EMI from a Slot in a Box

By Cody Weber and Bryon Neufeld

Benchmark Simulation Using EMA3D

It is important to demonstrate that EM simulation packages can reproduce measured data for problems of interest. EMI from a slot is a common EMC concern. This demonstration compares an EMA3D simulation to an existing measurement in the literature.

The electromagnetic interference (EMI) from a slot in a rectangular box has been explored using a FDTD technique and compared to measurements.[1] An FDTD simulation software, EMA3D,  has been used to analyze a similar problem and the results are presented herein. The simulation files, results and plotting scripts have been provided to assure the validity of the EMA3D modeling results.

EMA3D Model Setup

Mesh size: Δx = 1 cm, Δy = 0.5 cm, Δz = 1 cm
A thin wire with termination impedances of R1 = 50 Ω, and R2 = 47 Ω was used to model the source line (green line). A thin gap formalism was used to model the slot (blue line) with a width of 1 mm. Box surfaces (Lx = 22 cm, Ly = 14 cm, Lz = 30 cm) were modeled as perfect electrical conductors (PEC). A Gaussian pulse voltage source with amplitude 1 mV was used at the R1 end of the thin wire.
A box with a slot ready for EMI from a slot simulation

EMA3D Simulation Setup

A far-field electric field approximation was used to determine the electric field at a 3 m distance from the slot in the benchmark.[1] EMA3D has the ability to obtain far-field approximations similar to the ones performed in the paper. Because the problem is relatively small for the computing resources available, the actual electric field was computed at the 3 m distance. Only the y component of the electric field was considered.
This shows where the EMI measurement occurs from the slot

EMA3D Results Vs. Results in Benchmark [1]

 Comparison of EMI from a Slot experiment to simulation

Comparison of experiment to simulation

The plots demonstrate that the EMA3D simulation results compare well to the benchmark results. Every cavity-mode and slot generated resonance produced in the benchmark problem is captured in the EMA3D results for delivered power and electric field at 3 m.

Video Demonstration of EMA3D Modeling the Slotted Box

Instruction Document to Reproduce the Results


1.M. Li, J. Nuebel, J. L. Drewniak, R. E. DuBroff, T. H. Hubing, T. P. Van Doren, “EMI from Cavity Modes of Shielding Enclosures – FDTD Modeling and Measurements,”  IEEE Transactions on Electromagnetic Compatibility, Vol. 42, No. 1, pp. 29 – 38, Feb. 2000

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