Harmonizing Circuit Design and EMC DesignPart 23 EMC Calculation Methods and EMC Simulations (8): Three-Dimensional (3D) Plots

Hello! Inagaki of ROHM here.

In this 23rd installment I will again change the focus a bit, to talk about three-dimensional (3D) plots that are actually used in simulations and calculations of electromagnetic compatibility (EMC).

In order to execute circuit analysis and electromagnetic field analysis and ultimately determine conformance to an electromagnetic compatibility (EMC) standard, I think we will need to use two-dimensional plots to compare standard limiting values with calculated predictive values. For example, when an EMC countermeasure has been implemented, the frequency bands in which there is conformance to the limit values can be identified at a glance. However, in order to determine the frequency bands in which an EMC countermeasure is effective, and the extent of the effect, it will be necessary to compare a two-dimensional plot from prior to the EMC countermeasure with the two-dimensional plot that results after the EMC countermeasure has been applied. A three-dimensional plot (fence plot) is one method of displaying both these at once. Let’s take a look at an actual plot, programmed using GnuPlot (open source)!

(a)

(b)
Three-dimensional (3D) plot obtained using GnuPlot, and 3 meters method of the CISPR32 (formerly 22) standard

This is a calculated prediction result using the CISPR32 (formerly 22) standard 3 meters method.

In the plot screen in (a), red denotes calculated values and white indicates measured values; the two sequences in the background are results prior to an EMC countermeasure, and the two sequences in the foreground are for after applying the EMC countermeasure; green lines indicate standard limit values. All the necessary data can be displayed on a single plot. The screen can be freely rotated using mouse operations, so that the plots can be studied from any desired angle.

The plot in (b) is shown shifted once from the frequency axis by 90°. The thin red lines (calculated values) and thin white lines (measured values) are results prior to the EMC countermeasure, while the thick red lines (calculated) and thick white lines (measured) are results after EMC countermeasure application. In this example, we see that the EMC countermeasure is more effective at lower frequencies.

In this way, calculated predictions can be variously inspected in their entirety, and can be used to examine the directionality of an EMC countermeasure. Three-dimensional (3D) plots are automatically displayed for each calculated prediction of an electromagnetic compatibility (EMC) standard.

The GnuPlot tool is often used for two-dimensional (2D) plots, but the three-dimensional (3D) plot command is also a standard feature. Shell scripts can be utilized to expand the range of application by very simple means; an example is presented below.

Example of three-dimensional (3D) plot generation using GnuPlot
(click on the image to enlarge)

In this script example, the set command declares detailed settings for display options. A three-dimensional (3D) plot is generated using the splot command. It may seem that the script has many lines, but if one understands the syntax, it will probably just look like a collection of simple commands. Simply by providing these commands in such a shell script, plots can be displayed instantly and effortlessly. Please give shell scripts a try.

Thank you again for your kind attention.