Prevent and mitigate electromagnetic interference (EMI) issues with SimuTech Group’s simulation consulting services, allowing for reduced prototype/test cycles, conducting studies to isolate root causes, and validating proof-of-concept designs against electromagnetic compliance (EMC) standards.
Electromagnetic interference and compatibility (EMI/EMC) analysis is one of the most requested services as a result of its necessity to release products to market and because it characterizes precisely what many engineers do not fully capture or consider in their designs – unintentional behavior and coupling from a device under test to its environment.
Simulation allows engineers to replicate and mitigate these unintended electromagnetic effects that often become evident only during compliance testing. By visualizing these electromagnetic field effects and modes of coupling prior to building and testing, the costly cycle of prototyping and testing can be considerably reduced or eliminated entirely.
Isolating individual design facets of a system and assessing their impact on EMI-related issues additionally becomes possible, as does the ability to test design changes rapidly that would otherwise not be possible in a lab.
Below is a example list of EMC compliance standards categorized by industry that guide organizations through the process of ensuring their products meet regulatory requirements.
| Industry | Standards |
|---|---|
| Military | MIL-STD-461, MIL-STD-464, RTCA DO-160 |
| Automotive | CISPR 25, ISO 11451, ISO 11452 |
| Commercial | FCC Part 15 Subpart B, EN55014-1, EN 61000-6-1, EN 61000-6-3, IEC 61000-4-2 |
| Industrial | FCC Part 15 Subpart A, EN 61000-6-2, EN 61000-6-4 |
| Medical | IEC 60601-1-2 |
There are many additional standards in each category above and several additional categories of testing not listed, and while each standard seemingly contains its own exhaustive test descriptions, methods, calibration procedures, and limits, they all capture common aspects of testing that can be simulated. This normally includes impact of the equipment under test (EUT) on its environment, and susceptibility of the EUT to environmental effects. The components necessary to build a full model and replicate these effects are all discussed below.
While a major benefit of simulation over testing is the ability to reduce the model and setup in order to quickly determine the root cause of EMI risks, the desire for replicating a lab setup environment for validation or early signoff is met with several commonly used library models for test and measurement equipment. This includes models that facilitate simulations such as bulk current injection probes, test benches, anechoic chamber absorbers, antennas, and more.
For conducted susceptibility/immunity setups, a bulk current injection probe excites inputs derived from a ready-made calibration setup, as shown in the visuals below of some ANSYS HFSS library components of a coax calibration fixture (left) and a magnetic field excitation on an EUT harness (right).
For radiated emission and susceptibility analyses, calibrated antenna models are used to both excite and measure radiated fields.
Electrostatic discharge setups leverage an ESD gun model with output current calibrated per the simulated standard. The example below shows an animation of surface current density in a sample 2-ohm load target calibration setup.
Starting from layout files, a complete model of the circuit board is generated, including stackup, dielectric properties, metallization, vias, and components. A few items of special interest in PCB modeling for the purposes of analyzing EMI include:
Some examples of these items are pictured below. Near field emissions 3mm away from a board excited by a switch-mode supply are simulated which are mitigated with additional decoupling capacitors placed in areas where fields strengths are highest.
Radiated susceptibility is examined on an enclosure with seams modeled where screws fasten together the assembly components, showing leakage of electric fields and currents inside the chassis.
For designs involving PCBs, SimuTech Group engineers utilize full-wave electromagnetic solvers to understand efficacy of filters and safety circuits, decoupling capacitor choice and placement, routing of sensitive nets and their return paths, and geometric details of enclosures and other surrounding geometries and their implication on EMI-related issues. Our goal is to identify potential or existing issues with each of these components and suggest design changes.
Want to learn more about PCB and enclosure analysis? Visit our Ansys Sherlock and Signal and Power Integrity pages.
Design-related aspects of the construction and layout of cable assemblies can often make the most significant contributions to EMI-related failures in a system. Such features can include shielding, run length, crosstalk, terminations, and more. A complete analysis of a system that includes cabling must naturally account for these design features and their impact on emissions and susceptibility.
Using Ansys software, Simutech Group engineers start with a known cable construction, spec, or datasheets to derive the most applicable models, starting with shield transfer impedance data. An example of one such simulation input might be a copper-tinned overbraid with known coverage.
If measured or stated transfer impedance data isn’t provided, existing libraries of measured data for common shield constructions may be used. Or, an overbraid model with the desired material and coverage may be built and explicitly analyzed to derive a model.
This visual shows an Ansys EMC Plus 3D overbraid model built from specified construction parameters, from which a transfer impedance model for the cable shield can be developed.
With shielding known, interactions between the exterior and interior of the cable can be analyzed. Analysis of a nominal cable construction and projected cross-section can be performed, or a parametric study can capture design variance in conductor placement within the wire bundle.
With all routed cables in place, their electrical interactions with the surrounding environment can be analyzed in order to capture crosstalk effects, cable-induced resonances and antenna effects, impact of cable shield bonding to materials via pigtail or 360˚ backshell terminations, reflections for given conductor terminations or unterminated cable ends, and overall system susceptibility and emissions.
When discovering a potential issue with cable design, SimuTech Group engineers will typically suggest changes related to shielding and its termination, routing paths, filter circuitry or routing on board. From the often-stated caution that “cables make fantastic antennas,” our team simulates to reduce the risk of this adage becoming manifest during compliance testing.
Simulating EMC standard tests can usually be reduced to categories of emissions and susceptibility, in which emissions characterizes the levels and coupling paths of interference from the EUT to its environment, and susceptibility measures the impact on EUT performance when subjected to external EM effects.
The examples below demonstrate combinations of modeling cables, PCBs, enclosures, and calibrated test equipment such as benches, bulk current injection probes, and antennas. Several cases reference the setup below, which models multiple cable assemblies with high-speed signals routed through an enclosure with printed circuit boards.
In all cases of simulations that replicate standard-based testing for validation, SimuTech Group engineers use calibration setups to tune any injection sources and replicate test configurations for each respective standard section, including features such as test benches, expected cable routing, measurement antenna placement and polarization, LISN terminations, and more.
This example shows a MIL-STD-461G CS116 bulk current injection FDTD simulation, including an electric current field animation and induced voltage plot on an RF load.
This example demonstrates an RS103 setup with an incident plane wave excitation on a board, cable, and enclosure FDTD model. The electric field propagation is pictured alongside the spectral induced voltage profile on an RF load.
The example below demonstrates conducted emissions results for several active high-speed nets propagating on-board and on-cable within an enclosure. An electric current animation shows the field coupling to the power cable assembly outside of the enclosure alongside spectral emissions observed at a line impedance stabilization network (LISN) RF port.
The example below demonstrates radiated emissions results for several active high-speed nets propagating on-board and on-cable within an enclosure. The electric current is pictured across cable routing in and out of the enclosure, and the emissions spectrum one meter away from the EUT is shown, demonstrating the prevalence of noise deriving from a 400MHz clock signal.
This example demonstrates (both outside and inside of an enclosure) an ESD discharge at the corner of an enclosure near apertures and solves for the induced voltages/currents on the internal PCB.
This example shows field propagation across a helicopter body for a lightning strike analysis, in which coupling to the aircraft wiring harness is analyzed.
Our team of experienced engineers can assist you at any step of your process.
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