avoid arbitrary parameters in order to study exact propagation characteristics of nonlinear SPP supported by a linear–metal/nonlinear slab waveguide. It is observed that the position of soliton-like peak in nonlinear medium has significant contribution in determining dispersion characteristics of nonlinear SPP. The propagation properties and mode profiles of nonlinear SPP obtained could help in exploring further possibilities of exciting and guiding SPP efficiently in nanoscale waveguides using nonlinear substrate. [ABSTRACT FROM AUTHOR]

Vehicular ad hoc networks (VANETs) form an evolving field of wireless technology that focuses on a wide range of useful applications from safety-related applications to infotainment services. Radio propagation models (RPMs) in VANETs require a high level of realistic detail due to mobility, the nature of the network, technology limitations and urgency of information dissemination. Hence, developing realistic RPMs in VANETs is a challenging task. Nonetheless, a number of traditional models are considered realistic; however, the absence of a required level of detail is a critical aspect of currently employed RPMs. For instance, modeling obstacles in VANETs is a challenging research perspective. Two types of radio obstacles exist in an urban transportation environment: moving obstacles and static obstacles, both of which block radio signals in vehicle-to-infrastructure and vehicle-to-vehicle communication. In this paper, a thematic taxonomy of existing RPMs is proposed and the major challenges involved in modeling realistic radio propagation for VANETs, especially in urban environments, are presented. Existing RPMs are classified and compared using the proposed taxonomy. These RPMs are grouped according to obstacle modeling pattern and are analyzed using important parameters, such as received signal strength, packet delivery ratio, delivery latency and average path length. Issues and challenges with existing RPMs are put forward and recommendations that may be helpful for developing realistic RPMs are made. [ABSTRACT FROM AUTHOR]

The deployment of nodes in Wireless Sensor Networks (WSNs) arises as one of the biggest challenges of this field, which involves in distributing a large number of embedded systems to fulfill a specific application. The connectivity of WSNs is one of the main issues to assure the efficiency of the system implementation and the quality of the service of the deployment, which is difficult to estimate due to the diversity and irregularity of the applied environment and it affects the WSN designers’ decision on deploying sensor nodes. Therefore, in this paper, a new method is proposed to enhance the efficiency and accuracy on ZigBee propagation modeling and simulation in indoor environments. The method consists of two steps: automatic 3D indoor reconstruction and 3D ray-tracing based radio simulation. The automatic 3D indoor reconstruction employs unattended image classification algorithm and image vectorization algorithm to accurately build the environment database, which also significantly reduces time and efforts spent on non-radio propagation issues. The 3D ray tracing is developed by using a kd-tree space division algorithm and a modified polar sweep algorithm, which accelerates the searching of rays over the entire space. A ZigBee signal propagation model is proposed for the ray-tracing engine by considering both the materials of obstacles and the impact of positions along the ray path of the radio. Three different WSN deployments are realized in the indoor environment of an office and the simulation results are verified to be accurate. Experimental results also indicate that the proposed method is efficient in the pre-simulation strategy and the 3D ray searching scheme, and it is robust for different indoor environments. [ABSTRACT FROM AUTHOR]

In this work, we study the impact of antenna radiation patterns disturbed by urban furniture on propagation characteristics. The propagation in urban scenario is modeled with a ray-based deterministic tool. Different base station scenarios are discussed: antenna in proximity of a wall; antenna mounted on a lamp post; and antenna on a bus stop shelter. The statistical influence of the support is evaluated comparing the results in terms of pathloss with the ones obtained when the isolated antenna radiation patterns are considered. [ABSTRACT FROM PUBLISHER]

In this paper, we derive the backscattering coefficient/forward propagation equation for frequency-modulated waves of high-frequency radar over the sea. Numerical simulations have been performed in order to compare the characteristics of a constant frequency and frequency-modulated electromagnetic wave in the function of sea state and index profile. From these simulations, we have drawn some conclusion on the differences in the Doppler spectrum observed for the two waveforms. [ABSTRACT FROM PUBLISHER]

A novel deterministic approach to model the radio wave propagation channels in complex indoor environments reducing computational complexity is proposed. This technique combines a neural network and a 3-D ray launching algorithm in order to compute wireless channel performance in indoor scenarios. An example of applying the method for studying indoor radio wave propagation is presented and the results are compared with a very high resolution fully 3-D ray launching simulation as the reference solution. The new method allows the use of a lower number of launched rays in the simulation scenario whereas intermediate points can be predicted using neural network. Therefore a high gain in terms of computational efficiency (approximately 80% saving in simulation time) is achieved. [ABSTRACT FROM PUBLISHER]

Propagation of Radio Frequency (RF) waves in indoor corridors is very complex and diverse as the propagation effects in the indoor scenarios are those that change over fractions of wavelength. Therefore, understanding of RF propagation characteristics is vital for the design of air interface and estimation of propagation losses is very much needed especially for wireless networks such as randomly deplorable Wireless Sensor Communications. In this research work, short-range, near floor/ground RF propagation path loss measurements at low antenna heights of 2 cm and 50 cm from the floor were made in typical narrow and wide straight indoor corridors at 915/2400 MHz in a modern multi-storied building utilizing RF equipment. Comparisons between measured and simulated path loss values were made utilizing Matlab simulations of Ray-tracing technique, free space and ITU-R models. Mean path loss exponent values were deduced from the measured data. The research work reported in this paper is predominately geared towards characterizing radio link for Wireless Sensor Communications/Networks in typical indoor corridor environments. [ABSTRACT FROM AUTHOR]

In this paper, we present a new type of a double-negative metamaterial (MTM) absorber based with resonant-magnetic structures, with a periodic array composed of a split-ring resonator (SRR) and two open complementary split-ring resonators (OCSRRs). In contrast to common absorber configurations, the absorber proposed in this paper does not use a metallic back plate or a resistive sheet. In order to eliminate the need for this metallic back plate, a planar array of SRRs is placed parallel to the incident wave propagation direction. An appropriately designed combination structure of two OCSRRs and a SRR exhibits negative permittivity and negative permeability in the same frequency band. Each unit cell is printed on both sides of an FR-4 substrate. A prototype absorber was fabricated with a planar array of 75 x 42 unit cells. Both simulations and experiments verify the effectiveness of the proposed backplane-less MTM absorber. The proposed backplane-less absorber can be used for microwave applications. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a simulation model of the origin and propagation of speckle field within the Fresnel approximation and verification of the model through a speckle correlation method for determination of in-plane object''s translation. There is used a convolution form of the Fresnel–Kirchhoff diffraction integral in the simulation model instead of often used Fast Fourier Transform approach. A possible way of simulation of the light scattering by object''s surface and in-plane translation of the illuminated surface is mentioned, whereas two types of illumination (plane wave and Gaussian beam) are used. Finally, results of numerical correlation of generated displaced speckle fields are shown and compared with the results obtained by theoretical relations. [Copyright &y& Elsevier]

Suzuki distribution is a popular model in wireless communications. In this paper, a generalization of it is proposed and two moment estimates derived. The performance of the estimates is assessed by simulation. Finally, applications are discussed for two problems in wireless communications. [ABSTRACT FROM AUTHOR]

This study deals with the propagation of transverse andmicrorotational waves in micropolar thermodiffusion elastic half-space in context of non classical (generalized) theories of thermoelasticity developed by Lord and Shulman (L-S theory) and Green and Lindsay (G-L theory). The amplitude ratios are obtained in closed form and numerically simulated results are presented graphically against angle of incidence. The phenomenon of micropolarity, diffusion and impact of relaxation times are studied on the amplitude ratios. The results of some earlier investigations have also been deduced as particular case from the present investigation. [ABSTRACT FROM AUTHOR]

Abstract: Solitary wave evolution over a shelf including porous damping is investigated using Volume-Averaged Reynolds Averaged Navier–Stokes equations. Porous media induced damping is determined based on empirical formulations for relevant parameters, and numerical results are compared with experimental information available in the literature. The aim of this work is to investigate the effect of wave damping on soliton disintegration and evolution along the step for both breaking and non-breaking solitary waves. The influence of several parameters such as geometrical configuration (step height and still water level), porous media properties (porosity and nominal diameter) or solitary wave characteristics (wave height) is analyzed. Numerical simulations show the porous bed induced wave damping is able to modify wave evolution along the step. Step height is observed as a relevant parameter to influence wave evolution. Depth ratio upstream and downstream of the edge appears to be the more relevant parameter in the transmission and reflection coefficients than porosity or the ratio of wave height–water depth. Porous step also modifies the fission and the solitary wave disintegration process although the number of solitons is observed to be the same in both porous and impermeable steps. In the absence of breaking, porous bed triggers a faster fission of the incident wave into a second and a third soliton, and the leading and the second soliton reduces their amplitude while propagating. This decrement is observed to increase with porosity. Moreover, the second soliton is released before on an impermeable step. Breaking process is observed to dominate over the wave dissipation at the porous bottom. Fission is first produced on a porous bed revealing a clear influence of the bottom characteristics on the soliton generation. The amplitude of the second and third solitons is very similar in both impermeable and porous steps but they evolved differently due to the effect of bed damping. [Copyright &y& Elsevier]

ABSTRACT We analyse the overionization or proximity zone of the intergalactic matter around high-redshift quasars in a cosmological environment. In a box of 64 h−1 Mpc base length, we employ high-resolution dark-matter-only simulations with 10243 particles. For estimating the hydrogen temperature and density distribution, we use the effective equation of state by Hui & Gnedin. Hydrogen is assumed to be in photoionization equilibrium with a model background flux which is fitted to recent observations of the redshift dependence of the mean optical depth and the transmission flux statistics. At the redshifts z= 3, 4 and 4.8, we select model quasar positions at the centre of the 20 most massive haloes and 100 less massive haloes identified in the simulation box. From each assumed quasar position, we cast 100 random lines of sight for two box length, including the changes in the ionization fractions by the high-resolution quasar (QSO) flux field, and derive mock Lyman α spectra. The proximity effect describes the dependence of the mean normalized optical depth ξ=τeff, QSO/τeff, Lyα as a function of the ratio of the ionization rate by the QSO to that of the background field, ω=ΓQSO/ΓUVB, that is, the profile ξ= (1 +ω/ a)−0.5, where a strength parameter a is introduced. The strength parameter measures the deviation from the theoretical background model and is used to quantify any influence of the environmental density field. We improve the statistical analysis of the profile fitting in employing a moving average to the profile. We reproduce an unbiased measurement of the proximity effect which is not affected by the host halo mass. The scatter between the different lines of sight and different quasar host positions increases with decreasing redshift, σlog a≈ 0.08, 0.20 and 0.36 for z= 4.8, 4 and 3, respectively. Around the host haloes, we find only a slight average overdensity in the proximity zone at comoving radii of 1 < rc < 10 h−1 Mpc. However, a clear power-law correlation of the strength parameter with the average overdensity in rc is found, showing an overestimation of the ionizing background in overdense regions and an underestimation in underdense regions. [ABSTRACT FROM AUTHOR]

Abstract: The recently developed Morphological Acceleration Factor (MORFAC) approach for morphodynamic upscaling enables numerical model simulations of coastal evolution at decadal to millennial time scales. Primarily due to the massive increase in modeling time scales it affords, the MORFAC approach is now standard in state-of-the-art commercially available coastal morphodynamic modeling suites. However, the general validity of the MORFAC concept for coastal applications has not yet been comprehensively investigated. Furthermore, a robust and objective method (as opposed to the subjective and inelegant trial and error method) for the a priori determination of the highest MORFAC that is suitable for a given simulation (i.e. critical MORFAC) does not currently exist. This communication presents some initial results of an ongoing, long-term study that attempts to rigorously and methodically investigate the limitations and strengths of the MORFAC approach. Based on the results of a strategically designed numerical modeling exercise using the morphodynamic model Delft3D, two main outcomes are presented. First, the main dependencies and sensitivities of the MORFAC approach to fundamental forcing conditions and model parameters are elucidated. Second, a criterion based on the Courant–Friedrichs–Levy (CFL) condition for bed form propagation that maybe used as a guide to determine the critical MORFAC a priori is proposed. [Copyright &y& Elsevier]

Abstract: In this work, the large-wave simulation (LWS) method is adapted for application in spilling wave breaking over a constant slope beach. According to LWS, large scales of velocities, pressure and free-surface elevation are numerically resolved, while the corresponding unresolved scale effects are taken into consideration by a subgrid scale (SGS) model for wave and eddy stresses. The model may be not fully applicable in very shallow water, close to the shoreline, where the unresolved, turbulent, free-surface oscillation is of the same order with the water depth. Time integration of the Euler equations is achieved by a two-stage fractional scheme, combined with a hybrid scheme for spatial discretization, consisting of finite difference and pseudospectral approximation methods. Model parameters are calibrated by comparison to available experimental data of free-surface elevation and velocities in the surf zone for cross-shore incoming waves. The action of the wave SGS stresses in the outer coastal and surf zones initiates breaking and generates appropriate vorticity, in the form of an eddy structure (surface roller), at the breaking wavefront. At incipient breaking, both advection and gravity contribute to the vorticity flux at the free surface, while only after the full development of the surface roller, the effect of advection becomes stronger. The SGS model is also utilized to simulate propagation, refraction and breaking of oblique incoming waves. The gradual breaking and dissipation of wave crestlines and the surface roller structure along the breaking wavefront are automatically captured without any empirical input, such as data for the roller shape or the wave propagation angle at breaking. [Copyright &y& Elsevier]

In this work, a methodology of statistical channel modeling for 60 GHz WLAN systems is proposed and a channel model for the office conference room environment is developed. The proposed methodology takes into account the most important properties of the indoor 60 GHz propagation channel such as large propagation loss and necessity to use steerable directional antennas by the WLAN stations, quasi-optical propagation nature, clustering structure of the channel, and significant impact of the polarization characteristics. A general mathematical structure of the channel model that supports all the described 60 GHz propagation channel properties is suggested. Then the conference room scenario for 60 GHz WLAN systems is introduced. Development of the inter cluster, intra cluster, and polarization impact modeling parameters is considered in details first explaining the used methodology for each channel modeling aspect and then followed by its application to the conference room scenario. The raw data for the channel model development include the experimental results [1], [2] and ray-tracing simulations for the conference room scenario. The proposed channel modeling methodology and the developed conference room channel model were adopted by the IEEE 802.11ad committee for 60 GHz WLAN systems standardization. [ABSTRACT FROM AUTHOR]

This article describes the indoor IRLA (Intelligent Ray Launching Algorithm), which originates from an efficient outdoor propagation prediction model. Implementation and validation are given in detail. An indoor office scenario is selected and simulations via the IRLA model and two other reference models have been performed. Predictions are analyzed and recommendations are given. Results show that the indoor IRLA model is suitable for indoor wireless network planning and optimization process. [ABSTRACT FROM AUTHOR]

The potential implementation of personal communication systems inside buildings requires a thorough understanding of signal propagation within buildings. As practical measurements are costly, difficult in accuracy, and time consuming that translate into costly service for the consumer, there is an increasing demand for efficient and accurate simulation-based indoor radio propagation prediction tools. Therefore, this study explores a new, efficient, and faster ray-tracing technique based on the Binary Angle Division algorithm for indoor radio signal prediction. The obtained simulated results are compared with other existing techniques to prove the superiority of the proposed algorithm in terms of both computational efficiency and accuracy. The results obtained from this study show satisfactory performance and good agreement with the simulated results. [ABSTRACT FROM AUTHOR]

Abstract: Propagation of the air shock wave caused by explosion via the bend of a bend laneway has obvious nonlinear characteristics, compared with its propagation in a straight laneway. These characteristics are important bases to analyze the accident of gas explosion in underground mines and to estimate the blast resistance of underground structures in mines. In this work, the rule of the shock wave propagation via the laneway bend and the pressure distribution are studied by means of the numerical simulation approach. Theoretical results show that attenuation of the peak overpressure with distance does not obey exponent law when the air shock wave goes through the laneway bend. At some locations within the bend zone, the overpressures are higher than ones around those locations, the front of original plane wave bends in the bend of the laneway and after passing through the bend, it gradually returns to the state of plane wave propagation. There is a span dependent on the cross section dimension of laneway and the bend angle and increasing with the bend angle, in which the peak overpressure of shock wave does not uniformly attenuate with distance. When the bend angle is equal to 135°, this span is about five times as long as the corresponding equivalent diameter of the laneway. Additionally, the impulse of air shock wave attenuates uniformly via the laneway bend. On the end section of the complicated pressure distribution area in the bend, it is 66.65–98.7% of that in the straight laneway at the same scaled distance. [ABSTRACT FROM AUTHOR]

Abstract: Understanding guided wave propagation in multi-layered plates and interaction with discontinuities can be difficult, as well as the interpretation of the ultrasonic signals. Propagation of guided waves can be studied analytically solving the equations of motion with the proper boundary conditions; nevertheless analytical models can be difficult to solve for complex multi-layered structures or having inner discontinuities. The problem can be efficiently studied using numerical techniques. Simulation of guided wave propagation in multi-layered structures, for ultrasonic waves in the MHz range, is solved here with the finite element analysis based on an explicit integration rule to solve the equations of motion in a dynamic analysis. Simulation allows a better understanding of propagation and interference phenomena by creating a window of observation in the multi-layered plate. Numerical results determined for a three-layer Al plate, without or with discontinuities, matched very well with experiments, providing an efficient tool to visualize and extract significant information in the transmitted waves and to optimize wave mode and configuration for a rigorous ultrasonic inspection. [Copyright &y& Elsevier]

Abstract: An accurate solution for high-frequency pulse propagation in an axisymmetric elastic bar is obtained using a new finite element technique that yields accurate non-oscillatory solutions for wave propagation problems in solids. The solution of the problem is very important for the understanding of dynamics experiments in the split Hopkinson pressure bar (SHPB). In contrast to known approaches, no additional assumptions are necessary for the accurate solution of the considered problem. The new solution helps to elucidate the complicated distribution of parameters during high-frequency pulse propagation down the bar as well as to estimate the applicability of the traditional dispersion correction used in the literature for the analysis of wave propagation in a finite bar. Due to the dimensionless formulation of the problem, the numerical results obtained depend on Poisson''s ratio, the length of the bar and the pulse frequency, and are independent of Young''s modulus, the density and the radius of the bar. [Copyright &y& Elsevier]

It is shown that binary low-density generator matrix codes can achieve the rate-distortion bound of discrete memoryless sources with general distortion measure via multilevel quantization. A practical encoding scheme based on the survey-propagation algorithm is proposed. The effectiveness of the proposed scheme is verified through simulation. [ABSTRACT FROM AUTHOR]

Abstract: This article deals with several aspects relative to the MIMO propagation channel. Based on simulations and/or measurements, different approaches are used to model the propagation channel. These models are useful for the MIMO system design. Several studies are performed in order to realize realistic simulation of MIMO channel. Different measurement techniques are used in characterizing the propagation channel in various environments. Measurement campaigns made in different situations have been analyzed to obtain the relevant statistical parameters of the channel. Simulation of MIMO channel is then presented. Measurement and simulation results provide an evaluation of the capacity of MIMO channel. Obtained results show feasibility in the integration of MIMO techniques in practical wireless communication systems. [Copyright &y& Elsevier]

The theory of propagating waves near a surface is reviewed with an eye to gain insight into the mechanisms involved, and to provide analytical-based models, for power-efficient on-body propagation. The Zenneck wave, and in particular the Norton wave, are appraised as candidate mechanisms for the propagation. For flush-mounted ("band aid") antennas, desired for on-body sensors, the Norton wave is the only direct propagation mechanism between the sensors. The Norton wave fits very well to simulation results presented here, and comparisons are also made with available published physical experiments, although these measurements typically feature the optical paths of elevated, or non-flush, antennas. [ABSTRACT FROM AUTHOR]

Abstract: Use of large-eddy simulation (LES) data in electromagnetic wave propagation modeling is not very common because of the high computational cost involved. A new phase-screen method is proposed to model radio wave propagation, in the atmospheric turbulence, using the resolved scale refractivity obtained from LES. The proposed method offers the same level of accuracy, as the one already existing in the literature, at much cheaper cost. [Copyright &y& Elsevier]

Based on finite element analysis, we propose a simulation model for radio frequency identification (RFID) SAW tag devices. Electric properties of metal electrode on substrate greatly affect the characteristics of the device and are discussed in the paper. Then the right and left boundary conditions for the device are applied to remove large unwanted waves generated by wave propagation near the boundaries. To save computation time, a 2-D model is proposed, where some mesh skills are applied. The tag device is simulated in 2 steps. First, we use modal analysis to get the device phase velocity and harmonic frequency. Second, a tag with multireflectors is simulated. Based on the simulations, we have designed and fabricated a SAW tag. A comparison is made between simulation and experimental results and shows our simulation model agrees with the experiment very well. [ABSTRACT FROM AUTHOR]

The modelling of pressure wave propagation into internal combustion engine manifolds implies the knowledge of multi-dimensional phenomena. However, computational times can be very important and this complex system requires reducing the order of the models. In the current paper, a new one-dimensional modelling of the inflow boundary conditions for a plain open end is proposed. This is obtained with the use of a computational fluid dynamics code and an experimental test bench under unsteady state conditions. Numerical and experimental analyses show that the pressure losses can be modelled with a coefficient that depends on the Mach number as well as geometrical parameters. Finally, numerical results are compared with experimental data in a shock tube application with an intake manifold of internal combustion engine. The code enhancements significantly improve flow calculations. [ABSTRACT FROM AUTHOR]

The performance of an ultra-high-frequency RF identification (ID) system operating at 869 MHz, intended for the ID of persons in both indoor and open areas, has been validated using the propagation models, as well as the series of practical measurements. A two-ray propagation model and the 3-D ray-tracing model were used for calculations of all important system parameters in open and indoor areas, respectively. For the application mentioned above, a novel (electrically small and, at the same time, low-profile) wearable TAG antenna was designed. It was used in order to carry out the necessary tests as well. The antenna in question is based on an artificial-like surface. The latter provides an important screening effect and avoids detuning. Another virtue of the surface used is represented by the fact that it ensures the minimum loss of the antenna efficiency (resulting from the presence of a nearby human body). The simulations and measurements show that the optimized system can guarantee a reliable ID at distances up to 9 m in open areas and up to 16 m in corridors. [ABSTRACT FROM AUTHOR]

Green's functions for radar waves propagating in heterogeneous 2.5D media might be calculated in the frequency domain using a hybrid method. The model is defined in the Cartesian coordinate system, and its electromagnetic properties might vary in the x- and z-directions, but not in the y-direction. Wave propagation in the x- and z-directions is simulated with the finite-difference method, and wave propagation in the y-direction is simulated with an analytic function. The absorbing boundaries on the finite-difference grid are perfectly matched layers that have been modified to make them compatible with the hybrid method. The accuracy of these numerical Green's functions is assessed by comparing them with independently calculated Green's functions. For a homogeneous model, the magnitude errors range from -4.16% through 0.44%, and the phase errors range from -0.06% through 4.86%. For a layered model, the magnitude errors range from -2.60% through 2.06%, and the phase errors range from -0.49% through 2.73%. These numerical Green's functions might be used for forward modeling and full waveform inversion. [ABSTRACT FROM AUTHOR]

We examine two spurious numerical artifacts of the complex envelope (CE) alternating-direction-implicitfinite-difference time-domain (ADI-FDTD) method, viz, spurious charges and anomalous wave propagation (modes with positive phase velocity and negative group velocity). These artifacts are also present in the conventional ADI-FDTD; however, the spurious charges in CE-ADI-FDTD have a fundamental distinction from those of ADI-FDTD: they are static in ADI-FDTD and implicitly time-harmonic in CE-ADI-FDTD. Spurious charges are particularly detrimental to CE-ADI-FDTD simulations because they produce secondary radiation. We also show that spurious charges can be reduced by a fixed-point iterative correction in CE-ADI-FDTD. [ABSTRACT FROM AUTHOR]

The influence of ground clutter contamination on the estimation of polarimetric radar parameters, horizontal reflectivity (Zh), differential reflectivity (Zdr), correlation coefficient (ρhν), and differential propagation phase (φdp) was examined. This study aims to derive the critical level of ground clutter contamination for Zh, Zdr, ρhν, and φdp at which ground clutter influence exceeds predefined precision thresholds. Reference data with minimal ground clutter contamination consist of eight precipitation fields measured during three rain events characterized by stratiform and convective precipitation. Data were collected at an elevation angle of 0.8° by the Météo-France operational, polarimetric Doppler C-band weather radar located in Trappes, France, ∼30 km southwest of Paris. Nine different ground clutter signatures, ranging from point targets to more complex signatures typical for mountain ranges or urban obstacles, were added to the precipitation fields. This is done at the level of raw in-phase and quadrature component data in the two polarimetric channels. For each ground clutter signature, 30 simulations were conducted in which the mean reflectivity of ground clutter within the resolution volume varied between being 30 dB higher to 30 dB lower than the mean reflectivity of precipitation. Differences in Zh, Zdr, ρν, and φdp between simulation and reference were shown as a function of ratio between ground clutter and precipitation intensities. As a result of this study, horizontal reflectivity showed the lowest sensitivity to ground clutter contamination. Furthermore, a precision of 1.7 dBZ in Zh is achieved on average when the precipitation and ground clutter intensities are equal. Requiring a precision of 0.2 dB in Zdr and 3° in φdp, the reflectivity of precipitation needs to be on average ∼5.5 and ∼6 dB, respectively, higher compared to the reflectivity of ground clutter. The analysis also indicates that the highest sensitivity to the nine clutter signatures was derived for ρhν. To meet a predefined precision threshold of 0.02, reflectivity of precipitation needs to be ∼13.5 dB higher than the reflectivity of ground clutter. [ABSTRACT FROM AUTHOR]

Non-line-of-sight (NLOS) propagation degrades the performance of wireless location systems. Thus, developing algorithms that are robust to NLOS considerations is of great importance. Based on time-of-arrival (TOA) and angle-of-arrival (AOA) measurements, this paper introduces a new approach, which consists of incorporating the coordinates of dominant scatterers as unknowns in the location algorithm. It is assumed that the first arriving path signal at each base station (BS) experiences a single dominant scatterer, but the BSs are allowed to have different dominant scatterers. Locating the mobile station is accomplished by means of a nonlinear optimization procedure under nonlinear constraints. Two algorithms are proposed: The first algorithm assumes that hybrid TOA/AOA measurements are available at three BSs. In the second algorithm, the AOA is assumed to be available at the serving BS only. The performance of the proposed algorithms is assessed and compared with that of existing algorithms through extensive simulations. [ABSTRACT FROM AUTHOR]

The collision of two laser pulses can inject electrons into a wakefield accelerator, and has been found to produce stable and tunable quasimonoenergetic electron beams [J. Faure et al., Nature 444, 737 (2006)]. This colliding pulse scheme is studied here with 3D particle-in-cell simulations. The results are successfully compared with experimental data, showing the accuracy of the simulations. The involved mechanisms (laser propagation, wake inhibition, electron heating and trapping, beam loading) are presented in detail. We explain their interplay effects on the beam parameters. The experimental variations of beam charge and energy with collision position are explained. [ABSTRACT FROM AUTHOR]

Laser generated ultrasound holds substantial promise for use as a tool for defect detection in remote inspection thanks to its ability to produce frequencies in the MHz range, enabling fine spatial resolution of defects. Despite the potential impact of laser generated ultrasound in many areas of science and industry, robust tools for studying the phenomenon are lacking and thus limit the design and optimization of non-destructive testing and evaluation techniques. The laser generated ultrasound propagation in complex structures is an intricate phenomenon and is extremely hard to analyze. Only simple geometries can be studied analytically. Numerical techniques found in the literature have proved to be limited in their applicability, by the frequencies in the MHz range and very short wavelengths. The objective of this research is to prove that by using an explicit integration rule together with diagonal element mass matrices, instead of the almost universally adopted implicit integration rule to integrate the equations of motion in a dynamic analysis, it is possible to efficiently and accurately solve ultrasound wave propagation problems with frequencies in the MHz range travelling in relatively large bodies. Presented results on NDE testing of rails demonstrate that the proposed FE technique can provide a valuable tool for studying the laser generated ultrasound propagation. [ABSTRACT FROM AUTHOR]

Schelkunoff's method, also commonly refered to as Coupled Mode Method (CMM), is a numerical method which gives the propagation constants and the electromagnetic field in a general homogeneous medium bounded by perfect electric walls. In this paper, we test Schelkunoff's method for a waveguide filled with an isotropic chiral material (chirowaveguide) where the dimensions of the walls are electrically large compared with the wavelength. It is reasonable to foresee that, in this case, the results given by Schelkunoff's method must approach to the corresponding ones for the chiral unbounded medium. Effectively, we obtain the solutions for both circular polarized waves (right-handed and left-handed) in free propagation in a single calculation. These results are in opposition with those of other authors analyzing analogous cases. [ABSTRACT FROM AUTHOR]

A model is presented that extends the applicability of the propagation data collected during a long measurements campaign in a particular site and for a particular radiolink, to a generic link in a generic site. In fact, the objective of the model is to create a set of attenuation time series to be used in the design of advanced TLC systems. The model assumes that the marked differences of the rain statistics observed in various locations are, in first approximation, mainly due to the different frequency of occurrence of the various rainy events rather than to their shape. Starting from this assumption the model selects, from a large database of rain attenuation events collected in a particular site, a subset that, after an appropriate frequency and elevation scaling, can be used to represent time series of attenuation recorded in other experimental conditions (as for both site and link). The model has been applied to the attenuation data collected at Spino d'Adda (Milan, Italy) during the ITALSAT propagation campaign in order to simulate attenuation time series in several different links and sites. The model demonstrated good performance both in link conditions and climates, similar and different from the Spino d'Adda ones. [ABSTRACT FROM AUTHOR]

The novel folded substrate-integrated waveguide (FSIW) is 50% narrower than the substrate-integrated waveguide, but both have similar propagation characteristics. This paper derives the analytical formulas of propagation and cutoff characteristics of the FSIW, as well as the formulas to calculate the width and gap of the central metal septum. Very good agreements (<2% error) are observed among the results of the theoretical formulas, numerical simulations, and hardware experiments over wide frequency and parameter ranges. [ABSTRACT FROM AUTHOR]

Abstract: The paper describes a new efficient method for finding and simulation of electric and magnetic fields in homogeneous non-dispersive electrically anisotropic materials. Electromagnetic wave propagation in these materials is descried by the time-dependent Maxwell’s system which implies initial value problems (IVPs) for electric and magnetic fields. Our method essentially uses matrix symbolic calculations in MATLAB and allows us to compute explicit formulae of electric and magnetic fields. These formulae are used for generating images of electric and magnetic fields inside different materials. A collection of electric and magnetic field images is presented in the paper. [Copyright &y& Elsevier]

Abstract: In this paper, a semi-deterministic propagation model for predicting short-term fading statistics in urban environments is presented. An approach to include surface scattering into deterministic ray-optical propagation models in urban scenarios is derived. This approach considers the coherent and incoherent components of the scattered signal. A statistical characterisation of the received signal at the received position permits to model the short-term fading for a local area around the mobile position using the Nakagami-m distribution. The parameters of the Nakagami-m distribution are obtained taking into account the real environment from a digital map information of the urban area. Computer simulation results and experimental data are compared. [Copyright &y& Elsevier]