PCB Layout EMC Analysis
Theory and Physics
Overview
Teacher! Today's topic is about PCB layout EMC analysis, right? What is it about?
Analysis of EMC issues originating from printed circuit board layout. Slits in ground planes and discontinuities in return current paths increase noise radiation.
Wait, wait, you mean printed circuit board layout... so can it also be used in cases like this?
Governing Equations
Wow~, the talk about layout is super interesting! Please tell me more.
Discretization Methods
How do you actually solve these equations on a computer?
We use spatial discretization by the Finite Element Method (FEM). We assemble the element stiffness matrices and construct the global stiffness equation.
We perform transformation to the weak form (variational form) and use formulation by the Galerkin method using test functions and shape functions. The choice of element type (low-order elements vs. high-order elements, full integration vs. reduced integration) directly affects the trade-off between solution accuracy and computational cost.
Matrix Solution Algorithms
What exactly do you mean by matrix solution algorithms?
We solve the simultaneous equations using direct methods (LU decomposition, Cholesky decomposition) or iterative methods (CG method, GMRES method). For large-scale problems, preconditioned iterative methods are effective.
| Solver | Classification | Memory Usage | Applicable Scale |
|---|---|---|---|
| LU decomposition | Direct Method | O(n²) | Small to Medium Scale |
| Cholesky decomposition | Direct Method (Symmetric Positive Definite) | O(n²) | Small to Medium Scale |
| PCG Method | Iterative Method | O(n) | Large Scale |
| GMRES Method | Iterative Method | O(n·m) | Large Scale / Non-symmetric |
| AMG Preconditioner | Preprocessing | O(n) | Very Large Scale |
So, if you cut corners on the finite element method part, you'll pay for it later. I'll keep that in mind!
Implementation in Commercial Tools
So, what software can be used to do PCB layout EMC analysis?
| Tool Name | Developer/Current | Main File Format |
|---|---|---|
| CST Studio Suite | Dassault Systèmes SIMULIA | .cst |
| Ansys HFSS | Ansys Inc. | .aedt, .hfss |
| COMSOL Multiphysics | COMSOL AB | .mph |
Vendor Lineage and Product Integration History
Is the background of each software quite dramatic?
CST Studio Suite
What exactly is CST Studio?
Developed by Computer Simulation Technology (Germany). Acquired by Dassault Systèmes in 2016 and integrated into SIMULIA.
Current affiliation: Dassault Systèmes SIMULIA
Ansys HFSS
Next is the story about Ansys HFSS. What's it about?
A 3D high-frequency electromagnetic field simulator developed by Ansoft Corporation. Ansys acquired Ansoft in 2008.
Current affiliation: Ansys Inc.
COMSOL Multiphysics
Please tell me about "COMSOL Multiphysics"!
Founded in Sweden in 1986. Started as FEMLAB with MATLAB integration, later renamed to COMSOL. Strong in multiphysics.
Current affiliation: COMSOL AB
So, if you cut corners on the German part, you'll pay for it later. I'll keep that in mind!
File Formats and Interoperability
Are there any points to note when transferring data between different software?
| Format | Extension | Type | Overview |
|---|---|---|---|
| STEP | .stp/.step | Neutral CAD | 3D CAD data exchange format compliant with ISO 10303. Supports geometry + PMI. |
| IGES | .igs/.iges | Neutral CAD | Early CAD data exchange standard. Has issues with surface data compatibility. Transition to STEP is progressing. |
| VTK | .vtk/.vtu | Visualization | Visualization Toolkit format. Used by ParaView, etc. |
When converting models between different solvers, attention must be paid to the correspondence of element types, compatibility of material models, and differences in the representation of loads and boundary conditions. Particularly, high-order elements and special elements (cohesive elements, user-defined elements, etc.) often cannot be directly converted between solvers.
I see... formats seem simple at first glance, but they're actually very deep, aren't they?
Practical Considerations
Are there things like "field wisdom" that aren't in textbooks?
Verifying mesh convergence, validating the appropriateness of boundary conditions, and performing sensitivity analysis of material parameters are extremely important.
- Mesh dependency verification: Confirm convergence with at least 3 levels of mesh density.
- Boundary condition validity: Setting physically meaningful constraint conditions.
- Result verification: Comparison with theoretical solutions, experimental data, and known benchmark problems.
Wow, PCB layout EMC analysis is really deep... But thanks to your explanation, I've been able to organize my thoughts a lot!
Yeah, you're doing great! Actually getting hands-on is the best way to learn. If you have any questions, feel free to ask anytime.
PCB EMC—"Current Loop Area" is the Dominant Factor for Radiation
Radiated electromagnetic fields from a PCB are proportional to the current loop area A and the square of the frequency f (E∝A×f²). As this simple relational expression shows, reducing the loop area by half alone decreases radiation intensity by 6 dB. This is the basis for the adage in high-speed digital design to "use a solid ground plane." The image current theory, where signal return currents flow through the ground plane directly beneath the signal, was systematized by Clayton Paul in the 1970s and became the theoretical foundation for PCB layout EMC design.
Physical Meaning of Each Term
- Electric field term $\nabla \times \mathbf{E} = -\partial \mathbf{B}/\partial t$: Faraday's law of electromagnetic induction. A time-varying magnetic flux density generates an electromotive force. 【Everyday example】A bicycle dynamo (generator) generates voltage in a nearby coil by rotating a magnet—a direct application of this law that a changing magnetic field induces an electric field. An IH cooking heater also uses the same principle, where high-frequency magnetic field changes induce eddy currents in the pot bottom, heating it via Joule heat.
- Magnetic field term $\nabla \times \mathbf{H} = \mathbf{J} + \partial \mathbf{D}/\partial t$: Ampère-Maxwell's law. Current and displacement current generate a magnetic field. 【Everyday example】When current flows through a wire, a magnetic field is created around it—this is Ampère's law. An electromagnet operates on this principle, passing current through a coil to create a strong magnetic field. A smartphone speaker also works by converting current→magnetic field...
Related Topics
なった
詳しく
報告