Microwave Imaging Systems for Medical Applications​

We have come up with a fully functional module developed on WIPL-D Pro 3D EM simulation environment for Microwave Imaging applications.

For such applications, the software provides flexibility in the use of STL files with the help of STL editor to develop anthropomorphic phantoms. It enables the user to analyze complexity of triangular mesh structures and allows to significantly reduce the computational requirement for the EM Simulation. For better accuracy and efficacy STL files with triangular mesh are converted to quadrilateral mesh. Further, to create the whole imaging scenario, an antenna system is developed with semi-automatic procedure. The automation system closely packages the antennas in the vicinity of the desired area of head, considering no intersection between the plates.

The imaging scenario is simulated at 1 GHz frequency. To understand the efficiency and accuracy of EM simulation, differential S parameters are inspected through direct approach (simulation result) and also with the help of transfer function of TSVD (Truncated Singular Value Decomposition) microwave imaging algorithm. Subsequently, simulated data for two different scenarios with and without stroke is used as input to the TSVD algorithm to detect and estimate the size and location of stroke for brain stroke application.

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PC Case as EMC Cavity

WIPL-D Software suite offers a remarkable variety of tools and features for efficient simulation of EMC. They are rigorously demonstrated by using an EM simulation of metallic PC case tower. The realistic model is easily built in WIPL-D Pro CAD (the tool offers solid modeling capabilities and built in quadrilateral mesher). The PC case dimensions are 45 x 40 x 18 cm.

The meshed model has large regular quads on flat surfaces without details and small quads around numerous details. This shows precisely captured geometry and challenging large-to-small scale details included. The first scenario is meant to illustrate the complexity of EM simulation in the cavity. Wire dipole is inside of the case and the result of interest is input impedance. Such result reveals resonance for each of the mode of the cavity. A more complex compatibility scenario involves placing two microstrip filters into PC case and observing the S-parameters.

All simulations are run on standard desktop, lasting under a minute for frequency, even for the most complex scenario. The simulation can be partially speeded up by using inexpensive GPU card.

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EMI Shielding of RG-58

This application note demonstrates that WIPL-D can be efficiently used for simulating EMI propagation of field inside the cables and lines. The focus is on the advanced model of RG-58 coax cable with imperfection braid shield, which can be easily replaced with a very simple equivalent model. After such a transformation, run times are measured in seconds and even the most complicated simulations are analyzed easily and, most important, accurately.

We have used such an equivalent model to run a demanding scenario with the total of 2 m coax length. We have demonstrated that with even the smallest suppression of field, the field inside is two orders of magnitude smaller than the field when we leave a coax end open. Next, we show that the field induced in microstrip line is additional order of magnitude larger.

All runs can be carried out at standard desktop PC. Significant speed up is achieved if multicore CPU workstations are used. As an additional befit, run times can be shortened by using single inexpensive GPU card.

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EM Shielding of Conductive Spherical Shell

Electromagnetic shielding represents the process of reducing the electromagnetic (EM) field by blocking the field using barriers made of conductive and/or magnetic materials. The exact purpose of EM shielding is to protect devices from the undesirable coupling between interior and exterior space of the device.

In this application note we are focused on shielding which is performed by enclosing the area under protection by a conducting shell. As analytical solution for spherical shell is well known as MIE series result. In order to achieve significant reduction of interference field inside the shell, thickness of its walls would be few times larger than skin depth. The field on outer surface of the shell is much larger than field on inner surface, so EM simulation must be carried out rigorously.

Results presented in the application note show that WIPL-D software package can be used for very accurate analysis of electromagnetic shielding problems. Almost perfect agreement between simulated and analytical results is obtained for problems with shielding efficiency of more than 260 dB. All the models described here are simulated at standard desktop PC with low number of unknowns, in just a few seconds.

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MIMO OTA in Anechoic Chamber

Common systems in the modern engineering to be investigated are multiple-input and multiple-output (MIMO) systems. Quite often, the performances of such systems are verified solely through measurement since the electromagnetic (EM) simulations are rather complex. One of the investigation methods is to place two or more antennas inside of an anechoic chamber and to investigate MIMO device under test (DUT). In this particular case, over-the-air (OTA) analysis will be used to determine system performance.

This application notes describes a simplified MIMO scenario showing how multiple horn antennas can be placed inside a large material coated anechoic chamber to test their OTA compatibility. The material characteristic is often unknown, but we show a simple procedure to emulate the characteristic satisfying the simulation demands.

The simulations are carried out on multicore CPU and multi-GPU workstation so that simulation times are very short for a very wide frequency band. Built-in interpolation allows quite smooth results, even with 15 points in a very wide band. If a single point is needed, the simulation can be carried out on a regular desktop PC equipped with a single GPU card, wing to GPU solver. The simulation time dramatically depends whether the frequency point is closer to start or end of the band.

Although the realistic problem where 80 lambda long anechoic chamber is covered with absorbers seems unreachable to full-wave EM solvers, WIPL-D software suite proves otherwise. Efficient numerical kernel, usage of GPU cards and WIPL-D GPU solver, efficient characterization of the coating material lead to straightforward simulation carried out in reasonable time.

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Resonant Frequencies in Rectangular Waveguide Cavity

Determining a resonant frequency of a cavity is a frequent task in analyzing various microwave systems. Due to the shape and interior structure of the cavity, it is often not possible to perform resonant frequency calculations by applying analytical formulas. In such cases, direct calculations are replaced by numerical EM simulation
WIPL-D Pro CAD can be used as an accurate and easy to use software tool. Resonant frequencies are calculated with very high precision. This is verified by comparing WIPL-D results with EM theory.

The simulations are carried out at regular desktop PC in negligible time. The powerful built-in interpolation algorithm allows obtaining high precision frequency domain results with very low number of frequency points.

The comparison of the results suggests that exciting the cavity with a dipole and a generator is highly effective. All resonant frequencies can be identified and coincide with the values obtained using analytical formulas.

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Emulating Electrical Properties of Magnetic Ferrite Tiles

This application note demonstrates emulation of magnetic ferrite tile electrical properties in WIPL-D Pro, a full 3D EM method of moments based solver (with usage of the WIPL-D Optimizer). Usually, the electrical properties themselves are unknown, while the performance of magnetic materials is provided in standard datasheets. Such magnetic materials can be used as absorbers in electromagnetic compatibility (EMC) problems and thus, the problem is of significant importance to electrical engineers.

In measurements, the electrical properties of materials are usually determined via the coaxial tube method. A hollow tube is made of the material with the unknown properties (e.g. magnetic ferrite tiles) and then inserted into a coaxial line. By using a relatively simple expressions for electromagnetic (EM) properties of material, we can optimize their performance until they reach the specification given in datasheets. A coaxial tube method (employed in EM solver) is used as emulation tool, with simulation and optimization performed in WIPL-D software suite. The magnetic material in question was selected as TDK IB-017.

We demonstrate that efficient use of the EM software allows simulation of magnetic ferrite tile materials. Although the electrical properties are given as performance characteristic (from the datasheet), the EM properties of the material are obtained by the optimization. The simple linear characteristic model yields excellent results, while improved parabolic model yields almost the perfect agreement with the datasheet data. All simulations are extremely short and do not require any particular hardware.

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Windmills WIPL-D EM Simulations

The WIPL-D implementation of MoM is an ideal candidate for RCS simulations of electrically large structures. A number of features leads to this: unique quad mesh applying higher order basis functions, CAD tool providing the optimum mesh, efficient implementation at CPU/GPU platforms and number of methods to reduce number of unknowns at EM insignificant model parts.

The code is pushed to the limits for the case of wind turbines. The main challenge represents the electrical height of the mils which is very large at frequencies of interest, and presence of resistive dielectric layers. The usual result required for the case of wind turbines is near field in the shadow zone.

The application note offers an unconventional combination of three simulation methods. The first method is WIPL-D 2D solver allowing simulation of infinite cylinders, both, coated or PEC, in seconds. This is a good approximation for modeling of either windmill mast or nacelle.

In the next step, the DDS solver is used as high frequency method for electrically large structures. The accuracy of the tool for the particular case is verified first by simulating PEC mast and comparing results with the default MoM full wave simulation. The result of interest is near field up to 50 km behind 50 m tall mast, at the height of 25 m. The iterative DDS method yields accurate solution after two iterations.

The final goal is simulation of entire wind turbine coated with single dielectric resistive layer. The simulation frequency is 3 GHz. Such a simulation is impractically large for MoM as in that case resulting million unknowns simulation lasts around 2 days on a workstation with 2 CPUs with 12 cores, plenty of RAM, four inexpensive Nvidia GTX cards and 5 fast SSD discs. On the other hand, using the same machine, the DDS requires only as many cores as possible. The same applies to RAM. The simulation time is now a couple of hours for PEC windmill and 1‑2 days for the coated case (nearly 3 million unknowns).

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Box with Slot Shielding Effectiveness

The aim of this application note is to calculate the shielding effectiveness of a PEC box with a slot, excited with a plane wave incident in the direction perpendicular to the slot. The electric field shielding effectiveness is calculated as the ratio of the impinging field to the field measured at certain point within the waveguide, distant from the slot.

The theory assumes that a single TE10 waveguide mode propagates from the aperture and normal to it. Higher order modes, and modes propagating in other directions may exist which will complicate the results, and introduce need for EM simulation in order to predict the shielding effectiveness.

The results of EM simulation are in excellent agreement with results obtained by using intermediate level simulation tools from University of York, and easily obtainable by using their online calculator. The objective is to investigate the influence of changes in box and slot geometry as well as in position inside the box. in that sense, all parameters are fixed and single geometry variable or field position is then varied as a series of tests.

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SAR-Human Head Exposed to Mobile Phone

With common use of modern communication devices, it has become an imperative to calculate the impact of EM fields to human body. This application focuses to the effects of a mobile phone to human head at 1.8 GHz.

By using the WIPL-D MoM efficiency, it is possible to simulate realistic model of the cell phone and the human head. The geometries were provided as CAD files, imported, repaired and meshed in WIPL-D Pro CAD with all the details originating in the mechanical CAD model. The cell radiates via PIFA and exposes the human phantom to EM radiation, which is demonstrated via both near field and SAR. Results also include radiation pattern for 3 scenarios (PIFE in free space, mounted to cell and in vicinity of head).

All simulations are carried out at regular desktop quad core PC. For electrically more complicated models, the simulation time has been decreased by using WIPL-D GPU solver and widely available inexpensive Nvidia CPU cards. The GTX series offers large computing power for rather small investment. The end result is that simulation time are measured in seconds or minutes at most.

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Basic EMC Examples

Electromagnetic (EM) environment is an integral part of the modern world. The EM environment created intentionally and unintentionally by various sources. If the EM filed becomes strong enough, it can influence the operation of many electrical and electronics devices. The EM environment usually encompasses a receptor (a receiver of EM interference). The ability of a receptor (device/equipment/system) to operate satisfactory in EM environment without introducing intolerable EM disturbances to other devices/equipment/systems in the same environment is called electromagnetic compatibility (EMC).

WIPL-D Software suite can emulate numerous EM experiments. With remarkable variety of tools and features such as extremely efficient Method-of-Moments (MoM) based simulation kernel, GPU and CPU simulation on inexpensive computer platforms, ability to handle large-to-small details within one model, dedicated technical support team, WIPL-D is indispensable EM simulator for EMC.

EMC simulation capabilities are demonstrated with several basic examples: EM field in the vicinity of transmission line, waveguide resonator, wire in cavity, microstrip line with slot and printed circuit.

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