Miscellaneous

RF Propagation in Mining Tunnels

Due to inherent higher order basis functions, efficient parallelization on multi core CPUs and support for simulations on GPU platforms, WIPL-D software can be effectively used for radio frequency propagation problems. One such problem would be determining power transfer between transmitter and receiver antennas at radio frequency (RF) frequencies in under-ground tunnels of significant length (several hundreds of meters).

The simulation setup involves positioning two antennas (transmitter and receiver) inside a very long tunnel. Usually walls are made of concrete, where characteristics vary: Er between 4 and 7 and Sigma between 0.02 and 0.0002. Tunnel height is 7.2 feet and width is 6 feet. Simulation frequency of interest ar 455 and 915 MHz. The effects of using horizontal or vertical polarization are also discussed. Simulations show comparison of measured and simulated data, where the distance between antennas is spanned between 0 and 500 feet, where simulation time is measured in hours.

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Different Simulation Scenarios Involving Unmanned Aerial Vehicles (UAVs)

Real-life scenarios with three drones (UAVs) carrying a payload, flying in a line formation, and communicating at frequency band around 2.4 GHz were investigated focusing on pure electromagnetic topics related to the physical layer of communication link between the drones. The first scenario serves as a reference and encompasses the drones above ground plane which is approximated with an infinite PEC plane. In remaining scenarios, a metallic wire fence has been introduced between two of the drones. The difference between the later is in the method used to model the wire fence.

From the simulation results It can be clearly seen that presence of the fence influences S-parameters between drones’ antennas ports. Also, the way of modelling the fence influences the results.

All the simulations were carried out using WIPL-D Software, a full wave 3D electromagnetic Method-of-Moments based software which applies Surface Integral Equations. According to the simulation times, it can be concluded that all simulations were performed in an efficient manner and that WIPL-D software can be used successfully for the analysis of drone related scenarios.

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Electromagnetic Reflectometry with Coaxial Cable Models-Currents in Time Domain

This application note describes how electromagnetic simulations using WIPL-D Pro, 3D EM simulation software, can be used together with WIPL-D Time Domain Solver (TDS) module to perform the time domain reflectometry simulation. TDS performs transient analysis of a 3D electromagnetic structure. The time-domain response of a structure is calculated using frequency domain simulation and Fourier transform. The tool is integrated into WIPL-D Pro software environment so that the frequency domain simulation and conversion to the time-domain are performed automatically.

Reflectometers can be used for non-destructive locating and characterization of discontinuities in coaxial cables. In real-life, for example, time domain reflectometry is applied for locating faults in airplane wiring. For precise locating of cable faults, so called spread spectrum time domain reflectometry is used.

In order to show the speed and accuracy of WIPL-D electromagnetic solver, three models of coaxial cables were simulated and generator currents calculated in time domain. The first model represents a straight coaxial cable with a fault. The dielectric between the cable conductors is air. For this structure, a theoretical result is available and could be used as a referent result to compare with the results obtained from WIPL-D simulations. The second model corresponds to a plain, curved cable. Finally, the third model represents a curved coaxial cable with a fault. For the curved cables, dielectric between the conductors has frequency dependent characteristics. All three coaxial cables have the same length.

The location of the cable fault as obtained with WIPL-D simulation and the one calculated based on EM theory are in excellent agreement.

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Convergence Study and Numerical Kernel Settings in MPA Simulations

A demonstration example of convergence study of calculated S-parameters was presented in this application note. The convergence study relates to simulations using WIPL-D Pro CAD, which is a full wave 3D electromagnetic Method-of-Moments based software. The EM model used for demonstrational purposes is a microstrip patch antenna operating around 2.40 GHz. All the conclusions derived here can be directly applied to many EM components operating in this widely exploited frequency band.

The application note covered a convergence study of the results on the model which can be considered as a sample of widely simulated modest\lower electrical size EM models. This convergence study was based on proper increasing of Integral accuracy and Reference frequency parameters. Also, the application note contains a recommendation for applying Edge-ing in printed structures simulations.

It was shown that changing numerical settings can improve the convergence of the output results. Thus, it is highly recommended to be performed. It was also shown that optimal numerical kernel settings should be exploited, since changing of numerical settings increases simulation time and number of unknowns which becomes very important when working with electrically large or detailed models.

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Frequency Selective Surface

There is a growing demand for new materials to enhance device performances at low cost. For several years, many periodicals there have been published (built from large number of uniform cells) which show that such engineering issues can be resolved.

Numerous cases demonstrate how some typical problems can be solved by using WIPL-D software.

They include: dipole radiation modified by very close FSS at 13 GHz, coupling between dipoles over FSS (WIPL-D is inherently able to calculate very low values of antenna coupling, well below -100 dB), RCS from FSS on dielectric slab (7×7 cells), energy transfer through FSS (additional 30 dB isolation), rectangular horn covered with FSS metallic radome. All models are run on standard desktop PC equipped with inexpensive GPU card. Simulation time is under 1h even for the most complicated cases.

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Wire Equivalents of Antenna Standoffs

The paper presents an efficient technique to determine equivalents of antenna dielectric standoffs in the form of wires with distributed loadings. The capacitive coupling of the antenna tube with the ground is characterized by capacitance per unit length (e.g. in pF/foot) of the transmission line made by the tube and the ground. Influence of each dielectric standoff can be emulated by wire of properly determined radius and distributed loading. The equivalent radius and the distributed loading are determined by cross-section dimensions of the standoff and its electrical properties (relative dielectric constant). The relative dielectric constant can be determined the tube radius and capacitance per unit length in the presence of dielectric stand. Using reverse engineering, dielectric constant can be emulated if the capacity per unit length is known. If simple and fast model are required for fast simulation and optimization, replacement of the dielectric standoff with wires with distributed loadings is the right approach. It is shown that the results obtained using WIPL-D are very close to the theoretical result, which proves the concept.

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Log-Periodic Dipole Antenna in AW Modeler

Log-Periodic Dipole Antenna with the 52 printed dipoles is created in WIPL-D AW Modeler and then simulated in WIPL-D Pro. The symmetry has been applied, as well as edge manipulation (other simulation parameters are left at the default). Entire antenna is around 261 mm long and it is placed 4.25 mm away from the metallic circle with diameter 248 mm. The longest arm of the antenna is around 76.2 mm long and length of the shortest one is around 1.53 mm.

Simulation times and number of unknowns needed for simulating LPDA antenna at different operating frequencies in the frequency range from 1 GHz to 18 GHz, are presented in the application note. The simulation hardware is standard desktop PC, empowered by low-end Nvidia GPU card (GPU solves has been used to speed up matrix inversion).

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WIPL-D 2-D Solver

WIPL-D 2-D Electromagnetic Solver is indented for numerical electromagnetic analysis of cylindrical structures, theoretically infinitely long. The program works with 2-D cross-sections (cuts) of the analyzed structure.

Numerical engine is based on the surface integral equation formulation: electric field integral equations (EFIE) for metallic structures and PMCHWT formulation for dielectric and magnetic materials. It can handle arbitrary combinations of piecewise linear materials along with any combination of infinitely or finitely thin layers with distributed loadings.

The examples in the application note include near field in the vicinity of PEC elliptical scatterer, demo of complex 3-D structure with incorporated tool for extraction of cuts, and 12-decade frequency sweep of backscattered RCS from a perfectly conducting cylinder with circular cross section of 1 m radius.

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WIPL-D Optimizer

WIPL-D Optimizer is a powerful multi-algorithm optimization tool that is being used by many successful professionals around the world. The tool calculates single solution as well as multiple solutions for complex/multi-criteria optimizations. Thanks to its simple and intuitive graphical interface, you can quickly solve the problem at hand.

Built in optimization algorithms are: Particle Swarm, Genetic, Simulated Annealing, Random, Gradient, Systematic and Simplex. Unique feature is that two optimization procedures with different algorithms can be performed in succession. The first one is used for coarse optimization and the second one is used for fine tuning. The examples include optimized horn antenna and automated design of a waveguide filter.

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Radiation Patterns and VSWRs of Handheld Devices in Several Real-Life Scenarios

Four scenarios encompassing handheld communication device in various real-life environments are discussed. In all the scenarios, results of interest are VSWR and radiation pattern presented using absolute gain.

For the model of the device resting in operator’s hands, the minimum of the VSWR is shifted downwards in frequency. Thus, it can be claimed that presence of operator working with the device results in a different current distribution comparing to the scenarios without the human involved.

The presence of the real ground influences the radiation pattern comparing to the handheld device in free space, while placing the device into human phantom’s hand influences the radiation pattern even more, but adding the clump in the last instance does not have significant influence to the radiation pattern.

It can be also concluded that although VSWR minimum is shifted when modeling the influence of an operator, realized gain in all three scenarios, which include a ground plane, does not vary significantly. This can be explained with low values of VSWR, below 2.0.

All the simulations were performed in reasonable amount of time using an affordable computer workstation.

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Microwave Tomography in Biomedicine using (A)Symmetry

This application note provides detailed theoretical explanation on how the asymmetry feature is implemented in the WIPL-D suite. The user effectively models half, quarter or one eight part of the structure and sets asymmetry planes. The last step is to adjust the required voltages of generators (equal amplitudes are the default value). The code afterwards determines minimum number of simulations required (by combining simulations with PEC and PMC planes).

The usage of the feature reduces number of unknowns 2/4/8 times and simulation time up to 4/16/64 times. The simulation time reduction depends on the electrical size of the problem and is more pronounced for the electrically larger problems. The usage of the feature allows using tremendously less powerful WIPL-D license and extends the range of structures that can be simulated.

The simulations have been carried out on inexpensive hardware platforms owing to GPU technology and the GPU solver. The examples include a simple circularly placed array of dipoles (to verify accuracy), canonical PEC cuboid (to verify reduction of number of unknowns and simulation time) and realistic 3D microwave tomography system. Last example shows how asymmetry allows solving demanding example in engineering acceptable time in UWB application

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