CST – Computer Simulation Technology

TLM Solver


The TLM solver of CST MICROWAVE STUDIO® (CST MWS) is based on the 3D time-domain Transmission-Line Matrix (TLM) method. Developed over a period of more than 40 years, TLM is a well established method and offers particular advantages for EMC/EMI applications.

TLM can be classified as a full-wave, volume-meshing technique. Maxwell’s equations are rigorously solved in space and time. TLM uniquely uses a network of transmission lines or “nodes” to model electromagnetic fields locally in each hexahedral cell of space. A volume of space is modeled by a 3D array of such nodes. The solver runs an explicit time stepping algorithm. At each time step, pulses incident on the nodes are reflected according to the scattering matrix of the node and then connected to neighboring nodes. Electric and magnetic field components are derived from combinations of pulses.

TLM Node and Mesh

The CST MWS TLM solver uses a multi-grid formulation. The hexahedral mesh is first refined or graded to capture detail in the geometry. Small mesh cells are subsequently automatically combined or “lumped”, the level of lumping increasing with distance from geometric boundaries. This process removes any “bleeding” in the mesh, minimizing the cell count and reducing computer requirements to the absolute minimum. The end result is a multi-level Octree mesh. In many cases, the total number of mesh cells is reduced by over 90%.

The CST MWS TLM solver has been enhanced to include "compact modeling" technology. In EMC/EMI applications, objects with relatively small dimensions, such as slots/seams, vents, multi-wires, shielded cables, have a big impact on the performance of the system. Compact modeling enables these critical features to be represented by equivalent transmission-line models; it is not necessary to use a fine mesh to capture the small dimensions. Unlike many modeling techniques, the compact models are fully integrated into the electromagnetic field solution. Compact modeling can reduce the computer requirements by several orders of magnitude.

As previously stated, CST MWS TLM solver is a time-domain approach enabling a full-spectrum analysis to be performed through a single solve. This makes it ideal for broadband antenna design and EMC/EMI problems which can cover huge frequency ranges. The time-domain solver can be used to directly simulate transient phenomena such as EMP and lightning. In these applications it is often beneficial to visualize the flow of currents and propagation of fields in time and to determine the peak induced voltages/currents in internal cabling.

Integration of the CST MWS TLM solver into the CST STUDIO SUITE® now enables tight, bi-directional coupling with CST CABLE STUDIO® and CST DESIGN STUDIO™. It is possible to run the 3D TLM field solver in true transient co-simulation with CST CABLE STUDIO® and CST DESIGN STUDIO™. This offers unique and ground-breaking electromagnetic simulation capability for engineers facing challenging EMC/EMI and antenna problems.

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