Difference between revisions of "EM.Ferma"

Revision as of 15:22, 4 March 2014

EM.Ferma is a 3D electrostatic and quasi-static solver.

With EM.Ferma, one can explore the fields in the vicinity of charge distributions, voltage sources, and current sources. Transmission line parameters Z0 and EpsEff can also be solved for.

EM.Ferma is Methods Of Physical Optics ==

Physical Optics As An Asymptotic Technique

Many larger-scale electromagnetic problems deal with the modeling of radar scattering from large metallic structures (targets like aircraft or vehicles) or the radiation of antennas in the presence of large scatterer platforms. Although a full-wave analysis of such open-boundary computational problems using the method of moments (MoM) is conceptually feasible, it may not be practical due to the enormous memory requirements for storage of the resulting moment matrices. To solve this class of problems, you may instead pursue asymptotic electromagnetic analysis methods.

Asymptotic methods are usually valid at high frequencies as [math]k_0 R = 2\pi R/\lambda_0 \gt\gt 1[/math], where R is the distance between the source and observation points, k₀ is the free-space propagation constant and λ₀ is the free-space wavelength. Under such conditions, electromagnetic fields and waves start to behave more like optical fields and waves. Asymptotic methods are typically inspired by optical analysis. Two important examples of asymptotic methods are the Shoot-and-Bounce-Rays (SBR) method and Physical Optics (PO). The SBR method, which is featured in EM.Cube's Propagation Module, is a ray tracing method based on Geometrical Optics (GO). An SBR analysis starts by shooting a number of ray tubes (or beams) off a source. It then traces all the rays as they propagate in the scene or bounce off the surface of obstructing scatterers. T

Methods Of Electrostatics & Quasistatics

In EM.Ferma, we solve the Laplace equation (shown below) subject to specified sources and boundary conditions.

[math]\Delta\varphi(\vec r)=-\frac{\varrho(\vec r)}{\varepsilon_0}[/math]

Once the potential is computed, the electric fields can easily be computed via:

Sources in EM.Ferma

For static analysis, the model can be excited with any number of Voltage Sources, Charge Sources, or Current Sources. For Quasistatic analysis, only Voltage Sources are of use.

Voltage Sources

In EM.Ferma, Voltage Sources are applied to a specified PEC group that exists under Physical Structure in EM.CUBE's navigation tree. All CAD objects under the specified PEC group will act as Voltage Sources.

To add a new Voltage Source to a project, right-click on Voltage Sources on the navigation tree, and select "Insert Voltage Source...". In the Voltage Source dialog, select the PEC group to which the specified voltage will be applied. Enter any string as the Voltage -- a text string will be interpreted as a variable which can be used for parametric design, or a parameter sweep.

Charge Sources

Charge Sources in EM.Ferma apply a charge (or charge density) to a region defined by any of EM.CUBE's CAD objects.

Adding a new Charge Source is very similar to adding a new material in EM.CUBE. Find the Charge Source group label in the navigation tree and select "Insert New Charge Source..." A dialog will prompt the user to decide whether charge for this group will be defined in terms of total charge or charge density. If charge density is chosen, the specified charge density will be applied to all CAD objects defined in the present Charge Source group. If total charge is selected, the specified total charge will be distributed amongst the total volume of all objects under the present material group.

Current Sources

Current Sources in EM.Ferma apply a specified current to any number of one-dimensional CAD objects, such as Lines, Polylines, or Spirals. For any curve, such as a Parabola or a Circle, the user will be prompted to perform a one-time conversion to a Polyline just before running a simulation.

Adding a new Current Source is very similar to adding a new Charge Source. Keep in mind only one-dimensional objects can be drawn under this material group.

Domain and Boundary Conditions

In EM.Ferma, the Laplace equation is solved subject to specified boundary conditions. Here, we will discuss how to specify these boundary conditions.

3D Domain

EM.Ferma's computational domain defines where the boundary condition will be specified. It can be seen in figure 1 as a green cubic wireframe that surrounds all of the CAD objects in the model. To modify the domain boundary, find the "3D Static Domain" entry in the navigation tree, right-click on it, and select "Domain Settings...". The domain dialog will appear. In the domain dialog, the domain boundary can be specified in terms of either a custom, fixed location, or as custom offsets from CAD objects in the scene.

Boundary Condition

EM.Ferma allows the user to either specify the potential on the boundary (Dirichlet boundary condition), or specify the normal derivative on the boundary (Neumann boundary condition) via a specified field strength. To modify the boundary condition, find "Boundary Conditions" on the navigation tree, and select "Boundary Conditions...". The user will be prompted with the dialog seen in figure.

2D Solution Planes in EM.Ferma

EM.Ferma allows the user to specify a 2D plane in the scene as a longitudinally infinite

Setting up a Transmission Line Simulation

To perform a transmission line simulation, check the Quasistatic simulation mode for a selected 2D plane, as shown in Figure... If an analysis is run with this option checked, the characteristic impedance (Z0) and Effective Epsilon will be computed for the transmission line. This output can be found in aptly-named text files in the project directory upon completion of the simulation. Fields and potentials at the selected 2D plane will still be computed.

Quasistatic analysis can only be performed with a Dirichlet boundary condition with 0V specified on the boundaries.

For a step-by-step demonstration (including transmission line optimization), take a look at this video on our YouTube channel: EM.CUBE Microstrip Optimization

Simulation Examples / Gallery

Version History

• First available in EM.CUBE 14.2