What mesh density and excitation does the transient EMC solver need for accurate emissions up to 1 GHz?

The hexahedral mesh must resolve the smallest geometric features (trace width, gap, gasket) and provide at least 10 to 20 cells per wavelength at the highest frequency of interest. At 1 GHz the free-space wavelength is 300 mm, so 15 to 30 mm cells satisfy the wavelength criterion, but local mesh refinement down to a fraction of a millimeter is needed around thin slots, vias, and connector pins where the fields change rapidly. The transient solver is excited with a Gaussian pulse whose spectrum is flat across the analysis band, and the simulation runs until the energy in the structure has decayed below an accuracy threshold (commonly minus 30 dB or minus 40 dB). Resonant enclosures with high Q can require long run times because the energy decays slowly; an open boundary with a perfectly matched layer absorbs outgoing radiation so the far-field emission can be extracted cleanly.

Electromagnetic Compatibility

CST EMC

Q: Which CST solver should I use for radiated emissions versus shielding effectiveness?

For broadband radiated emissions from a PCB or enclosure, the time-domain transient solver is usually the best choice because a single simulation produces results across the entire CISPR band (30 MHz to 1 GHz, extended to 6 GHz) from one pulse excitation, and it handles electrically large, geometrically detailed models efficiently. For shielding effectiveness of a metal enclosure with seams and apertures, either the transient solver or the frequency-domain solver works, but the frequency-domain solver with tetrahedral meshing resolves thin slots and gaskets more accurately at discrete frequencies. For low-frequency conducted-emissions or cable problems where the structure is much smaller than a wavelength, combine the 3D field solver with the CST cable harness or the integral-equation solver to capture common-mode currents. A typical EMC project uses the transient solver for the field problem and co-simulates with a SPICE-based circuit model of the source through the schematic interface.

Q: How does CST predict EMI coupling between a noisy trace and a victim cable?

The noisy aggressor is modeled as a current or voltage source on a trace, and the victim is defined as a near-field probe, a field monitor, or an explicit cable in the cable-harness module. The finite integration technique discretizes Maxwell's equations on a structured hexahedral grid, computes the full 3D fields, and reports the induced voltage or current on the victim. For board-to-cable coupling you typically extract the radiated near field with a field monitor on a Huygens box surrounding the source, then import that box as an equivalent source illuminating the cable model. Coupling is reported as a transfer function in dB versus frequency. To correlate with a 3-meter or 10-meter compliance test, the far-field monitor converts near-field data to E-field strength in dBuV/m at the standard measurement distance, which can be compared directly against CISPR 22 or FCC Part 15 limit lines.

/see-ess-tee ee-em-see/

Within CST Studio Suite, the EMC workflow is the collection of solvers, monitors, and post-processing tools used to predict electromagnetic compatibility behavior before hardware exists. Built on the finite integration technique, the transient and frequency-domain solvers compute the full 3D fields radiated and coupled by a PCB, cable harness, or enclosure, then translate them into radiated-emission spectra, EMI coupling transfer functions, and shielding-effectiveness curves. Engineers use these results for pre-compliance verification against CISPR 22, CISPR 25, and FCC Part 15 limit lines, typically across 30 MHz to 6 GHz, so that filter, gasket, and grounding changes can be evaluated virtually rather than through repeated chamber visits at roughly 2,000 to 4,000 USD per day. The EMC tools share the same modeling environment as the broader CST Studio antenna and component design flows.

Category: Electromagnetic Compatibility

Core Method: Finite Integration Technique

Typical Band: 30 MHz to 6 GHz

How CST Models EMC and EMI Problems

The defining characteristic of the CST EMC workflow is that it solves Maxwell's equations directly on a discretized 3D model rather than relying on closed-form approximations. The finite integration technique (FIT) maps the integral form of Maxwell's equations onto a pair of staggered grids, producing matrix equations that the transient solver advances in time using an explicit leapfrog scheme. A single broadband pulse excitation therefore yields the emission spectrum across the entire CISPR band from one run, which is why the transient solver is the default choice for radiated-emissions prediction from circuit boards and enclosures.

EMC simulation differs from ordinary antenna or component analysis because the quantities of interest are weak parasitic effects: common-mode currents on cables, slot leakage through enclosure seams, and crosstalk between a noisy switching trace and a victim line. Capturing these requires fine local mesh refinement around apertures, gaskets, and connector pins, plus a perfectly matched layer (PML) open boundary so that outgoing radiation is absorbed and the far field can be extracted cleanly. Field monitors placed on a Huygens box around the source let the engineer export an equivalent near-field source and reuse it to illuminate a separate cable-harness model, decoupling the board solution from the system-level coupling problem.

Once the 3D fields are known, the far-field monitor converts near-field data into E-field strength in dBuV/m at a standard 3-meter or 10-meter measurement distance. These predicted spectra overlay directly on the CISPR or FCC limit lines, giving a margin in dB before any prototype is built. Because the same geometry can be re-solved after adding a ferrite, a feedthrough filter, or a conductive gasket, the workflow turns EMC troubleshooting into a design-space study rather than a sequence of expensive chamber failures.

Governing Field Equations

Maxwell Curl Equations (FIT discretized form):
∇ × E = −∂B/∂t ∇ × H = J + ∂D/∂t

Mesh Resolution Criterion:
Δx ≤ λ_min / 15 where λ_min = c / f_max

Radiated Field to Compliance Limit:
E_dBuV/m = 20 log₁₀(E_V/m × 10⁶) referenced at 3 m or 10 m

Shielding Effectiveness:
SE (dB) = 20 log₁₀(E_without / E_with) ≈ 20 log₁₀(H_without / H_with)

Where Δx = hexahedral cell size, f_max = highest analysis frequency, c ≈ 3 × 10⁸ m/s. Example: at f_max = 1 GHz, λ_min = 300 mm so Δx ≤ 20 mm, with local refinement below 1 mm at slots and pins.

CST EMC Solver Selection

Solver	Method	Best EMC Use	Typical Band	Mesh Type	Strength
Transient (T-solver)	FIT, time domain	Broadband radiated emissions	Broadband, to 6 GHz+	Hexahedral	Full band in one run
Frequency domain	FEM, tetrahedral	Shielding, slots, gaskets	Resonant, narrowband	Tetrahedral	Fine slot detail
Integral equation (IE)	MoM / MLFMM	Electrically large cables	1 MHz to 1 GHz	Surface	Open radiation problems
Cable harness	TL / hybrid	Conducted emissions, crosstalk	kHz to 400 MHz	1D network	Bundle coupling
PCB / RuleCheck	Geometry + rules	Pre-layout EMC checks	N/A	2.5D	Fast design screening

Common Questions

Frequently Asked Questions

Which CST solver should I use for radiated emissions versus shielding effectiveness?

For broadband radiated emissions from a board or enclosure, the transient solver is preferred because one Gaussian-pulse run covers the full CISPR band (30 MHz to 1 GHz, extended to 6 GHz). For shielding effectiveness of an enclosure with seams and apertures, the frequency-domain (tetrahedral FEM) solver resolves thin slots and gaskets more accurately at discrete frequencies. Low-frequency conducted-emissions and cable problems pair the 3D solver with the cable-harness or integral-equation solver to capture common-mode currents.

How does CST predict EMI coupling between a noisy trace and a victim cable?

The aggressor is a current or voltage source on a trace; the victim is a near-field probe, field monitor, or explicit cable in the harness module. FIT computes the full 3D fields and reports induced voltage or current as a transfer function in dB versus frequency. For board-to-cable problems you extract the near field on a Huygens box, then re-import that box as an equivalent source illuminating the cable. The far-field monitor converts the result to E-field in dBuV/m at 3 m or 10 m for direct comparison against CISPR 22 or FCC Part 15.

What mesh density and excitation does the transient EMC solver need up to 1 GHz?

The hexahedral mesh needs 10 to 20 cells per wavelength at f_max; at 1 GHz that is roughly 15 to 30 mm cells, with local refinement below 1 mm at slots, vias, and connector pins. The transient solver is excited with a Gaussian pulse whose spectrum is flat across the band, and the run continues until stored energy decays past a threshold (commonly minus 30 to minus 40 dB). High-Q resonant enclosures decay slowly and run longer; a PML open boundary absorbs outgoing radiation so the far-field emission extracts cleanly.

Related Terms

← CSP Assembly CST Studio →