Direction Finding Antenna (DFA)

Magnetic antenna system, patented by G. Wennerberg, is efficiently used as direction finding antenna. This magnetic system is an improved flush type magnetic antenna, suitable for mounting on an aircraft (it employs no moving parts).

The DFA actually consist of 2 coils wrapped around the magnetic material, but the two coils are winded in the orthogonal direction. The coupling between the two coils is especially important for the operation of the antenna.

MoM codes have been often challenged when the device under test is electrically moderate or small. The state-of-the-art MoM WIPL-D code can be used for electrically small structure efficiently, with extremely accurate and fast simulation. The smallest mesh element (0.2 mm large)represents approximately 1/8,000,000 fraction of lambda. No expensive hardware is needed, the simulation can be carried out at regular desktop PC or laptop. The simulation accuracy is extraordinary, showing the -60 dB levels for coupling between the two antenna ports.

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On-chip Capacitances

This report describes use of WIPL-D Software suite for analysis of self and mutual capacitances of pads and their connecting wires as parts of relatively small chip (2-3 mm). Range of frequencies of interest is between 10 KHz and 10 MHz, which makes the problem to be extreme low frequency. At 10 MHz, wavelength in air is 30 m. If chip was modeled with moderate details (1/10 of its size), size of model details would be 1/100,000 of wavelength. The requirements are such that chip device has significantly smaller details and EM simulation is challenging.

Double precision is needed for low frequency simulations. The level of Integral Accuracy (IA) parameter should be increased until the results converge. We have used a regular desktop computer with 4 cores and simulation times is in minutes.

In the entire simulation range, the behavior of the device is linearly proportional to frequency. Low frequency behavior can be obtained by extrapolation of result at higher frequencies. It is enough to perform simulation at single frequency in the upper frequency bands and to assume that the same capacitance is preserved at lower frequencies.

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Wire Thickness Effect in Winding Coils

This paper presents influence of wire thickness to simulation of winded coils with different density. The examples are direct comparison of identical WIPL-D projects created by using wires or plates. Wire models are very easy to build and simulate, but they apply thin wire approximation. The current distribution does not change on the circumference of the wire. For the winded coils, the field is mainly located inside of the coil. The simulations are further extended to toroid winded coils.

Wire model is very easy to build by using WIPL-D Pro helix built in object. Building the plate model is more demanding. The two models yield almost identical results although they are simulated in a completely different manner. The thin wire approximation applied to wire objects does not compromise the accuracy. It significantly reduces simulation time and requirements. The wire model is less reliable as the frequency and winding density is increased. Computer used in this application is regular desktop PC. Wire model runs in seconds, while the plate model runs in minutes.

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Buried Objects Detection via Magnetic Loop

This application note describes use of WIPL-D software suite for simulations of buried objects detection. Simulations are carried out via WIPL-D Pro, full wave EM solver. The product offers excellent speed, accuracy and reliability of results, even at extremely low frequencies (such as needed for this application).

The problem itself consists of thin metallic plate (made of aluminum) buried 3 m under the ground. Magnetic dipole is placed 2.2 m above the ground and swept above the metallic strip in order to detect it. The detection is performed by using the value of magnetic field 68 cm above the ground and below the magnetic dipole.

Simulation was carried out at 10 KHz operation frequency. Small wire loop has the shape of the circle with radius set to 1/3 m (33 cm). The magnetic loop was moved in the interval [-15 m, 15 m] so that its surface goes by directly above the metallic strip.

The simulation requires extremely low number of unknowns (under 500) and lasts typically 1-2 sec on everyday desktop or laptop PC.

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Modeling Wires in Planar Spiral Coils

WIPL-D Pro CAD is extremely powerful state-of-the-art 3D EM solver, based on unique implementation of MoM. It applies quadrilateral meshing and higher order basis functions (allowing both large and small mesh elements, up to 2 lambdas). No boundary box is requires, even for 2 coils spaced apart. The kernel uses thin wire approximation (no change of circular component of current distribution but only the current distribution along wire axis). Application note demonstrates efficient simulation at low frequencies (frequency range 5-10 MHz).

The modeling process is very simple, based on using of built-in spiral/helix objects. Each coil consists of 5 turns, with inner coil radius 190 mm. Wire radius is 1 mm and spacing between wires is 2 mm. The model can be made of wires, solid tubes and hollow tubes with 0.2 mm wall thickness.

The hollow and solid model yield almost the same results, while the wire model shows a small difference. All simulations can be performed on inexpensive (everyday) desktop or laptop. Simulation times is measured in seconds for wire or solid tube model, while it is in minutes for the hollow tube model.

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Coil with Continuously Variable Pitch

WIPL-D Pro is the state-of-the-art implementation of the Method of Moments code. Part of its features are unique and offer comparative advantage over other competitors: quadrilateral mesh, higher order basis functions, excellent parallelization of code on inexpensive CPU and GPU platforms. However, for the complex CAD geometries, the process of building the model might be time consuming.

WIPL-D Pro CAD offers modelling based on modelling of volumes and surfaces, powered with Boolean operations. WIPL-D Pro predefined primitive named Helix allows modeling of helix, spiral or coils. If the coil winding is non-uniform, or according to analytical expressions, it is more convenient to use WIPL-D Pro CAD. The entire process consists of setting symbols, creating the analytical defined curve and sweeping the profile along. The coil is then placed into a metallic frame. Modelling is straight-forward and can be done very fast. The model has very small number of mesh elements, and requires under 1,000 unknown coefficients to be simulated. Simulation typically lasts couple of seconds per frequency point on any given desktop PC or laptop.

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Verifying Accuracy for Inductive Loops with Lumped Elements

This application note aims at explaining analysis of simple wire loops (inductive in their nature) in WIPL-D software package. Special attention is devoted to the case when lumped elements are also included in the circuits.

Simple wire square loop is analyzed at 15.9155 MHz. Two loops are simulated with total circumference equal to 2 cm and 16 cm. The accuracy of EM simulation can be verified by checking the obtained values by using a number of free calculators available on the Internet. This calculator gives almost the same values as WIPL-D. These results illustrate accuracy of WIPL-D in determining low-frequency inductance. The simulation accuracy is verified with the same loops to which a lumped element is attached.

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