Analysis Options for Electromagnetic Simulation
The RF Module simulates electromagnetic fields in 3D, 2D, and 2D axisymmetric, as well as transmission line equations in 1D, and circuit (non-dimensional) modeling with SPICE netlists. The 3D formulation is based on the full-wave form of Maxwell's equations using vector edge elements, and includes material property relationships for modeling dielectric, metallic, dispersive, lossy, anisotropic, gyrotropic, and mixed media. The 2D formulations can solve for both in-plane and out-of-plane polarizations simultaneously or separately, as well as for out-of-plane propagation. The 2D axisymmetric formulations can solve for both azimuthal and in-plane fields simultaneously or separately, and can solve for a known azimuthal mode number.
Both total-wave and background-wave formulations are available. The full-wave formulation solves for the total fields due to all included sources in the model, while the background-wave formulation assumes a known background field from an external source – a common approach for radar cross section and electromagnetic scattering models.
Boundary conditions are available for modeling perfect electrically conducting surfaces, surfaces of finite conductivity, and faces that can represent thin lossy boundaries within the model. Symmetry and periodic boundary conditions allow you to model a subset of your entire model space, and scattering boundary conditions and perfectly matched layers (PMLs) are used to model boundaries to free space. Various different excitation boundary conditions exist for modeling ports: rectangular, circular, periodic, coaxial, approximate lumped, user-defined, and precise numerically computed port excitations are available. You can include boundary conditions representing cable terminations as well as lumped capacitive, inductive, and resistive elements. Line currents and point dipoles are also available for quick prototyping.
Simulations can be set up as eigenvalue problems, frequency domain problems, or fully transient solutions. Eigenvalue problems can find the resonances and Q-factors of a structure, as well as the propagation constants and losses in waveguides. Frequency domain problems can compute the electromagnetic fields at a single frequency, or over a range of frequencies. Fast frequency sweeps, using the method of Padé approximants, can dramatically improve solution times when computing the behavior over a frequency range. Transient simulations are available for both the second order full-wave vectorial formulation as well the more memory-efficient first order discontinuous Galerkin formulation. Transient simulations are used for modeling of nonlinear materials, signal propagation and return time, as well as for modeling of very broad-band behavior.
The equations in all models developed in COMSOL Multiphysics can be completely coupled such that the electromagnetic fields can both affect and be affected by any other physics. In particular, a dedicated user interface for microwave heating expands simulation capabilities beyond traditional power deposition analysis, with features such as SAR calculations and precise temperature rise predictions. By solving for Maxwell's equations in the frequency-domain, and the heat transfer equation in the stationary or time-domain, it is possible to compute the rise in temperature over time, and compute the effects of varying material properties with temperature.
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Extendable Results from Microwave and RF Simulations
The results of computations are presented using predefined plots of electric and magnetic fields, S-parameters, power flow, and losses. A fast postprocessing tool allows for quick generation of far-field radiation patterns. You can also display your results as plots of expressions that represent physical quantities you define freely, or as tabulated derived values obtained from the simulation. S-parameter matrices can be exported to the Touchstone format, and all data can be exported as tables, text files, raw data, and images.
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The workflow is straightforward and can be described by the following steps: define the geometry by creating it using the COMSOL native tools or import a CAD model, select materials, select a suitable user interface and analysis type, define ports and boundary conditions, automatically create the finite element mesh, solve with optional mesh adaptation, visualize, and postprocess the results. All steps are executed from the COMSOL Desktop®. The solver selection step automatically uses default settings that are tuned for each specific RF interface but can also be user-configured.
Many Example Models for RF and Microwave Design
The RF Module Model Library describes the interfaces and their distinct features through tutorial and benchmark examples. The library includes models addressing antennas, ferrite devices, microwave heating phenomena, passive devices, scattering and radar cross-section (RCS) analysis, transmission lines and waveguides in RF and microwave engineering, tutorial models for education, and benchmark models for verification and validation of the RF interfaces.